Focal Reducer / Field Flattener for Asteria 204-8 R35

[jaymocha]

Greetings Ales;

I am wondering if you have a recommendation for a flattener / reducer for my telescope?  I am pretty happy with how well it seems to be imaging and I am wondering if there is something on the market now that would be a good match for my scope.  Any ideas?

Jason

[Ales - iStar Optical]

Hello Jason,
Are you taking deep space photos now? We tested your s 204 F12 refractor and it performed quite well up to APS format. Full Frame did show field curvature. So if you are shooting on larger chip size, you will definitely need a field flattener.
most field flatteners / reducers are produced for F7 to F9 scopes, but some of them might work with this big F12. I would not go with cheap, mass produced flattener. One which just might work well is APM 3" refractor field flattener. Im not sure if this one is also a reducer and if it is, it will be around 0.8x or so. Please talk to Markus Ludes at APM, tell him that I sent you. He will give you his honest opinion if his field flattener will work well with F12 Asteria. And if it is not, he will recommend some alternative unit.
If there was at least 5 or 10 people interested in such field flattener / reducer, we might design and produce it, so ask around on ISC, CN, AM and other forums, if you find few more people, we would go ahead and offer such unit in 3" size. Since we are planning on producing other F11 and F12 refractors in several different CA reduction styles (R50, Semi APO, Visual APO) interest in such reducers might grow in the future. But even if we decide to produce such flattener, it would not be available sooner than one year from now.

Best regards,
Ales

[mikey cee]

Ales do you ever read your personal messages? Mike

[jaymocha]

Hello Ales;

Actually I have the f/8 version of the 204mm Asteria. And yes, I am now testing the waters of DSO imaging but my current camera (Canon 1000D) is not really up to the task. I took the image located at the link with the iStar and a Baader 8.5nm OIII filter as a test, but the winds kept messing up my exposures. So this image is only 13 exposures at 5 mins each. It gets pretty windy on my rooftop.

link to image: www.flickr.com/photos/86467741@N04/17138858764/in/dateposted-public/

As a side note, I did not see field curvature in my image at the link. I'm mostly interested in getting a bit more field of view out of my scope if i can, and i think a reducer / flattener will be the best combo for my scope.

I will contact Markus Ludes at APM and see what he has to say. But given that my scope is f/8 and not f/12, do you have any other recommendations?

Thanks,
Jason

[marcello]

Good result Jason, I like it!

[Ales - iStar Optical]

Hello Jason,

you are right, sorry. F8 is MUCH easier to match with a good field flattener / reducer. The APM 3" was a really good one, will match well this lens size-wise. Im not sure if this is also a reducer so talk to Markus, let us know what he said. From what you are saying, you do want a reducer. A good 0.8x will bring this system down to F/6.4, this is already pretty fast system.

I looked at your initial picture and I think that this is a damn good for a first try! The lens is showing a pretty pinpoint, high resolution image. Play with the focus a bit more, I think that you will get a really nice results with this lens. Ive never seen picture made with this 8" R35 SLIM Doublet and Im pleasantly surprised. It does produce a very nice flat field indeed.
So keep us all posted with more!
cheers,
Ales

[jaymocha]

Thanks Marcello!

And thanks for replying Ales.. My camera was without a doubt the limiting factor in the image i posted. I also think I need to play with the focus a bit more, I think I can get the stars a bit sharper. That image was as much a test of the iStar scope as it was my Baader OIII filter in my very light polluted skies. I wanted to see how much light pollution would be present with the 8.5nm narrowband filter.

So I decided to pull the trigger and get the QSI-6120ws imaging camera. qsimaging.com/6120-overview.html

It's probably a couple months out from getting here as it is on backorder, but that will be a much better camera than my Canon 1000D. I also ordered the Baader Ha filter (7nm). So, hopefully soon I will be able to produce some more "complete" images than just the bluish/green OIII from my light polluted skies in Seoul.

My goal with the Reducer/Flattener is simply to increase my field of view, I'm just afraid if I only purchase a reducer that the currently very nice flat field I'm getting will become not so nicely flat... so in that respect I would just assume purchase a Reducer/Flattener and not have to worry about field curvature. The 0.8x sounds good to me in that regard.

Once I get some more images I'll post for you.

Jason