building a follow focus

J

jmproductions13

Active member
ok ive found a couple technical sketches and detailed photographs of some common follow focuses. i now understand the workings of them. designing one like the jbk cinequipt one wouldnt be too difficult if only i knew the gear ratios. i have a friend who makes parts for nasa in a machine shop so i might consult him on how expensive it might be to make parts for one of these things. if anyone has a jbk cinequipt follow focus, it would be much appreciated if you could count the number of teeth on the gears and post them. if theres anyway to get access to the drive gears, the ones the wheel is connected to the tooth count on that would be appreciated also.
 
Re: building a follow focus

Played around with an old erector set for 1/2 an hour. this is a "prototype" i came up with. just needs the right gear ratios and a more sturdy design.

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anyone who has any ideas, please post :)
 
Re: building a follow focus

Again, the question becomes - how do you interface it with the DVX focus ring? Professional follow focus units aren't designed to work with the DVX, they use an industry-standard gear pitch that mates up with gears that you can mount on broadcast lenses, etc.

With the DVX, you can do it that way, but then you have to buy a $100 to $300 focus ring also.

Or, you could design your follow-focus unit so that the gear directly meshes with the focus ring on the dvx, so no additional purchase is necessary...
 
Re: building a follow focus

Whatever you do... keep the tire in the design! ;) :)

Good luck and God speed, young man.

May the focus be with you... ::) (rolling eyes at self)
 
Re: building a follow focus

yes.. there is a place in NY that will make a beveled gear that matches the DVX rings, As well, Clairmont Camera Mills a $50 ring that you can get from them that converts the DVX ring to standard gear pitch (kinda like what the Century $350 ring does).. but without the hardstop.
 
Re: building a follow focus

[quote author=Barry_Green link=board=Links;num=1087426948;start=0#2 date=06/16/04 at 21:47:32]Again, the question becomes - how do you interface it with the DVX focus ring?[/quote]

I've been thinking about this and wonder if using a R/C car tire would work. There are various sizes and materials of tires available. The wheel/tire would press against the focus ring. A spring adjustment could easily set the proper amount of friction.
 
Re: building a follow focus

[quote author=Terry_Lasater link=board=Links;num=1087426948;start=0#7 date=06/16/04 at 23:57:46]Keep the ideas and prototypes coming![/quote]

Ok, so here's where I really throw a crazy thought out there...

What about using a fishing (spinning) reel as the drive mechanism?

For example:

http://www.basspro.com/servlet/cata...arClassCode=1&hvarSubCode=2&hvarTarget=browse

A good spinning reel provides a very smooth and quiet direct drive mechanism. Remove the spinner and spooling portion to expose the spinner shaft. Then attach a gear to the shaft and over to the focus ring.

Whoo, can you follow that?

We will call it the Billy Bass Follow Focus! :D

But seriously... it could work ;)
 
Re: building a follow focus

:D  "Billy Bass Follow Focus"... or maybe, "The Pocket Focusman" or "Focus Fisher"... or perhaps something magical like "Focus Pocus"... maybe... "Focal Roller"... or something edgy like, "Focal Matter"... lol!... "Ewww! I got 'Focal Matter' on my camera. Quick, toss me a baby wipe.".

Hey, I like your thinking... keep the ideas flowing. Build one if you can.
 
Re: building a follow focus

see the real trick is the gear ratios. if anyone knows someone with a jbk follow focus, please have them post the diameter of the gear as well as how many teeth it has, as well as the diameter of the black knob. i would say the best idea involves designing a cheap follow focus with a changable interface gear, allowing usage with both the dvx lens, xl1 lenses and cine-lenses. obviously, dvx has priority lol
 
Re: building a follow focus

Why not use some sort of "spongy" rubber roller pressed up against the stock focus ring.. it would form to and grip the ring and spin her around without messing with teeth.
 
Re: building a follow focus

[quote author=Kai link=board=Links;num=1087426948;start=0#12 date=06/17/04 at 14:49:52]Why not use some sort of "spongy" rubber roller[/quote]

Yup, that's the thought I had above with the R/C car tire.
 
Re: building a follow focus

A skateboard busing might be better as it has the little angle you need. and is smooth. A RC tire can be rough, and you dont want something rough.
 
Re: building a follow focus

The skateboard bushing looks like it's at a good angle to go direct onto the focus ring.
 
Re: building a follow focus

ive been getting tips and trying to collaborate with some guys at www.chiefdelphi.com there are a lot of mechanical engineer type people there. i found a place i might be able to buy gears from. i just need measurements. if anyone has any sort of follow focus, especially the jbk one please post measurements for the good of the community.
 
Re: building a follow focus

does anyone know the "standard" measurements for the rods.  i know 15mm diameter, but how far apart from rod center to rod center.  how big should the block be and how far should the top of the rod be from the camera base?

im trying to create a cad sketch of the housing.
 
Re: building a follow focus

Not to be dissuading, but the whole "rods" thing is likely to lead you down the path of being way too expensive, and put you in square competition against existing established manufacturers like cavision, etc.

I know you may want to pursue that course because it'd let you make it compatible with other camera types, etc... but if you start needing a baseplate, rods, and all that stuff, precision machining, lightweight aluminum, etc... next thing you know you're going to end up with a $400 parts/manufacturing cost, which means you'll have fewer buyers, so you'll have to mark it way up to recover your R&D... so to sell at a reasonable profit means you're going to be offering it at $695 or $795... and that's right up there with the $1000 units already available.  Which means you might sell a couple, but the vast majority of people will probably pass...*

I'll throw in two cents worth... make a unit that works with the DVX.  Forget the rods and the industry-standard gear and all that stuff.  Make a little device that attaches using the two screwholes where the external mic-holder fits on.  All it has to do is reach over an inch and ride the focus ring.  Doesn't need a spring, doesn't need tension adjustment, it can be a fixed-pressure unit -- heck, it could be one piece of molded plastic, basically.  Make the whip or shaft come under the camera's built-in mic, over to the left (so an A.C. could operate it from the LCD side of the camera) and you're done.  The total cost of that is going to be more in the $50 ballpark, right?  That way you could sell it for $99, probably sell a thousand of 'em, I know there's got to be over 35,000 DVX's out there by now, plus a few thousand DVC80's, so there's maybe 40,000 potential customers.  If you can hit 2.5% of them, you'll sell a thousand units at $99, you'll gross nearly a hundred thousand dollars and clear $50,000 profit, and then you can design a similar unit for the GL2, XL1s, PD150/PD170/VX2000, etc.  Heck, charge $199 and you'll probably still sell 'em (and pocket $150,000).  At $295 I think you'll start running into resistance, and anything above that I think you'll seriously start impacting your numbers.

But hey, that's just my two cents' worth, (if it's worth even that!)  I just wish you well whichever path you pursue.

*footnote: market research and numbers are mixed with gray hair, dandruff, bird droppings and whatever else just came off the top of my head, so take with a grain of salt or, preferably, a salt lick.
 
Re: building a follow focus

thats a very good idea barry. my only concern is that a follow focus mounted so far forward might interfere with any cine-style matteboxes people might have mounted. i'll take it into consideration while im trying to develop my device
 
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