Astrophotography: Refractor VS SCT!!

In this video I compare a refracting telescope to a Schmidt Cassegrain Telescope (SCT). I discuss the strengths and weaknesses of both and show images of the same targets taken with each telescope.

Gear used:

Telescope: AT115EDT
Camera: ZWO ASI1600MM
Mount: SkyWatcher EQ6R Pro
Filters: Astrodon 5nm, Ha & Oiii

Telescope: Celestron Edge HD 8
Camera: ZWO ASI294MM
Mount: Skywatcher EQ6R Pro

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High Point Scientific

RC-Astro:

Clear Skies!

#astrophotography
#telescope
#pixinsight

[aw]

Very helpful and a super comparison. Clear skies

[legacysearches]

Great vid. I have never done this type of comparison with my scopes.

[ateiviz]

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.

[pduffy]

1:00 that's an awesome picture. Several galaxies visible. Your pictures are very high quality.

[AndreHd]

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

[mycarolinaskies]

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.

[ppoinha]

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

[bluecheetah]

I liked and subscribed because I’m a beginner and don’t know crap, now I am more informed on how to get to my next step-thanks

[mif]

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!

[jlecomte]

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!

[Owendinga]

Super helpful video... even a year later.

[steppen]

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!

[emuhead]

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

[SimonsAstro]

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!

[petesastrophotography]

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.

[aneyesky]

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.

[MrMrduke]

Awesome video sir! Exactly what I was looking for! I think you have helped make my decision on my upgrade from WO GT71 to the Askar 120

[NoxusGr]

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!

[avt_astro]

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!

[ttp_]

Superb video comparison, thanks for the video!