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Jacques
7th September 2009, 02:04 PM
Hi,
I've read a couple of times that some photographers are taking a reading through the filter before applying the filter factor. If you do that for example with a yellow filter with a factor of 2. What exposure factor are you giving to film after that? What about a green filter (2 stops), red filter (3 stops)....

Bob
7th September 2009, 03:25 PM
The theory is that you do not then apply any filter factor as you have taken the reading with the filter in place. However, many will argue that as a meter's colour response is not the same as the film's, this is at best only an approximation and for deep filters, such as a deep red or polariser, is likely to be so far out as to be pointless. Some meters claim to be modified to reflect film sensitivity (the Zone IV modified Pentax spotmeter comes to mind) but there have been doubts expressed about the reality of that too.

I do not meter through the filter but apply the filter factor - usually the one suggested by the manufacturer. I often bracket in any case so any inaccuracy in the filter factor is generally taken care of.

Daud
7th September 2009, 03:44 PM
I agree with Bob; it is far better applying the filter factor manually rather than letting the camera meter do this. (Meter – fit filter – apply filter factor).
In fact for some of my filters I have a printed 'aide-mémoire' on the case, after doing some testing for the film and developer – using a Kodak colour test card.

David.

Jacques
7th September 2009, 05:21 PM
Thank you guys. I will continue to apply the filter factor.

Steve Smith
8th September 2009, 07:17 AM
I don't meter through the filter but I set to meter's ISO to the films equivalent speed with the filter fitted.

e.g. If I have ISO 400 film and a red filter which needs a 3 stop compensation, I set the meter ISO to 50.


Steve.

Dave miller
8th September 2009, 08:26 AM
I don't meter through the filter but I set to meter's ISO to the films equivalent speed with the filter fitted.

e.g. If I have ISO 400 film and a red filter which needs a 3 stop compensation, I set the meter ISO to 50.


Steve.

Which is what I do, and then usually forget to change it with the filter. ;)

Bob
8th September 2009, 12:52 PM
I tend to do it on the camera: take a reading and set the speed & f-stop on the camera and then either open the aperture or use a slower speed depending on which is more important (except for the times I close the aperture or increase the speed during a photo-dyslexia event ).

Jacques
8th September 2009, 08:02 PM
I don't meter through the filter but I set to meter's ISO to the films equivalent speed with the filter fitted.

e.g. If I have ISO 400 film and a red filter which needs a 3 stop compensation, I set the meter ISO to 50.


Steve.

I understand what you do. But let's say that your development times are set to 400 ISO but you change it to 50 ISO, then your development times are not good anymore. Isn’t true?

Richard Gould
8th September 2009, 08:12 PM
Use the same development time for 400 iso, you are setting your meter to the lower setting simply to take into account the filter factor, but the film is still 400,this is the way I do it and I have done so for many years,but DO NOT change the dev times, dev as for 400,Richard

Tony Marlow
8th September 2009, 08:14 PM
I think it is not true. You are giving the film the correct amount of light appropriate for the box speed. The light has been dimmed by the filter so you need to open up the aperture or slow the shutter speed in the same way as someone dimming the lights. I guess altering the ASA rating is one way to offset the the reduced light levels and get a correct exposure reading.
Tony

Ian David
8th September 2009, 08:21 PM
Use the same development time for 400 iso, you are setting your meter to the lower setting simply to take into account the filter factor, but the film is still 400,this is the way I do it and I have done so for many years,but DO NOT change the dev times, dev as for 400,Richard

Yes, whatever you are doing with the filter doesn't change the film that is in your camera. Applying a filter factor just means that you need to find a way to increase the exposure a bit (eg 1 stop if the filter factor is 2). You can get that extra exposure by opening the aperture, or choosing a slower shutter speed, or changing the ISO on your metering device. None of these change the rating of the film itself.

Jacques
9th September 2009, 12:38 PM
Thanks guys.

Tom Stanworth
30th September 2009, 12:15 PM
I strongly recommend testing. Boring as hell, but it is one of the most useful things I have done, revealing that most filter factors were miles off for my usage.

If using pale filters such as a yellow or yellow-orange I wil let the TTL metering to its job. This works fine for me on my 35mm RFs and SLRs. If using deeper filters I find I get underexposure with red/deep red filters if using TTL due to the meter likely being more sensitive to the narrow spectrum of red light hitting it (more sensitive than the film), hence giving an exposure that is insufficient.

With my Mamiya 7 (which does NOT use TTL metering, same as the Bronica RF645), I use my own factors determined by shooting a number of scenes without a filter then adding the filter and using various factors. As the filter may change sky tones, shadow value from blue skylight etc you have to think a little but it soon becomes pretty obvious looking at the negs which factor is right for you. Pay attention to shadow detail and here you will find the neg that matches your 'no filter' exposure, or V close.

With B&W (brand) filters, they recommend factor or 2 for the medium yellow. I found +1/3 stop (Mamiya 7 in 1/3 stop intervals) much closer to the reality than + a whole stop. For their Orange, they recommend factor 4, which is 2 stops. I found + 1 1/3 stops right. For deep red I found +3 to 4 stops best depending on lighting. Using the B&W supplied factors I was getting significant over exposure. Using my values I know I will get the colour effect of the filter without losing shadow detail; however, if I wish to let the shadows drop down the scale a bit for harder blacks etc I just apply less of a factor.

If there is a heck of a lot of blue light about (and using a yellow/orange/red filter) you will need to use more of a factor. Examples of when this might come into play would include beside the sea/on the sea, under a big deep blue sky with sky illuminated shadows, or at altitude where there is a greater proportion of blue light.

This is my take anyway and it works for me! Testing will cost you a roll or two of film and some developer but whats that compared to the pain of fluffed shots?

Just remember COLOUR when using fillters on B&W. If shooting an orange sand dune in namibia with an orange filter for deeper blue skies, what factor do you apply? Well, apply the full factor (for me +1 1/3 stop) and I will likely get overexposed dunes as the orange dunes are going to pass unimpeded thru the filter. I might try bracketing, but for black skies I might apply no factor at all or even a negative value!

B&W Neil
30th September 2009, 01:07 PM
I go along with all that and very well explained. I have just done such testing with a R72 opaque red with i/r film to establish the true filter factor value for two different metering methods. But once done - you can move forward :-)

Neil.

Mike O'Pray
11th September 2011, 11:26 PM
I had thought of starting a thread on filter factors but fortunately tried a search and just as well as I hadn't realised how many threads there were on the subject.

So after looking at most of the threads it seemed that Jacques' thread was probably most appropriate.

I confess that until I obtained a new filter (green Hoya XI) I had subscribed to the idea that my TTL readings took account of the filters on the lens pretty accurately. I might be wrong but I recall that most books suggest that TTL metering was able to adjust exposure to allow for the filter.

Anyway I fitted my new green filter ( factor of 2 stops) to my P645N and compared the reading to the unfitered reading. It adjusted exposure by just over one and two third stops.

This might or might not be sufficiently close to the factor of two to make no appreciable difference.

On my 35mm Pentax I have used the full range of filters( except the new green) and the prints from the negs seem not to suffer so I had concluded that TTL metering was reasonably accurate

It would seem from other posters that the smaller factor filters( yellows and possibly orange) are reasonably accurately exposed via TTL but maybe greens( factor 6) and reds( factor 8) begin to go astray.

I should now give my readings on green on the P645N with a less than one third stop under exposure. It dropped from 1/500th to about 1/150th.

So my conclusion was that while I can adjust the dial to give another third stop exposure I should not be over concerned about the underexposure given that most B&W films have better than a one third stop latitude.

This may be a wrong conclusion but I'd be interested in others' views on a third stop underexposure and what readings they have got in terms of TTL v filter factors.

It might vary between cameras TTL meters. Certainly someone on another site quoted their Nikon readings and the differences were quite large.

I'll have to try the full range of filters on both my 35mm and 645 Pentaxes and quote them.

I'd be interested in others' readings who have tried this

Oh and just as a "by the way" I had always understood that the yellow/green filter had a lower filter factor than the green but the Hoya filter data show both to be 2 stops.

Mike

Dave miller
12th September 2011, 10:02 AM
I’ve just completed a simple check with the following filters and obtained the indicated shutter speed results shown, all were made at f8 through a standard lens on a Pentax 645. Without a filter the speed indicated was 1/20th. The readings were taken by holding the filter in front of the lens so that the unfiltered reading could be checked each time.
Yellow: 1/15
Green: 1/15
Deep yellow: 1/10
Orange: 1/10
Red (25a): 1/ 4

Mike O'Pray
12th September 2011, 10:36 PM
Thanks for taking this trouble, Dave. Interestingly it seems that all were underexposing by between about half a stop in the case of the yellow, 2/3rds of a stop in the case of orange and a whole stop in the case of green and red which suggests that as the filter factors get higher the discrepancy is greater.

This is exactly as one poster said his experience was.

So far with essentially the same camera as yours ( P645N v P645) my green meter reading seems to be much closer to what the filter factors says it should be.

I'll have to try all my filters soon in eactly the way you did and report my findings.

I'll wait until the wind dies down however in case that affects the readings :D

Mike

Carl V
13th September 2011, 12:34 PM
I can't remember whether I mentioned this already on another thread, but I have done TTL meter readings on my Nikons with and without the filters in place to see just how accurate they are.

With my medium yellow, which requires 1 stop extra, the meter reads OK and tells me the camera will underexpose by a stop.

With the orange filter however, which requires 2 stops, the meter would still underexpose by about half a stop so I would automatically add that to whatever reading the meter is suggesting.

Finally the red filter, which needs another 3 stops, the meter would underexpose by one and a half stops, so again I'd have to compensate when making the exposure settings.

Alternatively, I just meter with no filter attached, then add the required extra exposure once the filter is in place. It could be that these discrepancies vary from meter to meter but it's not normally a problem if you are familiar with it.

Martin Aislabie
13th September 2011, 05:47 PM
I have never bothered trying to Meter through any Filters - but make either a spot or incident reading and then apply a filter factor (kindly etched into the filter rim)

My conclusion is that the filter factor supplied is generous compared to an unfiltered shot - across a wide variety of external lighting conditions

Hoya & B+W are probably giving you a safe figure - just to take into account the most adverse lighting plus a bit to spare.

Using this technique you always end up with plenty of shadow detail on the Negs.

If you use a TTL meter and are worried about about the impact of the coloured filter, its probably worth investing in a secondhand Weston or something similar for peace of mind

Martin

Mike O'Pray
13th September 2011, 06:57 PM
My conclusion. Martin, from what you have said is that a small amount of underexposure from the TTL reading through the filter isn't critical as the filter factors may be a little generous in that the filter makers build in a safety margin.

Certainly this should make TTL reading with the filter attached reliable for the yellow and maybe the orange and depending on the camera's meter maybe the green.

The red seems to be the "bugbear".

I may have misunderstood what has been said about "not bothering to meter through a filter but it seems to me that if you have a TTL meter on the camera then the camera will always produce a filtered reading so this means in my case with an automatic sort of 35mm camera going to "metered manual" each time and setting it or with the P645N adding the appropriate exposure compensation via a dial

In some ways the less automatic P645N is easier to adjust and once adjusted then it can be point and shoot as long as the filter isn't changed.

I could stop and consider, hand meter, calculate etc but by the time I have caught up with the wife again she has got enough time and has lost enough patience with me to have instituted divorce proceedings on her mobile :D

Mike

Steve_F
18th September 2011, 08:43 AM
Just a quick note on the red filter that appears to be a "bug-bear". I've read, I think it was my old FM3A manual, that when using a red filter (TTL reading) you should add +1 stop exp. compensation.
I'm guessing Nikon have found that TTL still under exposes by that with a Red.

Steve.

Dave miller
18th September 2011, 09:01 AM
Just a quick note on the red filter that appears to be a "bug-bear". I've read, I think it was my old FM3A manual, that when using a red filter (TTL reading) you should add +1 stop exp. compensation.
I'm guessing Nikon have found that TTL still under exposes by that with a Red.

Steve.

That certainly ties up with my findings.