[mst]

Remember the exposure issue of the Tamron Di 60? Well, it seems we have another one ...



I've been shooting in the field with both the Nikon 70-300 VR and the Tamron 70-300 VC for a few days. Some of the Tamron shots looked rather fishy to me, they were a bit bright. A lot brighter than what the Nikon delivered in the same situations.



I did some tests with both lenses yesterday and this is what I got:







Left column is what the camera metered with the 70-300 VR (tried three copies, consistent results here). The center column is the 70-300 VC, manually set to the same exposure. As you can see, the results a very similar except stopped down at 70mm, where the Tamron either has higher transmission (unlikely IMO) or just does not set the aperture correctly (I did all these shots 10 times, so the possible variation in exposure due to the mechanical aperture lever is already ruled out).



The right columns shows what the camera metered with the 70-300 VC. Especially at lower focal lengths, the metering is way off. This matches what I saw in the field.



Currently, I have only one copy of the Tamron 70-300 VC. I'll try to find out if this is an issue of my copy only or a general issue of the lens (or more precisely the F-mount variant). Any help in this regard by owners of the lens is highly appreciated.



-- Markus

[Klaus]

Even though I'm repeating myself - a mechanically controlled aperture sucks.

[mst]

[quote name='Klaus' timestamp='1284624710' post='2823']

Even though I'm repeating myself - a mechanically controlled aperture sucks.

[/quote]



Yes, it's not that precise. However it works well enough for me in the field and in addition it's not the issue here. Plus: it doesn't explain the metering errors, which are done with wide open aperture.



-- Markus

[wim]

[quote name='mst' timestamp='1284625227' post='2824']

Yes, it's not that precise. However it works well enough for me in the field and in addition it's not the issue here. Plus: it doesn't explain the metering errors, which are done with wide open aperture.



-- Markus

[/quote]

Actually, it does. It means that the mechanical control is not very good, that's all, not even for wide open at different FLs.



Kind regards, Wim

[mst]

[quote name='wim' timestamp='1284627904' post='2826']

Actually, it does. It means that the mechanical control is not very good, that's all, not even for wide open at different FLs.

[/quote]



Sorry, no, it doesn't. The mechanical lever pulls the aperture wide open when mounted to the camera, regardless of the focal length (and of course I checked that visually, too). Works with almost any lens I have, only two exceptions: the Tamron Di 60 (currently at Tamron Europe again) and now the 70-300 VC.



And even if the lever was the reason: since the lever is not moved during exposure for wide open shots, the metering should at least be correct in this case.



Edit: actually, the metering should be correct in any case. Moving the lever to stop down might lead to under- or overexposed shots (see 70mm/f8 above), but the metered values should be correct. Unfortunately, they are not.



Another Edit: forgot one lens, that has expsoure issues on Nikon, too: the Voigtländer 20 SL II.



-- Markus

[joachim]

[quote name='mst' timestamp='1284624109' post='2821']

Remember the exposure issue of the Tamron Di 60? Well, it seems we have another one ...



I've been shooting in the field with both the Nikon 70-300 VR and the Tamron 70-300 VC for a few days. Some of the Tamron shots looked rather fishy to me, they were a bit bright. A lot brighter than what the Nikon delivered in the same situations.



I did some tests with both lenses yesterday and this is what I got:







Left column is what the camera metered with the 70-300 VR (tried three copies, consistent results here). The center column is the 70-300 VC, manually set to the same exposure. As you can see, the results a very similar except stopped down at 70mm, where the Tamron either has higher transmission (unlikely IMO) or just does not set the aperture correctly (I did all these shots 10 times, so the possible variation in exposure due to the mechanical aperture lever is already ruled out).



The right columns shows what the camera metered with the 70-300 VC. Especially at lower focal lengths, the metering is way off. This matches what I saw in the field.



Currently, I have only one copy of the Tamron 70-300 VC. I'll try to find out if this is an issue of my copy only or a general issue of the lens (or more precisely the F-mount variant). Any help in this regard by owners of the lens is highly appreciated.



-- Markus

[/quote]





Did you try different bodies? I mean radically different, e.g. D3000 and D3. Collimation effects in the light path (including mirror, prism, screen,...) from the lens to the exposure meter can have a lot of effect on the metering. With my 1976 Minolta XE-1 I have to dial in exposure correction for WA (brighter) and for telelenses (darker) to get decent metering. The 50mm lens is spot on. All lenses are genuine Minolta MD. This matches what I see in the finder: the WA is darker the telephoto is brighter. Over the years I saw similar reports from other people.



I understand modern CPU lenses transmit data to the camera how to compensate for this. I see no reason why one set of data should fit all bodies (different prism, different screen, different exposure metering element). If Tamron doesn't understand (reads: license) the genuine Nikon protocol but reverse engineers the thing, that data could easily be fine on one body and messed up on a different one.



Just an idea. From your reports on the 60/2 it seems that Tamron doesn't understand what they are doing.

[mst]

[quote name='joachim' timestamp='1284650064' post='2845']

Did you try different bodies?[/quote]



Not yet, but I will. I also posted this in two German forums with the intention to find out if this is an issue of my lens only or a general issue.



The underexposure of the Di 60 was independent of the camera used (tried several).



[quote name='joachim' timestamp='1284650064' post='2845']

Just an idea. From your reports on the 60/2 it seems that Tamron doesn't understand what they are doing.

[/quote]



Well, maybe they (finally) do. There have been reports of Di 60 lenses which no longer show underexposure, either purchased new just recently or repaired by Tamron. That's why I just sent mine in again.



-- Markus

[Bare]

[quote name='Klaus' timestamp='1284624710' post='2823']

Even though I'm repeating myself - a mechanically controlled aperture sucks.

[/quote]



I must disagree because many Canon failures are conected to electonic controled aperturture and was verry often in the '90-is.

[Klaus]

[quote name='Bare' timestamp='1284662980' post='2851']

I must disagree because many Canon failures are conected to electonic controled aperturture and was verry often in the '90-is.

[/quote]



I was referring to the exposure accuracy not reliability.

Canon & Olympus have both an electronically controlled aperture and they are, by quite a margin, the most accurate here.

Actually I've never experienced a failure here anyway throughout the years.

[Brightcolours]

[quote name='Klaus' timestamp='1284666808' post='2855']

I was referring to the exposure accuracy not reliability.

Canon & Olympus have both an electronically controlled aperture and they are, by quite a margin, the most accurate here.

Actually I've never experienced a failure here anyway throughout the years.

[/quote]

I have, with the Tokina 12-24mm f4. But that hardly has to do with the fact that Canon implemented electronically controlled apertures, it is a systematic fault from that particular Tokina model.