80mm Vs 102mm refractor for deep sky astrophotography?

[DougQuaidHauser]

Greetings

I was wondering which OTA would be best for deep sky astrophotography, an 80mm F/5 or a 102mm F/5, (Skywatcher Startravel 80 & 102, Orion, Bresser etc) or is there no real benefit to the extra aperture at my beginner status?

Currently I have been having great fun with my Celestron 127 Mak with a Nexstar Alt-Az GoTo mount using a DSLR camera for planetary imaging, but obviously this is terrible for deep sky due to the near F/13 scope. I am looking to buy a small refractor OTA whilst using this same mount (yes I know its an Alt-Az and not an equatorial mount) for some beginner deep sky imaging and learning the ropes.

So in a nutshell, is it better to go with the 80mm and lighter payload, or go with a 102mm (Not that either are easily available)?

All advice appreciated.

[Concordia000]

Neither.

Yes, the bigger aperture does help somewhat, but you have more problems before that. You need an apochromatic (APO) refractor. And an equatorial mount.

The scopes you listed are all achromats and if you use them for imaging, they will have severe fringing (false colour) on the picture. That means every star will have a purple halo around it and while it can be mitigated with an aggressive filter and post processing, it’s not recommended.

If you track with your mount, it will introduce field rotation into your picture and you won’t be able to take long exposures. Your mount can be used with an wedge to act as an EQ mount, but that wedge is very expensive and it’s hard to recommend.

What I would suggest is to get a star tracker, or AZ-GTi on a wedge, and a small APO — 50-60mm in aperture. The small aperture will mean those scopes are not very good visually, but for photography the F-ratio and focal lengths are more important. For two scopes with identical F-ratios, the larger scope has a bigger magnification and more resolution which might be desirable, but for many DSOs the short focal length is actually an advantage. Do not underestimate what star trackers and a small APO can do; the attached picture was taken with a WO RedCat 51mm on a Fornax Lightrack with an unmodded Sony A7R.

Aperture does matter a lot more for visual though, and presumably your scope would not be for visual only. A big achromat is best for visual use though your 127 Mak is already a fantastic visual scope.

[DougQuaidHauser]

Thanks for the advice. I completely forgot about about chromatic aberation being a Maksutov user, and a Newtonain user before that, not used to refractors so no point me purchasing the ones I mentioned as would only use the OTA for astrophotography, as you mentioned already, I have a real nice visual scope already in the Mak 127.

I dont want to break the bank so to speak (wife) so have been looking at the Skywatcher ED70 scope (£300) but in reviews people keep mention needing a £200 field flattener so not sure about that one now. Do all small refractors require a field flattener for astrophotography?

 

PS excellent photo of orion, Id be more than happy with images close to that

Edited October 16, 2021 by DougQuaidHauser

[Cosmic Geoff]

I suggest that you match your ambitions to your equipment and budget. Neither the achromats you mention nor your alt-az mount are suitable for "proper" deep space imaging. For the latter you need to spend a lot of money for an APO scope and a heavy imaging equatorial GoTo mount.

However if you tailor your ambition to dabbling in some EVAA imaging, you can use a Startravel 102mm and the Nexstar alt-az mount.  I have used a Startravel 102mm + a Nexstar SLT mount (albeit on a more rigid permanent tripod) + a ASI224MC camera to take many pleasing shots of galaxies, star clusters, planetary nebulae, comets etc.  An exposure of a few seconds suffices. The images can be live-stacked with suitable software.  

If you search in the EVAA reports section, you may find some of my results.

[DougQuaidHauser]

5 hours ago, Cosmic Geoff said:

I suggest that you match your ambitions to your equipment and budget. Neither the achromats you mention nor your alt-az mount are suitable for "proper" deep space imaging. For the latter you need to spend a lot of money for an APO scope and a heavy imaging equatorial GoTo mount.

However if you tailor your ambition to dabbling in some EVAA imaging, you can use a Startravel 102mm and the Nexstar alt-az mount.  I have used a Startravel 102mm + a Nexstar SLT mount (albeit on a more rigid permanent tripod) + a ASI224MC camera to take many pleasing shots of galaxies, star clusters, planetary nebulae, comets etc.  An exposure of a few seconds suffices. The images can be live-stacked with suitable software.  

If you search in the EVAA reports section, you may find some of my results.

Hi and thanks for the input. Trust me my ambitions at this stage are really low, hell Id be happy seeing a bit of nebulosity etc in some images at this point, the fun is in the learning for me, dont want to be one of those 'all the gear, no idea' guys. My plan is to get a small APO now, and then get an appropriate mount for it in time.

Could you clarify what EVAA means? Ive had a brief look in that forum. Thanks

[Andrew_B]

Have you done much astrophotography just using basic camera lenses? Shopping secondhand can get you some real bargains and you might be surprised how much detail you can capture with something like a short telephoto.

There are a few advantages with this approach - shorter focal length means tracking errors are less of an issue and camera lenses typically have faster focal ratios than scopes so even when stopping them down a bit to control aberrations you can normally get away with shorter exposures. You're still learning the same workflow that applies to shooting with a scope but it's easier and less likely to cause frustrations and astrophotography can be tricky enough without making things harder than they need to be when you're a beginner.

[DougQuaidHauser]

16 hours ago, Andrew_B said:

Have you done much astrophotography just using basic camera lenses? Shopping secondhand can get you some real bargains and you might be surprised how much detail you can capture with something like a short telephoto.

There are a few advantages with this approach - shorter focal length means tracking errors are less of an issue and camera lenses typically have faster focal ratios than scopes so even when stopping them down a bit to control aberrations you can normally get away with shorter exposures. You're still learning the same workflow that applies to shooting with a scope but it's easier and less likely to cause frustrations and astrophotography can be tricky enough without making things harder than they need to be when you're a beginner.

Hello, yes it is something I want to try as well, and to answer your question, I am a complete noob with regards to astrophotography at this stage. So far I have tried it this year without much success due to using a 127 Mak. Mostly done planetary imaging, post processing video up to now which has been a blast.

I have a Canon 1000D DSLR but bought it used just the body so would need to buy a lens, but zero clue at this point which lens would be compatible as never been a camera person. Once researched I could buy a used lens and give it a go.

[Concordia000]

1 hour ago, DougQuaidHauser said:

Hello, yes it is something I want to try as well, and to answer your question, I am a complete noob with regards to astrophotography at this stage. So far I have tried it this year without much success due to using a 127 Mak. Mostly done planetary imaging, post processing video up to now which has been a blast.

I have a Canon 1000D DSLR but bought it used just the body so would need to buy a lens, but zero clue at this point which lens would be compatible as never been a camera person. Once researched I could buy a used lens and give it a go.

If you mention to the customer service/shop keeper that you have a Canon camera they should be able to tell you which lenses are compatible.

Second hand lenses are what I will recommend too, because they can be had for dirt cheap, like £50 at local stores. A 135-200mm lens will be pretty good to begin AP with, but you will still need an equatorial mount.

The SW72ED needs a field flattener to have a flat field over APS-C sensors iirc and it will still show chromatic aberrations. An alternative is to get a short FL Newtonian with a coma corrector, even though the latter isn’t strictly necessary.

But before you get any optics, you really need an equatorial mount no matter what.

[Prathab]

On 17/10/2021 at 16:16, DougQuaidHauser said:

I have a Canon 1000D DSLR but bought it used just the body so would need to buy a lens, but zero clue at this point which lens would be compatible as never been a camera person. Once researched I could buy a used lens and give it a go.

Any EF or EF-S mount lens are compatible with your camera. If you are looking to buy used, a 70-300mm F/4-5.6 lens can be found around £100. In the £300-£400 range you can get a Rokinon/Samyang 135mm F/2 which is a no brainer or a 70-200mm F/2.8. The additional money will get you bigger aperture and cuts down on the required exposure time. There are 3rd party manufacturers (like Tamron, Sigma, Tokina) that make some great lenses and are cheaper than Canon made. Look in mpb and you'll have plenty to choose from.  Read some reviews online to make sure the specific model you are considering is not a dud.

As people have already suggested an Alt/az mount will be a limiting factor as DSO imaging is based on the premise of long exposures. A used star tracker is not a bad way to start and are not too much money.

 

[Skyline]

There's nothing wrong in experimenting with dso imaging with an achromatic.  You'll find if your narrowbanding you can even get away with using an achromatic rather then a apochromatic scope.

Why not just learn how to image on your current scopes,  then later on buy something better?

[Whistlin Bob]

On 16/10/2021 at 23:30, Andrew_B said:

Shopping secondhand can get you some real bargains and you might be surprised how much detail you can capture with something like a short telephoto.

This! I've had lots of fun doing this.

The image below was taken with a 2nd hand 600d, with the IR filter removed, on a Star Adventurer, using a second hand 135mm lens off eBay for about £25. 

And this one used the same lens on an Altair 183c fan cooled camera.

So it's definitely possible to do things on a budget- but as others have said, the mount is probably the most critical part.

[Dazzyt66]

49 minutes ago, Whistlin Bob said:

This! I've had lots of fun doing this.

The image below was taken with a 2nd hand 600d, with the IR filter removed, on a Star Adventurer, using a second hand 135mm lens off eBay for about £25. 

And this one used the same lens on an Altair 183c fan cooled camera.

So it's definitely possible to do things on a budget- but as others have said, the mount is probably the most critical part.

I agree with @Whistlin Bob I’ve been in a similar position to you (I own an ST80) and although I already had a HEQ5 mount I really didn’t want to spend £1000s more on equipment (especially as I do most of my ‘AP’ in my light polluted back garden). So, I modded my 1100d (£60 from eBay, £70 for the mod) and am now experimenting with various m42 prime lenses I’ve acquired from eBay (max around £25). The results are good enough for me (atm) and combined with automation using a raspberry pi and Ekos my imaging is just a joy, rewarding to do and quick and easy to setup. 

HTH

Daz

Edited October 21, 2021 by Dazzyt66

[happy-kat]

I would look for a prime none zoom lens sand old m42 lenses with an adaptor will fit the 1000d. Around £30 should sort that out. There's lots of pushing you can do with the mount you already own but you'll get more of you can mount your camera straight to the mount. The no eq dso challenge thread has lots of posts.