Re: [ATM] How dark is dark?

[hermit <hermit@outofoptions.org>]

GF wrote:
> I think three years ago at Stellafane a fellow showed a 6" or so 
> Newtonian that was baffled and gloss black inside. He claimed that with 
> the right baffle design less light reached the mirrors or eyepiece than 
> with flat because the reflections were directed away precisely and more 
> fully.
>
> It was a very bright day and compared to other scopes, his did indeed 
> look darker. With other scopes I could see down to the mirror support, 
> with his I could just barely make out the first baffle.
>   

Well, that is what I was 'surmising' in an earlier post.  Glossy black
always looks darker than flat.  Depending on the design of the scope it
should/could work better as in this example.

>  I do also think though that Leitz, Zeiss, Haselblad, Nikon, Canon, and 
> so on would have used this in their cameras and lenses years ago if it 
> was truly better.
>
>   
Well, we mainly build Newtonians so that is what much of the discussion
should turn on.  Flare is largely a neglected issue with camera lenses,
but Phil Davis in his "Beyond the Zone System" book suggest 10% is not
an unreasonable amount to plan on in a large format camera.  Remember,
these are more refractors than Newts.

But you also illustrate that some one has done the 'test' and indeed,
you noted a remarkable difference when using gloss paint.  My scope is
about due for an overhaul, and I will use it myself.  I have never
properly baffled it, but that will also happen.

I can paint some thin surfaces and pop them into the densitometer when I
do the rebuild. 

Ken Lowther
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