View Full Version : ND Filters (1 ISO)

13-Oct-2003, 19:23

I need some help whit ND filters.
I wonder if you can give me some advise.

I want to use a 4x5 film rated ISO 100 and I wont to reduce the ISO factor under 1 ISO (minimum 1 ISO).

I want to shot 90 minutes (aprox.) minimum 1 hour. Off course will depend also of the light available (exteriors).
I know some people have use a 16x ND filter to get such long exposition.

I was looking for ND filters and I find the B+W ND filter series, they are the only one I find whit high factor.
Bud I get a little confuse whit the filter factor and the f-stop reduction.
which filter I should use? a B+W 106, 110, 113, 120?

This is the link of B+W

I will really appreciate if you have some experience to share.

By the way, which holder system you recommend, certainly I will use other filters like Graduated ND, Polariser, B&W and temperature correction.
I shoot 4x5 and my first lens is a Rodenstock Sironar-N 210/5.6 MC if someone know what is the filter size for this lens I would really appreciate.

Thank you very much Salvador

Guy Boily
13-Oct-2003, 20:04
Salvador,I use a BW #106 very often. This is a 64X factor or 6 stop reduction to about ISO 1.5 for a 100 ISO film.If you use a #110, it will be 1000X or a 10 stop reduction. A #113-10,000X or 13 stop reduction. A #120-1,000,000X or 20 stop reduction. Selection an appropiate f-stop will get you the long exposure that you need. You will have to figure out the reciprocity failure by doing some tests and then your set. Hope this helps. Guy Boily, Canada

Ernest Purdum
13-Oct-2003, 20:05
Here are the f stop reduction amounts for the darker B&W filters:

#106 6 stops. 110 10 stops. 113 13 stops. 120 20 stops

If, instead of changing the stop, you increase the time of exposure, you need to double the exposure the same number of times. For example, if your meter gives a reading of 1/2 second, to use a 106 filter you would double the exposure 6 times: 1/2x2=1, 1x2=2, 2x2=4, 2x4=8, 2x8=16 2x16=32 seconds. Keep that going up to 20 times and you get extremely long exposures.

Are you familiar with reciprocity failure? Film doesn't work at its rated ISO speed at either extremely short or or extremely long exposures. In making 90 minute exposures, you will definitely run into this situation. I'd suggest you ask your film maker for guidance.

Could you get the result you want by multiple exposures? If you have a self-cocking shutter, this would probably be a less troublesome approach than ultra-;ong exposures.

Ernest Purdum
13-Oct-2003, 20:17
Your lens needs an M 67x0.75 filter. The outside dimension for push-on filter holders is 70mm.

14-Oct-2003, 06:50
Thanks for your help. You confirm I was thinking in the right direction. I think I was mixing factor and spot.

Filter factors must be multiplied together like 106 (64) x 110 (10000) = 64000x
And spot is just added like 106 (6) + 110 (10) = 10 f-spot.
And the density like 106 (1.8) if I divide by 3 I get the f-spot reduction = 6 f-spot reduction.
Thats rigth isn't?

One last thing, what it's the thickens of B+N ND filter. Will fit a Lee holder?

Thanks a lot, Salvador