Backfocus problems
 

After having had the camera for a few weeks (I just recently started using it with regularity), I've come to the conclusion that my camera's factory-set backfocus is seriously out of adjustment. At first I thought it was inattention on my part, but careful testing over the last few days points to a definite problem. I use manual focus almost exclusively, so I've not tested in servo-mode.

Zoom in to an object 50 feet away, focus, zoom wide, and the entire frame is soft. In fact, I must pull focus all the way to the closeup extreme for acceptable results on wide shots. Of course this becomes less pronounced as I stop down the iris.

Via another thread, I learned how to access the maintenance menu to set backfocus. I'm familiar with doing this on a pro lense, but I'm wondering if I should attempt it with the EX, in that it works much differently and I don't own a focus chart. If I tried this, would I void the warranty, and is this even possible without using a chart?

I'll ship it back for proper service if need be, but I'd prefer not to. I've not yet ruled out user error, either. Any ideas?

Bill

Bill,

I have done this - it took all of 30 seconds and seemed to work perfectly. I just googled a back focus chart on the net and printed it out. Taped the chart on a white door and set the camera up on a tripod about 3.5meters away - followed the instructions on the thread - and it all happened automatically.

Hope this helps.

Thanks, Graeme, I'll give it a shot. Did your camera arrive needing the backfocus adjustment or were you attempting to correct the vignetting issue?

On a side note, I can't understand how Sony could ship a camera so seriously out of whack. Maybe it got jostled around on the boat.

I have also done it - very simple and not too scary process.

Back focus seems spot-on afterward.

Bill,

I hadn't used the camera enough to see any substantial back focus issues - but yes I was trying to sort out the vignetting issue. My replacement camera arrives tomorrow. I will check its back focus during the week.

Graeme, please keep us informed.

me too
 

I also experienced the same simptom, and I fixed it for myself by using the information in this site. I'm quite happy now. Can't understand the QC level of Sony.

From the little I know about manual lenses it's not unusual to have to reset or at least check backfocus regularly. It may well have been correct when it left the factory. If my hunch is right it's not a fault, it's just how optics are, unless you want to spend a lot of money on exotic materials backfocus will be affected by temperature.

But unlike with manual lenses, Sony does not intend for the end user to adjust the backfocus. The backfocus adjustment is hidden in a secret maintenance menu intended for service personnel.

Even with that being the case, I intend to use adjust the backfocus in my EX1 with the almost the frequency that I would on a manual camera - especially after jarring transport.

The process is simple and arguably more foolproof on the EX1 than with manual lenses.

It's pretty impressive that Sony have created an automated, adjustable backfocus with some sort of internal motor that can be implemented from a soft menu - even if they never intended to let us use it!

Graeme, how big a chart is required for this purpose - from 3.5m looks like an A4 card suffices?

Just a thought - would just displaying it on a 24" LCD be OK for the purpose?

Piotr,

(though I am not Graeme)

A4 or the US equivalent 8.5x11" worked for me. It also didn't seem to matter too much about other objects in the room (though I did not have anything big between the chart and camera).

I am not sure that it's the case, but it would make sense that the backfocus algorithm looks at the center of frame when zoomed wide.

Thanks Eric,
this was my question regarding the backfocus adjustment.

So, you hung your Siemens focus chart on the wall about 12ft away with no closer objects in camera view to your side.
If it's using the center only, I imagine the distance and focus chart size are important.
Did the procedure outline the correct siemens chart size?

Steven,

Firstly, I am not sure that the camera looks at the center only - it's just a hunch and would make sense to me.

I hung the Siemens "bullet" (8.5x11) on the wall about 12 feet away an centered it in frame (fully zoomed in) and focused manually on it. Then I executed the menu item. I did have a few pieces of furniture and a fireplace at the periphery of frame (at full wide).

I don't really think the camera cares what the size is, or even what the chart looks like - it's only trying to find a sharp focus (as the camera's autofocus does) that stays sharp during the entire zoom range. It seems to do an iterative autofocus, but instead of changing the lens focus, it is changing the back focus. The bullet is a very easy target to establish that initial focus with, so I would recommend using it.

I really don't know what the algorithm is really doing, but it ultimately establishes a focus that stays sharp the whole way. All the rest is conjecture on my part.

Thanks Eric, sounds right to me.

We know that the lens is servo-focussed - even with the focus ring in the manual position, no objectives move if the power is off and sliding the ring to the manual position 'snaps' the focus to that range. This is different to zoom, where glass is directly geared to the ring and does move with the power off.

So the focus commanded by the ring is converted into the positions of the elements by way of some algorithm or (more likely) look up table which also takes into account the zoom position and probably contributes to the CAC setting. The backfocus adjustment will get a focus at telephoto, then repeat as it zooms out to calibrated the lookup table.

AIUI!

Nick