Tamron Focus issues
This was posted by 9000AF on Dixum but I doubt he will mind me reproducing it here. As there are several users of these lenses here I thought it was of particular interest especially as I have been critical of the slow AF of the 70-200mm in the past, although it still may not address the issues of low light focusing (not limited to Sony models).
I have run some unscientific tests with my Tamron 70-200mm f2.8 and Tamron 90mm f2.8 on the A500 before selling the A700. Those 2 lenses were my worst AF performers on the A700 and A300. I focused on vertical wood blinds and between them into my back yard from different distances to get AF to hunt. The A700 went the wrong way reliably every time while the A500 got the blind or the trees in my back yard in focus pretty much dead on with no hunting.
The A700 AF system only seemed to benefit from a higher torque motor than the A300 with otherwise unchanged algorithms and the same tendency to run all the way to the near focus end stop and then go back for strong defocus. The A500 does indeed behave differently, almost never hitting the near end stop, finding focus very quickly. So hunting is thankfully much reduced. Tracking seems to be about the same for the A500 as the A700. Under most practical circumstances the A500 AF system beats the A700 IMO.
My complaints about the Tamron 70-200 hunting are pretty much gone. The lens is just about perfect now.
It's good to know that Sony are not sitting still and have improved the AF algorithm in the A500/550 (presumably the A4xx as well) and it bodes well for the A7xx replacement although I'll be disappointed if there isn't a new AF module as well as software enhancement.
I wonder what AF setting he had the camera on. I have experienced the Tammy 70-200 hunting back and forth in indoors and low-light situations when the camera is set to wide focus area, somewhat better performance when set to local focus and pretty darn fast when set to spot focus. The times I had to switch to manual focus because the auto focus just couldn't get there has been limited to night pictures where the scene has very few discernable objects for the camera to focus on (e.g. alot of black areas).
Now, I will say that my Sony 50mm f/1.4 has virtually no problem focusing in similar settings and doing so quickly. But then again, that is a prime lens and it's usually wide open in those settings.
What would be really interesting to see is a comparison made between say the Tamron 70-200 f/2.8, the Sigma 70-200 f/2.8 and the Sony 70-200 f/2.8. Now, I'm sure the Sony with its SSM would probably blow the others away in AF speed, but that's at about double the cost ($1,799 at B&H) as compared to the Tamron ($730 at B&H) and Sigma ($799).
Zooms: Tamron SP AF70-200mm f2.8 Di LD Macro; Sigma 28-90mm D macro, Konica-Minolta 18-70 f3.5-5.6
Primes: Minolta 28mm f2.8; Sony 50mm f1.4
Minolta RC-1000 remote commander
Calumet Cambo CC400 4x5 View Camera
YashikaMat 6x6 TLR
Minolta Maxxum 7000
w/ Minolta 35-80mm f/4-5.6 & Minolta 2800 flash
Minolta Maxxum 5000i
& Vivitar 728 AFM flash
I think it's clear he was using spot focus otherwise it would always focus on the blind. The Tamron has always had issues acquiring focus in low light and it's a given(!!) that spot focus with it's extra 2.8 assist does a better job. The thread the text comes from was discussing the propensity of the A7/900 not to choose the correct direction to move when first acquiring focus thus causing the lens to hunt and waste time. This also happens with the Sony 70-210mm but it seems to have less difficulty in low light situations than the Tamron. It's clear from his test comparing the A500/A700 that the A500 shows an improved algorithm in the initial movement.
Originally Posted by DWessel
The test you propose would definitely be of interest but I'm not sure that "the Sony with its SSM would probably blow the others away in AF speed" in that SSM is not intrinsically faster. Certainly my 80-200 HSM with screw drive leaves my 70-300 G SSM behind.
It's never been a stellar focusing lens
Great optics at a great price, this lens has always been known for it's poor AF performance. From DPReview:
The big problem with this lens, however, lies in the focusing systems. The autofocus motor is relatively slow and noisy, which puts it at a major disadvantage compared to its ultrasonic motor-equipped competitors, simply because AF performance impacts strongly on many of the typical uses for a fast telezoom lens. The slow speed of the motor means focus tracking simply isn't fast enough for sports or action, or even children running around playing; it's also a distinct problem in low light or with low-contrast subjects, where the lens can take what feels like an eternity to achieve focus. This is compounded by the noise the motor makes, which could be a real problem in situations such as wedding or event photography for which the user wishes to remain unobtrusive; discrete it is not. Also the Tamron lacks a focus limiter switch, so has a tendency to hunt back and forwards through its entire range when it fails to lock focus first time. But perhaps the biggest problem we encountered was a tendency for the lens to mis-focus, seemingly at random and disturbingly frequently, such that F2.8 shots in particular were often not critically sharp (although it must be pointed out that this may be specific to either our test sample, or the Canon mount version).
A good photograph is knowing where to stand.
Rule books are paper, they will not cushion a sudden meeting of stone and metal.
Ernest K. Gann-Fate is the Hunter.
Yes but the motor only appears on the Nikon and Canon mounts, on the Sony mount it uses the camera screw drive. It probably uses the same gearing as the CaNikon, however, and the mis-focus seems to be a common denominator.