Resolved Possible to add single filter to AC4040 Camera?

I live in East Phoenix and we have Bortles 4-5 skies to the East , but 6-8 when pointing southwest to west. I have gotten good results from the Chroma LoGlow Lum filter in rejecting a great deal of light pollution and significantly reducing gradients. It is possible (and expensive) to have Chroma add the LoGlow coating to R,G,B filters. Before I go down that road, it occurs to me that adding a filter in front of the AC4040 sensor would accomplish the same result, allowing my current filter wheel to carry standard filters without the need for light pollution blocking. Is it possible to craft an adapter that would allow a filter to be mounted in camera for the Ac4040? Alternately, is there any other place in the optical train with the 7 position filter wheel and AO unit to craft an adapter to mount a single filter?

 

Yes, it would be in the optical path at all times.

 

Nylon would be fine as long as the mechanism for fastening the filter holds tight at all relevant temperatures. I realize it would add one more optical surface in the path but given some gradients I see, that slight negative would be worth it. I have verified the LoGlow filter works great for Lum subs so I am confident this would improve my RGB data and not interfere with Narrowband filters.

 

Absolutely! This is excellent Doug. At that cost it is worth the risk just to conduct the experiment. But the design looks perfect to make this a long term solution for folks in my situation. please let me know how I can place the order and make payment. I believe you have my email address.

Thanks again! Greg

 

Doug,

Perfect. I am out running errands but will get this ordered this afternoon.

thanks so much. Greg

 

Greg.

You probably know this already but as Doug didn’t mention it, besides adding an extra pair of optical surfaces to the path this method of filter mounting will increase the physical optical path length by the thickness of the filter mounting = 0.1800”, less 1/3 of the filter substrate thickness for focal path correction = 0.0262” for a 2mm thick filter.

An approximate conversion for the 2mm filter thickness to inches = 0.0787” and 1/3 of that = 0.0262”.

If you have a specific BFD requirement for a flattener or reducer you would need to subtract 0.1800” for the filter mount thickness, less 0.0262” for the optical path correction created by the filter substrate, from the distance between the front of the nosepiece and the flattener/reducer connection:

0.1800” - 0.0262” = 0.1538” (or ~3.9mm) from your current BFD spacing.

To maintain that BFD you would always need to have two filters in the path, if you rotated the wheel to an empty slot and use the fixed LPR filter only as a luminance filter then your optical path BFD will have changed and the flattener / reducer performance may be degraded.

You should double check yourself my calculations and path correction prediction when adding a filter holder behind the nosepiece, a late night in the observatory has left me with a fuzzy head this morning….

William.

 

Thanks for the advice William. I do have plenty of backfous room for the addition of the holder and plan to always have two filters in the path.

Greg