Joshua Dannais Posted April 21, 2008 Share Posted April 21, 2008 (edited) I'm using a slow lens on a slr to take reference pictures of locations i'm planning to shoot on 16mm... since the lens is slow and I'm planning to use a zeiss prime for the 16mm shoot, would shooting the stills at f4 rated at 1000 iso give a similar result as shooting at f1.4 rated at 500 iso? thanks Edited April 21, 2008 by Joshua Dannais Link to comment Share on other sites More sharing options...
Premium Member Michael Nash Posted April 21, 2008 Premium Member Share Posted April 21, 2008 1000 ISO is one stop faster than 500 ISO. f1.4 at 500 is f2.0 at 1000. F4 is three stops from f1.4; so you'd need to use an ISO that's three stops faster (4000), or a shutterspeed that's three stops slower than 1/48 (1/3 second). Link to comment Share on other sites More sharing options...
Joshua Dannais Posted April 21, 2008 Author Share Posted April 21, 2008 1000 ISO is one stop faster than 500 ISO. f1.4 at 500 is f2.0 at 1000. F4 is three stops from f1.4; so you'd need to use an ISO that's three stops faster (4000), or a shutterspeed that's three stops slower than 1/48 (1/3 second). thank you... On my light meter 640 was the next click up so I thought that was a stop for some reason. How did you come up with a shutter speed of 1/3? Is it half the speed three times: 1/48 -> 1/24 -> 1/12 -> 1/6? Link to comment Share on other sites More sharing options...
Premium Member Michael Nash Posted April 21, 2008 Premium Member Share Posted April 21, 2008 How did you come up with a shutter speed of 1/3? Is it half the speed three times: 1/48 -> 1/24 -> 1/12 -> 1/6? Oops! It's 1/6th. You've got the right idea; I somehow counted the wrong fingers! :P ISO numbers have a geometric relationship; double the number, you double the sensitivity (i.e. one stop). The common ISO speeds are divided in 1/3's of a stop. 640 is 1/3 stop faster than 500. Link to comment Share on other sites More sharing options...
Joshua Dannais Posted April 22, 2008 Author Share Posted April 22, 2008 Oops! It's 1/6th. You've got the right idea; I somehow counted the wrong fingers! :P ISO numbers have a geometric relationship; double the number, you double the sensitivity (i.e. one stop). The common ISO speeds are divided in 1/3's of a stop. 640 is 1/3 stop faster than 500. awesome, thats big help... i didn't know that. thanks Link to comment Share on other sites More sharing options...
Dominic Case Posted April 22, 2008 Share Posted April 22, 2008 Each stop of exposure is doubling or halving the actual exposure. But the various exposure-related scales work in several different ways. Shutter speeds work on a geometric scale, usually stepped in full stops: 1/1,000th; 1/500th; 1/250th; 1/60th; 1/30th etc. For a motion picture camera at 24fps, the shutter speed is normally 1/48th, (or 1/50th at 25fps) which is about 1/3rd stop slower than 1/60th. Shutter angles are related to shutter spped: halving the angle is the same as halving the speed (one stop). If 180deg is normal, then in one stop intervals you have 90deg; 45deg, 22deg. In one third stop intervals you have 180deg; 144deg; 113deg; 90deg; 72deg; 56deg; 45deg ISO ratings (aka ASA ratings aka EI ratings) are also geometric, and tend to progress in 1/3 stop increments: starting with the slowest (least sensitive) speed, you have: 50; 64; 80; 100; 125; 160; 200; 250; 320; 400; 500; 640; 800 etc. Note that every third number is double, which ever one you start from. Aperture (f or T stops) are different: they work on a square root of two scale, with a doubling or halving of the number representing two stops. Starting with the biggest aperture (the most light passing through the lens) you can go in one-stop intervals: f/1: f/1.4; f/2; f/2.8; f/4; f/5.6; f/8; f/11; f/16; f/22. In one third stop intervals (for part of the range as an example) they go f/2.8; f/3.2; f/3.5; f/4; f/4.5 f/5; f/5.6; f/6.3; f/7; f/8; f/9; f/10; f/11 etc. As another clue, each one third of a stop is a number about 12% more than the previous number. ND filters are different again: they go in additive steps: every time you add an ND3 (which has density 0.30), you alter the exposure by one stop: so the typical one third of a stop intervals are each 0.10ND. Then 0.30ND is one stop (half the light): 0.60ND is two stops (quarter the light); 0.90ND is three stops (one eighth the light) and so on. Link to comment Share on other sites More sharing options...
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