Focus shift with infrared filmgreenspun.com : LUSENET : Large format photography : One Thread
If I am using infrared film with my 4x5 and a 90mm lens stopped at f16 / f22 do I need to worry about focus shift? If so, what is a general rule when dealing with infrared focus (especially if I am using tilt). Thanks in advance for the responses. Dave.
-- Dave Anton (firstname.lastname@example.org), June 02, 2000
Dave I personally would not worry about focus shift with the the lens and f-stop you are using with IR.I use a slightly longer lens then the 90 with 4x5 IR and the images are as sharp as can be,certainly at f22 and I focus as if I'm using panchromatic film. Regards,Trevor.
-- Trevor Crone (email@example.com), June 02, 2000.
Focus shift will no longer be a problem: Kodak announced they are discontinuing 4x5 HSI film the end of 2000. The only infrared they are going to carry is 135 size.
Search http://www.kodak.com for the F-13 publication.
Formula for focus adjustment is add .0025% of focal length to the bellows extension. Kodak's example is "a 200 mm lens would require a 0.50 mm extension as 200 mm x 0.0025 = 0.50 mm."
-- Bruce Gavin (firstname.lastname@example.org), June 03, 2000.
I've used Kodak 35 mm infrared extensively and 4x5 infrared some. I've never found focus shift to be a problem with either format as long as you stop down to the F 16 or smaller range. When I first started with infrared in 35 mm I used to religously use the infrared marker on the lenses that had the markers and didn't do anything on the lenses that didn't have the markers. I couldn't see any difference in the results so I stopped bothering with it even on lenses that had the markers.
-- Brian Ellis (email@example.com), June 04, 2000.