Seeking high focal length telescope recommendations for deep sky imaging - Forums

Hello, I have been using medium to lower focal lengths for a few years and wanted to get into the realm of high focal lengths for deep sky.

I know that its usually more expensive then high focal length planetary, but I am willing to spend a few thousand (3-4k) on a scope. I have an eq6r pro which has never really failed me, but I know I would maybe need a new mount to carry something heavier. My main goal is just to get good detailed images of galaxies or small nebulae,. Having aperture fever, I’m looking for something with a minimum of 8-10”. A Schmidt Cassegrain or reflector is what I’m mostly thinking but I’m totally down to get a dob as well since I know its probably cheaper.

I’ve tried looking a bit online but I’m still not sure, I just wanted to get some actual peoples opinions.

What are some scopes/setups you would recommend?

I have a 13” newt on my EQ6R. It's up to the limit of the mount, but the mount handles it, especially when seeing is good. I DIY’d the scope so that it is only about 40lbs. So that would be probably the max option!

Tom

The EQ6r-pro works fine with my 6” Newt stretched out to 1580mm and could go further. Not the weight you’re looking for but consider it a data point.

We have the same mount, sensor and aim. I was looking for a C8 for that purpose which seems to be a strong option

Hi! I felt the same need as you, and I also own an EQ6R Pro. After a few years with a 150/600 Newtonian, I just got an RC8 Carbon. I've had limited opportunity to test it due to bad weather, but it seems to have potential. Initial impressions lead me to believe that for certain objects (such as rather bright planetary nebulae like M97) it's necessary to change imaging strategies, moving closer to lucky imaging. Collimation, a field flattener, and its backfocus all become important variables. It's certainly not a telescope you just set up and everything works right away!

As you already have a 200mm f4 Newt, I presume you are looking for at least 1600mm focal length?

I also presume your seeing (2arcsec or better) merits operating at this focal length to get thebetter detail you are looking for.

One option is a 8-12 inch f8 RC.

This is my telescope of choice for its ease of use and stability, once collimated. Much has been made here of collimation difficulties of these scopes, but I found it straightforward with the right tool (Takahashi colimator). Check collimation every few months. In comparison a fast Newt was much more challenging for me. My RC is permanently mounted in my observatory. I also bin-up x 2 because I am way oversampled. However, I feel that these disadvantages of oversampling (RN, fov loss) are outweighed (at least for me) by a much easier to use system than a Newt or SC. IN my case the larger scope is more of a light bucket than a detailed imager. Again if you want detail, you need to have the right conditions.

I also my use my 12inch GSO RC with a field-flattener (again may not be so impotant to you if you are just after small things).

With an 8inch RC you can use your existing mount, but you will need to upgrade the mount if you go larger. Despite having lots of success with my Skywatcher EQ5 and EQ6, my SW CQ350 bought for the RC12 was a very different story. Two have failed on me and I am now trading up to an EQ8.

Good luck in your search.

Brian

From what I heard and read on the internet Celestron's C8 and C9.25 Edge HD seem to be solid options. Very good illumination and correction at native focal length. Re-/Downsample to regain the SNR and you will fall in love with smaller targets.

Me personally, I used GSO's lineup of Ritchey-Chretien telescopes. One was a plain white 10 inch model and my current one is a 10 inch which was upgraded mechanially (carbon tube, different primary cell and housing, 2,5 inch feathertouch with tilting) which is a breeze to use. For smaller sensors you can use the AP CCDT67 0.67x reducer, for bigger ones I can recommend both the 2 inch and 3 inch flattener.

Collimation can be straightforward and is very stable.

I have gear acquisition syndrome, so I also have an ODK10 from OOUK sitting on my desk right now, which seems to be a solid alternative.

I’m not sure if your mount can take it but I use an Edge HD11 for imaging PNe. I have mine mounted on a Mesu 200 and it works very well. So I think a 8” or 9.25” SCT would work well with your eq6. You will need to use either an OAG look at the ONAG from Innovation Foresight for guiding.

Cheers, Ian.

I'd ask myself what is my median seeing and work the maximum focal length it can support and then max out the aperture my mount can handle. Anything else is wasted money and time.

andrea tasselli · Jan 23, 2026, 07:39 PM
I'd ask myself what is my median seeing and work the maximum focal length it can support and then max out the aperture my mount can handle. Anything else is wasted money and time.

Agreed. With 1” seeing on good nights at HCRO, my CDK14 is still seeing limited. Your mount probably should track at or below 0.5” rms if you are looking at 2000mm focal length

I have been using an 8” Meade LX200 ACF OTA with a reducer for several years which brings it to about 1550 f/l and f7.5. While theMeade scopes are not made anymore, the Edge SCT’s function in a similar fashion, and I believe they also have a mirror lock. This is a good complement for my wider field refractors and can also be used for planetary work in the native configuration.

I’d echo Andrea’s comment about first thinking about what your typical seeing is. Then matching your focal length (or more precisely imaging scale) to that.

I usually experience 2” seeing most of the time and I image at 0.76” pp (1m FL and 3.76um pixels). This gives my as much detail as I can get really. I’ve seen images from a C14 local to me that do not show any more fine detail than the images from my 200pds.

I currently have a Celestron 9.25” XLT SCT with an Eq6r Pro. For me, imaging with it reduced at about 1450mm and an OAG was probably the limit for the mount in ideal conditions.

I also take my setup in and out every night, and I don't really have anything to block the wind where I image, so I often ended up tossing about a good chunk of my subs because the scope and dew shield function as a sail in even gentle winds. On completely calm nights, I had some success and could usually guide in the .6”-.9” RMS range. Even backing down the focal length to about 525mm at f2 and shorter subs with the hyperstar still wasn't immune to light winds.

There's lots of good points here about appropriate sampling for your skies, but don't forget to consider your imaging environment as well. I typically have pretty good seeing where I am, but 1” skies don’t mean much if your setup is exposed to some wind that throws guiding all over the place.

I've actually been considering selling the SCT (even though I really love it!) since I can't do much about the wind where I am and I don't plan on moving anytime soon. I picked up a mid-length refractor for most nights (AT115EDT) since there's typically a light wind at a minimum, and may try right-sizing my SCT down to a C8 or C6 for calmer nights and focal lengths to see if I can use them more often than I've been able to use the 9.25.

I’ll add my .02

Running a Celestron 8 Edge (FL2033mm) f/10

With a reducer, the FL drops to 1423mm @ f7

I also added a Hyperstar v4 for a FL about 390mm at f2

Essentially 3 scopes in one. Unlike your wider FOV scopes. a planetary type SCT will/can get you great results, but you’re going to need a BUTTLOAD of time on target

Juju.Ziggy · Jan 23, 2026, 06:55 PM
What are some scopes/setups you would recommend?

Subsidiary question is : what focal length range are are you aiming at ? How good is your average seeing?

Fast solutions will be newtons with F/D between 4 and 6 , up to 250mm

Alternatives are Maks, RC , SCT with slower F/D and extended focal length.

As regards SCT, an XLT Celestron offers more flexibility (full focal, reducer, primary focus ) with a small quality penalty.

It really depends on the kind of target you are aiming at.

Take also into account that F above 1000-1200mm requires good sky conditions and good mount performances for deep sky.

My short list :

Newton 200 F6

Newton 250 F5 (beware of the wind, though !)

Celestron XLT 8” or 9.25” (not EDGEHD)

RC 8 with AP CCD67 (good combination at 1200mm , and the possibility to go up to 1600mm)

Vixen VMC 200, range 1200-1950 mm

Bear in mind that the mount will also bring some limitation

I run a C8 EdgeHD on my EQ6-R with an OAG. Sensor is the ASI2600MM. Guiding is typically around 0.5” RMS. My setup is reasonably shielded but it is a sail in wind, have to toss some data. On the scope, I have the reducer and find the blue is pretty bad, not well corrected. So I run f/10. I’m after tiny things anyway and I love it. I get some CA with the scope which is probably just me being lazy and not nailing backfocus or something. I’ve thought about the C9.25 and someone in my club has one, has mentioned there are similar issues with the reducer. While f/10 is doable it’s slow, I’ve been thinking about reducing focal length and pixel size and trying my SkyWatcher 150PDS (f/5 6” newt) with ATR585M which would go from pixel scale of 0.4”/px with the C8 @ f/10 to 0.8”/px on the 150PDS. I’m oversampled anyway with the C8 right now. Project for the spring I think.