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#11
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#12
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Thanks guys.
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#13
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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! Last edited by Tom Stanworth; 30th September 2009 at 12:19 PM. |
#14
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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.
__________________
"The aim of art is to represent not the outward appearance of things, but their inward significance." Aristotle Neil Souch |
#15
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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 |
#16
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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 |
#17
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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 Mike |
#18
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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.
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Carl. |
#19
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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 |
#20
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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 Mike |
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