DSO imaging with an achromat?

[sgazer]

hello all,

I'm just getting back into astronomy after being out of it for a few years. I have a Celestron C8 on an equatorial mount which I have started using for imaging with a DSLR, but I would like something with a short focal length too and I was after some advice please.

My budget is tight, so Borg and WO scopes are out I think and I think I'm going to be limited to an Achro rather than an Apo.

I've read reasonable reviews of the Skywatcher ST80, although it does show aberations on bright objects, it is only £85. However my question is, would it be suitable for DSO imaging with a DSLR? Would there still be objectional aberations on bright stars? Has anyone tried it?

Thank you in advance.

[jgs001]

I have done just this, although my ST80 is badged Konus. It works, but you will get halo's around the brighter stars. I was using a SemiAPO filter to help remove some of the CA, and that made a difference, but also removed blue form images, so Orion looked like it was shot with a modded camera (when it wasn't) and M45 showed very little neb at all. Here's a couple of examples I did with it mounted on my NexStar SLT

10x2, 15x30 and 9x45secs @ ISO1600

[johninderby]

Here's two alternatives. I've used both and the Star Sky 90 is surprisingly good for an achro and it is a very light weight OTA and comes with a single speed crayford focuser and retractable dew shield.

Star Sky 90 O.T.A. £149.00

http://www.opticstar.com/Run/Astronomy/Astro-Telescopes-Ascension.asp?p=0_10_1_6_110

Celestron C102mm Wide View - £114.00

This is being discontinued by Celestron and at this price it is a great buy. Don't know why Celestron put this one under spotting scopes as it's the same as the Skywatcher 102.

http://www.telescopesplus.co.uk/moreinfo.php/Spotting_Scopes/Clearance_Spotting_Scopes/Celestron_C102mm_Wide_View/3158

John

[MartinB]

You can produce images without any problem with an achro. When using a colour camera you will always have the problem of not being able to achieve a really tight focus, different parts of the spectrum come to focus at slightly different points. As John has shown, it isn't the end of the world especially given that funds are tight. If you want really sharp stars you can always image with RGB filters (cheap ones!). A blue filter would give you great results on M45 with much tighter stars than unfiltered. You would just need to convert the final image to mono.

[sgazer]

Exellent advice (and pictures) thank you. I'll give the ST80 some serious consideration.

I'm guessing that if I need a shorter focal length than 400mm (eg. 200-300mm), I'm looking at camera lenses rather than a scope, which is going to push the price up a bit.

Thanks

[steppenwolf]

When I first started imaging in 2004 I used the ST 80 for both observing and imaging. It is a lovely little 'scope but you need to accept that it does suffer from chromatic aberrations as discussed above. That said, the following image of comet Machholz was taken with a Canon EOS 300D and my ST 80 and I got it published in Sky at Night Magazine!! Careful processing in free imaging software like The GIMP can go some way to removing these aberrations. Chromatic aberration shows in my image of the comet as purple halos around the bright stars.

So, another vote for the ST 80 !!