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Ryan_86

Which Apo 80mm-110mm for Astrophotography?

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Hi all, 

Can anybody reccomend a good all round apo that sits somewhere between 600mm-800mmish. Something that will give me close enough images of galaxies with the off nebula or 20 lol. 

I have recently purchased a modded HEQ5 Pro & would like a decent scope that will give me nice images. I have recently sold my Zenithstar 61mm, the FPL53 glass gave me some lovely images. I have to take into account focal reducers/flatteners (ideally a scope with a matchihg field flattener, as I dont want reduce the focal legth). G

Does anybody have experience in using similar apo's without FPL53 glass? My options/budget are pretty good if I dont go for FPL53 glass, however I dont want to go to far backwards  (if I can help it).

Budget is around the £800ish mark. 

I would be ever so greatful if anybody can help me.

Thanks

Ryan

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The resolution needed for satisfying galaxy imaging comes from both focal length and pixel size. Yes, aperture also plays its role but I think you'll find that, in the ball park you're talking about, it won't much matter.  I'm currently imaging galaxies by using a focal length of about a metre and 4.5 micron pixels giving about 0.9"PP.  Previously I've used much larger aperture (14 inch) and much larger pixels giving 0.66"PP. There seems to me to be remarkably little difference between the two. The comparison is skewed by the fact that the small pixel camera I now use is more sensitive than the large pixel one I used in the 14inch. I'm well aware of all the arguments from theory but I'm describing what I actually find.

So I would say that you can do decent galaxy imaging with a FL of 800mm but you'll be wanting very small pixels - three point something.

I wouldn't get too excited about F ratio for imaging small targets. 

Which apo? I don't know, but mechanical things like the focuser will be a darned site more important than the much talked about glass recipes. Over on CN I've heard my TEC140 dismissed as a gloriied achromat. Well, I must be easy to please but I think it's fine. I've posted images of M51, M101 and the Whale galaxy recently on here.

However, at £800  I'd be strictly into the used market in order to get the longest FL possible. 

Olly

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Hi pal,

Thank you for your help and advice👍🏼 I currently image using a DSLR (Canon 600D modded), this gives me a 4.30um pixle size using the astronomy tools fov calculator and various apos. Is this not worhy of producing satisfying images of galaxies?  I hope to purchase a dedicated ccd/cmos imaging later in the year so will keep pixle sizes in mind before choosing a scope.

I totally agree with your suggestion about the 2nd hand market👍🏼 The new Sky Watcher EDS Pro series seem decent value for money, however I'v read that their focuser's are pretty naff🤔

Thanks again

Ryan

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Think a 600mm /80mm frac is more suited to nebulae than galaxies..its still performs on galaxies such as m51 but it be on the small side..where as most nebulae will fill the frame..depends on the sensor size of your camera that you're using

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On 28/04/2018 at 23:44, Ryan_86 said:

Hi pal,

Thank you for your help and advice👍🏼 I currently image using a DSLR (Canon 600D modded), this gives me a 4.30um pixle size using the astronomy tools fov calculator and various apos. Is this not worhy of producing satisfying images of galaxies?  .....

Use the Field of view calculator here - Put in a scope of your choice that you think will suit you, then put your DSLR into the camera section. Then there's an ability to pick a target to see how well it actually fits in the field of view. Sure M31 is big and M33 is OK, but look beyond these two galaxies and I'd be surprised if you feel that the FOV with the combo you are suggesting is sufficient. Good luck :) 

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I've been doing a lot of reading on this very topic lately because I'm considering the same thing. Based on everything I've read here, on other forums and other informational sites, if you're looking for galaxies, you'd be hard pressed to capture anything more than a few small fuzzies without much detail at 600-800mm, with a few exceptions that have been pointed out. Your options open up if you're also looking at nebulae, but even some of those can be rather small, such as a handful of planetaries and smaller emissions. I'm more interested in the nebulae than I am galaxies though, not that I wouldn't mind capturing one or two or even a cluster like Markarian's Chain or others in Virgo.

My main concerns are the weight and portability so these longer FL doublets that are lightweight catch my eye. I have an iOptron Skyguider Pro right now. While I know it's not anywhere close to the mounts you all use and are talking about, my camera, the mount, my tripod, all my lenses, cables, PC, etc. all fit in a backpack. I want to limit the amount of stuff I need to haul around so I can pack it in just about anywhere and setup for a night. I want to limit myself to a scope no more than 8.5lbs (3.8kg). Right now I have my eye on the Sky-Watcher Evostar ProED 80mm. It's light(ish) and has a decent focal length. It also gives me a little bit of room to add a really small guider like a QHY or the Orion Magnificent Mini. It's only a doublet and not a triplet, but I'm alright with that considering the price differential and that I'm only taking images for myself and not for professional use.

For the OP, with an HEQ5, you should be able to handle something considerably heavier and larger than I can. If you're wanting galaxies though, I think you're going to need more focal length as was pointed out unless your focus is just on the really big ones. If you're stuck on 600-800mm, Explore Scientific has a 102mm triplet that comes in around 714mm for roughly $1000US (725GBP), if you can get your hands on one over there.

And forgive my ignorance, but this just dawned on me and I've just never bothered to ask or look. Is there a reason someone wouldn't consider an extremely small, lightweight Mak-Cass with considerably more focal length than an apo for astrophotography? I know they're slower and will provide a narrower field of view so they may not be good for larger nebulae, but if you're interested in smaller galaxies, wouldn't that be acceptable? From my reading, it would be best to use an off-axis guider due to the mirror flop, but even that is still probably lighter than a larger apo. For example the SW Evo80 alone is 7.3lb (3.3kg). A SW Skymax 90 is only 3.6lb (1.63kg) and has a little more aperture and a longer focal length. Even a Skymax 102 is still lighter. Is there another drawback I'm missing?

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