In need of calibration?

Cris_L

Cris_L

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Cris
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I recently purchased a second hand sigma lens and am finding the focussing fairly soft compared to my kit lens. I've seen images that the seller had taken soon before selling and they are pin sharp.

I've read a few things about "front focussing etc" and from what I understand its not too uncommon for cameras and to have a slight focussing error. So if the camera has an error of say - 2 and the lens an error of +2 the difference may be too great. (at least i think thats how I understand it).

My camera is only a couple of months old (500D) so I'm wondering if i should send it to canon for calibration and then try the lens again?

has anyone been in this situation before?

Just to add, I in no way doubt the honesty of the seller so I'm not suggesting he sold me a lens that he knew was soft, the images from his camera are great.
 
Last edited:
What's yr camera like with other lenses? If it's fine then it's probably the lens that's the problem.
 
Post some examples up, and we'll have a looksee!

I was convinced my sigma lens was soft when I first got it, however with a bit of practice I soon realised it was user error! What lens is it?

Chris
 
Its fine with my kit lens and my 50mm prime but thats all I have.

The photos I have seen the seller take with this lens are great though, definately sharp and he's genuinely surprised to hear I'm having problems (also offering to help in any way he can).

I do have a friend with a Canon, maybe I should try his lenses first?
 
Ok here we go, The first of each pair is the sigma - the second is the 18 - 55 kit.

Used a variety of subjects for this test and tried to keep the camera in the same place (on the tripod) for each of them.

As mentioned the seller found this a great lens (and I have no reason to doubt his word, he is being very helpful).

all at f8, shutter speed 125, lencarta softbox providing the light. Tripod mounted camera to reduce the chance of shake. I usually shoot raw but did these jpg so they are straight out of the camera, just a crop in elements.

Hopefully it is user error although I'm just auto focussing as normal....?

sig
5058000298_4ba1a5c5c9.jpg


kit
5057997628_e3f9e8f5e5.jpg


sig - tree
5058003378_6a97677b97.jpg


kit - tree
5057393193_a146971d81.jpg

sigma -hair stuff
5057376265_62f6dec258.jpg


kit hair stuff
5057986464_501b6d5bdd.jpg
 
put the sigma in manual

put the camera in live view

zoom to 10x (on the screen ! )

manually focus

take the shot

see how that works for you :thumbs:

you are then ignoring what the camera AF sensor thinks, and going off the image the sensor is seeing, and capturing it.

This will be about the best your lens will give .

Try a few different apertures too

maybe F11 to F16 ... but you will start to get diffraction, if you go smaller than that
 
Please put up some 100% crops of those shots.

It's completely impossible to assess sharpness on images that small.
 
Sorry i can't work out how to get them much bigger...this is a little better. Can see full size ones at my flickr.

help greatly appreciated as i'm not sure which way to go...lens calibrated, body calibrated, sell lens on (could I have this issue with another lens if my camera is front focussing?),,,etc?

sig
5057607137_22c38e37db.jpg

kit
5057608689_f5c0e729f2.jpg


sig
5057610309_d935e62dde.jpg

kit
5057612227_649d20437f.jpg
 
I am the seller and thought I post as I might help.

I got the full size photos on the email by Chris. What I noticed:

1. The Sigma shots are not as sharp as they should be. Lens if front focusing on Chris' 500D
2. I used the lens on 3 cameras before I sold it and it was sharp even at f2.8 so for the lens to front focus at f8 on Chris' camera that leads me to believe that the AF on his body is off
3. No.2 seems to be the point also by looking at the full size photos of the kit lens where still there is some front focusing.

What I suggested:
Take some shots at home, on a tripod (or keep the camera stable in some way) at low apertures (f2.8 on the Sigma and nifty fifty and f3.5 on the 18-55mm).
Use one of the special printouts for checking focus you can find online.

If more than one lens front focuses then send the body to be calibrated.

If only the Sigma front focuses and the rest are ok then you can return the lens to me for a full refund.

Cheers
 
Ok thanks, I'll run a test at low apertures and compare the results. I'm able to borrow a 55-250 and also a 100mm macro so that'll be 4 different lenses to try.
We'll get there in the end!
 
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