Shake reduction and focal length


Froggy

Link Posted 01/10/2011 - 21:48
If,say, I put a 50mm A series lense on my K5 and I input the focal length for the purposes of shake reduction, what do I input? Should it be 50mm or the digital sensor equivalent of 75mm?

davidstorm

Link Posted 01/10/2011 - 22:02
That's a very good question. I haven't got a clue.

Regards
David
Flickr

Nicola's Apartments, Kassiopi, Corfu

Some cameras, some lenses, some bits 'n' bobs

ChrisA

Link Posted 01/10/2011 - 22:02
Froggy wrote:
If,say, I put a 50mm A series lense on my K5 and I input the focal length for the purposes of shake reduction, what do I input? Should it be 50mm or the digital sensor equivalent of 75mm?

50mm.

Always the actual focal length.

The focal length of a lens doesn't change just because the sensor happens to crop a smaller rectangle out of the image circle than a 35mm negative does.

Think about the amount the image moves because of the shake. The size of the sensor doesn't affect it, so the amount the sensor needs to be moved to compensate is not related to its size.
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Pentax K-3, DA18-135, DA35 F2.4, DA17-70, DA55-300, FA28-200, A50 F1.7, A100 F4 Macro, A400 F5.6, Sigma 10-20 EXDC, 50-500 F4.5-6.3 APO DG OS Samsung flash SEF-54PZF(x2)
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Last Edited by ChrisA on 01/10/2011 - 22:05

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davidstorm

Link Posted 01/10/2011 - 22:09
How does this change when you add Extension Tubes or a Teleconverter? I was using a 135mm SMC Takumar (M42 with adaptor) coupled to 68mm of Extension Tubes. What focal length should be input for this? It's still a 135mm lens, but is now 68mm further from the sensor. This must surely affect the calculation?

Regards
David
Flickr

Nicola's Apartments, Kassiopi, Corfu

Some cameras, some lenses, some bits 'n' bobs

sterretje

Link Posted 02/10/2011 - 05:56
Froggy wrote:
If,say, I put a 50mm A series lense on my K5 and I input the focal length for the purposes of shake reduction, what do I input? Should it be 50mm or the digital sensor equivalent of 75mm?

Focal length is focal length; it does not change when you put it on an APSc camera
Pentax K10D + Vivitar 55/2.8 macro + Super Takumar 55/1.8 + SuperMultiCoated Takumar 85/1.8 + SuperMultiCoated Takumar 135/3.5 + SuperMultiCoated Takumar 200/4 + Super Takumar 300/4
Pentax K100D + DA18-55ALII + DA55-300
Pentax K5 + FA31Ltd + M50/1.7 + DFA100WR + M120/2.8 (+ DA18-55WR at occasion)

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sterretje

Link Posted 02/10/2011 - 06:08
davidstorm wrote:
How does this change when you add Extension Tubes or a Teleconverter? I was using a 135mm SMC Takumar (M42 with adaptor) coupled to 68mm of Extension Tubes. What focal length should be input for this? It's still a 135mm lens, but is now 68mm further from the sensor. This must surely affect the calculation?

Regards
David

One post I found in http://www.flickr.com/groups/closer_and_closer/discuss/72157604389806550/ clearly states that focal length does not change with extension tubes. You might want to do some more research to get this confirmed by a second source (I don't have the knowledge about this).

I do think that the point is not really relevant because you more than likely use a tripod and have SR switched of in that case
Pentax K10D + Vivitar 55/2.8 macro + Super Takumar 55/1.8 + SuperMultiCoated Takumar 85/1.8 + SuperMultiCoated Takumar 135/3.5 + SuperMultiCoated Takumar 200/4 + Super Takumar 300/4
Pentax K100D + DA18-55ALII + DA55-300
Pentax K5 + FA31Ltd + M50/1.7 + DFA100WR + M120/2.8 (+ DA18-55WR at occasion)

dcweather

Link Posted 02/10/2011 - 21:36
But surely the SR requires a focal length input only to calculate the approx magnification and hence the shake? This would be more with extension tubes, teleconverters etc so why isn't more SR needed in the algorithm calculation when they are added?
Dave

Mike-P

Link Posted 02/10/2011 - 21:56
I always dial in 500mm when I use the A* 300mm f2.8 and Pentax 1.7x teleconverter (hand held). With extension tubes I use the lens focal length.
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Last Edited by Mike-P on 02/10/2011 - 21:57

Charlotte

Link Posted 02/10/2011 - 22:01
I also use the lens focal length with extension tubes, with the 2 x converter 2 x lens focal length and 3 x converter 3 x lens focal length.
Pentax Photo Gallery
Photography blog

ChrisA

Link Posted 02/10/2011 - 22:59
dcweather wrote:
But surely the SR requires a focal length input only to calculate the approx magnification and hence the shake? This would be more with extension tubes, teleconverters etc so why isn't more SR needed in the algorithm calculation when they are added?

For teleconverters, yes, more SR is needed, since they make the lens magnify more. For extension tubes, no, more is not needed, since they don't.

The thing is, if you use a longer focal length lens (or a teleconverter, which amounts to the same thing), you get extra magnification at the same distance from the subject.

If you use extension tubes, the only reason you get extra magnification is because you move the camera closer to the subject. Focusing is the moving of the lens along its axis towards or away from where you want the image to be in focus. Extension tubes do nothing except help you move the lens further away.

It's the same with macro lenses - they're macro lenses because they allow close focusing, not because they have a different focal length than a non-macro lens.

You dial in more SR with longer focal length lenses because they magnify more than shorter focal length lenses. So for a given angular displacement of the camera (read shake), the image on the sensor moves more than with the shorter lens, and hence needs more correction.

The lens with an extension tube is not magnifying more in the same sense. The image is bigger only because you're closer - there's no extra magnification. So for a given angular displacement, the amount the image moves is the same, so needs the same correction.
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Pentax K-3, DA18-135, DA35 F2.4, DA17-70, DA55-300, FA28-200, A50 F1.7, A100 F4 Macro, A400 F5.6, Sigma 10-20 EXDC, 50-500 F4.5-6.3 APO DG OS Samsung flash SEF-54PZF(x2)
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Last Edited by ChrisA on 02/10/2011 - 22:59

ChrisA

Link Posted 02/10/2011 - 23:15
Mike-P wrote:
I always dial in 500mm when I use the A* 300mm f2.8 and Pentax 1.7x teleconverter (hand held). With extension tubes I use the lens focal length.

What happens if you use the 1.7x TC with an AF lens?

Does it figure out the amount of SR automatically, or does it prompt you to tell it the way it does for a MF lens?
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Pentax K-3, DA18-135, DA35 F2.4, DA17-70, DA55-300, FA28-200, A50 F1.7, A100 F4 Macro, A400 F5.6, Sigma 10-20 EXDC, 50-500 F4.5-6.3 APO DG OS Samsung flash SEF-54PZF(x2)
.

davidstorm

Link Posted 03/10/2011 - 00:08
Quote:
One post I found in http://www.flickr.com/groups/closer_and_closer/discuss/72157604389806550/ clearly states that focal length does not change with extension tubes. You might want to do some more research to get this confirmed by a second source (I don't have the knowledge about this).

I do think that the point is not really relevant because you more than likely use a tripod and have SR switched of in that case

I almost never use a tripod with the tubes attached as I find it very restrictive. OK, if it's a static subject then the tripod may be used, but almost always the subject is moving if only becuase the wind is blowing. Therefore, the SR setting is fairly important to me.

Regards
David
Flickr

Nicola's Apartments, Kassiopi, Corfu

Some cameras, some lenses, some bits 'n' bobs

Mike-P

Link Posted 03/10/2011 - 13:43
ChrisA wrote:

Does it figure out the amount of SR automatically, or does it prompt you to tell it the way it does for a MF lens?

It asks for the focal length.

Pentax are a bit annoying in that respect, every tc I have tried bar the 1.7x does not report the extra focal length or aperture (and the 1.7x only does because you dial it in). With the Canon I put the Sigma 1.4x onto a 100-300mm f4 and everything in the exif is correct.
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dcweather

Link Posted 04/10/2011 - 13:42
ChrisA wrote:
dcweather wrote:
But surely the SR requires a focal length input only to calculate the approx magnification and hence the shake? This would be more with extension tubes, teleconverters etc so why isn't more SR needed in the algorithm calculation when they are added?

For teleconverters, yes, more SR is needed, since they make the lens magnify more. For extension tubes, no, more is not needed, since they don't.

The thing is, if you use a longer focal length lens (or a teleconverter, which amounts to the same thing), you get extra magnification at the same distance from the subject.

If you use extension tubes, the only reason you get extra magnification is because you move the camera closer to the subject. Focusing is the moving of the lens along its axis towards or away from where you want the image to be in focus. Extension tubes do nothing except help you move the lens further away.

It's the same with macro lenses - they're macro lenses because they allow close focusing, not because they have a different focal length than a non-macro lens.

You dial in more SR with longer focal length lenses because they magnify more than shorter focal length lenses. So for a given angular displacement of the camera (read shake), the image on the sensor moves more than with the shorter lens, and hence needs more correction.

The lens with an extension tube is not magnifying more in the same sense. The image is bigger only because you're closer - there's no extra magnification. So for a given angular displacement, the amount the image moves is the same, so needs the same correction.

---------------
Yes, that seems to make very good sense.
Dave

lemmy

Link Posted 04/10/2011 - 23:21
Theory on this sort of thing goes round in circles Why not try both and see which works best?
lemmy
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