Paper and reciprocal failure

[hoffy]

Howdy,

Last night I tried Ilford Warm Tone for the first time (RC base).

Firstly I produced a print using the standard Ilford paper, which gave me a time of around 26 secs @F8 on a 50mm lens with grade 4 filtering.

Now, according to the data sheet, the standard paper has an exposure index of ISO100 at grade 4. Warmtone RC paper is rated at ISO64 for Grade 4. I did a test strip (actually, I did a few!) and the best exposure was around 54 secs (& could have probably gone another few seconds to EXACTLY match the first print).

I have to admit that I was suprised, as this was over double the exposure.

I have been told that ISO ratings for paper are nominal at best, but would it be fair to say, that paper suffers the same reciprocal failure issues that film does?

Cheers

 

[E76]

Film does suffer from reciprocity failure like film, but I don't think that's what's going on here. It usually only comes into play with large magnification and low illumination. The speed of a paper is rather dependent on processing, so I'm not at all surprised that you didn't get the expected results. As you said yourself those ratings are merely nominal, and to be honest I don't think 2 stop increase as opposed to the expected 2/3 stop increase in exposure is anything to be worried about.

 

[hoffy]

Don't worry, I wasn't worried. That's why we do test strips afterall

More to the point, I was just curious and suprised, thats all!

 

[MattKing]

It's important to remember that the type of reciprocity failure you are considering is actually caused by a non-linear response to a reduction in light intensity, not an increase in time of exposure.

So if you are using the same light intensity for the two exposures, and it isn't extremely low, most likely reciprocity won't fail.

The situation is different for the reciprocity failure that occurs with extremely short duration exposures.

 

[el wacho]

mr Lindan did some work here regarding the reciprocity of paper.