RE: [APML] Fuji Provia 400 F Push Processing

["Jon Kolb" <jkolb@datawest.net>]

Tony, Sean, Shekhar,

>   I noticed that the Provia recorded a small blue reflection nebula
around the center of > the star in the middle of the big red nebula at
the bottom of your Antares image... I 
> wonder if that is really a nebula or some artifact of the film and/or
fast optical 
> system? Interesting!

> It looks like serious blue haloes to me (haze or fog during 
> an exposure?), but i could be wrong. Still great color and processing.

> I too am curious about this.   I was looking at some of 
> your other shots with the Borg and some show these blue 
> halos and others don't.  Is it the optics, the film, or 
> something else?

The way I see it, there are at least three primary causes of blue halos
possible in my shots:

1) The optics may not be corrected well for blue.  I don't know how to
test this myself, but I sure wouldn't doubt it.  Otherwise, why would
people wait 4+ years to get a Christen triplet when they could buy a
Borg doublet today.  On the other hand, the reducer lens group used to
configure this scope at f/4 might be doing it, or it might be mitigating
it.

2) High clouds.  This has certainly been the case on many occasions in
the past.  We had high cirrus every day I was down in AZ this year.  I
fight high haze frequently up here in CO, too, except for glorius
September.  However, I can usually see cloud-induced halos on the
lightbox, and the three slides used in this shot didn't have any that I
saw. 

3) The halos, from whatever the cause, are exaggerated by my processing
technique (or lack thereof, I guess).  This one sounds like a
contributing factor for sure.

A fourth possiblity is that, at least in this image, the reflection
nebulosity is actually there.  I can't rule this out either, since
there's so much going on in this part of the sky.  My personal theory is
that the halos are a combination of causes 1) and 3), frequently
exacerbated by 2).  I'm getting a TMB soon, so I might be able to refine
this list somewhat in the future.

Sincerely,
Jon Kolb
Adventures in Astrophotography
http://home.datawest.net/jkolb/
jkolb@datawest.net




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