----- Original Message ----- From: Brent Roberts Subject: Q: Metering and B&W filters
> I have found reasonable success using a yellow No. 8 filter with a 2X filter > factor, and opening up one extra stop (correct me if I misunderstand filter > factors). I've shot two pics at the end of a roll I was wanting to get > processed in a pinch with a red No. 25 filter (5X factor). Both of these > shots were opened up 2.5 extra stops, and both are overexposed. I was trying > to put anything in a zone or anything like that I was just using the incident > meter to get a normal photograph. Now here is the questions for real: > > Would I be better off using my meter as a reflected meter and metering > through the filter? Will I run into problems where the meter is more > sensitive to certain colors than others? How should I adjust the filter > factor for subjects that are overwhelmingly one color or another. Do I simply > have a misunderstanding about filter factors. Do your recomendations apply > for flash in the same manner? Thanks for all the help. Not knowing if the Gossen is colour blind (check with the manufacturer), I would not meter through a strongly coloured filter. If Gossen sez the meter is colour blind, that changes everything. I believe the #25 filter has a factor of 4, not 5. You didn't mention how overexposed the film is, or if you have good exposure in part of the scene and bad exposure in another part. When you start using the strong filters, you need to start looking very carefully at what colour of object you have in front of the camera. If you try to photograph a red barn with a blue sky with a red filter, the contrast of the neg will be so high as to be nearly impossible to print. Local exposure is more greatly affected by strong filters than weaker ones. Weak filters, such as #8 require little thought about use, but the strong ones, such as #21 or #25 do require some planning. Film spectral sensitivity also needs to be considered. Please see: http://www.ilford.com/html/us_english/pdf/FP4Plus.pdf http://www.ilford.com/html/us_english/pdf/Pan_F_Plus.pdf http://www.ilford.com/html/us_english/pdf/100_Delta.pdf (you will need Acrobat Reader). You will see that within the family of films from this manufacturer, the red sensitivity varies greatly from film to film. The stronger the filter colour, the more spectral sensitivity needs to be considered also. Generally, use the weakest filter you can to get the tonal separation you want. For most purposes, you won't need to go stronger than a #15, which I believe is a 3x. One thing you might try is going out and shooting the same scene with several different strengths of filter, with bracketed exposures (1/2 stops is sufficient for this exercise), then process the negs and make a contact sheet of the film. This way you get to see exactly what each filter does, in relation to other filters with the same scene type. HTH William Robb - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
