Mini35 Oscillating Ground Glass Idea

[Anders Floe]

I emailed Thorlabs and asked them if they sold anything which could rotate a 2" gg and they gave me the following link:

http://www.thorlabs.com/NewGroupPage.cfm?Guide=121&Category_ID=183&ObjectGroup_ID=1064

Would it work?

[Dan Diaconu]

Not for the GG.
This one can rotate "something" very precise (1 arch) but the roation
has a central axis. (Like P+S first run)
And the motion is fragmented (stepper motor)
Not to mention size and weight, oh yeah and price.

[Les Dit]

As many of you know, several months ago I built a 3 shaft GG orbiter and did a quick HD ( 720 P ) demo video posted at 7.5 megabits/sec. Many of you saw the slightly shaky video before my bandwidth was used up.
In preparation for making a small run of these as a parts kit type of deal, I also wasted a lot of paper coming up with other methods of moving the glass. I think I have a possible solution now. It still involves some very precise machining, but it simplifies the design considerably while still supporting the mechanism on precision ball bearings. I tossed ideas that slide the glass on a slider surface because of longevity concerns.

I just got my CNC mill up and running, so this weekend I'll test the the core of the design out a bit. I use a laser to test image plane stability.

Maybe the 45 micro bearings I just purchased for the 3 shaft design will have to be re-purposed now ;)

Cheers,
-Les

[James Hurd]

Nice Les! Keep us informed! I've got a cnc mill and lathe collecting dust! It's calling me!

[Frank Ladner]

Anyone know of a source for inexpensive (yet reliable) ball bearings? BocaBearings.com seems to be a bit expensive.

I am looking for something with a 50mm inner diameter. The outer diameter isn't critical.

Thanks for any help!

[Dan Diaconu]

It depends upon too many factors: what kind of balls, ceramic, steel, nonmagnetic, quantity, etc.
Try these guys:

http://www.canadianbearings.com/publicSite/content/products/productCard.aspx?Lang=en

Most likely, you will find something suitable.
For larger quantities here:

http://www.xlbearings.com/

For one or two, most cost efficient is scrap yard (used cars)

I hope this helps.

[Frank Ladner]

Thanks, Dan!

I'm looking for something lightweight, and preferably with a flanged inner diameter.

I'll try the sites you posted!

[Frank Ladner]

I'm wanting to move from using masking tape to mount my 35mm lenses to using a more permanent, professional looking mount. However, I don't want to use something that will work with just Canon or Pentax, for instance. I'd like to go with something that would allow me to use a variety of brands/types.

I understand T-Mount converters are pretty cheap, but to implement this, what sort of mount would be on the adapter in the first place? Would I just go with, say, a Canon mount and any time I needed to use a Pentax or Nikon lens, get the respective T-Mount for each?

I'm not a 35mm expert, so please forgive my ignorance. Any help is really appreciated!

-Frank

[Bob Hart]

Les.

Bearing inside another bearing in an eccentric ring? Would probably need to be two rows of each otherwise would need at least one guideplate. I would suggest magnetic if one row of bearings is used and guideplate is added to keep it faced with minimal friction.

Also suggest you use a double "O" ring belt drive for the outer eccentric and two "O" ring belts as anchors for the inner which carries the groundglass. there may be a little rocking but nowhere near that of a sliding radial keyway.

Truck axle should be adequate for machining the rings and the ball tracks. Drill out small reliefs to lose some weight and also to counterbalance the eccentric ring.

I would suggest something in the approx. size of loose 1/16" bearing balls or thereabouts whichever is the most commonly available. Alternatively you might get away with needle rollers from automotive driveshafts but these would need more power to spin them and a guideplate would be mandatory.

Keep on designing.

[Joel Aaron]

<<<-- Originally posted by Frank Ladner : Would I just go with, say, a Canon mount and any time I needed to use a Pentax or Nikon lens, get the respective T-Mount for each?

I'm not a 35mm expert, so please forgive my ignorance. Any help is really appreciated!
-Frank -->>>

Yeah that would do it. You'll have to figure out a way to get the SLR mount on your converter but once you solve that you'd just buy the lens adapter you needed for each lens type.

I got a lens mounting flange off a macro tube. It was simply screwed on there. Or pick up a broken camera and screw off the flange. I used brute force at that point and used epoxy to attach my mount instead of trying to tap tiny screw holes. It's rock solid though :-)

[Frank Ladner]

Thanks, Joel!

I have an old camera body I can try.

[Frank Ladner]

Ok, I took apart an old Mamiya 35mm camera body that yielded some good parts. I must say, they don't make em' like they used to. I was hard-pressed to find any plastic in this thing. It was all metal, right down to the miniature chain on pulleys.

Anyhow, I got a mount which I think is a M42. For now I will use that instead of getting a c-mount for Canon FD lenses, since I have three lenses that fit it. Plus I could just get adapters for any of the other lenses

One of the best things to come out of it was the little condenser. I tested this out on my microcrystalline wax adapter and was very happy with the image. It gave a bright picture from corner to corner. The only problem is that the condenser is small (24x36mm), so I wouldn't be able to use medium format lenses, or take advantage of the extra image projected from 35mm (not having to zoom in as much which ground glass this means smaller grain). However, even at this magnification, there is no grain with microcrystalline, so it might work just fine. I will try and put up some more test footage.

[Frank Ladner]

Here are some helpful links that deal with different lens types, t-mounts, etc...

http://www.photoimagenews.com/lens.htm
http://medfmt.8k.com/bronmounts.html

[Greg Bates]

Originally Posted by Les Dit

Rai,
It seems you would have to hit a very low price to interest people on this forum. I offered a kit for a 4 shaft 12 ball bearing kit, with motor,belt, misc parts to make a complete GG orbiter for $350, and there was ZERO interest. It's not a pipe dream on paper on my end, as my posted pic have shown.
Perhaps a price of $100 might work here. Or maybe we let them try to make one for a while, and then see what happens :)

It's *not* the cost of the parts. The labor of making the custom parts is the price here.

-Les

I'm new to the forum but have read thru many of these threads. While ideally i'd embrace the idea of building an oscillating gg on my own, the reality of everything else I have to do makes it improbable that I would finish (or start;). 350 sounds like a steal to me, i've blown more money on things of much less worth.