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Old Nov 17, 2006, 2:04 AM   #1
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I just got this lense, and I plan to get a converter for it. I hear alot of bad words on the norwegian forums about using a 2x converter with just about any lenses, and was wondering what people here experience, specially those with experience with this Sigma lense.

I will get a 1.4x converter as well, but not sure what kind to get. From what I hear, Kenko is both a cheeper, and compatible with more lenses than atleast Canons converter. My first choice would be Sigmas own converters, since im more guaranteed compatibility with the Sigma lense. Kenko's converter are a few bucks cheeper tho, and if I get the same result with both I migth as well get the Kenko version.

Also, I noticed that this lense is notisable sharper on F4 then it is on F2.8. But when using a 1.4x converter and using F4, will this means that my lense shoots wide open? If so that would mean I had to use F5.6 to get the same degree of sharpness as I normaly do with F4?
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Old Nov 17, 2006, 8:13 AM   #2
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Hanzo wrote:
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Also, I noticed that this lense is notisable sharper on F4 then it is on F2.8. But when using a 1.4x converter and using F4, will this means that my lense shoots wide open? If so that would mean I had to use F5.6 to get the same degree of sharpness as I normaly do with F4?
With every lenses the sharpness will increase when stopped down from wide open...
You are also experiencing the same issues here as some folks complaining about their 50mm f/1.8 are not as sharp @ wide open -> The perceived sharpness varies with contrast and lighting so try your lens again on a good sunny day @ f/2.8.

In fact according to the measured MTFs the 120-300 f/2.8 out resolves the famed EF -300mm f/2.8 L when wide open - Checked it out: :-)
http://www.photozone.de/8Reviews/len...28is/index.htm
http://www.photozone.de/8Reviews/len...0_28/index.htm


F/4 with a 1.4xTC means the lens is @ f/2.8 because you loose a stop with a teleconverter. Similarly you'll loose 2-stop with a 2x teleconverter -> f/5.6 will mean the lens is set to wide open!




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I will get a 1.4x converter as well, but not sure what kind to get. From what I hear, Kenko is both a cheeper, and compatible with more lenses than atleast Canons converter. My first choice would be Sigmas own converters, since im more guaranteed compatibility with the Sigma lense. Kenko's converter are a few bucks cheeper tho, and if I get the same result with both I migth as well get the Kenko version.
There's more to teleconverter than sharpness...

The Sigma and Canon's version are thicker for a reason: They have more corrective elements (and why they don't fit on certain lenses because they are thicker and will collide with the rear elements) to correct for CA. I've staked two of them on top of one another to multiply their power and the resulting image are relatively free of CA:
http://www.stevesforums.com/forums/v...640816#p640816

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Old Nov 17, 2006, 10:23 AM   #3
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NHL is right on the money. Every lens is sharper stopped down. And sharpness and focus accuracy increase with light and contrast.

I shoot a lot of sports with this lens so I'm always using it at 2.8 (sometimes because I need to in order to get focus speeds but always to get a shallower depth of field). No way am I getting as sharp of an image at a night game as I do during the day. And, even during the day, it depends on contrast. Same is true of any other lens out there.

This lens still performs very well for me with my Sigma 1.4x TC on it. Very, very slight degradation of focus speed - but if the lighting is really good it's still lightning quick.

The other thing to realize is depth of field plays a big part - going from f4 to f2.8 when you're shooting with a 300mm lens you need to have your focus dead-on. So while the lens is indeed sharper stopped down a contributing factor can also be depth of field.
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Old Nov 17, 2006, 11:00 AM   #4
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Good info guys as I am also looking at this combination. John how much loss of quality do you get when using the 1.4x Sigma Telecon as with mine on my 70-200 2.8 it seems to be quite a lot. Here is a typical shot http://www.photographysmith.co.uk/IMG_8456.JPG

Thanks,

Mark
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Old Nov 17, 2006, 11:08 AM   #5
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Mark,

I'll say I'm happy with my results. But I'm not a pixel peeper. Here are some galleries / photos when using the 120-300 plus 1.4x TC:

http://www.jagsportsphotos.com/gallery/1804928



This gallery from this page (page 4) on:

http://www.jagsportsphotos.com/galle...035/4/72115527

Those are the two I distinctly remember using the TC for. I know I have some other galleries where I used it but don't know which ones off the top of my head.


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Old Nov 17, 2006, 4:19 PM   #6
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They gave you the measured MTFs degradations from the 1.4x in the previous link: :idea:
http://www.photozone.de/8Reviews/len...0_28/index.htm
120-300 f/2.8 EX :
Sigma f/2.8 f/4 f/5.6 - (@300mm)
Center 1661 1709 1842
Border 1458 1530 1625

120-300 f/2.8 EX with a 1.4x on:
Sigma f/4 f/5.6 f/8 - (@420mm)
Center 1436 1605 1748
Border 1284 1558 1524


-> i.e if you stop down 1-stop with the 1.4x, you'll get the same sharpness back!
... which BTW still exceeds the EF 100-400L:

100-400L f5.6 f/8 f/11
Center 1488 1549 1508
Border 1489 1539 1512

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Old Nov 17, 2006, 5:53 PM   #7
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Nice, so you can't really complain about that and also you get the benefits of a f2.8 lens when you don't need the extra lenght.
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Old Nov 17, 2006, 8:05 PM   #8
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Mark1616

You can surely relate to this:
http://www.photozone.de/8Reviews/len...0_28/index.htm

70-200 f/2.8 EX :
Sigma f/2.8 f/4 f/5.6 - (@200mm)
Center 1562 1748 1902
Border 1481 1635 1745

-> The 120-300 will out-resolve your current 70-200
@ f/2.8 :idea:
(Also no need to use the 1.4x on that 70-200 anymore... which makes the MTFs even worse)
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