Broken Backfocus Knob..arrrghhh!

[Jay Webster]

Don't know if this is a question or just a rant & rave..etc.
Anyway, had the camera on a job this past weekend and when setting up realized the back focus knob wasn't locking down. Thing is, I don't know how or when this could have happened. I did have an assistant backfocus the last time the camera was out, but didn't notice any problems on that job (although there weren't many zoom shots involved).
So....I resorted to using a strip of camera tape to "lock" the backfocus.
Seems to work fine, but don't know if I feel secure using this as a long term solution. Also don't know if this is worth trying to get fixed or how much in time and money etc...
I guess if there is a question here it's: What do you guys think? What would you do? etc.
This is the stock 16x which I've never been overly thrilled with in the first place, so??
Tape or wallet? I'd just appreciate a little objective input from someone a little less hot headed than I am right now!
Thanks for any thoughts,

[Robert Adams]

Well, Jay, my pennyworth:

1: I'm not going to even start to lecture about the need to backfocus.. yadda yadda. You know, I guess, now. I try to check backfocus every week or so. Some check it every day. Not so sure that's necessary, but whatever makes you feel you know your camera.

2: This is not an expensive bit of glass.If you break down the component costs of the camera, the stock Fujinon lens is worth about 600 bucks tops, new. Which, it has to be said, is amazingly good value. I'm shooting a doc right now with a 22,000 dollar Canon HJ11 on a Sony HD730. My second cameraman is shooting on my little JVC with the stock Fujinon lens, and it is holding up really well.

3: With the various lens options around now for the JVC, there must be some almost-new stock lenses going cheap on the circuit. You might want to look at that option. Or you might want to lay waste to your wallet and invest in the Fujinon 18x or 13x lenses that are getting consistently rave reviews on this, and other, sites.

4: Given all this, you might not want to spend very much on repairing your lens. But if you do nothing, one day, for sure, that broken back focus is going to let you down badly.

Best wishes

Rob

[Greg Honeycutt]

Jay,

Look close to determine if:

the screw threads are stripped, or
the female threads of the insert are stripped, or
the threaded insert is spinning/loose in the b/f ring due to a crack in the ring.

Post if you can determine.

Greg

[Gary Nattrass]

I can sometimes get new 16x fujinon 1/3" replacement lenses that a lot of the Z7 guys also use.

Let us know what the problem is it may be an easy fix but I have seen some well used examples of these lenses where the plastic thread has cracked due to overtightening.

[Jay Webster]

Roberts points are well taken. That's the issue, how long can I get away with using camera tape to "lock" the backfocus and isn't that just asking for trouble? I'm in the North East and so reset backfocus everytime we make a move from an interior to much colder exteriors etc.

Anyway, took a closer look and it seems that the threads (both male and female) are OK.

There does seem to be a hairline crack in the ring just outside of the small "square" area where the locking screw threads in.

I guess the ring itself needs to be replaced. Don't know if that's a cheap fix or an expensive one (Roberts comment on the actual value of the lens comes into play here).
It wouldn't seem to be too major but who knows.
The lens is in pristine shape in every other way so it seems a shame to put it to rest just yet.
Comments, arguments, dissertations...etc. Are all welcome!
Thanks

[Greg Honeycutt]

With almost 30 years of field production work, multi-camera sports production with our truck, live sports, etc and maintaining a bunch of camera and other equipment, Ive see all kinds of stuff break and my first notion is to try and fix it, mostly for $ reasons. Often times my fixes work.

When a part-timer over cranked the b/f knob and cracked the ring, here's the fix I made.
Camera was back in operation 2 days later. Depending on your comfort level taking stuff apart, this may work for you.

I enlarged the hole and tapped threads in the ring, then installed a threaded metal insert.
JB weld mixed properly and left to dry is very strong. The proper screw for the metal insert replaces the smaller knob that was there.

Obviously, I wasn't going for style points on this fix but it works. Someday Il'll get a better knurled screw but it's functional

[Jay Webster]

Thanks for this Greg. I believe I'm gonna give it a try. Like you say it may not be pretty but looks like it will work. I just hope I don't break the ring entirely taking it off or putting it back on since for now I have just been camera taping it down after adjusting BF.
Any tips (besides the obvious holding your breath and praying) regarding removing and replacing the ring?
Thanks again!

[Greg Honeycutt]

It may be worth getting a price for a replacement ring since you will have the lens apart. I didn't have time to wait for a replacement ring in my case.

If you want to do the insert, it's not a bad job. Step-by-step from memory-

Take a picture of the assy. for reference before starting. Have a plastic sandwich bag ready for the parts.

Remove the phillips screws holding the bayonet to the lens assy. Caution, the heads are prone to strip, get the right size phillips and push fairly hard when turning at the start.

Bayonet comes off.

Slide off the macro ring. Note direction of ring.

Slide B/F ring off. note direction of ring. there's a valley on one side of the b/ ring that the macro lever locks in to.

I recommend a metal insert. Check your local hardware store for a insert and screw. The insert should have outer threads and inner threads. they make an insert for wood that's serrated on the outside and threaded on the inside. That may work as well. The metal insert makes the repair stronger because the insert will take the brunt of the locking force instead of the plastic threads. If you just epoxy the plastic ring back together without a metal insert, I doubt it will last.

I had to enlarge the hole in the B/F ring for the insert. I took a drill bit and worked it with my hand on the plastic. I tapped the hole with a tap set but if you don't have one, get a screw the same diameter and pitch as the outside threads on the insert, hold the ring together and run the screw in and out a few times to make some threads in the plastic.
Be sure that the crack comes together with the insert in place.

Put a little of jb weld in the hole, put the insert in, Use a strong rubber band around the b/f ring making sure that the ring is compressed where the crack is sealed. The rubber band will ensure the ring is compressed evenly and stays round. If you try and clamp the ring, it will distort. Let it sit for a day.


Assemble in reverse. good luck

[Jay Webster]

Thanks so much Greg. You da Man!
You did forget to mention the shot of Tequilla before you begin...Just to steady the nerves etc!
Thanks and cheers!
Jay...apparently part time surgeon!

[Jay Webster]

Well,
I checked in with Guy (pronounced Gee) Genin over at ZGC,Inc.
He can replace the part and repair everything for around $200. Most of the cost is the part itself.
I know the value of the lens is only about $500-600, but this is probably the cheapest solution and at least I know it will be done right. I dealt with these guys a lot back when I had my Aaton and was always pleased with their integrity and service....Good people!
Thanks to all who replied, greatly appreciated.
By the way, if the guy who bought my Aaton reads these boards...Can I have my Mattebox back? I think it must have been left in the case by mistake! :>)!! (oh well, worth a shot!)
Cheers to all and thanks again!