Opticallimits

Hey guys,



in your most updated review of the Tamron 60mm, you wrote that the underexposure problem had been corrected but "There is one exception, though: wide open the lens produces visibly darker images than at any other aperture setting."



What does this mean exactly? Are you saying that the 60mm at F2 is visibly darker than any other lens at F2? or are you saying that the 60mm at F2 is visibly darker than the 60mm at F22?



Also, when you say visibly darker - how much is it underexposing by? a stop? two stops?



Do you know why this is happening? Or do you have a reasonable guess as to what's going on?



Thanks for any help! (I'm sure you're sick to death of hearing about this unusual lens)



-curriguy

Usually, if you set aperture and shutter time to corresponding values, you can expect the final exposure (picture brightness) to be constant. So, if you close the aperture by one stop and double the exposure time, the resulting image should show the same brightness as before.



This is true for the Tamron, also, except for f/2. So, if you go from, say, f/2.8 with 1/125s shutter time to f/2.0 with 1/250s, the f/2 shot is darker than the f/2.8 shot.



[quote name='curriguy' timestamp='1297457039' post='6065']

Also, when you say visibly darker - how much is it underexposing by? a stop? two stops?

[/quote]



Around a half stop, I'd guess. The visible impression is a bit higher, since vignetting also increases at f/2.



[quote name='curriguy' timestamp='1297457039' post='6065']

Do you know why this is happening? Or do you have a reasonable guess as to what's going on?

[/quote]



Sorry, no idea. Except that f/2 might be really f/2 geometrically, but it's obviously not f/2 in terms of transmission.



[quote name='curriguy' timestamp='1297457039' post='6065']

(I'm sure you're sick to death of hearing about this unusual lens)

[/quote]



Not yet <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/wink.gif' class='bbc_emoticon' alt='' /> Apart from this issue, it's actually a nice piece of glass. I still own it, but that's mainly for the upcoming D7000 reviews. I'll probably sell it afterwards.



-- Markus

Thanks for the reply! It really does clarify things - quite an odd outcome.



One final question: A few other lens review sites have mentioned that the Tamron 60mm macro has a 1:1 working distance of approximately 4 inches from the front of the lens -- by comparison lenses like the Nikon 60mm AF-S Micro have a working distance of approximately 2" at 1:1



Is this true in your experience? Or are the reports of the Tamron's unusually high working distance for a 60mm Macro false?



Thanks again