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 DIY MoCo Zoom Prototype 
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Joined: Wed Apr 16, 2008 9:49 pm
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Location: Troutdale, OR http://www.vimeo.com/ac
Post DIY MoCo Zoom Prototype


This project has been on my mind for months now, I just finished it after a few weeks of sacrificing my lunch breaks at work. I've been on graveyard shift for the past month, so my mind wanders and I get anxious to build stuff. I bought another milapse unit to get the motors from, so this uses the "alt" motor. Part of the reason the design is so ugly is because I first made the motor and worm gear block separately so I can unbolt it and possibly use it for something else. I had the basic idea in my head but I was essentially making it up as I went, which is why there is no shortage of extra holes. The idea is the two pulleys have two rubber o-rings each, pinching the lens. The bottom one is powered by the motor and the other is free. The large o-ring is there to put tension on everything, and help turn the top pulley. Everything but the nuts and bolts were made from scratch, the grey is PVC and I think the white is Nylon. My electronics skills are nonexistant so I used cat5 and a connector to connect the 7 wires back together.

I'm heading out soon to test it out, results to follow hopefully today or tomorrow!

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Sat Sep 13, 2008 9:42 am
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Post Re: DIY MoCo Zoom Prototype
:shock: :shock: Oh snap! That is so hot! I love it. 8-) 8-)

Now... The thing I've been thinking about lately is taking an old 24mm F2, pulling the ball bearing that 'snap' the aperture, then slow dialing that dial to get very slow change in aperture for smooth sunset/sunrise.. What do you think? I was thinking about mounting an old ds motor to the flash shoe and somehow belt drive it...


Sat Sep 13, 2008 11:07 am
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Post Re: DIY MoCo Zoom Prototype
I had the exact same thought, using a wide lens you'd be less likely to notice DOF changes from the aperture, right? An aperture ring probably doesn't require a tenth the force it takes to zoom the lens.

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Sat Sep 13, 2008 11:48 am
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Post Re: DIY MoCo Zoom Prototype
Even if the DOF is changing it may look quite interesting... Yes it shouldn't take much torque at all!


Sat Sep 13, 2008 12:03 pm
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Post Re: DIY MoCo Zoom Prototype
milapse wrote:
Even if the DOF is changing it may look quite interesting... Yes it shouldn't take much torque at all!



That's ingenious again, Andrew! Great!

Now I wonder, how can you access "mechanically" the aperture ring? Open the lense?

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Sat Sep 13, 2008 12:15 pm
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Post Re: DIY MoCo Zoom Prototype
Michael wrote:
Now I wonder, how can you access "mechanically" the aperture ring? Open the lense?


Older manual lenses have a ring to adjust the aperture, just like the focus ring. Would be really easy to belt drive. For my project I had to even out the pressure on the lens with that top pulley so I wasn't shoving it one direction too hard.

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Sat Sep 13, 2008 10:06 pm
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Post Re: DIY MoCo Zoom Prototype
I like it! 8-)
Be great to see what results you get.

A few thoughts...
I was thinking of something along those lines except with 3 wheels to hold it firmly centered to apply all the pressure to the lens ring. Do you have any problems with sideways torque on the camera / lens mount?

How do you get on if you are still driving the lens when you get to the end of the zoom? I'm guessing you will get to that later if the drive works out OK. You could put a limit switch on it by placing an actuator of some sort on the lens.

One last thing, this is probably largely dependent on the lens you use... how do you get on for focus? You may be limited on the range you can zoom over if you stick with fixed manual focus. On my 28 - 300 zoom the focus need to be adjusted regularly throughout the zoom range, but on some of the shorter lenses they are reasonably steady.

I was considering trying was a worm drive on a push-pull zoom lens, which in theory would be relatively straight forward mechanically if mounted on a sliding rail setup.

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Sun Sep 14, 2008 12:54 am
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Post Re: DIY MoCo Zoom Prototype
Antz- Sideways pressure doesn't seem to be a problem (edit: ok, maybe it is). The D80 has a little hole in the bottom so I used a pin in the base block to locate the body. Much to my suprise it will actually run without the top pulley in place, although it would probably slip somewhere along the way. At this point I just have the lens marked where the end of the travel is, and I stop zooming manually. I thought about 3 wheels, but decided to go with 2 because my original plan was to have the pulleys bigger in diameter than the lens. I couldn't find any plastic rod that big so I had to add the two idler pulleys on the sides. As far as focus, I'll just stick with infinity for now and see what happens. If my subject is close enough I will have to use autofocus and see how it turns out. I did some test shots and I'm processing the results right now, hopefully they turned out!

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Sun Sep 14, 2008 2:48 am
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Post Re: DIY MoCo Zoom Prototype
Nice work.

I've been thinking about building something similar but as Dr Phil says, 'talkin aint do'n'.

I'm pretty sure that the trick with this is to build it around a lens which doesn't alter focus through it's zoom range so that you can reliably and accurately zoom without loosing focus. Canon people can adapt all kinds of lenses to their bodies so there are also more lens brands and physical configurations to choose from. Of course, if there's a nice cheap Canon (or Nikon) lens that does the trick then it makes life easier.

Look forward to seeing some time lapse from it.

JJ

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Sun Sep 14, 2008 4:41 am
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Post Re: DIY MoCo Zoom Prototype
Here's the first test:



I'm pretty happy with the results...the only problem seems to be the lens wandering from side to side, but that's understandable with all the pressure it takes to twist the lens. Looks like for the most part its only happening when I change directions, so I could probably fix that.

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Sun Sep 14, 2008 5:21 am
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Post Re: DIY MoCo Zoom Prototype
Very nice results! I've seen that 'wavy' motion with a lot of my MOCO experiments... It's ether very hard to get all the engineering tolerances dead on for consistent torque throughout the system or it's just the nature of the DC motor system. It wouldn't surprise me if the lens has changing resistance and 'floating' glass throughout the dial too... Hopefully it will all go away when you take the wobble out since the two look linked.


Sun Sep 14, 2008 5:32 am
Post Re: DIY MoCo Zoom Prototype
jjphoto wrote:
I'm pretty sure that the trick with this is to build it around a lens which doesn't alter focus through it's zoom range


Exactly, some do some don't...


Sun Sep 14, 2008 5:37 am
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Post Re: DIY MoCo Zoom Prototype
Mmmm, THX...

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Sun Sep 14, 2008 6:18 am
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Post Re: DIY MoCo Zoom Prototype
Good work!

How much speed control do you have w/ that thing? I'm not sure how you represent backlash in a pulley system, but I've wondered how much they get at very slow speeds. I guess you would just reduce it by applying extra tension to the pulleys.

!c


Sun Sep 14, 2008 6:57 am
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Post Re: DIY MoCo Zoom Prototype
Backlash as far as the pulleys is concerned is probably minimal, only amounting to the sideways pressure on the lens since the lens is flexing left and right from the turning pressure. There's quite a bit more backlash between the worm and gear so when I switch directions there's always a delay.

Speed control seems infinite- what you see in the demo video is the maximum speed but I can slow it down, I don't even know how slow. In the test video it was set to zoom the lens one way in about 15 minutes, but I could easily set it to take several hours.

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Sun Sep 14, 2008 8:28 am
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Post Re: DIY MoCo Zoom Prototype
Well, if the camera is moving, you're not experiencing backlash. You're right that most of it will occur in the worm gear and also in the transfer gear from the worm to the shaft. You'll recognize backlash when you get to a speed that moves it at a rate lower than your backlash amount - that is, you'll think it's just moving very slowly but it ends up not moving at all. I think the standard backlash for high-precision acetal/delrin gears is around 0.015% -- so, if that's a 48-pitch gear, you'd be looking at any discrete movement not followed by another immediate movement of less than 0.0003" (1/pitch * backlash, if I'm correct in my math here) will likely be lost to backlash. That's probably what you're seeing in that delay, it's ramping up the motor, and you either have not enough torque or too much backlash.

On the subject of torque, It looks like you've got it torqued up pretty good, but you're going to reduce torque using a standard DC motor as you speed it down. To go really slow you might need to trade out that bottom pulley for a very small one, and put your two big pulleys on the side. Or, just use one - rotation caused by the pulley should only push when movement starts (pushing the camera away from the movement until the camera refuses to rotate any further). It may be that the two pulleys are causing counter-forces on the camera, but I'm betting that motion you're seeing in the deep zoom is more related to vibrations from the motor setup? Perhaps some foam or rubber used to isolate the motor from the camera mount will help a lot.

!c


Sun Sep 14, 2008 9:09 am
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