DV Info Net - Homemade 35mm -- Edited Copy for Reading

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Re: My ghetto attempt

<<<-- Originally posted by Yang Wen : Ok I grabbed a fake CD thing from my spindle and got my Sigma 35-135 AF zoom lens and just held the two things up in front of my DVX100. I had the DVX's lense focus into macro-mode and the CD was in focus but As you can see, there is incredible vignetting. It seems I can only get a small round image to project. What is the trick of having the 35mm lens image fill the entire frame?

http://www.umich.edu/~ywenz/DVX/GhettoAttempt.wmv

thanks -->>>

Hey, why you call it Ghetto ?? it should be Agus35 :)

Ok, you got several problems... first, you need to use the whole spindle plastic case, cause that will not permit the light from outside to ruin the image in the ground glass... then... you need to adapt a Magnifying glass to the dv camera, so in that way you will get more of the image projected, then you need to close as much as you can the GG to the camera lens...

http://altoque.tv/maserati.wmv

Take a look to the second 20 of the video, and the last scene, and there is no vigneting

Check it out, it doesnt have too much quality but i really dont have any time, working a lot with a 3d spot.

Mike,
you can email them to me also...

check my profile for my email.

Agus, that's the best footage yet. It really looks like film, especially the last shot. This thing will be amazingly useful for making short films.. I mean there are big problems trying to follow a car as it speeds round a track (good work on that by the way) but in a scene that you've planned out it'll be fine..

Yang, you need to understand how the adapter works. Your DV camera is effectively being used as some sort of telecine unit - its only purpose is to capture the image created by the 35mm lens. It's like ghetto telecine - videoing your film footage as you project it against a wall. That means the only thing you need to be able to do with your video camera is zoom and focus until the image fills the screen. Also take the camera completely out of auto mode, so there's no gain, no focus problems, and a standard shutter speed.

Next you need to understand what's going on with the lens and the housing and the spinning cd. The housing stops any light getting in. Just like an ordinary stills camera - the only light you want coming in is the light that comes in through the lens. The role of the the sand-papered CD is to act as a projection screen. It's like the film in a stills camera - it's where the image from the lens is focused. The reason it needs to spin is so that you get rid of the grain caused by sanding the cd.

So what you're doing is using the 35mm lens to create the image - to zoom, to set the exposure, etc. And you're using the video camera to capture this image.

By the way Agus, have you experienced the "spinning vortex" that mini35 users refer to?

Kieran

Concept - As I understand it.

Stage One

Subject being videod/filmed >>> via SLR camera lens >>> onto a semi-opaque screen (like a rear projection TV screen) positioned on the lens focal plane --- the same position the film would be if if the SLR lens was mounted to a camera. (This is a focal plane for that lens.)

Stage Two

That image (like a projected image) on the semi-opaque screen >>> via video camcorder lens >>> onto 1 x CCD chip or (3 x CCD chip array) To get that image to appear large enough to fill your video camcorder viewfinder, you may have to use a close-up lens or if that is not powerful enough, make up a relay lens to get the camcorder to focus on the projected image sharply enough.

The relay lens might be something like the eyepiece out of a telescope. I have used a lens set out of a 42mm telescope eyepiece and placed that between the camcorder lens and the projected image for another similar application.

SUMMARY: There are two stages of focussing. The SLR lens focussing sharp onto the semi-opaque screen. The camcorder aquiring a sharp image of that projected image. You are taking a picture of a picture. This is not realy the most efficient way of aquiring an image but ---

from this point is where it gets interesting. You just can't get a frosted glass texture fine enough to display the image from the SLR lens sharply enough. If the texture is too fine, then you can see through the glass beyond the focal plane into the guts of the SLR lens and through that all the way to your subject. So all you see is a bright hole. If the frosted glass texture is too course, then all you see is a pattern of rough pits and scratches colored vaguely in the form of the image.

If you try to look through a raindrop blinded windscreen on your car or the wire mesh on a screen door, you discover that if you move your head about, you can see through the obstruction. P&S Tecknik, cleverly worked this principle by moving the windscreen instead of the viewpoint.

You are not looking at your subject through the groudnglass screen with the Mini35 adaptor, you are looking at an image projected onto the groundglass screen which is made to seem finer by being moved faster than the camera can see its rough texture. The Mini35 adaptor moves this screen by spinning it across the SLR lens focal plane. Agus' earlier prototype as I understand it rapidly moved a screen back and forth across the SLR lens focal plane.

The Mini35 operating notes tell you that you must keep your camcorder shutter speed selected slow so that you do not freeze the motion of the rotating screen and thus detect the frosted texture on it and spoil the image.

I hope this has not confused you too much.

That's a very good description indeed.

I'm still not sure if a relay lens is strictly needed. With the original mini35 and the XL1s it was simply more practical to take advantage of the fact that you could remove the XL1s' stock lens - it makes everything less bulky. The only problem with optics for the Agus35 is being able to 1) focus the image 2) zoom until it fills the screen, which, as people are discovering, can be difficult to do simultaneously.

I'm thinking about using some kind of sliding close up filter between the XL1s lens and the cd so I can experiment a bit with zoom and focus.

Only a week till I start work on it :o)

Kieran

About connecting it to our cameras - this has become a major concern between my video compadre Spencer Houck and I. We're both concerned about the best way to secure this beast to our cameras. I noticed someone had a 58mm thread glued into the back of the spindle - I had that same idea, but since this thing is a little front heavy methinks it'll put a lot of strain on the threads. It might not be such a idea to secure it that way and warp the threads, after all, I really do like the ability to switch adapters and filters!

We were thinking more along the lines of a bayonet mount (for those of us that have lens hoods). We tried looking for a place that sells the lens hood alone for the GL1/VX2K, but alas, no dice. I think it's an important issuse, I'd like to hear what others have to say - esp. those that don't have a bayonet mount. How do you do it Agus?

I used WMV 9 to encode the footage, if you do'nt ahve Media Player 9, you can't view it. Sorry.

On the mount... I guess you can also constructut a plate that attaches to the Agus35, that your camera screws into. That way, the weight is not on the mounting threads to hold the entire assembly up. It'd be a big unit all together, but it would give you more weight and would resemble a film camera even more!

Wow i suspect if I can get a 3D model of this Agus35 caseing made, I can use the prototype machine at my school and get a 3D copy of it printed. Then somewhere on campus I can get copies of this thing made. Perhaps get a two piece design that screws togeether, compelete with the holes to accept adapter rings?

<<<-- Originally posted by Devin Doyle :
We were thinking more along the lines of a bayonet mount (for those of us that have lens hoods). We tried looking for a place that sells the lens hood alone for the GL1/VX2K, but alas, no dice. I think it's an important issuse, I'd like to hear what others have to say - esp. those that don't have a bayonet mount. How do you do it Agus? -->>>

I use a metal piece that connects to the tripod hole in the camera, so the whole piece is more stable

try to make a metal skeleton from the camera to the adapter

BTW those rings looks beatiful, but how is that you will lock your lens ? you need a release button like the SLR camera have. i am about to post some footage, but i am low in webspace...

I'm about 1/2 way done my Agus35 Pro :)

I picked up a black "project box" from Radio Shack yesterday ($6.99), and a few other miscelanea...a switch, some wire, 9v batteries, a 9v battery clasp, etc. I spent about $18 total.

Then I went to Home Depot and picked up some epoxy ($5), a length of scrap 1/2inch PVC piping (for support rails - $0), a velcro strap ($5), and to attach the camera to the Agus35, a 3"-3" adjustable pipe coupling ($5).

I've got the other parts here already - an old Sony disc man, a clear CD from a spindle, and an array of cutting/drilling tools.

Incidently - if you plan on making more than one of these things, there are 54 and 57mm diameter dremel bits at Home Depot, that fit into a standard drill. Might be perfect for lens mounts.

The Radio Shack project box (dimensions: 8x6x3 inches; fitted back) is the perfect thickness for lens mounting - you just cut a hole the size of your lens, cutting notches where the lens pops in, and give it a twist - presto!

Preliminary pics:

http://ideaspora.net/box-front.jpg

http://ideaspora.net/inside-rear.jpg

Agus - email me if you need server space for footage. I've got a dedicated server with room to host plenty.

- jim

Yeah, the lens mount worked out OK, I guess. Little rough around the edges, but...it does lock into place.

Bob, over at Indieclub.com, advised using a F-to-C mount adapter to mount the lenses. You wound then just have to mill a hole in your adapter box and then you could switch lenses freely.

He also suggested using a chroziel matte box to connect the camera to the unit.

Here's an F-C mount from Century Optics, costing $60.

Here's the link to the thread I've started, including Bob's advice.

- jim

I some people have been concerned with flipping the image in post. Maybe you could build an adapter that would "hold" the camera upside down??? Would this work??? Agus, have you tried this? I realize that you would not have accessibility to all controls, but as I understand it you get the camcorder dialed in and leave it alone....just thinking out loud....

That is the most ridiculous, absurd, WONDERFUL idea I think I've ever heard -- just mount the camera upside-down! That might actually work! And it'd give you a hair better picture quality because you'd eliminate the need for mirrors and prisms!

You'd have to use an external monitor, because your LCD and viewfinder would now be upside down, but that is a cool idea! You'd also have to rig up a mounting system so you still had a tripod socket, etc...

Not sure I'd want to show up in front of a client with it, but for guerilla indie filmmaking, that kind of thinking is the bomb!