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Focal Lenght Question...

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Posted by David Gede on November 20, 2003 13:39:59 UTC

I just want to make sure I understand the results of what I did so I don't go in the wrong direction.

Following some information picked up from a web site, I used a flashlight and card to find the ROC.

I started the 8" glass with a diamond generation of f6.8. This would mean that the fl should be 54.4 inches.

I have worked through the grits and hit some issues using the 5micron powder (scrathes - but that is not the issue). While stepping back I decided to measure the ROC with the flashlight test. The test resulted in a 77" ROC. This would come out to a focal lenght of 38.5" or an f ratio of about 4.8.

I want to lengthen the ROC and the focal length out to about 108 inches and 54 inches respectively.

My solution was going to be to go back to 220 grit with the tool on top until I get a lot closer then work back down to the micron level (keeping a much closer eye on the ROC).

Does this seem correct?


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