[pure-silver] Re: Infrared Focusing Test
- From: Ken Sinclair <photo1@xxxxxxxxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Tue, 15 May 2007 18:20:37 -0600
On 15-May-07, at 6:52 PM, Peter De Smidt wrote:
So I have some sheets of 4x5 infrared film that I'd like to try
out. I would like to spend on sheet testing focus. Here's what I
plan to do. Setup a yardstick and my 4x5 camera system in a safe
place. Focus on a middle point of the yardstick, put the infrared
filter on the lens and expose the film with the lens wide open.
After developing the film, determine the distance of sharpest focus
on the film, and figure out the focusing adjustment to use with
that lens by noting the position of the standards for the original
focus position, and then focus on the part of yardstick that was
sharpest on the film. The distance the standards have to be moved
between these two points should give the required adjustment. Does
that sound right?
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Peter.
The correct increase in distance between the front and rear standards
when using IR, is one
quarter of one percent of the total distance when focussing with
visible light.
(The increased measured distance will be greater with close-up than
at infinity).
Ken
Seagoon: Any cases of frozen feet?
Eccles: You didn't order any cases of frozen feet!
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