How far is this front focusing?

[danbroad]

Hi folks, long time away - more time taking piccies.... anyway, advice gratefully received here.

Not best pleased with my Sigma 24mm f/1.8 at the moment. Here's why - a boring shot of my kitchen, I'm afraid, with terrible WB etc etc... - anyway, f/2.8, mirror lockup, ISO 100, tripod, NR off, central focus point only. No USM or postprocessing. Focus point is on the word welcome. Distance is 1.1 metres from 'welcome' to the sensor. These are both crops - 'welcome' was dead centre, so no DoF parallax errors attributable here..

IMG_1221 by danbroad1000, on Flickr

IMG_1221-2 by danbroad1000, on Flickr

larger versions on flickr, forum rules observed here..

Anyway, shot a wedding as a guest recently, and many of the shots with this lens were blurred. Couldn't figure out why - though perhaps my technique with a relatively new camera was to blame. Haven't gotten round to performing this test until now. I make it about 18cm - agree?

Bought new from Jacob's on 1st September.


Cheers, Dan


*edit - just off to give that telly a wipe down... done!*

 

[gman]

That seems really bad and agree that 18cm appears to be sharpest!

What about try a shot of just the tape measure laid flat at an angle away from the camera. Extend say 50cm and focus on the 25cm mark, then you can go back and say exactly how many cm it is out by (or mm which will sound higher!)

 

[foggy4ever]

Looking at your exif and using dofmaster focusing at 1.1m gives you a dof of 31.9cm....13.7cm in front and 18.2cm behind. I think your test subject is too far away and the writing needs to be bolder with crisp edges. Try the spines of a few books staggered and work out your dof first.

 

[magicaxeman]

Yep that sigma is way off...

 

[danbroad]

Looking at your exif and using dofmaster focusing at 1.1m gives you a dof of 31.9cm....13.7cm in front and 18.2cm behind. I think your test subject is too far away and the writing needs to be bolder with crisp edges. Try the spines of a few books staggered and work out your dof first.

Ian, foggy, gman - thanks for all the advice, folks - I'll try the book spines test. I am interested in the subject distance, though - at 1.1 metres, this is pretty much where I'm shooting upper body portraits etc - none of my shots at this distance came back with eyes in focus!

 

[danbroad]

Anyway, to tie up this thread - the book test showed exactly the same. So, back to Jacob's the lens went.

Jacob's had another of these in stock, so we set about testing it in store using the same 'lab' conditions - ruler, text, tripod, MLU, base ISO and 2 sec timer..

Mine is front focusing about 18cm, the other one seemed to front focus by about 12cm. So, both those lenses are heading back to Sigma UK for checking. Shame, because it's a lovely lens otherwise, which offers so much....

Anyway, Jacob's Liverpool were fantastic, and worthy of praise here for putting up with me... I'll return to them for future business, and I'd have no hesitation in recommending them to anyone.

Cheers, Jacob's!