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09-25-2013, 08:57 PM   #1
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Not what I expected
Lens: 70-200 F2.8 Tamron Camera: K-30 Photo Location: Minnesota ISO: 400 Shutter Speed: 1/4000s Aperture: F2.8 

So I went to the store I purchased my K-30 from and they had a referb Tamron 70-200 F2.8 on sale. I want this lens to shot indoor hockey. The store was kind enough to let me take it out side with my K-30 and shoot at moving cars. This is one of the photos I took. I expected that with this lens all the way open at F2.8 I would get a very shallow depth of field As you can see from the image that is not what I got. This is the discription of the lense from B& H Tamron 70-200 F/2.8 Di LD (IF) Macro AF lens for Pentax AF. I was zoomed out to 200 MM. I'm a serious nubie at DSLR so any advice would be appreciated.

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09-25-2013, 09:12 PM   #2
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At long distance you will not get so "very shallow" depth of focus. You will notice it more at closer distances. I love mine :-)
09-25-2013, 09:21 PM   #3
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As stated above at that distance the DOF will be what you see here. Several feet worth . If focused on something closer it would be more apparent. In this example the foreground is soft as is the background. If the subject was the car the focus was missed. The car is soft too, the grass behind it is the sharpest part of the image.
09-26-2013, 01:43 AM   #4
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At guess the distance to your subject was in the order of 40 metres. Just a guess mind you. But at that distance the depth of field from a 200mm lens on a Pentax DSLR at f2.8 is some 4.5 metres. At f1.2 (if you can get such a lens) it is just under 2 metres. Also bear in mind there is not a sharp cutoff from sharp focus to total out of focus. It is a gradual transition.

There is an online Dof calculator here that may assist. Online Depth of Field Calculator

09-26-2013, 05:11 AM   #5
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Using something like DOFmaster's calculation tool, you see that focusing on a subject at 250 feet with a 200mm lens at f2,8, your DOF will be about 55 feet deep.

However, focus on something 100 feet away and your DOF becomes 8.5 feet deep. At 70 feet it is 4 feet deep. At 30 feet it is 0.75 feet deep... So there you are
09-26-2013, 06:08 PM   #6
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Thanks for the info everyone. When using a lens like this and shooting at a moving subject what focus setting would you use. The attached photo was not the only focus point I missed. Almost all of them were focused behind the intended target. When I shooting with my Sigma 28-200 (this is a 10year old lens I purchased for my zx-7) at my children's soccer games I'm shooting in Continuous with 11 point. In most of these shots I set the camera to AV and opened the lens all the way up. If I'm going to spend this much money on glass I would like to know why I'm missing the focus and what I can do to get it to work the way i want it. Also any opinions on this lens compared to the Sigma with the HSM. I played around with a Sony A77 with the Tamron lens that has the USD motor and it seemed to focus a lot faster. When I set up that camera I used a single dot for my focus but i was not tracking moving targets. I've attached two more photos one that I think is in focus and one that is way out. I don't know how you miss focus on something as big as a truck but I'm pretty sure it was something I did not the camera or lens.
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09-27-2013, 03:25 AM   #7
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The truck looks like the focus is behind it.

Had you focussed on the truck when it was further away slightly, but not pressed the shutter until it had moved closer?


Car/motorsport photography I would suggest using single centre point AF, and focussing on the section of bitumen where you want the car, follow the car with the camera and press the shutter as you reach the point you focussed on earlier.

For the kids soccer matches it might be a bit harder since they aren't as predictable.



Ideally I'd suggest using manual focus.
With practice a person can manually focus much faster than pretty much every AF system.
09-27-2013, 04:51 AM   #8
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QuoteOriginally posted by munch008 Quote
If I'm going to spend this much money on glass I would like to know why I'm missing the focus and what I can do to get it to work the way i want it.
Your older lens's depth of field is so hugely wider that everything will look in focus most of the time

QuoteOriginally posted by munch008 Quote
Also any opinions on this lens compared to the Sigma with the HSM
I suggest reading the lens review database.

09-28-2013, 07:52 AM   #9
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Lens itself may also be back focussing when matched with your camera and needs to have focus adjustment applied via the camera menu.
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