Back focussing?

D

DRZ

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120
Name
Martin
Edit My Images
Yes
Hi,

I took my Sigma 70-200 F/2.8 (APO Non-macro) around to a fellow TP member's house today as I have it up for sale. Anyway, he tested the lens as is normal and he revealed to me shots that showed that the lens was quite severely back-focussing. I honestly could not at all believe what I was seeing as I had tested for the same myself when I bought the lens and I have used it a few times with no issues and have got some reasonable (IMO, of course) shots with it.

So... I went about the rest of my day today and tonight I took some test shots. Not exactly ideal lighting circumstances but I just had to know.

http://www.twobeds.com/upload/userfiles/DRZ/_DSC1176.jpg
http://www.twobeds.com/upload/userfiles/DRZ/_DSC1179.jpg

In both of these shots I had the centre focus point selected. In the image with the tie, the point of the tie was selected and I was stood approximately 15ft away. In the shot of the wood the lower knot was selected and I was stood about 18-20ish ft away.

I will need to sort my printer out and print a focus test chart out etc but from these quick shots it looks pretty bob on to me?

If it does need to be calibrated, what am I looking at as a likely cost for this to be done?
 
I can't see evidence of back-focussing but of course that is only my opinion.
 
I'd be quite happy with those images at the focus point you say. Perhaps your mates camera is out?
 
arad85 said:
I'd be quite happy with those images at the focus point you say. Perhaps your mates camera is out?
Click to expand...

Well, he put on a Tamron lens and re-took the shots and those seemed to be right. Could of course be that that lens is front-focussing and his camera is back-focussing to result in a perfect shot, but I would rather give him the benefit of the doubt on that as I am the seller and he is the buyer :)
 
seeing as the tie was shot at f/2.8, I can't see any backfocussing issues with it.

Perhaps he was using this as an excuse to haggle on price ?
 
My only criticism would be the choice of tie with shirt, and the fact that the skirting had not been primed and painted white, other than that the point of focus seemed fine.;)
 
andy700 said:
My only criticism would be the choice of tie with shirt, and the fact that the skirting had not been primed and painted white, other than that the point of focus seemed fine.;)
Click to expand...

:D

Grabbed a tie from the rack and a shirt from the laundry basket. Skirting is waiting to go in once the new floor is down (hence the rolled up carpet too!).

Thanks for all the replies folks - I will try and do some more testing and see, don't want to sell a dud (and I don't think this one is at the moment? :shrug:) but I do need to be sure either way.
 
Hi all, just tought I would post the test pics I took yesterday

First is the Sigma both focus points on front post

lenstest001 by Ballpix Sports Photography, on Flickr

and the Tamron


lenstest002 by Ballpix Sports Photography, on Flickr

Olly, the op is asking for opinions on the lens, we already agreed a price. We are both decent guys and fellow TP'ers, he wants to sell a good lens, I want to buy a good lens. ;)
Phil.
 
phil8139 said:
Hi all, just tought I would post the test pics I took yesterday

First is the Sigma both focus points on front post

lenstest001 by Ballpix Sports Photography, on Flickr

and the Tamron


lenstest002 by Ballpix Sports Photography, on Flickr

Olly, the op is asking for opinions on the lens, we already agreed a price. We are both decent guys and fellow TP'ers, he wants to sell a good lens, I want to buy a good lens. ;)
Phil.
Click to expand...

Hi Phil

I'm not an expert on front / back focusing, but would have thought your best shot would have been to focus on the 2nd main post wide open, this would then allow you to see the post or spindle that is best focused.

To me the spindles just after the main post look slightly more in focus on the 1st shot, but a few quick questions

Was the Camera tripod mounted or hand held ?

Were the settings identical for both shots (shutter & app etc) ?

Have you cropped either photo - if you hover your mouse over the front corner of the main post in the 2nd photo - which I presume is the focal point and scroll up and down - the spindles that are in focus line up with the mouse. It looks a slightly different composition, the camera has moved slightly to the right for the 2nd photo.

Not sure if it is of any use, but did you try the same shots on the OP's camera body ?


Hope this is of some help....

Andy
 
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andyred said:
Hi Phil

I'm not an expert on front / back focusing, but would have thought your best shot would have been to focus on the 2nd main post wide open, this would then allow you to see the post or spindle that is best focused.

To me the spindles just after the main post look slightly more in focus on the 1st shot, but a few quick questions

Was the Camera tripod mounted or hand held ?

Were the settings identical for both shots (shutter & app etc) ?

Have you cropped either photo - if you hover your mouse over the front corner of the main post in the 2nd photo - which I presume is the focal point and scroll up and down - the spindles that are in focus line up with the mouse. It looks a slightly different composition, the camera has moved slightly to the right for the 2nd photo.

Not sure if it is of any use, but did you try the same shots on the OP's camera body ?


Hope this is of some help....

Andy
Click to expand...

Hi Andy, Both shots hand held, Sigma is 2.8 tamron is 4.8 and yes the dof will be slightly larger, but both focus points are the front post which should be sharp in both. Pics just resized not cropped. Composition is slightly different as I had to guess the tamron focal distance, but exif shows it at 210mm, both were taken from the same spot.

OP never brought his body, he was selling the lens ;)

HTH,
Phil.

BTW if this lens is good, I will buy it, so im not haggling. Just need a 70-200
 
proper test should be the same lenses siggy 70-200mm at 2.8 and a tamron 70-200mm at 2.8 both mounted on tripod, set both at 200mm and set to afs and when positioned correctly both lens set to infinity then focus and take a shot then redo the same shot a couple times, then change lenses and do the same with that.
 
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Can only work with what we have Scott. I know it's not scientific, but if it's not focussing then it's not focussing.

What are your thoughts on the images ? That is what the thread is about. If the lens needs calibrating, the seller will get it done and I will buy it, if the lens is ok i'll look for another as it doesn't seem right on my camera.

Phil.
 
Afraid not, Martin took the lens with him. I took 7/8 pics with the sigma, all the same, I'm sure Martin will do the same on his body then we can compare. I have pm'd him to meet up and try both lens on both bodies then we can find a solution.

So, your opinion on the posted pics is still not out :shrug:
 
I am about to go out and try a couple of shots now!

Phil, I will reply to your PM in a moment :)
 
Phil, no offence meant, was just saying it might be possible :)

Haven't read all the replies but the tests are inconsistent in my eyes as one is shot at f/2.8 and the other at f/4.8. ISO on one is 200 and on the other 1600 too.

The Tamron pics looks better than then it's had more favorable settings. Get them both on a tripod, Av mode, same ISO and then compare :)
 
http://www.static-hiss.co.uk/Sigma/_DSC1211.jpg
http://www.static-hiss.co.uk/Sigma/_DSC1212.jpg
http://www.static-hiss.co.uk/Sigma/_DSC1213.jpg
http://www.static-hiss.co.uk/Sigma/_DSC1214.jpg
http://www.static-hiss.co.uk/Sigma/_DSC1215.jpg
http://www.static-hiss.co.uk/Sigma/_DSC1216.jpg

These are hand-held because my tripod is really truly terrible and I just couldn't be accurate enough (pressing the shutter would move the camera off what I wanted to focus on...)

I converted them to B&W as I think it brings out the detail a bit more.
 
Thanks Martin, tell me what you think about those shots.

#14 not loading for me btw.
 
DRZ said:
I converted them to B&W as I think it brings out the detail a bit more.
Click to expand...

I think it helps to emboss the images when looking for the focus point.

9cBpc.jpg


FjNGl.jpg
 
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