Meter through B&W Filters

RalphLambrecht · Feb 13, 2014

StoneNYC said:
Or Acros100

I'd wish Iwould have a better understanding of the spectral sensitivity of film and how that is affected by filters:munch:I have and understand the diagrams but,thry don't seem to correlate to actual testing.for example a sharp-cutting red should block the light of most laser pointersbut,I can still see the pointer through it.How can that be? I don't trust tspectral sensitivity diagrams.

fotch · Feb 13, 2014

If using one of my Nikon SLR's, I filter thru the filter that is mounted on the camera. Never had a problem. If using any other camera, I use a handheld meter and apply a filter factor. Seems like a lot of work otherwise, removing filter, holding it in front of a meter, trying not to drop anything, replacing filter on lens. Other than landscapes, I would not think it would work anyway. JMHO

ROL · Feb 13, 2014

lhalcong said:
Metering with a sekonik through B&W red or orange filter does not work

How exactly do you mean that it doesn't work? No change in exposure, incorrect or unexpected additional exposure??

FWIW, I've always added exposure using the filter's published filter factor, plus my own experience with the filter, particular film and lighting – all as acquired by developing and printing my own work. I have never fully trusted metering through the filter with my spot meter because of the (to me) unknown spectral response, even though it does seem the most logical and direct way of measurement, and despite the fact that Hutchings preferred it in the one and only workshop (Azo printing) I have ever taken.

Mr Bill · Feb 13, 2014

RalphLambrecht said:
for example a sharp-cutting red should block the light of most laser pointersbut,I can still see the pointer through it.How can that be?

Ralph, if the laser pointer is red (~ 635 or 650 nm perhaps?), then it should pass easily through a Wratten 25, or even the higher cutting #29. Either will transmit over 80% of that light. I think you're just having a temporary brain freeze about filters. If a filter looks red, that's because it lets red light come through.

If you have the companion tri-color filters to #25, the #58 green or the #47B blue, either of these should stop a red laser dead. (Assuming around either 635 or 650 nm).

Thomas Bertilsson · Feb 13, 2014

However this works out I make one observation:

1. If you use a hand held meter, it seems very impractical to take the filter off the lens just to meter through it. Instead just meter and add the filter factor.
2. If you use an in-camera meter, it seems very impractical to remove the filter to take a light reading and then add the filter factor.

Two main scenarios. I can tell from experience that my Pentax 35mm SLRs do not measure correctly through red filters. The scenes always come out underexposed.
Therefore, when I use filters I always use a hand held meter and add the filter factor, and those negatives always come out right.

Mainecoonmaniac · Feb 13, 2014

Gee I didn't know that about the light sensors and light meters. So I assume that light meters see the whole visible spectrum?

fretlessdavis · Feb 13, 2014

I use filter factors for exposure, but I have spot metered through filters to see what the contrast will be between different tones in the scene. I don't do that for exposure readings, though.

As far as my experience goes, older meters do fine with yellow, orange, and warming (with color). Metering through Red and Green filters gave negatives that were .5-1 stops off, but were still easily workable. You have to be careful with filter factors, too, because different scenes and tones respond to filters differently. A scene with water and foliage, for example, gets quite a bit darker with red, and I'll usually do a full 3 stops. Other times, for example, where there's a lot of red sandstone present, I'll do 2 stops.

Sirius Glass · Feb 13, 2014

Mainecoonmaniac said:
Gee I didn't know that about the light sensors and light meters. So I assume that light meters see the whole visible spectrum?

No they do not. Not all light sensors and light meters are created equal. If I had had a CdS built-in light meter in the 1960s I would have never metered through the lens and filter. When using the external CdS light meter which I did have in the 1960s, I never metered through the filter.

pentaxuser · Feb 13, 2014

I think it was Les McLean who advocated using a filter on camera, using the exposure given and then bracketing around it so you had the camera exposure, any additional exposure that the filter factor produced and maybe one even higher factor. Printing from all three negs allows you to choose the best print and from that you know how to compensate for that particular filter on that particular camera using that particular film.

This sounds sensible and pretty exact. Not tried it myself. With both my pentaxes I have been satisfied with the in-camera meter's exposure but the above method may well reveal that I could have got a more accurate exposure for the filter/camera/film combo

pentaxuuser

Xmas · Feb 13, 2014

Mainecoonmaniac said:
Gee I didn't know that about the light sensors and light meters. So I assume that light meters see the whole visible spectrum?

The CdS sensors are normally also near infra red sensitive (so unless the light meter has an expensive infra red filter in front of them) the effect of a visual filter is different on the cell and the film, the cell can ignore a minus blue (yellow) filter to a greater extent than the film, so you will underexpose a little.

In tungsten filament light the effect is more pronounced the light is mainly infrared, as you use a dimmer on the tungsten bulb the bias gets progressively worse.

So you need to be cautious with a CdS TTL SLR like an OM1 when you use a filter - I remove the battery when using filters and use a Weston.

As Ben says the bias effect is less with silicon cells, but he still does not meter through a filter, careful technique...

The next problem is the filter factors are not really exact anyway, and ortho, a true pan and a super pan film will need different factors, though the super pan would not have the near infra sensitivity of a CdS still. The film data sheet should provide a graph, few films match the spectral sensitivity of the eye.

If you use filters with deep colours e.g. orange or red you need to be more careful e.g. you can use a dim dark red safelight when developing some orthos is a clue...

An instruction book should tell you any difference in spectral sensitivity of the photo sensor... should... Bracket for critical work with strong filters.

Noel

Alan Klein · Feb 13, 2014

Mr Bill said:
I'm in the camp of metering the subject directly, then apply the filter factor.

An important point is where you get your filter factors from. I recently posted in a thread about filter factors for some sharp-cutting red filter (like Wratten 25). Someone was using factors supplied by the filter manufacturer, which I maintain is the wrong place to get them from - you should ideally get them from the film maker, and ideally for the light source you use.

Since I went to the trouble of writing an explanation, I'm also going to paste it in here:

Most of the time your exposure won't be so sensitive to filters - this is sort of a worst-case situation. The #25 red cuts sharply at about 600 nm (at 580 nm and lower virtually nothing comes through) so exposure only occurs from there on up. This means that there can be a big exposure difference between films with different amounts of red sensitivity, such as the two listed.

If anyone is inclined to meter THRU the filter, they ought to consider how the meter would handle the difference between these two films: Tmax 100 vs Tech Pan.

Bill: That was me. The problem was the filter manufacturer of my filters (B+W Schnieder) does not use the Wratten numbering system belonging to Kodak. So the Wratten 25 and 29 indicated on the Kodak Tmax 100 film have no relationship to B+W's numbering system. They use 090 and 091 for light red and dark red. So that's why I used their filter factor. As it turns out, I believe the factor of 5 (2 1/3 stops) they gave for their light red filter is too low. (Can they be wrong?!?) I plan on using a factor of 8 or three stops and then bracket +1 and -1 until I get a clear understanding of what the filter really requires. I want to thank you for adding clarity to this issue.

benjiboy · Feb 13, 2014

If you have a Kodak Grey Card it's easy to ascertain your personal filter factor for each of the filters you own by using your hand held meter at the grey card first, then through the filter .

Poisson Du Jour · Feb 13, 2014

Alan Klein said:
Bill: That was me. The problem was the filter manufacturer of my filters (B+W Schnieder) does not use the Wratten numbering system belonging to Kodak. So the Wratten 25 and 29 indicated on the Kodak Tmax 100 film have no relationship to B+W's numbering system. They use 090 and 091 for light red and dark red. So that's why I used their filter factor. As it turns out, I believe the factor of 5 (2 1/3 stops) they gave for their light red filter is too low. (Can they be wrong?!?) I plan on using a factor of 8 or three stops and then bracket +1 and -1 until I get a clear understanding of what the filter really requires. I want to thank you for adding clarity to this issue.

+3 ( FF8 ) is the setting I have used with a Hoya HMC red filter and ACROS 100 with correct results, and this should be the end of the matter; certainly all the discourse about types of in-camera or separate meters is not especially relevant' what is relevant is learning practical photographic skill and applying it and judging the results. B+W filters, especially their polarisers (Kasemanns in particular) have been described as dense which may be the basis for cautionary bracketing, but bracketing would be done anyhow for first-time users.

benjiboy · Feb 13, 2014

Poisson Du Jour said:
+3 ( FF8 ) is the setting I have used with a Hoya HMC red filter and ACROS 100 with correct results, and this should be the end of the matter; certainly all the discourse about types of in-camera or separate meters is not especially relevant' what is relevant is learning practical photographic skill and applying it and judging the results. B+W filters, especially their polarisers (Kasemanns in particular) have been described as dense which may be the basis for cautionary bracketing, but bracketing would be done anyhow for first-time users.

I agree, it's about testing your own equipment and processes to be able to anticipate your final result.

brian steinberger · Feb 13, 2014

benjiboy said:
If you have a Kodak Grey Card it's easy to ascertain your personal filter factor for each of the filters you own by using your hand held meter at the grey card first, then through the filter .

This is exactly what I did. And every meter reading matched the manufacturers filter factor except one, the deep red. For this filter I give 3-4 stops not 2-2 1/2 as my meter indicates. So for me I trust metering through the filters except the red which I rarely use. I prefer to meter through the filter to see how the values are affected by the filter. Works for me.

I also should note that I shoot rangefinders which do not meter TTL so it's easy to put a filter on and just dial in exposure compensation when I want to use in camera metering.

MattKing · Feb 13, 2014

benjiboy said:
If you have a Kodak Grey Card it's easy to ascertain your personal filter factor for each of the filters you own by using your hand held meter at the grey card first, then through the filter .

Well ....

This depends on your light source, and the spectral sensitivity of your meter.

If you don't believe me, try it with a fluorescent light, then daylight, then a tungsten source.

Tom1956 · Feb 13, 2014

I have located a link to the spectral response of CdS cells. Now mind you, as many times as I have searched response curves on the internet, I've found not to stop at 1 and consider it gospel. About mid page of this web page is a link to see more detailed info regarding the product. Click that link and you will download a 7 page PDF. I believe the graph is on p2.
http://www.token.com.tw/resistor/photo-cds.htm

Mr Bill · Feb 13, 2014

Alan Klein said:
Bill: That was me. The problem was the filter manufacturer of my filters (B+W Schnieder) does not use the Wratten numbering system belonging to Kodak. So the Wratten 25 and 29 indicated on the Kodak Tmax 100 film have no relationship to B+W's numbering system. They use 090 and 091 for light red and dark red. So that's why I used their filter factor. As it turns out, I believe the factor of 5 (2 1/3 stops) they gave for their light red filter is too low. (Can they be wrong?!?) I plan on using a factor of 8 or three stops and then bracket +1 and -1 until I get a clear understanding of what the filter really requires. I want to thank you for adding clarity to this issue.

Hi Alan, I remember, I just didn't want to be putting you on the spot here.

It sounds like you didn't see the post I clipped this out of, as it linked to the Schneider (B+W) filter handbook, which seems to confirm B+W 090 red = Wratten 25. Here's the link to my earlier post, which itself contains the link to the handbook: (there was a url link here which no longer exists)

Alan Klein said:
(Can they [B+W] be wrong?!?)

Of course they're wrong! That's what I'm trying to show. They (B+W) give a single suggested filter factor, whereas the real authorities - the film manufacturers - give different values for different films and conditions. So how can the filter maker's single factor possibly be "correct" across different films which list different factors?

Of course, the filter-maker's factor may be close enough for a starting point, and in fact, most photographers may be perfectly happy with it. The fact that many people are happy with their meter-thru-the-filter results supports this, even though their meter has no way to tell the difference between an extended-red sensitivity film like Tech-Pan vs T-max or the like.

Alan Klein · Feb 13, 2014

No I didn't see that link or the B+W manual. Pg 34/35 shows that their 090 and 091 light red filter and dark red filter are respectively 25 and 29. It's interesting that they call their 25 a factor of 5 and 29 a factor of 8. In their manual unlike their filter web site they hedge and say approximately5. But if it is 8, I wonder what the real value for the dark red 091 (29) would be for Tmax 100?

They also recommend bracketing 1/2 to 1 stop with TTL cameras when darker filters are used.

B+W Light Red Filter 090 (25)
This is the classic filter for architectural photography. White façades glow brightly, the blue sky is darkened dramatically and clouds become more impressive. It is also excellent for spectacular landscape photo -graphs with greatly improved distant views. Its filter factor is approximately 5.

B+W Red Filter 091 (29) Compared to the lighter red filter described above, this one even darkens the reds near the yellow tones in the spectrum, as its transparency only begins in the orange-red region. It produces dramatic effects and extreme tonal separation for graphic effects. That accounts for the large filter factor of appr. 8.

Still, with darker filters (very dense colors), exposure bracketing of ±¡/2 to ±¡ aperture stops is recommended, even with TTL exposure metering, because the spectral sensitivity of the metering cell can be significantly different from that of the film.

Mr Bill · Feb 14, 2014

Alan Klein said:
But if it [B+W 090 (25) is 8, I wonder what the real value for the dark red 091 (29) would be for Tmax 100?

Kodak doesn't give data for T-max with a Wratten #29, only for the #25.

But just for fun, I did some calcs comparing the two. I used a dozen steps of spectral data in the important range, multiplying filter transmission by the film's sensitivity (estimated from the T-max datasheet graph). (I ignored the light source, tungsten vs daylight shouldn't make much difference in this case.)

I figure the additional filter factor, beyond the #25, to be about 1.8X, or about 7/8 of a stop. That is, if you have a good factor for the #25, swapping in the #29 should require nearly another full stop. This is for T-max 100, if you used an extended-red sensitivity film, the change would be smaller.

250swb · Feb 14, 2014

pdeeh said:
well, I wouldn't dignify it with the epithet 'satire' but, yes, to be clear, it was intended to be humorous.

Well I 'got it' and thought it funny.

The point is all the elaborate rules that people are coming up with are entirely dependent on exactly where you point the meter, and the contrast and spectral range of the scene. The Gould method (the common sense approach), of simply compensating for the filter factor via the ISO dial and then use some intuition depending on the scene and contrast, will only go catastrophically wrong if you are devoid of intuition (a bit more, a bit less). It's no good talking about 'the Zone System' or any other precise approach for exposing the individual negative because this is the 35mm section of the Forum. It has been known for me to process an entire roll of 36 based on optimising one exposure/frame I think may be a 'winner', but otherwise an average approach to metering with filters wins on the 'all for one and one for all' basis as part of a chain of interlinking decisions.

Steve

BrianShaw · Feb 14, 2014

Xmas said:
An instruction book should tell you any difference in spectral sensitivity of the photo sensor... should...

I agree, but the manuals that come with meters don't... at least none of the ones I've read.

StoneNYC · Feb 14, 2014

BrianShaw said:
I agree, but the manuals that come with meters don't... at least none of the ones I've read.

There's a rule in sales about TOO much info, if you make them sound complicated people are less like I to buy them, I'm not talking pro's I mean the average joe, so they probably don't want to add too much detail, and for the most part unless you're increadibly persnickety, the exposure will be just fine following the filter factor.

BrianShaw · Feb 14, 2014

I totally understand that, Stone, and agree but these are meters/mauals for professionals (two samples for this AM: older = LunaPro; newer = L-558). If the information is indeed important to making images I would expect it to at least be mentioned. What they do is basically fluff the issue off by saying "YMMV" - know what you are doing. (I'm good with that, BTW.)

p.s. I am the exact opposite of persnickity regarding this... because in 30 years of photography have never had a significant issue directly attributable to these issues. Maybe I've been lucky; maybe I don't know good from bad... it's anyone's guess. My known failures have always been "something else" - and something much mroe obvious than the spectral characteristic of my meter cell. My inner scientist/engineer is struggling to understand the persnickityisms. Photography boils down to lots of error (using the statistical definition of the word; "margin" to most engineers) in most phases which can either be controlled or they cancel out. If one wants to control then they test and standardize their process and materials. But I remain perplexed by the engineering postmorums of decades old equipment that has proven their worthiness, and the postmortums leading to conclusions that the engineers didn't know bumpkuss and the sellers were liars.

StoneNYC · Feb 14, 2014

BrianShaw said:
I totally understand that, Stone, and agree but these are meters/mauals for professionals (two samples for this AM: older = LunaPro; newer = L-558). If the information is indeed important to making images I would expect it to at least be mentioned. What they do is basically fluff the issue off by saying "YMMV" - know what you are doing. (I'm good with that, BTW.)

p.s. I am the exact opposite of persnickity regarding this... because in 30 years of photography have never had a significant issue directly attributable to these issues. Maybe I've been lucky; maybe I don't know good from bad... it's anyone's guess. My known failures have always been "something else" - and something much mroe obvious than the spectral characteristic of my meter cell. My inner scientist/engineer is struggling to understand the persnickityisms. Photography boils down to lots of error (using the statistical definition of the word; "margin" to most engineers) in most phases which can either be controlled or they cancel out. If one wants to control then they test and standardize their process and materials. But I remain perplexed by the engineering postmorums of decades old equipment that has proven their worthiness, and the postmortums leading to conclusions that the engineers didn't know bumpkuss and the sellers were liars.

I apologize, for some reason I thought that it had been mentioned that the question was why they didn't put the spectral sensitivity info in the FILTER information when they sell them. Imagine mom and pop buy a filter and then have to try and understand spectral sensitivity.

But yes for a professional meter... I agree completely it should be in there, then again, most these days are assuming color only.

Meter through B&W Filters

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