red filter factor

[hubert_seremak]

hi there

 

I have hust bought tiffen 25 A filter for my rollei (using 49 mm adapter, as it is way cheaper than genuine

rollei filters) - my question:

 

Tiffen says increase light 3 stops or so. When I put it against my lighmeter (pretty good gossen lightmeter, very

reliable and acurate) it shows only 1 stop increase.

 

I assume the lightmeter measures it wrong way? It shows also 1 stop increase on yellow filter as well - what is

usually correct, and red what I have red, need 3-5 stops increase, here 3 stops as indicated in small booklet?

 

I use it for film of course, B&W.

 

anyone had experience with Tiffen 25A red filter and regular films like trix or hp5?

[vincent_peri]

I have the Tiffen "Quick Reference Guide," and it says a 23A filter needs a 2-2/3 stop increase in exposure. A Tiffen 25 red needs a 3 stop increase in exposure. I don't see a 25A filter listed.

[hubert_seremak]

i have a small tiffen filter facts booklet - added to the filter box itself, small , about few pages - it says

25A needs 3 stops (yet the very filter has "25" description on the edge, not 25A - I do not know what is the

difference, dont't care too much). I will use 3 stops more for this filter, ok.

[Matthew Currie]

It may depend on your meter, but many older meters with CdS cells, such as my Nikon F, do not read correctly through a red filter because the cell itself is not panchromatic. You're best off overriding the meter reading and using the published filter factor. I always got good results with +3 for red.