Tok. 100/2.8 & Nik. 105VR help please

Joined
Dec 20, 2005
Messages
300
Location
Tampa Florida
Hello all,

I bought the Tokina 100/2.8, put it on my D200, set to aperture priority at 2.8 and started to take pictures. I noticed that the aperture was not holding at 2.8. When focused to infinity, the aperture was 2.8 but as I focused towards the closest distance the aperture would change incrementally until it reached 4.2 at the minimum focusing distance. Without moving the camera, simply changing the focus caused the aperture to change.

The camera store agreed to exchange it because that seemed like a defective lens. Well, I didn't want to wait 2 weeks for the next shipment, so I exchanged it for the Nikon 105/2.8 VR and it did the same thing??:confused:

My friend put the 105 on his D200 and had the same issue??:confused:

This does not happen with my Nikon 50/1.4, 28/2.8 or my Tokina 12-24/4.0

Another friend of mine who bought the Tokina for his canon 30D did not experience this issue.

Can somebody please help me out here? I am new to macro and do not understand why focusing distance would change the aperture - is there something really simple I am not understanding?

Or do I just have the dumb luck to get a lemon each time?

Again, camera was set to aperture priority, no flash, sunny mid afternoon, indoors and outside.

Thanks for help
Peace
Mark
 
Joined
Jan 8, 2007
Messages
904
Location
Ottawa, Ontario, Canada
This is normal for macro lens. It's only f/2.8 at infinity. At less than infinity, it will not be at its widest aperture. Why the Tokina did not register this on the 30D, I can't say. I've tried several macro lenses and they all exhibited this behaviour. At 1:1 or close to, f/2.8 would be so narrow you'd have almost nothing in focus anyways.
 
Joined
Mar 5, 2007
Messages
546
Location
Greensboro, NC
Mine does the same thing

I have a Tamron SP AF DI II 90mm with a minimu f2.8 (only at infinity). At minimum focus distance....aperture jumps to f5.6.

It probably has to do with length of the lens at closest focus distance. At minimum focus, the lens grows to the maximum length, several inches longer. Most (cheaper) telephoto lens work the same way, with variable apertures.

Next look at a prime lens, like the 50mm. From minimum to maximum focus distances the lens only grows about a half inch.

This is just an observation....someone can probably explain this better.

Rob
 
Joined
Dec 20, 2005
Messages
300
Location
Tampa Florida
Thanks all - had a feeling I was missing something simple :redface:

Gee, the camera shop guy missed it as well - oh well, not a problem since I am happy with the 105VR - should have bought it in the first place. :smile:

Peace
Mark
 
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