Focal Reducer Vignetting - Normal Amount?

[BlueAstra]

I have an unbranded F6.3 focal reducer with the name 'series 4000' on it and made in China. I believe it is similar (if not the same as) the Celestron or Meade reducer. My question is how much vignetting should I expect with it?

Below is a single unprocessed sub taken with it with my Celestron C8 on an EQ6. The camera is a Canon 1000d with a SW LPF, 1600iso, 30s exposure.

Does the amount of vignetting look normal and what I should expect? Or should bin it and go for one of the branded versions?

[Merlin66]

The design field for these reducers was around 18mm which was "acceptable" at the time. With the larger CCD chips this will give problems. Such is life!!!

[Psychobilly]

Are you using a 55mm long SCT - T adpator with the reducer?

I doubt if you would see that much difference , I use a Celestron f6.3 reducer with my 8" together with a 55mm spacer and by takign and including some flats in the stacking process they seem to sort things out quite nicely...

Here's a single "Raw" uncropped frame from the 350D ont he 8" with the Celestron f6.3 55mm spacer combo...

[ATTACH]24244[/ATTACH]

Peter....

[BlueAstra]

This is a photo of my camera+ T adapter, and the camera + reducer on the scope. The camera is pushed in as far as it will go. I found I had to take the 90deg mirror off to get focus on the camera with the reducer on. I guess what I haven't done is take any flats yet, so I will do that before processing.

[Psychobilly]

Theres the Source of your vignetting then.. the 1.25" T adaptor... You want to maximise the diameter of the connections to the camera...

I use a 55mmm long SCT -T adaptor this gives the required 110mm distance between the rear of the Focal reuced and the sensor in the camera......

I use a Meade ones ... I have one fixed 55mm one and one Variable one which gives 3 different lengths...

FLO sell a Celestron one ... Looks about the right lenght but I am sure a call to Steve will confirm its 55mm...

Peter...

[BlueAstra]

Thanks for the information. I thought the vignetting looked a bit extreme. I'll contact FLO and check the distance. Hmm, guess I'll need a bigger LPF as well !

I suppose I'm right in thinking the large dia ring screws onto the reducer, and the camera T ring screws onto the visible thread at the small end.

[Psychobilly]

Yep that's it...

Possibly your best option LP filter wise would be to get an Astronomik CLS-CCD clip in... not cheap but a very worthwhile investment....

Your other option would be to get an SCT-2" visual back and a Maxdslr adaptor you could then use a 2" filter...

Peter...