Reciprocity failure times

[Paul Corcoran]

Hi All,

So i've heard back from my friend and he uses a similar general rule as mentioned at the end of Al's post basically the general rule he works to goes as follows:

upto 30sec add 1/2 stop
30sec-1min add 1 stop
1min-1 1/2min add 1 1/2 stop
1 1/2 min - 2 min add 2 stops

and so on its basically 1/2 a stop for every thirty seconds you read of your meter.

hope this helps.

[Liam:]

Thanks for reporting back Paul.

I thought reciprocity always increased exponentially...

[Paul Corcoran]

Hi All,

Just got back some negs from my test with the above set of guidelines and thought i'd share the result. I determined the exposure was 2m 15 secs at f22 and so opened up two stops and shot at f11. I'm quite happy with the result, this is the raw scan with no adjustments so i'd say those guidelines are are good starting point for this kinda work.

All the best

Paul

http://www.flickr.com/photos/paulcorcoran/5428403226/

[peter ramm]

So how does this translate to multiflash? Recently, I ran a series of trials and needed 35 x 1000ws pops (but reduced about two stops through a polarizing filter). This gave me proper exposure on 8 x 10 HP4 with a 240mm at almost 1:1, lens polarizer, f35. In this situation, I seem to remember my film plane metering was not sensitive enough to read anything so I got an incident light guide value. Of course, that was less than 10% of what I actually needed.

Factors are close to full bellows extension on the P2 and successive flashes. I can get the bellows factor, but have not found a reciprocity treatment for multiple flashes. In this case, the bellows factor appeared to account for most of the required increase in exposure. I guess each successive flash is less efficient than the one before but how much?

Any guidance?

[Robert Hughes]

So how does this translate to multiflash?

Reciprocity failure is a consequence of long exposure. Since flash photography is instantaneous, reciprocity failure is not an issue.

Edit: guess not - as bobwysiwyg link shows below.
How short duration is an electronic flash, anyway?

[bobwysiwyg]

It's also a consequence of short exposures.

http://glenstone.sdsmt.edu/My-files/...eciprocity.pdf

[peter ramm]

As I understand it reciprocity arises because the noise floor eats a proportion of photons in dark areas - however the darkness arises. Can be from low levels of continuous lighting over time, low levels of flash illumination over pops, or short exposures.

My informal observation was that flash reciprocity was less than I expected given that the continuous exposure would have been some minutes. Just wondering if there is a common wisdom about correcting for the use of repeated flashes vs long exposures.

[Eric Bryan]

I am not sure where I found the following rule, perhaps in one of the older Kodak film guides: A rule-of-thumb used by many photographers is to increase the aperture by ½ to one EV if the exposure exceeds one second, by one to two EV if it exceeds 10 seconds, and increase the exposure by 2 to 3 EVs if the exposure is over 100 seconds.

Good info. I am going to give it a try with Portra 160.

[ataim]

I use this and Its never failed me. I only use Ilford HP5 and Delta

http://www.largeformatphotography.in...city-Timer-1-0

[DavyG]

I use this and Its never failed me. I only use Ilford HP5 and Delta

http://www.largeformatphotography.in...city-Timer-1-0

+1 ... That is a very excellent app. And it's easier to use than remembering the generic formula which I did before. It also works for colour film.