[rollei_list] Re: Rollei Flash
- From: Laurence Cuffe <cuffe@xxxxxxx>
- To: rollei_list@xxxxxxxxxxxxx
- Date: Fri, 11 Jan 2008 10:11:43 -0800
On Friday, January 11, 2008, at 12:11PM, "Peter J Nebergall" <iusar4s@xxxxxxxx>
wrote:
>At this time almost all my flash work is with my little Nikon SBs, used
>in TTL. I know TTL adjusts by flash duration (it is an amazing product,
>and justifyably so) -- are you saying some of those short durations can
>produce reciprocity failure?
>
>P.J. Nebergall
>
Yes.
This typically shows up on film data sheets in phrasing such as "No exposure
compensation should be required for exposures in the 1/4000-128 second range"
Implying that this is a problem with both short and long exposures. People
taking high speed flash shots of birds in flight have run into this.
I have found more information in, Engineering and Scientific High-Speed
Photography by Hyzer (1962) and in paper's in the various proceedings of the
International congress on high speed photography.(SMPT)
Some more details on this. The effect of very short exposures is to reduce
sensitivity and to reduce Gamma. This can normally be compensated for by
increasing development time at the cost of increasing grain size, due to grain
clumping. In the case of extremely short exposure times it may in some cases be
useful to let film develop to "completion", not something one would normally
consider. This for for the kind of people who photograph explosives and atomic
bombs and other fast things.
Short duration Reciprocity failure is more pronounced with larger grain films
which have been aged as part of the production process and and may well be a
function of the sensitization. In particular Sensitization based on Sodium
Thiosulfate can be problematic, while gold sensitization is less likely to show
problems.
For color film the color balance can be adversely affected by very short
duration exposures.
All the best
Laurence Cuffe
>On Thu, 10 Jan 2008 17:58:11 -0600 Don Williams <dwilli10@xxxxxxx>
>writes:
>At 03:13 PM 1/10/2008 -0800, you wrote:
>
>These figures look more realistic. Early strobes used higher voltages and
>achieved shorter flash durations however this resulted in short duration
>reciprocity failure, leading to colour imbalance with colour emulsions
>and underexposure with BW emulsions. Modern flashes use larger capacitors
>with longer discharge times leading to a safer and more usable product.
>My memory is that Bron flashes can still do very short duration stuff.
>All the best
>Laurence Cuffe
>All the best
>
>Just for the heck of it I did a Google search on reciprocity failure and
>by far the most citations were for long exposure, but there were some for
>short exposure failure.
>
>There are even Kodak sites with correction values and recommendations for
>minimum exposure times for various Kodak films.
>
>Bottom line, however, is that emulsions were changed some time back to
>better handle the short duration failures, and of course, as mentioned
>above, strobe flash durations have become longer with larger capacitors.
>
>On this same subject, Carlos mentions that he still uses a Vivitar 283,
>and I do also. Mine is very-very old, and has the high-voltage
>high-current trigger for the flash contacts and I feel sorry for the
>contacts every time I use it. There are low level adapters but since
>nothing in a camera has failed yet I just continue to use my old model.
>
>DAW
---
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