Homemade 35mm Adapter

[Bob Hart]

Wayne.

My version is old news. The original glass disk was broken last March. With a number of distracting things going on I did not get around to making another. I experimented with split DVD+R disks and these looked promising but actually take as long as glass to dress in the machine I made to do it.

Glass disks with holes in them can be ordered from Ohara in Japan. That's the good bit. The bad bit is you have to figure and polish them yourself, then after you have a clear disk, then apply the 5 micron finish to one surface.

The other bad bit is you have to order about 10 of them to make it worthwhile for Ohara to do the job. They are otherwise courteous and turn the order around in good time. The disks are thin 1.3mm slices off a 5" approx optical glass round. After dressing they come down to 0.9mm.

It's not a task for the faint-hearted. I broke 6 getting the process right and also attempting to make wax composite disks. I broke another one because I did not see it attached to the dressing platen which had been stored away. Then the good one got broke at Cunderdin.

They arrive in Australia raw at approx $50 each which is also not for the faint-hearted.

I have one remaining raw disk and one remaining clear finished disk and one other gg which has to be repolished on the front face.

As for fixed groundglasses, they can be made to work well but have to be more closely managed for acceptable results, which is another piece of workload to get in the way of inspired creativity.

Even the combination of spinning groundglass erecting versions and permanent non-detachable lens style camcorders still challenges spontaneous camera work. - For the camera operator familiar with the camera type, the first instinct is to go for the camera's own lens controls, rather than the objective lens on front.

There are occasions when you forget to turn on the disk motor and the grain is not initially noticeable until a change of light occurs or you pan across a dark area. A moving groundglass takes away one layer of unpredictability. Using an erecting path takes away another and eliminates extra post work.

A bit of re-grading of colour and contrast in something like After-Effects or similar is all that is needed.

When you can handhold the device and walkabout with it, then it is of practical use.

If I can find somebody with fast broadband, I'll send a demo .avi DVD+R by post for upload. Unfortunately it is in PAL. I have also written a rough user guide but have not published as I don't want to get sued. Any volunteers to convert and upload the vision for me?

I've just been doing 2 small single scene shoots for the PAC Screen workshop and one more to go. I have been doing them all with the AGUS/PD150/Nikon combination. From a directorial viewpoint they are not good, but do demonstrate the desirability of using film fomat lenses.

[Rob Lyons]

Thanks guys. Spinning ground glass it is!

[Sean Seah]

Wow Matthew's stuff ROCKS!! Would u be able to post the configuration?

1. SLR>PCX>GG>Camcorder ?
2. SLR>GG>PCX>x7Macro>Camcorder ?

Recommended GG thickness=0.9mm? (Optical Glass)
Recommened PCX size=24mmx18mm

[Bob Hart]

Sean.

I can only speak for my own version of the appliance.

Optical path is :-

SLR Lens (Nikon Primes - 28mm 50mm 85mm, all f1.8) >> +46.5mm from lens mount flange face to rear face of glass disk which is the groundglass side, >> two right-angle prisms 40mm x 40mm x 52mm all 40mm common thickness, in 90 degree opposition (like binocular prisms) >> Century Optics 7+ Achromatic Dioptre, 58mm thread mount type >> PD150 camcorder.

There is no PCX or other condenser arrangement in my device as there is not enough space within to fit added optics. A lesser power dioptre would enable this but would result in a longer device.

The GG finish is 5 micron, with a slight backpolish with cerium oxide to get a trace of aerial image through for sharpness and less light loss. This comes at the cost of an image which is more like video than film and in certain lighting conditions, where there are strong overlit sharp edged highlights, there will be seen a fairly distinct shape surrounded by a halo effect. If normal lighting methods are used, the creative depth-of-field effects can be realised without artifacts most of the time.

This arrangement suits my need to be able to intercut AGUS origination with normal video.

[Bob Hart]

HDV and the AGUS35

I managed to get my greasy hands upon a Sony HDV for long enough to examine if the 58mm filter mount Century Optics 7+ Achromatic Dioptre will work as a relay lens into this camera.

The good news is that it does with some limitations. The lens obviously is going to vignette in a cruel way on this camera. However, by the time you zoom in to frame a groundglass image about 24mm wide, the vignette has gone from the TV safe area at least. Zoom in appears to be about the same as for the PD150 in practical terms. The HDV camera has a zoom lens of shorter focal length, but the CCD set may be smaller also as the framing seems about the same for a similar setting.

The bad news is you have to make up an adaptor with 72mm filter thread on outside and 58mm filter thread on inside to mount this lens and the making of it is a bit awkward.

The Tamron lens I used as a pattern for the 72mm filter mount has a different flavour of 72mm diameter. The plastic Sony case with its molded thread was a bit snug by about 0.2mm for a smooth fit on the Tamron.

It seems on my enquiries so far that there is no 72mm filter mount 7+ Achromatic dioptre available from anybody yet.

The appliance was offered up to the front of the camera by hand after the lens was mounted. The image seemed sharp across the width of the TV safe area viewable in the LCD. I did not have access to an underscanning HD monitor.

After I have made up the rear mount to the pattern I have taken from the camera, I'll see if I can get hold of it again and do some tests. This camera was the Sony HDR-FX1E. I understand there is a semi-professional camera based on this one.

If anyone has the computer hardware which can digest HDV for PAL and is willing to offer to capture the tape to HDV standard, I will send the test tape to a postal address.

Regards and all the best for the Christmas just past and for the coming New Year.

[Bob Hart]

For HD via Sony's HDR-FX1E via the AGUS35 principle, certainly with the CD-R sized spinner versions, there appear likely two issues.


Steadyness of the image. -

Apparently HD broadcast compression cannot continuously deal with change of the whole image from one frame to the next frame, only partial changes in the image. (I have already observed the artifact of the far wall of a valley, framed by edges of a roadside forest, staying put when the camera view moves very slightly.)

There has been mention of certain Super16 capable film cameras being unsuitable because of lateral weave due to no positive pressure applied to the film edge in the gate.

AGUS versions using the CD sized disk seem to be prone to a little flicker in the image from plastic disks or slight shiver of movement of the whole image due to run-out of these disks or the glass disks I have so far attempted to make.


Resolution limits.

A 24mm x 18mm movie frame appears to require too much magnification to permit HD quality detail from my combination of 5 micron AO finished glass disk prisms and dioptre. My erecting version does not permit a larger frame to be used due to the prism size (28mm width limit).

Subjectively, the resolution seems to fall somewhere between SD and HD. Some of this might be in the prism/dioptre/camcorder lens combination, as it seems difficult to get a really sharp focus on the grain of the stationary groundglass. It rests within the focal range of the lens.


Another issue appears with the widescreen (16:9) view. The camera zoom hits its limit just on the point where the edges of the farmost prism move outside the frame in the viewfinder which means they will be there in underscan.

The 40mm x 40mm x 56mm prism pair only supports an image width of 28mm at best (ie., half of 56mm). They require about 120mm distance in the image path disk-to-lens by the time you make up mounts etc.. and the front prism is within 8mm of the disk, the apex of the rear within 3mm of the rim of the dioptre lens on the camcorder.

You could get a shorter path by glueing the prisms together and clamping them from the sides, but then the construction gets really complex.

Bigger prisms to allow a bigger image frame on the groundglass (assuming you can fit in a condenser as well to deal with the hotspot) require a longer path which means a lower power dioptre which means a furthur zoom-in which is not available on the HDR-FX1 except by the doubler function.

I guess this is why P+S Technik seem to have gone with a hybrid prism and mirror arrangement and have a 21mm frame off the groundglass as I understand their design to be from their website. I guess it took them a lot of R&D to arrive there.

So, the simple home-build erecting version may have hit the resolution wall in terms of how far it can go. The only saviour that I can see may be the wax groundglass which may confer a higher resolution off the available 24mm wide frame. Except for the flickering I know how good these can be.

I did some tests in Kings Park in Perth city today. I can send SD .jpg images to be posted but these are probably pointless except for demonstrating the framing/fields of view/depths of field.

[Bob Hart]

I've sent three jpg images to Chris Hurd with a request if he can kindly place them at www.dvinfo.net/media/hart. These are from the Sony HDR-FX1.

These will have filenames like FX1 TESTS MERGE 01.JPG or similar. This will depend on whether my webmail provider can actually send them on. They are not representative of true resolution as they are frame grabs off downconverted feed out to MiniDV from the camera's HD recording.

Since my wailings about not being able to frame within the prism boundaries at full zoom on this camera on my appliance, I have found that I might just be able to get more than the 24mm frame width if I mount the prisms differently. Presently the frame area is enclosed by support structure.

[Leo Mandy]

I can't see them Bob on the site.

[Bob Hart]

Chris advises he is away and will post them after he returns.

[Bob Hart]

Furthur adjustments and tests determine that there is just enough space in the 40mm x 40mm x 56mm 40mm common thickness right angle prism to place a 24mm wide image off the groundglass through a Century Optics 58mm filter mount achromatic dioptre into a HDR-FX1.

The image off the groundglass is effectively cropped top and bottom as the widescreen feature of the FX1 actually sees less of the groundglass than the PD150 at this magnification. You can creep about another millimetre width if you zoom back a fraction but at risk of picking up an edge.

The frame has to be slightly higher and right of centre to clear the apex of the rearmost prism which intrudes into the left edge when the camera is zoomed in. It was this and not a poorly centred lens which created the edge defect.

With the PD150 and its trait of walking across the image towards the right edge when you zoom in, this problem had never become apparent.

If anyone in Australia is making image tubes containing prisms, using PVC 100mm sewer pipe as a case and mounting to camera via a pipe cap, there is another cap which is of a thinner wall thickness than the Iplex caps. They are Ausplastics 100mm dust cap 31.100. The barcode is 9 323745 005552.

These caps are not as robust as the Iplex but are the exact wall thickness to match the channel behind the bayonet lugs on the PD150 and HDRFX1.

If you choose to mount the appliance to the camcorder via the lens hood bayonet fitting, then all you have to do is cut out the matching hole and reliefs for the lugs out of this cap and it will go on snugly without need for filing or scraping the face of the cap.

The dioptre still needs to be attached direct to the camcorder via the filter mount.

[Bob Hart]

Furthur info.

In some real world tests yesterday, in high contrast, low light conditions or late afternoon/early evening, there remained a slight brightness falloff on the left (rear prism) side of the image. Like with a fixed groundglass, the defect is not readily apparent until the camera is panned and the image travels across the frame.

I opened up the path a little more with only 0.25mm supprt remaining to the front prism edge and this seems to have helped. The centering of the front prism apex relative to the edge of the rear prism seems a lot more critical than I had thought. This also cleaned it up some more.

[Bob Hart]

Furthur info.

What I thought was a doubler function on the FX1 which would work like the doubler on ENG cameras is actually a focussing aid only and does not record.

As a potential newscam, I thought this was an excellent feature. So I was wrong.

[Bob Hart]

Furthur to previous posts, I have tried the Nikon SLR lens >> 5 micron dressed groundglass disk >> 40mm x 40mm x 56mm common thickness prism pair >> Century Optics 7+ achromatic dioptre >> combination, as adjusted for the Sony HDRFX1 into a Panasonic DVX100 (PAL) and it seems it should work fine.

The appliance was positioned in front of the camcorder by hand as there was no rear adaptor mount made. In the LCD screen there was a clean image however an underscanning monitor was not used, so what is outside of the TV safe area is not known. Lenses tested were Sigma 50 - 500mm F4 zoom and an older Nikon f2.8 zoom. There was no vignette with these so f1.8 prime lenses should be okay. The DVX100 is an early model with 4:3 CCDs.

PS - Does anyone know how to stop this wretched McAfee Instant Updater phoning home and freezing the screen all the time whilst on-line.?

[Chris Hurd]

Sorry for the delay Bob, I will try to get those images up today.

Thanks for keeping this thread alive, it's the one which started this forum!

[Bob Hart]

Chris.

Is no problem. If you can hold on them for a little longer, I've a few more to send which I shall do now.

Regards.