Sigma 70-300APO is really soft

rgrebby

rgrebby

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Ive been taking a some pictures of wildlife with my sigma lens but it seems that it is very soft.
I know that at 300mm its not the best lens but I thought it would be ok. Also, im using a tripod, cable release, high shutter speed.
I'll post some pics without any post sharpening as soon as my girlfriend stops playing sherlock holmes on my main computer :p
 
Are you shooting with the lens wide open, stop down to around f8 and see if the results are the same.
 
I will add use a tripod or fast shutter as it is a long lens and the finest of movement is magnified. But as you are the advice is try a f stop of f8 like Sbowler says.
 
Already use a tripod, fast shutter like I said.
I'll try F8, what is the reason behind this?

Excuse my stupidity but wide open, do you mean 300mm? As im really just worried about the softness at the top end.

Heh, now I understand, the apature wide open, yeah sorry im having one of those days...
Usually im at a very low F number, pretty much the min, I'll try and see what happens with around F8.

Still I dont understand why this helps
 
It's just about optics. With almost every lens, by stopping down a bit, you get better results (better sharpness, better contrast, less chromatic abberations). Some lenses get their best performance at f/8, others at f/11. Try finding an MTF chart for your lens and see where it performs best

EDIT: Just found This. It's in Polish so i don't understand what it sais but I can read the chart.

This is an MTF chart for your camera. Each coloured dot represents the focal length that sais on the right, the horizontal axis shows the apertures and the vertical axis shows the sharpness, with 50 being the max, as you can see, at f/8 it achieves the highest sharpness rating on all focal lenghts. But again, as you can see again, at 300mm (the black dots) it's considerably softer than other focal lengths. It's actually soft at any standards.
 
I had the same lens before getting a longer one, I found 70-300 a good lens ,even better on a tripod. I also found it a little soft at 300mm, F8 seemed to be the sweet spot and a faster shutter speed 300 and above if possible gave me the best results, I usually went as far as around 275-285mm and used to keep things sharp.
 
Thanks, this all helps a great deal. I'll post some before and after images when I get a chance, the diagram on that website looks very interesting, i'll have to find one for my sigma 17-70 lens too.

Also, on that link, which table is the right one, they both hold info but the results are very different, which is the right one?
 
Well as I said I can't speak Polish, but to my understanding the first chart shows center sharpness while the second one shows sharpness towards the edge of the frame.

Here is a test for your 17-70. It looks great actually from the MTF charts.

Towards the bottom of the page there is a list of 12 options, that says Spis treści on top. Numbers 4 and 11 are MTF charts and Test photos respectively.
 
Yep, this lens performs much better at f/8. It's usable wide open but I always stop down toward f/8, usually f/7.1 actually as it does give you that bit extra shutter speed but only a very small difference between that and f/8.
 
Ive been looking at the charts on photozone.de for my sigma lens and it seems that F8 is the sweet spot, its making some sense which hopefully will be proven when I view the pictures.
One this I do notice, at 200mm F8 the sigma lens has a score of 1931 at the center.
However the Canon 70-200mm f2.8 USM L IS lens only has 1880 at 200mm f8. I would have thought that an L glass lens would be a whole lot sharper than a £100 sigma. Or am I reading all the numbers wrong?
 
I find that the 70-300 APO needs to be stopped down to at least 7.1 to get good results from it.
 
rgrebby said:
Ive been looking at the charts on photozone.de for my sigma lens and it seems that F8 is the sweet spot, its making some sense which hopefully will be proven when I view the pictures.
One this I do notice, at 200mm F8 the sigma lens has a score of 1931 at the center.
However the Canon 70-200mm f2.8 USM L IS lens only has 1880 at 200mm f8. I would have thought that an L glass lens would be a whole lot sharper than a £100 sigma. Or am I reading all the numbers wrong?
Click to expand...

You might be right, don't know the charts you are saying but, don't forget that 200mm is at the middle of the focal range of the Sigma, but at the long end of the Canon. Most of the times, if not always, the long end of a zoom is the one that suffers from IQ loss.
 
rgrebby said:
Ive been taking a some pictures of wildlife with my sigma lens but it seems that it is very soft.
I know that at 300mm its not the best lens but I thought it would be ok. Also, im using a tripod, cable release, high shutter speed.
I'll post some pics without any post sharpening as soon as my girlfriend stops playing sherlock holmes on my main computer :p
Click to expand...

I rarely use mine beyond 200mm if I can help it because it's basically unusable in terms of sharpness beyond that most of the time.
 
I use the 70-300mm sigma DG, I dont know what the difference is between mine and the APO but I get the same problem at 300mm.
Although it doesnt take too much to sharpen it.. it would be better if it was sharp when taken.
I will try F8 and see how that comes out :)
 
This is why I got rid of my sigma, way too soft anything less than about f7. It’s a bit of a catch 22 as you need to shoot fairly wide open to get your shutter speed up.
 
Yeah I agree with you Slapo, I don't use mine a great deal but I've shot it at 300m at 5.6 and got some great shots with plenty of sharpness. I expect they differ from lens to lens.
 
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