TTL metering with red filter on, I am confused!

[mehmetsaygin]

First, I want to say I read related threads but it is still not clear

for me.

 

I have a B+W 090(25)red filter and I always use it, almost never take

it off.I mostly use spot metering and meter directly with my Eos

Elan7e camera. I guess I always get the right exposure.

 

A professional photographer which I really trust told me that the

results of TTL metering with the filter are always wrong at least 1

stop,I need to meter without the filter and use the filter factor.

 

I came home and made metering tests with filter and without

filter+filter factor, both results were same.I have my own results

but his words, I am confused.

 

Thanks,

[silent1]

Results win.

 

If you're getting good negatives with the way you're doing it, ignore the pro; he might be talking about a different film, different light conditions, different meter sensitivity curve or coverage angle, or simply different metering technique. In any case, he's not talking about you, because you're finding the same exposure through the filter as without the filter but with filter factor applied, and your negatives are the proof that you're doing it correctly.

[mehmetsaygin]

Thanks Donald,

 

Yes, you are right and I will stick to my method but I want to learn what is the common method.

Well, maybe there is no common method, everyone can have the best result of his own in different ways. So,lets say what is the recommended method.

 

Best,

[andrew_limiti]

I guess it depends on your equipment. When I first started shooting B&W I did some tests shooting the same subject without a filter, then shooting with the filter on using the camera's meter reading, and then increasing the exposure +1,2,3 stops. I found that the red 25 filter required 3 stops additional exposure from the exposure without any filter, and two additional stops more than my camera's metered reading, when I reviewed the contact sheet. So the meter on my camera was off by two stops when metering through a red filter. Now that I have a spot meter, I meter the scene without a filter, and adjust the exposure on the camera +3 stops and I get consistent results.

Even though you are getting good results, it sounds like you want to understand why.

[chris_waller]

When I shoot IR (Kodak HIE)I use an incident light-meter, setting it at 50 ASA. That is, rating the film at 400 ASA and allowing 3 stops for the R25 filter. If you are going to shoot using the camera's TTL metering then you need to establish the metering error with an R25. Some meters are more sensitive to red light so a red filter will cause some underexposure. Meter a scene without the filter, then with the filter, noting the difference in the meter readings. It should be 3 stops. If it is less then you need to down rate the film (or compensate on the exposure) by the difference. E.g if you get a 2 stop difference with the R25 in place, then you need either to increase the indicated exposure by 1 stop or downrate the film by one stop.

[Mike Gammill]

The degree of success with TTL metering with a R25 filter depends on the meter's sensitivity to the red wavelengths passed by the filter. Apparently, the older CDS cells found in many manual cameras are more sensitive to red light than silicon or other meter types. My Maxxums, X-700, XD-5, Yashica FX-3 meter perfectly through R25. My SRT 201, Konica Auto S2, Canonet GIII 17, and Olympus XA all underexpose with R25 due to their CDS cells. My SRT is so sensitive to the longer wavelengths that the meter needle will jump slightly if I point an infrared remote at the lens.

[david choo]

Your professional photographer friend was correct. As for your metering and getting the same readings with it on and off, it probably had to do with the subject matter.

 

TTL metering with the red filter is only off during certain conditions.

[stephen sullivan]

Yes Mehmet,

 

TTL metering with a colored filter(s) on it will be off.

 

I shot with an EOS 1 and B&W 090. To make a long story short: A professional camera repair store, using his Shutter Speed / Light meter test equipment, tested my camera's light meter with and without a B&W 090 on the lens.

 

Without a filter: Accurate.

 

With a B&W 090 filter: -2/3 of a stop.

 

Suggestion: When using a Red filter, change your exposure compensator to +2/3 of a stop. When using a Yellow or Orange filter add +1/3 of a stop. That should help you with achieving a normal exposure.

[andrew_hull]

Only 2/3s of a stop? Isn't a typical red filter a factor of 4? Meaning 2 stops (roughly)?

[andrew_limiti]

Andrew,

 

I think Stephen is saying +2/3 stop adjustment from the reading when

metering through a red filter. That is not the same as the difference in

exposure with and without a red filter. When I use my camera meter with the

red filter on I have to adjust +2 stops, to get the correct exposure (Canon

FTQL).

[al_divenuti]

To make a long story short - yes, with B&W contrast filters of relatively high saturation you usually will need to dial in some postive exposure compensation. Schenider optic recommends 1 full stop though this is a bit of a generalization

 

The reason for this is that the spectral sensitivity of your camera's metering cell is going to be different than that of the film. This, unfortunately, is true even for modern SPD cells.

[andrew_hull]

Andrew & Al, intersting, I never knew that.

[mehmetsaygin]

Thank you very much, this is really a helpful thread for me now.

Well, I made my test indoors with spot metering, then when I see the results are same,I gave up thinking I was right.

Now, I need to spend a whole day outdoors and make lots of test metering with all exposure methods and with different subjects.

 

I also make my meterings mostly with spot metering from faces.White skins reflects %35 of light, which means I underexposure 1 stop normally, right? Plus, 1 stop from red filter, that makes total of 2 stops underexposure which we can easily notice.

 

I guess I need to make the tests and see myself.I will share my results when I am done.

 

Thank you very much.

 

Best,

[mehmetsaygin]

@Al, can you direct me to a link with Schneider's recommendation?

What I found in their site is;

 

Almost all cameras today have a built-in light meter. The multiplying factor is then automatically included in the calculation.

 

This must be a general term, please help me to find the link.

 

Thanks,

[silent1]

Not only does this vary with different meters (as mentioned, my old selenium Gossen Sixtomat will respond differently to different colors of light than the CdS cell in my Spotmatic, the silicon cell in a Rollei 35S, or the SPD cell in modern cameras), but it also varies with different film types. You'll need a lot of compensation even from a TTL meter if you use a red filter on Efke 25 (with its reduced red sensitivity, it's like an old style Type A panchromatic film), somewhat less with Tri-X (a standard Type B pan film), less again with TMY (a slightly red-enhanced or blue-reduced Type B), and still less with Tech Pan or Plus-X Aero (strongly red enhanced, Type C pan films). IR is a special case, too, because it is strongly sensitive to blue as well as red and IR, but has little green sensitivity.

 

The case with your camera's meter sounds as if the meter is color compensated to match Type B films like Tri-X and Plus-X; if you're getting the same reading with external meter and filter factor as with TTL meter reading through filter, then it should be fine to use the TTL filter reading -- as long as you're using a standard Type B film. Start using other films with different spectral sensitivity curves, and you'll start needing other compensations for either metering method -- and may have to arrive at those factors yourself, for the TTL meter in your camera, because the manufacturer's data will be for one kind of meter, at best (and may only be for unfiltered metering).

[mehmetsaygin]

Thanks Donald,

I always use Tri-X.As I decided I will go and make more tests outdoor first, then I may have more questions.

Thank you all again for your interest.

[al_divenuti]

Mehmet,

 

Schnedier Optics (the maker of B+W filters) has a new filter handbook at:

 

http://www.schneideroptics.com/filters/filters_for_still_photography/handbook/

 

Note that you will need adobe acrobat to read it.

 

Their recommendation is to dial-in +1 stop of exposure for filters that are close to a pure color (e.g. 090, 091, etc.). I tend to dial-in about +1/2 stop with my EOS5 meter for the 022 (Dark Yellow) and 090 (Light Red) filters that I own.

 

As others have stated, the actual amount of exposure compensation needed really does vary somewhat by the metering cell in your camera and Schneider's recommendation is a general one.

[jan_brittenson]

Leica R9 with 90mm (SAA) lens at f/8. Overcast, set it up on a tripod and pointed it out the window at a building across the street with some mix of shadows and sky lit areas.<br><p>

 

No filter - f/8 1/30s<br>

B+W 090 (#25) - f/8 1/8s (4x, filter marked 5x)<br>

B+W 091 (#29) - f/8 1/4s (8x, same as filter)<br>

B+W 060 (#11) - f/8 1/15s (2x, same as filter)<br>

B+W 099 (#12) - f/8 1/15s (2x, same as filter)<br>

Hoya R72 (720nm) - f/8 6s (about 8 stops) - I was just curious about this<br>

<p>

While perhaps not exact, for the more common filters it's close enough not to worry about. It could also be the meter is actually more accurate, while the display readout is rounded to the nearest 1/2 stop.

[mehmetsaygin]

Thanks for the link Al and thanks for the test results Jan.

I read the Scheneider hand book and found the related text.

So after so much posts, we can say that it is all depends on your equipment, metering cells, films etc.

I am still not able to make my own outdoor test btu will share as soon as I make it.

 

Thank you very much.

[al_divenuti]

Mehmet,

 

Basically, I've concluded that (like many situations) it is wise to bracket exposures when using a filter of a highly-saturated color. My bracketing is usually +0, +1/2, +1 though additional compensation can occur for backlighting, etc.

[steve_stracquodaine1]

I'm commenting on a thread from 18 years ago!  Yikes!!

I put a dark red filter on my Minolta SRT-101.  I understood that I had to adjust exposure by 3 stops.  I ran a roll of Ilford PF4 (125), so I set my ASA to 15 (3 stops to compensate for the dark filter.  Then I metered normally with the Minolta's internal TTL meter.  By the way, the meter is accurate and the battery fresh.  Anyway, the results were severely over-exposed images.  So, considering that I was using TTL metering, should I have just left the ASA at the box rating of 125?

[SCL]

1 hour ago, steve_stracquodaine1 said:

I'm commenting on a thread from 18 years ago!  Yikes!!

I put a dark red filter on my Minolta SRT-101.  I understood that I had to adjust exposure by 3 stops.  I ran a roll of Ilford PF4 (125), so I set my ASA to 15 (3 stops to compensate for the dark filter.  Then I metered normally with the Minolta's internal TTL meter.  By the way, the meter is accurate and the battery fresh.  Anyway, the results were severely over-exposed images.  So, considering that I was using TTL metering, should I have just left the ASA at the box rating of 125?

Different films and meters have different spectral sensitivity....that's the lesson from previous posts. Until you have established the correction factors for your setup and subject matter, you should have bracketed your exposures. I had a similar issue to yours when I got my first dark red filter. Once I determined the proper filter factor for the film, meter and subject, everything subsequently came out fine. Do a sacrificial roll with standard development and you should be set for future success.