[Johnny Brown]

The camera won't know if there's an adaptor fitted. If its the wrong thickness (too thick), it may be preventing you achieving infinity focus completely though, which would create results like your shots.

Again, fire up liveview, zoom in and try to focus on the horizon (or anything >100yds away). A lens of that length will probably focus slightly beyond infinity, so it should be obvious if it can or not.

If you can, its more likely the focus confirmation is either out or too vague.

[Paul B]

ah I think that'll be it then as from what I've read the ring is 0.6mm thickness so it doesn't bend and it needs to be 0.4mm to achieve infinity focus. How the hell would it still be fine on video stuff though?

[Johnny Brown]

I doubt 0.2mm would create the error in those shots by itself.

If its right on the video, either you're not as critical due to the lower resolution, or you're getting the focus right for some reason.

I'm guessing for still you use the viewfinder, but for video the playback screen? I'd guess correct focus is easier due to the pixel scintillation acting as a focus aid.

As I said, have a play in liveview before drawing any conclusions.

[dave]

If you can get infinity focus as marked on the lens  then the adaptor thickness is right.

Video is lower resm which could hide a lot of sins.

[Paul B]

shall do boss. Might even need the manual to figure out how on this one.

If you can get infinity focus as marked on the lens  then the adaptor thickness is right.

I can't get infinity focus, the manufacturer is honest about that.

[Johnny Brown]

Mentioning that at the start might have been an idea, or is this some kind of test?

I'd still test it yourself though - 0.2mm is fuck all, quite literally.

On old manual, metal built lenses most of these things can be adjusted with somewhere. Infinity focus is set in the factory when the external focus ring is coupled to the actual moving elements. The will be some grub screws somewhere, possibly under the rubber grip. Or you might need to take the back off. I'd be very surprised if it wasn't manufactured with the ability to adjust ~1 mm of focus throw either way.

[Paul B]

Mentioning that at the start might have been an idea, or is this some kind of test?

thought you might be having a boring day thats all, or I just forgot.

[Paul B]

Not too exciting but there you have it. Infinity focus problem.
The video work was all done very close to me ~1-2m, I'd say I was about 5-10m away for the two shots above and of course the above shot is at 'infinity'. I'm taking it this matters and its nothing to do with the AF or me being a dimwit.
There are 3 grub screws around the focussing ring. I'm thinking of tethering it to my rather large monitor sticking it on a tripod and repeating the last shot until its correct, this should solve the infinity problem but will that in turn fix the front focussing issues?

[dave]

 To be honest, the infinity being unacheivable shouldn't make any odds to your focus confirmation light, or your ability to focus on anything closer than infinity, it just means where you are focussed and the distance scale won't correlate. Its just like using a 0.2mm extension tube, shouldn't stop you getting sharp shots.

[Johnny Brown]

What Dave said. I don't think you have a front focussing issue at all - due to the extension caused by the adaptor you just can't focus beyond a certain point - looks to be somewhere between 5 & 10m. Grimer and Ross were beyond that limit, whereas your video stuff wasn't.

[cofe]

have you tried it on a D3?

[Paul B]

What Dave said. I don't think you have a front focussing issue at all - due to the extension caused by the adaptor you just can't focus beyond a certain point - looks to be somewhere between 5 & 10m. Grimer and Ross were beyond that limit, whereas your video stuff wasn't.

d'ya reckon some grub screw action could fix this? or am I f*cked.

[Johnny Brown]

Its worth a try. If its really only 0.2mm I'd be surprised if you can't. What is it, a Practica 135mm? It won't be worth any less if you fuck it up.

[Paul B]

Its a Praktica 135mm F/2.8. and the thickness error is certainly 0.2mm. Some people have dremmel'd them down but warn they flex a little too much for comfort.

I've got the mother of all liveview setups with the Canon EOS utility and a tether to my PC.

[Paul B]

http://farm5.static.flickr.com/4036/4569214826_2be3a3d732_o.jpg

before I get going with the screwdriver, is this one the same or much better? No post.

[Johnny Brown]

That looks to be pretty much in focus, though you've got a bit of movement blur softening things. But then he's not very far away.

[Paul B]

That looks to be pretty much in focus, though you've got a bit of movement blur softening things. But then he's not very far away.

yeh but Grimer ain't much further?

[Johnny Brown]

No, not much, which is why the flowers in fornt of him are sharp. What's your point?

[Paul B]

No, not much, which is why the flowers in fornt of him are sharp. What's your point?

Just that if its going to get worse with distance then i'd expect dan and G to both be about the same level of shittness which they clearly aren't.

[Johnny Brown]

You've lost me. What are you driving at?

Did you measure the distance to them at the time? Is it possible they were not exactly the same distance away? Did you check the focus scale to see where the lens was focussed? These could all cause the same results.

Without any of this information, all you can go on is the evidence in your photos - that there are sharp areas, but not beyond a certain distance - which matches perfectly with the hypothesis so far. I thought you were a scientist?

[cofe]

i'd say the lens is massively overgraded, 'soft' if you will.

[Paul B]

All my work is iterative, I go round in circles daily. 

Are you saying that due to infinity focus not being achievable there is a limit (distance) at which I just can't get anything in focus and below that I'm fine?
I was thinking it was more of a gradual thing as it tended towards infinity. Hence not being certain of the two distances that give very different results.

Cheers cofe.

[dave]

Are you saying that due to infinity focus not being achievable there is a limit (distance) at which I just can't get anything in focus and below that I'm fine?

[cofe]

glad to be of help.

[Paul B]

I guess I was just getting a bit confused because at that limit its 'nearly' ok and then gets progressively worse as you tend towards infinity. Oh well... I guess I can try tweaking it and see where it gets me. Was worth a play given the cost of the EOS equivalent.