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  1. #1

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    Odd things going on with filter factors

    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. #2
    Amund's Avatar
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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
    Amund
    __________________________________________
    -Digital is nice but film is like having sex with light-

  3. #3

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    Amund,

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

    Tom

  4. #4
    Paul Sorensen's Avatar
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    Quote Originally Posted by Amund
    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
    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. #5

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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. #6
    Paul Sorensen's Avatar
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    Quote Originally Posted by Peter Schrager
    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
    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. #7

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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. #8

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    Quote Originally Posted by Peter Schrager
    "... the ONLY spot meter you can use is the ZoneVI modified meter..."
    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. #9
    BruceN's Avatar
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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.

    Bruce

  10. #10
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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

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