Hi Vaughan...you missed out the second 2s exposure in your calculation....i.e. the second strip only got four seconds (the intial 2s for the whole sheet plus another 2s), the 3rd strip got those 4 sec0nds plus another 4seconds...i.e. 8 etc., the fourth strip got those 8seconds plus another 8seconds...i.e. 16secs.etc.
Just saw your second comment on your post Vaughan. The use of the aperture on the lens would not work, since it would not be a cumulative effect for the overall exposure of the exposed parts...i.e. you would ned to make sure each strip is exposed while protecting the rest of the paper. It would also need you to recalculate the exposure times, since generally you print at a selected aperture...at least that is waht I think...Will go off and see if I am correct now! Rgds, K
It will work. For one stop series the exposures are 1x, 1x, 2x, 4x ...
Originally Posted by Shangheye
It doesn't matter how each exposure is doubled: it can be either time or light intensity.
The aperture method is easier if you are working at one stop intervals. The problem is that a 1 stop interval is 2 zones on normal #2 paper, more on higher contrast paper.
You will usually end up having to make a fine test strip with a timer after a one-stop series.
The one stop series can be useful for judging dodges and burns which are often in the 1/2 to 2 stop range.
I own one of the venerable Kodak Projection Print Scales. It's excellent for a first shot, especially if trying a new paper. After that I can generally operate with small test strips in important areas and "informed guessing" to refine the exposure.
Thanks! I should not try to do simple math nor try to follow simple instructions when I am up all night printing!
Originally Posted by Shangheye
Let me recap a bit.
1. Using the Projection Print Scales is most convienient. You only have to expose just one time and the steps spacing is good.
2. The aperture method works fine and doesn't need to do much calculations. You can get good steps spacing this way. You do need a way to expose just one strip at a time like the test strip printer.
3. Using just a piece of card board and varying the time works better if the you do it by first expose the entire sheet and then cover 1 strip and 2 strip and so on. If you do it by uncovering 1 strip and then 2 strips and so on it doesn't work as well. The timing should be increased as a percentage of the last step. For example double for 1 stop steps, 1.4 times for 1/2 stop steps etc..
4. The spacing of 1 stop per step is a bit much in my opinion as 1 stop even with grade 2 paper would change the print density about 0.50 and that's too much. I think a 1/2 stop steps are better.
Why is it important to think in terms of stops at the enlarger? How will that benefit me?
I guess I can't see the advantage to the test strip method that Kal has described (I'm feeling dense today). If I determined that a 36 second exposure is too weak, a 38 second exposure is too dark, and a 37.5 second exposure would be just right, how can I discern information this accurate using the method Kal has described? When dodging, burning, or creating straight prints, I find a second of exposure here, and a second of exposure there to be quite critical to the final print. In Kal's method for example, there would be 32 seconds of exposure time residing between the 32-second and 64-second exposures on the test strip.
The reason to think in term of stops because the effects are equal. Increase of decrease exposure by 1 stop produces the same effect while increase of decrease exposure by 1 sec doesn't. If your original exposure is 1 sec and you increase 1 sec and make it 2 sec the effect is quite great. If the original exposure is 30 sec and you increase by 1 sec to 31 sec I don't think you can see any change at all. You don't have to make the steps 1 stop apart, you can make it 1/2, 1/3, 1/5 etc.. depending how closely you want them to be.
In your example increasing exposure from 32 to 64 sec has the same effect as increasing from 5 to 10 sec.
32 seconds of exposure has the same effect as 5 seconds of exposure ????
Originally Posted by Chan Tran
It's the change in exposure that counts, and it is logarithmic.
Originally Posted by DannL
Take an example. You have a negative that you like, and a pleasing 8x10 print results from an 8 second exposure.
You decide to print it big - 16x20. Everything being equal, a 32 second exposure at the same aperture will yield similar tones in the bigger print.
Now, you decide you want to try it darker, for a more moody effect. You experiment a bit, and decide that the 8x10 dark version looks best with one stop more exposure - 16 seconds (an increase of 8 seconds). If you want the same result on the big print, you don't increase that exposure by 8 seconds - instead you increase that exposure by 32 seconds, to get the same one stop increase in density.
Now the numbers here are simplified, and there are other real-life issues to contend with (reciprocity, shift in contrast, etc.) but basically this works.