Front/Back Focus Check

[eosdigital]

Yes, one of the countless threads regarding this topic.

Just got my new lens yesterday, and tested for focus accuracy today.
Is the results acceptable? There seems to be a little back focus biasness in both tele and wide end.




If this is completely unacceptable, i can sent in to CSC but very troublesome and hassle-some.
Thank goodness there's FTM so i can adjust minor focus during shooting

[eosdigital]

More test shots

[flipfreak]

the black focus line didnt appear in focus in the first place.

[eosdigital]

Hello, are you referrring to the rear black bar to the Focus Bar?

In my tests, i was looking at the millimeters description to the left and right of the focus bar. My assumption of slight back focus biasness was because the 2,6 and partly 10mm after the Bar was more sharp than the one below it.

Am i wrong to assume that, and in this case this is normal focusing radius?

[engrmariano]

try shooting the real world.

[eosdigital]

Originally Posted by engrmariano try shooting the real world.

Yup i know that. But im wary of this problem and want to confirm if it's one because i do not want to go out shooting one day and find out after that most of the shots are OOF or Minor OOF because of this issue

[Octarine]

What lens are you testing here? Looks to me that your aperture is not set to maximum opening. Not sure about the angle (seems a bit steep) and if you are at minimum focusing distance.

[eosdigital]

Originally Posted by Octarine What lens are you testing here? Looks to me that your aperture is not set to maximum opening. Not sure about the angle (seems a bit steep) and if you are at minimum focusing distance.

Should be at MTF. Im using handheld because the cheapo tripod i have ended up damaging my batt grip so i dont want to use that.

Aperture is wide open at F/4. Lens is the 17-40mm f/4 L USM

[calebk]

Originally Posted by eosdigital Should be at MTF. Im using handheld because the cheapo tripod i have ended up damaging my batt grip so i dont want to use that. Aperture is wide open at F/4. Lens is the 17-40mm f/4 L USM

Remove your battery grip and use the tripod. You have to remove all elements that may cause error. Here, because it is handheld, the most likely cause of error is slight movement back and forth.

BTW, it's not MTF (that's resolution charts), it's MFD (minimum focusing distance).

As an aside, why not just shoot some stuff in the real world today as a test? At least it's a non-critical application.

[gman23xx]

Try shooting outdoors. Like some subjects or flowers. You can get a rough gauge. From what i see it's not that bad, but back focus is a little off. Sometimes, lens don't work well on paper based tests, try real life subjects with more light.


gman

[muvouser]

is your cam mounted EXACTLY 45 degrees when you shoot the chart?

[catchlights]

if you want to do the test, at least use a tripod lar,
and also get your exposure right too.

btw, you only tested on the 17mm,

how about other focal length?

anyway, since the dof is 1/3 at the front and 2/3 at the back of the focusing point, so the test seem rather OK to me,

don't forget, even you have a very sharp lens with no front or back focus issue,

in a real world application, many time can't even get sharp focus due to user problems, so unless your really really think your lens have some issues, else doing the test it is not necessary.

[eosdigital]

Originally Posted by catchlights if you want to do the test, at least use a tripod lar, and also get your exposure right too. btw, you only tested on the 17mm, how about other focal length? anyway, since the dof is 1/3 at the front and 2/3 at the back of the focusing point, so the test seem rather OK to me, don't forget, even you have a very sharp lens with no front or back focus issue, in a real world application, many time can't even get sharp focus due to user problems, so unless your really really think your lens have some issues, else doing the test it is not necessary.

Er.. the first and 3rd photos were in 17mm, the others in 40mm end.
But thanks for the advise anyway