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04-27-2009, 09:52 AM   #1
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Manual lens focal length for shake reduction

When setting up a manual lens, should the number entered be the actual focal length or the effective length adjusted for sensor size?

Thanks

Debi

04-27-2009, 09:58 AM   #2
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The actual focal length. The focal length corresponds with the distance register from the focus plane. This is always constant. 50mm lens is a 50mm lens on a FF Film camera and a APS-C digital camera.
04-27-2009, 11:00 PM   #3
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QuoteOriginally posted by MrApollinax Quote
The actual focal length. The focal length corresponds with the distance register from the focus plane. This is always constant. 50mm lens is a 50mm lens on a FF Film camera and a APS-C digital camera.
What about with a TC?
04-27-2009, 11:04 PM   #4
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You should multiply it with the TC's magnification.

04-27-2009, 11:12 PM   #5
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QuoteOriginally posted by StarDust Quote
You should multiply it with the TC's magnification.
Thanks StarDust!

That is what I thought.
04-28-2009, 12:30 AM   #6
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With- and without TC I was already using actual focal lenth. Thanks for confirming. What about macro extension tubes though? Does one add the length of the tube (e.a. 12mm, 20mm etc.) to the focal length of the lens or....??
04-28-2009, 12:55 AM   #7
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QuoteOriginally posted by newmikey Quote
With- and without TC I was already using actual focal lenth. Thanks for confirming. What about macro extension tubes though? Does one add the length of the tube (e.a. 12mm, 20mm etc.) to the focal length of the lens or....??
One turns off SR and uses a tripod for macro....
04-28-2009, 03:15 AM   #8
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From the K100D manual (presumably this applies to other models as well):

"The Shake Reduction function may not fully reduce camera shake when taking close-up shots. In this case, it is recommended that the Shake Reduction function be turned off and the camera be used with a tripod."

I know it's a geeky thing to do, but it's amazing what one can learn by reading the manual.

04-28-2009, 03:57 AM   #9
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For "regular" macro shots with a handheld macro lens, (Tamron 90mm etc) I leave SR on. I've tried it both on and off and found a slight benefit with it on. For tripod shots of course turn it off. The only time I use extension tubes is in conjuction with a macro lens and tripod is absolutely necessary for that combo.

NaCl(macro is fun)H2O
04-28-2009, 11:42 AM   #10
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Extension tubes don't change focal length - they only change the focus distance. So in theory, no adjstment to SR focal length needed. But as noted in the manual, SR doesn't work that well when dealing with very close focus. Not sure why, but I've seen this myself, too.
04-28-2009, 02:12 PM   #11
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I don't know how extension tubes work but I'm guessing they zoom in without changing the focal length, somewhat like the APS-C sensor does compared with 35 mm. That would mean that you would have to increase the SR.

Just a guess.
04-28-2009, 04:47 PM   #12
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No, all they do is allow you to focus closer than the lens normally can. So they change neither focal length nor field of view; the "crop factor" changes FOV (comparing 35mm and APS-C) and thus provides the illusion of having changed focal length.
04-28-2009, 07:16 PM   #13
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QuoteOriginally posted by Marc Sabatella Quote
But as noted in the manual, SR doesn't work that well when dealing with very close focus. Not sure why, but I've seen this myself, too.
I think it would have to do with SR not being quick enough to compensate over such a short distance, speed of light and all that. But I am just guessing here.
04-28-2009, 10:18 PM   #14
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QuoteOriginally posted by Marc Sabatella Quote
Extension tubes don't change focal length - they only change the focus distance. So in theory, no adjstment to SR focal length needed. But as noted in the manual, SR doesn't work that well when dealing with very close focus. Not sure why, but I've seen this myself, too.
I believe that the close focus problem is the same as the long lens problem that caused SR to be invented. It is the angular motion of the subject that the camera has to offset. Some mathematical genius can probably give us a formula like those that come for exposure at extreme extension.
05-05-2009, 08:34 AM   #15
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QuoteOriginally posted by Canada_Rockies Quote
I believe that the close focus problem is the same as the long lens problem that caused SR to be invented. It is the angular motion of the subject that the camera has to offset. Some mathematical genius can probably give us a formula like those that come for exposure at extreme extension.
The optical "lever arm" that sweeps the image across the sensor during angular motion of the camera is the lens-sensor distance.

The relationship is:
Lens_sensor_distance=Focal_length(1+magnification)

For regular photography magnification is very small and can be ignored, but for macro photography it should be accounted for.

A 1:1 macro with a 50mm lens would have a "shake reduction focal length" of 50(1+1)=100mm.

Iowa Dave

PS Shake reduction will help with side-side camera shake, but not with in-out shake. In-out shake is important for macros because depth of field is small.
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