Re: [APML] how to test for base fog?

[Brian larmay <power_windows4789@yahoo.com>]

Thanks to both of you....

I will be using fast lenses for this, 50mm-105mm,
which will all be of the milky way region of course.

I remember taking a 25 min shot of the scutum through
my 105 on hypered tp with some lumicon film, equiped
on the lens was a lumicon Ha filter and the shot came
out almost completley black.
I had to hold it up to a lightbulb to make out what i
captured.
The deveopment time was around 5 mins, but thats with
the lumicon hypered TP.

Ill be giving it a shot tonight ..my skies are the
clearest most transparent skies I have seen here or
anywhere in a looooong time.

Thanks for the info!
Brian

 

> 
> In a message dated 7/2/05 10:48:01 AM,
> power_windows4789@yahoo.com writes:
> 
> 
> > Brian, properly hypered tech pan should have
> between
> > > a
> > > .7 and 1 ND base fog.  Otherwise its damn
> clear.  So
> > > what does that look like?  Get an ND filter set
> from
> > > a
> > > photo store and go see...
> > 
> 
> Brian: 
> I disagree somewhat.
> The usually accepted target base fog density for
> hypered Tech Pan film is 
> 0.6.
> This means that the density of an unexposed but
> developed area of the film 
> reads 0.6 on a transmission densitometer. To the eye
> it appears more than 
> slightly grey.   
> 
> What is the 'correct' base fog level? 
> That depends on your optical system and the object
> you are imaging.
> If you're going after really faint fuzzies with an
> F10 SCT you'll want 0.6 
> abd process 10 minutes in D-19 @ 68 degrees F. If
> you are after brighter objects 
> with faster systems you might want 0.4 or 0.5 and
> process for only 5 or 6 
> minutes. This is the case with my Schmidt Camera
> which is f1.5. If you use HC110 
> dilution B (for less contrast) you'll have to run
> some tests for yourself.
> 
> You can take the test film to a photolab and they
> will usually gladly read he 
> density for you.
> Even the camera shop or 'moto photos' will do it as
> well.
> 
> The above suggestion about getting a set of Neutral
> Density filters and use 
> these as a comparison is another solution. Kodak
> makes a whole line of Gel ND 
> filters in 1/3 f-stop increments; 0.1, 0.2, 0.3,
> 0.4, 0.5, 0.6, etc. They come 
> in 2x2 and 3x3 inch sizes. You can somtimes find
> them at flea-market type 
> camera shows for a few bucks each.
> 
> Kent Kirkley
> > _______________________________________________
> Astro-Photo mailing list
> Astro-Photo@seds.org
> http://seds.org/mailman/listinfo/astro-photo
> 



		
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