Re: [APML] My first light shots with Canon 20Da

[Alan Voetsch <alanv12952@yahoo.com>]

Hey Chuck,

--- Chuck Vaughn <aa6g@aa6g.org> wrote:
> > Blues seem to be more white, among other little things. Does
> > anyone have an explanation of why this is?
> 
> I've certainly noticed the same thing. Believe it or not I processed 
> 
> that m31 to get it to be more yellow in the middle and more blue at  
> the outer edges. This was taken with the unmodified 20Da so the Ha  
> response is way down which is probably why the nebulas aren't even  
> pink. Now that it is modified I'll see what happens.
> 
> OTOH, tricolor TP shots of M31 and M33 show nebulas as mostly white  
> with a hint of pink. I think the bright red nebulas you see in some  
> shots come from the addition of H-a data.
> 
> If you care to dig deep in the APML archives, years ago Brad Wallis  
> was asked what color M31 would be if you could see it. he said it  
> would be mostly gray with a bit yellower in the middle and a bit  
> bluer in the outer arms, not the bright yellow/orange and blue you  
> typically see.

Which brings up the question: do we process to show the object as seen
visually (my understanding is that extended objects will only show very
subdued colors, if any at all), or are we dealing with so much more
data due to the long exposures that we have many more options as far as
how to render the color? My un-educated guess would be the latter.
 
> Here's a question we need to ask ourselves:
> 
> If the 20D takes normal daylight balanced images that look  
> satisfactory to our color seeing eyes, why would a shot of M31 with  
> the same camera not produce an image balanced the way it appear if we
>  
> could see it in color through a telescope? I believe the inescapable 
> 
> answer is that it does take the image correctly and Brad was right.
> 
> When we see something presented in a certain way, we become  
> conditioned to it and any other presentation we judge as wrong. We're
>  
> conditioned to seeing a certain presentation of M31 based most likely
 
> on how a few people initially processed it; old yellow stars in the  
> middle and young blue ones in the arms so it must be bright yellow  
> and blue.

It would be interesting to see a side by side comparison of certain
marquee objects over the years. A few years back, I remember asking Rob
G. or Tony H. why they were processing M31 to be so blue in the arms.
Don't remember the exact response, but he had his reasons. Since that
time, M31 is typically shown to be quite blue. Before then it was
mostly shown as white with a touch of blue in the outer arms.
 
> I've got a couple of very old M31 images taken on Konica films and  
> processed and printed in a photo lab and they're all sort of a gray- 
> magenta color. Yet on the same roll nebulas look completely "normal."
> 
> Another thing to consider is if the foreground star colors appear  
> correct in the image, orange, yellow and blue, how could the color of
> the galaxy be wrong?

An individual, much closer point source as compared to hundreds of
billions of dimmer, and much fainter stars which I'm not even sure
would still qualify as point sources at that distance. Possibly, the
closer, brighter stars trigger different responses than far dimmer
stars thousands of times further away.  
 
> I've pretty much given up on what color these objects are supposed to
>  be and look at the quality of the image overall.

Yeah, I don't blame you. I'll keep doing the same thing and see what
develops. 8-)

Alan



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