How to use Filter factor

S

Stelios

Guest
I've noticed that manufacturers give Filter factors to use with film. How is filter factor used? What is a filter factor of 8 for example?

Thanks in advance
 
Dear Stelios,

8x = 3 stops (f/8>f/5.6>f/4>f/2.8) or 3 shutter speed steps (1/250>1/125>1/60>1/30) or of course a combination of the two -- 2 stops, 1 shutter speed step, or vice versa.

Likewise 2x = 1 stop/shutter speed step, 4x = 2 stops/shutter speed steps.

Cheers,

R.
 
The same thing can be represented a few ways as well depending on the manufacturer

  • filter factor 8 (factor of light passed, ie 1/8th)
  • 3x (number of stops reduced)
  • 0.9 (logarithmic change in density)

...all are 3 stops less
 
craygc said:
The same thing can be represented a few ways as well depending on the manufacturer

  • filter factor 8 (factor of light passed, ie 1/8th)
  • 3x (number of stops reduced)
  • 0.9 (logarithmic change in density)

...all are 3 stops less
Click to expand...

Dear Craig,

Very true. I'd add that log densities are normally used only for ND filters and that 'ND2' can be a real bar steward as I have seen people use it to refer to 2x, 2 stops (4x) and even occasionally the log (100x).

Cheers,

R.
 
Is there a reason this was never standardized? For me, the most logical choice is number of stops, but others might have other opinions.
 
degruyl said:
Is there a reason this was never standardized? For me, the most logical choice is number of stops, but others might have other opinions.
Click to expand...

Dear David,

The problem is, who's going to standardize it? I think the clue lies in 'other opinions'.

Cheers,

R.
 
degruyl said:
Is there a reason this was never standardized? For me, the most logical choice is number of stops, but others might have other opinions.
Click to expand...

It WAS standardized... just not to a single standard but several different standards. :)

This is not uncommon when there is not a single controlling standardization body. Plus... engineers like talking in terms that are familiar to them and often don't think to the needs of the end-user. And, the general trend of how to expresss filter factors seems to have differed over time.

Like you, I'd prefer that filter makers exrpess in terms of stops rather than multipliers or log-density detlas, but...
 
Gumby said:
Like you, I'd prefer that filter makers exrpess in terms of stops rather than multipliers or log-density detlas, but...
Click to expand...

Well, you get used to it. In motion picture film use, ND's are always designated by their Log Density delta, i.e. ND.3 (1 stop), ND.6 (2 stops), ND.9 (3 stops), ND 1.2 (4 stops), ND 1.5 (5 stops), etc. On the other hand, Polarizers are often called 1 stop Polas or 2 stop Polas respectively.

Any other over all filtration I use, I tend to just spot meter it with an 18% gray card. There's never enough time to look up filter factors for uncommon filtration.

Sometimes I feel like some of the arcane terms commonly used on film sets are there to keep a built in "pay your dues" factor. If you hear a string of common commands employed when setting lights or camera parameters, you would think we were speaking in a foreign language. In a sense, I guess we are.
 
LADP said:
Well, you get used to it. In motion picture film use, ND's are always designated by their Log Density delta, i.e. ND.3 (1 stop), ND.6 (2 stops), ND.9 (3 stops), ND 1.2 (4 stops), ND 1.5 (5 stops), etc. On the other hand, Polarizers are often called 1 stop Polas or 2 stop Polas respectively.

Any other over all filtration I use, I tend to just spot meter it with an 18% gray card. There's never enough time to look up filter factors for uncommon filtration.

Sometimes I feel like some of the arcane terms commonly used on film sets are there to keep a built in "pay your dues" factor. If you hear a string of common commands employed when setting lights or camera parameters, you would think we were speaking in a foreign language. In a sense, I guess we are.
Click to expand...

Not just movies. Scrim the inky? Kill the brute? Flag the bottom half of the strip? Wind the swimming pool up a bit? That's from advertising using 4x5 and 8x10 in the 70s.

But of course with still photography we just used Rolapoids.

Cheers,

R.
 
Roger Hicks said:
Not just movies. Scrim the inky? Kill the brute? Flag the bottom half of the strip? Wind the swimming pool up a bit? That's from advertising using 4x5 and 8x10 in the 70s.

But of course with still photography we just used Rolapoids.

Cheers,

R.
Click to expand...

Now you're talking old school, Roger! Some of the terms have "evolved" since the 70's (or devolved depending on your perspective). ;)
 
Roger Hicks said:
Not just movies. Scrim the inky? Kill the brute? Flag the bottom half of the strip? Wind the swimming pool up a bit? That's from advertising using 4x5 and 8x10 in the 70s.

But of course with still photography we just used Rolapoids.

Cheers,

R.
Click to expand...

Roger -

I don't want to hijack this thread... but how about a thread on all these pieces of argot? Just what we need to pop onto the digi-crowd. :)

I will start one in your RFF cafe.

KenD
 
May Not Be Applicable....

May Not Be Applicable....

If your camera meters through the lens, filter factor is accounted for in the metering process. You DON'T factor for the effect of the filter on the exposure, if your camera meter is already measuring through the filter.

One of the advantages of SLR's and many RF cameras that had the meter spot/pickup in the surround on the lens, or TTL.

Adjusting for the effect of the filter (the factor) is necessary on shooting hand held meters, or where the meter on the camera is measured in the body outside the lens.
 
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