Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 (Tek) 9/28/84 based on 9/17/84; site mako.UUCP Path: utzoo!watmath!clyde!cbosgd!cbdkc1!desoto!packard!edsel!bentley!hoxna!houxm!ihnp4!zehntel!tektronix!orca!mako!jans From: jans@mako.UUCP (Jan Steinman) Newsgroups: net.rec.photo Subject: Re: Multiple exposures ?? Message-ID: <439@mako.UUCP> Date: Mon, 10-Dec-84 13:04:46 EST Article-I.D.: mako.439 Posted: Mon Dec 10 13:04:46 1984 Date-Received: Wed, 12-Dec-84 05:16:37 EST References: <41600001@hpfcms.UUCP> <1539@drutx.UUCP> <4257@cbscc.UUCP> Reply-To: jans@mako.UUCP (Jan Steinman) Organization: Tektronix, Wilsonville OR Lines: 56 Summary: In article <4257@cbscc.UUCP> rsg@cbscc.UUCP (Bob Garmise) writes: > 1) backwind the film until it's tightly wound, then... > 2) press/flip the release button/knob > 3) thumb wind the film as if you were advancing to a new frame... A cleaner solution exists for some cameras, notably Olympus OM1, OM2 and some Cannons. Many cameras have a ratchet mechanism for the rewind button which causes it to pop up after re-winding a bit. This keeps you from leaving the camera in rewind mode after loading a new roll. (If your camera instructions tell you something like "hold in the rewind button while turning the crank", you probably have such a mechanism. Follow steps 1) and 2), above, then rewind the film a tiny bit and release the rewind button. Continue rewinding until the rewind button pops up -- the film should not rewind further if there is such a ratchet mechanism. The mechanism is usually keyed to fractions of a frame (I think the Olympii take four rewind-button-pop-up cycles per frame, but it's so easy to find out, I haven't memorized it.) To find out how many times to repeat the procedure in order to rewind exactly one frame, follow step 1), above, note carefully where the rewind knob/crank is positioned (a grease pencil is great for this), shoot the first exposure and wind the film slowly, noting how far the rewind knob/ crank has moved, and perform enough of the push-rewind-button-rewind-tiny-bit- release-rewind-button-rewind procedures to get the rewind crank/knob back to it's original position. It sounds complicated, is difficult to describe, and is somewhat more awkward than the simpler method cited, but it results in much greater accuracy and removes the requirement to waste a frame on either side of the multi-exposure shot. If step 1) is performed prior to the FIRST shot, pin-registration accuracy can be achieved. (Auto-processing equipment also tend to get confused by the first method if registration is off slightly. Before discovering the method presented, I got back a roll of slides with every frame after the multi cut neatly in half, due to sloppy the registration of the first method!) As far as I know, this method has not been presented in instruction manuals or magazines, although it works with every camera I've tried it with. >Now for my question...let's say you're taking a picture of a lake and it's a >sunny day. On top of that you wish to multiply expose a car to make it look >like the car is hovering over the lake. For the sake of argument let's also >say the proper settings for each individual picture would be: > 1) Lake: f8 at 1/250 sec > 2) Car: f4 at 1/60 sec >To make a multiple exposure, what settings do I use? The key is to think in terms of exposure value. Each single f-stop change doubles or halves the amount of light reaching the focal plane. Reduce each exposure by one stop for a double exposure, two stops for a quad, etc: Lake: f11 @ 1/250 OR f8 @ 1/500 Car: f5.6 @ 1/60 OR f4 @ 1/120 This rule of thumb is sometimes tempered by reciprocity -- if in doubt, bracket using 2/3 stop and 1 1/3 stop decrease per exposure. -- :::::: Jan Steinman Box 1000, MS 61-161 (w)503/685-2843 :::::: :::::: tektronix!tekecs!jans Wilsonville, OR 97070 (h)503/657-7703 ::::::