Easyest way to make a GG oscillator.

[Toenis Liivamaegi]

When MPIC started to take shape I had an idea that if I suspend lets say a smaller UV filter based DIY ground glass inside a macro tube with soft open cell foam I might be able to oscillate it with coin type vibrators found in cell phones etc.
I tested my idea and it worked.

And by so far it is the easiest way to make an oscillator.
Of course as the design is so simple there is lot of trial and error to get this design work.
The softness and thickness of foam and gluing all that precisely in place but in the end one has a oscillator that fits in a macro tube and covers the academy frame.

In principle it should look something like this with bigger "o" in the middle: (o)

I really don’t know why anybody hasn’t opened up that design possibility already.

I guess in next few days a there will be a breakthrough even in that grain reducer design.
I have been participating in product development team that has designed one-piece mechanism for oscillating a ground glass or frensel focusing screen.
More than ten months of research has concluded that it is possible to oscillate ground glass inside a housing that has inner diameter of only 56,7mm with coin type vibration motor and therefore reducing visible grain and all that with one-piece GG oscillator that has no external moving mechanical parts.
Let’s hope that today’s laser cutting tests are positive. The design allows only 0.05mm of tolerance.

Thank you,
T

[Nick Outram]

Toenis,

you have just described the Letus35... It uses the same method -a very small 3v motor- 'button cell size' to vibrate a 35mm sized ground glass plate...

It works very well and is 1/4 the price of a RedRock...

There are a couple of mods I would make -the tube should be of carbon fibre to reduce weight. It would also be possible to house two rechargeable AAA baterries inside the unit.


Nick.

[Toenis Liivamaegi]

Hmm, I thought that Letus35 is still using it`s original syringe type oscillating system. Then I guess I missed the design change if it was public at all.
AAA batteries cann`t fit inside such a unit as most flange to image plane distances wouldn`t allow it but 2 AAAA batteries can be fitted even into a macro tube kind of adapter design. Then again one cann`t recharge such batteries with standard size chargers and should use something similar to Ansmann ACS110 NiCd / NiMH TRAVELLER CHARGER that`s a hell of a charger for any DIY project around the world.

Regs,
T

[Dennis Wood]

Toenis...a few items for discussion:

1. How do you prevent pieces of foam from breaking down under the vibration (small pieces ending up in optics) over time?

2. Being that foam is equally resistive in all directions, how do you prevent z axis movement in your foam mount?

3. What happens at -10C ?

[Toenis Liivamaegi]

1. As diy application there can’t be a guarantee that small pieces wouldn’t end up on optical path so routine, before shot maintenance with blower should keep all particles away. Being that many foams have nominal flexibility of 30% there wouldn’t be a mechanical stresses that would cause serious problems at all.
2. Z axis movement is minimal given that coin type vibrators I mentioned align themselves to X and Y. Of course when put in place correctly.
3. I guess that temperature stresses are the most delicate but given that most cameras aren’t meant to be used below zero there wouldn’t be much to be worried about as the vibration motor itself provides little bit of heat emission.

One more thing to say about lets say that foam mount is that if foam is flexible and thin enough to fill the full perimeter of gg or focusing screen holder it really is quite quiet.

After all that kind of cheap diy foam construction is not meant for serious professionals by all means.

Regs,
T

[Bill Porter]

Toenis is right; there are foams that can flex quite a bit over many cycles without breakdown. Further, there are solid rubbers with a low durometer number that would work fine, perhaps even better. Finally, rubber could be captured within a metal or even plastic frame to limit motion in the Z axis.

Also, an aluminum housing could be just as light as a carbon fiber one, and it would be very inexpensive.

Keep up the good work!

[Bob Hart]

Firstly, a long and boring historical preamble.

The very old sony EIAJ standard B&W VTR's drum motors had commutator brushes mounted on fine brass full ellipse leaf springs. - think very old motor car back axle springs only two of them back-to-back. - A good solution in this case for maintaining the lightest constant and contact pressure to extend the lifetime of the conductive material.

Trouble was, dampening of such a long spring is required. Has to happen with automobiles too which use shock absorbers. The VTR damper was a piece of black foam cut to the shape of the hole in between the two long sections of the springs. - Also a good solution.

Trouble was the foam deteriorated and shrunk and pulled the contact away from the commutator. The failure would occur after storage or in use. The cause seems to have been a chemical interaction between the foam and the adhesive used to keep it in place, then a drying and shrinkage. The stuff was by then almost loose powder.

If it got to the stage of becoming loose powder, the machines might spontaneously become operational again after longer storage or through some moving and shaking on their way to the repair shop. Whatever, removing the foam solved the problem.

Whatever the original damping problem was, it did not seem to become apparent when the motor was closed up again. Maybe the remnants of adhesive and foam remaining on the spring surfaces was enough to do the job - who knows?

I suspect more than a few otherwise good drum motors got changed out or whole machines discarded later on when they were obsolete and some were used as experimental digital audio recorders.

In the 35mm adaptor, if adhesive has to be used, chemical interaction with the foam may be a real problem. Controlling the penetration of adhesive into the foam and the degree it hardens the foam will be a challenge.

This is the why of double sided tape on foam DIY door seals and one of the whys of the closed rubber seals on car doors when open foam would be cheaper. The foam in the adaptor may have to be sealed on its surfaces likewise.

Temperature rise from internal friction in the material might also cause premature breakdown. There might have to be a regular pattern of holes in the foam to allow flex with less friction and passage of air to keep the temp down. This should also help conserve the motors and battery life.

Keeping the GG correctly located on the focal plane will likely be a problem and probably requires a precise surface to surface contact to keep it in place. Loose small wide solid pillars or balls entrained in the foam between the faces might do the job.

Go for it. I think it should be a viable solution and should be quiet too. But I am no engineer so doubt my words severely.

[Dennis Wood]

Toenis, my points were not to dissuade you...just raise discussion. Your idea certainly has merit and is certainly worth exploring. Implemented well, there's no reason for it not to make its way into professional adapters.

[Toenis Liivamaegi]

Not much to worry about.
For professional solutions we developed something like this. (A leaf spring oscillator in principle.)
A biaxial, self canceling focusing screen oscillator that even dampens vibration before it reaches adaptor housing. It oscillates about 0.2-0.4mm in diameter and has snap-in snap-out screen holder.
All in one-piece design to save production/assembly time and costs.

Should I take the honor of inventing and publishing that biaxial oscillator principle?

Cheers,
T

[Frank Hool]

I' ve seen such. In the place of leaf springs were just rubber couplings. Overall design was very robust and plain.

[Solomon Chase]

Very unique design man. Looks like it should work good, if it's rigid enough to resist Z axis movement (and if the motor is mostly X + Y movement)

[Bob Hart]

The snap-in screen holder is going to cause you problems at the frequencies I anticipate you will be moving the GG.

Three points of contact on the GG is good for avoiding any strain on the GG but on the centred release clip edge, leaves unsupported overhanging mass which may spring and resonate.

In your arrangement, other than by precise fit, the GG is retained against forces only along one axis by mechanical prressure, less positively retained along another by friction only and reliant on precise fit or spring pressure of the mounting components along the third.

It will want to move under the retainers and depending on how strong the spring pressure of the release clip is, a resonance may occur which will aggravate tendency for the GG to move and maybe wear the retainers to point of noisy operation due to developing clearances or to point of failure.

Positive retention of the GG in the directions of three axes is desirable, in the direction of two axes is essential.

The mass of all retention parts will need to be balanced across the centre of the entire moving mass parallel to the focal plane otherwise the moving assembly will eventually develop a rocking motion, probably not enough to move the edges off the focal plane noticably but maybe enough to eventually crack the GG especially if it is glass and if the three point retention arrangement is kept.

May as well get it right from the beginning.

Test my assumptions critically as I am no engineer and thus could be totaly wrong.

[Toenis Liivamaegi]

Bob, thanks for your assumptions.

It`s really related to moving mass. It will evetually cancel itself out.
As for snap-in screen holder it`ll have tolerance of 0.2mm only and as that one piece leaf spring oscillator design uses GG/frensel combo weighting no more than 0.4g and biaxial off axis vibrator it really realignes itself.

I`m no engineer too but foutunately I`m able to work with engineering students from local college.

Next week we`ll test jet cut prototypes in different coditions with different Panasonic cameras (HVX included).

Estimates are that HVX will require only +3/4 dioptre correction at zoom 77 and the best part of it is that achromat should be only in 58mm in diametre and it still wouldn`t cause vignetting.

Let`s keep it up in the creative department,
T