Faststar/Hyperstar??

[Veloman]

I've got a Celestron C9.25 which I'm really happy with, but I'm thinking of putting my toe into the world of AP. My question is: do I investigate Faststar ( or it's successor Hyperstar), or do I buy myself a small fast refractor - maybe SkyWatcher evostar 72ed?

Rob

Edited September 9, 2023 by Veloman
Typo

[Neil_104]

I don't have any experience with Hyperstar myself, but something that has always put me off getting one for my C6 is the odd-shaped stars. I'm sure it's possible to route the cables well enough to get round (sorry) it, but they always stand out to me if not well-controlled. But I'm fussy about my star shapes. Too much time using the Celestron f6.3 reducer will do that to you 😂

What I can recommend for your C9.25 is the Starizona reducer/corrector. It gives a really good flat field with my C6. I think they have a bigger-sized one for the C9.25/C11.

But all that said, if you're just starting off with AP, my advice would be to start with the small fast refractor 😄

Edited September 9, 2023 by Neil_104

[Peter Drew]

Start with a small fast refractor, that's a "toe dip".  A "Faststar" or "Hyperstar" is a full body plunge.    🙂

[Elp]

A lot of people are afraid of F2 imaging (is it the perfect collimation thing that does it?), I don't find it particularly troublesome at all, as long as you're not too fussy. I don't particularly care about getting a completely flat field, tilt and such, as long as my tracking is decent and the target looks good to me that's all that matters, you can drive yourself nuts getting into the nitty gritty unnecessarily. My F2s are the Samyang 135 and Hyperstar 6, I have used faster camera lenses but usually you have to stop their apertures down to reduce CA at the edges.

Regarding star shapes with the HS (or RASA I'd presume is the same), as long as your cable router is round in shape, almost like a full circle from the edge to the central obstruction, you'll get a diffraction effect very similar to a refractor (similar but not the same, a few minutes on M45 and you'll see the difference, I'd prefer to use a refractor on such a target), I've tried a few iterations on design starting from a semi circle until I reached the full circle type as I can design and print them myself.

As long as your EQ mount is capable, the 9.25 inch aperture will trounce any refractor for raw light gathering capability and resolution. The refractor however will provide the crispest stars and edge definition.

BUT, if you haven't done AP before, HS might not be the best starting point. If you're good with tinkering, understand what's involved with successful AP imaging setup, and problem solving and you have the right all other required equipment to get started I don't think it'd be too difficult, otherwise a widefield refractor type setup is a better place to start.

Or try the reducer on the 925, ive found your scope balance is critical and autoguiding settings need to be very good imaging at such a focal length (assuming your tripod and mount are up to the stability test too). Or simpler still, a Dwarf2 or Seestar scope will open your eyes to what's possible from your back yard with minimal outlay and trouble.

Edited September 9, 2023 by Elp

[Veloman]

Many thanks for the replies. I should have said, in my original post, that the 'scope is on a CG5 Advanced GT mount and I not too sure about adding further to its load!

[Elp]

Have you got any experience doing AP?

[Veloman]

No practical experience at all. I've just got a copy of Bracken's Deep Sky Imaging Primer and I'm looking to join a local society.

Rob

[Elp]

If you've got a camera handy (dslr/compact anything), I'd try with that first. Learn to polar align as best as possible if you don't already do it, start learning computer software to aid this process (PHD2, Nina, apt or equivalent the latter two are full AP programs) in parallel, take images with the camera and see what you get. Learn about nailing focus and framing. The shorter focal length of a camera is forgiving, and all the control and image acquisition is within the camera body so minimal initial expenditure. Learn about stacking and how to process using calibration frames. I started with a compact camera on a fixed tripod, it was a good learning experience and guided me to what I needed next.

I think if you try with your existing equipment straight away you may get frustrated with it, deep sky ideally requires automatic autoguiding and computer control to get good results. The benefit of your sized scope and a hyperstar will be you can take very short exposures and don't necessarily need to have accurate polar alignment (as it can also be used alt az if desired), but if you don't know about the process it may seem like a dark art.

Making Every Photon Counts is supposed to be a good book in explaining AP, havent read it myself as I've learned it all through experience and online sources with help from forums like this and others.

If you're familiar with polar aligning your current setup, and use it well for visual, it Goto's fairly accurately and keeps a target in the centre of an eyepiece FOV fairly well without adjustment, you're already part way there. You'd next need to learn what camera you wish to use (astro, dslr), how to attach it to the scope (determining the correct backfocus so the scope image focuses onto the focal plane of the camera sensor, setting this distance physically with adaptors), how you plan to image (eyepiece projection imaging (camera attached to the focuser or on top of an eyepiece), straight through the visual back with a focal reducer and camera attached, or HS where the camera is attached to the front of the corrector plate (the HS replaces the secondary mirror)), if using an astro camera you'll need to learn some sort of computer software to control the image acquisition. As you can see, there's a bit more to learn, and this is before you get into the issues with problem solving optical errors, setting up fully automated computer control, autoguiding etc.

Start simple, whichever way you decide. It's good to discuss with other APers, see their rigs first.

Edited September 10, 2023 by Elp

[Veloman]

Elp,

Many thanks for taking the time to reply and for your very valuable experience. I'm impressed with how helpful members of this forum are.

Rob