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05-13-2019, 12:03 AM   #1
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How to accurately select focal length DA lens

https://www.pentaxforums.com/lensreviews/SMC-Pentax-DA-18-55mm-F3.5-5.6-WR-W...Zoom-Lens.html

Hi,
This is the standard lens on the Pentax K-5, the lens does not show the exact points for each focal length. It only shows 18, 24, 35, 45 and 55 on it.
Is there a way to find out where exactly it’s sitting? Nothing in the screen menu.


Last edited by Zooland; 05-13-2019 at 12:32 AM. Reason: URL
05-13-2019, 12:36 AM   #2
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QuoteOriginally posted by Zooland Quote
https://www.pentaxforums.com/lensreviews/SMC-Pentax-DA-18-55mm-F3.5-5.6-WR-W...Version-Zoom-L

Hi,
This is the standard lens on the Pentax K-5, the lens does not show the exact points for each focal length. It only shows 18, 24, 35, 45 and 55 on it.
Is there a way to find out where exactly it’s sitting? Nothing in the screen menu.
The easiest way is to use one of the tethering programs (PKTether or PKTriggercord) to read off the focal length live on a connected PC. Then stick a bit of masking tape on the side of the lens and mark on it your focal length numbers.

Otherwise it is down to trial and error ...

You may struggle to find PKTether - a good copy is here, archived by Blacknight659

Last edited by kh1234567890; 05-13-2019 at 12:45 AM.
05-13-2019, 03:11 AM   #3
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It is something I miss from my K10D. Earlier Pentax DSLR showed focal lengt on rear info screen.

For some reason Pentax removed FL info on K7 and later cameras.
05-13-2019, 04:18 AM - 4 Likes   #4
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QuoteOriginally posted by Zooland Quote
Is there a way to find out where exactly itís sitting?
Does it matter? Get the framing you want at capture time and find out what the actual focal length was when you process the image.

05-13-2019, 04:40 AM   #5
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QuoteOriginally posted by Sandy Hancock Quote
Does it matter? Get the framing you want at capture time and find out what the actual focal length was when you process the image.
Exactly! This is the idea behind using a zoom: you mostly care about framing.
05-13-2019, 06:46 AM   #6
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If you want a precise focal length ... get a prime. Though even then, you may have to contend with focus breathing.
05-13-2019, 09:33 AM   #7
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QuoteOriginally posted by Fogel70 Quote
It is something I miss from my K10D. Earlier Pentax DSLR showed focal lengt on rear info screen.

For some reason Pentax removed FL info on K7 and later cameras.


The feature has been re-introduced on the K-70. I don't use it very often, but I know it's there
05-13-2019, 10:46 AM   #8
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Surely if it is important you can see it in preview ?

05-13-2019, 02:02 PM - 2 Likes   #9
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QuoteOriginally posted by Zooland Quote
. . .

Is there a way to find out where exactly it’s sitting? Nothing in the screen menu.

Yes - more or less.
Just take an example shot and then bring it up on the review screen with detailed info.







But you might not be able to (nominally) get the precise length you want. My DA 18-55 WR on my K-5iis doesn't list some focal lengths. For example, my lens goes from an indicated 30mm to 32 to 35 - no matter how finely the zoom ring is adjusted.
05-15-2019, 01:16 PM   #10
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Does it really matter?

Since on many zoom lenses the focal length is only true at infinity who really cares?

Not meant to show disrespect to the OP or any other posters, but I h ave never once, in all my life ever concerned myself with the exact focal length I was shooting with a zoom
05-17-2019, 08:13 AM - 1 Like   #11
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I've often read the advice for people starting out with DSLRs to set their zoom (which is what most beginners have as their first lens) to a certain focal length to see if they like shooting at that focal length before investing money into a prime. It might offer better quality than a zoom, but brings some serious limitations with it and one can see what those are when setting a certain focal length on a zoom and fixing it with tape or something and shooting with it as if it were a prime.
05-18-2019, 11:21 PM   #12
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QuoteOriginally posted by ehrwien Quote
I've often read the advice for people starting out with DSLRs to set their zoom (which is what most beginners have as their first lens) to a certain focal length to see if they like shooting at that focal length before investing money into a prime. It might offer better quality than a zoom, but brings some serious limitations with it and one can see what those are when setting a certain focal length on a zoom and fixing it with tape or something and shooting with it as if it were a prime.
This may be true, but you can also use tools like ExposurePlot to see what you shoot most often. ExposurePlot jpg exif lens length analyzer for photographers

The risk with zooms is you often frame the shot exactly , or you are at one of the two focal length extremes but you will still be able to see this in the data,

The problem remains however that most zooms change focal length as you focus so what the lens is set to is not relevant at other than infinity focus. This means what someone learns with a zoom, may not translate to the liking a prime at that focal length, unless they always shoot at infinity focus
05-19-2019, 02:36 AM   #13
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QuoteOriginally posted by Lowell Goudge Quote
This may be true, but you can also use tools like ExposurePlot to see what you shoot most often.
The important difference being that with this approach you do not work with the limitations of a fixed focal lenght, try to work your subject with your feet and explore, you may fall into just changing the focal length, snapping away and potentially missing the most interesting perspectives. And this could also be a reason for using a zoom the most at both its ends, "I have to get closer" / "I am too close", changing the focal length as much as possible et voila.
05-19-2019, 03:47 AM   #14
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QuoteOriginally posted by Lowell Goudge Quote
Does it really matter?

Since on many zoom lenses the focal length is only true at infinity who really cares?

Not meant to show disrespect to the OP or any other posters, but I h ave never once, in all my life ever concerned myself with the exact focal length I was shooting with a zoom
Quite. See post #4
05-19-2019, 10:23 AM - 1 Like   #15
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QuoteOriginally posted by ehrwien Quote
The important difference being that with this approach you do not work with the limitations of a fixed focal lenght, try to work your subject with your feet and explore, you may fall into just changing the focal length, snapping away and potentially missing the most interesting perspectives. And this could also be a reason for using a zoom the most at both its ends, "I have to get closer" / "I am too close", changing the focal length as much as possible et voila.
But the problem, as I identified, is that since most zooms change focal length as they focus, means that the working distance impression you get is wrong. As I said, the experience with a zoom will not be replicated with a prime
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