New Sigma 120-300 having trouble judging focus/softness

menthel

menthel

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Right, received my 120-300 today, great looking lens and I love the internal zoom and focus in comparison to my 150-500. It looks better than that but I still have some doubts over the lens, both with and without x2 TC on it.

If you could have a look at my test shots I would be grateful. If my tests are crap then please advise me how to do it better. All taken on tripod using 10sec self timer. The images are available full size on flickr if you click through, as are shots at intermediate f stops.

300mm @f2.8

120-300 first test-138 by menthel, on Flickr

300mm @f5.6

120-300 first test-144 by menthel, on Flickr

600mm @f5.6

120-300 first test-145 by menthel, on Flickr

600mm @f8

120-300 first test-148 by menthel, on Flickr

Thanks in advance!
 
artyman said:
They look pretty good to me, the only drawback over my 150-500 is the weight :)
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Thanks, I did wonder if it was just my eyes. I am not too worried about the weight as the internal mechanisms actually makes it a little better balanced. It will also save gym fees!

I guess the comparison with the 150-500 is rather telling!


120-300 first test-114 by menthel, on Flickr
 
postcardcv said:
massively better than the non-OS copy that I tested a couple of weeks ago, I really want to get my hands on one of these.
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It does look good now I have thought about it. I think that I may have expected a little too much of the lens with x2 but it does look very usable- technique will have to be improved though.
 
postcardcv said:
I keep thinking about getting one of these but would want to test one first (bad experience with the non-OS), and would need to sell some stuff first. Just not convinced that I would use it enough to justify the cost.
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Well this is my last ditch attempt to keep myself going with wildlife. If it doesn't work out the DSLR kit will go and be replaced by a smaller mirrorless system and more film kit!
 
If you're testing focus there, and assuming the box is square to the lens (doesn't look like it is) then it's front focusing a bit. Though you may be provoking a slight error there as you are a bit close to the target. You may get a better result at more distance, and it may be very slightly different at shorter focal lengths, and different again with the extender. Such is life, pick the best compromise.

Need to know exactly where the front of the box is on the rule though, it looks around 15cm but hard to tell exactly. Always test at lowest f/number to see more clearly.

You should be able to get it better than that with AF micro adjust.
 
simonblue said:
Have to say the photo look fine to me :)
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In terms of focus, look at the first and the third pic, which are both at lowest f/number.

Sharpest point on the rule is about 13cm, which looks like it might be about 1cm in front of the box at 15cm (which presumably was focused on).

Now the box isn't quite square, though not far off. But if what we're seeing is kosha, then being 1cm out on a head shot of a garden bird is just not good enough, and that lens should be able to do better.

Looks like a simple thing to sort with AF microadjust - that's what it's for.
 
HoppyUK said:
In terms of focus, look at the first and the third pic, which are both at lowest f/number.

Sharpest point on the rule is about 13cm, which looks like it might be about 1cm in front of the box at 15cm (which presumably was focused on).

Now the box isn't quite square, though not far off. But if what we're seeing is kosha, then being 1cm out on a head shot of a garden bird is just not good enough, and that lens should be able to do better.

Looks like a simple thing to sort with AF microadjust - that's what it's for.
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Fair enought,but till it is given a full field shoot,its going to be hard to tell,the ruler is an at an angle,so its hard to tell :)
 
Thanks all. One last, stupid question- what direction does then adjustment need to be in? + or -?
 
menthel said:
Thanks all. One last, stupid question- what direction does then adjustment need to be in? + or -?
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I think it's plus, but it could be minus!

Just do the shots again, preferably at a bit more distance, making sure all is flat and square. Then shoot at say +10, 0, -10. Then find the sharpest one, and do +5, 0, -5 around that, then fine tune around there.

Final consistency check, at your chosen setting, shoot another set of four or five frames, defocusing the lens between each, and make sure they're all spot on.

With a decent LCD, you can zoom in on that to see what's what. No need for computer.
 
HoppyUK said:
I think it's plus, but it could be minus!

Just do the shots again, preferably at a bit more distance, making sure all is flat and square. Then shoot at say +10, 0, -10. Then find the sharpest one, and do +5, 0, -5 around that, then fine tune around there.

Final consistency check, at your chosen setting, shoot another set of four or five frames, defocusing the lens between each, and make sure they're all spot on.

With a decent LCD, you can zoom in on that to see what's what. No need for computer.
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Thanks. Part of the problem is my eyesight- I don't trust it too much with the LCD. I may well post up some shots just to make sure I have it right!
 
menthel said:
Thanks. Part of the problem is my eyesight- I don't trust it too much with the LCD. I may well post up some shots just to make sure I have it right!
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Cool. Yeah, post 'em up :)

Another way of doing it, sometimes easier from a practical point of view. Pin a magazine page or similar to a wall, or BluTack it. Something with nice bold graphics to give the AF a good lock, and also some fine text to examine. Set camera up square/tripod.

Same procedure, +10, 0, -10 at lowest f/number. Examine on PC at 100% and pick the sharpest one. Then +5, 0, -5 around that. Then fine tune +/- 3 or +/- 2around that again. When you get down to increments of five, you're very close to as good as it gets. The difference between say +/- 2 is pretty hard to spot, and the lens/camera might vary by that much shot to shot.

It's important to do a final check for consistency with a series all on the same setting, defocusing between each shot.

And if you really want to go to town, a thorough check at different focal lengths, with/without extender, closer/further distance will pick up any variables there. Take careful notes! Best setting can be a bit of a compromise between all those. But you can take this stuff too far and do your head in with loads of data.

For what it's worth, with my own lenses (all good quality Canon L) once I've optimised a zoom once at a sensible distance, that setting has held good for all other focal lengths. Only shift I got was very slight when using a Kenko 1.4x on the 70-200L, and that combo comes up as a different lens option so I was able to give it an individual tweak.

Be interesting to see how you get on. It's a good lens that one though :)
 
Thanks for all of the help. It does seem like a decent lens for the price. IT also registers as 2 seperatel lenses for adjustments, once as a 120-300 and then as a 240-600 with the 2x TC. Handy really!
 
If you take a few shots of the Queen on the £5 note using the settings below then you can compare the sharpness of your lens with the tests I did with:

1. Canon 300mm II + 2x
2. Sigma 120-300mm OS + 2x
3. Sigma 120-300mm NON-DG + 2x
4. Sigma 50-500mm OS
5. Sigma 50-500mm DG

Procedure
---------
2.5 meters from the £5 note
4 Shots at 600mm: 5.6, 6.3, 7.1, 8
ISO 200
On Tripod
With Remote shutter release
Mirror lock-up enabled
 
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micloi said:
If you take a few shots of the Queen on the £5 note using the settings below then you can compare the sharpness of your lens with the tests I did with:

1. Canon 300mm II + 2x
2. Sigma 120-300mm OS + 2x
3. Sigma 120-300mm NON-DG + 2x
4. Sigma 50-500mm OS
5. Sigma 50-500mm DG

Procedure
---------
2.5 meters from the £5 note
4 Shots at 600mm: 5.6, 6.3, 7.1, 8
ISO 200
On Tripod
With Remote shutter release
Mirror lock-up enabled
Click to expand...

micloi said:
You might find these useful:

Canon 300 II 600mm f6.3
Canon 300mm f4 non-IS at 588mm f8
Sigma 50-500 500mm f6.3
Sigma 120-300mm non-OS non-DG 600mm f6.3

http://dl.dropbox.com/u/16187250/telephoto comparision/Comparison.zip
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Thanks Michael. When I have some time I will have a look.
 
Just as a postscript- ended up with +3 dialled in and do far the focus looks good and the picture quality both with and without x2 looks great, even wide open. Very, very happy with the lens and it really is a big upgrade (bloody well should be for the price!) over my old 150-500.
 
:thumbs:
 
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