Tamron 90mm Di... confused

D_Fivehundred

D_Fivehundred

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Darren
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Just picked up a mint Tamron 90mm Di Macro lens. One thing I've noticed is that although it states it's a f2.8 lens, in low light the widest aperture is maybe f3.5 (aperture mode).

I would have expected to dial in f2.8 and then shutter speed would be whatever was required.

I've tried in manual mode and I get the same effect.

The manual does suggest that this is normal... but then surely it's not a true f2.8 lens... or am i really missing something here (which is probably the case :thinking:).

Perhaps some other users can bring me up to speed on this... :(

Anyway, still a great lens, looking to get some images up soon :D
 
I asked this very question on Tamron and received this reply.

Please see instructions ref Fig 12:

"Where the lens is moved outward to increase the magnification ratio for shooting close-ups, the actual brightness on the film or CCD decreases and the effective F-number changes therefore from f2.8 to f5.6"
 
Does this happen with all macro lenses or just the Tamron? I used to have the Sigma 105 but never noticed if this happened.
 
AFAIK,it happens with all macro lenses.

It was discussed in great technological detail on here last year,can`t find the thread though.
 
I've never noticed this with any of my primes although only two are "macro," Canon 50mm f2.5 and Sigma 150mm f2.8. I've deffo used both wide open and exif shows the wide open setting.

I'll watch out in future.
 
I had the same problem with my Sigma 150 f2.8. Seems that it happens because of "SCIENCE" and is perfectly normal, so don't worry just accept the "SCIENCE". :cuckoo::cuckoo:

Cheers Paul
 
Ok, thanks for the replies... no if this train would just start moving again I could get home and play with the lens some more...!
 
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