Refractors - large diameter vs high quality glass

[rwilkey]

FIrstly cameras are more sensitive down towards the UV than the eye, so a scope wich is visually apochromatic may be far from that photographically. My Mk 1 F5 Pearl River TV Genesis was a classic example, stunning visually but not photographcally corrected to the same degree. It was never designed for digital imaging.

The colour correction of doublets also breaks down in proportion to the speed, so the slow ED100 is particularly good visually but the speed is against it photographically. The faster the refractor the harder it is to correct, and indeed the bigger it is the harder it is for a given F ratio.

I think that when folks talk about processing the artefacts from badly corrected scopes they are talking about correcting the stars, in the main. But all the detail is out of focus in whatever channel we are talking about. (Usually blue.) Using a programme which resises and re-curves layers when it registers them is a help. Pixinsight and Registar come to mind.

Best to get a real apo though! It comes at a price but there really is only one top dog and it is way ahead of the rest in its aperture class. The Takahashi FSQ85ED. Very few scopes have no rivals but I know of none for this one. (Nor does any other come at such a price!)

Olly

Thanks Olly, always wondered about this!

[kev]

Dont feel giulty. Folk here would rather help and assist you not to spend hard earned money unwisely. I also bet theres a lot of folk in your situation reading this thread.

Sent from my iPhone so excuse the typos!

[Christopher Davenport]

I think, that will be my setup (SW ED80 + HEQ5mount). I would like to stay away from Newtonians because the way I understand it, they are either set up for imaging or for observation, but not for both. In addition collimating them frequently sounds daunting. I would then sink additional funds into guiding optics. By now I feel guilty that I caused so much fuss. Thanks to everyone who answered my query. You get all these puzzle pieces and eventually you see the picture !

You won't be going far wrong to start with a ed80 with matching reducer and a heq5.

Don't discount the 130pds or 150pds with coma correctors, especially if you are using a DSLR, because the speed helps.

I am thinking of adding a 150pds to my arsenal along side the ed80.

If you have light pollution and are going to use a filter you need additional aperture or increased sub length to compensate.