[mst]

[quote name='popo' timestamp='1312826616' post='10513']

That is my guess also. If you use a 1.4x on it, the focus range is limited to a shorter region than without, and the combination from memory is about 1:1 magnification at that point. I guess with a 2x they could have limited it further out again to maintain enough effective aperture, but for whatever reason they chose not to.

[/quote]



Thanks for the hint, I hadn't noticed this behaviour yet. I just tried it with the Sigma converters, and indeed the lens only focuses down to 0.5m with the 1.4 TC attached. That's exactly where the effective aperture jumps from f/5.6 to f/6.



You can of course focus closer manually. At MFD, the combination has an effective aperture of f/8 wide open (and for the record: f/11 with the 2x TC).



With the 2x TC, the lens should principally be able to AF from infinity down to 3m ... that's where the effective aperture decreases from f/5.6 (wide open) to f/6. No success, though, AF is nonfunctional with this TC, regardless of the focus distance.



-- Markus

[popo]

[quote name='mst' timestamp='1312831276' post='10523']

You can of course focus closer manually. At MFD, the combination has an effective aperture of f/8 wide open (and for the record: f/11 with the 2x TC).

[/quote]

I noticed that when I was buying the non-OS version of the lens. Sigma's own web pages also state no AF with 2x on it, although not why.



Maybe my calculations are a little out, but I make it effective f/9.6 and f/16.8 with the 1.4x and 2x both at MFD. That's based on (1+magnification)*aperture so:

(1+1.4)*2.8*1.4=9.6

(1+2)*2.8*2=16.8



Or am I applying that incorrectly, or fails to take consideration of some other effect?

[miro]

[quote name='Klaus' timestamp='1312827580' post='10514']

160 degrees here I'd say.

[/quote]



By my Sigma 150 non OS

270 degregree between MFD and next limiter.

around 260 degree between MFD and Infinity mark.

[karlmera]

[quote name='Brightcolours' timestamp='1312806797' post='10500']

Yes, that is the nature of MTF tests.

[/quote]



Are the MTF-curves of Schneider and Rodenstock macro lenses the results of infinity-testing?

[mst]

[quote name='popo' timestamp='1312832497' post='10525']

Or am I applying that incorrectly, or fails to take consideration of some other effect?

[/quote]



Maybe ... I did not calculate, but simply read the values from the D3x's LCD <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/wink.gif' class='bbc_emoticon' alt='' />



In the end, there's not much calculation needed. The naked lens has an effective aperture of f/5.6. A 1.4x TC adds one stop (f/8), a 2x TC another stop (f/11).



-- Markus

[Klaus]

[quote name='karlmera' timestamp='1312833947' post='10528']

Are the MTF-curves of Schneider and Rodenstock macro lenses the results of infinity-testing?

[/quote]



The industry standard is to supply MTFs at infinity focus unless otherwise specified.

At least conventional lenses are primarily optimized to perform best here AFAIK.

That said you always have a multi-parameter optimization.

[popo]

[quote name='mst' timestamp='1312834903' post='10529']

Maybe ... I did not calculate, but simply read the values from the D3x's LCD <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/wink.gif' class='bbc_emoticon' alt='' />



In the end, there's not much calculation needed. The naked lens has an effective aperture of f/5.6. A 1.4x TC adds one stop (f/8), a 2x TC another stop (f/11).



-- Markus

[/quote]

I think that doesn't take into consideration the extra magnification. I first saw the equation I used in the MP-E65 manual. Things get scary rapidly at 5x magnification...

[karlmera]

[quote name='Klaus' timestamp='1312835041' post='10530']

The industry standard is to supply MTFs at infinity focus unless otherwise specified.

At least conventional lenses are primarily optimized to perform best here AFAIK.



[/quote]



And macro lenses?

[miro]

[quote name='karlmera' timestamp='1312875537' post='10534']

And macro lenses?

[/quote]

As already Klaus mentioned, he cannot perform tests at macro distances at reasonable price.

If you have idea how he/we can do such test please let me/us know.

It makes no sense to discus /dream/ something that cannot be made. Isn’t it?

[Klaus]

[quote name='karlmera' timestamp='1312875537' post='10534']

And macro lenses?

[/quote]



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.