Hi Klaus,
I have two questions
1. you metioned "min. focus distance 0.38m (max. magnification ratio ~1:1)"
From where you get this info? The sigma site not metioned MFD of OS version
2. According to PZ reviews the non OS and OS version have the same MFD. Since OS version is longer it means that min working distance of OS version is shorter. Am I correct?
I'm asking this question because most people choose longer macro lens for greater working distance
08-09-2011, 08:27 AM
(This post was last modified: 08-09-2011, 08:29 AM by Klaus.)
[quote name='miro' timestamp='1312878286' post='10537']
Hi Klaus,
I have two questions
1. you metioned "min. focus distance 0.38m (max. magnification ratio ~1:1)"
From where you get this info? The sigma site not metioned MFD of OS version
2. According to PZ reviews the non OS and OS version have the same MFD. Since OS version is longer it means that min working distance of OS version is shorter. Am I correct?
I'm asking this question because most people choose longer macro lens for greater working distance
[/quote]
[url="http://www.sigma-photo.co.jp/english/lens/macro/150_28_os.htm"]http://www.sigma-pho...o/150_28_os.htm[/url]
The OS is longer but I think the MFD is measured from the nodal point (is it ? I'm always mixing this up) and its exact position is unknown.
[quote name='Klaus' timestamp='1312878470' post='10538']
the MFD is measured from the nodal point (is it ?
[/quote]
Usually from the sensor. So MFD - lens length - flange distance = working distance.
-- Markus
Editor
opticallimits.com
[quote name='mst' timestamp='1312878691' post='10539']
Usually from the sensor. So MFD - lens length - flange distance = working distance.
-- Markus
[/quote]
That's how I know it also... And that's why knowing the "working distance" is crucial when it comes to macro lenses...
So for Canon EOS mount, minimum working distance for this lens = 380mm - 150mm - 44mm = 186mm (=18,6cm). And this is the distance you get max reproduction ratio of 1:1...
Serkan
It's a great lens. I only wish it had appeared 2 years ago, when I got tired of waiting for it and settled for the 100/2.8 IS. Oh well, at least it's lighter....
08-09-2011, 10:24 AM
(This post was last modified: 08-09-2011, 10:24 AM by Klaus.)
[quote name='PuxaVida' timestamp='1312880628' post='10545']
That's how I know it also... And that's why knowing the "working distance" is crucial when it comes to macro lenses...
So for Canon EOS mount, minimum working distance for this lens = 380mm - 150mm - 44mm = 186mm (=18,6cm). And this is the distance you get max reproduction ratio of 1:1...
Serkan
[/quote]
Really ... ?
[url="http://savazzi.freehostia.com/photography/workingdistance.htm"]http://savazzi.freeh...ingdistance.htm[/url]
[quote name='Klaus' timestamp='1312877510' post='10536']
Well, as mentioned it all depends upon design priorities. A macro lens is certainly optimized to deliver great results at max. magnification but this doesn't mean that it's worse at infinity. If you look at the Zeiss 100/2 MTF charts you will notice that it's still better at infinity and 1:10 than at 1:2. At infinity it seems even insignificantly better than at 1:10 (40lp/mm = resolution).
I'm not a designer but basically they feed the optimization points into their optimization algorithms. So for a prime lens they define a couple of hot spots within the focus range that are supposed to be important. Infinity focus will always be in there. Macro lenses will certainly have a hot spot at max. mag whereas portrait lenses have a hot spot at -say- 3 meters. That's all simplified of course.
True macro lenses tend to have FEs (floating elements( (just like the Sigma or the Zeiss lens) which are meant to optimize the close focus performance. Technically this is the primary differentiator compared to conventional lenses.
Remember that many users own macro lenses but will rarely use them as such - after all they are compact and offer high performance and their comparatively large max. aperture makes them suitable for portrait photography as well. I also used to own a couple of macro lenses without doing actual macro work. Even macro photographers don't always shoot at 1:1 but often just at 1:5 or 1:10. That's also something that the manufacturer keep in mind when designing such lenses.
[/quote]
This is a good explanation. It is a matter of point of view. I use macro lenses only from 1:1 - 1:10, not at infinity. And that is why I would be interested in performances there. The best lens for me would be a lens with peak performance at 1:2-1:5.
[quote name='Klaus' timestamp='1312885450' post='10548']
Really ... ?
[url="http://savazzi.freehostia.com/photography/workingdistance.htm"]http://savazzi.freeh...ingdistance.htm[/url]
[/quote]
Well, as long as the lens has an IF design (no change in length while focusing), I think the formula is still valid (or am I missing something?)....
The figures given for Sigma 180mm in this article proves it. The WD was calculated as 232mm for 1:1 ratio. The physical length of the Sigma 180mm f/3.5 is 179,5 mm. The flange focal distance for F-Mount is 46,5 mm and the MFD for Sigma lens is 460mm.
460 - 179,5 - 46,5 = 234mm (not sure about the 2mm difference from the 232mm give in the article, maybe the precise length of the lens was different for the F-mount version).
Serkan
Well the simple substraction formular posted above of course contains a small error: normally the manufacturers post the physical length of a lens including mount (to my knowledge at least). Theoretically one would have to substract the depth of the mount from the physical length of the lens.
However, for MFD (or (usually) 1:1) physical length and MFD is all you really need to know to get a good idea about the working distance. The only thing you usually don't know is the depth of the hood, which should be substracted, too. In the field, though, you can simply leave the hood in the bag to increase the effective working distance.
As is written in the text Klaus linked to: calculating the working distance for other reproduction ratios requires knowledge about the lens that is usually not available.
-- Markus
Editor
opticallimits.com
[quote name='mst' timestamp='1312893539' post='10552']
Well the simple substraction formular posted above of course contains a small error: normally the manufacturers post the physical length of a lens including mount (to my knowledge at least). Theoretically one would have to substract the depth of the mount from the physical length of the lens.
However, for MFD (or (usually) 1:1) physical length and MFD is all you really need to know to get a good idea about the working distance. The only thing you usually don't know is the depth of the hood, which should be substracted, too. In the field, though, you can simply leave the hood in the bag to increase the effective working distance.
As is written in the text Klaus linked to: calculating the working distance for other reproduction ratios requires knowledge about the lens that is usually not available.
-- Markus
[/quote]
Some lenses do show the reproduction ratios on the lens barrel, so with those it is easier to calculate working distance. My old Sigma 70-300mm macro used to give markings for 1:3.5, 1:3, 1:2.5 and 1:2. And my Micro-Nikkor Auto 55mm f3.5 has markings for 1:10/9/8/7/6/5/4/3/2.5/2/1.5/1. My Tamron SP 90mm f2.8 Di Macro has markings for 1:10/7/5/4/3/2.8/2/1.8/1.5/1.3/1 .
