OSC vs Mono Astrophotography From a City: Which Works Best?
First published June 2021
Last updated January 2026
Intro
If you’re an astrophotographer based in a city and are looking to buy a dedicated camera for imaging deep sky objects such as galaxies and nebulae, one decision quickly becomes unavoidable: One Shot Colour or Mono. Perhaps you’ve been using a DSLR and want to take the next step, or maybe you’re starting out with specialist equipment from the beginning. Either way, the OSC versus Mono debate is hard to avoid, especially on astronomy forums where Mono is often presented as the only serious option for urban imaging.
Until recently, I would have agreed. I spent years imaging from a city location using a Mono camera. But I’ve since switched to OSC, which is a relatively uncommon move in astrophotography. In this article, I share my reasons for doing so and offer a fair comparison of the strengths and limitations of both camera types, based on practical experience of using each from a light polluted urban environment. We’ll start with a brief overview of the basics, before digging into how these choices play out in real world city imaging.
Definitions
OSC stands for One Shot Colour. This type of camera allows you to capture full colour images in single shots — hence the name. They’re convenient and give good colour images with a minimum of hassle. Note than when using an OSC camera for astrophotography you should take lots of photos and integrate (also called stacking) them to get a good final result. The “one shot” aspect of the camera is to get a simple colour image, not an awesome final picture.
Mono cameras work differently. Instead of making colour images, they see in monochrome (i.e. black and white). To get colour images from them you need to put filters in front of the camera sensor. To make an image like an OSC manages in one shot, you’d put a red filter in front of your camera sensor and take a photo; then put a green filter in front of your camera sensor and take a photo; then put a blue filter in front of your camera sensor and take a photo; then digitally combine them all to make a final Red Green Blue (RGB) image. As with OSC cameras, you need to take lots of images and then integrate them to get a good image that you can then go onto edit.
Benefits of Mono
Those brief descriptions make it sound like going for an OSC camera is a no-brainer, but actually most astrophotographers choose Mono, and for good reasons. Although it’s more hassle to put all those filters in front of your camera sensor, in principle you can get a higher quality final image in the end. One reason for this is that OSC cameras tend to record lots of green light (simulating how our eyes work), but there’s not that much green in space, so for astro work that’s a bit of a waste. Mono also lets you shoot Luminance data, which adds to image quality and lets you create LRGB images.
But perhaps the biggest benefit of Mono is that you’re not restricted to gathering RGB data — you can use special filters that only allow very specific wavelengths of light through to your sensor. These are called narrowband filters. Prime examples are filters for Sulphur II, Hydrogen-alpha (Hα), and Oxygen III, often abbreviated to SHO. This is the Holy Trinity for astrophotographers because lots of astronomical objects like nebulae are almost invisible in RGB, but shine brightly in SHO.
Very helpfully for us urban astrophotographers, those SHO narrowband wavelengths are in a different part of the spectrum to the light pollution that we have in cities, so in effect our SHO filters allow us to see right through bright urban skies. It’s like flicking a switch and turning off all the streetlights.
As a side-note, objects like galaxies and star clusters give out most of their light in RGB rather than SHO. Getting good images of them from a city is a real challenge, regardless of whether you’re using an OSC or Mono camera.
OSC dualband filters
Now we’ve gone from thinking that OSC is the obvious choice to being convinced that Mono is clearly best, and actually essential if you’ve got light-polluted city skies. This was the case until recently, and is what a lot of astroimagers still think. But now OSC, our urban astrophotography underdog, has a secret weapon: dual-band filters.
Just as Mono imagers have access to loads of great narrowband filters, dual-band filters offer similar for OSC imagers. These dualband filters come in two main varieties: Hα/OIII (e.g. Optolong L-Ultimate) and SII/OIII (e.g. Askar E2). Each of these filters lets you capture two of the Holy Trinity wavelengths simultaneously.
Hα/OIII dualband filters are most common, because Hα-rich nebulae are plentiful. You can create some really striking images just using one of those filters. They may not be as scientifically accurate as a full Mono SHO set-up, but it’s hugely cheaper and a fair bit easier.
Then, if you’re very keen, you could go on to add an SII/OIII filter to your collection. During processing you can combine the SII/OIII with Hα/OIII data, and create a full SHO image. The result isn’t as scientifically accurate as you’d get with Mono plus SHO filters, but it‘s not far off, and can look great.
I think that these dual-band filters are real game-changers for OSC astrophotographers, especially those of us in cities. They allow us to keep the benefits of OSC and mitigate the main drawback, i.e. not being able to take narrowband images. To be clear, Mono plus filters has advantages over OSC plus dual-band in many cases, and dual-band filters aren’t effective for every telescope or every target. But for the first time OSC can compete from a city.
I would like to quickly mention a drawback to many of these dualband filters that not everyone is aware of: they tend to lose effectiveness at fast focal ratios. See the graph on page 11 of this test report by Jim Thompson for details. If your telescope is faster than around f/5, you may want to scout out other options.
For more about filters, check out my article which filter should I use with my OSC camera?
OK, with all that said, let’s try to break the issue down into five different criteria so we can compare the advantages and disadvantages of each camera type.
1. Cost
Winner: OSC
To do Mono you need more equipment, and that comes with a cost.
OSC:
OSC camera, dualband filters, filter drawer.
Mono:
Mono camera, LRGB filters, SHO filters, mororised filter wheel.
Most notable there are the filters. With a Mono camera you typically need seven filters (Luminance, Red, Green, Blue, Hα, OIII, SII). With OSC you can achieve most of that using two dualband filters (Hα/OIII and SII/OIII). The image quality may not be quite equivalent — more on that later — but just regarding cost alone, expect a Mono set-up to cost about 140% of an OSC equivalent.
2. Data acquisition
Winner: OSC, but not by much if you’ve automated your Mono set-up.
Taking images with an OSC camera is relatively straight-forward (well, as much as anything in this hobby ever is). With Mono you’ve got extra kit to think about and you need to put a bit more thought into planning your imaging session. And no-one enjoys taking Flats (a type of calibration frame) for lots of filters. You can use software and buy gadgets like motorised filter wheels that automate a lot of the leg-work, but that’s more expense and complexity.
Note that in principle you can actually make good images faster with a Mono camera. That’s for a few reasons, most notably because OSC wastes pixels by having so much green. If your absolute primary concern is speed, then Mono has a bigger advantage in this category.
3. Versatility
Winner: Mono
No doubt about it, Mono is more versatile than OSC. You’ve got access to more filters and can combine their data however you like. Want to keep things simple and just record Hα? Easy. Keen to combine SHO data to make images with the same colour scheme that the Hubble Space Telescope uses? Sure, you can do this. (As mentioned, that’s also possible using an OSC camera plus Hα/OIII and SII/OIII dualband filters, but it isn’t quite as accurate as the pure Mono route).
You can also shoot a greater variety of targets, and be better equipped to try photometry and spectroscopy.
With Mono, the world — or rather, Universe — is your oyster.
4. Image quality
Winner: Mono, but only just
This is a tough criterion to judge. In theory, Mono is the clear winner. It’s very sensitive, and you get lots of detail with a Luminance filter. You also often hear that Mono images achieve higher resolutions. In theory this is true, but how noticeable is it? Can you look at an image and tell whether it was taken with an OSC or Mono camera by its resolution? Personally, I can’t.
I’d like to do a good side-by-side comparison sometime; if the difference if evident then I’d accept the resolution argument. But for now, I think that your image’s total integration time and your skill in processing has far more impact on the final image quality than whether you used OSC or Mono. So, I’m going to give this one to Mono, but only just.
5. Fun factor
Winner: entirely depends on what you want
When deciding whether to buy an OSC or Mono camera, we have a tendency to get our heads stuck in the fine print of camera specifications and theoretical limits. Here’s the thing though: most of us are into this hobby for fun, so don’t lose sight of that. Which camera type would you find more fun to use? That’s the one that you’ll use the most.
Let me tell you a little story. Back when I was imaging with my Mono camera, I was finding it rather frustrating, and I didn’t have enough spare time to put into it. I just wasn’t having fun. I started to consider an OSC set-up, because that would be more streamlined. Most of the advice I received was to absolutely definitely not go OSC, because that was madness to even attempt from a city. I ignored that advice and decided to go for it. I’m glad I did, because otherwise I’m fairly sure I would have quit astrophotography altogether. It’s not that the advice I received wasn’t technically sound, but it didn’t take into account what I was personally finding challenging about the hobby, and what I’d find most fun!
What should I choose?!
Sorry, there’s not an easy answer here. Given the theme of this website you were probably expecting me to say that you should get an OSC. If only it were that simple.
If you’ve got a big budget, plenty of free time, and want the greatest versatility, then Mono is probably the right choice for you. But if you fall down in any of those categories it’s worth considering OSC. This is thanks to the development of those wonderful dual-band filters. Before they came along, I’d be saying that from a city, Mono was the only real choice. Now, OSC with a dual-band filter can work really well (which I hope this website’s gallery proves).
The price difference alone may push you into the OSC camp. It’s worth noting that the second-hand market for astro equipment is very good. The people that buy this kind of kit tend to take good care of it, often with a mind to sell it on to fund upgrades in the future. So if you’re set on Mono, you could likely get an older-generation set-up second-hand for around the price of a brand new latest generation OSC. Or, you could find a bargain OSC camera and get imaging for less than you think. Maybe the money saved could be used to buy some useful upgrades?
If you’re still stuck with analysis paralysis choosing an astrocamera, here’s a tip that might help you decide. We tend to think we’re putting ourselves in the OSC or Mono camp for life. But it doesn’t work that way; you won’t be using your new camera forever. Consider how long you expect to use it before you’ll want to sell it and get an upgrade. Technology is always moving on, after all.
Let’s say that figure is five years. Which camera type will you get the most use out of in that timeframe? If you’re short on time, cash, or just want something (relatively) simple to produce pretty pictures, maybe OSC is right for you. If you want to get really deep into the hobby and can dedicate all the necessary resources to it, perhaps Mono is the answer. I used to shoot Mono, and am now OSC. Maybe I’ll go back to Mono in the future.
In the end, whatever you choose, the most important thing is to have fun and get your camera out there collecting photons.
Where to buy
Here’s some OSC-specific equipment that’s particuarly useful. Click here for my complete kit list.
Affiliate links help support the site at no extra cost to you.
Camera: ZWO ASI 2600MC Pro
Read my review
Buy from Astroshop.eu
Buy from High Point Scientific
Filter: Optolong L-Quad Enhance
Read my review
Buy from Astroshop.eu
Buy from High Point Scientific
Filter: Optolong L-Ultimate
Read my review
Buy from Astroshop.eu
Buy from High Point Scientific
Filter: Optolong L-eXtreme
Read my review
Buy fromAstroshop.eu
Buy from High Point Scientific
Filter: Askar E2
Read my review
Buy from High Point Scientific
ZWO Filter Drawer
Buy from Astroshop.eu
Buy from High Point Scientific
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Thanks indeed for all the time and trouble you have gone to creating this resource. It will help me decide out of the analysis paralysis whether to go OSC or mono in the near future. I like your ideas and some thoughts I hadn’t entertained or placed so much weight on before such as the weather’s effect on the number of imaging occasions per year. You are also right on the fun aspect which ought not to be forgotten. I’m constantly jmpressed how technology is making previously impossible things achievable and widening up the hobby to more in the process.
Thanks Steve, I’m glad you found this useful. Best of luck with whatever you decide!
Very thorough post, thank you for taking the time to put so much valuable information together.
Hundred percent agree, in the end, it depends on what you will end up using the most. Going OSC to Mono on my journey but I see myself switching from one to the other depending on the conditions, targets and time. I will keep both cameras.
I think OSC is a no brainer for beginning although it will most likely draw one towards wanting to go mono eventually. From my experience the learning curve was steep enough as a beginner that I enjoyed not having to deal with unnecessary frustration handling more equipment and processing with OSC.
It’s a hobby, some spend money to play golf, drive expensive cars, collect stuff, it’s all about gratification, sense of accomplishment and pleasure.
Well said!
Thanks so very much for all this information! I am purchasing my first of everything in just starting out in astrophotography and was delighted to find your website as you confirmed the choices I had already made! I do have a question for you regarding filters. With the setup you have, it looks as though you use 2″ filters and not 36mm. I have seen discussions stating one can use either. Is that true? Thanks so much and your work is breathtaking!
Hi, and thanks for your message! The optimal size of filter depends on the camera sensor that you have. 2″ filters are a good match for my ZWO ASI2600MC-PRO camera, with its APS-C sensor. Also, 2″ filters fit in the filter drawer I have.
Oops! Forgot to ask you how much your set up weighs? Thanks!
I think a little shy of 5kg in total. I can easily lift it with one hand. I would offer to weight it for you, but I’m actually in the process of setting up a new telescope so have dismantled most of my Askar FRA400 rig.
Dear Lee,
Dear Lee,
Thank you for going to the trouble to create your astrophotography website. I really enjoy visiting from time to time. Though I am an experienced photographer and have studied astronomy since I was a boy, I am only 8 months into astrophotography and love every aspect of this fascinating pursuit. I purchased the Askar 130PHQ after reading your review and am really glad I did, it’s a great telescope and I’m really enjoying using it.
Sincerely,
Jerry Gerber
https://www.jerrygerber.com
https://www.astrobin.com/users/jsg
Hi Jerry, I’m glad you enjoy visiting my site. The Askar 130PHQ is really good isn’t it. You’re brave to be using it only eight months into astrophotography!