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12-22-2012, 11:10 PM   #1
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Q. about the kit 18-55 lens

Curious.

Is the DA L 18-55 lens that is included with the KX, K30, etc. really 18-55mm. Did Pentax produce this lens to take in account the crop factor of the smaller sensor, or is this lens really a 27-82 on the K30?

Thanks

12-22-2012, 11:16 PM   #2
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It is "really" an 18-55mm, as 18mm = 18mm and 55mm = 55mm. But yes, it will be similar to a 28-85 on a full-frame in terms of field of view.
12-23-2012, 04:31 AM   #3
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18-55mm is always 18-55mm no matter the sensor, it's purely an optical characteristic of the lens. The lens always projects the same image it's just that a smaller sensor only sees a part of it and it changes the field of view you get, still the focal length stays the same.

People often mix it up but as you can see they are entirelly diffent things:
Focal length - Wikipedia, the free encyclopedia
Field of view - Wikipedia, the free encyclopedia
12-23-2012, 09:26 AM   #4
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So basically if you want to use a lenses field of view on film as a standard, then you have to multiply by the crop factor. Or you can just enjoy using your lenses without worrying about weird equivalences to make-believe standards
Most people like to think in terms of standard film (which was the most popular format for a while, but it wasn't the only format), which is where the idea of "full frame" and "crop" comes from, but these are value judgements and not very helpful technically, unless you already have a very good idea of how film would capture a projected image and want to use that to understand how it would be captured on other film/sensor formats. The Q has a much smaller sensor than Pentax DSLRs, for example, so for "equivalence" you will need to multiply it by a higher number.

12-23-2012, 09:53 AM   #5
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So if you want something equivalent (field of view) to how 18mm looks in fullframe you need to multiply with 2/3 (1.5 crop factor).
03-27-2013, 06:57 AM   #6
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QuoteOriginally posted by VisualDarkness Quote
So if you want something equivalent (field of view) to how 18mm looks in fullframe you need to multiply with 2/3 (1.5 crop factor).
That should be ... multiply with 3/2 ...
03-27-2013, 07:23 AM   #7
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QuoteOriginally posted by GXRUser Quote
That should be ... multiply with 3/2 ...
Nope, I said that if you have a 18mm on a fullframe camera and want the same FOV on your APS-c you need to multiply with 2/3.

FOV at 18mm on FF = 12mm on APS-C
18*2/3=12

FOV at 18mm on FF =/= 27mm on APS-C
18*3/2=27
03-27-2013, 08:23 AM   #8
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QuoteOriginally posted by Na Horuk Quote
So basically if you want to use a lenses field of view on film as a standard, then you have to multiply by the crop factor. Or you can just enjoy using your lenses without worrying about weird equivalences to make-believe standards
Most people like to think in terms of standard film (which was the most popular format for a while, but it wasn't the only format), which is where the idea of "full frame" and "crop" comes from, but these are value judgements and not very helpful technically, unless you already have a very good idea of how film would capture a projected image and want to use that to understand how it would be captured on other film/sensor formats. The Q has a much smaller sensor than Pentax DSLRs, for example, so for "equivalence" you will need to multiply it by a higher number.
Agree.

03-27-2013, 08:55 AM   #9
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QuoteOriginally posted by VisualDarkness Quote
Nope, I said that if you have a 18mm on a fullframe camera and want the same FOV on your APS-c you need to multiply with 2/3.

FOV at 18mm on FF = 12mm on APS-C
18*2/3=12

FOV at 18mm on FF =/= 27mm on APS-C
18*3/2=27
Oh

I get it... I had it backwards...
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