Camera dependent blue bloat: interesting.

[ollypenrice]

I came across this on CN. http://www.cloudynights.com/topic/476528-bloated-stars-with-my-tec140trius/

It seems that the Sony chipped cameras show considerable blue (and so luminance) bloat in the TEC140 and that the TEC flattener mitigates this fairly well. I'm very glad that I chanced on this because I had been wondering about using our TEC as a galaxy imager with a very small pixel Sony to take me below an arcsecond per pixel. This has given me pause. In the past I've been baffled by claims, occasionally seen, that the TEC is not a real Apo. This struck me as absurd. My standard response was to post this Alnitak image made of 10 minute luminance subs and given a pure log stretch which still leaves Alniak perfectly split as a double.

 

However, it seems that there is something about the Sony chips which makes them a poor match with the TEC. In the CN thread the Borgs also come up but I've never been very impressed by their control of blue. I wonder how other big apos perform with the Sonys? I know several imagers who get great results with the TEC but they are all using the 8300 chip. I use the 11000 chip. Both seem to work superbly.

The idea that the camera might affect the blue performance had never occurred to me.

Olly

[michael.h.f.wilkinson]

Interesting indeed. Blue light is much more prone to scattering, so maybe something on the surface of the Sony chips causes scatter. The phenomenon is difficult to explain otherwise

[ollypenrice]

5 minutes ago, michael.h.f.wilkinson said:

Interesting indeed. Blue light is much more prone to scattering, so maybe something on the surface of the Sony chips causes scatter. The phenomenon is difficult to explain otherwise

Indeed. It might also be the level of chip sensitivity at that critical end of the spectrum where the blue filter cuts off.

Olly

[ChrisLX200]

Hmm. Would a UV filter help? Some sets of LRGB have UV/IR coatings if I remember correctly. Astrodon for e.g., list:

•Highest efficiency blue filter with less UV

•Significant reflection and star halo reduction (see Alnitak image)

- as significant product features. Not sure about Baader LRGB filters as they don't appear to say anything specific about UV rejection. I use Baader LRGB together with an Atik490EX but then I don't use a TEC140.

ChrisH

[michael.h.f.wilkinson]

UV is probably not corrected well, so that could be an issue, indeed

[vlaiv]

It might be some weird issue with UV part of the spectrum, light cone angle and microlensing on camera?

ICX694 is quite sensitive below 400nm, some filters pass light below 400nm and modification of light cone (adding field flattener / reducer) seems to affect it.

Just a guess.

[ChrisLX200]

Astronomic sell three different Lum filters (with UV/IR coatings) that supposedly address this problem: http://www.iankingimaging.com/show_product.php?id=1623

ChrisH

[Merlin66]

I believe most of these questions - camera CCD and filter sensitivity etc. can quickly and easily be resolved by applying a spectrograph to the optical system.

This will dramatically show the issues which are affected by wavelength.

A small Alpy spectrograph has enough resolution to give you the answers.