[rollei_list] Re: "different types of black boxes" (was: OT / prove it !)
- From: "John A. Lind" <jalind@xxxxxxxxxxxxx>
- To: rollei_list@xxxxxxxxxxxxx
- Date: Sun, 03 Apr 2005 19:48:15 -0500
At 09:00 AM 4/3/2005, someone wrote:
> > The maximum speed is not really an issue. This
> > was a sales point only and Leica was able to
> > increase the top speed to 1/1000th easily. It is
> > also doubtful if the Contax shutter actually ran at
> > 1/1200th.
I haven't been able to sort out who posted this piece of the thread . . .
I don't know and won't comment on the pre-WWII Contax. My post-WWII IIIa
"Color Dial" is not 1/1200th, it is 1/1250th, and is repeatably accurate to
less than 1/6th stop error at that shutter speed. I've shot enough chromes
through it at the fastest shutter speed that I would have noticed if it
were behaving badly.
That said, the shutter in mine was rebuilt a few years ago and it has not
been used that heavily since then. It would not surprise me in the least
that after 50 years or more shutter speeds might be a bit off unless
they've been properly overhauled . . . likely the very fast and/or very
slow speeds (BTW, the 1 second speed is dead on as best I can measure
it). My assertion is that, at the least, the post-WWII Contax IIa and IIIa
"Color Dial" bodies were certainly capable of 1/1250th and would do so
reliably. IMVHO, the vertical shutter concept helped with achieving that
speed. Having periodically checked the faster shutter speeds visually
since the shutter rebuild, it seems to be maintaining relative accuracy
quite nicely. I do this by taking the back off, aiming at the computer
screen and firing the shutter. The diagonal band is roughly half the width
with each increase in shutter speed until I reach 1/1250th. This can only
be done at speeds of 1/50th and faster. Longer speeds can be roughly
judged by starting at 1 second (timing it) and working toward
1/25th. These speeds are slow enough that one can tell whether or not
there's a serious problem by listening to the duration.
Also note there was a modification made to the shutter rails some time
shortly after the "Color Dial" IIa and IIIa were introduced to eliminate
curtain "bounce" at the end of curtain travel . . . something that would
show more in photographs made using the fastest shutter speeds.
Finally, one must consider how accurate a shutter needs to be in practical
use. IMVHO (and in my experience), accuracy better than 1/6th stop is
sufficient. In terms of some of the very long exposures I've made . . . a
whole second inaccuracy with 4 second and 8 second exposures doesn't make
one whit of difference, even with the most finicky of films, such as
Kodachrome. I can slowly count those exposures and not worry about it.
-- John Lind
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