Re: lens questions

I don't pretend to be an expert on anything- especially not with this
group- but I -have- noticed some interesting things when using a digital
camera (in my case a D-100) to photograph scenes with a high IR content.
If the infrared source is intense enough you can get appreciable 'leakage'
through the IR block filter in front of the imaging sensor. I've seen this
effect most recently while shooting a raku class- the glowing pottery not
only was a bit brighter than it should have been relative to the
background but had a definite color shift. It's probable that there is
sufficient IR (and, come to think of it, UV) in welding (arc welding
especially) to make a difference in exposure between digital and film.

-B

On Wed, July 6, 2005 1:31 am, Barry Kleider said:
> Last week, I was shooting some welders.
>
> My ultimate goal was to shoot them with a Hasselblad and a 150 f4 lens.
> (No internal meter.)
>
> Since these exposures are obviously tricky, I started with my Nikon D-1
> and a Tamron 28-70 f2.8
>
> I was getting some decent exposures - nothing great, but certainly
> within tolerance for a first attempt. So I decided to switch over to the
> Hassy using the same readings.
>
> Since the Nikon was running at ISO 200 and my provia is 100, I gave it a
> full stop. I got the lab results today: $%#^$%. (Translation: way too
> dark and looks like s**t.)
>
> So my question is: what's the relationship between a medium format Hassy
> with a 150 f4 lens, and a 35mm Nikon with a 28-70 f2.8 lens (running
> close to 70 if not full on)?
>
> I assume there's a very straight-forward (though possibly hard to
> follow) explanation having to do with the difference in lens designs
> rather than a format comparison or a digital vs. analog thing (as my lab
> guy surmised.)
>
> Barry
>

-- 
Bob Tilden, rntilden@lotus.phys.northwestern.edu
High Energy Physics Group
Northwestern University