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[photography] How do I calculate the new focal length and aperture? (piefed.cdn.blahaj.zone)
submitted 3 weeks ago by to c/techsupport@lemmy.world
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I bought these possibly Kenko cfe auto extension tubes (26 + 12 + 11 [mm]) with Canon FD mounts. I'm using them on a really sweet Canon FD 135/f2.5. Normally, I simply input those values into the digital camera's "manual lens info" slot in order for the in body image stabilization to work better, but I'm not sure what to input here. Should I simply add the above tube lengths to the total focal length (135 + 49)? And what about the visually obvious loss in light/aperture. What would the new value be there?

Bredit (brag edit): CDUMRxi2czpbVzU.png

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[–] [S] 3 points 3 weeks ago (1 child)

No optics, just extensions.

You're a living library of optics and photography. 🤣 I did actually wing it today, just using the same values regardless of having put on the tubes. The image was a bit more shaky handheld, but it did alright. The magnification wreaked havoc on the depth of field though. We were talking millimeters even at the smallest physical aperture. The leaf above was shot at f11. 😱

Anyway, thanks!

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  • [–] 1 point 3 weeks ago

    Yes, depth of field is directly correlated to focal length but also distance to the objective. The closer the front of your lens is to the subject the less depth of field you'll get. I don't know the math for that offhand. The relationship is geometric somehow, I'm sure. What I do know is that using e.g. my 100mm macro lens and with the subject only a couple of inches away, my effective depth of field is only a couple of millimeters. Focus stacking is your friend if both you and your subject are the sort that can hold still.

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