Re: [APML] Poor Blue in 400F?

[Alen Koebel <akoebel@rogers.com>]

--- Wei-Hao Wang <astrophoto@gmail.com> wrote:

> Hi everyone,
> 
> I think Alen's case is very rare.  I would expect to
> see A LOT on a 30min/F5.6 shot on M45 with Provia
> 400F.  
> 
> Look at my picture:
>
http://www.ifa.hawaii.edu/~wang/gallery/picutres/m45-2003.htm
> This is a 85min/F9.4 shot.  

Wow. That's impressive. Of course, all of your
published shots are impressive. (I'm sure you don't
show us your big mistakes. <g>)

[snip]
> As Jim pointed out, sky condition may be the reason.
> In addition, reciprocity failure might be another
> factor.  If the shot was taken in a humid and warm
> environment, reciprocity failure may be stronger
> than usual.  

That's interesting. I hadn't heard about this
relationship before. Yes, it was a warm and humid
August night, whereas the shots on the previous roll
that did turn out were back in November of last year,
when it was cold (-8 C) and relatively dry. 

I'd be willing to bet light pollution is also a
contributing factor. You have very little on Mauna
Kea; I have a lot where I am. A slightly hazy night
seems to "intensify" the sky glow. 

I should try the Pleiades again in October or November
with the cluster positioned as overhead as possible,
on a very transparent night (assuming one happens 
near new moon), autoguided for 1 hour and push the 
400F one stop (as per general recommendations here).
If I don't get a good result then, I'll hang up my
AP hat! <g> 


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