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Old Jun 7, 2007, 3:34 PM   #1
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Until I recently posted about what some have called the "focus trap" technique, I had never heard of anything like this. I wish someone told me about it sooner, there's a lot of shots I would have been able to catch with this method.

For anyone who doesn't know what I'm talking about, the "focus trap" technique is where, when using a manual focus lens, you set the camera to auto focus, hold the shutter button down, then adjust the focus. Once the camera sees focus it will automatically snap a shot.

Yesterday I spent about an hour and a half at the Buffalo Marina practicing photographing birds in flight on the seagulls of which there is no shortage. All shots were taken with a K100D using an old Sears 80-200 f/4. I shot JPG for the most part so that I could pull off longer bursts, though for the most part I could have done fine with RAW. I ended up with a few dozen decent shots, so this is a small sample of what I captured.

Here's one of my favorites. This is one of 3 shots I captured in a burst that are all pretty similar and all in good focus.

One thing to be careful of is to not turn the focus ring too fast. The more gradual the adjustment, the better your odds of getting a sharp photo.

This is another of my favorites. A slightly more advanced technique is to get the focus about right, and then set the focus closer and hold down the button while you wait for the subject to get closer. It can be tricky to get the focus right, but if the subject comes into the zone you're more likely to get a few good ones.

An advantage to manually focusing is that you're not likely to accidentally focus on the background.

This shot isn't cropped, it was just that close.

This one had about a third of the height cropped off.

Thanks for looking, and if you're shooting with manual lenses, be sure to give this method a try!
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Old Jun 7, 2007, 3:44 PM   #2
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Real Good shots. Looks like that lens works well for you, together with the focus trap.

I have used that method ever since I accidently discovered it with my first manual lens last year.


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Old Jun 7, 2007, 8:53 PM   #3
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Certainly looks like you are making good use of this feature - I love second one because its so unusual.
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Old Jun 8, 2007, 4:33 AM   #4
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Well I'll be buttered on both sides, have just tried the "focus trap" with my 10d with a Takumar 135 2.5 it works well. This could be a great tip for someone like me who has somthing other than 20 : 20 eye sight.
Thanks Corpsy
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Old Jun 8, 2007, 5:43 AM   #5
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Interesting..... as I was going to say something about this on the other thread.....VERY surprised it worked that well on a moving target at long zoom. (Iwas going to say great for static stuff if you didn't want to split a shallow DOF between two points)

Though you certainly probably didn't get the instant of shot you might have liked (though all quite nice)

You mention burst, so out of how many just out of curiosity? And how many not real acceptable?

Oh and being a M lens not reported in EXIF, so again out of curiosity what was the f/stop and FL mostly? (I know a zoom)
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Old Jun 8, 2007, 8:22 AM   #6
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Excellent captures!! I did not know about the focus trap, till last week. Thanks for posting the technique as well as the excellent results that you got!!

Best regards,

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Old Jun 8, 2007, 12:26 PM   #7
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Great pictures Corpsy. It's interesting to see the different uses each photographer can find for using a focus trap. It's not the final cure all option, but in many cases, it's the best option to get sharp focus. This was a good example of that. Trying to focus on a moving bird is not easy. Good job Corspy- Bruce
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Old Jun 8, 2007, 2:36 PM   #8
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great shots corps

i've tried this with my 500mm but could not get it to work.
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Old Jun 9, 2007, 12:03 AM   #9
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Should work with any MF (A or M/M42) lens and the camera still in AF.
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Old Jun 9, 2007, 5:20 AM   #10
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Hmmmm, I dont think it will work with every manual lens on every model of Pentax DSLR. I can get it to work with an 'A' lens on my *ist DS but not with any other type of manual lens I have. I have seen reference to shorting out the electrical pins to make it work with other lens but although I tried and tried I had no success doing that.
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