~.6x focal reducers for ED80 and DSLR

troypiggo (Troy) · #1 09-11-2009, 10:09 AM

Been doing a lot of reading about getting flat fields for my ED80 and DSLR, and from some brief/quick testing of the WO FF IV the other night, I'm fairly happy with that although will continue testing.

Now starting to think about fields of view, and wondering about a FR in the .6x ballpark. I know of the WO .8x but think I want something slightly wider. Bit concerned about vignetting, though.

Read Paul "[1ponders]" article about flattener comparisons again, but it was more about flattening than reducers.

I have the Meade Series 4000 6.3 FR, it came thrown in with the used C8 I bought. I know Paul included it in his test above, and that just proved it's more for SCTs than refractors.

So what options are there for my combo?

[1ponders] (Paul) · #2 10-11-2009, 11:08 AM

You could look at the mogg adapter, but there was signicant CA present though. Another options could be as astrophysics (probably damn expensive) I couldn't get an adapter though to fit when I was doing the trial (yes I had one thanks to Gary Beal).

troypiggo (Troy) · #3 10-11-2009, 11:26 AM

Thanks Paul. I've been doing some more reading since making this post and I gather from a chat over at Cloudy Nights that most of the .6x focal reducers are more for SCTs and Maks. They introduce coma(?) at the edges on refractors.

I actually have a Mogg .66 reducer that I've never used for reasons posted here. Might have to make a separate post asking how to repair it so I can test it out.

citivolus (Ric) · #4 10-11-2009, 02:28 PM

I have the AP CCDT67 0.67 reducer if you wanted to bring your scope by and check field curvature.

troypiggo (Troy) · #5 10-11-2009, 02:46 PM

Hmm, tempting offer Ric. Might have to take you up on that some time soon. You've used it on an ED80 with a DSLR?

avandonk · #6 10-11-2009, 03:40 PM

Troy the only way to get a focal reduction of about 0.6 and have a flat field is with a very long focal length FR. You are then starting to get into Petzval territory where alignment is a major problem.

Bert

troypiggo (Troy) · #7 10-11-2009, 03:50 PM

Thanks Bert - I don't want to go down that path, so looks like you've saved me some heartache.

Ric - been doing some googling on that reducer you mentioned, and it appears it's more for smaller sensors, not so much DSLRs on the ED80? Might give this whole thing a miss. I'll try fixing the Mogg .66x I have, that way I haven't lost any (more) dough. If that doesn't work, so be it.

citivolus (Ric) · #8 10-11-2009, 04:05 PM

I'll give it a try on the FLT98 to check curvature. I have not tried it on any refractors, as I got it for the LX200-ACF.

avandonk · #9 10-11-2009, 04:52 PM

Troy the best focal reducer field flattener that works with a variety of focal lengths is this one.

Here
http://www.sciencecenter.net/hutech/.../html/7887.htm

I have used it with an 80ED 100ED Tal 200K and a Skywatcher 150mm diam F5 achro.

It is only 0.85 reduction but the field is flat even with a full frame camera such as my Canon 5DH.

Bert

citivolus (Ric) · #10 11-11-2009, 03:33 AM

Quote:

Originally Posted by avandonk

Troy the best focal reducer field flattener that works with a variety of focal lengths is this one.

Here
http://www.sciencecenter.net/hutech/.../html/7887.htm

I have used it with an 80ED 100ED Tal 200K and a Skywatcher 150mm diam F5 achro.

It is only 0.85 reduction but the field is flat even with a full frame camera such as my Canon 5DH.

Bert

I have that one for my refractors. I've measured mine at 0.89x when used on the FLT98.

Regards,
Eric