Astrodon 3nm filters with a Meade f/3.3 reducer and a C8 SCT for an Atik 428EX? Bandpass shift issues?

[Josef]

I have - slowly but surely - acquired a full set of (second hand) 1.25" 3nm Astrodon Ha, SII, OIII and NII filters (as well as a V-band filter, intending to do some light curve measurements), and am on the lookout for a camera to match to my system.

I have 2 scopes - a 130PDS and an 8" SCT. Currently on the market for a CCD which would best fit both scopes, allowing me to image with both without being too over/under-sampled. I understand that 3nm filters would benefit from the higher QE of CMOS sensors, but CCDs are still king for scientific measurements.

Originally, my intention was to go for the Atik 460EX, with its wider FoV being a plus when compared to the Atik 428EX. Pairing the f/6.3 reducer with both cameras would leave me with a slightly oversampled image (0.73"/px) with the C8, with the f/3.3 reducer giving a well-sampled image (approx. 1.54"/px). With the 130PDS and a 0.9x coma corrector/reducer, both cameras would also give a well-sampled image (at approx. 1.74"/px).

The Atik 428EX of course suffers from the smaller sensor when it comes to imaging FoV, which would likely mean that I would, for the most part, be imaging with the f/3.3 reducer (for the C8) to get as much FoV as I can. However, the difference in price - even on the second hand market - is a thing of consideration - the 460EX is still significantly pricier at my currently available budget.

My main concern with the f/3.3 reducer is the fast f ratio, and whether this is going to impact my Astrodon 3nms with a noticeable bandpass shift, enough to make me lose valuable photons and require significantly longer imaging times. Has anyone here successfully used the f/3.3 reducer with Astrodon 3nm filters?

Thanks!



 

[ollypenrice]

The F3.3 reducer is years past its sell-by date. It was designed to work with the tiny webcam chips (eg Toucam) of that period. I tried it on a small Sony 16.9mm diagonal chip about thirteen years ago and it was just a nightmare of distortions off axis. I don't know the diagonal on your camera but that of the Toucam is just 4.5mm (!!!)

Olly

[Josef]

8 minutes ago, ollypenrice said:

The F3.3 reducer is years past its sell-by date. It was designed to work with the tiny webcam chips (eg Toucam) of that period. I tried it on a small Sony 16.9mm diagonal chip about thirteen years ago and it was just a nightmare of distortions off axis. I don't know the diagonal on your camera but that of the Toucam is just 4.5mm (!!!)

Olly

Thanks Olly!

That is indeed another reason why I'm worried about this. The small imaging circle (and thus, vignetting) and distortions introduced by the f/3.3 could be a nightmare. That's why, in truth, using the f/6.3 with the 460EX would be better. With the f/6.3, the 428EX would have a small FoV, just below what I would have liked to have.

Might just have to save up some more from the look of things

 

[ollypenrice]

10 hours ago, Josef said:

Thanks Olly!

That is indeed another reason why I'm worried about this. The small imaging circle (and thus, vignetting) and distortions introduced by the f/3.3 could be a nightmare. That's why, in truth, using the f/6.3 with the 460EX would be better. With the f/6.3, the 428EX would have a small FoV, just below what I would have liked to have.

Might just have to save up some more from the look of things

 

You could buy a 460EX for peanuts these days, since nobody wants to buy CCDs, despite their fantastic performance. I have one not in use myself but am not yet ready to sell it because it is such a gem when used with my TEC140 (also not in use at the moment.)

Olly