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02-04-2009, 05:45 PM   #1
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SR Focal Length Input for a Manual Zoom Lens?

Hi All,

Just wonder what focal length you'd input when using a manual zoom lens (M or A)? The only manual zoom lenses I ever used was an A35-105, and I put in 105mm for the focal length for the entire focal range, seemed working pretty well. But just wanna check what you guys would do w/ a manual zoom lens

02-04-2009, 05:55 PM   #2
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QuoteOriginally posted by frank Quote
But just wanna check what you guys would do w/ a manual zoom lens
I dial in the approximate focal length that I'm actually using. For example if I'm shooting at 50mm with my 28-70mm zoom, I dial in "50mm".
02-04-2009, 06:56 PM   #3
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If you don't want to be turning the camera off and then on again every time you want to take a picture, set the SR to the shortest focal length of the lens.
It seems better to under correct for shake than to over correct.
02-04-2009, 08:01 PM   #4
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QuoteOriginally posted by Sean Nelson Quote
I dial in the approximate focal length that I'm actually using. For example if I'm shooting at 50mm with my 28-70mm zoom, I dial in "50mm".
Hmm, that sounds pretty busy when taking photos don't you think? But I guess that's the way to go if we want to get the best sharpness

02-04-2009, 08:04 PM   #5
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QuoteOriginally posted by Wheatfield Quote
If you don't want to be turning the camera off and then on again every time you want to take a picture, set the SR to the shortest focal length of the lens.
It seems better to under correct for shake than to over correct.
Actually you don't need to switch the camera off and on to change focal length for SR. Just press menu and type in focal length under the first submenu, an menu item at the bottom.

I guess you are right about the shorter end. I'm asking this is because I'm getting an A70-210 soon, probably will keep it for the zoom since I don't want to carry the much bigger and heavier FA*80200 all the time, especially w/ two small kids around
02-26-2009, 06:29 AM   #6
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hi... i'd read somewhere, (can't remember though), that to set the f.l., split the difference,
i.e., i too have the smc a 35-105 f3.5, so when the body asks for the focal length, i set
the body for 70.... seems to work ok.....
02-26-2009, 06:39 AM   #7
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I think all the answers are correct to a point.

Normally, I would set the FL to what I was shooting at the time, since with a zoom, although in theory you could be constantly back and forth, you generally tend to stick to one end or the other.

But here is another idea.

SR is really only needed if yoou are shooting below 1/effective focal length

I say effective focal length because you need to consider the crop factor here.

if you have enough light, just turn SR off.

if not, then start thinking about setting it to the middle if you are always going to be switching back and fourth, and remember that even with SR, your technique is everything. if you are steady, it doesn't matter where it is set, because there is no shake
02-26-2009, 07:10 AM   #8
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I've had this same conundrum- I'd like to pick up a manual zoom, but this question always haunted me.

However, I have a feeling I'd be shooting outdoors quite a bit at f/8 with a zoom (as I do now with my AF zoom). I'm wondering- in good light conditions, is it best to simply shut off SR to avoid any impact it may have on your shots?

Although I completely understand what was being said about setting the SR to the longer end- that's where it would be the most helpful. Also, I can see it really depends on the lens!

02-26-2009, 09:34 AM   #9
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QuoteOriginally posted by Wheatfield Quote
If you don't want to be turning the camera off and then on again every time you want to take a picture, set the SR to the shortest focal length of the lens.
It seems better to under correct for shake than to over correct.
I did quite a bit of testing of this and Wheatfield is absolutely right. You get much better results with the setting shorter than actual focal length than you do the other way around.
02-27-2009, 09:30 AM   #10
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I would agree that with a manual zoom, turning SR off when not needed makes total sense. I don't have any MF zooms, but with my primes, I'm reluctant to turn of SR because I like having the focal length recorded in the EXIF (pity it won't do that with SR off). But with a zoom, th focal length recorded in EXIF isn't likely to be of much value anyhow - unless perhaps you get in the habit of always entering a particular focal length (or set of lengths) for a particular zoom, so you can easily identify the lens used from the EXIF later.
02-27-2009, 11:10 AM   #11
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QuoteOriginally posted by Parallax Quote
I did quite a bit of testing of this and Wheatfield is absolutely right. You get much better results with the setting shorter than actual focal length than you do the other way around.
That is how I set SR focal length -- the shorter or the exact number of your current focal length. It is troublesome for zoom as compared to manual prime as you set the SR focal length once at power on! And for casual shooting in a fast pace, I dial in the average or the most used one in the zoom range, but I always prefer to have the lower number as I try to avoid over-compensation in the SR calculation. I see less a reason to turn off SR as I want that expensive VR/IS features on my $50 zoom lens as much as my DA* 50-135 . This is the luxury in Pentaxian world not enjoyed by other brands though the extra step involved.


There are two ways to dial in the SR focal length
  1. Power off/on
  2. Menu button -> Up arrow ->SR focal length change

Due to the cumbersome in setting SR focal length, I recently find myself liking two touch zooms more than one touch zoom.



Vivitar 70-150mm f/3.8 from Kiron
two-touch zoom

An inexpensive lens that I highly recommend,
especially the M42 version for Av mode


It is easier to remember to change SR focal length. With a two touch zoom, I engage the zoom to a zoom position and I put it into practice that I do #2 above consciously. Same can be done on one-touch zoom but my aged mind can remember easier.

Last edited by hinman; 02-27-2009 at 11:37 AM.
03-13-2009, 03:09 PM   #12
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I love it when the forum search function works as desired! I just received my A70-210/4. Mint is an understatement of the physical appearance at least and was about to do some test shots on the K20D when the input focal length screen came up. I was going to split the difference (140mm) but figured I'd check here first.

Thanks! I'm off to make some photos now!
03-15-2009, 01:03 PM   #13
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QuoteOriginally posted by Marc Sabatella Quote
I would agree that with a manual zoom, turning SR off when not needed makes total sense. I don't have any MF zooms, but with my primes, I'm reluctant to turn of SR because I like having the focal length recorded in the EXIF (pity it won't do that with SR off). But with a zoom, th focal length recorded in EXIF isn't likely to be of much value anyhow - unless perhaps you get in the habit of always entering a particular focal length (or set of lengths) for a particular zoom, so you can easily identify the lens used from the EXIF later.
If you turn on the camera with SR enabled and input FL then turn off SR it'll still record FL in the exif, at lease my k200d does...
03-15-2009, 03:04 PM   #14
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QuoteOriginally posted by kristoffon Quote
If you turn on the camera with SR enabled and input FL then turn off SR it'll still record FL in the exif, at lease my k200d does...
Odd - that's not my experience at all. Unless perhaps it is recording the FL in the Pentax "makernotes" section as opposed to the standard place. That's actually been a common complaint on these forums - "why doesn't FL get recorded when SR is off", so I know it's not just me...
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