Tamron 17-50mm 2.8: Missed Focus Woes

[Fluke]

I recently did some publicity stills and behind the scenes stills on a local short film. When I got the call from the producer, the only lenses I had were the 50mm 1.8 II and the crappy kit lens that came with my 400D years back, so I decided it was about time for me to purchase a least a little upgrade. I pulled the trigger on the Tamron 17-50mm 2.8 (without the IS, as it hasn't been released here yet) and set off to work.

At first I started shooting using the viewfinder and AF but, when reviewing the photos of the day, I found I had to cull a good portion of my shots due to missed focus.

Here is one of the stills from Digital Photo Professional with the AF points enabled...

As you can see, the AF system chose to lock onto the kid facing the camera, which is what I wanted it to do. The problem is, the kid's face is not in focus. Instead, to my eyes at least, the back of the kid facing away from the camera is in focus...

Here are some more examples...

However, strangely enough, this didn't happen all the time...

Needless to say, I was a little horrified at the results. For the rest of the shoot I shot in Live View mode with manual focus, using the foucs assist feature. I also found Live View mode helpful for judging 16:9 framing.

I was wondering if this was an error with the lens or if this is a user error... If it happened consistantly, every time, I would have no doubt that it was a manufacture error, but there were some adequate shots - though, I'd say they were probably in the minority - so I don't know what's happening.

Does anyone have any advice, observations or suggestions?

To end on a lighter note, the lens still did a decent enough job when using manual focus...

 

[morgan_moore]

Buy a D3 for stills and 2.8 zooms or faster primes

Seriously those overpriced pro bodies the AF actually works

I have never had a APS chipped digicam that I trusted - stills is my paying day job

Or learn to work within the limit of your toolkit

I think DPreview has many threads on canon AF - maybe you need to 'calibrate' the lens which I think is possible with the 7d

Edit looking at the pics it is consistently front focussing - get calibrating

S

 

[Gene Sung]

I just got the VC version of this lens and it seems to be great. The autofocus is quick and the pics are nice and sharp. The manual focus for video has been good too. Maybe I just got a good one.

I ran this focus test that Stephenmick (Thanks for all the info) passed to me, and this lens checked out.

http://photo.net/learn/focustest

I ran a traditional tape measured focus test from 2,3.5 and 7 feet away (based on the markings), and the lens was off by a few inches. I then read however, that due to the DOF in Canon's cameras, the traditional tape measure method for checking focus isn't accurate. Tamron's tech support said the same thing. They said that if the lens is taking sharp pics, then it's a good lens.

Any thoughts on this? I guess i've always figured the tape/measure method was the best way to check focus (at least on Motion Picture cameras), but maybe it's a sign of the times, and the focus test mentioned above is better approach for DSLRs.

 

[morgan_moore]

With focusing with a tape you need the numbers on the ring to read the right thing

in cine lenses this is critiacal

but with video DSLRs 99% of people are aquiring focus using a monitor and the zoom facility

at that point the numbers dont have to match

Most DSLRs the nubers on the lens are joke because the dont matter..

taking stills in DSLR person aquire focus using either the viewfinder or AF

if the distance from the mirror/af modules from the Ground glass is different from the chip then these cause misfocus

Better DSLRs allow calibration of this using hardware in the camera

the above shots were taken using AF and are front focussed, this may be curable in camera - im not sure if the 7d has focus tuning someone needs to read the manual

S

 

[Fluke]

Okay, a little update.

So I found out how to calibrate lenses through the camera body. The scale runs from -20 to +20. I set up a crude focusing test using a DVD cover and a tripod, focusing on the small print copyright text on the back of the DVD cover.

First, I locked off the camera's position, set the timer to 2 seconds and manually focused using live view and the x10 focus assist to get it as perfect as I could (no small feat as the throw on the Tammy is very short). I then went through the calibrations from 0 to +20, using auto focus to get the sharps.

As suspected, the further through the focus adjustments I went, the clearer the image became. At +20 it is at its sharpest, pretty much to the same clarity as my initial manual focus.

The short film I was shooting stills for had 2 pick up days on the weekend just been, so I took my recalibrated lens out for a real world test. The lens performed much better than last time. At least, I got a far better proportion of usable shots from it. I still wasn't entirely satisfied by its performance, though, but maybe I'm expecting too much from a Tamron.

The lens is now at a point where it is usable and I could most likely get by without sending it in to Tamron to get recalibrated, but should I really settle for having to use a lens that has to be set at +20 to start to get passable results?

 

[Fluke]

And the saga reaches its timely end...

I took the Tammy back to the store to show them the front-focus issues. The guy who served me agreed that the lens was terribly calibrated (he used the word "scary" when he first looked through the viewfinder) and was also suffering from larger than normal amounts of CA that I had not noticed, though I wasn't really looking for it to be honest, as I was so preoccupied by the focus issues.

He said that there was nothing they could do in-store and that I'd best send it to Tamron for recalibration. I was a bit miffed. Thankfully, he was so bemused by the defect, he gave it to someone else working behind the counter to have a look at. This person was equally horrified by the defect but was more helpful. He gave me a store credit refund for the lens (I guess he didn't hear the other guys saying they couldn't refund it!).

This little encounter with third party QC issues has made me decide to splash on a Canon lens, as I don't want to have to go through that again. The two I am tossing up between are the EF-S 17-55mm f/2.8 IS and the EF 24-70mm L f/2.8... and I seriously can't decide.

The 17-55mm is wider and has IS and is (very marginally) cheaper while the 24-70mm has a longer reach and better build quality.

The longer reach is appealing, as I found I spent most my time between 30-50mm on the Tamron and felt like I could do with a little extra push. However, I know how advantageous IS is for video and still (not moving) subjects and, while I tend not to use 17mm, I wonder if I would find myself regretting losing it (you don't know what you've got 'til it's gone, afterall).

Any advice?

 

[b0rderman]

Sorry to bump, but what'd you go with? I am in a similar situation, but haven't had--or owned--the bad experience with the Tamron, although your experience worries me a bit.

I've got the Tokina 11-16 to cover the wide so I don't know what to do...

 

[Fluke]

After trying them both in the store, I ended up going with the 17-55 2.8, but they were both great lenses. There were a few reasons I went for the 17-55mm 2.8, though...

Firstly, I don't have a dedicated wide-angle lens and, before I purchase a wide lens, I'm going to get a telephoto. With that in mind, I don't think the 24-70mm would give me enough wideness on its own. The sensation of 70mm can pretty easily be recreated (or at least, near enough) by taking a few steps forward at 55mm, but the sensation of 17mm compared to 24mm can't be gained by taking a few steps back. It just doesn't have that wide feel.

Secondly, when testing both lenses handheld, side by side, it was clear how much of a difference IS makes to completely barebones handheld video. the 24-70 was microjitter city, while the 17-55 was noticeably smoother and free of microjitters. This may not be a concern if you can always use a weighted shoulder rig, though, but that's not always an option for me.

Thirdly, and lastly, the 24-70 is damn heavy! They call that thing "the brick" for a reason. This is mostly down to the increased size and sturdier construction. The construction and weather-proofing was certainly appealing but, in the end, I decided it wasn't as important to me as a more useful range and IS. When Canon talk about "weather-sealing" they don't mean your everyday weather; they mean extreme weather - blizzards, sandstorms, sea-spray, mud flats and the like. I figured I wouldn't be facing any of those conditions any time soon, so I didn't really need the L quality weather sealing. The 17-55 is well built and, while it's not "L quality" in construction, it's built more than well enough that I don't have any hesitations putting this lens to work.

So, yeah, that was my thinking. I haven't had a chance to put it through its paces in a "professional" situation yet, but I've been more than impressed with the snaps/videos I've taken so far. I have another short film photography job coming up in a few weeks and it will no doubt get some serious use for that.

I hope that helped in some way.

 

[b0rderman]

thanks for your thoughts