Spotmetering with filters?

Andrey · Apr 13, 2008

I only have one red-orange filter so far for black/white. I'm planning on getting a deep red as well soon.

I was wondering if it's worth it to keep a yellow filter on the lens?
I also have a yellow 15 mired filter, can that be used as a general filter?

How would I approach a scene with a camera, a filter and a spotmeter?

I started playing around with filtering today and it's slow, for one.

The second issue is that the only way I see to actually use a spotmeter properly is to take the filter off the camera lens and meter through the filter.

Are there snap-on sekonic attachments that correspond to standard filters?

Also, does sekonic publish the sensitivity curves for their meters? I'd want to see how close it matches the films I'm using.

Thanks

nickandre · Apr 13, 2008

A filter has an exposure factor (a standard yellow is something like 1/3 stop, really won't matter with B+W). You can simply add 1/3 stop to your EV that your meter reads. You should just leave the yellow filter on all the time to counteract the extreme blue sensitivity of these B+W films.

Polarizers are great too.

Nick Zentena · Apr 14, 2008

IIRC my Sekonic takes 30.5mm filters. They might make a step up ring to a slightly larger size.

If you really care you could get a second set of filters in the size the meter takes. Not much point for most people. But you can mount filters.

Do you mean a Wratten #15? That's basically orange.

Why do you want a deep red? I think most end up finding a 15 and a 21 a pretty good set of darker filters. The amount of time a 25 or 29 gets used isn't that great for me.

Uhner · Apr 14, 2008

Hi Andrey.

My advice is to go to the library and do some reading on the subject. It will make things easier and perhaps save you some money. You can, for instance, check out Ansel Adams The Negative – in particular the chapter on Filters and pre-exposure.

Steve Smith · Apr 14, 2008

I generally add one stop for yellow, two stops for orange and three for red.

When metering I put the filter factor correction into the film speed setting.

i.e. if using ISO 400 film:

Yellow filter - rate as ISO 200
Orange filter - rate as ISO 100
Red filter - rate as ISO 50

Steve.

RobC · Apr 14, 2008

Metering through filters doesn't always work. Your meters spectral sensitivity will be different from film spectral sensitivity and some filters, such as deep reds, can have a very sharp spectral cut off which give wildly wrong readings.

All filters come with a "Filter Factor" which you should use as a starting point for making adjustment to your exposure. This is just a quick mental calculation which is far simpler than pratting about trying to meter through a filter.

There are commonly two systems of notation for filter factors. They are either given in Log of density which whilst it may seem confusing at first is actually very simple. Each 0.1 of density equates to a third of a stop. So a 0.3 filter factor requires one stop more exposure. A 0.6 factor requires 2 stops of additional exposure and a 0.5 would require 1 2/3 stops. Simple.

The other method is to give a multiplication factor so a factor of 2X would mean two times metered exposure time. 4X would mean 4 times metered exposure time. Careful with this one because 6X does mean 6 times the metered time and not 3 lots of 2X. So a 3 stop factor would be 8X.

Start by using the filter factor for your filter and use trial and error to determine what works well because its not an exact science as light colour temp varies during the day and different parts the scene are affected differently which is another reason why metering through a filter won't necessarily give you what you might expect. Shadows tend to have more blue light (outdoors).

Basically you have to learn when and how much filtration to use for any subject and lighting conditions and that takes practice.

Andrey · Apr 14, 2008

rob champagne said:
Metering through filters doesn't always work. Your meters spectral sensitivity will be different from film spectral sensitivity and some filters, such as deep reds, can have a very sharp spectral cut off which give wildly wrong readings.

That's what I was wondering.

Is there any data published on spectral sensitivity of sekonic meters? The 508 mostly.

haris · Apr 14, 2008

Manual for my Gossen said it will work with metering through filter and thus find correction factor. But, I would also read literature and learn. For beginning, read what is said on filter, on every filter is written (or atleast it should to be written) exposure compensation factor. It is good for start, and you can experiment from that point. If you are not sure, for example if your meterig showing f16 1/125 without filter and you think it is 2x compensation, but you are not sure, you can use f16 1/30 instad of f16 1/60. One stop overexposure of b/w film not only will not harm you exposure, but it can help

You don't need data of spectral sensitivity of your meter (unless you really want to go scientific route), for practical purposes, and especially for beginning of filter using, I think it is better to find data of exposure compensation needed for your filters

You already got very good advices from others who answered your question.

phaedrus · Apr 14, 2008

The films I'm using aren't overly blue-sensitive. Most modern emulsions aren't. So I'm only using a yellow filter when it's effect is warranted, e.g. for differentiation in vegetation or certain kinds of rock. You can actually see that looking through the filter.

CBG · Apr 14, 2008

Whether to keep a yellow filter on the lens permanently is subjective. Most common modern films have enough green and red sensitivity to separate sky values from cloud values, the most common reason for the yellow / orange / red filter uses. If the film(s) you like to use are workable on that score, the addition of a filter is not mandatory. If you find you always want more separation, then maybe a filter all the time would be your choice.

Just meter with your spot and apply any filter factor needed. I'm not a fan of metering through the filter although others here are.

C

Doremus Scudder · Apr 20, 2008

Metering thru filters technique

I routinely spot meter through my filters with good results

BUT, I use a system that adjusts exposure/contrast for extreme filters.

For example, I find that the red Wratten #25 filter needs about a stop more exposure than my meter says and an N-1 development with Tri-X (N+1 with Tmax... go figure).

I have done tests to arrive at these "fudge factors" and keep refining them. They are different for different film/filter combinations.

The weaker filters, i.e. yellow, light orange, #11 yellow-green, etc. don't need the fudge factors, but a #58 green does, as does my #44 cyan.

I believe working this way is way more accurate than just applying the published factor.

I use a Zone VI modified meter most of the time, but it is not much more than 1/3 stop different from my unmodified Pentax, so I wouldn't worry to much about spectral response. More important is the different response films have to different colors (i.e. the increase in contrast and loss of speed of Tri-X with predominantly red light mentioned above).

So, bottom line, begin with just metering through your filters, but be aware that you will have to develop some "fudge factors" for stronger filters. You can "field test" and adjust as you go if you keep good records, or test before you go shooting. The worst possible case I can foresee is about a stop underexposure and a step too much contrast (which can be hard to deal with...) Err on the side of overexposure or bracket if you don't do calibration tests.

Good luck,

Doremus Scudder

www.DoremusScudder.com

Curt · Apr 20, 2008

Fred Picker told me I would have no problem metering though the Zone IV modified meter, I bought one and have used it ever since. It works great, of course you can still check and or use the filter factor or test for your own factor.

Doremus Scudder · Apr 24, 2008

Just a comment on the above...

Theoretically, a meter that has the same spectral response as the film should yield accurate exposure information when metering through filters. Even a meter that was relatively close would be well withing the ball park, so to speak.

There is one catch, however, and that lies in the response of the film itself when exposed to just one color of light. My experience with Tri-X leads me to believe that when exposed to predominantly red light, the contrast of the film is increased and the effective EI is reduced by about 2/3 of a stop. Predominantly blue or green light tends in the other direction. Hence the "fudge factors" I mentioned above. Other film/filter combinations react differently.

This same would apply to filter factors as well, so, for the most accuracy, the "fudge factors" should be developed and applied whether you use filter factors or meter through the filter.

I believe that metering through the filter is a superior method to applying filter factors, especially when using the Zone System and a spot meter. By metering through the filter, one can get an idea of where areas of high color saturation will fall in relation to other areas of the scene. An example: metering a blue sky over a green field with a spot meter gives different EVs for each area, indicating the number of stops, or Zones of separation. Metering with no filter, a yellow filter, a green filter and a red filter successively will give different spreads between the two areas, allowing one choose the best filter to better "place" the values in the desired relation to each other. This is something that you cannot do by applying a filter factor.

This, I think, is still by far more more accurate than applying filter factors and "guestimating" the placement of areas most strongly affected by the filter. When one develops fudge factors for compensating for the response of a particular film/filter combination, the accuracy increases even more. Even without the "fudge factors," the worst possible case is missing the goal by a stop, or getting a more or less contrasty negative than expected (the same would happen with filter factors).

Best,

Doremus Scudder

www.DoremusScudder.com

Andrey · Apr 24, 2008

My thoughts exactly

I think I got the wrong meter then, my L508 doesn't have any filter threads - maybe I'll be able to switch it to L558 someday or similar.

Doremus Scudder said:
Just a comment on the above...

Theoretically, a meter that has the same spectral response as the film should yield accurate exposure information when metering through filters. Even a meter that was relatively close would be well withing the ball park, so to speak.

There is one catch, however, and that lies in the response of the film itself when exposed to just one color of light. My experience with Tri-X leads me to believe that when exposed to predominantly red light, the contrast of the film is increased and the effective EI is reduced by about 2/3 of a stop. Predominantly blue or green light tends in the other direction. Hence the "fudge factors" I mentioned above. Other film/filter combinations react differently.

This same would apply to filter factors as well, so, for the most accuracy, the "fudge factors" should be developed and applied whether you use filter factors or meter through the filter.

I believe that metering through the filter is a superior method to applying filter factors, especially when using the Zone System and a spot meter. By metering through the filter, one can get an idea of where areas of high color saturation will fall in relation to other areas of the scene. An example: metering a blue sky over a green field with a spot meter gives different EVs for each area, indicating the number of stops, or Zones of separation. Metering with no filter, a yellow filter, a green filter and a red filter successively will give different spreads between the two areas, allowing one choose the best filter to better "place" the values in the desired relation to each other. This is something that you cannot do by applying a filter factor.

This, I think, is still by far more more accurate than applying filter factors and "guestimating" the placement of areas most strongly affected by the filter. When one develops fudge factors for compensating for the response of a particular film/filter combination, the accuracy increases even more. Even without the "fudge factors," the worst possible case is missing the goal by a stop, or getting a more or less contrasty negative than expected (the same would happen with filter factors).

Best,

Doremus Scudder

www.DoremusScudder.com

Doremus Scudder · Apr 25, 2008

Audrey,

You don't need filter threads on your meter, just hold the filter of choice over the meter lens with your free hand while metering. It seems less than economic to buy a bunch of filters for your meter that do not fit a camera lens...

Good luck,

Doremus Scudder

www.DoremusScudder.com

John Koehrer · Apr 26, 2008

The interesting thing to me Is that Doremus is using his very own filter factors And that's the exactly the proper way to do it. His explanation is just a tad bit wordy.
Andrey, don't use separate filter to meter through, if they're not the same brand they most likely won't give the same results because of the difference in dyes and glass compositons.

Doremus Scudder · Apr 27, 2008

John,

Sorry my explanation was so long ... I didn't have the time to write a shorter one.

Doremus

www.DoremusScudder.com

timbo10ca · Apr 27, 2008

Check out this post:

(there was a url link here which no longer exists)

I have come to the conclusion that for me, metering through the filter is the way to go but some correction must still be applied, especially for the dark filters. Some testing is required and you can't just go with some standard amount all the time and be accurate in your exposure. There is some good info in the thread, as well as one of the same title on the LF forum:
http://www.largeformatphotography.info/forum/showthread.php?t=33613
I was having a specific problem ( I thought) so you may need to weed through some stuff......

Tim

Spotmetering with filters?

haris

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