Astro Cameras: OSC vs. Mono - Which is Best?

Written By Patrick A. Cosgrove

February 19, 2022

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    Choosing Your Astro Camera

    When you decide to take your first steps into Astrophotography, you must assemble the gear required to take images of the night sky. This is likely to start with a telescope and a suitable mount, leading quickly to the other gear that is needed to build your first Astrophotographic rig. At some point, you will need to think about cameras.

    You will need both the main imaging camera and a guide camera.

    Guide cameras are typically small Astro-dictated Mono cameras that mount on a small guide scope. These cameras are not super expensive but they play a key support role in allowing your mount to track the stars accurately.

    The main imaging camera, however, will be the focus (pun intended) of your whole rig. It captures the photons in each subframe that will ultimately be stacked and processed to create your final image.

    Many people will start by using their existing DSLR camera. For many, this is a great way to get started. You can use a camera that you already have, or pick up one for a good price on the used market.

    Adapters make it relatively easy to attach this to your telescope. This will get you going, but many such cameras are impeded by an IR filter mounted in front of the sensor to screen out IR wavelengths. Unfortunately, sometimes these filtered wavelengths include H-alpha wavelengths of 656nm. DSLR cameras can be modified to capture the full spectrum by removing these filters, which is a help, but they typically do not have the means to cool the sensors during operation, so thermal noise can be an issue.

    At some point in your journey, you are likely to consider an Astro-dedicated camera. There are two fundamental forms of Astro cameras:

    • One-Shot-Color (or OSC) Cameras.

    • Mono Cameras

    Which one should you buy?

    Which one is “better"?”

    In this post, I will explore this question. We will look at the fundamental differences between the two systems, the Pros, and Cons associated with each, and make some high-level recommendations.

    We will also explore how some people, including myself, have come down on this issue.

    So let’s start by looking at both systems and see what we are dealing with.

    OSC Cameras

    OSC cameras consist of a sensor, support electronics, and if you are doing Deepsky imaging, probably a thermoelectric cooler. These cameras are called One-Shot-Color cameras because every time you capture a subframe, you are capturing a complete color RGB image. To enable this, the sensor is coated with a grid of small red, green and blue color filters in a pattern that spans the entire area of the sensor.

     

    The ZWO ASI294MC-Pro OSC Camera

    The back end of the ZWO ASI294MC-Pro OSC Camera

    This grid, known as the Bayer Filter Pattern, is typically a 2x2 pixel pattern that is repeated across the sensor. The Bayer Filter Pattern can be found in various forms, however the most common is the RGGB pattern. In this pattern, each 2x2 grid consists of one red pixel, one blue pixel, and two green pixels.

    The RGGB Bayer Pattern superimposed over the sensor array. Image from Wikipedia.

    The goal here is to create an RGB image with color information for every pixel. To do this, it is necessary to mathematically extract and interpolate the captured data. This is known as Demosaicing. This computation is quite sophisticated and does a very good job at synthesizing pixel data that is missing from the raw data.

    If you have used a DSLR camera for your imaging - you have in fact already used an OSC camera - as most of them use the Bayer filter pattern.


    Wikipedia Article on the Bayer Filter System

    OPT Article on the Bayer Filter System

    The Bayer Pattern was originally created for terrestrial photography - in other words - for making color images of the world around us. To make the colors accurate, it is designed to mimic the spectral response of the human eye. The human eye has its peak sensitivity at about 550nm - a mid-green color. The response of the human eye is in turn a product of evolution and the fact that humans developed in a world with a sun that had a given color temperature and in a natural world made very green by the presence of chlorophyll-based plant life.

    The filters themselves are relatively broadband and overlapping. The Astrophotography world has adapted these sensors for use in dedicated Astro cameras for a very simple reason - they are broadly available for other common uses and this broad-base manufacturing and economy of scale makes these sensors cost-effective. But let’s remember that these sensors were never specifically designed for Astro Imaging.

    The RGGB filter pattern means that for a given exposure, we will have 50% of the pixel area capturing Green light and only 25% of the pixel area capturing Red or Blue.

    How light is collected with the RGGB Bayer Filter Pattern.

     

    The CFA Demosaicing Process

     

    While this capture is not balanced across the three color channels - it does have a distinct advantage of capturing RGB data simultaneously. This, of course, is something that the Mono camera cannot do. For a given subframe exposure you will capture R, G, and B data where the Mono camera can only capture data for the single filer in place for that exposure.

    Is the RGGB Bayer Capture Pattern the most efficient for Astro Imaging?

    Probably not. I worked in Kodak Research Labs a few years back and in 2007, we developed a new pattern that was RGBW. The idea here was to have a Bayer-like Pattern approach that had traditional RGB pixel filters, but it also had an additional filter in the pattern that was panchromatic. In other words, one pixel in the pattern had no filter (or a filter that was extremely broad in its response) and was thus able to capture light from all wavelengths. This was the same idea as the L filter in the LRGB filter set for Mono cameras that we will talk about soon. The repeating pattern for this approach used a larger tile than the traditional 2x2 Bayer pattern, but it was shown to be significantly more efficient than the traditional approach. I believe this could make a much better pattern for Astrophotography - but while that pattern was produced on small sensors designed for smartphone cameras, it was never adopted for larger sensor sizes. As a result, there is no sensor chip using this approach that could be sourced to support a dedicated Astro camera at this time.

     

    The Bayer RGGB pattern is seen on the Left (a), and the Kodak RGBW pattern is seen on the right (b).

     

    So, does all of this mean that the Bayer pattern is not useful for Astrophotographic applications? Absolutely not - as can be seen by the amazing results that Astrophotographers routinely achieve. It also produces a camera that is affordable, simple to use, and produces images that are relatively easy to process.

    Mono Cameras

    Mono cameras are very similar to OSC cameras in that they share similar body designs, and have a sensor and cooling circuitry. What makes Mono cameras fundamentally different is that the sensor has no filters applied to its surface. No Bayer Pattern is used at all. Every pixel sees the full spectrum of light that the sensor is capable of responding to. When you expose a subframe with just the camera, you get an image that collects photons from across the spectrum. While this allows the sensor to maximize the capture of photons, it does so with no color information - all color detail is lost.

    This is the ZWO ASI2600MM-Pro Mono Camera

    Looking down at the sensor of the ZWO ASI2600MM-Pro Mono Camera.

    This situation can be improved by the use of filters. Putting a filter in front of the sensor shapes the light being measured. Placing a red filter in front of the sensor would allow you to selectively measure light from only the red part of the spectrum. If I used separate Red, Green, and Blue filters to create a series of subframes, I could stack the frames from each filter to create an R, G, and B master image, which to then be combined to form a color image. I can play further games by using precision filters that carefully target the light I want to measure. This can work to eliminate the light that you don’t want to measure (i.e. light pollution), ensuring that the light I am measuring is coming from the selected target.

     

    This is the ZWO ASI1600MM-Pro kit that includes the camera, the filter wheel, and a complete set of filters.

     

    While a filter drawer can be affixed to your imaging chain, allowing you to swap out one filter at a time, it is much more common and convenient to use a filter wheel that can hold 7 or 8 filters. The filter wheel can then be rotated to select the filter desired at any given point.

     

    This is a ZWO 7x36mm filter wheel with LRGB and Ha, O3, and S2 filters mounted.

     

    If you are interested in doing a "normal" or broadband color image, four filters are typically used. These are commonly referred to as LRGB. The RGB part of this covers the broad areas of the spectrum we associate with each color. The "L" part spans a very wide portion of the spectrum - including the R, G & B regions. This creates a "mono" view of the target catching all of the photons available. The L or luminance image carries a lot of information about the tone scale and the structure of the image. Color information can be added to this from the RGB filter data to create a final color image. This can be very efficient. Every pixel on the sensor is hard at work collecting data from that filter. Whereas in the OSC case, we have seen that the filters are fixed, and during any given exposure, 25% of the pixels are collecting light from Red & Blue, while 50% are collecting the Green light.

    Here is a plot from Atronomiks which shows the spectral cut of the LRGB filter set. Note the L curve spans the entire space of the R, G, and B filters.

    Since the filters on a Mono camera are not fixed to the sensor, we can take advantage of this and use more and different filters.

    We have already talked about Broadband Imaging. Now let's talk about Narrowband Imaging.

    We know that many nebulae glow from light emitted by molecular clouds that are excited by bright nearby stars. The most common of these molecules are Hydrogen II, Oxygen III, and Sulfur II. When excited - these emit light in an emission line that spans only a very tiny slice of the spectrum. If we have a very narrow cut filter, we could measure just that light and exclude the light from the rest of the spectrum. This results in an image that is greatly enhanced in contrast and detail. Rejecting all the extraneous signal allow us to capture details that cannot be seen in a typical broadband image.

    This Astronomiks plot shows and contrasts the cuts of both the LRGB and the Narrowband filters

    Here is an example of using 3 narrowband filters (Ha, O3, and S2) to capture different images of M27. These are then processed and combined to create a color image.

    Since you can collect light through different filters, you can also create unique blends of these filter signals. You can even create blends of broadband and narrowband data! I have created narrowband images rendered in the Hubble SHO Palette that also have stars captured with RGB broadband filters. I have also enhanced LRGB images of galaxies by adding Ha data. The resulting LHaRGB images highlight H2 regions that are associated with new star formation.

    Costs

    There are, however, costs involved in the use of Mono-based cameras.

    Filters of various sizes, spectral cut widths, and quality levels are available. Be forewarned - a good set of filters can cost as much as the camera! In addition, you will likely want to throw in a filter wheel, thus increasing your costs.

    Another cost is in capture time for some filters. Narrowband filters may only allow light from a 3-7nm slice of the whole spectrum. Depending on your scope and camera, you may be running 5 or 6-minute subs to get as much signal as you get with a 90-second sub for LRGB. Also - every time you change your filter, you will likely want to re-run the focus series to ensure a sharp image. This takes time away from capturing photons!

    Finally, you will want to have a set of calibration data collected for each filter. It will take time to shoot these and later, to process these for each filter used.

    So Which Is Better?

    That, of course, is the $64K question. In general, Astrophotographers tend to fall into two camps - the OSC Brotherhood, and the dark side of the force, the Mono Maniacs.

    Go to any Astronomy Social Network site and I guarantee that you can find many threads that are debating this very question.

    If you are interested in looking at one, I would suggest this thread on Cloudy Nights:

    https://www.cloudynights.com/topic/731353-galaxies-convince-me-lrgb-vs-osc/

    I know many accomplished Astrophotographers who only use OSC cameras - and their work is exemplary. I know others that shoot only Mono and again their work is exemplary.

    So which is Better? I can answer that question very concisely: It depends!

    What? - "It depends"!? What a cop-out!

    Well, not really.

    These cameras are tools. Like all tools, they have particular attributes, and like anything else in life, they have their own strengths and weakness. They need to be used appropriately. The right tool for the right job. In addition, tools need to be wielded. WHO is wielding the tool can often have more impact than the tool itself.

    It is kind of like those Photographic challenges that you sometimes see online. The noob photographer with $10K of professional gear is pitted against an accomplished professional photographer with an inexpensive DSLR and a kit lens. The professional images are usually much better - despite the gear he is using - and we find that the noob is not been transformed into a photographic wizard merely by the use of professional-level great gear.

    Often the most critical aspect of creating a great image is how you go about capturing data and then how data is processed.

    So let's look at the Pros and Cons of each camera type and see if we can make some recommendations for which camera may be best for you.

    Pros and Cons for OSC Cameras

    Pros

    • Lower cost

      • There is no need for a filter wheel or set of expensive filters

      • When building multi-camera systems this distinct cost advantage multiplies by the number of cameras used

    • Ease of use

      • RGB color information is collected simultaneously during a single sub exposure. There is only one kind of sub for you to take, and each sub captures a color image

      • Sequences are easier to set up

      • Only one set of calibration files needed

      • Capture does not require a change in the filter and the resulting need to adjust focus. Sequences are thus simpler and more time is spent on data capture

      • You can stop collecting at any time and still have enough data for a color image. This is a huge advantage when your weather is poor, unstable, or hard to predict.

    • More Accurate Color

      • The Bayer filers have overlapping spectral fields that are well matched to the human-eye response and can have greater color accuracy than LRGB - which have steeper cuts and less overlap. This often results in O3 contributions being seen as an accurate Teal color rather than the blue most often seen with LRGB filters.

    • File Storage

      • Fewer light files to capture

      • Fewer calibration files to capture

      • Fewer interim processing files are created during pre-processing and image processing

    • Ease of Processing

      • Only one set of lights to deal with

      • No need to replicate processing for different channels

      • Master images are already color

      • Easier to support Mosaics as each master is already a color image

    • Simpler Optical Path

      • Fewer air-surface gaps to deal with than with filter/filter-wheel, where there is the potential of creating interreflections and halos for bright stars and features

    • Form Factor

      • Smaller and more compact

        • No need for a filter wheel

      • Less weight (small difference)

    • More convenient to use for Hyperstar or RASA configs

      • The smaller form-factor for a front-mounted camera

      • Mono cameras cannot use a filter wheel and would need a filter tray - reducing automation capability

    Cons

    • Not Very Flexible

      • Basic filters are coated onto the sensor and shape all exposures

      • The Bayer Pattern Filters on the sensor cannot be changed or removed. (They can be modified further by stacking additional filters.)

    • Less Efficient

      • RGGB Bayer filter pattern captures a 50% Green and 25% Red and Blue image.

        • Optimized for terrestrial imaging circumstances by matching spectral sensitivities of the eye, not for astronomical imaging.

      • Cannot capture equivalent to "L" super wideband for all pixels

      • Cannot efficiently do Narrowband imaging (added filters with a duo or triple NB notches still have to be used with Bayer filters)

      • Loss of resolution (Bayer interpolation does not make up for this but the differences are very small)

    • Processing is not as flexible

      • Harder to address color-specific noise and gradient issues

        • You can extract color layers and process but this often is not seen to be as clean as Mono

    Pros and Cons for Mono Cameras

    Pros

    • Flexibility

      • Can do broadband RGB capture as well as very broad L captures

      • Can do Narrowband capture

      • Allows for mixes of NB and Broadband signal to create unique looks

      • Many filters to choose from, different frequency targets, bandwidths, and quality levels available

    • Very Efficient

      • All pixels used to full benefit for each filter exposure

      • L filter can maximize light being captured

      • Narrowband can reject all but most important wavelengths for nebulae, dramatically increasing contrast for some objects

      • No dependence upon Bayer interpolations

    • Processing Flexibility

      • Each color filter can be pre-processed and processed as needed to maximize quality

      • Color combinations and blend methods are rich and varied

      • Easier to address color channel specific noise or gradients, which yields - according to many - yielding cleaner backgrounds

    • Robustness

      • Better able to deal with gradients from Light Pollution and Moonlight (with Narrowband)

    Cons

    • More Expensive

      • The cost of a complete set of filters can be very high

      • The cost of the filter wheel

    • Larger Form Factor

      • The resulting Camera/Filter wheel combination is bulkier and less streamlined

      • The resulting Camera/Filter wheel combination is slightly heavier and contributed to Z-axis balance issues

    • More Complicated to Use

      • Greater setup complexity - need to mount camera, filter wheel, and filters

      • Need to capture more flavors of subs to create a color image - no ability to capture a color image with a single sub

      • Subs for Narrowband will require longer exposures

      • Additional calibration files will be required for each color filter used

      • Focus adjustment needed after filter swap

      • You need a complete set of subs for each filter used in order to process the image

        • If you have to stop early you may not end up with a full set

        • This is particularly critical for those with weather issues

    • More Complicated Optical path

      • Adding a filter near the sensor can cause reflections and halos

    • Processing Takes Additional Effort

      • Separate calibration paths for preprocessing

      • Separate paths for Processing

      • More ways to combine and create color images

      • Mono is cable of producing better images but only if the user understands and is able to process the image data appropriately

      • Mosaics can multiply the amount of processing necessary

    General Recommendations

    Based on these Pros and Cons, it is easy to see use cases where each system might be a good choice. I would summarize these with a set of high-level recommendations.

    When is an OSC Camera System a Better Choice?

    • When you are a beginner - just starting out

    • When you are cost-sensitive

    • When you are dealing with Multi-Scope, Multi-camera systems

    • When you are dealing with RASA or Hyperstar systems

    • When you are doing Mosaics

    • When you desire simpler, easier capture and processing

    • When you are dealing with very poor and unstable weather conditions

    When is a Mono Camera System a Better Choice?

    • When cost is not an issue

    • When you want to wring the theoretical best out of the system

    • When you have the processing expertise to take full advantage of the data captured

    • When you want to easily add Ha to RGB

    • When you want to do narrowband or multi-band imaging

    • When you love processing and want maximum flexibility in data access and handling

    OSCs are capable of doing a great job and have the benefit of being cheaper, smaller, and easier to use. For beginners, OSCs are clearly the better system to start with and to learn with. Having said that, in the hands of an experienced practitioner, they are capable of achieving excellent results.

    Mono Cameras seem to be harder to use, much more expensive, and a lot more work. So why use them?

    They offer the ultimate flexibility and allow for the greatest potential for peak-quality images over OSC cameras. While there is a lot of debate about this point - and clearly OSCs are getting better and better with time - Mono still has the advantage.

    At the beginning of this post, I shared a link to a discussion on this topic found in Cloudy Nights. As pointed out in that discussion, you tend to see more experienced imagers moving from OSC to Mono, but rarely do you see them swap from Mono to OSC. It does happen, but that is not the trend.

    Also mentioned was the point that you don’t see OSC being used on the Hubble Space Telescope or research-grade telescope systems. In those use cases, the efficiency and flexibility of Mono outweigh costs or ease of use concerns.

    As you become more experienced, you develop a foundation of knowledge and skills that makes it easier for you to take on the extra work and complexity of Mono. Also - you begin to develop an eye for what makes for an excellent Astro Image and you become motivated to improve your results. Mono cameras can give the edge to do that. In the Cloudy Night’s thread, Dan Kuchta put it very well:

    The thing is, the difference between the two, for normal color images, is distinct, but not huge. If you're starting out, you can be very happy with OSC images and the level of quality you're getting. And looking at OSC vs. mono images, you are not likely to think the difference is worth it.

    But as you gain more experience, you'll find that small things in your images become more important. You'll look at your images more closely and find lot of perceived room for improvement. The stars could be rounder, the contrast better, the color more distinct, the background more noiseless, guiding tighter, etc. And you'll start going to greater lengths to remove those "defects" and get better images. That's when mono becomes more enticing. The improvements that mono offers will begin to seem larger, and more worth it.

    So it really comes down to use cases. So let’s look at some real-world case histories.

    Case Histories

    When I first began my journey into Astrophotography, I was very fortunate to meet two gentlemen that were members of the local Astronomy club (The Astronomy Section of Rochester Academy of Science). I had shared some early images with the group, and these two gentlemen reached out and welcomed me as a fellow traveler on the Astro Imaging road.

    This was so very fortuitous. I was just starting out and they each had about a decade of experience under their belts, each had a portfolio of impressive images, and both have had their work published.

    During the Covid era where there was very little face-to-face socializing going on, Dan, Gary, myself and a few others were routinely in touch via email - on almost a daily basis. They both have been very generous with their feedback and assistance and greatly helped me to develop as an astrophotographer.

    It was also interesting because they have both taken very different tracks.

    Dan uses OSC cameras exclusively and purposefully. Dan does not do anything for a random reason. He is an Engineer's engineer and he makes carefully reasoned decisions. His work with OSCs is second to none.

    Gary, on the other hand, moved into the Mono world, where he quickly found it to be just what he was looking for. He has mastered Pixinsight and has developed his noise reduction and sharpening methods to a very fine artform. His narrowband SHO images are as smooth as silk and create a standard that I have struggled to duplicate to this very day.

    There is a lot of good-natured ribbing about the whole OSC vs. Mono issue. Gary keeps temping Dan to "come over to the dark side of the force", but Dan has held off so far. Let's explore what each is doing further.

    Dan Kuchta

    As I indicated, Dan is very methodical in his approach and he had analyzed almost every aspect of the imaging system he uses. I asked Dan to explain why he thought OSC was right for him and this is what he had to say:

    My Reasons for using OSC?

    The first is that I want to be able to choose whatever target I want for the night, regardless of size, and without having to change my scope, camera, filters, rewire, rebalance, etc. To achieve this, I have 3 scopes on my mount, each with its own camera, and with different focal lengths. Adding a filter wheel and filters to all 3 scopes would cost a fortune and add a lot of complexity. OSC imaging avoids that. I do have a filter drawer on each scope so I can easily add a dual-band filter to a scope get some of the advantages of narrowband without the complexity and cost.

    The second reason has to do with the abysmal weather where I live. Fully clear nights are rare and many of the nights I image will have one or more imaging windows that come and go and limit the amount of imaging time I can get. I’m never sure how much time I’ll ultimately get on a target. OSC imaging lets me make use of whatever windows show up, without worrying about whether I’ll get time for that last filter.

    Overall it seems simpler, less expensive, and easier to make use of limited imaging opportunities


    Dan's reason for choosing OSC seems to be very pragmatic and practical. But I think that he would not be using OSC if he felt that he could not get the quality he wanted.

    Dan has a small observatory with an impressive rig that he designed to work the way he wants to work. He has a heavy-duty IOptron CEM120 mount with three scopes mounted on it. His observatory is heavily automated. He picks his target and then decides which scope he wants to use on it and sets up a capture sequence.

     

    Dan’s three telescope rig - sitting in his backyard observatory. (Image by Dan Kuchta @2021 - used with permission)

     

    Dan typically goes for very deep exposures. For him, this means capturing as many subs as he can with his OSC camera. He then analyzes his frames and selects the very best and carefully integrates and processes his data. He is very careful and meticulous with his processing.

    He has consistently shown that he can generate extremely high-quality images with OSC and does not feel held back by its use. He values the cost-effectiveness, simplicity, and convenience of OSC. He is quick to say that he may someday dip his toes into Mono waters, but he feels no need to do so at this time. For Dan - OSC is the best choice.

    Here is a sample of Dan's work.

    Dan Kuchta’s Image of Messier 33 was a Top Pick on Astrobin. This was a 13 hour 20-minute exposure. (Image by Dan Kuchta ©2021 - used with permission)

    Details for this image can be seen here: https://astrob.in/g7yefh/0/

    More of Dan’s work can be seen on Astrobin: https://www.astrobin.com/users/dkuchta5/

    Gary Opitz

    I will talk a bit more about my own use case next but suffice it to say that I am now in the Mono camp. One of the reasons that I ended up here is because of Gary. I was drawn to his beautiful narrowband Hubble SHO Palette images as a moth is drawn to a flame. I wanted to be able to create images like that. As you will see, Gary's images are beautifully done with a smooth ethereal look that is compelling.

    I asked Gary why Mono was right for him, and this was his response:

    My Reasons for using Mono?

    It just seemed a natural progression for me. I started in deep sky imaging with a basic DSLR setup - a completely stock DSLR. Then I moved to an astronomically modified DSLR and shortly thereafter to an astronomically dedicated OSC camera. I was very happy with my results from both the DSLRs and the OSC cameras, but I felt that I needed to reach what is perceived by some to be the absolute pinnacle in resolution, fidelity, and flexibility - mono imaging.

    And I am so happy I did.

    Initially, I was afraid to try it because of the purported complexity entailed in the entire mono process - but I took to it like a duck to water, and - speaking for just myself - I found it to be intuitively easy and extremely satisfying. I think it is important though for anyone contemplating deepsky imaging to follow the path that I took - work your way through the different procedures and systems and each step along the way becomes less challenging.

    Gary shoots both LRGB and narrowband. He runs a single telescope in a small roll-off roof observatory in his backyard. Gary does not strike me as an equipment hound. He has just what he needs to create the images that he likes to do, and he has developed a method and process for his images that create his signature look. He has shared with me in great detail how he goes about processing his image. I follow his method to a "T" but still cannot achieve the silky smoothness I see in his images. At this point. such processing is an art form and the look created is the signature of the artist at the helm.

    For Gary, Narrowband allows him to capture the details in his nebulae that he wants, and he has mastered the processing to create great images from his captured Data.

    For him, Mono is the best solution!


    Here is Gary’s setup:

    Gary’s telescope rig. (Image by Gary Opitz @2021 - used with permission)

    Gary’s ROR Observatory in his backyard (Image by Gary Opitz @2021 - used with permission)

    Here is a sample of Gary's work:

    Here is Gary’s IC 5070 - The Pelican Nebula. This is the result of a 14-hour integration. It is one of my favorites and was an Astrobin Top Pick. (Image by Gary Opitz ©2021 - used with permission)

    More details for this image can be seen here: https://astrob.in/pkxl1x/0/

    See more of Gary’s images here: https://www.astrobin.com/users/chilistars67/

    My Own Case History

    I retired in the summer of 2019 and soon thereafter decided that I wanted to begin my journey into Astrophotography. I soon ordered the gear for my first telescope platform which included an OSC camera. The choice for OSC at that time was easy. I was a complete beginner and did not know what I was doing. The OSC was in many ways similar to the digital camera I had always used so I was more comfortable with it.

    I actually considered a mono system - but it sounded crazy to me! The cost of all those filters? You have to reset the focus for each filter change? (I did not yet even know about autofocus), all of those cal files to collect? Stacking? I was using Deepsky Stacker and had no idea how to handle Mono images with it. Processing? I was using Photoshop and it seemed very awkward when it came to handling mono image sets. In my mind - people who did mono imaging were masochists. No - OSC was the clearly right choice for me at that time.

    And it was - the reduced cost allowed to get things going quicker. The simplicity was just what I needed at that point in my journey. I had a lot to learn without the added complexity of Mono!

     

    My Initial platform - was a Williams Optics 132mm FL APO with an IOptron CEM60 mount and my first camera - the ZWO AIS294MC-Pro!

     

    But as I became more comfortable with the blocking and tackling of astrophotography I think I was becoming ready to take on the next set of challenges. I had begun to use Pixinsight and could see how it had the ability to master mono-based images. I had been seeing narrowband imaging of nebulae and was very interested in doing that. I saw Gary's silky smooth images and I wanted to produce images like those.

    Long story short, around this time I stumbled upon the opportunity of a lifetime to pick up an Astro-Physics refractor and jumped at the chance. I now needed a new camera for that rig. I decided to get my first mono camera and learn the ropes with that.

     

    Here was my second rig - and the first with a Mono camera. This was an Astro-Physics 130mm f/8.35 Starfire on an IOptronics CEM60 and the camera was a ZWO ASI1600MM-Pro with a ZWO EFW filter wheel and a set of LRGB and NB ZWO filters.

     

    The first time I started capturing Ha subs I was blown away at the level of detail I was able to capture - so much more detail than I was seeing with my RGB OSC. I loved it.

    I would set up both scopes in the driveway and pick a good target for narrowband for one scope, and then go after galaxies and such with the OSC.

    At one point I decided to shoot something head-to-head and see what the differences between the systems were. I choose NGC 6946 - The Fireworks Galaxy. This was not a scientific test. One scope had a focal length of 920mm and a f/ratio of 7.0 and the other had a focal length of 1080 and a f/ratio of 8.35. The images scales were close but not exact. I shot 5.4 hours on the OSC and 6 hours of LRGB on the Mono system. I processed each image to get the best image I thought I could at the time - but I did not try to match backgrounds or colors. What came out is what came out.

    Here is the comparison:

    NGC 6946 - The Fireworks Galaxy - 5.4 hours OSC (click to enlarge)

    NGC 6946 - The Fireworks Galaxy - 6 hours Mono LRGB (click to enlarge)

    My conclusion is that the image quality of each was actually quite good. But there was a difference. Which is better? I showed the images to a bunch of people. Some liked the OSC, some liked the Mono. In general, more people liked the Mono image. That was my conclusion as well. But the OSC is still pretty darn nice.

    This brings us to today. Today I run 3 telescope platforms and each is now sporting a Mono camera. For me - Mono is the right way to go.

    This path is more expensive. Some people retire and buy fishing boats. I bought telescope stuff. I am serious about Astrophotography and I could justify in my mind the cost.

    My professional background is in image science and consumer imaging. I love digital image processing. For me - having the great flexibility that Mono brings with it is just what the doctor ordered. I love shooting Narrowband and I love using custom blends to get custom results.

    One common reason that people use to avoid going down the Mono path is the local weather. If you live in an area with crummy weather - you may find that it takes a very long time to complete enough capture to create a balanced color data set.

    You may get all of your Ha subs but then the weather changes and you come back in a few weeks to capture O3 data - and a few more weeks until you finish the S2 and can start processing. With poor or unstable weather - this can stretch out. With OSC, you might have a complete data set whenever you stop capturing data!

    I live in Western New York and I can tell you we have lousy weather for Astrophotography. Dan deals with this by choosing OSC. Gary Deals with this by being very patient as he captures his data sets.

    My strategy is twofold:

    • First, when I have good weather, I run three scopes in parallel to capture as many photons as I can. Grab all of the photons you can while you can!

    • Second, every night I try to capture a balanced set of subs. I might grab 15 Ha subs, 15 O3 subs, and 15 S2 subs. If the next night is clear, I do it again. And again. Until the weather, window shuts me down. This way I tend to end up with a reasonably balanced data set whenever the weather changes.

    This seems to work for me. I like being able to capture Galaxies with LRGB and then add in some Ha data to make the H2 star-forming regions pop. I like blending broadband and narrowband data. I like doing narrowband nebulae while adding in RGB stars.

    This is Caldwell 49 - showing the core of the Rosette Nebula. This shot has only 3.3 hours of integration but I love the result I was able to achieve here with Narrowband and how I do the SHO Hubble palette.

    To see more detail around this image of the Rosette Nebula, click HERE.

    This is an M27 shot in Narrowband. This first image is an SHO palette blend.

    THis version is an HOO palette blend

    Finally here is an off-the-wall blend I did with the SHO-AIP script. I love the flexibility to blend!

    To see more details around the story of these images of M27, click HERE.

    This is my most recent M31 shot. This consists of 6 hours of LHaRGB. I loved being able to capture Ha narrowband and blend it into my Image.

    To see the story behind this image of M31, click HERE.

    Finally - For me - I think my ability to handle noise is better in Mono than what I was able to do in OSC. I was also never able to get good results with deconvolution in my OSC images but I have been able to make significant improvements with my Mono images.

    So, a Mono Camera is the right choice for me.

    • I have dealt with the cost

    • The form factor is not an issue

    • The additional complexity has been something I have been able to navigate

    • I greatly value the flexibility

    • I greatly value the ability to do highly efficient narrowband imaging

    • The additional processing is something I actually enjoy doing!

    My three Mono-based Telescope Platforms set up in the driveway and ready to collect photons!!

    Don’t let the fact that I feel Mono is the right system for me deter you from being in the OSC camp. I know for fact how good OSC image can be. Every time I see a new image from Dan, I am reminded of that.

    The #Astrophotography Twitter Community Weighs In

    As I sometimes do when I am considering big questions in Astrophotography, I consulted with my local Astrophotography friends and I also consulted with the broader #Astrophoography Community on Twitter. I sent out the tweet shown below:

    I was surprised by the response I got. I had a lot of people weighing here - and as always - I very much appreciated those that took a few minutes out of their day to respond to my question. While I’ve summarized a lot of the points made in this thread in my section of Pros and Cons and my recommendation, I thought it would be good for folks interested in this question to see some of the comments themselves. While I don’t have room here to share them all, I wanted to share a number of them with you. Scanning through these gives you a sense of how that community is thinking and acting around this topic.

    Conclusion

    I think that physics makes the Mono camera the system most capable of yielding the best possible image results - it does so at a significant cost. This cost can be in the form of:

    • cash for equipment outlays

    • time and effort for data collection and processing

    • Experience and skill to deliver on the theoretical advantages in the system.

    If you are not in a position to bear these costs, the OSC Camera System avoids or minimizes many of them, and allows users to still make beautiful and impressive images of the night sky.

    The bottom line? Both systems can be the right choice for you - based on your needs, experience, and skill level, the type of imaging you are engaged in, and your preferences for workflow.

    Patrick A. Cosgrove

    A retired technology geek leveraging his background and skills in Imaging Systems and Computers to pursue the challenging realm of Astrophotography. This has been a fascinating journey where Art and Technology confront the beauty and scale of a universe that boggles the mind…. It’s all about capturing ancient light - those whispering photons that have traveled long and far….

    https://cosgrovescosmos.com/
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