Gremlin?

[Demonperformer]

Following on from Friday's fiasco, I have been working on ensuring I don't have the same problems again.

Thanks to Julian the syncing problem has now been resolved, which leaves the focussing problem.

The setup I am using is not exactly complicated: Camera > nosepiece > adapter > lens. One hardly needs to be a nobel prize winner to get that right. It is not even one of those new-fangled adapters that can have an extra 5mm extender or not depending on which camera you use (although I am not sure how that works, as I have used my non-changeable adapter successfully with both my 224 [use the 5mm extender] and my 1600 [don't use the 5mm extender] in the past ... but I digress).

I have put it all back together and tried focussing on a distant object (a treeline 800m away) and it focussed perfectly well. If anything, the focus was a bit inside the infinity-stop, but 800m is not infinity and changes in focus at this sort of distance tend to be miniscule anyway, so genuine infinity should not be unobtainable. It isn't a particularly long lens (80mm) and it was set to manual-focus, not auto-focus. So now I am stuck wondering what went wrong? Some might say "It's working now, why worry?" But I tend to think if it happened before it could happen again and it would be good to know why it happened, so I can correct it if it does.

The fact that I was approaching focus as I got to the infinity-stop and that the lens length decreases as it focusses nearer infinity suggests to me that there was too much distance between the lens and the camera. But, as suggested above, there are not a lot of ways I could have got this wrong. The lens fits into the adapter and is locked, which leaves only the two screwed connections. I find it hard to believe that I could have just left the adapter only half screwed into the nosepiece or the nosepiece only half screwed into the camera. If I had done that, when I was tightening the focus to infinity, the whole thing would have moved when I hit the stop and alarm bells would have started ringing. But I am at a total loss as to what else could have been the cause.

So it is time to tap into that vast resource of experience that is SGL ... what did I do wrong? Send answers, on a £50 note, to ... [or just post them to this thread]

Thanks.

[michael8554]

Had a similar experience getting a telephoto lens in focus to use as a guidescope.

One day it was fine, continued working on it the next day and it wouldn't focus.

It turned out the gremlins had picked up the thinnest ring of the adapter set off the work bench and installed it on the lens.

You have to watch them Gremlins all the time......

Michael

[Demonperformer]

Thanks for the response, Michael. 

I have tracked down my problem. And, although I did not realise it while writing it, the answer is in my post when I said focus on the treeline was "a bit inside" the infinity stop. It turns out that that is where infinity focus is with this lens/camera setup.

The impression that focus was beyond the stop arose because of the time lag between me altering focus and the image displaying on the screen.

Small adjustments, giving the system time to catch up, would appear to be the way to go. 

Thanks.