Aperture issue with Sigma Lens

[gilbouk]

I went to look at a Sigma 105mm Macro OS lens this afternoon and from the outset it looked absolutely minted - however when trying the lens, I found that the maximum aperture my camera would allow me to select was f3 as opposed to f2.8. Upon taking some test photos, I found that that I was able to attain f2.8, however when removing and reseating the lens - the aperture would not open up further than f3 again, even after further test shots. What kind of issue is this? I ended up not taking the lens as I was worried there may be a fault.

 

[Cagey75]

Did you try stopping down past f/3 to f4 or 5.6? We're you testing it for close ups only? Macro lenses force the aperture to stop down at close focus distances, at 1:1 many have a max of f5 or so. Did you try shooting something in the distance at 2.8

 

[gilbouk]

Did you try stopping down past f/3 to f4 or 5.6? We're you testing it for close ups only? Macro lenses force the aperture to stop down at close focus distances, at 1:1 many have a max of f5 or so. Did you try shooting something in the distance at 2.8

Ahh, I didn't correlate the aperture to distance I'm afraid. I was able to stop down no problem. First time experiencing a prime behaving in this manner, however the only macro lens I've had experience of using was the Nikon 105mm f2.8 and I can't recall that behaviour

 

[Cagey75]

Ahh, I didn't correlate the aperture to distance I'm afraid. I was able to stop down no problem. First time experiencing a prime behaving in this manner, however the only macro lens I've had experience of using was the Nikon 105mm f2.8 and I can't recall that behaviour

I'm not great at explaining technicalities, but it's more that the camera is reporting the true light gathering at closer focal distances with macro lenses, as they are optimized for this purpose. Unlike standard lenses they are relaying the information of light loss - some macro lenses don't report this information back, like the Nikon. It'll say f/2.8 up close, but in reality you're losing a stop or two of light depending how close you're focusing. It usually doesn't matter, as for extreme close ups you want to be stopped down anyway or the DOF is insanely shallow and barely anything would be in focus. This is why most macro shooters use off camera flash, they're regularly stopping down to f/11 or smaller. These lenses will do f/2,8 at infinity though, or regular shooting like for a portrait.

 

[gilbouk]

I'm not great at explaining technicalities, but it's more that the camera is reporting the true light gathering at closer focal distances with macro lenses, as they are optimized for this purpose. Unlike standard lenses they are relaying the information of light loss - some macro lenses don't report this information back, like the Nikon. It'll say f/2.8 up close, but in reality you're losing a stop or two of light depending how close you're focusing.

You learn something new everyday

 

[Cagey75]

You learn something new everyday

If you do a search on macro lens stopping down at close focus or something along those lines, you'll get much better explanations In short though, i think the Sigma you tested was probably just fine.

 

[gilbouk]

If you do a search on macro lens stopping down at close focus or something along those lines, you'll get much better explanations In short though, i think the Sigma you tested was probably just fine.

I've arranged to go back to see it - it was a good price too. Thanks for the quick reply - I may have missed it through ignorance had it not been for you!!

 

[Cagey75]

I've arranged to go back to see it - it was a good price too. Thanks for the quick reply - I may have missed it through ignorance had it not been for you!!

Just make sure it will open up to 2.8 for longer distances before you commit

 

[the black fox]

If I recall from when I had sigma macro lenses Keith is 100% right

 

[gilbouk]

Ended up taking it - it was exactly the behaviour it demonstrated - further away it was f2.8 and then upon moving the camera towards a much closer subject the aperture value increased from f2.8 to around f5. Thanks folks

 

[Cagey75]

Glad it worked out for you, good lens the Sigma. I remember being confused by macro lenses when I first started to dabble in macro photography, I was annoyed that they behaved this way, what I thought was the lens force stopping down. But the more I shot macro the more sense it made and I rarely shoot macro below f8-11 now often f16 is required to keep enough in focus. But these lenses also work perfectly fine as portraiture lenses where you can avail of the wider aperture.