Backfocus plug for 35mm adapters

[Bob Gruen]

I built a backfocus plug for my HVX-200 / hard mounted RR Micro 35 system, and you can too!

What does it do? Simply jack the plug into the remote focus jack and it locks focus on to the ground glass, every time. It disables the focus ring so you can quit putting gaffers tape on your expensive camera. The remote focus jack works by testing the resistance between the base and center node of a 1/8th inch stereo plug. From Radio Shack You will need:

A pack of 1K resistors (271-1118)
1K Ohm, 15 turn Cermet Pot (271-342)
1/8 inch stereo plug (274-284 )To start, I did some testing with a 20K pot and a 1/8th jack and found that the resistance value I needed was about 4.25K Ohms (this sets the focus value at 15/16 juncture). I then wired four 1K resistors and the 1K pot in series (end to end) so that I can adjust the load between 4K Ohms and 5K Ohms. My exact value turned out to be 4.32K Ohms, but yours may be different due to the GG position and hardmount / softmount issues.

Bob

http://www.mindspring.com/~bgruen/images/0005BL.jpg


http://www.mindspring.com/~bgruen/images/1005BL.jpg


http://www.mindspring.com/~bgruen/images/2005BL.jpg



http://www.mindspring.com/~bgruen/images/PlugDiagram.JPG


For more info...

http://www.dvxuser.com/V6/showthread.php?t=104801

[Bob Hill]

Hiya Bob,

I made one of these up right after you mentioned it on the other thread. This is must have for folks with 35mm adapters.

[mikkowilson]

This is an awsome invention Bob. I've bounced it through the 35mm section to leave a redirect, before making it one of the few DIY stickys. :thumbsup:

I'd love to see a couple of pictures of your unit.

- Mikko

[MarcMalkowski]

So if I need a 21juncture, what will I need?

[Bob Hill]

I need to finish off a unit that lets you set a fixed focus and still have the iris adjustment available. I should have that done this week and I will post up pics and plans. Again, great idea Bob.

[Noah]

For me, ideally, I'd love to have fixed focus and zoom while still having iris control. Is this possible?

And thanks for doing this much already. The slipping focus issue has become a big problem, especially when doing handheld stuff.

[JasonFox]

Very, very cool! But I'll definitely need to see some pics before heading down to The Shack. But this will be such a handy thing to have. http://www.dvxuser.com/V6/images/smilies/thumbsup.gif

[Bob Hill]

Noah,

The basics of the focus control are the same for the zoom. I think ideally everyone is going to want to have fixed focus and zoom but still have control of the iris and rec/pause functions remotely. Basically the difference between the two units would be the size of the plugs. I'll post up details as soon as I have something sorted out for an off the shelf case for the trim pot and female plug.

[snodart]

This is going on my list of DIY things build. Looking forward to those details :thumbup:

:beer:

[Noah]

Gotcha. It would be amazing to be able to customize what you need vs the size of the unit. For instance, I have no need for the rec/pause, iris, focus, or zoom remote capabilities. All I would really want is to lock the focus and zoom where they are and still have control over the iris and record buttons on the camera. This would then be a much smaller unit than having everything with remote capabilities (which if I'm not mistaken already exists - just not in the cheaper diy world).

[Bob Gruen]

For me, ideally, I'd love to have fixed focus and zoom while still having iris control. Is this possible?

Zoom maps the resistance to the rate of change of the zoom value. At 10K Ohms the zoom does not move. At 9K or 11K Ohm is zooms slowly in one direction or the other. At 15K or 5K Ohms it is zooming very quickly in one direction or the other. Think of it like the zoom rockers on the handle, it will control the zoom servo, but bumping the zoom ring (which is purely mechanical) will override or damage it.

To effectively lock down the zoom, simply set it where you want it, engage the servo switch, and unscrew the micro-knob on the zoom ring and store it in a safe place. The reason I remove the knob is that snagging it on something with the servo gears engaged could damage the gears. I have yet to mess up a shot by hitting one of the zoom rocker switch. I'm not sure if inserting a plug disables the toggle switches or not.

Bob

[Bob Hill]

Bob,

I was thinking that the plug disables the toggle switch but I could be wrong. I'll check it out. I am still waiting on some tiny cases to make up a final piece that lets you use an iris controller and rec/pause button in conjunction with the focus lock. I'll post pics and plans once I get it all sorted out.

[Jason Ramsey]

Wild. Thanks for sharing this, Bob.

[Bob Hill]

Just wanted to let everyone know that I am still working on getting a good set of plans with a parts list put together for this. I have the parts list mostly worked out but finding small cases is a real PITA! I should have something for everyone this weekend though.

[Avenger007]

hows this coming along? Any updates?

[Bob Hill]

Sorry for not getting back sooner. I should have a downloadable .pdf for everyone shortly. These are simple and take only a few parts and I think with the .pf anyone should be able to make one of these.

[arno]

Is it possible to combine this back focus plug with a diy Record Start/Stop control for a rig?

Arno

[Bob Hill]

Arno,

Yes you can use a backfocus plug and a record start/stop controller. The focus control is on a different plug than the start/stop. Just wire up the relevant portion of the circuit for the start/stop and you are in business.

[arno]

Thanks Bob!

Arno

[Bob Gruen]

Just wanted to let everyone know that I am still working on getting a good set of plans with a parts list put together for this. I have the parts list mostly worked out but finding small cases is a real PITA! I should have something for everyone this weekend though.

I mixed up some epoxy and micro balloons and brushed it on. Looks like hell, but I could find a way to make it pretty if I wanted to.

Bob

[Christopher Barry]

Bob, I am looking forward to making one of these, thank you.

[ChosenWay]

Any new info on this? with plans?

[majormorgan]

Anyone making and selling these?

thanks
Richard

[stephen_nugent]

Hey bob,

your little DIY sounds fantastic, but i followed all the instructions and seems i aint getting it to work for some reason. I do get a variable resistance between the base and the center between 4-5 KOHMS when adjusting the POT, but it seems that the plug doesnt override the camera, does nothing actually. Tested with camera both manual and auto focus. Any ideas or anybody else who has built one?

thanks,
stephen.

[Bob Hill]

Stephen,

I would really check to see if is plugged all the way in. I sometimes have trouble with the plug on my HVXs. Also, you would know if it is plugged in because the camera will say that it is in manual mode.

Bob

[stephen_nugent]

bob you were right, needed an extra push, this thing sure is flimsy without a cover. just realised though my range is off so will have to experiment a little with the resistors. thanks!

[stephen_nugent]

Here's my version on Bob's original. I found a different type of 1K POT that can be adjusted with a small philips screwdriver to adjust the focus. I'ts in series with a 2.7K Ohm 1/2W resistor, enclosed in a 1/4" female jack case cut to size connected to a 1/8" right angle stereo jack. This can vary from camera to camera as Bob said. Doesn't obstruct the record button and works like a charm!

http://www.dvxuser6.com/uploaded/23330/1199812431.jpghttp://www.dvxuser6.com/uploaded/23330/1199812481.jpg

[mcgeedigital]

Damn, I'd be in for buying one of those.....

[Hans Moleman]

Here's mine that I whipped up using the design. works perfect :)

http://www.dvxuser6.com/uploaded/9586/1200180237.jpg

[JasonFox]

Here's mine that I whipped up using the design. works perfect :)]


Slick! You going into business?

[Hans Moleman]

I dunno about that. its somewhat labor intensive. I'd need to know there's demand enough to do it. if you want one, pm me. if it turns out that people will buy enough (10+), ill make a batch and happily sell em. they'd have to go for about $50 or so to warrant that kinda work, though.

[Hans Moleman]

edit: problem solved

[JasonFox]

I'd happily pay 50 bucks. I've got babies on the way and an HV20 and D80 to figure out. No time for more tinkering!

[Charlie Anderson]

Need to figure out a reset button as well, I've been working on that in my spare time b ut can't get it to work out as planned.

[Bob Hill]

Charle,

When you say "reset" do you mean record/pause? If that is the case I can help you.

[Lucas Adamson]

Bob - I can't thank you enough for this. I made one of these today in about 3 hours, including experimentation and epoxying all the parts when I'd finished, and it is simply a brilliant thing. Furthermore, a few people have seen it, and now think I'm a genius, which is always nice, especially when it's not true. It cost me £3 in total as I had an old jack plug. Really people - in terms of an effort and cost to benefit ratio, this is the overall DIY winner by a mile for 35mm adapter users. God bless Bob!

Lucas

[Lucas Adamson]

Make that - God Bless the Bobs! ;)

Lucas

[Bob Hill]

Lucas,

Glad to hear it worked out well for you. The backfocus plug and regular focus/iris/rec/pause/zoom control are the best DIY projects for HVX. They really expand the capabilities of the camera.

[Avenger007]

So did you guys above figure out how to only lock Zoom/Focus and leave on camera Iris available? Can you share the plans, I have 4 more weeks solid of 35 adapter shooting left and I'm tired of checking the settings between every take.

[JasonFox]

Seriously, who wants to make one for me (for money)? We just had twins and I barely have any time to mess with the camera itself, let alone building something for it. :)

[mcgeedigital]

Seriously, who wants to make one for me (for money)? We just had twins and I barely have any time to mess with the camera itself, let alone building something for it. :)

+1 I'd pay for one.

[waefre]

Sign me up

[mark brindle]

Id buy a couple of them too..
or id make them if someone posts the plans..

thanks
mark

[JimmyC]

Does anyone know if a similar trick could work using the LANC input on an XHA1?

What a great widget!

Jim

[Ted Arabian]

This is an amazing device. How freaking clever.

Will it work on the DVX100B ? I can't imagine that it wouldn't.

[Bob Hill]

Works just fine on the DVX100B.

[mikkowilson]

Does anyone know if a similar trick could work using the LANC input on an XHA1?

What a great widget!

Jim

Nope, unfortuneately not.

LANC is a serial protocol, not an analog input. And it has no provision for "absolute" focus position control, like the analog control inputs on the Panasonics.


- Mikko

[JimmyC]

Yeah thats fair enough mikko!

But I wonder if there is any way to 'lock' the manual controls by an input in the lanc control socket? That way you can do away with the taping and/or seting from preset every take.

Any ideas?

Jim

[IjabaFilms]

I'm not trying to be clueless but is this thing to help make sure your footage is accurately in focus when using 35mm adapters? I have a Go35Pro and I'm reluctant to use it a lot for fear of thinking the footage is clear in the viewfinder only to find its slightly out of focus. Someone told me it was a backfocus problem but I didn't really know what to do about it.

[TAMIM AMINI]

i love that video thanks for taking the time to do that .

[TAMIM AMINI]

i am want to sale my jvc hd 110 if any one need it .

[IjabaFilms]

Here is the one I just built. I think it's working but I'm unsure. What exactly should I be looking for. I did notice it immediately focused.

http://www.ijabafilms.com/Plug/Plug.jpg

http://www.ijabafilms.com/Plug/Plug2.jpg

http://www.ijabafilms.com/Plug/Plug3.jpg

http://www.ijabafilms.com/Plug/Plug4.jpg

[IjabaFilms]

Something is off. Using the autofocus puts the focus at 30 and the back focus at 4.8 but when I plug the thing in all I get is a focus of 26 and a backfocus of 3.2 and it won't change even when I turn the screw and it is of course, out of focus then.

I did find this video which was very helpful:
http://www.youtube.com/watch?v=at9Fv24yXgQ

[alfred]

Does somebody know how the trick works with a Sony PD 150?

[Lucas Adamson]

I have successfully built two of these adapters now. My first has a limited range of between MF66 - MF71. It was made with a 1K pot and 3 resistors (2x 5.6K & 1x 1K) I no longer need it as my adapter has a new lens mount and the range no longer covers my adapter. I need MF61 now.

My second I made this evening. It has a 5K pot which makes the useable range much wider, but tuning the focus requires fewer turns of the pot. It is combined with 2x 1K resistors & 1x 5.6K resistor, making a total of 7.6K to 12.6K resistance, which results in a DVX100B MF range of MF38 to MF70. Much more useful. I have a long 35mm adapter and need MF61/MF62.

If you use a 1K pot, you have to loosely solder together resistors to get very close to your desired MF value. With a 2K pot you'll have a bigger range. With a 5K pot you get a huge range. It is the way to go, I think.

Also, I used a good right angled Neutrik 3.5mm jack with a 10cm wire to the resistors block, so that it would not be resistant to breaking off in the socket during use. The pot and resistors I Epoxy-resined to form a strong unit with no chance of a connection failure at the solder joints. Araldite is a good insulator.

If anybody needs MF66 - MF71 on a DVX100B, let me know. I have a nice little unit for that value.

All the best
Lucas

[DustBowl]

Also, I used a good right angled Neutrik 3.5mm jack with a 10cm wire to the resistors block, so that it would not be resistant to breaking off in the socket during use. The pot and resistors I Epoxy-resined to form a strong unit with no chance of a connection failure at the solder joints. Araldite is a good insulator.


Got any pics of the unit - sounds nice.

[Joe Kocsis]

Did anyone ever start selling these?