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Shooting f/2.8 with Tamron 17-50mm and Focusing Problems - Lens Problem?
I just got a Canon 40D and also bought the Tamron 17-50mm 2.8 lens to go along with my 28-135mm IS kit lens. I have been experimenting with shooting at f/2.8 with varying focal lenghts on my Tamron and find that I have trouble getting in focus shots at 50mm (long end of the Tamron). I understand that DOF is affected by wider apertures and that increasing focal lengths at f/2.8 for example will really make the DOF shallow. I was experimenting with portrait shots and found of the 30 or so shots I took only maybe 2-3 were sharp enough for me and the rest were were softer than I liked. I had sufficient lighting and shot no slower than 1/30s but even my outdoor 1/640s shutter speed shots were not that sharp. It wasn't until I stopped down to f/4 that the focus was to my liking.

How far does the subject have to be at f/2.8 and 50mm to get a reasonably sharp picture?..

Comments (6)

You need to read up on depth of field. The more open the lens, the shallower the DOF. In a portrait, it is possible to have the eyes in focus and the nose and ears out of focus. If you stop the lens down, more of the subject will come into focus..

Put several objects on a table about 2 inches apart going from front to back. Focus on the center object and shoot images at several f-stops. Look at the images. That is how it works...

Comment #1

I understand there is a shallow depth of field. I used a DOF calculator and according to my measurements at my aperture, focal length, and distance I am suppose to have 0.1M of in focus, that is not a lot to work with however shouldn't I see 0.1M in focus? In my case not even the 0.1M was in focus (the eyes I focused on using center point focusing). Everything was soft including the eyes. Just wondering what I did wrong or if my lens is bad. Maybe I'm too close to the subject?..

Comment #2

It is possible that you or the subject moved slightly (a few cm would be enough)..

Do what the previous poster said, and put the camera on a tripod so that when you have locked the centre focus point (disable the others) on one of the objects on the table there is no possibility of anything moving. If an object in front of / behind the object you focussed on is sharper than the one you focussed on, there is a technical fault and you can get it sorted out under warranty..

Best wishesMike..

Comment #3

I had the 28-75 f/2.8 for "X"-Canon Xti....

It was soft until f/4 by a test on a large vinyl sign I photographed from about 100 feet away at all "Numbered" FL on the barrel. (28, 35, 50, 75)..And at f/2.8, 3.2, 4, 4.5, 5, 5.6, 7.1, 8...At f/4 at all FLs, the Sharpness and Contrast were great...But at F/2.8 and F/3.2 it was lower than it should be a top tier lens....

I sent it back with a set of 4x6 photos for f/2.8 and f/3.2 and f/4 at the 4 marked FLs on the barrel..And asked Tamron NJ to check and see if the lens was within their specs... It was out...not by much...And They did fix it and I had it within 20 days round trip. It performed at f/2.8 performed like f4...I was happy..

You have to Print a Form from the Tamron website for a warranty repair or adjustment..and send it back with that form and lens..

Tamron has very few QC issues, and they will take care of it. quickly. They will accept a delivery that needs a signature to be released from the Mail service you choose..

Good luckIt is a sweet lens...Sorry you may have one that needs adj..

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What I shoot with - in Profile.Arbib..

Comment #4

Ok after a lot of experimenting with my lens over the weekend I finally realized that the problem is front-focus! I lined up a bunch of batteries and set my lens at 50mm about 1 foot away from the target battery using center AF and f/2.8 (according to DOF calculations I have about 0.1M of focus). Well to my surprise it was actually the battery just in front closer to me that was sharper. This test was repeated several times. I tried my 28-135mm IS kit lens and didn't see this problem although the widest on that lens is f/3.5 but the focus target was ok on this lens so I figured it wasn't the body. I then tried manual focusing with the Tamron and voila, the focus target was now in focus. So something is up with the AutoFocus on the Tamron, I just got an RMA for this lens so will ship it out today and hopefully get a better copy...

Comment #5

Most likely, they will "Re-Adjust" the lens/chip, and you will be totaly amased when it comes back...It will even beter in MF too..

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What I shoot with - in Profile.Arbib..

Comment #6

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This question was taken from a support group/message board and re-posted here so others can learn from it.

 

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