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03-25-2009, 07:06 AM   #1
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Shake Reduction with internal focus lenses

This was a sub-question on a thread I started in the lens forum, but it seems better suited to the DSLR section.

Whilst playing with a new (second-hand) Tamron 28-200, I thought I found that the 200 wasn't in fact 200mm. Turns out this is a well-known issue with internal-focus lenses which only reach their stated focal length when focusing on infinity.

My question relates to using shake reduction with such lenses. If the lens tells the camera that it's at 200mm, when in fact it behaves as a 180mm lens (or whatever), does that mean that the camera will make the *wrong* compensations for movement, or can the body make the necessary adjustments? I've had a look through some threads talking about internal-focus lenses, but haven't managed to find any mention of this.

Many thanks for any thoughts,

Philip

03-25-2009, 07:45 AM   #2
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Good question. I expect it depends on what information the lens is sending to the camera. There really isn't much you can do about it though, and I think you'll find that your lens is very close to the marked focal length until you start hitting very close focus nearing the macro range, at which time you should probably be on a tripod with SR turned off anyway.
03-25-2009, 07:48 AM   #3
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QuoteOriginally posted by pa79 Quote
My question relates to using shake reduction with such lenses. If the lens tells the camera that it's at 200mm, when in fact it behaves as a 180mm lens (or whatever), does that mean that the camera will make the *wrong* compensations for movement, or can the body make the necessary adjustments?
If you know what the actual focal length is -
I would suggest using that and setting the closest number.
Personally I don't think that between 180 and 200 is going to make a big difference - but since you have the actual focal length why not use it?

03-25-2009, 12:13 PM   #4
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I've never been able to enter the SR screen if I have a lens attached that transmits focal length information.

03-25-2009, 12:26 PM   #5
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wow, i was just searching for similar information! thanks for starting this thread, pa79.

in my case, i've got a *50-135 + tamron 1.4x TC. it "seems" like SR isn't taking the tc into account, though it might simply be i've now got a heavier and physically longer lens with the tc in place.

not to hijack this thread - i haven't been able to enter SR values either and would like to know how for this combination. --- but if any of you know, how does using this tc (Pz-AF MC4) affect SR, and why doesn't the adjusted focal length show up in the exif?

many thanks.
03-25-2009, 01:21 PM   #6
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QuoteOriginally posted by kauaiguy Quote
wow, i was just searching for similar information! thanks for starting this thread, pa79.

in my case, i've got a *50-135 + tamron 1.4x TC. it "seems" like SR isn't taking the tc into account, though it might simply be i've now got a heavier and physically longer lens with the tc in place.

not to hijack this thread - i haven't been able to enter SR values either and would like to know how for this combination. --- but if any of you know, how does using this tc (Pz-AF MC4) affect SR, and why doesn't the adjusted focal length show up in the exif?

many thanks.
Your camera doesn't support teleconverters.
Or, more to the point, your teleconverter doesn't support shake reduction.
03-25-2009, 01:28 PM   #7
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pa79, I posted something in your other thread that might shed some light on this:

https://www.pentaxforums.com/forums/536435-post10.html

It's something you can check but I can't, because I don't have that lens.
03-25-2009, 03:54 PM   #8
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Hi Vincent,

Thanks for the suggestion, but as Wheatfield, I am unable to get in to the SR menu when I'm using a lens which transmits focal length information. In any case, I'm not sure it'd be workable as the effective focal length changes depending on how close the object in focus is - you'd never know exactly what the focal length was at any given moment, especially since distance scales are so much less detailed now than on older manual lenses.

Thanks Quicksand - I replied to your post on the other thread (the perils of having two similar threads on the go at once!)

03-25-2009, 08:00 PM   #9
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QuoteOriginally posted by pa79 Quote
My question relates to using shake reduction with such lenses. If the lens tells the camera that it's at 200mm, when in fact it behaves as a 180mm lens (or whatever)
I don't know about your Tamron but newer lenses transmit focus distace info to the body that gets registered on the exif. Also nothing stops them from sending a hidden info field with actual focal lenght based on focal distance that isn't visible to the user. So it definitely can be compensated.
03-25-2009, 08:36 PM   #10
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QuoteOriginally posted by kristoffon Quote
I don't know about your Tamron but newer lenses transmit focus distace info to the body that gets registered on the exif. Also nothing stops them from sending a hidden info field with actual focal lenght based on focal distance that isn't visible to the user. So it definitely can be compensated.
Dangerous statement. Unless you know for a fact that the lens is transmitting focus position modified focal length, it's probably best to presume that it doesn't.
It is, however, an easy check to make. See if your focal length changes in the EXIF when two images are taken at the same marked focal length, but on at infinity, the other at minimum distance.
03-25-2009, 09:18 PM   #11
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Interesting concept - so I did a quick test using two different lenses, the Pentax 18-55 kit lens and a 70-300 Sigma.

Took the shots with each lens, doing only the min-max for each:

18 minimum
18 infinity
55 minimum
55 infinity
70 minimum
70 infinity
300 minimum
300 infinite

Per the Exif (PhotoME) they all registered the focus distance as per the lens, regardless of whether focusing was at minimum distance or infinity.
03-30-2009, 08:19 AM   #12
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First of all, I would doubt, that a SR setting of 200mm would produce visibly different results from 180mm setting, so this should easily accomodate for IF lenses.

Also most lenses do not have exactly the focal length, the name states. By convention Nikon would not man a 25.2mm lens as*such, but use the conventional 24mm designation. This is the same with all manufacturers. A 5% to 10% variation is usual, as at short focal lengthes this only between 1mm or 2mm etc. - I guess nobody would even doubt SR settings then.

Also, change of focal length is not limited to IF lenses. Especially with longer lenses at short distances fl variations gets noticeable.

Ben
03-30-2009, 04:50 PM   #13
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Alright then. I use an IF lens with a TC on it (but the camera can't tell there's a TC on). Should I leave SR on? Does it help a bit, but not as much as it could?
03-31-2009, 01:35 AM   #14
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QuoteOriginally posted by Arpe Quote
Alright then. I use an IF lens with a TC on it (but the camera can't tell there's a TC on). Should I leave SR on? Does it help a bit, but not as much as it could?
In my experience SR still works to some extend, if the camera recognizes a too short focal length (which would be the case with the tc). Anyway better, than SR which works for a too long fl.

Ben
03-31-2009, 04:13 PM   #15
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That's what I was thinking (something is better than nothing), but of course, have no proof.
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