Determining exposure in LF and its general step by step proceduregreenspun.com : LUSENET : Large format photography : One Thread
Hi, I've taken some polaroid pictures with my new LF camera. I used only a lightmeter (not film plane metering) and leaf shutter without any sophisticated aid like auto shutter (anyway I would continue doing this since I'm mostly in field or at location taking landscape and architecture.) I felt very awkward to decide the exposure value when I took a first couple of films; particularly compensating for bellows extension and reciprocity failure using a lightmeter. My temporary procedure (using my Sinar) is as follows:
I'm sorry if this is too long. But is this procedure correct? What procedure do you take in order to determine the correct exposure value? Thank you so much! Masayoshi
- Determine the optimum depth of field of the object using the built in depth of field calculator. Set the aperture of shutter as indicated, then turn the focusing knob two stops (decreasing the f number on the scale of the calculator. Now the camera is set at the optimum depth of field. (The optimum depth of field is the largest aperture possible to cover the object. The smaller aperture fails to cover this range. Is it correct?)
- Meter the light in shutter priority mode (Sekonic L-508) because (my) leaf shutter can only be set in full stop increments.
- Measure the bellows extension. (What if the camera isn't at normal position (e.g.. tilted, shifted etc.)? Do I (still) measure the distance from the rear nodal point (approx.. center of lensboard) to the center of ground glass?)
- Compensate the factor by decreasing the f number of the LIGHTMETER if it has an exposure compensation feature. (What if there isn't such a feature?)
- Look at the reciprocity failure chart of the film in use. Then, compensate accordingly by decreasing the f number of the LIGHT METER in exposure compensation mode again.
- Now read the f number. Of course now the f number is lower than the original value desired. So turn the dial of the light meter (Shutter priority mode) so that the shutter speed increases in full stops and the f number increases. Choose the combination where the f number is the lowest high to the original f number set in shutter. (Aperture increment is continuous so it's ok to be in fraction.) Set the shutter speed of shutter as indicated by the light meter. (If the shutter speed is higher than 1 sec, do I use B or T with stopwatch?)
- Wind the shutter, close the blade, set the film and shoot!
- Ask if I'm doing right.
-- Masayoshi Hayashi (email@example.com), July 02, 1998
1. Correct, assuming you Dof scale says you need f/22 to cover near- to-far depth of field, you would then focus your camera so that the indicator arrow lines up with f/11 (two stops) this gives an optimum focus point around which you have a hyperfocally based depth of field (i.e zone of in which everything is acceptably sharp) sharp image if you set your lens to f/22. 2.) you need to find the shutter speed which is closest to your f-stop. You do not want to open up your f/stop on your camera any wider (Example: Do not go from f/22 to f/16.5, as this will result in a narrower zone of focus) so if your meter says f/16.5 @ 1/30second, set your camera to f/22.5 @ 1/15second. 3.) bellows extention factor (BEF) does not need to factored into your calculations until you start doing close up work where your image is about 25% of actual size of of subject. 4.) If you need compensation, try changing the ISO setting on your meter. Example: calculations say open up 2/3 stop change meter's ISO setting downward 2/3 stop (from ISO 100 to ISO 64 for example.) KEEP YOUR F/STOP THE SAME. 5.) In the real world, Reciprocity Failure only becomes a factor if your calculated exposures are very long, more than 4 seconds. otherwise ignore. 6.) All along you need to have been working to keeping your f/stop the same as you originally calculated for your Depth of field. What it looks like from here is we have approached the solution to the problem from two different lines of thinking. Your methodology involves a very long equation with all the different possible factors involved. My reasoning has been to break the problem down into smaller problems. Some of my decisions about the relevancy or non-relevancy of some aspects are based on intution and experience. 7.) After setting depth of field and visually inspecting the image, I always close the shutter and then do the exposure calculations. If i am photographing architecture or landscapes, it is usually a metter of Composing, setting DoF, a quick look through, closing lens, cocking shutter, inserting film holder and pulling darkslide, metering, and triggering (assuming the light is not changing, in which case I'll be taking constant meter readings in aperture priority mode. (there is your answer to question 2.) 8.) I am always asking this question. We forgot one step: Polaroid! a field check of the negative from Type 55 can tell you immediately if you are in focus. And if everything mechanical is working the way it should be. I rate the Type 55 at ISO 50 for the print or ISO 32 for the negative (if I am going to save it for later use.) the Type Pro 100 Color I have found to be a very good (not perfect) match for Fuji Provia (RDPII)in terms of both color saturation and film speed. 9.) Don't forget your filter factor. Does this help? Ellis
-- Ellis Vener (firstname.lastname@example.org), July 03, 1998.
Don't make it so complicated, unless you are comfortable with all the steps you seem to want to take. I set up the camera after basically deciding how I want the scene to look-choosing the lens by eyeballing the scene to see which lens will do it justice.(this takes practice but after a bit you will probably know which lens you want to use with a short look). Then I decide what the exposure should be by looking at my light quality and whether the scene has predominantly dark, light or reflective surfaces I need to consider. Focus, set the aperture & shutter speed(after checking with either a spot or incident meter if I feel the need) and shoot. The one qualifier is bellows extension. I check it on closer images and compensate by longer exposure times as it "feels good". Not too scientific I know, but it works from experience. With reciprocity on longer exposures(up to about 20 minutes) I rely on the "feels good" rather than charts. None of the damn charts agree with any other & so I again rely on experience. Bracket a bit the first few times and then you hone in on what is pretty good and the brackets are much fewer and more accurate. If anything(in B&W) I overexpose a bit. With chromes I am usually right on or very close(the reason for light brackets when I am not quite sure). Whatever system you use, make sure you get familiar with it and do it in the same sequence each time. That way it flows & you feel better about it and the results will show that.
-- Dan Smith (email@example.com), July 09, 1998.
You might be interested in purchasing a Casio pocket computer loaded with a program written by Phil Davis that will automatically do the various things it looks like you're now doing manually. To determine exposure you simply meter the most important highlight, place it on a zone (usually VI to VIII), meter the most important shadow (usually III to V), tell the computer what aperture you want to use (or what shutter speed you want to use) and the computer calculates the exposure (or, alternatively, you can use an incident meter but I've never done that). The computer will factor bellows extension and reciprocity into the exposure calculation, keep a record of each exposure, tell you the correct aperture to obtain the desired depth of field, tell you the depth of field with the aperture you have selected, and probably some other things that don't immediately come to mind. The computer can be purchased from Darkroom Innovations in Arizona. I don't have their e mail address or phone # handy but they usually advertise in "View Camera" magazine. If wyou wish to pursue this but can't find them send me an e mail and I'll get the information for you.
-- Brian Ellis (firstname.lastname@example.org), July 09, 1998.
Do you intend to explore the use of the "Zone" system to calibrate your film / developer / enlarger / paper into a cohesive, predictable outfit so that you have a solid idea how your exposure choices are going to wind up in the final print?
Many fine texts exist that will introduce you to this.
The one thing to keep in mind with almost any light metering system is that when you center the needle or line up the marks, what you are doing is setting a camera exposure that will produce a middle grey value in the final print, regardless of the how light or dark the object was that you metered.
At its simplest, "Zone" systems "place" subject values at their appropriate place on the exposure scale of the negative, so that they will produce a value in the final print that corresponds (OR DIFFERS) from the original subject value.
The rest of the procedures are aimed at working with your own outfit so that you can "see" the finished print before you trip the shutter.
See: Camera and Lens, The Negative, The Print by Ansel Adams. The New Zone System Manual by White, Zakia & Lorenz Zone Systemizer by Dowdell & Zakia Zone VI Workshop by Fred Picker
Sounds a lot more formidable than it really is. Once you get a feel for it, it is very intuitive.
-- Tony Brent (email@example.com), September 07, 1998.