If you actually had been following the thread carefully you'd know that the ground glass is the one part that this entire adaptor revolves around. It is because of the ground glass that we get such short depth of field. The image from the 35mm lens gets projects onto the ground glass and then this projection gets taped by your dv camera. Without the ground glass, the depth of field we are attempting to get with this adaptor would be lost.

This may kick off some debate as I know that the working theory is that you need the ground glass... but I, for one, think that you could do it without the GG, but you would need a relay lens in its place.

In the 80's Panavision did exactly this with their first Panacam EF cameras... they took Panavision 35mm Cine lenses and projected the image from them onto a 2/3" tube. To accomplish this with the same DoF and image characteristics as the 35mm lens, they just had a relay lens which changes the image size from the 27mm diagonal of a 35mm film plane down to the 11mm diagonal.

As I understand it, they stopped making these because the abberations created by the relay lens become unacceptable at high-resolutions (like HD), but were perfectly acceptable for standard resolutions. I'm not sure where this stands by today's standards of optics manufacture.

I've got a couple of bi-convex lenses (curved outwards on both sides) lying around. I held my SLR up and positioned the bi-convex lens behind it at about focal flange distance - looking into this at the right angle, and from the right distance, I see a big bright fat inverted image. Seems like it should work.

Others?

--- references:
http://www.dvinfo.net/dv-l/869.htm (search for Panacam)

http://www.cinematography.net/[cml-h...%20cameras.htm (no real resolution, but an interesting discussion)

that was my intention to have the condenser lens acting as the gg until i see the result given wth the gg and the condenser with the flat side towards the video lens (no vignetting) from Alain.
as i got only one lens for instance, i would be happy to hear what is the result with a condenser lens that is reversed.

<<<-- Originally posted by John Gaspain :
I havent been all-stop though. Here is what ive done in the meantime. I made this rail dealie., this thing is rock solid.

pic
http://aequantum.com/DSCF0003.JPG

John -->>>

I like the look of the adapter, what materials did you use? That doesn't look like the PVC pipe they sell @ my home depot

about relay lens, you skip the most important of your references.
quote:
In conclusion, even an excellent cine lens, combined with a theoretically perfect relay lens, will produce a relatively poor image on a 2/3" CCD camera when compared to even an average quality video lens.

Yes, but if you continue reading that article, the guy in the very next post completely disagrees - and so on and so on - back and forth. This is what I meant by "no real resolution"

Unfortunately, none of us (lurkers notwithstanding) are qualified to understand the optics of this. I am continuing with the ground glass idea because its easy and works pretty well. I just threw out the thought and links because I don't believe its set in stone that you couldn't make it work without the GG if you had a good understanding of optics and a very high-quality relay lens. I have neither, so its GG for me :)

Just a'waitin' for my grit. (there's a tune in there somewhere).

Any lurking optical-degree-holders care to join in the fray and set us straight?

<<<-- Originally posted by Ari Shomair : <<<-- Originally posted by John Gaspain :
I havent been all-stop though. Here is what ive done in the meantime. I made this rail dealie., this thing is rock solid.

pic
http://aequantum.com/DSCF0003.JPG

John -->>>

I like the look of the adapter, what materials did you use? That doesn't look like the PVC pipe they sell @ my home depot -->>>

Its a Lowes model :)

1200 Grit Aluminum Oxide
 

I don't know if this has been brought up before, but I found a source for 1200 Grit Aluminum oxide powder -
http://www.whiteabrasives.com/aluminum_oxide.htm .

Only problem is they sell in minimum quantitys of 10 pounds. Are there 9 of you out there which want to split some with me? Email me if interested, or if you know a place to get smaller quantities.

http://www.gotgrit.com/default.php/cPath/2_7 has aluminum oxide powder that sells by the 1/4 lb. According to this chart http://www.facetingmachines.com/grit-mesh-micron.shtml, 1200 grit is the equivalent of 15 micron. Dick Dokas's article on making your own ground glass (http://www.phototechmag.com/previous...kas/dokas.html) speaks of going down to 3 micron/8000 grit. Gotgrit doesn't sell that small, but they do have 5 micron/4500 grit. I plan on buying some from here soon.

sTRANGE IDEAr
 

WHIT CANON XL1 CAMERA

YOU REMOVE THE LENS

iF YOU PUTT VERY STRONG CONDENSER LENS (after GG) THAT CONCENTER LIGHT RAY DIRECT IN TO 1/3 " CCD SIZE ????

what about this ????

Nicholi-
I know there is a point when choosing the right grit that if you using something thats TOO FINE it acts as a polisher and not a grinder. In other words it wont make ground glass. Im not totally certain what that grit number because I keep getting conflicting info on this thread. But I can tell you alot of the suppliers on the net seem to put the cut off point just after 9 microns. For this reason I myself decided to use 9 micron Aluminum Oxide powder.

A interesting note is Canon uses lasers to etch/pitt their ground glass for some of their still cameras. The process promises not only finer grain ground glass but brighter as well. The problem is that their GG always seems to have some type of focusing assist marks on them making them useless for our needs. Still looking though.

-Brett Erskine

Canon type C
 

Brett this link about what you hare talking

All mate GG is type C, J, K

look
[url]http://www.mir.com.my/rb/photography/hardwares/classics/canonf1n/metering/screens/screens.htm

Thanks to all
 

I say the best part of this thread is all of the great, hard to find links. Thanks to Nicholi for the gotgrit link.

Brett, did you notice a great difference in performance using the 9micron GG vs. the 1000 grit GG? I've been pleased with the GG I created with 1000 grit but am always striving for more.

One more thing, Paolo Rudelli posed a great question earlier today and I would love to read a respnse from someone who's already corrected for hotspotting and vignetting. (I'm still waiting for condenser lenses to come in so I can experiment)


My questions are similar to his:
1. has anyone tried to grind the flat side of the condenser lens?How did it work?
2. has anyone tried to place the condenser between the SLR lens and the GG? It would be great if anyone who has already done condenser placement experimentation to share their findings and the steps taken to get their results.
If it has already been posted and I simply missed it, could someone please post a link? Thanks, Joe

Stuck testing condensers
 

I've got a variety of cheap lenses that I got from American Science Supply. Of interest are:

1) A larger-than-35mm-film-size diameter biconvex lens with a large radius (it's a fairly thin lens, about 4mm at its thickest point).

2) A larger-than-35mm-film-size diameter biconvex lens with a smaller radius (bigger curves). Probably 15-20mm at the thick part. However, the 'thin part' is still a good 5mm across, feeling like two plano-convex lenses which have been put back-to-back - but I can't see any seam.

3) A larger-than 35-mm-film-size diameter biconvex lens with a large difference in the two sides... One side is slightly convex - but nearly flat - the other has a serious curve. This is about the closest thing I have to a usable single-element condenser.

4) A smaller plano-convex lens - truly flat on one side, curved on the other. Too small to use though.

5) A rectangular exactly-the-same-size-as-35mm-film plano-convex that was the condenser from my AE-1. Very thin at its thickest point - probably 3mm.

6) A couple of small achromats. These seem like plano convex in their entirety because their flat on one side and curve out on the other - but they are actually two elements cemented together - a plano convex cemented into a concave/convex lense, like this:

The tough part is I haven't yet come up with a good way to mount these odd-sized lenses such that I can get them into my actual PVC adapter assembly. This makes it very difficult to guage their effects on vignetting, because this really only gets visible when you're all locked down and light-tight. The best I've been able to do is hold them up in some open-air experiments. ALL lenses seem to significantly brighten the image on my GG, regardless of whether they are between the SLR and the GG, or between the GG and the macro - and the direction (curved vs. flat) also doesn't seem to affect brightness at all - they're all the same.

Any tips from you builders out there on how to get one of these held in place and locked into a PVC assembly near my GG? I'll be happy to measure the focal lengths, and radii more accurately, but frankly, without some measure of the difference in their effects in a real 'lightless' environment that displays various amounts of vignetting, it doesn't seem like it will help much.

Additionally, I'm still waiting for my real grit to show up, so I have some ground glass I got from American Scientific Supply - which works and is fairly even, but has large visible grain. I also have my quick/ugly, but mountable GG with I made with (choke) sandpaper and steel wool. I also see an image - but it has large scratches and shows even more vignetting due to the unnevenness of the surface.

In short - I need to complete my real ground glass and figure out a way to mount these odd-shaped condensers before I can do any definitive testing. I'd love to hear mounting suggestions for the condensers.