Filter Factors

When shooting black and white film with a filter on the lens, I get confused about what the filter factor represents. If the filter factor is say 4, does that mean that I make the exposure 4 times longer than the unfiltered exposure? Or does it mean I add 4 stops? I am thinking the former, but would appreciate some clarification.

Thanks!

The filter factor depicts the exposure correction for a neutral (grey) subject to be rendered at same density as without the respective filter.

Factor = times something

4 times longer (2 stops).
See http://www.schneiderkreuznach.com/f...icks/B_W_Filter_Tip_Exposure_Compensation.pdf (Schneider manufacture B+W filters, which are some of the best available).

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newcan1 said:

When shooting black and white film with a filter on the lens, I get confused about what the filter factor represents. If the filter factor is say 4, does that mean that I make the exposure 4 times longer than the unfiltered exposure? Or does it mean I add 4 stops? I am thinking the former, but would appreciate some clarification.

Thanks!

Click to expand...

Yes, the filter factor is a simple time multiplier'4' simply means multiply the expoureby 4xYoy can vonvrt that into f/stop if you esire by calculating how many doublings you need to get to 4x, which in this case are 2,following he equationf/stops=(log filterfactor)/(log2)or log(4)/log(2).he internal lightmeter of your camera will compensate for the filter but it works better to measurewithout the filter and add the filter factor afterwards;thatavoids issues with the spectral sensitivity of the particular metering cell.

Rather than relying on the published filter factor (which will not represent the particulars of the scene that you wish to photograph), it is much easier to determine the correction out in the field.

Meter the scene using a reflected light meter and note the indicated exposure and then hold the filter in front of the meter cell and note the difference. This is the compensation required for that particular scene, at the moment of the day with the prevailing colour/intensity of light.

Now meter the scene in your usual manner (for example I would meter the darkest shadow where I wish to retain detail and then place this on Zone III - which means closing down the aperture or increasing the shutter speed by two stops compared to what the meter indicated) and then apply the filter factor that you you have determined for that particular scene.

Bests,

David.
www.dsallen.de

... and hope the filter didn't throw off the spectral sensitiity of the metering cell