Tokina 12-24: inconsistent exposure


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johnyu

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Nov 4, 2003
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I just realized my Tokina 12-24 showed inconsistent exposure: At the wide-end, it underexposed by about -0.5ev at smaller apertures (e.g. f/16). i.e. If I set it to 12mm, set the camera (D70) to A mode and spot meter, take a shot of a graycard @ f/4 and then take another shot @ f/16, the f/16 shot appears darker and has its histogram peak moved left.

- I don't think it's corner light fall-off. Otherwise, it would've been darker at the wide aperture because of darker corner.

- I went back to the shop from where I bought the lens and tried another sample. Same result.

- I talked to an experienced photographer. He told me it's not uncommon certain lens designs will result in minor inconsistent exposure at different apertures and +/-0.5ev is well within the acceptable tolerance.

- I asked a friend who owns the same lens to try his. His showed inconsistent exposure at the long-end, not the wide-end!

- I went to Tokina Service (i.e. Ricoh) and talked to a technician, the technician reckoned it could be the lens design as it only showed by at certain zoom settings, not all, but so far no customer had report similar problem.

- I asked about this on dpreview.com forum. But only a couple of people said they saw similar behaviour.

So, it's still inconclusive. Not sure it's a sample-to-sample calibration issue or it's a lens design issue affects all lenses. Although 0.5ev is not a huge inconsistency I can't live with, I still want to get rid of it if I can.

Could Tokina 12-24 owners please do some quick tests to see if you see similar behaviour? Thanks.
 

Zerstorer

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Yes, the problem exists. Actually if you observe the histrogram there is a slight progressive darkening of exposure from f4 onwards and its about 0.7EV at f16 or so. It only exists on the 12mm end and not at 24mm.
 

johnyu

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Zerstorer said:
Yes, the problem exists. Actually if you observe the histrogram there is a slight progressive darkening of exposure from f4 onwards and its about 0.7EV at f16 or so. It only exists on the 12mm end and not at 24mm.
Yup, that's exactly what I observed on mine.
 

johnyu

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Being curious, I tried some of my other lenses:

18-70DX: shows also underexposure at the wide-end at small apertures

17-55/2.8DX: shows slight underexposure (less than 0.3ev, I think) at the wide-end at small apertures

80-200/2.8D: interestingly, this lens shows slight overexposure at the long-end at small apertures.

20/2.8: consistent

50/1.8: consistent
 

Zerstorer

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johnyu said:
Being curious, I tried some of my other lenses:

18-70DX: shows also underexposure at the wide-end at small apertures

17-55/2.8DX: shows slight underexposure (less than 0.3ev, I think) at the wide-end at small apertures

80-200/2.8D: interestingly, this lens shows slight overexposure at the long-end at small apertures.

20/2.8: consistent

50/1.8: consistent
My results are slightly different:

17-55 similar magnitude of underexposure as the tokina, about 2/3EV at f16.
85 f1.4 about about 0.3EV drop from 1.4 to 2 and a gradual decrease of about .3EV till f16.

Whether its a function of the lens design? lens manufacturing tolerance? or simply the accuracy/precision of the mechanical aperture lever system in nikon cameras....it remains to be seen.

But it's not as uncommon as originally thought. We've all been living with it for some degree without realizing it that's all.:)
 

johnyu

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Zerstorer said:
85 f1.4 about about 0.3EV drop from 1.4 to 2 and a gradual decrease of about .3EV till f16.
85/1.4... :lovegrin:

Zerstorer said:
But it's not as uncommon as originally thought. We've all been living with it for some degree without realizing it that's all.:)
Well said.
 

pianodancer

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Sep 15, 2003
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Thanks to this post, I did some simple exposure comparison test shots with my recently-acquired Tamron 28-75mm. On first look I found that it is underexposed by 0.5 stops. But when I compared against Nikon 50mm prime, exposure is correct. Thanks to this post, I realised that the Tamron 28-75mm is probably overexposed by 0.5 stops. Is that cool or what?
My review on the Tokina lens here, in brief comparison to Tamron 11-18mm.
 

Zerstorer

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pianodancer said:
Thanks to this post, I realised that the Tamron 28-75mm is probably overexposed by 0.5 stops. Is that cool or what?
My review on the Tokina lens here, in brief comparison to Tamron 11-18mm.
Yes. The tamron is 0.3-0.5EV brighter than some of my nikon lenses when I last compared. You can only tell the difference when you shoot at fixed exposure settings on while swapping lenses in studio. Didn't bother me at all.
 

pianodancer

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Zerstorer said:
Yes. The tamron is 0.3-0.5EV brighter than some of my nikon lenses when I last compared. You can only tell the difference when you shoot at fixed exposure settings on while swapping lenses in studio. Didn't bother me at all.
Thanks for confirming my doubts!
 

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