Timescapes - Digital Timelapse Discussion

focus motor and apiture motors
Page 1 of 1

Author:  chardie [ Thu Dec 29, 2016 4:08 pm ]
Post subject:  focus motor and apiture motors

been looking at motorizing my m42 lenses was looking at the pentax 300mm f4 first because its bigger with more room for experimentation however on closer inspection its not internal focus which means the lens moves about 12-15 mm from close focus to infinity and the aperture ring is near the front of the lens here's a pic


was curious as to how its been done before. can you get enough friction between a gt2 belt and the rubberized area to ensure no slippage while focusing or is a gear round the lens the way to go. the real problem i think is with the aperture moving forward and backwards i cant think of any cheap fix for motorizing the aperture ring while its moving.
here a pic of my other m42 lens i think the smaller lenses will be ok as they all have the aperture ring in the normal place at the back of the lenses


any thoughts greatly appropriated :)
oh and an early happy new year :D

Author:  geraldft [ Fri Dec 30, 2016 3:11 am ]
Post subject:  Re: focus motor and apiture motors

No way round it - you need a very wide gear... :!

Actually you'd also need some lens support - the torque of the lens motor will tend to force the barrel sideways...

Author:  chardie [ Fri Dec 30, 2016 6:22 am ]
Post subject:  Re: focus motor and apiture motors

i had hoped that between the tripod socket on the camera and the socket on the lens and a suitable base that would be enough but will look at another point of support as well.

Author:  sciencelookers [ Fri Dec 30, 2016 3:25 pm ]
Post subject:  Re: focus motor and apiture motors

We usually ship D-gears from Jag35 with our focus motors. They come with an assortment of different length feet to adapt them to different lens diameters and clamp onto the lens. They can be removed from one lens and be adapted to another in a few minutes. Another possibility would be to get seamless follow focus gears made for each of your favorite lenses. A place called followfocusgears.com can 3-D print them for any lens. I got some for focus and zoom on my 6D. You also need a way to mount the motor to your camera. We use a 15mm rod system which is pretty much an industry standard. The light video rail system places two 15mm rods 80mm below the lens center and separated from each other by 60mm. There are hoods and filter holders which also attach to these rods.

You also need to make some sort of bracket that clamps onto the 15mm rod and lets you screw your motor to the other end of the bracket. You can see what our brackets look like on our website Stepoutmoco.com. Our brackets are drawn in a CAD program and then a mold is made to produce the brackets from plastic. Any method which works for you is good. My original prototype was hand machined from a half inch thick sheet of PVC, then subsequent models were CNC milled before we went to the molding process which allowed us to sell at more competitive prices.

Most focus gears are 32p diammetral pitch. Servocity sells 32p gears and hubs to mount them onto different sizes motor shafts. The Jag35 and the seamless follow focus gears will mesh with these. Get the thickest ones you can.

Of course, any method of attaching this stuff to the camera that works is good. Please post some pictures of what you wind up making.

Author:  Doug K [ Mon Jan 02, 2017 3:46 pm ]
Post subject:  Re: focus motor and apiture motors

Hey Chardie,
if possible try and mount the motor to the lens. It is not always easy to do but it would help prevent the motor torquing the lens in the camera mount. But as I said it is not easy or possible to do on certain lenses.

Good luck.

Author:  sciencelookers [ Tue Jan 03, 2017 6:33 am ]
Post subject:  Re: focus motor and apiture motors

I agree with what Doug said completely. One of the least talked about problems is thatfocus motors and manual follow focus knobs push against the side of the lens and when using DSLR bodies, this causes the camera to be pushed up or down slightly when the movement starts. Biolapse had posted a picture of a special mount he made to attach a focus motor directly to one of his lenses. This eliminated the "bump" from his films entirely. Its brilliant if you are working with a lens which is physically long enough for you to do this. The unwanted movement happens both at the lens mount and in the camera body. The bottom of plastic bodied DSLRs tends to flex, allowing the threaded insert where the tripod attaches to lift slightly. The lens mounts on the camera and on most DSLR lenses also move slightly. Good cine lenses and digital cinema cameras are built much more robustly for this reason.

That said, most people use a standard light video rail system to attach lens accessories. These are sometimes called 15mm rod system or 15mm baseplate by Chinese guys who make them. Here is a very long video showing how to attach a focus motor to a camera which I made for our customers who may have never seen a 15mm light video rail system before. Be warned,its 20 minutes,but the intention was to leave nothing out so success is assured without the need to call and ask questions.

https://www.youtube.com/watch?v=syh-V2D ... e=youtu.be


Author:  amongstmyselves [ Tue Jan 03, 2017 7:44 pm ]
Post subject:  Re: focus motor and apiture motors

Hi all,

I've been busy moving house for the last 3 months and only just finding time to get back to the norm. Great place where the stars shine brighter and the horizon is wide.

My system uses the geared approach with a large gear on the lens and a small gear on the motor. It uses the pressure approach of meshing the gears. I've not really had a major issue with the movement being noticeable but then again I've not gone above 50mm on the full frame camera. To modify my system to anything else would be a great pain as I don't use the rail system but just have a camera platform. I've seen pictures of people using velcro straps and tying down the lens to their platform.

I use several of the Samyang video lenses which have the gear built into the lens but find that they are a little small in their diameter and my stepper can't quite move them. Attaching the large gear ring to these is also necessary.

I like the idea of mounting the motor to the lens. How are people doing this ?

Steve - apologies if this sounds a bit hijackish

Author:  edward [ Wed Jan 04, 2017 5:26 am ]
Post subject:  Re: focus motor and apiture motors

Hi guys,

I think you can see in this video how I do it. I've tried every other system, but this one works and eliminates the initial motor jerk and it's so simple to do. I machined a lens collar that supports the motor, which is attached to the collar using the rear bolts of the motor. (Be careful doing this. You don't want the motor to fall to pieces).

On my other lenses I 3D printed everything, including the big lens gear ring (which you can see in the second video). Every lens is different, so I designed the collar accordingly. Bespoke, as they say.

I used Shapeways for the printing, with the black finish they offer. The lens gear ring is designed to almost fit around the lens barrel, but the fitting is just a bit undersized, deliberately, so it won't go in. To make it go in, I put this lens gear ring inside a bucket with hot water for about 3 minutes. The hot water expands the plastic ring sufficiently to allow it to slide into the lens without much effort. When it cools down, it shrinks a little and you have a nice tight grip that doesn't move. There you have it, no screws and a complete gear circle with no obstacles or split. Obviously you can use a commercial gear ring, but I just fancy making them bespoke.

Also notice that I don't use a geared motor. The motors shown have more than enough torque for all the lenses i have, so by using the motor direct, backlash is reduced as much as possible. The backlash on the geared ring itself is so minimal that it doesn't affect the video filming when you change focus direction.

Don't ask me how to remove the ring from the lens, because I haven't tried it yet, if the worst comes to the worst, I'll have to break the ring, but I would try other things first, like warming it gently with a hairdryer so that it expands sufficiently to praise it out, maybe. I don't need to remove them anyway. You need to be quite precise for doing this, if you cock it up in the alignment, you may not have another chance and you'll have to throw away your lens, your camera and your dog:)


Author:  chardie [ Sat Jan 14, 2017 12:33 am ]
Post subject:  Re: focus motor and apiture motors

edward it looks like you have the lens motor mounted to the lens. it looks like there is another motor mounted further back under the camera is that for the aperture ?

Author:  edward [ Sat Jan 14, 2017 1:09 am ]
Post subject:  Re: focus motor and apiture motors

Only one motor attached to the lens. I think in your case, with the old lenses, they may have some slop in the gearing through usage over the years? If so it may be difficult to avoid some jerky movement when changing focus direction.


Page 1 of 1 All times are UTC - 8 hours
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group