How effective is a CPC reducer?

[AlistairHowie]

Hello - I'm still mulling over my potential first scope purchase, and am leaning towards a CPC 800 or 925. I know this isn't ideal for imaging because of the long focal legth, but had thought a reducer would take care of that.

Having downloaded the CPC manual and looked at the description of the f/6.3 reducer, it says that it will produce "crisp images all the way across the field when used visually. When used photographically, there is some vignetting that produces a 26mm circular image on the processed film. It also increases the field of view significantly and is ideal for wide-field, deep-space viewing."

I'm trying to interpret that paragraph, being completely new to this hobby. Seems like the reducer does the business for visual, but doesn't particularly work well for photography. Seems like one would be better off trying long exposure photography rather than putting up with "a 26mm circular image on the film" ... whatever that is/looks like.

Can someone please help me understand the words in the manual and whether a 6.3 reducer really is a good idea for photographs?

Many thanks

[cgarry]

Both those scopes would be excellent for planetary imaging but no good for imaging DSOs. The main problem is the mount being an alt-azimuth type instead of an equatorial mount. This will lead to field rotation in long exposure images.

Next, onto the focal reducer. In my opinion a focal reducer is a complete waste of money for visual observing, you will not get a wider view than can be achieved with widefield eye pieces.

I have used a f/6.3 reducer for imaging with my C9.25 OTA on a equatorial mount and I find the information about "a 26mm circular image on the film" very interesting. I had not read that myself despite what feels like endless research trying to figure out an issue I had with images taken with that set up.

Here is an image I took showing a circular smearing of the stars:

If you use a camera with a small sensor then this probably would not be an issue.

Cheers,

Chris

[AlistairHowie]

Thanks, Chris. I understand about the field rotation and was presuming I'd further break the bank and get a wedge if I decided to do long exposure photography. Then again, I'm inclined to wait and see some reviews on the Meade LX80 alt/az and eqm all-in-one mount after it's imminent release. If they are good, that might just be my answer, either with the Meade OTA or a Celstron one.

Alas I don't believe the LX80 has GPS, which seems like a nice to have, so maybe I'm just back to my CPC800/925 dilemma again ... as long as I understand the implications of using the corrector lens when doing digital imaging of some, as yet, undecided sort (the comment in the manual talks about an image on the "film", but I presume that is just a general reference that is applicable to both digital or wet film).

[cgarry]

Yes, the new Meade mounts do look very interesting, but like you I would wait until others had used them first to know how good they really are. I am not sure how much effort imaging with a wedged alt/az mount is, hopefully somebody who has done this could comment. Personally I would follow the crowd and use an equatorial mount for imaging.

I use an NEQ6 mount controlled with EQMOD running on a laptop. With this set up I can use any old cheap GPS dongle to get you location/time. If I am not out and about the laptop gets accurate time from the internet and the GPS dongle is not needed. Actually I think EQMOD is so good that I would not buy a mount that it did not support.

Cheers,

Chris

[AlistairHowie]

Thanks, Chris.

Does anyone else have any thoughts on the wording in the manual? Seeing that photo earlier makes me think the reducers really aren't fit for purpose for photography.

[Peter Drew]

It very much depends on the type of camera in use. I've had excellent results with the F6.3 and F3.3 reducers using 1/3" and 1/2" chip integrating video cameras on a 12" SCT, however they don't work well with DSLR's.

[cgarry]

It very much depends on the type of camera in use. I've had excellent results with the F6.3 and F3.3 reducers using 1/3" and 1/2" chip integrating video cameras on a 12" SCT, however they don't work well with DSLR's.

That is a good point. The photo I posted above was taken with a QHY8L camera that has a 15.6mm x 23.4mm sensor.

Cheers,

Chris

[Merlin66]

Which CCD camera do you intend to use?

It's only the far more expensive CCD which have chips large enough to be a problem...

With a DSLR , if the spacing is correctly set you'll get workable images - by that I mean they will be very nice but not up to the "cutting" edge, crisp star images, edge to edge you may aspire to....

(Olly will tell you how to achieve that with smaller refractors.....)