Tokina 100mm 2.8 lens won't shoot at 2.8?

[NickRummy]

Sorry this is probably a basic question but I've been searching and searching and can't figure this out....

The lens is a Tokina 100mm 2.8 Macro lens and I'm using a D200 body. On the lens there is a ring close to the lens mount with F-stop settings on it, 32 through 2.8. The only time the camera will function is when that ring is on 32.

When that ring is on 32 I can't really adjust my aperture to what I want. It will only let me choose a setting based on the focal length the lens is at. Does that make any sense? If I try to focus on something close it might let me shoot at 4.5, farther away I might be able to drop to 2.8.

This happens in any mode that I'm shooting in, manual, aperture priority etc etc

Thanks in advance for the help!

Nick

 

[Derrel]

It's a macro lens, so this behavior is normal. it's a modern Nikon body, so the lens's aperture ring must be set to f/32 and that is when a modern consumer Nikon will function. Only the older, and the "professional" Nikon bodies allow f/stop input via the aperture ring on the lens.

When a 100mm macro lens on a Nikon is focused close, to 1:1, the typical maximum aperture will be f/5.6. The behaviors you describe above are all well-known, typical, expected, normal behaviors with macro lenses.

 

[Overread]

+1 to what Derrel said - note that this change in aperture is something that isn't reported in all camera bodies. Nikon report this change in actual aperture, however Canon (by example) do not. Hence you'll see plenty of canon shots (even on the canon version of the lens you have) from macro lenses at f2.8 because that is what the camera is telling them. The actual aperture is still f5.6, the same as yours, its just that canon users don't know it .

At the smaller end of the scale this also causes a difference since f13 is the typicall cut off point for many canon shooters (the point where thereafter smaller apertures give a net loss of sharpness next to the gain in depth of field) - whilst on your nikon it will be around one stop less from there (because that f13 on the canon still isn't taking into account the 1 stop loss that the lens has taken in focusing that close).

 

[NickRummy]

Thanks guys, I appreciate the replies. I just wanted to make sure I wasn't going crazy.

Is there a reason why Macro lenses do this and not normal style lenses?

 

[Overread]

It's part of how they achieve their close focusing ability with current optical setups and technologies. They also change their focal length (it reduces) as they go into that close up mode as well.

Far as I know the only macro lens that might be a true f2.8 is the MPE since it starts out at 1:1 at f2.8 (it has no ability to focus outside of macro distances). Even that lens as it boosts its magnification reduces is focal length and max aperture.
It starts out 1:1 at 65mm f2.8 and ends up at 5:1 around 40mmish (not sure of the value but that is a ballpark figure) and around f16.8 max aperture

 

[ksangree]

+1 for the question and +1 for the answers. I was in a panic when I couldn't stop down lower then f/3. However, after reading this thread, I tried focusing at an object that was at a further distance away and voila! f/2.8. Thanks guys!