temperature affect backfocus?
 

I have been using my H1 with 16x manual lens for 2 years and never had this issue. I have checked the backfocus on a few occassions and it is typically spot on after I set it. However, last week I was shooting an event that had an indoor reception and then about 30 minutes of outdoor fireworks in February in Ohio. Yeah. Real smart.

Anyway, I was inside for 2 hours, then went outside into the freezing rain. I covered the camera with a makesift rainslicker and only the very end of my 20 servo lens was exposed. I got a lot of water right on the lens but the rest of the unit stayed pretty dry. After 30 minutes out in the cold wet night, we
headed back inside. Because there was some concern with water on the lens, I decided to switch to my 16x manual (which was warm inside) for the remainder of the evening, just to let the 20x lens dry off completely. All seemed fined.

Upon watching the footage, there is a severe backfocus problem. I zoom in 20ft, focus on the subject, hit record and do a slow zoom out and the subject goes out of focus.....bad! This happens 4-5 times in the rest of my footage. This has never been an issue prior to this.

Can cold temperatures affect the backfocus this badly? I don't have my camera with me here at the office to check, but maybe the backfocus knob worked it's way free and moved, causing the issue. I didn't notice that....but it is a possibility.

Thanks in advance.

Also....one other note and maybe I just never noticed this before. When I was drying off my 20x lens, I noticed a "clunking" sound internally when tipping it. I do not remember hearing this before. It is the exact same sound made so famous by the DVx100 image stabilizer that would do this when the power on that camera was turned off and you tipped it.

It may have always been this way, but I just noticed it..

Thanks all!
Peace!

dry cold is one thing - wet cold an entirely different beast, once condensation enters the equation. I would guess weather could be to blame, but not temperature alone in your case - if it was wet it couldn't have been that cold.

The temperature was around 25 degrees farenheit, but the snow falling was wet in nature.......freezing rain if you will.

Either way, I went home at lunch and setup my H1 to adjust backfocus and sure thing, it was off. The screw was still snug so I doubt that it shifted but you never know. A few times through the process and it is looking great again. So if the 16x wasn't moved, does that mean that the mount on the H1 has shifted or something? What could have caused this?

Oh....one other thing is I trevelled to and from California on 3 737s with my 16x manual in the case with the H1, but I never mounted it on the camera until after I retruend on the night in question. It was in the overhead compartment, so I know it didn't get banged around obscenely.

Thanks.

There is a current that passes from the lens to the camera - that could have been interrupted by moisture. You could have 2 pieces of material - maybe the screw and its housing - that expand/contract at different rates as temp/humidity rise and fall.

great that it caused no permanent damage.

Um Yeah, the camera had a chance to "cool down" and then was warmed up again. The other thing that's interesting is you changed lenses, is it possible the manual back focus know just got bumped? I've done it before. Maybe I'm misunderstanding the situation.

Nick,
Maybe you didn't catch the other answers in the thread. In regards to the 16x manual, I checked and the backfocus was off, despite the fact that the screw was still snug and not loose on the flange adjustment. So if it came loose,and moved, it somehow got magically re-tightened. In 4 years of using the manual lens, this is the first time it has been off after Ihad previously set it up.

I have since reset the backfocus and it is good again. So I am 99% sure that the backfocus issues are not related to the temperature in this case.

Peace.

Some will say that back focus should be checked anytime the lens has been off the camera and then replaced. Temperature can also affect the mounting as the metal expands or contracts. Think of how short the FB distance is and it will be easier to visualize just how little shifting has to occur before it's off.

-gb-

Greg,

I have set in many times in the last 4 years. In fact, I have used it on the XL2 and 2 different XL-H1 units. I generally check it from time to time and it has held up well. I guess after so many non-issues you tend to take it for granted, which I did. I went to this event having not checked it....so I wasn't prepared I guess. It's like checking the air in your tires.......if they never need any extra air, you tend to give this task less significance and let it slip by.

Lesson learned. Always double check this.

SO does anyone hear the clunking sound in the 20x lens when tilted?

Can't recall if mine did or not, but I have heard others speak of it happening with power off. With no power attached to the servos that drive the VAP, it can move when tilted to an extreme position.

-gb-