Odd things going on with filter factors

Discussion in 'Exposure Discussion' started by Tom Stanworth, Apr 15, 2006.

  1. Tom Stanworth

    Tom Stanworth Member

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    Hi,

    This has never been an issue for me as with LF I meter independently and apply the filter factor BUT I have recently been shooting a fair bit of 35mm SLR using filters for B&W and metering thru the filter (as speed has required).

    When I initially got the filters (a Hoya Orange 'G'-med orange and a B&W 091 - a wratten #29 deep red) I checked the listed exposure factors and unless I am very mistaken it was factor 4 for the orange (2 stops) and 8 for the deep red (3 stops). This seemd to make visually very little sense as the orange is not even close to the deepness of the deep red. Upon metering thru the lens with the filter ON, I lost one stop with the orange (well below the 2 stops of the filter factor) and 2&2/3 stops with the deep red (ie very close to the 3 stops stated. I have also read that meters (mine is and eos 3) can be more sensitive to red thn other wavelengths resulting in not enough increase in exposure when red filters are used with TTL metering, but in this case the camera was close to smack on with the deep red and a stop out on the medium orange.

    I realise that bacground would have an effect so chose a neutral grey wall to do the initial test.

    As a fudge I have bracketed a stop ether side as well as applied exposure compensation where required for backlit scenes etc to hopefully keep me on 'zero' and thus allow the +1 frame to save teh day should my orange filter really need 2 stops.

    Personally, I doubt that this orange filter needs two stops, but also doubt that one would be enough. As a related aside I have stopped giving a full 2 stops to my lee orange polyester filter as i kept marginally overexposing and now give 1.5 stops.

    Any idea what is going on here? Why does the deep red meter seemingly accurately (I have never used a deep red before so should be interesting...) when one hears that metering with deep reds is notoriously erratic TTL and so far off manufacurers exposure factor when using the orange?

    Rgds,

    Tom
     
  2. Amund

    Amund Member

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    You got the orange filter factor wrong. On the Hoya filter factor chart it`s a filter factor of 2.5 for the G, in other words : adjust exposure 1.3 stops.

    Hoya Filter chart
     
  3. Tom Stanworth

    Tom Stanworth Member

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    Amund,

    Mr Thickie McThickie here........

    Tom
     
  4. Paul Sorensen

    Paul Sorensen Member

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    This chart has a 25A at 3 stops. According to the B&H web site, a wratten 29 filter has a 16 filter factor, meaning 4 stops. I just stumbled upon a cheap wratten 29 gel I was planning on playing with, anyone have any experience as to whether 4 stops is really adequate? Also, is it possible to use a spot meter through the filter and get decent results?
     
  5. Peter Schrager

    Peter Schrager Subscriber

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    Meter

    Paul-the ONLY spot meter you can use is the ZoneVI modified meter. I regularly use mine through the filter to make the reading and it is rarely off. Filter factors?
    I leave that for others to figure out. Also saves alot of time. In reality how many different filters is one using? So I think it can be pretty much memorized if you standardize on 1 film.
    Best, Peter
     
  6. Paul Sorensen

    Paul Sorensen Member

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    True enough, but I also wonder if there might be differences in filter factor depending on the particular scene being photographed. If that is the case, it would seem that being able to meter through the filter would be of great benefit.

    Thanks!
     
  7. Tom Stanworth

    Tom Stanworth Member

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    The B&W #091 (which I have seen in many places equated to a Wratten #29) has factor x8 written on the box and and also on the filter mount. I also remember x16 being the filter factor for the wratten #29 so was surprised....unless of course the #091 B&W is just not as dense as a 29 and the two are not actually directly comparable. Visually it is both darker and deeper than a regular #25 red of which I have a few from other systems but as I have not had anything actually labelled #29 I cannot say what a 'real' #29 should look like!

    I am just hoping that as using my orange lost me a stop (instead of 1 & 1/3) and the deep red 2%2/3 (rather than 3) I should be OK. As well as bracketing I also took the precauion of downrating the film a fair bit (TriX at 250 and APX100 at 64) so that if after bracketing I am still in trouble after using Paterson Aculux 2 on a test roll of each I can bring out the Ilford DDX and gain back a good 1/2 a stop.

    I ended up in this stupid position as I arrived here with no idea that I would be able to safely get out and about shooting film. I rather expected to be holed up staring at concrete walls. When I realised that I had lots of opportunities and that 35mm SLR was the way to go (speed, speed, speed and flexibility), I bought a used eos 3 and some lenses to add to the exisiting system I have in storage in the UK (I am between homes). I was not able to get hold of my kit in storage and had not ever metered thru my filters before. Mainly doing MF and LF landscapes I had been able to take time, use hand held meters etc. Therefore I ordered some filters and just had to meter thru them for the sake of speed.

    Before I leave I will shoot a test roll with each film with a mixture orange and deep red filters and develop it to see what is going on and whether I need to use the DDX)

    This country is really very beautiful, but often in a melancholy way. Whilst I do not believe that all shots should be molested by heavy filtration there is something about the harshness of the environment and the recent past which suits a fairly hard look. For me there has to be some sense of adversity in the shots as this represents everyday survival for Afghans. I did not think that shooting everything thru a pale yellow would look at all right. I have therefore shot everything (apart from portraits) through the (fairly light) orange and deep red (prob 80+% thru the orange and the rest thru the deep red).

    I have struggled a fair bit with this fast moving 35mm game as I have never had to learn to use my cameras as fast and instinctively as I have here. I am FAR quicker than I was 2 months ago and missing far fewer shot. I am also getting to know the pattern of life better and the areas where the locals are more camera friendly. My access is still very limited (no wandering off into settlements...dark homes....or accross the flat valley bottoms which are ususally vast mine fields) but I have had enough to keep busy (19 rolls so far). Whats more I am also really enjoying shooting 35mm again and introducing many of my colleagues to photography.

    Thanks for all your help.

    Tom
     
  8. bob01721

    bob01721 Member

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    Interesting. But... why is that? "Common sense" says that light passing through a filter should have the same effect on a meter as it does on film. Is this because meters have a different color sensitivity than film?
     
  9. BruceN

    BruceN Member

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    I routinely meter through the filter with my Minolta Spotmeter F and haven't run into any odd results yet... At least none that can be blamed on the meter/filter. :wink:

    Bruce
     
  10. juan

    juan Subscriber

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    Bob, Fred Picker, when he created his Zone VI meter, said that meters and film see light differently and made his meters to see light the same way as the 80s version of Tri-X. He had a Harvard physicist designing the modifications.

    Some photographers disagree and say the Zone VI meter modifications do nothing. I don't know who is right.

    juan
     
  11. noseoil

    noseoil Member

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    When in doubt, I will meter off of a gray card with the filter of choice. Don't use a blue sky, shadows or other areas of the shot where the filter can affect vlaues. This has worked pretty well for me, but who knows? tim
     
  12. bob01721

    bob01721 Member

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    Okay... I thought it might be something like that. But what about the TTL meters on SLRs? They don't seem to have a problem metering through a filter.

    Sounds like one of those things that has a basis in theory but is insignificant in actual practice. Thanks.
     
  13. bob01721

    bob01721 Member

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    While taking a walk around the net this afternoon, I came across this article about the Zone VI meter mods. Seems like a pretty expensive way to give up a bit of low-light sensitivity.
     
  14. p krentz

    p krentz Member

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    Years ago (12?) there was a pamplet by Harris&Harris, filter makers, about the no filter factor, factor. I tried it and was really impressed with the results. My red roses looked red in B/W, not white because the filter factor caused a color change. Try to find the article and then try it. Pat :D
     
  15. Roger Hicks

    Roger Hicks Member

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    Dear Tom,

    Yes, it depends on

    1 The filter

    2 The film

    3 The light

    4 The subject

    1 The precise absorbtion of any filter varies. One of my favourites is a weak (2.8x) orange from the Soviet era. Other 'orange' filters are usually 4x.

    2 Different films have differing red sensitivities. A film with a high red sensitivity will show less effect from a yellow, orange or red filter than one with a low red sensitivity.

    3 Late afternoon sunlight (just before sunset on a clear day) is about the same colour temperature as tungsten light, 2600-2900K. As there is more red light around, and less blue, the effect of blue-blocking filters (yellow, orange, red) will be less.

    4 A red brick wall is already reflecting lots of red and will be less influenced than a blue sky.

    Yes, you can measure all this, but life ain't long enough, so it's best to live with a series of rough approximations, +/- 1/2 stop to 1 stop based on guesswork and experience.

    Beware of anyone who pretends that there is more precision in photography than really exists.

    Cheers,

    Roger (www.rogerandfrances.com)
     
  16. Gerald Koch

    Gerald Koch Member

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    When you meter through a deeply colored filter you are making the assumption that the meter's spectral sensitivity is the same as the film's. This is probably not correct. Therefore it is better to meter without the filter and then apply the filter correction (that's what its for). Even so I would bracket until I was familiar with the filter/film combination.
     
  17. Gerald Koch

    Gerald Koch Member

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    Amen! You can spend all your life in endless testing or you can spend it taking pictures. Just bracket when in doubt.
     
  18. Lee Shively

    Lee Shively Member

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    Ansel Adams was a closet bracketer.