From: gsmlrn@gsm001.mendelson.com (Geoffrey S. Mendelson)
Subject: Re: Questions about everything
Organization: Mendelson.com
Date: Wed, 6 Jan 1993 01:41:40 GMT

In article <1993Jan5.114632.29209@spider.co.uk> mikec@spider.co.uk (Mike Coren) writes:

>2)  Why does film speed (ASA) increment in 1/3 stops, while shutters and
>apertures typically increment in 1/2 stops or whole stops?

Back in the old days of photography a 1/2 stop was what you needed to make
a noticable change in exposure.  Films were ASA 10, etc. Shutters were
1/2, 1/5, 1/10, 1/25, 1/50, etc. Sometime in the 50's they were "normalized"
to powers of 2, e.g. 1/2, 1/4, 1/8........ 

Lenses were f3.5, 4.5, 5.6 etc. usually with click stops in between, but you
could set them anywhere you wanted by hand. Shutters were limited to full stops
as they required a change in gears or something like that.

>3)  Why doesn't exposure value take film speed into account?  An EV by
>itself seems useless if you don't know what film speed is being used.  Is
>there something like an EV-ASA product that's commonly used?

EV is a constant exposure at any shutter/appeture combination.

Light meters are aligned at ev 12 (1/125, f5.6, asa 100) and checked at 
ev 15 and 9 for "balance".


>4)  Does the light in the refrigerator turn off when you close the door?


Mine does.

>5)  Guide numbers on flashes are typically given for 100 speed film.  If I'm
>using 400 speed film, should the guide number be quadrupled, or only doubled,
>since light intensity decreases with the square of the distance, or something
>completely different?  (Actually, I think I know the answer to this one based
>on EV's, but humor me anyway).

It's quadrupeled. For example assume you are getting a good exposure at
10 feet using f8 for asa 100. The proper exposure for asa 400 would be
f16 (+2 stops) guide numbers asa 100 = 80, asa 400 = 160, oops, it's doubled.

>6)  I recently bought a bunch of 35mm Fuji film, which comes in clear plastic
>cannisters.  If I want to put those cannisters into the film loops of my
>camera bag, should I be worried about having direct sunlight hit them (not
>that we get much direct sunlight in Scotland, but...)?  Should I put a few
>at a time into black Agfa or Kodak cannisters before going out?

Yes, there may be some light leakage at the felt light trap.

>7)  Are UV filters for black & white only?  I read where this guy was fairly
>adamant that UV filters are only for B&W, and you should use a skylight filter
>for color.

Usually UV and skylight refer to the same filter. However, UV is a much broader
base, there being 1a (aka skylight), 2a, 2b UV filters.

UV filters a mostly worthless for B&W as most panchromatic film is not uv
sensitive (I don't know about tmax, and tech pan is too RED sensitive).

The filters are required for color work as the blue layer of the film is
also sensative to UV and may produce "bluer" pictures than the eye sees.
It is especially needed in hugh altitiudes as uv is much more present there.

>8)  What is the air speed velocity of an unlaiden swallow?

African or European swallow?

>Thanks in advance,
>Mike
>
>-- 
>Michael D. Coren, Electrical Engineer             mikec@spider.co.uk
>Telecommunications Techniques Corporation, Germantown, Maryland, USA.
>Temporarily at Spider Systems Limited, Edinburgh, Scotland, UK.


-- 
Geoffrey S. Mendelson 
(215) 242-8712
gsm@mendelson.com     or uunet!gsm001!gsm