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# Thread: Simple question: time and "stops"

1. ## Simple question: time and "stops"

Probably and easy question:

How do I figure out how to add a third of a stop to a particular amount of time (keeping fixed aperature)?

For instance, if I want to add 2/3 a stop to 19 seconds of time, how do I determine that?

I know adding a stop doubles the time, it is the 1/3 and 2/3 increases that I'm not sure how to figure out properly..

2. Originally Posted by Michael Scarpitti
1/3 of a stop is 1/3 of 2x.

19 secs + 19 secs = 38 secs would be one stop

1/3 of 19 secs is about 7 secs.

19 + 7 = 26 secs.

That sounds about right. But, doesn't exposure increase at a non arithmetic fashion? In otherwords, isn't 2/3 a stop actually more than 2 * 7 seconds?

Or, maybe I'm confusing something I have read.

Short times it probably doesn't matter much at all, but I am trying to think through a reciprocity problem.

3. Using your example. One stop would be 38 seconds total time. One third stop additional would be 25.3 seconds total time. Two thirds stop addtional would be 31.6 seconds.

Originally Posted by JeffD
Probably and easy question:

How do I figure out how to add a third of a stop to a particular amount of time (keeping fixed aperature)?

For instance, if I want to add 2/3 a stop to 19 seconds of time, how do I determine that?

I know adding a stop doubles the time, it is the 1/3 and 2/3 increases that I'm not sure how to figure out properly..

4. There are a couple of good F stop printing charts available on the internet too. I keep one on my darkroom wall.

5. Hi Jeff, are there any simple questions?

My method is to use percentage increases/decreases. A one stop increase of exposure for 19 seconds is a 100% increase; 38 seconds. A 1/3 stop increase would be 19 seconds + 33%, 0r 25.27 seconds...I'd round it up to 26 seconds.

This way, if at a later date you're making a larger print of the same image and want to burn the sky the same way, you just apply the original percentage increase to your new exposure for the larger print.

Murray

6. One chart is available at

http://www.darkroomagic.com/library/library.htm

It´s the chart published by Lambrecht and Woodhouse in their book "Way beyond monochrome".

7. From Ed Buffaloes' page on test exposure for printing, I think principle is the same for camera exposure increases:

BASE 19.0
PLUS------Net change---new exp
1/4 STOP----0.19--------22.6
1/2 STOP ----0.41--------26.8
3/4 STOP----0.68--------31.9
1 STOP--- --1.00--------38.0

http://unblinkingeye.com/Articles/Te.../testexpo.html

The queston was about 1/3 stop increase and my answer is about 1/4 stop increases but for greater detail on the reasoning please see Ed Buffaloes' site, he explains it all much better than I can.

8. ## OOPS,

Originally Posted by Bruce (Camclicker)
From Ed Buffaloes' page on test exposure for printing, I think principle is the same for camera exposure increases:

BASE 19.0
PLUS------Net change---new exp
1/4 STOP----0.19--------22.6
1/2 STOP ----0.41--------26.8
3/4 STOP----0.68--------31.9
1 STOP--- --1.00--------38.0

http://unblinkingeye.com/Articles/Te.../testexpo.html

The queston was about 1/3 stop increase and my answer is about 1/4 stop increases but for greater detail on the reasoning please see Ed Buffaloes' site, he explains it all much better than I can.
My colulmn titled Net change should be titled MULTIPLIER and the numbers should be expressed as 1.19; 1.41; 1.68 and 2.00.

I was once told by a boss that you can make all the mistakes you want as long as you keep them on your desk. Sorry this got off.

9. I was reading in my Way Beyond Monochrome book about f/stop printing, but it went way over my head at the time. Does anyone have a good basic link that I could start with to try and get into this?

10. As I understand it, to calculate new times, you need to raise the number 2 to the power of the number of stops.

Therefore, for a 19 second exposure, one stop increase would be 2 to the power of 1, which is 2, and 2 x 19 is 38s.

For a 1/3 stop increase, 2 to the 1/3 = 1.2599
1.2599 x 19 = 23.94s

For 2/3 stop, 2 to the 2/3 = 1.5874
1.5874 x 19 = 30.16s

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