Sigma 105mm f2.8 ex dg macro os not working correctly.

[peanut170]

Just bought this lens, seems to take great pictures, but having trouble getting the aperature to 2.8. have tried in m, a, and s. its even saying f3.0 f3.3 f3.8. I kept messing with it and finally could get it to 2.8. So I changed lenses just to see of it would do the sane thing and when I put it back on, same thing f3.8 was the widest it would go. Which I've never even seen those aperatures numbers anyway on my other lenses. Any suggestions, or anyone had the same problem? I have a Nikon d90.

 

[Overread]

I think this might be detailed in the info slip that comes with the lens (or it should be for a Nikon version).

In short there is absolutely nothing wrong with your lens at all and it is working exactly as it should. Most (all?) of the current crop of prime macro lenses on the market achieve their close focusing ability by reducing their effective aperture and focal length as you shift the focus into the 1:1 magnification range. As such the aperture (on all) does reduce. Canon camera bodies don't report this change to the user, it happens but we only see it as a dimming of the light through the lens and in the fact that diffraction softening appears to start at wider apertures on our cameras.
Nikon camera bodies do report the change in effective aperture to the user and this is what you're seeing. In practical terms this means you can often use a (reported) smaller aperture than Canon users before diffraction softening kicks in - however the actual apertures will be similar on both.

 

[peanut170]

Ok I will play with it some more and thanks for the reply. It has 3 selection switches, and at times it wouldn't go to 2.8 in any of the modes, and was getting random aperature numbers that I hadn't seen before so was confused. So its the same way on the Nikon 105 macro also?

 

[Overread]

Yep it will do exactly the same things. Also read the manual. The switch on the side is a focus limiter switch which will limit the lenses focus to certain ranges (but if you use it whilst its outside of the range you set it to the AF won't engage and you'll have to manually adjust the focus till its in the limited range). Also the other switch is the OS control.

 

[peanut170]

I understand the af/ manual switch and the os switch, except it has 2 settings? It's the focus limiter switch has 3 settings which confuse me. Thanks for u help though.