Dear All,
I would like to give some information about metering with a view camera and LF.
We all know that a film has a certain, limited contrast range/dynamic. With transparancies it is about 6 to 6 1/3 f-stops, with colour negatives it is about 7 f-stops, and with B&W film around 10 f-stops.
Beside the obvious problem and difficulty to "fit" your scene contrast into these 6 stops of a transparancy, the most important is that you are limited by the print medium: the best offset print, with the best screening, the best inks and the best paper can ONLY print 4 f-stops (from details in the high-lights to details in the shadows), or in other words, these 4 f-stops correspond to 1.8 density values in print.
I pass on the fact that the E6 processing will add to the contrast with the Gamma factor of 1,7, but basically, if you want to print something with details in the shadows and in the high-lights, then the MEASURED contrast between these 2 points SHOULD NOT BE OVER 4 f-stops. This EVEN if your film can accept more!
What does this mean? It becomes obvious that any "GREY" metering does not make any sense. The "Grey Card" is only a mathematical way to balance the light in lightmeters, a method and standard on which manufacturers agreed (18% reflecting grey) which DOES NOT give ANY information of the contrast in your particular scene. You might have a right and well exposed film, by making a grey-metering, but you won't have any clue of the contrast and if you would be able to print what you have seen.
The only way to have control over the whole printing process and to make sure that you will have details in the zones of your images where you want it, is to make a 2-point CONTRAST METERING.
To make a 2-point contrast metering, there are 2 methods, both metering the REFLECTED light from the subject, NOT the incident. Reflected light can be very different to the incident one (absorbtion, reflections, angle of metering, ...).
One can do a metering of the reflected light either by using a spotmeter or then metering this reflected light IN the film plane of the camera:
1. Spotmetering
This is a very good method, provided one makes the metering excatly in the same axis as the optical axis of the camera (by moving around your scene you will notice that the reflection of the light is different), and provided that you do calculate as well the "Correction Factor" due to your belows extension.
2. Metering of the reflected light in the film plane
There are different probes out in the market, from different manufacturers. This probe can be slided inside the groundglass, just in place of the image plane, there where the light is hitting the film, thus metering EXACTLY the amount of light hitting and exposing the film.
This method is of course the most precise and convenient, taking automatically in account any bellows extension and any filter placed in front of the lens.
3. How to meter?
For both methods, spotmetering and metering in the film plane, one makes a 2-point metering: the first point to be measured is e.g. the darkest point in your scene for which you still wish to have some little details in the print. You will measure this point and give it an exposure value of 2 f-stops UNDER (Zone 3) the medium grey (Zone 5): in other words, you under-expose it by maximum 2 f-stops.
Then you measure the point in the high-lights for which you still want to have some little details in the print: you should then over-expose this high-light by maximum 2 f-stops (Zone 7).
The total of contrast in your scene will then be exactly 4 f-stops, just the amount which will be printable. You will make sure that you have details in your print and that you have those details at the place where you want it to be!
You have FULL control of your contrast and of your image rendering in print, by doing this way.
Now, this is easy to achieve in studio (to balance the light to have -2 and +2 f-stops between the shadows and the high-lights): you just have to make use of your light and set it up the right way to achieve this.
When you are on location, you won't have any other alternative, if the contrast between your 2 extreme points exceeds 4 f-stops, than to wait for a better, less contrasty day, WHEN shooting on transparancies or colour negatives. If you are using B&W films, then you have the possibility to compensate and correct the excessive (or to little) contrast by adusting the B&W process, means by under- or over-developping your film: that is by using the so-called "Zone System", made famous by Anselm Adams. I won't elaborate on this, since there are many books to get the information.
4. Compensating for the Bellows Extension with a Spotmetering
Since the spotmeter DOES NOT take in account the lost light hitting the film due to the bellows extension (or due to a filter in front of your lens), you will have to calculate this factor.
There is a formula to calculate this very precisely, but I will give you here the different factors depending on the different reproduction scales you shall encounter. Here the values of compensation:
- below a reproduction of 1:8 you can use the exposure value given by your spotmeter
- for a reproduction scale of 1:8 to 1:5 use a factor of +1/3 f-stop (increase exposure by 1/3 of f-stop)
- for a reproduction scale of 1:4 use a factor of +1/2 f-stop
- for a reproduction scale of 1:3 use a factor of +2/3 f-stop
- for a reproduction scale of 1:2 use a factor of 1 & 1/3 f-stop
- for a reproduction scale of 1:1 use a factor of 2 f-stop
- for a reproduction scale of 2:1 use a factor of 3 f-stop
- for a reproduction scale of 3:1 use a factor of 4 f-stop
- for a reproduction scale of 4:1 use a factor of 4 & 2/3 f-stop
- for a reproduction scale of 5:1 use a factor of 5 f-stop
These factores are easy to keep in mindd, and are the same for any lens used. No need to make other calculations, or to take a calculator with you. You don't even need to have a ruller, to calculate your reproduction scale (magnification).
How to understand "Reproduction Scale" and how to calculate it?
- 1:8 means that you are having an image on your groundglass which is 8 times smaller than your subject
- 1:1 means that your image has excatly the same size as your subject
- 2:1 means that your image is 2 times larger than your subject
- etc ...
So all you have to do is to measure a part of your subject and measure the same part on your groundglass, then compare it to get the reproduction scale.
I hope this can help some to have a better control of their images. Try it out and you won't need to expose x films to be sure to have the right one. But more importanly, it gives you total control.
Best regards,
Thierry