Bowl in Sink/Reciprocity/Bellows Experiment

kdthomas · Jul 4, 2016

Last night I saw a bowl in my sink, inside another bowl, inside a pyrex measuring cup. There was some leftover ice cream that had formed this kind of halocline ... Thought it might it be a good time to experiment with tilts on the 4x5, but also realized, it was a good experiment for factoring bellows expansion and reciprocity failure.

This is HP5 plus rated at ISO 400, 4x5 with a 210 mm lens. The incident meter gave me a base reading of f/32 at 8 seconds. However I measured that the standards were 330 mm apart. I used this measurement to arrive at a correction of adding 1.3 stops, bringing the time to 20 secs. Then using the reciprocity corrections chart in the HP5 manual, this came to 83 seconds.

I then backed off to f/22 and (using the chart for 10 secs) arrived at 31 secs for the second set.

As it turned out ... the images are almost perfectly identical. It worked! Here's the final result (this is the f/32 image, after scanning and a bit of styling in LR)

Ysarex · Jul 4, 2016

You're doing the bellows factor the hard way. It's easier to just measure magnification at the ground glass to calculate the bellows factor. Magnification of X1 is a 2 stop exposure increase, X.5 is 1 stop and so forth. Get a small plastic ruler (mm or inches -- whatever) let's do mm. Cut a paper or plastic chip exactly 50mm square. Put the chip in the photo at the focus plane. Use the ruler to measure the image of the chip on the ground glass. If the chip measures 50mm on the ground glass you've got a 2 stop bellows factor. If the chip measures 25mm on the ground glass then a 1 stop bellows factor and you can fill in the 1/3 stops no problem. What I always did was just pick up a piece of paper and fold it in half and again and again and again, etc. Then I'd tear off the end (chip) to place in the photo and unfold the paper to use as a ruler -- marked bellows factor stops on the fold lines.

Joe

Rick50 · Jul 7, 2016

Ysarex said:
You're doing the bellows factor the hard way. It's easier to just measure magnification at the ground glass to calculate the bellows factor. Magnification of X1 is a 2 stop exposure increase, X.5 is 1 stop and so forth. Get a small plastic ruler (mm or inches -- whatever) let's do mm. Cut a paper or plastic chip exactly 50mm square. Put the chip in the photo at the focus plane. Use the ruler to measure the image of the chip on the ground glass. If the chip measures 50mm on the ground glass you've got a 2 stop bellows factor. If the chip measures 25mm on the ground glass then a 1 stop bellows factor and you can fill in the 1/3 stops no problem. What I always did was just pick up a piece of paper and fold it in half and again and again and again, etc. Then I'd tear off the end (chip) to place in the photo and unfold the paper to use as a ruler -- marked bellows factor stops on the fold lines.

Joe

Seems simple but now I'll use a couple sheets to try this.