Canon 28mm f1.8 on 30D (problem?)

[rfdesigner]

Hi

I picked up a used but mint 28f1.8 yesterday, tested it for flair, autofocus accuracy, focus accuracy across the field and so on.. all good.

Today I play with it again and suddenly it's noticably out of focus (about 8 feet away for 6 foot target), focussing substantially beyond target, the difference is I'm using the edge AF points rather than the centre, recheck with centre and it's still bang on. Top and bottom points seem fine, but the left and right points miss target... focus with the centre point and recompose to put the target on the left or right points and focus accuracy is much better.

Is this a common problem with 28f1.8s on old 9 point AF? I've never noticed this problem with either of my other lenses (100 f2 and a kit 18-55)

I can't see that I can blame the lens when it's sharp across the field (no dislodged elements) and focusses accurately on the centre point.

I could manage this situation, but it would be nice to sort it out,

 

[Sporgon]

I tried one of these lenses a while ago. Because we lock focus with an open aperture I think it has something to do with the fact this lens is so poor mid edge frame at f/1.8 it has something to do with that. I found a similar problem on the FF cameras with the far outer points.

 

[rfdesigner]

I tried one of these lenses a while ago. Because we lock focus with an open aperture I think it has something to do with the fact this lens is so poor mid edge frame at f/1.8 it has something to do with that. I found a similar problem on the FF cameras with the far outer points.

Thanks

Can I ask if the problem you experienced was with the 9 point AF?.. i.e. 5D classic or 5DII

(if it's the 9 point then FF or crop makes no difference, it's the same AF chip and the same offset in mm of the outer AF points)

(ps, just checked your site.. some extremely beautiful images, most impressed)

 

[Marsu42]

Is this a common problem with 28f1.8s on old 9 point AF?

I would guess so - af'ing with thin dof and outer points isn't easy. For example the 1dx/5d3 af array loses some points or at least their precision on older or cheaper lenses. As what you've got is as old and cheap as it gets, be happy it works with the center point ... this way, you're basically operating at the same af level as the €1600 6d :->

 

[Sporgon]

I tried one of these lenses a while ago. Because we lock focus with an open aperture I think it has something to do with the fact this lens is so poor mid edge frame at f/1.8 it has something to do with that. I found a similar problem on the FF cameras with the far outer points.

Thanks

Can I ask if the problem you experienced was with the 9 point AF?.. i.e. 5D classic or 5DII

(if it's the 9 point then FF or crop makes no difference, it's the same AF chip and the same offset in mm of the outer AF points)

(ps, just checked your site.. some extremely beautiful images, most impressed)

Thanks for that, appreciated.

Yes I tried it on a 5DII, so the AF is probably identical to yours.

As a creative lens I think it has some potential; it's just that I don't see the world in shallow dof 28 mm focal length !
I found that in the centre from about f/2.8 is was really quite good. Also very low distortion. The very extreme edges ( on FF) were also good, it was just the bit in between that caused me issues. It also had a lot of CA's but that is not necessarily an issue for everyone.

 

[rfdesigner]

I tried one of these lenses a while ago. Because we lock focus with an open aperture I think it has something to do with the fact this lens is so poor mid edge frame at f/1.8 it has something to do with that. I found a similar problem on the FF cameras with the far outer points.

Thanks

Can I ask if the problem you experienced was with the 9 point AF?.. i.e. 5D classic or 5DII

(if it's the 9 point then FF or crop makes no difference, it's the same AF chip and the same offset in mm of the outer AF points)

(ps, just checked your site.. some extremely beautiful images, most impressed)

Thanks for that, appreciated.

Yes I tried it on a 5DII, so the AF is probably identical to yours.

As a creative lens I think it has some potential; it's just that I don't see the world in shallow dof 28 mm focal length !
I found that in the centre from about f/2.8 is was really quite good. Also very low distortion. The very extreme edges ( on FF) were also good, it was just the bit in between that caused me issues. It also had a lot of CA's but that is not necessarily an issue for everyone.

Brilliant!, so it's to be expected... fine I can live with that, thanks.

I want it as a low light people lens (kids / family shots, indoors, groups etc).. in that regard it seems well suited, it's bought me 2 full stops of light over the zoom.

Distortion & CA wise I don't worry too much, I always shoot RAW and then apply lens profiles in DPP, as I'm not a pro so I'm not shooting as much nor under any time pressures.