actual focal length of 55-300DA

tibbitts · 01-26-2013, 02:22 PM

It seems like I read a review/test of the 55-300DA that indicated that the measured focal length at infinity focus of the sample tested was somewhat longer than 300mm. Of course I can't find that review now and am wondering if anyone has a link, or knows of an actual measurement (at both ends) of the focal length range of this lens? Thanks

Paul

**Lowell Goudge** · 01-26-2013, 03:13 PM

Why not measure it yourself

Take your camera and look at the sensor size, get this exactly, don't use 16x24 but the actual one,

Take a shot of something you can measure at. A reasonable butnknown distance, and then measure the pixels of thenobject. Work out the magnification from that

glasbak · 01-26-2013, 03:39 PM

Although the lens has no IF in its name, I am pretty sure the focal length will change as function of the focus distance, so beware at what object distance you measure the focal length, best do it at the infinity setting.

tibbitts · 01-27-2013, 10:27 AM

Originally posted by Lowell Goudge

Why not measure it yourself

Take your camera and look at the sensor size, get this exactly, don't use 16x24 but the actual one,

Take a shot of something you can measure at. A reasonable butnknown distance, and then measure the pixels of thenobject. Work out the magnification from that

I don't know how lens test identify the focal length, but I know they can seemingly do it to a fraction of a mm... and I don't think measuring pixels of objects at infinity would be precise enough. I'm pretty sure the infinity part is required, and wouldn't that require testing with very, very large objects of precisely known dimensions?

Paul

older not wiser · 01-27-2013, 01:27 PM

Amateur Photographer in the UK used to have a chap who did technical measurements of lenses as part of their reviews. As I remember very few lenses actually had the focal length stated. I think manufactures put a focal length on the lens that is near to a logical number such as 55-300 mm as opposed to 53.9-306.2 mm, it just looks neater.

01-26-2013, 02:22 PM	#1
tibbitts Pentaxian Join Date: Apr 2007 Location: Oklahoma USA Posts: 2,196	actual focal length of 55-300DA It seems like I read a review/test of the 55-300DA that indicated that the measured focal length at infinity focus of the sample tested was somewhat longer than 300mm. Of course I can't find that review now and am wondering if anyone has a link, or knows of an actual measurement (at both ends) of the focal length range of this lens? Thanks Paul

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01-26-2013, 03:13 PM	#2
Lowell Goudge Site Supporter Join Date: Jan 2007 Location: Toronto Photos: Gallery \| Albums Posts: 17,891	Why not measure it yourself Take your camera and look at the sensor size, get this exactly, don't use 16x24 but the actual one, Take a shot of something you can measure at. A reasonable butnknown distance, and then measure the pixels of thenobject. Work out the magnification from that

01-26-2013, 03:39 PM	#3
glasbak Veteran Member Join Date: Apr 2009 Location: Netherlands Posts: 369	Although the lens has no IF in its name, I am pretty sure the focal length will change as function of the focus distance, so beware at what object distance you measure the focal length, best do it at the infinity setting.

01-27-2013, 10:27 AM	#4
tibbitts Pentaxian Join Date: Apr 2007 Location: Oklahoma USA Posts: 2,196 Original Poster	Originally posted by Lowell Goudge Why not measure it yourself Take your camera and look at the sensor size, get this exactly, don't use 16x24 but the actual one, Take a shot of something you can measure at. A reasonable butnknown distance, and then measure the pixels of thenobject. Work out the magnification from that I don't know how lens test identify the focal length, but I know they can seemingly do it to a fraction of a mm... and I don't think measuring pixels of objects at infinity would be precise enough. I'm pretty sure the infinity part is required, and wouldn't that require testing with very, very large objects of precisely known dimensions? Paul

01-27-2013, 01:27 PM	#5
older not wiser Senior Member Join Date: Dec 2009 Location: East Yorkshire Posts: 120	Amateur Photographer in the UK used to have a chap who did technical measurements of lenses as part of their reviews. As I remember very few lenses actually had the focal length stated. I think manufactures put a focal length on the lens that is near to a logical number such as 55-300 mm as opposed to 53.9-306.2 mm, it just looks neater.