I’m looking at picking up a William Red Cat 91 with a ZWO ASI2600MC Air. I played around with the FOV of that combo on Stellarium and found that while it was great for Andrometa galaxy and M42, it just didn’t have the reach for most of the galaxies out there that I wanted to capture. Just for kicks I decided to enter in the parameters of a IMX585 sensor camera to see how that changed things up. I was surprised at how well it worked for those smaller targets, albeit at less resolution than the apc sensor. Seems to be a better solution than getting an ultra long focal length telescope as well. Is this a typical approach as how to capture both nebulae and galaxies with the same setup?
Two cameras two fov options?
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I’m interested in the responses from the more learned minds, as a landscape photographer entering the Astro realm I’ve been trying to figure out similar trade offs. I have always run the mantra that MP can be cropped but not easily added (ignoring stitching mosaics), so I would think that more data captured on the larger sensor could be cropped to fit the need better than the smaller sensor precroping the fov. But that’s the position of a landscape guy so I don’t know if it transfers or not to Astro.
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Jonathan Spool:
I’m looking at picking up a William Red Cat 91 with a ZWO ASI2600MC Air. I played around with the FOV of that combo on Stellarium and found that while it was great for Andrometa galaxy and M42, it just didn’t have the reach for most of the galaxies out there that I wanted to capture. Just for kicks I decided to enter in the parameters of a IMX585 sensor camera to see how that changed things up. I was surprised at how well it worked for those smaller targets, albeit at less resolution than the apc sensor. Seems to be a better solution than getting an ultra long focal length telescope as well. Is this a typical approach as how to capture both nebulae and galaxies with the same setup?
No. Size matters as well as focal length.
Can’t speak to the image circle of the Redcat, but I use the 2600 on a Celestron Edge 8, and with THAT image circle, the 220 guide camera sits right on the edge of the image. It’s fine for guiding (even at the full 2033mm Focal Length), but I wouldn’t be able to make anything useful from it image-wise.
YMMV
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Jonathan Spool · Dec 16, 2025, 10:44 PM
…. IMX585 sensor camera to see how that changed things up. I was surprised at how well it worked for those smaller targets, albeit at less resolution than the apc sensor. Seems to be a better solution than getting an ultra long focal length telescope as well. Is this a typical approach as how to capture both nebulae and galaxies with the same setup?
You aren’t gaining much, if anything. On the contrary, you’re loosing a massive pixel count. The 585 is an amazing sensor, but it’s simply not big enough, not enough pixels.
Just for science, I swapped out my IMX571 for a Minicam8 (585) one night on an Esprit 100, which is roughly the same size as your scope. The FOV made target selection almost impossible. I compared the datasets side by side and my FWHM’s were exactly the same. There was no increase in sharpness. Nothing gained by changing cameras. Only pixels lost. If you have an APS-C, don’t ditch it for a 585 please. Maybe some day we’ll get an APS-C starvis 2, but until then….
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On my Ultra-Cat 108 (518mm Focal Length) I use a Player One Uranus-M Pro (IMX585), and a Poseidon-M Pro (APS-C), and while I haven’t published yet using my new APS-C camera you can see my IMX585 shot here (I will be adding RGB stars to it next week) https://app.astrobin.com/u/AstroJeep?i=vrbd6q#gallery
I have about two more nights of shooting with the Poseidon-M Pro on the Rosette Nebula before I publish it, and last night’s subs are fantastic. While I agree that nothing can replace focal length for the absolute best in magnification you can absolutely use two different cameras to get two different fields of view out of one telescope. Remember your APS-C sensor size is 3.76 pixels, and the IMX585 is 2.9 pixels if I remember correctly. While the IMX585 sensor is smaller there are still a lot of pixels crammed into that smaller field of view so you can use it to get good results of those mid range galaxies, like M51, on a budget, and it will still look good. I would have needed at least 900mm of focal length with my APS-C to approximate what I got with my Ultra-Cat 108/IMX585 shot shown in the above link. While I am no where near as good as most on this site, and even though I am still fairly new to this, I will let the link to my image speak for itself concerning the focal length/IMX585 question.
If you can swing it get both the ASI2600 and an IMX585 camera for your Cat 91. I think you would be happier. Like someone said above though don’t get rid of the 2600 camera. You can always get the IMX585 later, or vice versa.
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Thanks for the replies. I was not intending to replace the apc camera with a 585 one. I would own both and utilize the 585 for tne smaller targets rather than lose even more pixels with an extreme crop of the image from the apc. I priced out going with non duo/air cameras and pick up an asiair plus, a guiding scope and camera to save some $, but the cost turned out to be the same so I’ll stick with the air cameras.
I think this approach makes total sense. Use the large sensor with large pixels for those large targets and use the smaller sensor with small pixels for smaller targets. My usual camera is a 585 but if I replace that with my QHY5iii715c which has about the same number of pixels but half the size of the 585’s already tiny 2.9 microns . It’s like going from 900mm to 1800mm with the same aperture. Another way to look at it, it’s like replacing my 150mm F/6 Newt. with a 150mm F/12 Cass. I know that’s a very extreme example for most people but it proves the concept. If the QHY was mono and cooled, I’d do it a lot more often.
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I think a combination of skies quality and optical performances drive the rest of the story, assuming you get decent tracking figures.
For a given focal length, there are not many ways to widen the possibilities :
focal reducers are probably the most innocent solution, providing shorter f and faster F/D, which are interesting for deep sky larger targets.
barlow may increase reach, but at the expense of f/d (longer exposures needed) and unchanged separation power (linked to d)
So each instrument has its own set of limitation , or should I say its own set of capabilities to be optimistic, but there is definitely no “one size fits all” approach, especially for deep sky where targets size range is tremendous, from larger nebulae (eg Spaghetti) or smaller planetary nebulae.
I don’t think playing with camera sensor size is a good path, for several reasons :
unless you want to cover extreme opposite targets (high speed solar vs deep sky for instance) , multiplying camera is expensive and rather inefficient, because it doesn’t dramatically change optical constraints of a given instrument
as of today, APS-C cooled camera are the sweet spot solution for deep sky imaging; moreover, it is possible to tackle with binning to address smaller target and longer-f instruments, should the pixels be too small
As regards instrument, I would (and I did it, btw) acquire something with a focal length close to the limit of available seeing conditions. In my opinion, this is in the range 1000-1200mm. Refractor vs reflector is a mater of personal choice, I’ve no religion about it. For refractor, the sweet spot is around 120mm for d, to my opinion.
For that reason, I have (too, according to my wife) many instruments, from camera lenses up to 180mm, then four scopes (350, 550, 900, 1200) and a RC8 @1600mm. For deep sky imaging , I only use APS-C format.
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