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Thread: Determining exposure in LF and its general step by step procedure

  1. #1

    Determining exposure in LF and its general step by step procedure

    Hi, I've taken some polaroid pictures with my new LF camera. I used only a light meter (not film plane metering) and leaf shutter without any sophisticated aid l ike auto shutter (anyway I would continue doing this since I'm mostly in field o r at location taking landscape and architecture.) I felt very awkward to decide the exposure value when I took a first couple of films; particularly compensatin g for bellows extension and reciprocity failure using a lightmeter. My temporary procedure (using my Sinar) is as follows: <ol> <li>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 foc using knob two stops (decreasing the f number on the scale of the calculator. No w the camera is set at the optimum depth of field. (The optimum depth of field i s the largest aperture possible to cover the object. The smaller aperture fails to cover this range. Is it correct?) <li>Meter the light in shutter priority mode (Sekonic L-508) because (my) leaf s hutter can only be set in full stop increments. <li>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 no dal point (approx.. center of lensboard) to the center of ground glass?) <li>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?) <li>Look at the reciprocity failure chart of the film in use. Then, compensate a ccordingly by decreasing the f number of the LIGHT METER in exposure compensatio n mode again. <li>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 t hat 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 shutt er speed is higher than 1 sec, do I use B or T with stopwatch?) <li>Wind the shutter, close the blade, set the film and shoot! <li>Ask if I'm doing right. </ol> 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! Ma sayoshi

  2. #2

    Join Date
    Mar 1998
    Posts
    1,973

    Determining exposure in LF and its general step by step procedure

    1. Correct, assuming you Dof scale says you need f/22 to cover near- to-far dept h of field, you would then focus your camera so that the indicator arrow lines u p 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 accepta bly 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 n ot 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 me ter 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 calculati ons 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. Exampl e: calculations say open up 2/3 stop change meter's ISO setting downward 2/3 sto p (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 calcula ted 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 y ou originally calculated for your Depth of field. What it looks like from here i s we have approached the solution to the problem from two different lines of thi nking. Your methodology involves a very long equation with all the different pos sible factors involved. My reasoning has been to break the problem down into sma ller 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 clo se the shutter and then do the exposure calculations. If i am photographing architecture or landscapes, it is usually a metter of Comp osing, setting DoF, a quick look through, closing lens, cocking shutter, inserti ng film holder and pulling darkslide, metering, and triggering (assuming the lig ht is not changing, in which case I'll be taking constant meter readings in aper ture 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 i n focus. And if everything mechanical is working the way it should be. I rate th e Type 55 at ISO 50 for the print or ISO 32 for the negative (if I am going to s ave it for later use.) the Type Pro 100 Color I have found to be a very good (no t perfect) match for Fuji Provia (RDPII)in terms of both color saturation and fi lm speed. 9.) Don't forget your filter factor. Does this help? Ellis

  3. #3

    Join Date
    Dec 1997
    Location
    Baraboo, Wisconsin
    Posts
    7,695

    Determining exposure in LF and its general step by step procedure

    You might be interested in purchasing a Casio pocket computer loaded with a prog ram 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 im portant shadow (usually III to V), tell the computer what aperture you want to u se (or what shutter speed you want to use) and the computer calculates the expos ure (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 ca lculation, keep a record of each exposure, tell you the correct aperture to obta in 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 mi nd. 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 C amera" magazine. If wyou wish to pursue this but can't find them send me an e ma il and I'll get the information for you.
    Brian Ellis
    Before you criticize someone, walk a mile in their shoes. That way when you do criticize them you'll be
    a mile away and you'll have their shoes.

  4. #4

    Join Date
    Sep 1998
    Posts
    206

    Determining exposure in LF and its general step by step procedure

    Do you intend to explore the use of the "Zone" system to calibrate your film / d eveloper / 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 cam era exposure that will produce a middle grey value in the final print, regardles s of the how light or dark the object was that you metered.

    At its simplest, "Zone" systems "place" subject values at their appropriate plac e on the exposure scale of the negative, so that they will produce a value in th e 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 i s very intuitive.

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