View Full Version : Help reading chart

17-Jan-2018, 15:01
I purchased a 10" Kodak Commercial Ektar and dropped it off at a local shop to have the shutter speed tested. They handed everything back today with a little chart. I didn't open it up and read it at the shop and now that I am back at the office, I wasn't too sure how to read it correctly. Or maybe I am. Either way, I was going to ask if anyone on here could shed some light on the situation.

To me, it looks like the base line is the middle black section marked "Speed" and if it was firing correctly, that would be where the highlighted marks should be. So am I correct in thinking that the 1/25th (random example) is slow by 30% of its speed?


Dan Fromm
17-Jan-2018, 15:20
I read the “speed” row as the ideal shutter open time in milliseconds.

1000 ms for 1 sec, 500 for ½, 250 for ¼. 125 for 1/8, 1/67 for 1/15, 33 for 1/30, 17 for 1/60, 8 for 1/125, 4 for 1/250

Your measured shutter open times in ms are penciled in in the row below “speed”, equivalent fractions are penciled in at the top. Your shutter’s slower speeds are fast, faster speeds are slow.

If the measured speeds are for a single shot, the table isn't very informative. The shops I use report three or five shots and the average. This allows us to see how variable a speed it (more variability, worse) and how close to nominal the shutter is on average. When I test my shutters I do five shots at every marked speed, calculate how many stops the average is off. I find it easier to think in terms of "stops off" than in terms of "percentage off."

17-Jan-2018, 15:52
Makes perfect sense. Thank you for the help. Would you say they are severely off? Maybe a decent cleaning is in order

Dan Fromm
17-Jan-2018, 16:46
Whether a CLA is needed depends mainly on whether the speeds are erratic. A CLA wouldn't hurt, but if the shutter is consistent you can adjust ...

FWIW, I carry a calibration chart. The stub is shutter, the heading is speed as set, the cells contain "stops off." So I can meter, find the stop needed for a nominal shutter speed, set the speed and set the aperture to "needed" and then move the pointer "stops off" away from "needed."

Pere Casals
17-Jan-2018, 17:32
Makes perfect sense. Thank you for the help. Would you say they are severely off? Maybe a decent cleaning is in order

Even a brand new mechanical shutter could have +/-30% exposure time missmatch, mechanical shutters can be very repetitive, but usually they differ a bit from marked speed. It was common manufacturers specified that +/-30% tolerance, under that level warranty was not in force.

That +/-30% can be tolerated with negative (BW or color) film if one overexposes a bit by routine, for slide film it is important to measure owned shutter speeds with a shutter tester, it is nice to nail exposure with slide film.