Spotmeter through a filter or use filter factor.

Camerashy

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Is it advisable to use the filter factor written on the filter or spotmeter through the filter? If you take a spotmeter reading through the filter, what do you aim the spotmeter at?
If I am using a yellow filter that lightens yellow, green and red subjects and darkens blue subjects, should I be thinking in terms of doing some testing to evaluate how much these colours are lightened or darkened. One test using filter factors another test metering through the filter?
What do you do?
 
Measure using the spotmeter and then apply any filter factors. Coloured filters will affect the amount of white light entering the meter and could give a false reading
 
As Joanna says, unless you know the spectral sensitivity of the spotmeter, you could be swaying the reading if you put the filter in front of the meter.

Mike
 
Years ago, Zone VI modified a Pentax Digital spotmeter with the claim that that it corrected for the aforementioned spectral sensitivity so that it would properly meter through filters. I own one of these meters and it's a fine instrument but I think it misses that mark, at least for some colours. These days, I meter w/o the filter and just apply known filter factors as a matter of consistency.
 
If using a spot meter reading from a digital camera, the spectral sensitivity of the meter & the sensor should match well. But this certainly isn't the case when the meter is a separate entity, let alone with film, where it can depend very much on the film used.
The changes with LF films can be very great as some films & film substitutes are orthochromatic rather than panchromatic.

I've often felt filters should have two factors listed, one for the full visual spectrum, and one for the average orthochromatic materials. However it's quite possible even this would prove to be an oversimplification.
 
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I've tried both methods, from time to time, but not for very strong filters. In practice, it didn't seem to make much difference. I haven't made direct side-by-side comparisons.
Most feral scenes are a bit too complex for detailed analysis, but it might be possible to construct a still life with (say) a red apple, a green cabbage, a blue vase and so on, for detailed testing. In fact, many older textbooks often contain something similar, but it's intended to demonstrate the comparative effects of different coloured filters, not to explore different ways of calculating the exposure.

I've read mixed reports on the modified Pentax meter, but the unmodified one is an excellent device.
 
The reason I asked the question was that I have just read Les Meehan's book Creative Exposure Control. He advocates doing tests, metering through the filter to accertain your exposure when pointing the spotmeter at different colour patches. As mentioned in your replies,that would not be a lot of help when taking metering a riot of colours. My main interest is in darkening blue sky with a yellow filter I may try, applying the filter factor and also spotmetering through the filter whilst pointing the meter at the sky. I suspect the difference will be minimal. I agree that metering a complex scene and then using the filter factor would work best for me, unless I needed to lighten or darken objects to stop them blending into the background, (photographing flowers for instance).
 
Maybe you are in danger of over-thinking this. Just take an exposure reading of the subject, then add the filter factor if you are intending using a filter. To see the real effect of a filter you need to take two photographs, one with a filter in place, and one without it. Then develop both negatives, then make two prints, and compare them.
 
If it’s sky you’re after, it’s usually possible to adjust the tone in printing, but that’s not the question here.
On a bright day, preferably with a few clouds, it should be possible to set the meter on a tripod and make successive exposures, using both methods on each of your filters. 35mm (on another tripod) would seem a reasonable option, with a blank space between each group and very careful note-taking.
It’s quite possible that you’ll find that those filter factors are rounded off to a convenient simple number. That’s if you have an appetite for very precise and careful testing. Happy days!
In the case of sky, there’s ultra-violet as a complicating factor.
If you are using an incident meter (which is generally reliable for most “normal” scenes), you have no alternative but to use the factor method.
 
Over thinking, I will agree with that, I definitely have read more photography books than I need to and concentrated on theory instead of practice. I need to get out of my armchair and make more photographs.
 
I read through this thread and I think I will just stick with a UV filter on the lens for the time being.
 
A very good question this. Been wondering about it for a while, ideally the meter should measure all colours the same way, would be useful when using B&W filters to determine the effect on say using a red filter on the sky etc. I take the point about the spectral sensitivity not being equal and therefore giving misleading results. I wonder if this is a way of testing this out.
 
The late Fred Picker, who has been mentioned here before, sold a modified Pentax spot meter, which was claimed to give “correct” metering with filters. Some people were enthusiastic, some were not. The unmodified meter was once the weapon of choice for LF photographers, because of its light weight and convenient operation.
It might be worth looking up any references you can find. Nobody has repeated the project, although this may be no reflection on the meter itself.
 
I've got a Minolta Spotmeter-F and Reveni Spot, probably need a card like the Naked Photographer uses for his film tests.
 
it depends, as always, a pol filter, yellow red green or orange can easily be used infant of the spot meter.
 
I’m beginning to wonder what the practical application of all this might be. Are we considering the effect of a filter on the whole scene, or are we looking for the effect of a particular filter on a particular colour within the scene? What kind of scene needs such precision?
There may be scientific applications that I don’t know about, but my normal experience is that every scene is different, and one takes what is given, makes the best of it and is thankful.

Here is a situation where digital capture has its advantages. Each colour channel can be adjusted individually to get the desired tonality. It would be possible (for instance) to shift from RGB to CMYK and back again for the utmost control and no doubt, even more exotic manipulations are possible. There may an app. There is always an app. Then the image could be converted to monochrome and printed. Converted to monochrome, because we only use these strongly-coloured filters for monochrome images.

There is one advantage of measuring through the filter. You don’t have to remember the different factors and juggle with mental arithmetic under an unruly darkcloth in the wind.
 
Doesn't the shadow area you're measuring vary in Ev depending on it's color and wouldn't that be different depending which contrast filter you use?
 
I’m beginning to wonder what the practical application of all this might be. Are we considering the effect of a filter on the whole scene, or are we looking for the effect of a particular filter on a particular colour within the scene? What kind of scene needs such precision?
There may be scientific applications that I don’t know about, but my normal experience is that every scene is different, and one takes what is given, makes the best of it and is thankful.

Here is a situation where digital capture has its advantages. Each colour channel can be adjusted individually to get the desired tonality. It would be possible (for instance) to shift from RGB to CMYK and back again for the utmost control and no doubt, even more exotic manipulations are possible. There may an app. There is always an app. Then the image could be converted to monochrome and printed. Converted to monochrome, because we only use these strongly-coloured filters for monochrome images.

There is one advantage of measuring through the filter. You don’t have to remember the different factors and juggle with mental arithmetic under an unruly darkcloth in the wind.

I have a Zone VI modified Pentax spotmeter that claimed spectral correction for filters. In practice, this seems mostly to only be approximately correct for Tri-X sheet film.

So, I will confess to be a Philistine in this matter. When I am shooting something I care about and want to use a filter, I shoot it at least twice - once with the recommended filter exposure correction, and a second "safety" exposure that adds 1/2-2/3 stops of more exposure. I find film far more forgiving of overexposure than lack of exposure.

Analytical? No. Carefully calibrated? No. Practical? Yes.
 
Yes.
The idea of using these coloured filters is to darken some colours or to lighten others, or both. The warm coloured filters - red, orange, yellow - will darken complementary colours (that is, on the opposite side of the colour wheel) in the scene, so that blue skies will be darker. A green filter will darken skies too, but the effect on foliage and grass will be to lighten it. The most frequent use is probably to make white clouds more visible against a blue sky.
However, this isn’t the only use. It might be desirable to adjust the colours of other objects. If something is painted red and green (a steam locomotive with decorative lettering, perhaps) both colours will record as much the same tone and the lettering may be almost invisible. Either a red or a green filter would lighten its own hue and the contrast between the two paints would be restored. The decorative text will be made more legible, giving a truer subjective impression although not an optically correct one.
This is quite a long way from the factor/through-the-lens discussion.

These days, graduated rectangular filters of staggering price and stupendous strength seem to have taken over from the once ubiquitous yellow filter.
 
These days, graduated rectangular filters of staggering price and stupendous strength seem to have taken over from the once ubiquitous yellow filter.

These days :D Rectangular and circular graduated filters were available long before WW1 . . . . . . . . . . . . Surprisingly.

The only filter I use is a Green one, it lightens some of the green leaves/foloiage and darkens any red brick work. It's effects on foliage and leaves can be remarkable, light green newer leaves/foliage get lightened but older darker leaves are less affected, so you accentuate the differences.

Ian
 
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