Macro Extension Tube Help

I'm considering buying either a PK-11, 12 or 13 for my 50mm lens to

do some amateur closeup work. Given that these are 8mm, 14mm, and

27.5mm extension tubes, can someone explain to me how to calculate in

advance what the effect might be?

 

Thanks.

Sorry Jim I can't.... But when I bought mine, I got a sheet with the set that gave info for various lenses. Including, exposure modification. I through mine away, now I just slap em on and experiment.

Jim - I don't know alot about the math and calculations - but I have taken hundreds if not thousands of exposures with the 50 mm AIS lens and the PK 11 & 12 extension tubes. The results are outstanding. The 50 lens is one of the sharpest around. You'll lose your infinity focus and the distance from the film plane to the object will be about 1 foot. With the older lens ( AIS manual focus ) turning the focus ring will vary the magnification ( and also the focus distance). A ringflash handheld gives very nice results. You'll probably need to stop down to f16 & f22. You'll be close to your object. A tripod, cable release and good technique are advised with tripod work. You'll lose matrix metering with the extension tubes. This is a cheap way to get some excellent results. I hope this helps. Rich

total extension = 46.5 mm + tube length + focusing travel (of the lens' helical, measure it) + 3.5 mm. The 3.5 mm is the distance from the lens' rear nodal point to the flange when the lens is focused at infinity.

 

magnification = (total extension/focal length) - 1.

 

exposure compensation, in stops, is approximately (m + 1) [you need to know this only if using non-ttl flash]

Jim

 

I have been using the PX-13 extension with my 55mm f2.8 since

Pontius was a pilot and have never made a calculation when on

my F2A. My meter in the viewfinder knows all and sees all.

 

Jerry