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04-06-2009, 07:14 AM   #1
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Rear converter and Extention Tubes

Can you stack the 645 rear converter with extension tubes, and if so, what would the magnification factor end up being? Is there a formula to figure out the magnification ratio using the focal length of the Lens used with the tubes and converter?

Also, what factor(s) should I adjust my aperture by to compensate for the increased length


Last edited by robertdyne; 04-06-2009 at 07:31 AM. Reason: more information sought
04-06-2009, 08:00 AM   #2
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QuoteOriginally posted by robertdyne Quote
Can you stack the 645 rear converter with extension tubes, and if so, what would the magnification factor end up being? Is there a formula to figure out the magnification ratio using the focal length of the Lens used with the tubes and converter?

Also, what factor(s) should I adjust my aperture by to compensate for the increased length

I just checked a 1.5X TC on the rear of a bellows at a fixed extension. The magnification was changed but not the working distance (from the front of the lens to the subject.)

This means the magnification is just TCX what it is without the TC.

New_mag = (Old_mag + Extension/Focal_length)*TC

Iowa Dave
04-06-2009, 08:28 AM   #3
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QuoteOriginally posted by robertdyne Quote
Also, what factor(s) should I adjust my aperture by to compensate for the increased length
The approximate correction for magnification m is:

F_new=F_old/(1+m)

Iowa Dave

See: Pupil magnification ratios and macro lens DoF - Photo.net Nature Forum
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