front focus!

[captnj]

I was checking my lenses today becase the results i got for my 80-200 APG g and my 28-75 d were not as good as i had hoped with certain subjects. I get the Focus chart from a website (the one that tells u to focus on the center thick line and looks like a ruler on both sides. My other lenses are ok but these 2, the "infocus" area is MUCH bigger in from of the line than behind the thick line. This means "front focus" right? e.g 40mm in focus in front, 10mm in focus behind (before it gets blury) all test done with tripod and flash and wide open. trip to servicing center for me? The 28-75 only gives me sharp pics stopped down to f4 but i heard so much good stuff abt this lense that i dont beleive that to be the way it should be.
ugh!

[apchoo]

Originally Posted by captnj I was checking my lenses today becase the results i got for my 80-200 APG g and my 28-75 d were not as good as i had hoped with certain subjects. I get the Focus chart from a website (t eone that tell su to focus on the center thick line and looks like a ruler on both sides. My other lenses are ok but these 2, the "infocus" area is MUCH bigger in from of the line than behind the thick line. This means "front focus" right? e.g 40mm in focus in front, 10mm in focus behind (before it gets blury) all test done with tripod and flash and wide open. trip to servicing center for me? ugh!

Were you using Tim Jackson's focus test chart v2.1? If you read the doco, he says that it's ok if the focused area is shifted slightly rearward for longer lenses AS LONG AS THE FOCUS IS BANG ON THE CENTRE LINE. If your centre line is in focus, then I won't worry too much about it.

I did the test on 3 of my lenses and the above holds true for my 28-100mm at 100mm. No front or back focus issues with my 7D.

[captnj]

Originally Posted by apchoo Were you using Tim Jackson's focus test chart v2.1? If you read the doco, he says that it's ok if the focused area is shifted slightly rearward for longer lenses AS LONG AS THE FOCUS IS BANG ON THE CENTRE LINE. If your centre line is in focus, then I won't worry too much about it. I did the test on 3 of my lenses and the above holds true for my 28-100mm at 100mm. No front or back focus issues with my 7D.

yup thats the one... but the problem is that my focus area is not shifted back, its shifted front

here is the pic for my 28-75mm minolta 2.8 D...



here is the 80-200APO G



just for comparison, below is the 17-35 f4 (d) at 35mm wide open

[Drudkh]

its much easier to tell if you show a 100% crop.

[UY79]

The 17-35 at f/4 has more DOF. But all of them showed more DOF in front than the back. It may not matter much since the point in question is still in focus. You might want to send it in if you feel uneasy.

[TME]

The 28-75 seems a little off... the 'focus here' part is little fuzzy but the 10mm mark is very sharp... the 80-200 cannot tell, too small while the 17-35 is spot on... actually for the 28-75 is it that bad... unless maybe u are doing really large macros the slight off focus cannot be seen right even in enlarged portraiture shots?

[captnj]

Originally Posted by TME The 28-75 seems a little off... the 'focus here' part is little fuzzy but the 10mm mark is very sharp... the 80-200 cannot tell, too small while the 17-35 is spot on... actually for the 28-75 is it that bad... unless maybe u are doing really large macros the slight off focus cannot be seen right even in enlarged portraiture shots?

its not sharp when focused on text and edges of objects a bit blury.. i check cos heard such good thigns abt this lense so i couldt beleive my eyes