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Screws for zoom and focus barrels


Nacho Guzman
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Hi everyone, I live in the UK and I was wondering where do you AC's usually get your precision tools?

 

Every now and then we face this common issue of having a lens with a late focus response, because of the barrel missing a couple of screws...so I was thinking, time to get this in my kit.

 

 

Any preferences?

 

thanks in advance

 

 

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I don't think it matters- a jeweller's screwdriver is a jeweller's screwdriver. I'd hardly call it a precision tool. Even a kit from a pound shop will do if carefully used. The ones with rotating ends are a bit easier to use and a bit more durable, but that's about all. Maybe you rental house can help you out- probably at top price though!

But if you are actually missing screws and need to replace them that's another matter. You can muck up the thread with the wrong size replacement.

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What lenses are you thinking of in particular?

Different lenses use different types of screws and different methods of fixing the focus or zoom barrel. It’s usually not as simple as just tightening or replacing a screw. 

The most common example I come across for loose focus barrels is Zeiss Super Speeds. They use very specific and tiny slotted dog point set screws that locate in holes in the helical beneath. Sourcing replacements is very difficult (Zeiss no longer sell them) and if you overtighten them you can cause the focus to bind. If you damage the slotted end they will need to be precision drilled out, which is not an easy job. 

Angenieux zooms use tiny socket set screws that are sealed with very strong lacquer which makes it very easy to strip the socket if you don’t use a combination of light heat and acetone to soften the seal first, and they are also very susceptible to over-tightening and changing the barrel torque. Some of the set screws are pointed, some are flat, and it matters which ones are used where.

Ultra Primes use Phillips Head screws that pull on an inner friction ring - if the barrel is loose the distance marks will need to be re-calibrated before you tighten the screws back up.

Often play in a zoom or focus barrel is actually a symptom of something loose or worn internally, and it can’t be fixed by just tightening or replacing some screws on the outside.

Etc, etc.

Unless you know exactly how the lens in question works and what the method of fastening is, and you have the right tools, my advice is to leave any lens adjustments like this to an experienced technician. I understand the pressure to quickly fix a problem on set, but with cine lenses you can easily cause far worse problems.

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1 hour ago, Mark Dunn said:

I don't think it matters- a jeweller's screwdriver is a jeweller's screwdriver. I'd hardly call it a precision tool. Even a kit from a pound shop will do if carefully used.

You’d be amazed how much difference a good quality tool can make. Cheap jeweller’s drivers are usually very easy to burr or deform, which in turn can deform the screw head. And if you’ve ever had to drill a 1.2mm steel grub screw out of an aluminium housing because the head was damaged, you’ll happily pay a bit extra for good quality tools. It’s why actual jewellers or watchmakers will spend hundreds on a beautiful set of Bergeon drivers. 

Good quality hex drivers and keys are particularly important when the socket is say 0.7mm, and the screw is sealed in with lacquer. Lower cost ones use softer metals and can be undersized, which is just a recipe for turning the socket round. 

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Standard Speeds are the same as Super Speeds, using special dog point set screws. Do not try to use anything other than the original screws. If you find a lens is missing a screw in the focus barrel, it may be because the thread has been stripped or someone had to drill out a damaged screw, or the locating hole beneath is damaged/not aligned etc. Don’t assume it just needs a new screw. A tech could tell you after assessing the lens.

If the barrel feels a little loose, you could try using a black handle (1.0 mm) jeweller’s driver to nip the set screws up, but be very careful not to damage the heads or over tighten them. The dog point of the screw should locate in the hole beneath without exerting any pressure, otherwise you can deform the focus helical, causing the focus to start binding, and accelerating wear to the threads. So don’t tighten any screw past when it starts to resist turning. The screws should be secured with a light sealing lacquer or black nail polish. Again, I think it’s best to let the rental house techs do it (absolutely no question if they are rental house lenses), as there may be other issues you’re not aware of causing the play. Lag in the focus marks is more likely to be caused by worn threads inside the lens.

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One more tip: the reason focus barrels become loose is usually because of motors slamming them into end stops, something older lenses weren’t designed to deal with. So turning the motor torque down to the minimum required to turn them is very helpful in preventing these faults from arising. (It also helps reduce thread wear, damage to the end stops, and broken iris pins on the iris ring, all things I spend a lot of time fixing these days.)

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  • 1 month later...
On 10/5/2020 at 11:20 AM, Nacho Guzman said:

Hi everyone, I live in the UK and I was wondering where do you AC's usually get your precision tools?

 

Every now and then we face this common issue of having a lens with a late focus response, because of the barrel missing a couple of screws...so I was thinking, time to get this in my kit.

NACHO I MISS U

You'd think there'd be guild of some kind. 

Have you ever been to Hatton Gardens? It's the part of London with all the jeweller's shops. It's been there forever. 

Maybe go down and ask them if any of them sell tools, there might be one dealer who supplies all the jewellers...

On 10/5/2020 at 11:20 AM, Nacho Guzman said:

 

Any preferences?

 

thanks in advance

 

 

 

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