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Old January 9th, 2009, 07:53 PM   #1
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Your comments/ideas needed...

Hi all, well I have decided (like many I am sure) to build my own 35mm DOF adapter. After looking at the very good information from Daniel Schweinert and from studying other examples on the net and ebay I have come up with the plans in the link below. I also took a photo of the parts I have accumulated so far. ($35 from Radio Shack & Hobby Lobby) I will need a +7 or +10 Diopter, GG, and some aluminum plate or nice wood for the base and GG holder.

Let me know what you think of my plans if you have the time or inclination to help out a newbie :)

Thanks!

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BTW: I will be using this on a Canon GL2.

Parts list already obtained:

Vibration Motor
Battery Holder
25 ohm Linear Rheostat
Wire
Box
50mm f1.8 lens (M42)
49mm Rubber Lens Hood (for 50mm Lens)
72mm +10 Diopter
72-58mm Step Down Ring (Diopter to GL2)
55mm Rubber Lens Hood
55-62mm Step Down Ring (to hold the 55mm lens hood to the box from the inside)
#1 M42 Extention Tube (to hold the M42 lens from the inside)

Still need to buy:

Ground Glass
Ground Glass Mount (still deciding on having an aluminum plate machined or using wood)
Base for mounting the GL2 & Adapter together (still thinking on aluminum or wood)

Last edited by Colin Pritchett; January 9th, 2009 at 09:06 PM.
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Old January 9th, 2009, 10:57 PM   #2
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Colin,
I have some doubts on the way your motor and gg mount is designed. it seems from your sketch you'll have z-axis movement instead of x-y. please clarify how you plan to mount that.
If this is vibrating then your rods are suppose to be parallel to the z-axis. Unless this is a new concept you are trying?

Ted
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Old January 10th, 2009, 08:43 AM   #3
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Unfortunately, As I read the diagram, I don't think it can work.

A phone vibrator motor mounted through the rigid 10mm panel in which the groundglass is mounted cannot do anything except make a noise. There is too much mass for it to move anything.

The groundglass excursion must be no less than about 0.75mm as an absolute minimum and move in a circular or near-circular motion otherwise you will get fixed pattern artifacts ("film of grain").

The groundglass texture would have to be very fine and on the threshold of passing aerial image through.

The movement must be entirely across the optical axis with absolutely no movement parallel to the optical axis otherwise sharp focus will be impossible or a phasing focal effect will occur.

If your 10mm panel is rigidly fixed to the external casework with the mass of the batteries also attached to it, as the diagram seems to indicate, then it has no way of moving with just a tiny phone motor trying to shake it.

A large vibro-massager motor would just about do it but it would also have to shake the unmitigated s--t out of the entire assembly as well plus the camera attached to it for any movement of the groundglass to occur.

Then the movement of the groundglass would still not be relative to the camcorder's view through it and the texture of the groundglass would remain visible. The image would vibrate instead.

The groundglass needs to be mounted in as light a floating frame (or groundglass carrier as I call it) as you can make. It needs to be mounted on a light and flimsy flexible support system if you are using counter-reaction to the mass of the eccentric on the phone vibrator motor to shake it.

Phone vibrator motors yielded a smaller excursion than was the minimum to de-resolve the groundglass texture unless the rpm of the motor was slowed to at or near to the natural resonant period of the groundglass mass on its flexible supports.

Quyen Le achieved this on the early Letus models with a slightly lower supply voltage, which enabled the motors to endure longer periods of duty, a dropping resistor and a piece of semi-hardening adhesive intended to add air friction resistence to the eccentric and slow the motor rpm the slight amount needed to bring it into resonance with the combined motor/groundglass/groundglass carrier/support pillar assembly's natural vibration period. It was an elegently simple solution which impressed quite a few of us at the time.

The motor must be mounted as close to edge of image frame as you can get it, otherwise there will be an almost stationary place in the groundglass movement somewhere on the groundglass area. This will show as a softedged sandy patch surrounded by clearer image.

There are various flexible lightweight mounting schemes ranging from pillars in flexible supports laid out parallel to the optical axis, thin bits of spring wire laid out as pillars parallel to the optical axis, bits of bottom "E" guitar string laid out similarly and a unique one-piece integral system of quarter-elliptical spring supports which work across the optical axis, machined out of the entire disk shaped groundglass carrier material itself on a precision computer-managed milling machine.

The quarter-elliptical scheme has some advantages but must be handled gently during assembly as the spring sections are apparently quite fragile.

There seems to be a lot of wasted casework in your adaptor. The principal reason for using vibrating groundglasses is to keep the appliance as small as possible to allow rods or rails to pass through or under the appliance from the camera support and to keep weight down.

If the casework is a project box similar to early evolutions of adaptors here at dvinfo, then you might as well use the space to accommodate a groundglass disk.

Your design seems to make no provision for adjusting the flange to focal plane distance for the SLR lens on front (backfocus), except perhaps for allowing fixed shims to be fitted between the M42 mount and the case.

Last edited by Bob Hart; January 10th, 2009 at 09:02 AM. Reason: error
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Old January 10th, 2009, 11:28 AM   #4
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As Bob said, you need to isolate the ground glass from the housing, otherwise any vibration you apply to the ground glass will be applied to the rest of the assembly which is ineffective. A popular method is to mount the ground glass on a protrusion suspended by a few thin plastic legs, perhaps secured by rubber gromets to further allow freedom of groundglass movement. As the length of the sticks does not change, proper backfocus is ensured.
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Old January 11th, 2009, 11:36 AM   #5
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Ok, you all are definatly smarter in this area than I am, thus my need for input so I am going to summarize the info that you gave to make sure I am getting it right.

1. The mount the glass is in needs to be plastic or at least isolated to allow sufficent vibration. I need to mount the motor on the top or bottom ot the gg .vs the side to get the correct axis movement.

2. You all indicate using a phone vibration motor, I picked up a 3V vibration motor from Radio Shack that has a max 16,000 rpm and is variable via the rheostat (already tried it out) 3VDC Micro-Vibration Motor - RadioShack.com

3. I planned on getting the flange to focal length distance right and then placing "blocks" in to keep the GG mount isolated in the box so it didnt move around. Shims for fine adjustment were also a possibility.

3. Here is a prepared wooden GG holder, just need to cut the holes and outside to fit in the box, the circle represents the hole for the vibration motor, I was going to place it at the bottom of the GG, 10mm below.

Zenfolio | C.M.Pritchett Photography | 35mm DOF Machine Plans/Parts

With the ideas you have given I guess the GG holder needs to modified to place a plastic portion for the GG to be in (in the middle of the wood) I have purchased a 40X60mm piece of very fine grain GG from a guy on ebay to use. I guess it will be trial and error, this is basically a fun project for me as I have always loved to build stuff and has the added benefit of being usable (if I get it right) :) I do understand the principles of this type of adapter but dont have any practical experience in this area so learning is fun too.

If the GG needs to move in a circular pattern that transverses all axises I will most likely have to design a different GG holder out of a thinner material (plastic) and maybe suspend a seperate GG holder on the plastic. If anyone has a link to a schematic or plan for this part of the adapter I would be forever grateful (I am a visual person)

Thanks for all your input!
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Old January 11th, 2009, 06:26 PM   #6
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Okay, here is some more progress. I used a guitar string as the basis for a mount. I have a hard plastic piece (80mm X 80mm) that will be suspended on the guitar string allowing for vibration to reach the ground glass. I will leave a 1mm tolerance around the plastic so it can move.

I also got the lens mounted and the hole cut for the 55mm lens hood in the rear. I found out the M42 film to flange distance is 45.46mm so now to think of a way to get the GG mount aligned in the box so I will get edge to edge focus and be able to focus to infinity.

Again your constructive criticism is appreciated, thanks.

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The last three photos are the most recent...
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Old January 11th, 2009, 08:41 PM   #7
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Colin.


I waxed a bit pedantic in my earlier post. Ben said the same stuff I expressed in about one paragraph. Am not meaning to put you down in any way.

If using guitar string, you will need at least three for triangular location of the groundglass on the focal plane, probably more like about six or even more. Depending on how heavy your screen and motor combination becomes, it may sink down and touch the case.

Your use of the guitar strings in a microphone suspension arrangement puts the guitar strings in tension against the movment you want which is across the lens optical axis. Less tension will allow movement off the focal plane along the optical axis. You would need the lower frequency "E" string which has a coiled mass around it and is thicker.

I have obviously confused you with the "Bottom "E" remark. When you look at a guitar being played, the "Top E" is actually the lowermost string. Sorry for that.

Most arrangements of this type seem to have pillars, sticks on rubber or very thin wires, mounted on one base surface to hold the screen a measured distance away.

If the guitar strings are not strong enough as pillars, you might like to try a suspension arrangement. The guitar strings would come right through the groundglass support panel and be mounted securely to a base plate each side of the groundglass panel.

You might need to have some sort of grub screw clamping arrangement on the ends or simply glue them in to holes and likewise glue the pass-throughs in the groundglass screen carrier.

With a suspension you may only need three guitar strings. A span of about 25mm or about 12mm either side of the groundglass may be enough. As pillars, they might only need to be as long as 12mm between the base support and the groundglass carrier panel. There will be a lot of frgging around with lengths before you get it right.

I would get a reliable working version of the vibrating system sorted before building anything else around it.

As for backfocus, a method I used for an oversized glass disk system might work for you. It was three threaded studs mounted to the front face of the box, (gutterbolts and nuts), then a small stiff coil spring about 25mm long slipped over each stud, then a plate with my groundglass mounted to it on the studs on top of the springs and then a washer and nut to pull down against the springs for fine adjustment.

Adjusting all nuts equally together will give you a backfocus adjustment. Angular trims by loosening or tightening individual nuts will deal with soft edges or corners. I was forced to use an offset arrangement which did not surround the optical centre equally but it worked just as well. Each corner adjustment interacts with the others slightly.

If you are viewing an upright image, flipped or with upside-down monitor, which screw affects what becomes confusing as it is the opposite of what you expect.

Just squeezing a spring down a bit while looking at a monitor will tell you which one does what soon enough. Once the adjustments are done,a bit of water clean-up bathroom sealer will lock the nuts, but is easy to pick away for later re-adjustment.

Quyen Le put his motor on the bottom. In his adaptor the position was left of centre. I'm not sure why his motor is offcentre. The tendency of the movement the motor induces is an elliptoid not truly circular shape. Elliptoid is like football or grain of wheat shape.

This means two of the three supports are at the bottom left and right corners of a triangle. One support is in centre at the top. This is a sensible arrangement as it keeps the most weight to the bottom as a pendant load.

Once you have your groundglass motion system assembled, if you want to see what it is doing before you invest effort into mounting it, place it close in front of an operating CRT television set and either view the groundglass texture through the glass with magnifier or make a few white marks on the frame around the groundglass, at least three equally around.

The strobe effect of the CRT display will slow down or almost freeze the groundglass motion to something you can see. Pay attention to the upper centre of the groundglass opposite the motor.

If there is a stationary spot, this is where it will be seen. To move it off the frame, you may have to lose some weight from the frame opposite the motor mass by drilling some holes.

If this does not work, you might then have to add resistive mass between the motor's centreline and the lower edge of the groundglass support panel.

Air-rifle waisted pellets or slugs are handy for this as they are made of lead and are already formed into a rivet shape. Just shove them into a drilled hole and flatten them.

You will have to experiment with motor speed for best effect. Faster does not mean better. Quyen Le's design seems to vibrate the screen in the ballpark of about 6O Hz. Faster also means less battery endurance and shortened motor life. As Quyen did with the early Letus35, you may have to add a bit of glue to the outside edge of the eccentric weight to cause air friction and slow the motor.

Use too much built-in electrical resistance in the power supply circuit and the motor may not reliably start, especially if the battery has drawn down. If you need to add weight to the eccentric on the motor, a trim of thin wire solder glued on will help. The added weight may mean you have motor which won't start if there is a dropping resister in the circuit.

You will likely have to use an adjustable resistance like you suggest or a bypass switch to supply full power to get the motor started then switch back to the resistive circuit for best speed.

The power supply wires to the motor will be a weak link, prone to breakage at soldered joints. They have to be very thin and flexible, othjerwise they tether the movement.

Quyen Le added a little bit of semi-hardening glue over the soldered joints back onto the plastic insulation to transfer the flexing furthur out from the joint where the wire plus insulation is stronger. You may want to form your wires into a coil spring shape of about three turns and no more. Too much wire in coils will add mass and upset the groundglass movement.

Good luck with it and don't be shy of coming back for more info.


Here is a link to a home made adaptor which shows the stud and spring method of achieving backfocus adjustment.

http://www.youtube.com/watch?v=CnweOEEqlRY


Here is a link to a clip which explores the innards of the LETUS35 XL.

http://www.youtube.com/watch?v=yugfv4ZVXgg

Last edited by Bob Hart; January 11th, 2009 at 09:15 PM. Reason: added URL
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Old January 12th, 2009, 11:53 AM   #8
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Ok, good info, the video helped me alot. I am still unsure if the AGUS35 uses a spinning GG or Vibrating but I have drawn out a new GG holder. Please let me know if I am getting closer to useable :)


http://cmpritchett.zenfolio.com/img/v6/p926934640-4.jpg
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Old January 12th, 2009, 12:04 PM   #9
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Colin,

that holder is still similar in concept to your initial design and would still be unusable.

It must be rigid but still retain flexibility to give you x-y axis vibration while maintaining a fixed z- axis movement.

I strongly recommend you refer to these links to start with.

35mm Adapters: Construction; Function; Pros/Cons - DVXuser.com -- The online community for filmmaking

DOF tutorial for 35mm adapter users (20 min) - DVXuser.com -- The online community for filmmaking


Although its on another site it will help you grasp the concept faster.
If you are not sure where to begin, I recommend you start with the spinning as it is more forgiving to beginners.

For vibrating,
think of a four or three legged table in a small room with a low flat ceiling with transparent skylight.
Now think of the table top as your gg holder, now cut a hole on your table top to place your GG.
Think of the skyroof as the rear element of your 35lens where the image, the floor is your video cam lens.

The image from the sky coming through the roof falls on your table top (GG)
the legs of your table must be flexible so when you vibrate the table top it will move side to side but not up and down.

I hope i am illustrating the concept for you better.


Ted

Last edited by Ted Ramasola; January 12th, 2009 at 12:13 PM. Reason: added text
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Old January 12th, 2009, 09:46 PM   #10
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Ted.


You are a genius at describing things in a digestable way.


Colin.

Unless you are using medium format or plate camera lenses, you could go a lot smaller on the groundglass size. For a vibrating groundglass with a phone motor you would have to do this for weight reasons.

My three x stud, nut and spring arrangement sits well below the groundglass for unique reasons, laziness and shortage of materials being two of them, the third is too complex and not relevent to your design.

For a vibrating arrangement, I'll try to describe what my brains imagine as what you need to have there.

Front of case >>>> Lens mount (ability to shim forward if possible) >>> + 65mm approx to a flat board with a rectangular hole about 36mm x 24mm cut out of it or a round hole with corner-to-corner diameter same as the rectangular hole.

From the board <<< forward about 20mm towards lens should be the groundglass, its carrier and motor supported on flexible pillars or the guitar strings - the wobbly table legs in Ted's analogy. The pillars are between the board and the groundglass carrier.

This board is fixed to the front face of your project box with the spring arrangement. It is convenient to mount the battery box on it as you have done on the front side. There may not be enough room on the back between the board and the rear face of the box.

The nuts pull down on the board to pull it forward along the studs against the springs to bring the groundglass into the lens focal plane.

Think of a Mercedes Benz star. For your arrangement, the centre of the star has to be the optical centre-axis or near to it. Centering accuracy to within 5mm would be fine. (I designed my own adaptor to be buildable by home hobbyists to 5mm errors and still work because of available adjustments.).

The three screws and springs need to be on the points of that star around the outside of the hole in the board. The three head of the pillar studs will be around the outside of the lens mount in the front face of the case.

Where they come through to the rear face of the case, they may however get in the way of your camera port mounting arrangement unless you make them far enough apart.

You may have to make the image path holes in the front of case, rear of case and board lower to get room around the camera port, the front of the camera, yet have workspace to adjust those nuts. You will need to offer you camera up to back to make sure the case does not go so high as to be blocked by the built-in camera mike on the handle.

On my design, I take the lower half-door off the case to get at the adjusting nuts. I was going to replace them with long tube nuts which would come through rubber grommets on the rear so I could adjust backfocus and alignment from the outside.

Because the lower half-door also fastened onto two of those studs, I did not do this because I was going to have to drill more holes and add two more studs.

With three tube nuts sticking out through the back of your case around the front of your camera, you would be able to easily get at them to adjust backfocus with everything mounted and operating. With mine, I have to run a bridging wire because the switch comes off with the half-door.

If you remember your trig from school, you'll know how to calculate that diameter as the hypotenuse side of a triangle. It's easier to draw the rectangle on paper and measure corner-to-corner.

If you roughly copy the Letus arrangement from the video clip but face the pillars and groundglass forward of the board instead of backward you should do okay. The newer Letus Extreme is also set up this way.

If you use the plungers out of diabetic syringes to make your pillars, you would best cut off and use the last 8mm or so of the syringe barrels at the needle-end as sockets to hold the rubber pistons.

These barrel ends you would glue into holes in the board. With timber board, you can't hope to drill holes anywhere near smooth enough to accurately fit the piston ends.

With guitar strings, just three or in three groups if you need more support, the fit of the board holes to the strings is not so critical and glue and shaved down match sticks or toothpicks will resize the holes around the string-ends for you.

The holes in the groundglass carrier will have to be better.


A vibrating arrangement in brief summary :-


The board and the groundglass/groundglass carrier/motor assembly cannot be a single part but must be two pieces joined with a flexible support.

The board has to be supported at three points around the optical centre, not below like my AGUS35.

The groundglass/groundglass carrier/motor assembly has to be able to "float" on its supports to the board.

The batteries must be on the board or the case, not the groudnglass carrier - too heavy.

The wires to the motor must be very thin and light and not tightly pulled up between the board and the motor.

The board must be able to be moved forward towards the lens to move the groundglass into focus.

Last edited by Bob Hart; January 12th, 2009 at 09:51 PM. Reason: error
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Old January 13th, 2009, 09:34 AM   #11
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Colin,
After attempting several builds myself I can tell you the best way to learn is to simply start building and learn from observing your designs in operation (or non-operation!) But that's how you learn. I would say go for it--vibrator motors, plastic sticks...they're all incredibly cheap and you won't be sacrificing a lot if you get it wrong.
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Old January 13th, 2009, 12:26 PM   #12
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After looking at several designs I went on smallparts.com and ordered the plastic threaded rod and nuts, found a ebay seller with black abs plastic (1/8" thick) and am going to try the "wobbly legs" method. I wanted to go with a bigger ground glass to have the option to use a lower magnification diopter on the front of my GL2 so I could take in the whole image circle (black outer area and all) for some shots if I wanted. If it seems too heavy once I get it mounted I will order a smaller piece or get it cut at a glass place nearby to me.

I was also thinking about using 2 82mm lens hoods (3" long) with some adapter rings to create a tubular design (like a brevis) and using the wobbly legs method.

I will keep you updated once I have something fashioned and have tried it out, just waiting now for my pieces to arrive from several mail order places. Thanks for the great input all!
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Old January 13th, 2009, 12:34 PM   #13
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Colin,

Unfortunately, the size of the image that is usable on the GG is not totally dependent on the GG size but on the lens format you will use.

with 35mm lenses there are those that can get 32mm image across, some at 24mm, some even smaller.

You cant go any better than that.

A medium format lens casts a bigger image. I was able to get a bigger image BUT after comparing pros and cons decided to abandon my mid format lens for a hybrid approach since 35mm lenses are more abundant and cheaper.

Also, 35mm has more options in the long and wide types.

All the best,

Ted
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Old January 13th, 2009, 04:23 PM   #14
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I am pretty versed in photography, I have shot 35mm, 645, 6X7, and 4X5. Although the image circle is only sharp from corner to corner on a 24X36mm neg/sensor there is a 3-4mm area around this that fades to black at the edges and kind of looks like viginetting, kind of a cool old look I like.
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Old January 13th, 2009, 10:04 PM   #15
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Colin.

That "old look" you like, you will be getting by the spadeful as lens images projected to a groundglass, especially wides exhibit brightness falloff to edges and corners more so than film or sensors they were designed for.

What Ted says is for real.

You need that groundglass to be small as described otherwise it will not vibrate enough with the horsepower you are putting on it.

Quyen Le spent a lot of time and effort getting the Letus to work. His is the largest groundglass of the lot for usable area.
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