Film, Polariser, Metering, Filter Factors, Mamiya RB

I have a question regarding a combination of factors, namely one

polariser, Velvia 120 roll and E100VS, my Sekonic L-358 and my Pro-S.

The deal is this, I have just bought a polariser for my RB and

thought I had a handle on exposure compensation of filter factors for

my Polariser. This seemed to be borne out by my metering and

bracketing whilst using the VS. I determined that my hand is one stop

lighter than 18% Grey so when I was shooting from waterfront leafy

shade out into open water, boats, and sunlight I would merely stand

in the same open light that the boats were in, take a reflected

reading off my hand and add a stop of light for the polariser which

apparently has a filter factor of 4 which equals 2 stops. This may be

crude but I wanted to try something different from straight reflected

readings in situations where I couldn't take incident readings. I

assumed that if I can determine 18% grey for any given scene and then

compensate for any filters by the given factors I should be close to

where I need to be or spot on.

 

Now the problem. With the VS I shot rated at 100 I got good results

with the above method and the trannies were only overexposed where I

opened up more because I didn't trust my original readings. Having

thought I had it all sussed after the VS I figured that using the

same method with the Velvia (rated 40), would be in the same light,

under the same circumstances, correct. Boy was I wrong, when I got

the trannies back they were in many cases anywhere between 1, 2 and

up to 2-1/2 stops underexposed! Now how can this happen? I spent a

while trying to suss it all out with my E6 guy who suggested that I

run some film tests of my own, but I can't figure out how one system

can be bang on for one film, the VS, and be so far off base for the

Velvia. E6 guy suggested that perhaps the wider latitude of the VS is

the reason and again testing the Velvia would be the way to go.

 

The other issue for me is that judging the saturation and loss of

light with a polariser is difficult when it's always slightly

different given ones relative angle to the sun. How then with a hand

held meter (I don't have a spot yet} should I run a filter factor,

film latitude test for the Velvia and my Polariser that will yeild

the proper results? Any advice on testing would be greatly apreciated

because my shots were killer but just too dark, not too killer at

all. Not all shots were lost and it seems the closest I got to right

on was when I used the reflected reading for the Velvia! I know the

18% method works but I just need to run a decent test for the Velvia

and work out how much extra light the Polariser wants for the Velvia

to expose correctly. Any thoughts?

 

Simon

Simon,

 

As far as the polariser is concerned surely it terms of light going

through it, it must have the same effect on both films, or any

films. If you got the VS right then the problem must be with the

velvia.

 

Velvia is a very tricky film to get right in my experience and i am

still trying to get it sorted. I have tried all sorts of methods with

velvia and trying to get one nailed. Everybody varies in what they

rate it from 40 to 25. If like me you use polaroid at 100, rating it at

32 doesn't help matters. I have now decided to stick with 50 and

adjust method of reading light and then development. I do a lot of

close up flowers and food. I find i take an incident reading and

point meter not directly back at camera, but a bit more towards

ground, can change reading by 1/2 stop. I dial this in and then

bracket around here but normally +1/3 or +1/2. Then process the

film at +1/3 (making it effectively a 40 rated film). This is starting

to work for me, but i find the right one is often the bracketed

exposures at +1/2. This means Velvia could really be 25 if i took

normal incident reading towards camera and dev. normal. This

might account for you being easily a stop or more out.

 

My advice is suss a sytem and try lots of Velvia, just bracket lots

normally in the + direction. It very, very rarely comes out too light.

Good luck.

 

Jon

Simon,

If your hand is one stop lighter than 18% you need to open up one stop for that plus 2 stops for the filter(if you are not metering through it). This totals 3 stops and I gather that you are only opening one stop. Thus you should be off 2 stops as your film shows. Its been my experience that Velvia is over rated by about a stop also.

 

John

Thanks to both Johns,

I have discovered something else about the Grey Card readings which is that they recommend you open up 1/2 a stop after you take a reading! What I was doing was this. Say I take a hand reading in open sunlight and assume that the same light falling on a subject far away is the same sunlight falling on my hand here. I am shooting from dappled waterside shade with overhanging branches from tree's acting as a frame, into bright open sunlit harbour, water, and boats with 1/3 given to sky top of the frame. If I get a reading of f22 @ 1/30, then assuming that the correct grey card reading is 1 stop darker than my hand - 1/60, then shouldn't I just add two stops - 1/15 to get my correct reading, or have I messed up my Funken and Wagnels? John, are you saying that my reading should be 1/8 in this situation?

 

In any case it seems that The exposure meter handbook suggests adding half a stop after taking a grey card reading which would mean it's no wonder I was so far off in some circumstances! So given that a Polariser is 2 stops and a grey card is 1 stop darker and they recommend opening up half a stop if I get f22 @ 1/30 (18% = 1/60) then ostensibly 1/60 + 2-1/2 stops should given me 1/15 @ f16 1/2 or some other means of adding the half stop compensation. Is this completely wrong or not? I am already rating my Velvia at 40 which is plus 1/3 of a stop. ANd I am wondering whether I should be giving 2 -1/2 stops to the Polariser not 2 stops...

 

Simon

My experience has been that polarizers require about 1-1/2 stop adjustment when using an incident meter. If metering with a hand-held reflected meter, it might be fooled by excessive reflections that the polarizer will cancel, resulting in underexposure.

 

Also, you just discovered that meters aren't calibrated to 18% gray. The myth won't die. 18% gray is a only a reference standard.

Curt,

Thanks, I've actually been hip to the 18% thing for a long time I was only using the 18% reflectance as a relative factor by which I could calculate my destruction. I think I may have solved my own problem and you may be right that the reflected light reading with my meter is being tricked, so I did a test that has allowed me to achieve a consensus of results.

 

So having read that my Polarizer has a filter factor of between 2.5-3 and in other cases 4 I decided enough was enough and did a reflective reading through the Polarizer off the Mamiya using the hand held Sekonic meter looking through the back of it and here's what I found out as I turned the thing. With the Polarizer simply metered but showing no apreciable effect I got 1/30 @ f8 looking out across a sunny harbour from indoors through a window. I went outside and did this, aiming the meter at the same scene with no window and got the same result, consensus.

 

Next I turned the Polarizer until maximum saturation occured both in doors through the window and outdoors, and it gave me a reading of 1/15 @ f8! So what we have learned is that the filter factor of 4 is just a starting point for the filter with no effect applied! This is not what they lead one to believe, and without the polarizer the scene was read from the same place giving a reading of 1/125 @ f8 which would totally confirm why my readings were so far off base! Now I have read that increasing exposure as the Polarized saturation increases would negate the effect of the Polarization effect but I have experienced the results if you don't do that and it spells 1 and a half to 2-3 stops, underexposed trannies!

 

Add to this the fact that I wasn't adding the 1/2 stop increase when treating my hand like a 1 stop brighter 18% grey reference and I am looking at 3 and a 1/2 stops under! Hmmm I have yet to go and re-shoot the Velvia to support my findings but I will run a test this afternoon get the trannies back Monday and file my report Monday night on the fine tuning.

 

Simon

 

Well...

 

I have just returned from shooting my test roll on Velvia and in regard to metering from your hand, I discovered something curious, though hardly a revelation. Bob Shell and others in the Hand Metering book discuss metering from your hand and if you are caucasian generally you will find that the mythical (though incorrect) number, 18% grey, is one stop darker than your hand. Add to this that because 18% grey is not a standardised representation we are thus advised to open up 1/2 a stop.

 

Bob Shell and others discuss how this sillyness came to pass, I think Ctein is the supreme leader of *how* this came to pass. Essentially Ansel Adams found out that the standard of 18% was to be changed by Kodak back in 79 (?) and Ansel camped out at Kodak HQ saying that he would not leave until he was assured that 18% was retained as the standard because he used it in his Zone system. To appease AA they kept the standard 18% but then thought of telling people to add a half stop when metering from the grey card. I think the realistic standard is more like 12.5 to 14%. The guys here at Mamiya may be able to correct me on any and all of this, and this may explain why people have stated their Sekonic meters felt to be anywhere between 1/3rd -2/3's to 1 stop off the money. I have read this many times so I am not being controversial for the sake of it. I love my L-358 I just want to calibrate it to some standard that is relevent to my film, camera and filters.

 

Now that all that's out of the way the interesting bit about hand metering that Bob Shell (A very nice bloke who I have exchanged e-mail with) and others didn't quite go into was that depending on how you tilt your hand in relation to the sun, and the meter, you can get two different readings 1 stop apart. For instance I think you are meant to hold your hand/card at a 30 to 40 degree angle relative to the meter and slightly angled perhaps 15-20 degrees tilted face up towards the sun. This as I understand it is how you correctly meter for your hand readings. What I noticed was that the light that struck my hand at a certain angle would light up like the light when it reflects off water and give a stop less on the meter. When I slightly angled my hand I could see that I was getting the flat light response off my skin which was far more reasonable.

 

The silly hand reading gave 1/500 @ F8, the flat, proper reading gave me 250 @ F8. The thing is to be aware of the possibility in strong sunlight for the surface of your hand to create a false shine or shimmer which increases shutter speed and thus tricks your light meter like any other TTL aimed at sparkling water or direct sunlight.

 

So the formula should look something like...

 

Hand = 1/250 @ f8 - 1 stop = 18% ~ 500 + 1/2 stop compensation = f5.6 and a 1/2 @ 1/500

 

This is all relative ofcourse...

 

Using my Polarizer and depending on if there is 3 stops given for maxiumum saturation or 2.5 for half effect and 2 for no effect, it would look like...

 

Hand = 1/250 @ F8 - 1 stop = 18% ~ 500 + 1/2 stop card/hand compensation + 2 - 2.5 or 3 stops compensation for Polarizer = 1/60 @ F5.6 and a 1/2 (This last figure is given for maximum Pola saturation)

 

This is how my thinking is working right now. I may well be wrong or way off base again but I will let you know when the trannies come whether I was right or wrong. I hope I am right, I'm sick to death of testing. :o)

 

Update...

 

Well I got my trannies back today and it appears that all my calculations were right on the money! All that is required now is a bit of fine tuning this technique to get it relatively uniform for all the films I use and the rest is F8 and be there. I also tried basic reflective readings in a comparison test against my hand readings and the reflective readings showed over exposed trannies in every instance, up to 1-1/2 - 2 stops + . My hand reading method has at worst left me 1/2 a stop under/over at worst and spot on elsewhere. If I want to get a bit of local light into some of these shots I can pump a bit of flash. Anyway it's pretty rewarding to nut out a problem from beginning to end and get a result you are happy with.

 

Simon,

 

 

 

Hi Simon,

I think you are making life unnecessarily complicated for your self. First of all go this website http://www.kinesisgear.com/opinion.html , adjust your meter to give a -.7 reading. Then meter the scene instead of your hand. As you have found metering either your hand or a gray card is full of variables. I use a Sekonic L 608 to meter, expose Velvia at iso 50 and give a polariser 2 stops more regardless of rotation.

 

Geoff

www.geoffmurray.com

Before you jump to any conclusions you have to recall if you were using the same shutter speed with the VS and the Velvia. There is hardly any "latitude" with 'chromes and actual shutter speeds can be far different than indicated. With your camera on a tripod, meter a clear blue sky. Shoot 12 frames at the same exposure but adjusting the shutter speed (and f-stop)for each shot. Examine the roll after processing. F-stops are constants, but that's not always the case with shutter speeds. Don't be surprised if 1/30th may be going off at a 1/60th or 1/125th. Just "remember" which speeds look off and don't use those when shooting transparencies. [With in-lens shutters, this kind of testing is a pain but it's better than having to drive 50 miles back someplace to re-shoot a job.]

Thanks fella's,

I will shoot another test for my in lens shutter speeds and see where that gets me. I have seen to the website for the Sekonic calibration before, I'm just not too sure if it is specifically useful for me as the guy shoots mainly studio ports and uses incident readings exclusively. I am outdoors mostly and it's far more useful for me to have a system of off hand readings that are standardised for me, that are workable. I have worked this system out now and pretty well know what to look for so it's easier for me to do that rather than shoot everything at 50 asa and change the settings on my Sekonic now I am getting some standardsation from my test. Also I would never give a Polarizer only 2 stops ever again, as I have explained earlier. Thanks both!

 

Simon