Potential dead horse: how bad is FF's deep DoF disadvantage?

Started 7 months ago | Discussions thread
joejack951
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Re: no disadvantage
In reply to Steen Bay, 7 months ago

Steen Bay wrote:

joejack951 wrote:

Steen Bay wrote:

joejack951 wrote:

tko wrote:

And I own a FF lens that stops down to F/50 or something silly.

What lens? My 105VR will display f/57 when stopped down to f/22 and at minimum focusing distance, but that's just Nikon's way of displaying the light loss at close focus distances (effective aperture as explained in the lens manual). DoF is still f/22.

If you shoot af f/22 at 1:1 magnification, then I think that you're effectively shooting at app. f/44 in terms of both exposure, DoF and diffraction. Kind of like using a 2x TC.

I misspoke when I said f/22. The 105VR stops down to f/32 and will display f/57 (IIRC) at minimum focusing distance.

Unless I've always read/understood incorrectly, effective aperture only affects exposure. DoF and diffraction are not affected because the aperture blades aren't actually moving. TC's have glass in them that changes the image being projected by the lens. That's a lot different than moving the lens elements further from the sensor (like an extension tube).

I swear that my lens manual went into detail about this but the Nikon lens manual online mentions nothing about effective aperture. Weird. I need to check that when I get home.

Any care to chime in on the true effects of shooting up close?

Found a bit about it here : http://www.cambridgeincolour.com/tutorials/macro-lenses.htm

"However, at high magnification the effective f-stop is actually what determines the diffraction limit — not necessarily the one set by your camera."

Thanks! The bit about the focal length changing as the lens extends makes everything fall into place for me, at least for extending macro lenses. I will have to do some more reading though as I don't believe the examples given directly relate to internal focusing, non-extending macro lenses. My 105VR actually loses focal length as you focus closer which goes against the principal of having a higher number f-stop at closer focus distances. There's obviously something else going on though, and it seems that it has to do with the focusing group, that is causing the effective aperture to decrease.

My guess is that since the aperture of a lens isn't really the physical size of the aperture (as if one used some calipers and measured the opening of the blades) but the size it appears to be as viewed from the front of the lens, the floating lens groups must change this apparent size.

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