Homemade 35mm Adapter

[Brett Erskine]

Louis please post or send me a link to your resource.

BErskine@CinematographerReels.com

To hopefully answer your question about back focus. Take your condenser lens (PCX) outside and point the curved side down. Raise and lower the lens untill you see the image of the sun sharp in focus. Measure the distance between the lens and the ground to find your focal length. But I'm not sure if would call this your back focal length in this situation or not.

As far as your the lens you have right now....not going to work...well. It will do the job of removing the hot spot but will have serious barrel distortion problems no matter what 35mm lens you put in front of it. What you have there is a aspherical lens which, if you read the definition of a aspherical lens, sounds like it would work great at correcting barrel distortion but apparently in simple lenses it does not. Its strange because film lens manufacturers often call their wide angle lens a aspherical lens if it can correct for barrel distortion.

Hope I didnt give you more questions than answers.

-Brett

[Bob Hart]

Trevor. Don't sell yourself short. Oft times it is the straight-to-the-point offering of a solution to a problem from left field which cuts through the complicated thinking of others who might be caused to think it can't be done for this or that reason. There is apparently a lens around called the Frazier which like the bumblebee perhaps should not work in theory but does in practice. The designer marched to the beat of his own drum and this lens became a stalwart of nature documentary making.

As a scriptwriter, you will have run into the one about a classroom full of chimps and typewriters and the possibilities or otherwise of a cogent screenplay being writ - eventually. Truly, no matter at how basic a technical level of understanding any idea might be, collectivisation of all ideas in forums such as this will get us somewhere.

You are not wrong on the mirror principle and in the form of prisms is a commonly used optical solution. I've proven it by building one. The problem is the quality of the mirrors which cannot be simple wardrobe mirror glass but precision surface coated mirrors which don't have internal reflections which cause multiple images into the camcorder.

The AGUS35 evolution presents an interesting conundrum which ahs had an airing here once or twice. For about US$30 you can build the simplest one. If care is taken in the construction you can get near to professional quality results from it and it thus liberates no-budget film-makers with handicams into a whole new area of very real creative visual options.

Taking it up through incremental levels to easier usability and reliability is achievable but at what point does the whole principle become more costly than the professional level products it performs against.

An AGUS35 can be thrown together from bits and pieces from a pawnshop and computer store in about two afternoons (or even less if one becomes practiced at it), about the same time it takes to get the professional gear from the other side of the country where it can be hired at. For the low/no-budge player who needs a good now result with maybe some in-field repairs with gaffer tape, that's all it needs to be.

Then there are those of us who enjoy a technical challenge who like to do things thoroughly and properly. To this end, pushing the evolution to its highest development when it can be grabbed anytime taken out and used with confidence, is just as valid.

[Louis Demontez]

Brett- My resource is well known to this forum I think, it's :

http://www.knightoptical.co.uk/acata...ishedgrade.htm

At the bottom it says,"Specific requirements
We can source Glass Aspheric Condenser lenses to most sizes or focal length at short notice, so if your requirements are not listed please contact us by telephone/ fax or email: stockrequirement@knightoptical.co.uk"

Also
http://www.knightoptical.co.uk/acata...alitygrade.htm

It also says,"Specific requirements
We can manufacture Planoconvex Lens to any size or focal length at short notice, so if your requirements are not listed please contact us by telephone / fax or email: stockrequirement@knightoptical.co.uk"

This site is handy for me as it is in the uk.

[Bob Hart]

I have made another attempt to get an AGUS35 demo clip posted. If Chris receives it intact and undamaged it may appear here in the address www.dvinfo.net/media/hart

It will also be accompanied by a .pdf file which contains some info relating to the clip and appropriate copyright cautions as to the musical performance.

The clip is a severely cut-down version and is a quicktime file of about 9Mb.

The files are titled "AGUSDEMO.MOV" and "AGUSDEMO README.PDF" (DOS filenames = "AGUSDEMO.MOV" and "AGUSDE~1.PDF").

It is not a piece of inspired film-making. The performer was in shadow, the lighting was alternating light overcast and sunlight.

Through error, exposure was about three stops over and aperture variation in the zoom objective lens itself was nearly two stops. The quicktime version has ended up being subjectively about 1.5 stops darker and of considerably poorer resolution than the .avi and DVD-Video versions, but as a practical example of the AGUS35 in action it may suffice.

In future, I shall favour using two or three pieces of neutral density gel across the back of the objective lens to try to limit flare from highlights in the disk image. Managing two levels of exposure control, one manual and the other an electronic pretender to manual, plus two layers of focussing and zoom control, again one purely manual and the other electronic, gets a bit tricky and requires vigilence to make sure something has not got bumped and shifted.

[Bob Hart]

Furthur to the above, the video file and .pdf read me file made it and Chris has put them up. The video file was sent in a form which has to be copied in one piece.

[Wayne Morellini]

Hi

Good job, and it is good to see that you guys intend to address the issue of optical problems/distortions.

I've spent over 20 hours (and around 300 web pages) on the 35mm adapter topic, though I still haven't gotten to read this thread fully (a bit reading impaired), but I have some questions.

I thought I saw something, in one of the posts, about a very bright filter/screen/diffuser that worked by having a surface of microscopic lenses/beads that increase light transmission. But I can't find it again and have spent many hours looking and searching through threads. Can anybody help me?

This diffuser reminds reminded me of a coating for TV and computer screens developed over 10 years ago to. The coating would blend in the shadowmask between pixels to hide it and give a pseudo High Definition look, it would be excellent for the projection surface in an adaptor, as it is a controlled substance that would let through the maximun amount of light (compared to the spread in a ground glass).

I have been thinking about optical stuff for a while and I have these ideas. That the courser and higher the diffusing surface the wider the angle of light spread you will get, includng back into the surrounding grain, producing bleed and washout. To reduce this it needs to be finer and thinner. Instead of condensers there should be some matarial out there that will take light from a wide arc and transmit it in a smaller arc. I think the holo diffusers (yet to read up on it) does this, but the micro lense system I mentioned above could also be designed to do this (if not just projecting through the back of it instead). The lenticular lenses could be designed to do this, but being plastic the optical qualities might not be beast.

So what is the best solutions so far for the projection surface? I hear that Louis and Dino are doing adapters with holographic diffusers. How is brightness, contrast and low light ability with these compared to spinning ground glass. I have seen demo footage from different systems on the web and there is a big difference, some are much better than others, but I am uncertian where ever it is the adaptor type, or personal or camera model style? The Marlar movie is great. I can see the light dropping off to black quickly because of the spinning disk, the glimmer of the spinning grain as their arch of movement sweeps reflections outwards, the circular streaking (presumably from the disk), or the encoder), the amazing film like softness and contrast levels. But the Dino one seems more like normal video in contrast and everything, , presumable from a lack of GG grain and softening. I saw another, with a racing cart that was just bright and glary like normal video. There was a number with the soft film look. Of course they all have good DOF, but which systems are best for visual performance?

Is it possible to have a website with a breakdown list of all the solutions and parts, with the science and their plusses and minuses, and links to parts, peoples adapters and example footage?

Thanks

Wayne.

[Jonathon Wilson]

Don't forget about post - Marla was pretty heavily worked in Post. Most of the things you mention as liking about the 'film look' are probably more apt to come from post-processing rather than the adapter's qualities. Color balance and saturation and blooming of highlights being two biggies. In the collection of examples, it would be good to see unaltered footage for better comparison.

[Wayne Morellini]

I have seen footage before (I remember ceramic tea pots) that seems unaltered but simular. I think the difference is post, but also lighting, they have sequences with center lighting and leaving the rest go to black, and there is a lot of black, a style, I think is, suited to miniDV adapters. Even the new film look in cinema, I think, is also computerised in post production, so I am expecting post production. The problem is that different cameras and lense performances are also going to effect the amount of processing needed. I take your meaning, so we really need to decide which has the best raw footage. The raw performance is what we have to work with in post. So each adapter technique has to be tested to see what it will look like on a range of cameras, could I suggest that Sony PD170 and an XL1s have significantly different picture and probably would be the best reference cameras (for miniDV). The problem is that different adapter techniques coould simulate the XLS1 softness and range, and enhance the PD170, or alternatively look better on the XL1s.

[Agus Casse]

Bob, so what is your final configuration for the agus35 ? you using a plastic GG, discman motor, are you correcting the image or recording it upside down ? post a picture :)

[Bob Hart]

Hello again Agus.

Re: your question above, I have not developed the Agus any furthur and won't until I receive my glass disks. It is my original "plumbers version" made from sewer pipe caps and other plastic plumbers parts. There is an image of it in www.dvinfo.net/media/hart.

I replaced the potplant saucer CD spindle motor mount, which clipped into the housing with a flexible plate style mount which is adjustable at three points for lens back-focus and tilt. There is enough compliance to enable to disc to run true but the mount is stiff plastic which does not slump like the potplant saucer material did.

I have not done any more work on the mirrors or prisms. I'll see if I get my glass disks sorted first. Except for having to invert the image in post it is quite useable the way it is.

With careful adjustment of the motor mount and re-setting the objective lens back-focus which gets thrown out, the image through the telescope lens set can be made so that there is no barrel or pincushion distortion. But in the best position, the camcorder has to be zoomed in almost to the point where its own close-up focus crashes.

There is an image from the final set-up in media/hart.

The image path for the music video and for the still titled Agusprob was :-

Objective Lens = CIMKO 28mm - 80mm zoom.

Nikon Mount = home made from plastic pipe cap.
(This mount allows some backfocus adjustment as it slides on a pipe which runs right through the case and has the camcorder bayonet mount on the other end. There is a cut-out clearance for the disk.)

Rotary groundglass. = CD-R pack clear spacer disk prepared by the pressed method, furthur dressed with aluminium oxide and partially polished back with a soft flannel cloth to improve light transmission.

Groundglass is rotated by a CD player spindle motor, simple 1.5v to 12v DC type (Mabuchi style). The motor is fixed to a compliant plastic plate which is retained by three nuts on pillar bolts and supported from beneath by stiff springs on the pillars. This arrangement provides a second back-focus, camcorder focus and tilt correction adjustment.

Power is from two x 1.5v pen cells = 3v DC in pack fixed inside the case.

The close-up/macro lens set remains the SW5042 Tasco telescope eyepiece lens set, reversed with the composite element itself reversed. This set is in a custom brass mount, home-made to screw into the 58mm filter mount of the camcorder. Distance from front element to groundglass is about 12mm.

The Agus assembly fits around the close-up/macro lens and fixes to the lens hood bayonet mount.

My chosen image frame size is the 4:3 academy motion picture frame of 24mm x 18mm. (Brett Erskine's template). There was no hot spot problem with the image frame this size with the CIMKO lens.

Camcorder settings were DVCAM with electronic 16:9
selected. Shutter speed was 50fps, the image interlaced. Camcorder exposure setting was manual, ND notch 1, f5.6 selected. There is no progressive scan on the PD150P faster than 12.5fps

Inversion, colour, gamma, brightness, contrast and letterbox was adjusted afterward. The image in the clip does not represent the raw image quality.

The camcorder is a Sony DSR PD150P.

When I get some time, I'll break down the Agus35 and photo the current assembly method.

[Wayne Morellini]

Thanks Rob for putting up the media pages, it answered some of my questions and even answered one I was expecting to research myself. Thank goodness I did not read all the 1000 posts before before seeing the pdf's.

It is interesting that ARRI is offereing a custom ground glass making process (for those that want the softer feel). The glass will probably produce a more subtler image than the variouse holo and reflexite screens I am looking at. So now just to research the optical quality of these holo and Reflexite screens. Anybody allready know if they are highly suitable for HDV, and where ever they distort or discolour the image, I assume they don't do contrast any harm?

Great work guys, thanks and hope to see all your designs when your done.

[Alex Raskin]

Hi all, I experimented with static GG adapter (aldu35) but it did not work out for me even with "grainless" Bosscreen material as GG because of the visible grain.

I'm making it for JVC HD10 high def camcorder, so unfortunately (or otherwise) the cam's high resolution imposes higher requirements than the SD cams'.

WMoving on to agus35, rotating GG version.

Looking for a custom-made quality CD-shaped ground glass.

Suppliers?

[Jonathon Wilson]

Just a thought here - at HD resolution, if even the paraffin structure of the boss screen is too visible, I think you'll be bothered by some facets of the inherent 'swirling' grain structure of the rotating glass too. One of the issues with the original Agus is the fact that the imaging happens up on a 'corner' of the spinning GG - which means that the 'grain' is always moving in the same direction. Some people complained about this even at SD. I would think at HD rez, you'd want to think about alternative methods of moving the GG, so as to not have this problem. Possibly a 'vibrating' GG - or one the moves not in a spinning motion but in an elliptical path (like the new version of the P&S Mini does). Whatever you choose, I'd think you'd want the grain's movement pattern to more or less center itself around the imaging area. I've only built a static adapter, so my knowledge here is purely theoretical.

I only mention it because you seem quite serious about building a very high-quality adapter for HD.

[Alex Raskin]

Jonathon, I did experiment with the VERY roughly ground blank CD as rotating GG, with a lot of really bad scratches on both surfaces, and still while rotating, it looked so much better than static GG of even highest quality "grainless" Bosscreen.

I did see *some* pattern, but I thought it was because of the rough scratches on CD.

Thus I'm intending to have a quality-made GG in shape of CD and try it. I'm sure with 3-5 micron ground, there will be no more visible pattern on the rotating GG.

Do you know of any optical labs who make such small order items?

And yes I'm damn serious about making a good quality adapter :)

Will report the progress back to the group for everyone to employ it if successful.

[Bob Hart]

With any moving groundglass, the groundglass texture will be "seen" by the video camcorder as a fixed groundglass if the shutter speed is not slowed down, desirably to 1/50th of a second.

This is contrary to one recommended practice of video at 1/100th of second be it right or wrong, I was advised to follow.

In none of my tests have I had any texture from the groundglass showing up except when I forget to turn it on. However where there are large density defects in the groundglass, creating areas of varying transparency, this will show as a strobing effect, especially if the disk rpm is close to the camcorder frame rate or multiples of it.

This effect can be made to emulate the variable density of motion film if the disk surface travels from bottom of the frame to top of the frame as seen in the Agus35 itself, not the camera image, in which it will travel from top to bottom.

As for glass disks, you'll have to polish them locally but Ohara in Japan are prepared to make glass disks of CD dimensions. At a rough guess, going on exchange rates, ten unfinished precision disks will cost you about US$420-00 landed in the US.

If you want the raw disks and a quote for your requirements, contact Hiro at Ohara Glass in Japan. His email is Hiro@ohara-inc.co.jp