Sigma 150mm f2.8 won't stop down past f6

So do "WE" think it's broken or OK? has anybody tried the same experiment on a Canon?

Cheers Paul
 
The canon mount version stays at f/2.8 no matter what the focus point is.
 
OK, but does the aperture decrease when you look though the lens adjusting the focus from inf to mfd whilst off the camera, if so then that should prove Stewart right that Nikon and Canon meter it differently.
 
diggerz said:
OK, but does the aperture decrease when you look though it when adjusting the focus from inf to mfd whilst off the camera, if so then that should prove Stewart right that Nikon and Canon meter it differently.
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The aperture decreases (diameter) as the lens is focusssed towards MFD. This decrease is there to maintain the same maximum f-stop due to the focal length decreasing.

Surfing around, I found mention on this site that has produced similar results to the ones I obtained with my Canon EF100 macro. My results (as stated earlier) showed the lens to be 98mm at infinity and 79mm at MFD whilst the reviewer here obtained 100mm at infinity and 78mm at MFD. Measurement isn't a precise art and a mm or two is within acceptable tolerance.

I questioned why the aperture can't remain wide open at reduced focal length and result in a faster lens. I suspect that the refraction towards the edges when the internal elements compress would likely cause some longitudinal chromatic aberration.

To sum up, your Sigma 150 isn't behaving as it would on a Canon body so you need another Nikon user to provide the reference.

Bob
 
chimponarope said:
http://www.nikonians.org/forums/dcb...146&page=&topic_id=13313&prev_page=show_topic

There's a whole huge discussion in that thread about it (including the physics behind it) if you have Nikonians access (I just registered for free so I could look again at it).

It appears that canon report the actual lens aperture where as the nikons report the effective aperture.
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In which case that is a brilliant summary of that huge discussion. Thanks for confirming :thumbs:

That's what I thought was happening with the OP, but the test numbers posted don't stack up so I'm confused and still wonder what is happening to the mechanical function of the OP's lens diaphragm.
 
Hoppy, when you say the test numbers don't stack up what would you expect to see? any other tests I can do to confirm that it's working properly or not I would be happy to try because I'm still bemused.

Cheers Paul
 
Pulled out the other thread I linked to, Nikon's own explaination:

http://nikoneurope-en.custhelp.com/app/answers/detail/a_id/13945

Wife got the same explaination when buying her 105VR:

http://www.avforums.com/forums/digi...al-chat/894866-new-macro-lens-d80-normal.html

Diggerz are you sure it's reporting f6 and not f5.6? That would be the 2 stops of light lost at mimimum focussing distance. F6 seems like an awfully funny number for it to be giving, I'm no genius at these things but looking at wiki it's not even 1/3 of a stop.
 
Yes it's definitely f6 but it would appear quite a lot of people have had the same experience as me and we can't all have Joey lenses, can we?

Cheers Paul
 
I shouldn't think so. Any shops near you to go and try out a brand new one on your body just to be sure?
 
There are a couple but one is Jessops and from what I hear Sigma have given them the boot.
 
diggerz said:
There are a couple but one is Jessops and from what I hear Sigma have given them the boot.
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Probably because they kept sending all the 150's back with faulty apertures :shrug:

Bob
 
I have just done the obvious thing and phoned Sigma UK, where a very nice Gentleman confirmed that what was happening to my lens was exactly what should be happening. Apparently it meters the actual aperture (at the request of Nikon) and the closing of the blades as you focus closer is to stop vignetting. So there it is from the Horses mouth so to speak.

Cheers Paul
 
diggerz said:
Hoppy, when you say the test numbers don't stack up what would you expect to see? any other tests I can do to confirm that it's working properly or not I would be happy to try because I'm still bemused.

Cheers Paul
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Glad you have sorted it out Paul :)

But the thing that confused me was your post #38, when the f/number went up, the shutter speed should have got longer :thinking:

And I too was distracted by reference to f/6 which is a strange number. Two stops down from f/2.8 should be f/5.6 and while f/6 is close enough if it was a Canon it would have gone to the nearest 1/3rd stop which is f/6.3. Canons don't do f/6 but that must just be another brand thing. I don't know Nikons very well.

The explanation from Sigma makes perfect sense :thumbs:
 
Sorry Hoppy it should have read 1/8 @ f6. Just had to check it again, no wonder it was confusing you.

Cheers Paul
 
diggerz said:
Sorry Hoppy it should have read 1/8 @ f6. Just had to check it again, no wonder it was confusing you.

Cheers Paul
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Haha! :lol: I did wonder how it could go completely the wrong way :thinking: It all fits now :thumbs: :)
 
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