Velvia 50 and 100 Reciprocity Correction

[Brian_A]

Hello All,

This may seem retarded and all, but I'd love to know the answer in a plain way. For example, with Ilford Delta 100 and PanF the way to find out your adjusted shutter speed for measured times greater than 1/2 second is to do this algorithm:

Y=1.465^X+1 (Measured Time + 1 to the power of 1.465 = Adjusted time - where 120 seconds adjusted is 18.76 minutes)

Does anyone know this way of figuring out the adjusted time for Velvia 50 and/or 100? The only thing I can get off of the Fuji website is to use a magenta filter and to add 1/3 of a stop to 2/3 of a stop. But that should be just to offset the filter it recommends.

Thank you!

-Brian

[Ron Marshall]

The corrections listed on the Fuji site are to both correct for reciprocity failure and for the color shift that occurs with long exposures.

For Velvia 50 you need to increase the metered exposure by an extra 1/3 stop at 4 seconds (or the aperture); at 8 sec. 1/2 stop; 16 sec. 2/3 stop; 32 sec. 1 stop:

http://www.fujifilm.co.uk/profession...e_velvia50.pdf

[Brian_A]

I already understand that way of doing it as I noted in the last part of the first post. Now, if I'm not using the filters (As I intend to fix the color shift in Photoshop) do I need to bother using the extra stops as the stops are there, in my opinion, to offset the filter density? Or should I do it anyway - even if I'm not using the filters?

Thanks!

-Brian

[Ron Marshall]

I already understand that way of doing it as I noted in the last part of the first post. Now, if I'm not using the filters (As I intend to fix the color shift in Photoshop) do I need to bother using the extra stops as the stops are there, in my opinion, to offset the filter density? Or should I do it anyway - even if I'm not using the filters?

Thanks!

-Brian

Yes, you need the extra exposure to account for the reciprocity failure, with or without the color correction.

[marschp]

Yes, you need the extra exposure to account for the reciprocity failure, with or without the color correction.

The Fuji recommendation does include the adjustment for the filter. However, if you are excluding the filter at image capture then you simply need to strip out the filter adjustment factor. I measured this at about 1/3rd of a stop for a 10M filter. When NOT using a filter I have used the following RF adjustments:

4s - no adjustment, 8s add 1/3rd stop, 16s add 1/2stop, 32s add 2/3rd stop.

Obviously I've rounded the adjustment to the nearest 1/3rd of a stop. Incidentally, instead of using the M series of filters you could try either a Lee 85c, or the Tiffen 812.

Cheers

Paul

[thrice]

Brian, based on experimental evidence acquired by another photographer my father plotted and derived the following formula.
Corrected = 0.90842 * Indicated^1.24
Applies only once the indicated exposure hits about 2s and agrees pretty closely with the information posted by Ron and Paul.
Should note the resulting value assumes a colour correction filter is in place that will have a filter factor of 1.3 to 1.5... I may see if we can work out a formula for unfiltered.

[thrice]

I should add that is for Velvia 50.

[Corran]

I always wondered why reciprocity failure wasn't plotted to an equation just like you posted. Thanks, I will definitely be using this!! Do you have any other equations for other films?

[douglas gove]

Brian...My personal guidelines for Velvia 50...I rate the film at asa 50...I do not use color correction filters...4 sec-5, 8 sec-11, 16 sec-24, 30 sec-54, 60 sec-115, 120 sec-260...The longer exposures require a bit of intuition as I find the light values often change during exposure...This has worked for me for years...As to the 100 speed films I have no experience with them...Hope this works for you Doug

[thrice]

An almost perfect fit for the reciprocity failure of Ilford black & white films (they provide the same graph for every film) is the equation:
y = 1.953x + 0.1064x^2
Where x is the metered exposure and y is the corrected exposure.
I have a table of corrected values for Provia 100F I will plot and derive an equation, if anyone has any other verified film reciprocity data for example Kodak Ektar, Kodak E100G, Kodak Portra 400 or any other film for that matter, please share