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08-24-2009, 01:58 PM   #1
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Takumar 200mm F3.5 question

I while ago I used this lens at my sons soccer game, and I got favorable result considering it was my first time shooting a soccer game. I've tried a couple times after the initial go at it, and results were poor. My shutter speed was plenty fast, but I just couldn't get a sharp shot. Unfortunately I don't remember the setting from the first round, so I can't duplicate the set up. I'm thinking that it's due to DOF. I was basically shooting at F4. I guess the main question is, if I'm shooting kids that are about 4' tall, and I'm getting them in the full frame, how small / large would my DOF be at F4? I'm thinking maybe I should be using F8, but I'm worried about losing to much shutter speed. (Not at 8 year old kids are running at mach 1) Any opinions?

08-24-2009, 02:21 PM   #2
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Samples... I would say it was my focusing, but first round, 90% were sharp, other rounds, lucky to get any sharp. I can't imagine I was that badly off on my other attempts, that's why I suspect it's DOF related.

1. First time round of pictures. I was happy with them for first time out.



2. My last attempt.

08-24-2009, 02:48 PM   #3
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I have that lens and I love it -- it gives terrific results when you get the focus right! I think you are correct that you just had a bad-focus-day, as it doesn't look like motion blur to me.

Here's my back-of-the-envelope calculation:

Diagonal field of view on APS-C is 2 * arctan (14.2mm / focal length ). Plugging in 200mm gives you a *diagonal* field of view of approximately 8 degrees.

That second shot of yours (assuming it's not a crop) shows the subject size to be, well, let's say 5/8 of the length of the diagonal of the frame. I just eyeballed it. So your subject subtends about a 5 degree arc, more or less.

The distance to your subject, then, assuming a four foot height is 4 ft / tan (5 degrees), or about 46 ft.

Plug that configuration into DOFMaster:

Online Depth of Field Calculator

And you get a DOF of about 2.5 feet at f/4 with a 200mm lens. That ain't much.

It's a little bit hard to tell from that photo, but it appears that the grass is a little sharper right against the bottom of the frame. So my guess is you front-focused a bit.

And this concludes my wholly unauthoritative analysis.

Practice, practice, practice. Personally, my manual focus technique stinks, but it's getting better.

---

EDIT: Gah! My math is wrong! Distance to a frame-centered subject is actually 2 ft / Tan (2.5 degrees), but that's still 46 feet! Stupid envelope!

Last edited by Quicksand; 08-24-2009 at 03:01 PM.
08-24-2009, 03:16 PM   #4
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Thanks for the reply. I noticed that it appeared as that one was front focused as well. I looked at some of the others, and pictures that have kids spread out over the area of the shot, still had some unsharpness. (is that a word? ) Definitely not as sharp as my first go. 1.5 feet is definitely not that much to work with when kids are running. I must have been using a F8 on the first round. That's the only logical conclusion I can come to.

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