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10-06-2014, 10:43 AM   #1
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Manual lens and shake reduction

A trivial question.
When you set the focal lenght of a manual focus, non A, lens, which value you input: exact lenght, shorter or longer? I read somewhere (i remember in pentaxforums) that with pentax Q and manual focus lens, better shake reduction is with lenght different from real lens lenght, i don't remember if shorter or longer.

Is the same with DSRL? Your exeperience?

10-06-2014, 10:55 AM   #2
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The Crop Factor doesn't apply. If it's a 50mm lens, tell the camera it's 50mm.
10-06-2014, 01:11 PM   #3
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QuoteOriginally posted by atar Quote
A trivial question.
When you set the focal lenght of a manual focus, non A, lens, which value you input: exact lenght, shorter or longer? I read somewhere (i remember in pentaxforums) that with pentax Q and manual focus lens, better shake reduction is with lenght different from real lens lenght, i don't remember if shorter or longer.

Is the same with DSRL? Your exeperience?
You input the focal length that's printed on the lens. If it's a zoom lens, however, you can choose to either go with the shortest focal length (set it and forget it, but sub-optimal performance at longer focal lengths), the longest focal length (best if you're always shooting at the long end), the middle (best if you zoom all over the place), or exactly the FL you're currently using (for best performance if you don't mind going into the menu often).

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10-06-2014, 01:37 PM   #4
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The Q thing with the SR tending to be overactive (I have not really tested it enough) doesn't seem to affect the DSLR cameras as I haven't read about it. It wouldn't be surprising as they use different modules for the SR.

10-06-2014, 02:36 PM   #5
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For the 2 manual lenses I use most often on my K-5:

An old 135mm gets set to exactly 135mm. Images are sharp handheld even at slow shutter speeds, confirming that SR is working well.

The K-5 length selection at the wide end jumps from 12mm to 15mm. I use 12mm for the Samyang 14mm. My logic is it's better to undercorrect than overcorrect. Photos look sharp but 14mm is so wide that it is difficult to judge focus and SR. Maybe telling the camera the lens is 15mm instead of 12mm would work better, maybe it wouldn't.
10-06-2014, 02:43 PM   #6
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QuoteOriginally posted by atar Quote
A trivial question.
When you set the focal lenght of a manual focus, non A, lens, which value you input: exact lenght, shorter or longer? I read somewhere (i remember in pentaxforums) that with pentax Q and manual focus lens, better shake reduction is with lenght different from real lens lenght, i don't remember if shorter or longer.

Is the same with DSRL? Your exeperience?
It seems I started that little rumor, so it is best i answer.

I have found that SR for DSLRs is quite good with exact values. ThenQ is a different beast. I usually putn70-90% of the FL on a Q because FOR ME I get best results in this range. For my DSLRs I put the closest value equal or below what the focal length is. If there is an exact match. I use it
10-07-2014, 02:24 AM   #7
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Thank you very much to all.
Normally i use to input the exact focal length, but i was curious to kwon if somebody tried with shorter or longer length to "improve" shake reduction.
10-09-2014, 11:02 PM   #8
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Depending on what I'm shooting, I use the focal length as stated on the lens for my (prime) lenses, for zoom lenses the longest focal length as I'm mostly shooting them at the long end.
Or I just turn of shake reduction and use the rule of s1/focal length (multiply by 1.6 on APS-sensors) and adjust aperture and/or ISO to get a good exposure. If shooting high speed (1/125 or above) in dim-lit situations, this seems the way to go as well (and least I tend to keep more sharp pictures this way).
For what it's worth: as I learned to photograph using film camera's, shake reduction reduction didn't exist so it was up to yourself to shoot longer exposures (than s1/focal length) and maintain a sharp picture by technique (breating, arm/hand position, standing position,...). For more information check this link: Making the Most of Long Exposure Handhelds - Introduction - In-Depth Articles

10-14-2014, 04:37 AM   #9
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QuoteOriginally posted by atar Quote
Thank you very much to all.
Normally i use to input the exact focal length, but i was curious to kwon if somebody tried with shorter or longer length to "improve" shake reduction.
Shake reduction is something that I have always wondered about, in terms of having the ability to to tune it, in the same way that you can tune for example AF.

On the K10 and using tele photos on the K7 I had no reason to question SR, but on the K7 with shorter lenses, and specifically with my tamron. XR di 28-75F2.8 I have issues with some slightly blurred images, which when I shoot flash are perfectly sharp. This suggests that it is not focus but camera shake

With the Q as I tried shooting long lenses, I found that again, I had a lot of not quite sharp shots, even when stopped done and using high shutter speeds (with the pentax K/Q adaptor). High shutter speed should remove shake, and stopping down should remove focusing errors. I thought why not and tried different focal lengths and found that by selecting between 70-80% of the actual focal length! images became much sharper.

I also thought about the way you hold a Q with and without long K mount lenses and it is different. The Q in its own, you hold like a P&S but the body at arms length. Camera shake will largely be the result of vertical or horizontal movement.
Now put a long lens on the adaptor, you don't hold the Q by the body any longer but typically you hold the adaptor, and the shake is nolonger vertical or horizontal movement, but pitch and yaw around the adaptor, or movement at the adaptor, not the camera body itself. I suspect that the result is that the camera may be over sensitive to movement.

You should try yourself if you have a Q. With older MF lenses on a DSLR, I have never had an issue with SR, so I input the correct focal length, but when you consider the Q, we are discussing extremes.

Perhaps I should try my K300/4 plus 1.7x AFA to see if de tuning the SR on my K5 has an improvement.
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