35mm Adapter Static Aldu35

[Nick Conti]

Hello all,

Just wanted to say thanks again and great work to brett, james, jon, joel and everyone who is putting their minds to this project. I'm still in the baby stages, but I'll be grinding my ground glass this week and I'll be shooting tests with the 100A to see if I can really fill the 36x24 frame while in sharp focus without diopters. I'll fill you guys in as soon as I can.

Hopefully I will be able to achieve a nice frame in focus without any help from additional achromats. But even if its real close maybe just the 72mm +3.5 will do the trick, in which case I'll let you guys know how it works cause I'll most likely end up buying it.

Be back soon,

Nick

[Brett Erskine]

A physical mechanical shutter like the ones found in a cine camera and electronic shutter speeds in a digital video camera work towards the same basic end but a mechanical shutter creates a different look. Its slightly less jittery motion. I've talked to other people about this and have come to the conclusion that its due to how a mechanical shutter exposes film (in this case its a CCD) to light. For thoughs of us that dont shoot film a 180 degree mechanical shutter generally looks like a half circle that rotates. When it rotates it basically exposes the CCD half of the time and then blocks the light the other half of the time - 24 times a second. But if you slow down the process and think about it you'll realise that the whole CCD isn't being either all exposed or all not expose like someone switched on and off a light. Instead that half circle is progressively exposing the CCD to more then less light as it makes its circular path across the CCD. If you used the example of a light switch again the you could say its more like if someone dimmed up, held and then dimmed down the light. If Im right this should take the hard edge off of the motion blur on progessive digital cameras. On top of that your only one step away from having rotating GG which makes the whole idea much more attractive. Anyways I hope that answered your question.

-Brett Erskine
www.CinematographerReels.com

[John Cabrera]

Brett,

You shutter idea does sound interesting. Although I have a feeling that the instantaneous nature of progressive capture (basically the same as the electronic shutter in the sense that it just snaps a photo for an exact period of time, then instantly starts on to the next), versus the pricipal of a film strip moving across the lens contributes, at least partially, to the more natural fluid motion blur. But I don't doubt that having the light fade on an then off in that very rigid 1/24/second progressive scan will help out. It's a pretty simple experiment that can be done without the aldu35 or any adapter. Just take a dremmel and attach a 180 degree shutter to the front of it that 's exactly wide enough to cover the lens completely at the 0 degree mark. Set the DVX to 1/24 electronic shutter which is equivalent to no shutter or a completely open shutter and see what it does. You'll have to get just the right speed on the dremmel (1440rpm) and I'm not sure if there's a way to tell. But a Ground glass adapter shouldn't have anything to do with getting the smooth kind of blur you're talking about from the experiment. It would be a good starting place to test out this theory before combining it with the Aldu35 or Agus35. We should start another post about it.

[Bob Hart]

If you glue a half circle of paper on a rotating AGUS groundglass you get some weird stuff. Interesting things might happen if the rotary groundglass could be driven by a syncable electric motor.

As to the image erector. With other committments and an AGUS arrangement which works well enough for the time being I haven't pushed the erector for much the same reasons - light loss and degraded image which will require a whole lot more time and effort in development to get right.
There's also a sort of white sheer with mirrors which is also a bit of a spoiler.

Brett as to creative effects, controlled artificial light onto the groundglass for a faked fogging effect might be worth examining.

[Jonathon Wilson]

Ah... that helps. Thanks.

CCDs work conceptually just like film - the photosensitive diodes measure an increase in voltage over a certain period of time (1/48th of a second, for example) before dumping that number out as its (the diodes) 'exposure.' If you were to 'wave' a moving shutter over the diode during this time period, it would have the same effect that putting a mechanical shutter over film has.

It would have to be either very-well secured, or very light (or both) to not introduce vibration. Remember that virtually all 'vibrating motors' work on this principle - spin a half-circle off-axis very very fast. You'd need to create a vibrating motor without the vibration :)

[Paolo Rudelli]

To erect image dont use mirror because you have a lose of light use 90° prism in a posso configurations..

[Jonathon Wilson]

I was testing double-weave mylar architectural drafting film as a ground glass and I came across some interesting information.

I was specifically looking at the diffusion and grain characteristics of the mylar, so I removed my condensor for testing. My camcorder has a built-in macro feature, so I can focus on something that's very close to the lens (1.5 cm). I have always attached my adapter right onto the end of the camcorder because I could and hadn't built any additional tubing. This created a situation with the condensor where the ground glass is about 3.25 cm from the camcorder lens which acts as my macro. I had always had to zoom in a bit past the edges of the hotspot, but thought this was normal.

Once I removed the condensor, I had the ground glass right up against the camcorder lens - about 1.75 cm. With the camcorder zoomed all the way out, the image completely fills the frame, but there's a big fat hotspot with literally a hard-ringed edge the same size as the aperture of the 35. As I open and close the aperture I can see the hotspot change size.

I took the adapter off the camcorder and looked through it directly... zero hotpot - I mean none. Perfectly flat even image across the entire 52mm gg surface. (?!). What the heck?!

So I tried taking some of my leftover PVC tubing (I think we all have buckets full of the stuff), and built a short extension tube such that I could manually hold the adapter at a longer distance from the camcorder - in this case, the pvc was about 5.5 cm long.

This time, when viewing zoomed all the way out, I (of course) could see the tube. However - at the end of the tube was a circle of almost completely even hotspotless image. I zoomed in just past the edge of the circle of the tube and was left with a very very nice image with a slight darkening in the corners... remember though - there's no condensor!

So... I'm wondering if a bit of space (at least a few cm) between the GG/Condensor and Macro is actually mandatory to allow the diffusion to happen. If you're too close (like I was), I think you still get the hotspot because there's no room for any diffusing to happen.

Just thinking out loud - thought it was interesting. By the way, the Mylar is a pretty good ground glass substitute. I don't think it will be quite fine enough for final product but for those getting started who haven't ground a real glass - it's super cheap and works awfully well. It's better than the focusing screen that came on my Canon AE-1. It would be awesome for a spinning ground glass version.

[Brett Erskine]

Jonathon-
The reason that your getting a hotspot on your GG when its real close to your macro is because all of that stray/diffused light near the outter side of the frame isnt being redirected towards the lens. The closer you are to the GG the more the angle of the stray light will need to be corrected. This is why you need a condenser -particularly at short distances.


Mechanical shutter-
A simple/even weighted example would be to simple spray paint half of the CD if your using a design with a rotating CD. Use flat black paint. Also the motor would need to be synced. The camera already sends out a electronic pulse to do this automatically.


-Brett Erskine
www.CinematographerReels.com

[Luis Caffesse]

"If Im right this should take the hard edge off of the motion blur on progessive digital cameras."

Brett, you should ask Dan Vance about this.
He built his 1/2" Progressive scan camera with a mechanical shutter, I'm sure he'd have some insights on it.

http://home.teleport.com/~gdi/vancecam.htm

[Brett Erskine]

Luis-
Already done. ;-)

[Brett Erskine]

I met Dan Vance at NAB. We talked briefly on the subject. He's a incredible guy. I mean jez the guy MADE his own progressive scan video camera before any of us knew what the DVX100 was. I hope hops in this thread and helps us out.

[Brett Erskine]

Damn I really have to slow down and proof read my post. Hope you guys can understand me.

[Justin Burris]

Joel,

Your question about an anamorphic lens can probably best be answered by checking out this thread:

http://www.dvinfo.net/conf/showthrea...5&pagenumber=1

Check out the pictures. I think they make it pretty clear what the options are for an anamorphic lens within the adaptor.

Justin

[Joel Corkin]

Hi Justin, thanks for the link. I read through everything on that thread, but still don't understand why you wouldn't want to place a cylinder lens in front of your GG that expands your image vertically. The benefit of this is that you spread the same image out over a larger area of ground glass. This has two nice repurcussions for the final image since the weaknesses of the GG are limited resolving power and visible grain.

I haven't seen a real reason not to take advantage of a larger projection area.

[Brett Erskine]

Joel-
Heres why. When you stretch it out you create a image that may be 2.35 in aspect ratio but the image is also distorted as well. Correcting for this will only take you back to a 4:3 image. Now you are right about the fact that by using a larger area of the GG your going to have smaller/less noticeable grain in the picture which may be all that your looking for. What Im doing is squeezing a 2.35 image to fit into a 4:3 aspect ratio full frame on the GG so I can use ALL of my CCD. This will give you a higher res.

So to sum up your idea gives you less grain and my idea gives more electronic resolution.

-Brett