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Old 22-09-2014, 09:47 AM
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PRejto (Peter)
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Join Date: Jan 2011
Location: Sydney, Australia
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Originally Posted by Shiraz View Post
hi Peter. if it is a violet halo due to CA in the APO, it would be there in the lum image as well, so a UV cut filter would need to be applied there as well - probably best to just put in front of the camera and use it for all channels.

figure 149, example 17 in the reference shows the spots diags for your scope design (multi-band is the top spot diagram) - it definitely has an extensive halo at the blue end (about 10x the diffraction spot) and presumably would be even less well corrected in the violet. The reference notes that the designer could have chosen to pull in the violet by sacrificing performance elsewhere. However, the general characteristic of a significant violet halo will probably still be there.

Many thanks for the spot diagrams link. That is most interesting. Remember that I am imaging with two scopes simultaneously! The TEC180 for luminance with a CLS filter (strong UV cut!) and the TEC140 for RGB/narrow band. I put a similar post at Cloudy Nights and received some very interesting info there re the ICX694 on a TEC140 (not a Trius, a QSI). Using Astrodon blue he is getting decent results and put a link to a blue fits file. It is a big improvement over what I'm getting. The Astrodon seems to cut at 400 nm whereas the Baader cuts at ca 380. Enough of a difference? Perhaps. At least with the QSI it seems to be. Could camera electronics come into the equation, or cover glass material? Also, yes, Greg Bradly shows bloated stars in luminance with his Trius on the TEC180. If you are curious here is the CN post:

Now, if I could just incorporate a CLS filter with just BLUE I might be quite happy. The CLS cuts at 450 nm.


Last edited by PRejto; 22-09-2014 at 10:17 AM.
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