Camera and FF/FR for SV 70 ED?

[lazjen]

I recently got a Stellarvue SV 70 ED with no flattener or reducer. I've done some googling and see a few options around the 0.8x reducer. Would a "Orion Focal Reducer 0.8x for Refractor" work? I couldn't find references that matched the 70 ED scope to that FR. Any other options, especially just a suitable 2" flattener (the "Orion Field Flattener"?).

Ideally, I'd like to use this as an option for a travel setup, so I'm considering getting a cooled OSC to go with it, although I'm a bit concerned since it's just an ED doublet. I'm thinking of doing some tests with my DSLR to see what the colour is like. Assuming it's ok, what would be a good cooled OSC to go with it?

If OSC doesn't work, I might just drop back to my ASI1600MM-C + Filters for now (it would mean camera swapping though).

[lazjen]

Ok, I can now answer one of my questions - not getting an OSC. Managed to do a test with the DSLR and the colour wasn't great.

Also, most definitely needs a FR or FF when used with a DSLR.

[Camelopardalis]

Chris, you'd almost certainly want (at least) a field flattener as the radius of curvature is quite tight on a small refractor, so you'll most likely see a fair bit of field curvature even with the 1600.

I've not used the Orion reducer myself, but the Televue TRF 0.8x is reportedly good on small, fast-ish refractors.

[lazjen]

You're 100% correct actually Dunk - it will still need something because that field curvature is quite apparent.

I got in contact with StellarVue and the 0.8x for the SV70T works for the ED as well. However, I'm taking a punt on the Orion 0.8x working as well (grabbing the one that was advertised here recently). If it doesn't, well I'll sell that off and get the more expensive version.

[Camelopardalis]

Cool! Don’t be surprised if you need to play the game of “find the spacing sweet spot”, with any flattener or reducer...it doesn’t always match the manufacturers claims :sadeyes:

[The_bluester]

The ED80 reducer/corrector that Skywatcher sell with the Evostar 72 needed closer to 60mm than the advertised 55 in my setup.

[Xeteth]

What's the best way to test this? I'm assuming taking pictures and checking them in CCDInspector?

[lazjen]

Ah, great to know. What a surprise that there's variance with these things.

[The_bluester]

If you have CCD inspector that is a good option but you can get a pretty decent handle on it visually as well.

Seems that for most correctors (Sensor spacing on a RASA seems to be the opposite) if you have radial streaks (Warp speed0 in the corners the sensor is too close to the sensor, if you have arcs (Fishbowl) it is too far away.

[lazjen]

253434

I grabbed this image off a post in IIS a few years ago I think. Very useful visualisation of the problem.

[lazjen]

I've got the Orion 0.8x reducer now, and there's a few holes in the clouds tonight. I haven't quite got the spacing correct, but I'm not too far off and I can see that most of the frame seems fine. I think with suitable experimentation on the exact back focus required, I can expect this reducer to work.

[Nikolas]

I know this isnt very helpful but I used the orion 0.8 field reducer on my ts 130 and it seemed to do the job, not 100% perfect but a fairly decent flat field

[lazjen]

That's what I'm expecting - not 100% perfect, but fairly decent flat field overall.

I've done some more swaps to the spacing to bring it closer to the alleged correct spacing, so tonight I hope to do some more tests.

On another note, I've added the ZWO EAF to it now. Biggest hassle was the mounting bracket for the focuser. The screws supplied didn't match the mount points on the scope, so I've improvised with some others.

[lazjen]

So damn typical - I just got everything setup tonight, configured various bits of software, etc, and the clouds rolled in.

:cloudy:

*sigh*