[Gilly B]

I am really worried about this lens I have just bought 2nd hand. Can anyone give me some advice on how I can tell if this lens is a bad copy. It appears really soft at f2.8 and f4 and 24mm and 35mm. Thanks

[Steve]

Set your camera up on a tripod in front of a well and evenly lit, detailed scene, use mirrior lockup and remote shutter release and take shots at a whole range of different settings. Make sure you do a set using manual focus and then do another set with autofocus.

Open the unprocessed shots on your computer and compare the results. You should be able to tell where in the frame the lens is the sharpest (all lenses have some detail falloff at the sides ), which F stops give the best results (usually around F8), if there is any autofocus issues (compare the shots from manual and AF at the same F stops for an accurate assessment).

Once that is done you can repeat the whole process with a known trusted lens for a very rough comparison. Remember that without exception, the smaller the Fstop used the less sharp the results will be, no matter which lens. You should therefore not expect the same results from the same lens at f2.8 as at f8.

Hope that helps.

[Gilly B]

Thank you. I will try that later on an let you know the outcome.

[Soupdragon]

Some examples with EXIF data would be really usefull in assessing if there was a problem.

[Gilly B]

Originally Posted by Soupdragon

Some examples with EXIF data would be really usefull in assessing if there was a problem.

I am going to test it again as per Steve's advice tomorrow and then if I am still concerned, I will post a few for your comments.

Just come off the phone with Fixation and they charge £95 +VAT to calibrate a lens, so I will need to be sure. Thanks Guys.

[Steve]

Originally Posted by Gilly B

Just come off the phone with Fixation and they charge £95 +VAT to calibrate a lens, so I will need to be sure. Thanks Guys.

Ref this point, if you do decide to have the lens calibrated, get it done together with your camera. You'll always get better results that way

[Gilly B]

Okay, I tested the lens on a tripod, with a cable release and the mirror lock up enabled. I used 17-40mm @24, 35 & 40mm and the 70-200 2.8 IS @70mm right through the range from f2.8 - f11. Cropped to 100% and the 24-70mm looks pin sharp. Thanks for the advise guys and if I knew how to post them to show you, I would. Maybe you could point me in the right direction for this information.

[Sonsey]

Originally Posted by Gilly B

Thanks for the advise guys and if I knew how to post them to show you, I would. Maybe you could point me in the right direction for this information.

Here you go -

Guidelines for Members Gallery - How to Upload

Guidelines for Members Gallery - Where to Upload

Don't hesitate to post back if you've any further problems.

[Steve]

I'm glad you got it sorted

To carry those pin sharp results through to your everyday photography, keep a close eye on your shutter speeds. From your original post and the results you obtained through your controlled tests it tells me that the initial poor results are more than likely due to camera shake causing image blur. Using faster shutter speeds will help combat that, especially when shooting hand held.

[brian wright22]

I have also noticed this problem with "unsharp" pictures sometimes,especially when I gave up using my film camera and went digital.

I think I have solved my problem by increasing the shutter speed for every shot I take when the lens focal length is longer that 60mm.
On my Canon DSLR this equates to a focal length of nearly 100mm when compared to using a full frame 35mm camera ,where 60mm would be 60mm!.

Any movement of the digital DSLR camera is magnified by about 60%, a frightening thought. Brian

[Gilly B]

Originally Posted by Steve

I'm glad you got it sorted

To carry those pin sharp results through to your everyday photography, keep a close eye on your shutter speeds. From your original post and the results you obtained through your controlled tests it tells me that the initial poor results are more than likely due to camera shake causing image blur. Using faster shutter speeds will help combat that, especially when shooting hand held.

I am inclined to agree with you. It is much heavier than the 24-105 and 14-40 so it was probably a bit of camera shake.

Thanks Sonsey for the guides - I will have a read later.

[polka]

It should certainly be as sharp if not sharper than the equivalent Siggy.

Sigma 24-70mm f/2.8 EX DG Lens Review Test Images

They say that the Sigma is slower at focusing but as sharp at the wide end fully open as the 24-70L, of course it's a third of the price!