300mm 2.8 poor IQ with pics

Hmmmm,
After thinking I had a problem with my TC, after a few more tests the lens appears to be the issue. I carried out some tests today, and the difference between wide open and stepped down is huge.
Should the results be better than I am getting ? I accept the lens may improve a bit stepped down but should there be this much of a difference. The whole point of a wide aperture telephoto is the ability to shoot at wide apertures in low light conditions.
The details are,
Camera 7d, ( I have done MA )
Lens Sigma 300mm 2.8
Tripod mounted,
Mirror lock up,
10 sec timer,
First pic wide open at 2.8. the second pic stepped down to F8.

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manual focus?

if not try it.
if it sharpens.. AF might be out of wack. have it calibrated.

You can stop down the big 300?

My copy is wicked sharp wide open on a 10mp 1.6 and a 21mp FF.

Something is not right here IMHO.

aerosmith9110 wrote in post #12458796
manual focus?

if not try it.
if it sharpens.. AF might be out of wack. have it calibrated.

I did try manual focus and it did improve. I bought this lens off ebay the other day and this is the first chance I've had to put it through its paces. I have sent the seller an email tonight and I'm waiting for a reply.....

dave kadolph wrote in post #12458805
You can stop down the big 300?

My copy is wicked sharp wide open on a 10mp 1.6 and a 21mp FF.

Something is not right here IMHO.

I already have a 100-400 and I was wanting this lens for its wide aperture, so I could shoot in low light. My 100-400 has better IQ than this.....

Shoot something along the length of a fence so you can spot if it's miss-focusing a little and inspect the in-focus area. If the sharpest point is still poor then unfortunately it looks like the lens isn't very sharp.

How does it look between F/2.8 and F/8? Sometimes a lens that is a bit soft wide open can show a fair improvement just 1/3rd stop down (i.e. F/3.2), which although not ideal is still a significant advantage over F/4, for example, and isn't so bad.

h14nha wrote in post #12458832
I did try manual focus and it did improve. I bought this lens off ebay the other day and this is the first chance I've had to put it through its paces. I have sent the seller an email tonight and I'm waiting for a reply.....

Manual focus improved it? I think you answered your question and should check your MA adjustments. Try manual focus with live view at the highest magnification, I bet you will be suprised how sharp it is when you get it in proper focus.

Thanks both,
I will try the fence shot tomorrow in the daylight, and I'll shoot in increments up to F8.
I did MA the set up the other day and it was spot on. I will repeat the MA to make sure I didn't make a mistake in the process and repost the example shots.
Cheers, off to bed now as its my bedtime

normally if you have problems with 300mm 2,8 IS you are not a good photographer

vreeke wrote in post #12494573
normally if you have problems with 300mm 2,8 IS you are not a good photographer

May I ask how you arrived at that conclusion? Have you met a number of photographers, all having problems with their 300 2.8, and most of these photogs were no good?

vreeke wrote in post #12494573
normally if you have problems with 300mm 2,8 IS you are not a good photographer

...but people not reading the original post are just plain dumb

(For those who read the 300 2.8 bit and not the SIGMA bit!)

300 2.8 is very sensitive for focusing errors at wider apertures. Dof is just so narrow.. So AF microadjustment has to be done very carefully. It has to be spot on in accuracy of 1-2 steps.
As example, 7D has 40 total steps for AF fine tuning ( -20----0----+20). If you get bad IQ at -7, it is possible that IQ is perfect when adjusted back to -5.
Believe me, I have been there and done that for my 300 2.8L and it was not that easy task.
I had similar problems with poor IQ..

Wow, Ian, I would be concerned, too, but follow the advice given earlier by other posters, and don't forget to let us know how this turned out!

Julius

Keep us posted, I don't see many posts of problems with this lens. I'm curious what the seller says. Are there any marks on the exterior body indicating trauma?

Sigma lens, how much you paid? If too good a deal then I would say it is the lens. It is better to buy this kind of gear in person where you can check things before paying.