Macro lens: 1:1 ratio and Min focus distance ??

Canon EF-S 17-85mm f/4-5.6 IS USM

05/05/2005 05:09:26 PM · #1

Is there any relation ?

Canon 100mm has minimum focus distance of ~6in and 1:1 ratio
Sigma 105mm has minimum focus distance of ~12in and 1:1 ratio
Canon 60mm has minimum focus distance of ~8in and 1:1 ratio

how does that work ?

I would expect if 100mm has 1:1 ratio at 6in, 60mm will have the same 1:1 ratio at 6 * 60/100 = 3.6in distance

Is this flawed ? where ?

papa

Canon EOS-350D Rebel XT

05/05/2005 05:13:23 PM · #2

I believe all things being equal, your right. But I would wager that those 2 lenses have differing element counts and configurations. That, I believe is your difference.

Disclaimer: I'm not a photographer, but I did stay at a Holiday Inn Express last night! Just kidding.

hopper

Canon EOS-80D

Canon EF 35mm f/2 IS USM

05/05/2005 05:17:34 PM · #3

60mm

The new lens focuses from infinity down to 1:1 (lifesize) at a generous working distance of approximately four inches from the subject.

taken from Bob Atkins site

here

Message edited by author 2005-05-05 17:18:16.

05/05/2005 05:21:20 PM · #4

specs at bhphoto say
Filter Size 52mm
f/Stop Range 2.8-32
Minimum Focus Distance 7.9" (20 cm)
Magnification 1:1 (life size)

so the minimum focus distance is not the distance for 1:1 magnification ?

hopper

Canon EOS-80D

Canon EF 35mm f/2 IS USM

05/05/2005 05:32:49 PM · #5

i'd say b&h specs are inaccurate

Originally posted by gaurawa:

specs at bhphoto say
Filter Size 52mm
f/Stop Range 2.8-32
Minimum Focus Distance 7.9" (20 cm)
Magnification 1:1 (life size)

so the minimum focus distance is not the distance for 1:1 magnification ?

05/05/2005 05:41:29 PM · #6

Originally posted by hopper:

i'd say b&h specs are inaccurate

I thought so too, so I looked up Canon's site and this is what I found..
Focal Length & Maximum Aperture 60mm 1:2.8
Lens Construction 12 elements in 8 groups
Diagonal Angle of View 25Â°
Focus Adjustment Manual
Closest Focusing Distance 0.2m /0.65 ft.

0.65ft is 7.8in

edit: add link to canon site
Specs from Canon

Message edited by author 2005-05-05 17:42:15.

KiwiChris

Canon EF 17-40mm f/4.0L USM

05/05/2005 06:39:46 PM · #7

The confusion here is that Canon list the focus distance in two ways.. From the focal plane (Film/sensor) and from the front of the lens...

The 17-40 for e.g. lists as 28cm closest focus, but you can get down to about 13cm from the front of the lens, even though the distance scale on the lens shows 0.28m

On some consumer lenses it appears to be the other way around, the distance is from the front element. (The 18-55 kit lens for e.g.).

Sigma I believe quote it from the front element, sometimes..

Cheers, Me.

Message edited by author 2005-05-05 18:40:04.

kirbic

Canon EOS R5

Canon RF 24-70mm f/2.8 L IS

05/05/2005 06:50:29 PM · #8

Originally posted by KiwiChris:

The confusion here is that Canon list the focus distance in two ways.. From the focal plane (Film/sensor) and from the front of the lens...

Yep, you have to carefully watch the terminology. Closest focusing distance often (but certainly not always) refers to the distance from the sensor plane to the subject. Working distance, OTOH, always refers to the distance from the front element to the subject. When the marketeers get carried away, they tend to use the working distance as "closest focus", since it sounds a lot closer.
Another little-known fact is that some of these lenses actually change focal length more than a little bit as they change magnification. The Canon 100mm apparently is actually shorter than 100mm at 1:1. Just how much shorter, I'm not sure, and I've never tested it myself to confirm.

soup

Canon EOS-30D

Canon EF 17-40mm f/4.0L USM

05/05/2005 08:21:22 PM · #9

damn marketing folks - always trying to trick you ;}