Refractor vs. Astrograph Reflector for DSOs

I guess “win” is a relative term. The refractor is plug and play with little worries about backfocus and collimation. The Carbonstar will not cover Full Frame with the Coma corrector if that’s a factor and it requires 55mm backfocus.

Aperture wins out in resolving finer details and collecting more photons, and the reflector will have less CA to deal with (although still some with the glass in the corrector). But, like Arun said, refractors are much easier to deal with with a portable setup.

I don’t know the edge correction of either optic, but especially if you’re looking at APSC, you’d have to compare raw images from each. I know with my 10” f4 Quattro with the well regarded Quattro coma corrector, I very much struggled to get a FWHM anywhere below the low 3”s. I was able to get similar or slightly better FWHM numbers from an Askar 140 APO despite the much smaller aperture, partly because it’s less prone to wind by a good bit and had nice optics. And my TOA-130 gets in the 2”s on a regular basis despite being yet smaller because of it’s incredible optics.

So all other things equal, yes, aperture “wins”. But all things are seldom equal.

I have three f4 newtonians (600-1000 mm), one RC 1360 mm and one apo 480 mm. For details of galaxies (except the giat M31) clearly wins a higher focal length of 800-1000 mm as mentioned already. My personal prefererence are newtonians, which however always have the collimation problem. If you buy one, you have to deal with collimation which needs special equipment such as a laser or an ocal system and experience. However, it pays out on a long term run.

CS Peter

I am currently using the CarbonStar 200 newt with CS flattener. It’s on a pier in a roll off roof observatory. Its definitely a refractor killer on a permanent setup. Collimation takes 10 minutes if needed. I would not hesitate taking it on a road trip, unless I had to fly, because the view is worth the climb.

“Unless you need rain. Clear Skies”! Heavenly Backyard astronomy.

I have gone down this path and have finally chosen to just use my refractors over my reflectors. In fact I just ditched my Epsilon 160ED in my remote observatory for an UltraCat 108. My long focal length setup is just a TOA-130 5.1 inch refractor.

Obviously people have had incredible results with the Epsilon and it is a fantastic instrument, but there are some intangibles that you don’t hear about at first, like the significant illumination drop towards the corners on a full frame sensor, and the very very difficult process of getting your stars in the corners to look remotely acceptable. Add to that the immense amount of diffraction spikes you have to deal with when imaging rich star regions in the milky way.

Personally I found that processing the data out of my refractors was a far more enjoyable experience than it was out of the Epsilon, even if they were substantially “slower”. All my setups are under B1 skies. I never spent 20 hours on a target with my TOA and thought at the end, “I just wish I used an f/3.3 Epsilon instead”. This included dark and reflection nebulae targets, and IFN.

While larger aperture reflectors in theory should be able to get better details, I think the vast majority of them are wasted under skies with subpar seeing conditions that don’t support that aperture and focal length. Eventually I would love to have a massive reflector under pristine skies, but for now refractors are doing fine.

Alex Nicholas · Nov 25, 2025, 12:31 AM

If your focus is Galaxies, 6” F/4 might be a little short, but then, not worse than a 3.6” f/6.7 refractor.

You have to factor in that the newtonian has more light gathering area (even accounting for the central obstruction), and at f/4, its almost twice as ‘fast’ at gathering light…

If you’re running a smaller sensor like the IMX585, IMX533 or IMX294, then a ~600mm focal length may be just fine for plenty of galaxies, but regardless of the desired target, a 6” F/4 is better than a 3.6” F/6.7.

Depending on your mount - the cost difference between the 150mm and the 200mm might be worth considering. 800mm will give you a lot more options regarding targets, and again, another massive step up in light gathering area.

Running those sensors at F6.7 would require an eye watering amount of time to get a good SNR. They really only make sense if you can get the focal ratio down to around F/3 and below. Even then, by that point there are so many optical errors that become magnified at those focal ratios that small pixels might be a wash anyways.

As for the stated goal of shooting galaxies, the OP might find 600mm lacking. The fun really begins around 1000mm, ± 200mm. By that point, refractors start to get expensive, assuming you want a decent focal ratio.

If you do switch to reflectors, be prepared for soft images for a bit while you get the collimation situation down. Reflectors can be pretty fun though; your knowledge of optical issues (and how to deal with them) will increase exponentially and your wallet will thank you. The only cost you have to pay is a bit of your sanity.