Q. about the kit 18-55 lens

dmfw · 12-22-2012, 11:10 PM

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

vonBaloney · 12-22-2012, 11:16 PM

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.

VisualDarkness · 12-23-2012, 04:31 AM

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

Na Horuk · 12-23-2012, 09:26 AM

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.

VisualDarkness · 12-23-2012, 09:53 AM

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).

GXRUser · 03-27-2013, 06:57 AM

Originally posted by VisualDarkness

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 ...

VisualDarkness · 03-27-2013, 07:23 AM

Originally posted by GXRUser

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

Ken T · 03-27-2013, 08:23 AM

Originally posted by Na Horuk

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.

GXRUser · 03-27-2013, 08:55 AM

Originally posted by VisualDarkness

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...

12-22-2012, 11:10 PM	#1
dmfw Senior Member Join Date: Dec 2009 Location: Dallas, Tx Photos: Albums Posts: 159	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

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Buying a K5 - but with 18-135mm lens kit? Or an 18-55 + 50-200mm lens kit?	robinfaz	Pentax K-5 & K-5 II	12	06-04-2012 01:44 PM
For Sale - Sold: White k-r + 18 - 55 and 55 - 300 kit lens	kaiserz	Sold Items	4	04-06-2012 11:31 AM
Question about manual focus on 18-55 kit lens	Matso	Pentax K-r	6	03-09-2011 12:15 PM
For Sale - Sold: WTT Pentax 18-55 AL II kit lens for 18-55 AL kit lens + money	wallyb	Sold Items	2	11-11-2009 02:26 PM

12-22-2012, 11:16 PM	#2
vonBaloney Pentaxian Join Date: Oct 2011 Location: Albuquerque, NM Posts: 6,029	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
VisualDarkness Veteran Member Join Date: Nov 2011 Location: Uppsala, Sweden Photos: Gallery Posts: 4,439	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
Na Horuk Veteran Member Join Date: Feb 2012 Location: Slovenia, probably Photos: Gallery \| Albums Posts: 11,186	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
VisualDarkness Veteran Member Join Date: Nov 2011 Location: Uppsala, Sweden Photos: Gallery Posts: 4,439	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
GXRUser Senior Member Join Date: May 2012 Posts: 165	Originally posted by VisualDarkness 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
VisualDarkness Veteran Member Join Date: Nov 2011 Location: Uppsala, Sweden Photos: Gallery Posts: 4,439	Originally posted by GXRUser 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 182/3=12 FOV at 18mm on FF =/= 27mm on APS-C 183/2=27

03-27-2013, 08:23 AM	#8
Ken T Veteran Member Join Date: Mar 2008 Location: California, USA Posts: 536	Originally posted by Na Horuk 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
GXRUser Senior Member Join Date: May 2012 Posts: 165	Originally posted by VisualDarkness 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 182/3=12 FOV at 18mm on FF =/= 27mm on APS-C 183/2=27 Oh I get it... I had it backwards...