Imaging Train Questions

[Ellery]

Hey there , I'm just gathering the last bits needed to get started with imaging, I've got a 2" Astronomik UHC filter now and will pick up a focal reducer next week. My doubts are how to put it all together though so I've drawn a quick sketch picturing how I thought of ordering them first. How does it look ? And a couple more questions (bear with me):

Does the filter have a preferred position relative to the focal reducer, should it go before it (just after the focuser) or after ? Am I right that both its threads are m48 ?

I also have an m42 nikon ring already and have seen a few 2" nosepieces with m48 threads on one side and m42 on the ring side, I guess if I go this route it will cause vignetting ?

[red dwalf]

i`d try to get the filter as close to the camera chip as possible, the other issue you may have if your using a focal reducer is spacing from the rear of the reducer to the chip, these can be very critical so you may need a spacer. 

[Ellery]

Thanks! I've looked into the spacing yesterday, the telecompressor needs 101mm to achieve 0.67x reduction and itself takes up 16mm, the UHC filter cell is 5mm and Nikon F's flange distance is 46.5 so we're at 67.5mm. Hopefully the T adapter and T ring will cover the remaining distance. Just in case it will be needed the spacer would go between the nosepiece and filter ?

[red dwalf]

I'd screw it onto the rear of the reducer if possible.

[derrickf]

" the other issue you may have if your using a focal reducer is spacing from the rear of the reducer to the chip, these can be very critical so you may need a spacer"

 

The spacing to the CCDT67 is not critical to image quality - I think the poster is confusing reducers with  field flatteners where spacing is critical. Take a look at the documentation for the CCDT67 on the Astrophysics website if you need confirmation that spacing only affects reduction ratio and size of the unvignetted field. IIRC you can calculate the expected reduction and unvignetted field using the formulae on the AP website

 

HTH

Derrick

[Ellery]

I have its tech data page among my favourites  I have been wondering about field flattening, I've read that the SW100ED has a pretty good corrected field but the little spherical aberration present, will it be amplified with a focal reduction or remain unchanged ?

[derrickf]

My understanding is that there will be little or no effect (it is designed to have no flattening effect) on the native flatness.