How to meter correct with centerfilter

[cyron123]

Hello guys,
I have a light meter and a center filter on my lens. I am new in this. How could I meter correct?
I take the lightest area of my Photo. And after this I measure the darkest area. I take the middle of it. After this I open two aperture digits bed as use of my center filter...
Is this the right way?
Thank you.

 

[Dan Fromm]

The center filters I have are denser in the center than towards the periphery. Their density gradients compensate (approximately) for falloff of illumination off-axis with the lenses they're designed for. Each is marked with a compensation factor.

To use them, I meter normally and then adjust shutter speed or aperture as required by the compensation factor. Here's a fuller explanation: http://www.bhphotovideo.com/c/product/44702-REG/Rodenstock_170003_82mm_Center_Filter.html

 

[David A. Goldfarb]

Treat it as if it were a regular filter using whatever metering system you use. So if the density of the filter at the center is 1.25 stops, then meter normally and open the aperture or increase the exposure time by 1.25 stops. Then determine bellows factor and then reciprocity compensation, if necessary.

 

[cyron123]

Hello Dan,
thank you. At BH there is something with 1.5 Stops..Hmm
I have a centerfilter from Sinar Rodenstock with ND 0,45. What does this means? Bloody question.. I know sorry..
Thank you..

 

[David A. Goldfarb]

I have a centerfilter from Sinar Rodenstock with ND 0,45. What does this means?

1.5 stops.

 

[cyron123]

I have googled and find it too.. Thank you David..
This means: if i measure f22 and 4 sec with my meter..i turn the wheel on my meter 3 digits...and i have aperture 45 (=22+3 steps) now with 15 sec... This is my new time...?!?! Hmm

 

[Dan Fromm]

4 sec @ f/22 + 1.5 stops? + 1 stop = 8 sec. + 2 stop = 16 sec. 12 sec, plus adjustment for reciprocity failure will do.

1.5 stops means 1.5 stops, not 3 stops.

cyron123, you know so little that you're doomed to waste quite a lot of money. You need to learn photography before you spend more money on film or equipment. The best beginner's book for general photography that I know is Alfred Blaker's Field Photography, available used at reasonable prices from sellers on, in alphabetical order, abebooks.com, alibris.com, amazon.com, ... Field Photography is focused on 35 mm but contains what you seem not to know and explains it all well.

 

[cyron123]

You are right. Your infos here are like gold for me. Thank you..

 

[DREW WILEY]

The mfg published correction specs on specific filters seem to be right. Each full EV (f-stop of full step of speed, but NOT both at the same time) equate to a .30 density change in film exposure. Density is measured in logarithms. So a density offset of .45 means 1-1/2 stops. You can obviously adjust you time instead, but might encounter the need for reciprocity corrections if you do it that way. It is also important to note that these CF filters are designed not only for specific lenses and their own illumination falloff characteristics, but are intended for use at
certain f-stops if they are to perform according to design, providing even illumination.