What Have I Done Wrong?

[David McClave]

I built my dof adapter similar to all the tutorials out there, but most similar to the one at jetsetmodels.info. Instead of using a focusing screen from a camera, however, I ordered a custom GG from a focusing screen maker that was nearly the same size an the inner diameter of my extension tubes. It looks GREAT with the naked eye, though little dark.
I attached the vibrating motor directly to the glass. I see absolutely no difference in the grain (which is pretty obvious) when the motor is turned on. What have I done wrong?


HELP HELP HELP!

[Rich Hibner]

I've noticed with vibrating products you really have to have it vibrate a lot. Daniel says you need 1.2v to 1.5v and through personal exp, you need at least 1.55 or more to make the grain go completely away. Problem with that, the leaf springs aren't very strong and any higher, you have a chance of them snapping.

Edit: afte reading your post again, what setup do you have exactly?

[Bob Hart]

The replacement screen you have had custom made is likely to be quite a bit heavier than the original in percentage terms.

The eccentric mass in a micromotor sized vibrator may no longer be of enough weight to move the larger screen.

How have you mounted this larger full diameter screen. Is it attached on the face of the jetsetmodels vibrating panel.

If it is, then you also may have a screen that also vibrates in a rocking motion relative to the focal plane which will both reduce the excursion and possible cause a pulsating softness in the image.

My understanding of the jet vibrating screen is that the centre of screen mass and centre of springs co-incide.

Check the direction of rotation of the vibrator motor. Ideally the torque from this motor as feeble as it may be, should load the "leaf springs in tension, not compression, which may cause concentrated bending loads at points along the span of the leaf spring. In your circumstance, it may just enable a little more movement.

You could cut a tiny piece of lead sheet to add mass to the eccentric but the problem then occurs that the motor may not start unless you point the camera directly to ground.

Talkiing generally now relating to reported failures of the "springs", the "springs" as I understand them, are machined out of a solid piece of plastic material. The machining process may leave a surface finish which may have scallops or even tiny pits. Corner chamfers and an additional polishing process for the spring surfaces may help reduce these stress risers.

[David McClave]

Originally Posted by Bob Hart

The replacement screen you have had custom made is likely to be quite a bit heavier than the original in percentage terms.

Ah, yes....

I mounted it inside the extension tube with silicone. I assumes it would need to move.

I think I'm going to have to break down and buy the screen and mount, eh?

You've been a great help!

[Bob Hart]

Before you give up on it entirely, have you got enough room around the outer rim between the tube.

You might be able to get away with suspending it on about 5 to 7 pieces of 20mm lengths of "E" or "A" guitar string from ring bulkheads either side of the groundglass if there is enough space between the outer rim and the tube for the guitar strings to glue at their midpoint on the glass rim.

There would need to be still enough space for an excursion of at least 0.7mm, otherwise it will touch and buzz very loudly.

[David McClave]

Bob - Well, the silicone is extremely flexible, so I assume that the real problem is that the heavy glass simply has too much inertia for the vibrating motor to do the trick. In addition, some test footage ( http://www.youtube.com/watch?v=9ZBqk914N54 ) shows that the glass is simply too course. Or is it? Is this level of grain NORMAL for these? Holy smokes! not bad for a special effect, but everything is highly stylized. I went ahead and ordered the Ee-A screen - we'll see how it does. Let me know what you think of my test footage.

http://www.youtube.com/watch?v=9ZBqk914N54

[Bob Hart]

Dave.


YouTube does not tell a lot of truth resolution-wise so it is a bit difficult to analyse your clip validly.

The groundglass texture does seem a bit coarse. This will affect advserely your light transmission and sharpness but yield better bokeh.

Groundglass texture is often a matter of personal preference as to which means more to the image maker. Too fine a grade of texture yields, bright image, sharpness with halos (aerial image feedthrough) and oily bokeh.

Too coarse a texture yeilds a softer, darker image and better bokeh. The trick is to find the best compromise.


You will observe where you have brighter sections in your clip, you lose some of the groundglass artifact (grain). This relates to a normal operating circumstance with adaptors, that of avoiding aperture settings tighter than f5.6.

There seems to be also an edge softness issue. What close-up lens or achromatic dioptre are you using on front of your camcorder?

[David McClave]

I used the achromat suggested at the jetsetmodels site - the one from the surplusshed.com. It seems like a nice one. The fuzzyness on the edges could be something else, maybe. fingerprints? If I were to post video where you could see it better, where would I do it, and what's the best codec for most people?

I sure appreciate all the help!

[Bob Hart]

.jpg frame grabs might be a better way to go. Downloads of higher quality motion imaging to here are quite slow and expensive (for me anyway) whereas frame grabs tell as much as one needs to know resolution-wise.

[Chris Barcellos]

Dave:

I'm experimenting with the same achromat, using an extension tube DIY adapter and I am shooting with a HV20.

I also have a Letus35a to compare things with.

When I shoot the standard set up with the Letus35a, I have very little zoom room. So I add a second achromat, a Cinevate achromat, and I seem to lose a bit of sharpness but gain the ability to zoom better and thus avoid the vignetting.

So I bought the extension tubes set up, and ordered one of Daniel's vibrating holders. After ordering, Daniel hits you with be careful how you mount it, its fragile, etc., etc. Almost immediately after I got it, I broke the dang springs at two places.... at that point I turned the screen holder into a mount for the screen, and made my own makeshift rods to float the screen on, ala Letus35a. After some experimenting, this has worked out pretty well, but with a wax screen, I still felt I seeing to much edge drop off.

So now I got the Canon EE-a focusing screen. And have mounted it in place of the wax screen. It seems to reduce the vignetting/hotspot issues to some degree. In coming days I will post some grabs and maybe a video at vimeo....

[Chris Barcellos]

Lastest news.

With my HV20, and I assume it will work with my FX1, I took the Letus 35a, punched out the Letus achromat, and then used the remaining ring to screw and mount the Cinevate achromat to the Letus, and it gives me plenty of zoom room, and a much sharper image.