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10-07-2009, 03:49 PM   #1
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Zoom lens and SR ?'s

Do af zoom lenses always report the correct focal length to the camera? For example, if I'm using a 28-80 at 28mm and switch to 80mm will the lens update the camera?

EDIT: I checked with my 28-80 Sigma and it does.


Last edited by Steve Beswick; 10-11-2009 at 03:55 PM.
10-07-2009, 03:51 PM   #2
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I think it begins with the SMC-FA lenses, I am not sure the SMC -F lenses report it, but the FA for sure because they also control the zoom on the flash head through the body.
10-07-2009, 03:53 PM   #3
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Yes.

But don't take my words for it.

Check the EXIF data of the photos. There should be a field called "Focal Length."
10-07-2009, 03:55 PM   #4
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QuoteOriginally posted by SOldBear Quote
Yes.

But don't take my words for it.

Check the EXIF data of the photos. There should be a field called "Focal Length."
Doh! Thanks, I'll try that when I get a chance and report back.

10-07-2009, 04:17 PM   #5
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Shouldn't any zoom that doesn't report focal length prompt newer bodies to ask you to input a focal length when you turn on the camera if shake reduction is on?
10-07-2009, 04:53 PM   #6
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QuoteQuote:
Shouldn't any zoom that doesn't report focal length prompt newer bodies to ask you to input a focal length when you turn on the camera if shake reduction is on?
So far, any AF lens I used worked properly with SR.

You can actually check if your lens reports focal length by pressing info button - if it says what focal length you're using, then lens reports that info to the camera.
10-07-2009, 05:07 PM   #7
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QuoteOriginally posted by Steinback Quote
Shouldn't any zoom that doesn't report focal length prompt newer bodies to ask you to input a focal length when you turn on the camera if shake reduction is on?
You'll only get to input it once, hence the OP's question. What happens when you zoom- it won't ask you to change the SR focal length again.
10-07-2009, 05:13 PM   #8
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I've always wondered this about "F" (not FA) zooms, too. Someone must own one?

10-07-2009, 06:23 PM   #9
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QuoteOriginally posted by PentHassyKon Quote
You'll only get to input it once, hence the OP's question. What happens when you zoom- it won't ask you to change the SR focal length again.
That's what I'm getting at, if the body asks you for a focal length you know it isn't being reported by the lens and that the value will not change as you zoom.
10-07-2009, 06:59 PM   #10
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F zooms also report focal length.
10-07-2009, 08:50 PM   #11
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For lenses that do no transmit focal length info when you first turn the camera on, they certainly won't start trnasmitting it just because you turn the zoom ring. Which is to say, if you want the SR to perform optimially, you'll have to go into the menu and change the setting. Ir do what most people probably do and choose a "compromise" focal length - something toward the middle or shorter end of the zoom range - and leave it there. You don't want to set SR *too* much higher than the actual focal length or SR could overcompensate and become counterproductive. But setting it *little* higher won't hurt. And setting it too low won't hurt either - you won't gain full neneift of SR, but it won't ever be worse than nothing, as setting it *too* much higher that the actual focal length can potentially be.
10-08-2009, 01:49 AM   #12
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I think there may be some confusion regarding my inital post, so please allow me to attempt clarification. My question is this: do lenses that report focal length info to the camera update the info based upon zoom changes. For example, if I put my autofocus Sigma on the camera it is usually set to around 50mm. When I rotate it to 80mm does the lens say to the camera "I'm at 80mm now", or does it leave the camera thinking it's at 50mm?
10-08-2009, 06:46 AM   #13
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QuoteOriginally posted by Steve Beswick Quote
I think there may be some confusion regarding my inital post, so please allow me to attempt clarification. My question is this: do lenses that report focal length info to the camera update the info based upon zoom changes. For example, if I put my autofocus Sigma on the camera it is usually set to around 50mm. When I rotate it to 80mm does the lens say to the camera "I'm at 80mm now", or does it leave the camera thinking it's at 50mm?
Why don't you just put your autofocus Sigma onto your camera, take a few pictures and check the EXIF.
Then you'll know what your equipment is doing.
It's really hard to predict how third party equipment is going to work, as sometimes it is inexplicably crippled due to poor implementation of technology.
I believe one poster mentioned that Pentax F lenses and later report focal length to the camera, I know my 60-250 reports focal length as it is zoomed.
Perhaps it's time to turn off the computer and pick up the camera and see what your equipment is doing.
10-08-2009, 08:20 AM   #14
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Just started reviewing photos from my recent trip to Iceland/East Greenland, and the big Sigma 100-300mm faithfully reports its focal length after zooming. I don't seem to have used it quite as much as I remember, but thats probably because its so difficult to ignore when its on the camera!

Last edited by Talisker; 10-08-2009 at 08:23 AM. Reason: typo
10-08-2009, 10:09 AM   #15
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QuoteOriginally posted by Steve Beswick Quote
I think there may be some confusion regarding my inital post, so please allow me to attempt clarification. My question is this: do lenses that report focal length info to the camera update the info based upon zoom changes. For example, if I put my autofocus Sigma on the camera it is usually set to around 50mm. When I rotate it to 80mm does the lens say to the camera "I'm at 80mm now", or does it leave the camera thinking it's at 50mm?
the answer is yes.

one easy way to tell, as I commented previously is to put an AF540FGZ on the body and you will have the flash zoom in and out as you change focal length on the lens.

it uses this for shake reduction also.

On my PZ-1 the body had an additional feature called image size tracking, which used focal length info, and focus distance info such that once you achieved focus on a moving object, the camera would zoom the lens in or out to maintain the same subject size in the frame.
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