Astrophotography: Refractor VS SCT!! 

Very helpful and a super comparison. Clear skies

For SCTs the cooling isn't an issue when you start using an insulating blanket to stop the thin wall tube from quickly equalizing temperature. This means you can get to imaging much quicker. Mirror shift of an SCT and external guiding have no special relationship, an OAG will be affected as well as the star being tracked will move suddenly. If the mirror moves it's only in one frame of exposure and a very fractional amount less than actually bumping the tripod leg. In fact you are more likely to have issues from wind pushing(and stop pushing) on an OTA (regardless of style of telescope). The external guider supplies a much wider field of view for more stars especially in relatively starless fields. If the guider is properly mounted, where issues arise is whether the sampling rate and the pixel scale are too far off and mismatched between the guiding system and the imaging system. If the pixel scale of the guider is too dissimilar then guiding corrections will move the mount in the corresponding corrective direction at a rate too fast or too slow and result in star trailing. For SCTs this is more critical because the much longer focal length has little fudge-factor for guiding error. Whether the guide scope is 30mm or 80mm, if the pixel scale figured by the focal length and guide camera pixel size is poorly matched there will be problems especially as focal lengths >800mm. At one time there wasn't as much of an issue when the pixel sizes of the CCD cameras were ~6-9um and using an 80mm ASI120mm 2x barlow was close enough guiding. However, as pixel sizes dropped in cameras, pixel scales did too and guiding for those with the newest equipment began to believe long focal length imaging was impossible for DSOs. Currently a good SCT external guide camera package would be guidescopes around 200-250mm with either ASI678mc or QHY5-III-715c and 2x or 3x depending on focal length of the SCT. Yes an ST80 could be used, but the key isn't the aperture of the guidescope as much as the focal length guide camera pixel scale.

Very informative video, I'm the perfect target audience for this subject. Been working with a DSLR and a 73mm refractor and considering what my options are going forward into mono and later greater focal length.

Nice comparison!

What a fantastic and thorough comparison! Thank you so much for this... I was between exactly those two scopes and I went with a vintage C8 just because I found a great deal, so the Edge will come in a future time... planing on having a hyperstar whne the time is right... So the first time I used the C8 reduced to 6.3 I had a blast on resolution and light gathering, I was amazed to have capture so much detail on the Iris Nebula just undr 45 minutes on the tail end of the night under Bortle 8-9 skyes, I was just very curious to understand how the F ration woudl compare with the extra aperture and there you got the perfect example on how much aperture actually means in a pratical standpoint... awesome job

+1 for SCT and then just get a hyperstar for shorter focal lengths. You can have 2000mm, 1400mm and 400mm all in one scope.

Very informative, thanks!

Excellent comparison and video, James! I am only imaging with refractors to date (80mm and 110mm aperture) and I am still shying away from going to mirror telescopes. This video gave me a lot of insight of pros and cons! Thank you!

Hey James, super comparison video mate! Interesting stuff indeed! Being a refractor guy! I love my 120, so sounding a bit bias, I thought your 115 stood it’s ground against the reflector, the crescent images were excellent from both! That being said, I have thought I wouldn’t mind a little more reach for those distant galaxies! And I thought the SCT 8 would be nice! We’ll see how the funds go🤣 Great job mate and clear skies!

Great video, as always! To deal with filter offsets and an OAG, I created an OAG focuser and corresponding software that solves that problem once and for all. CS!

That's a fantastic comparison James. I love my small refractors for taking widefield images, but I do sometimes crave something with a longer focal length for galaxy work. My concern has always been that the weather/seeing here in north east Scotland is rarely that good, so while something like an 8" EdgeHD would provide higher resolution, it's debatable if that could be fully exploited. Lovely images btw, I've always believed that stars on SCT's weren't as good as refractors due to the central obstruction etc, but your images prove otherwise.

Great video. I have a C8 Edge which I use for DSO at f/7. I have experienced pretty much everything you described in your video. Just recently I got the OAG to work with the C8 for guiding and it's a game changer. I also have a small refractor for wide field (500 mm), and have considered getting a 700 - 800 mm for galaxies, but your video is changing my mind. The details will not compare with what I can get with the C8. And it's such a short time when I can image Galaxies anyway. This is a very useful comparison. Thank you!

I started with a 6”SCT and went to a 72mm refractor. I’ll keep the SCT and one day even invest in a hyperstar. As it is I’ve decided for now to buy two refractors (80,115) and change the FOV by camera (294,533,2600). Yes more expensive but I find using the refractors more fun and less hassle to use

Really helpful video comparison. Your SCT images are among the best I've seen. How about an SCT image showcase?

Side note-the Crescent neb has always reminded me of a horseshoe crab, not a “Euro sign or Crescent. Especially in your fine images. Excellent video btw.

Great video and great comparison, loved the technicalities and the accurate way of describing your process. I own an Evolux 82ED and I absolutely love the possibility of framing multiple targets in my image but man... I have to admit that those details in the SCT are juicy! Sure you can expect that because of the higher resolving power but still makes me want to order an edge HD right now!

Great Video James! As a Reflector owner, Im used to High Magnfication shooting Deep Sky Objects to, lol. But Then There are Big Wide field Targets like Clusters and Some Nebula! Though, My Dream Setup is To own a Larger scope (for Visual/Photography ) along with a DSLR for Widefield and a Tracker. Clear skies!

I do electronic assisted astronomy (EEA) with Sharp Cap, so I do not use or need guiding. I do not do any post possessing. Being elderly and feeble, I use a Star Adventurer GTi go to mount which can handle 11 pounds. I have been using a Celestron short tube 80/400, a Skyoptikst short tube 90/500 with a x0.80 reducer/ corrector and an SvBony sv305 80mm ed with a x0.80 reducer/ corrector. I use a SvBony cls filter and a ZWO asi294mc camera. I have found, oddly enough, that the 90/500 takes the best photos. I also have an Orion 130/650 Newtonian reflector, which takes good photos and has a smaller field of view. I just bought a Celstron 6" Schmidt Cassesgrain and a x0.63 reducer/corrector, the largest my mount can handle. I am going to see how it works and may buy a HyperStar 6 v4.

This was a really great comparison, James. I see the Celestron 8" EdgeHD offered as a package with an AVX mount (30 lb capacity). Would you consider the AVX mount to be suitable with use for the 8" EdgeHD after all the accessories (OAG, astro cam, filter wheel, etc) are added? I have an Askar 107PHQ (750mm fl) right now and I'm using a ZWO AM5 mount which works great with the 107PHQ. As you mentioned in the video, though, galaxy season was a bit of a letdown using the 107PHQ and I'd like to have something bigger for the next go-around, and also for some planetary imaging and observation. However, I'm sure I'd need a different mount to accommodate the 2032mm focal length of the SCT. I've heard so many different opinions about the AVX mount I was unsure if it's worth getting the EdgeHD/mount package. Thanks again for a great video!

very informative. I've been debating getting an Edge HD8 for months. Anyway, I love the background image for this video. Which part of space? I really like some good visible small galaxies in a wide field image.

One more thing to add (under the umbrella of "consider your targets"), I presume that an SCT is really the best (only?) option for planetary imaging.

Your video has alot of information James. Personally, since i have started using refractors, that has been my goto, aside from the Rokinon that is 😂. Clear skies !

Great comparison video James, I have the Askar 65 PHQ currently and I’m now wondering if I should think about mounting my 8” Dobsonian for galaxy’s 🤔

I have 8HD, ASI2600MC Pro on EQ6R Pro, used Canon 5D M3 before. Stars are definitely bigger IF YOU DON'T USE FILTERS. I did few nights with L-Ultimate dual narrowband filter on Crescent nebula and it blew my mind compared to my old unfiltered photo using my old Canon. However with filters you may expect halo around bright stars due to internal reflection between the filter and secondary/corrector plate? If too windy, but dark, remove the dew shield from SCT and you will be fine. Also with SCT you have smaller chance of your camera hitting the tripod legs while slewing. The point of balance is much lower which makes your setup ending up higher and you will be able to keep tracking even well past meridian without worrying about it hitting something. The main question should be: DO YOU PLAN TO SEE AND IMAGE PLANETS OR NOT? If you want to image planets, get SCT.

What about dew challenges on the corrector plate? I see you are using a dew shield. Do you need to use a dew heater? If so, does that affect star size/shape as others have noted?

Have seen tests between the edge 8 and standard 9.25. While the edge 8 has a slightly flatter field, its not that much flatter then the 9,25. Certianly the edge 8 is costs more, but price and performance wise better off with the 9,25. The 9,25 has the better mirror, as it F4.2 rather then an F4

AM5 Works pretty darn good on my C11 and FLT 132 btw.. easy peasy 300s subs.

During presentation on TAIC, Garry Imm mentioned that 9.25 Edge is sightly better in resolution than TOA 130mm (finest refractor there is). Then, I asked him to send examples showing it. He did. But margin was absolutely tiny, which could be seen after massive magnification. However, his TOA was old version. New version has incredible flattener producing 1um star test. In my opinion, top end 130-180mm refractors are equal to SCT. However, their price and their weight are not justified. Thus, I have TEC 140mm on order. I am not sure that purchase will be justified, when I have 9.25 Edge.

Q. You actually started with a "Baby Sized" 70mm scope? W O W ! I know plenty of folks that began with an ancient or even homemade 6 inch Newtonian. But a 70mm ? I'm speechless!

so your saying I should buy more telescopes....

Should compare same aperture, same image scale, same mount.

Great video How Meade etx 90 or 125 is on galaxies.

Ok, let me start by saying that I make this comment with the greatest of respect to DSO Imager and any other subscribers: this is my opinion. Respectfully, I had a 7" Astro Physics Starfire refractor (I sold it) - and I presently have an F10 and an F8 Meade SCT. (Yes, I have both and they are pristine, and yes I'm an idiot for having both - there is a reason, but that's not part of my rambling now.) I found that the 7" AP was NOT nearly as good as what the reviews had stated. (It was greatly wanting! Oh yes, I like AP, but perhaps Roland rushed the last production of 7" Starfire refractors - I don't know.) I truly believe that many, not all, but many of these reviews are PAID by the supplier/manufacturer - which is a shame. It (some of these paid-for reviews are not real) it misleads the new astronomer. The Meades - they work, and let me be clear, I am not a Meade paid stooge, and quite honestly I have had many BAD experiences with Meade - I do NOT love Meade! Obviously, I can't compare the 7" to the 16" OTA's, (its not an apple to apple comparison) but I'm old: I've been observing for over 60 years, and I've used/observed through a 74", a 24" and I have seen the ccd images from a 100" (2.5 m), and through a 1 m. So, let me return to the 7" refractor and the 16" Meade(s). I also have and use a 100mm Skywatcher Esprit - the 100mm Esprite gave better images than the 7" AP - really. The visual images from the 16" Meade ACF (f10 or f8) far exceed the images from the 7" AP or from the 4" Esprit. There is no substitute for aperture; really, on reasonable nights where there is reasonable (NOT perfect, but reasonable) sky stability, there is no substitute for a large OTA. Respectfully, I hear all of these reviews on various scopes - you get what you pay for: really - the larger the aperture (when reasonable viewing allows) the views from a large OTA are best. I hope that I have not offended anyone: please - this is just my comment. Perhaps I am wrong! Good review though: and thank you.