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Tamron SP 300mm f5.6 questions
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PostPosted: Sun Jun 03, 2018 5:13 pm    Post subject: Tamron SP 300mm f5.6 questions Reply with quote

Hello all,

I recently got on an Adaptall kick and the 135 f2.5 and 200 f3.5 have impressed me enough that I figured I ought to get the 300 5.6 SP as well.... It hasn't worked out quite like I imagined Wink

The lens is in very nice shape, with extremely clean glass (just a few dust specks) and seemingly flawless focus and aperture function.

I'm using these lenses on a Sony a900, so FF and 24MP, a moderately demanding sensor, which can show up shortcomings in glass that smaller sensors might gloss over.

So far, I have had issues with the lens producing drastic overexposure with in-camera (stop-down) metering and have also had very odd results with sharpness being hit-or miss, even when shot off a tripod with mirror lockup. The a900 has a big and acute enough viewfinder that it shouldn't be the issue, especially since I have been hitting critical focus with the 200mm no problem.

Any experienced users of this lens with suggestions on how to get the best out of this lens, or what might be going wrong here?

Thanks!


PostPosted: Wed Jun 13, 2018 7:20 pm    Post subject: Reply with quote

Try again! Smile

Let us know if problems continue.


PostPosted: Wed Jun 13, 2018 8:02 pm    Post subject: Reply with quote

OK, so I am still getting fairly consistent 1 stop overexposures and metering also seems to be a bit fussier with this lens in place than with other long lenses I own (Tamron 200mm, Tamron 200-400, Minolta 100-200, Minolta 100-300 APO, Sigma 300 macro). There doesn't seem to be a problem with the aperture mechanics, and I'm shooting old-school stop-down aperture priority, which yields good exposures on all my other vintage glass.

As far as sharpness, there really seems to be a very narrow window where tack sharp images can be had, even very high shutter speeds often give soft results compared to the other 300mm optics in my collection, whereas hand held shots with the Tamron 200mm f3.5 close focus give excellent sharpness even close to reciprocal value shutter speeds...

If none of you have ever had any of these issues, I'll just have to assume that either this lens hates the a900 or I got a bad copy.


PostPosted: Tue Jul 03, 2018 7:17 am    Post subject: Reply with quote

awa54 wrote:
OK, so I am still getting fairly consistent 1 stop overexposures and metering also seems to be a bit fussier with this lens in place than with other long lenses I own (Tamron 200mm, Tamron 200-400, Minolta 100-200, Minolta 100-300 APO, Sigma 300 macro). There doesn't seem to be a problem with the aperture mechanics, and I'm shooting old-school stop-down aperture priority, which yields good exposures on all my other vintage glass.

As far as sharpness, there really seems to be a very narrow window where tack sharp images can be had, even very high shutter speeds often give soft results compared to the other 300mm optics in my collection, whereas hand held shots with the Tamron 200mm f3.5 close focus give excellent sharpness even close to reciprocal value shutter speeds...

If none of you have ever had any of these issues, I'll just have to assume that either this lens hates the a900 or I got a bad copy.


I realise that my experiences may not apply directly to your camera/lens combinations, but they may give a little food for thought.

I use a few Tamron Adaptall lenses on my Pentaxes and have found that the several slightly differing types of Adaptall and Adaptall-II PK mounts can give differing results on different lenses, the only fully reliable mount for anything other than fully manual metering being the late model mount designed for auto-aperture metering.

Just wondering whether it's a mount/adaptor combination that's causing you problems rather than the lenses themselves.

I don't have the 300mm f/5.6 (unfortunately) but my 135mm f/2.5, 200mm f/3.5, 500mm f/8 mirror (and a few others) can all be encouraged to "behave themselves" when fitted with an Adaptall-II mount that the camera is "happy with".


PostPosted: Tue Jul 03, 2018 12:40 pm    Post subject: Reply with quote

There are no lens to camera interactions with the Adaptall to A-mount interface, so it's strictly stop-down metering.

Since the OP I have had similar issues with several other Adaptall lenses, it seems that there is some sort of optical artifact in these lenses that causes the Sony JPEG engine to over compress dynamic range causing what look like over exposed images. The solution is to turn off DRO and to use a "creative style" that doesn't decrease contrast (I usually use "portrait" which lowers contrast slightly as well as altering color rendering) .

Interestingly, there are a number of Adaptall lenses that cause no issues with these settings and produce JPEGs that reflect the content of the RAW files faithfully, but a few trigger the JPEG engine to make poor processing decisions, leading to the issues I have been experiencing.

The fact that the RAW files don't show any unusual optical flaws, like extreme flare or an obvious sensor to rear element reflection, makes understanding the cause for this quirk even more baffling, despite now knowing how to fix it.