35 mm lens adapter for mini dv camcorders?

January 4, 2006

Hey all,

I'm always trying to learn new things, and I've discovered about the use of 35 mm SLR camera lens being attached to mini dv camcorders, came across this site

http://www.mediachance.com/dvdlab/dof/index.htm

I have an old slr camera with a telephoto lens as well, I'm thinking about making one of these things, because the pictures and images I've seen from them really impressed me, having that shallow depth of field. Is anybody on this board well versed in these adapters, and if so what is the best one and easiest/cheapest to build for a small mini dv camcorder?

Luke

January 4, 2006

Hey all,

I'm always trying to learn new things, and I've discovered about the use of 35 mm SLR camera lens being attached to mini dv camcorders, came across this site

http://www.mediachance.com/dvdlab/dof/index.htm

I have an old slr camera with a telephoto lens as well, I'm thinking about making one of these things, because the pictures and images I've seen from them really impressed me, having that shallow depth of field. Is anybody on this board well versed in these adapters, and if so what is the best one and easiest/cheapest to build for a small mini dv camcorder?

Luke

I have testing experience along with hours on the phone with P+S technik and I can give you some tips, though I have never actaully built one. I would not recomend using the setup shown in the link you provided, though the idea is right.

first you need to search the web for the proper backlash of your lenses (the distance from the rear lens element to the filmplane.

If you dont get this right (within less than .5mm, so get a good feeler guide from an auto store so your not guessing) then the focus marks on the lens barrel will be wrong and everything will be much harder. You also change the minimum focus distance, lens vinnetting properties and veiw angle (making the lens more tele or wide than it really is)

Also dont use the CD idea. There is no way this disc is optically clear, and making it ground...er plastic will make it way softer than you want.

use ground glass. buy some ground glass or look up on photographic websites on how to do them (several people do it to make their own 'view cameras')

Dont use the lenscap idea for the mount. No way this will hold up for even a day, even if you have the lightest shortest lens availible, but you also said you had a tele lens

Salvage the mount from the camera. if the body is metal drill and tap it and attach that to the Ground Glass mounting plate

have the glass ossilate. a simple round motion wil make the GG produce a recognizable pattern. a center spot in a rotating GG, or an arch if its set up like the website you showed me.

You need a relay lens. you can do that with the macro lens they have, or use high quality optic glass (can be found at scientific shops) so you can get a sharp picture. Use a sharpness chart to set this up, and make sure the camera settings are easy to setup, so you dont have to precisely focus the camera everytime, just throw its focus to its closest setting (then break the focus ring. jk but do put tape over it)

Do lots of research there are lots of resources to see how its done. In the end the mini-35 and pro35 are used because of their quality construction, you cant destroy them(practically) and the optics are presice

Luke Prendergast · January 4, 2006

backlash of your lenses (the distance from the rear lens element to the filmplane.

It's flange focal depth. Backlash is slop in the gearing.

January 4, 2006

I'm still pretty confused, so I'm guessing you can't just take a step up ring or a few and attach the lenses, right? I'm looking for the simplest and best working way to make one. I've heard they cost a pretty penny to buy.

Phil Rhodes · January 4, 2006

Hi,

> simplest and best

The two are mutually exclusive. The best way isn't the simplest; the simplest way isn't the best.

Personally, I can hold up one of those mock CDs and actually see the ripples in it, so I'm not sure I'd want to go anywhere near using it as an imaging device. I'd look around for a supplier of a finished optical component; or find someone who can abrasive-jet cut an optical flat into shape, although cutting the holes in the thing is not going to be that easy even then, as cutting internal openings can cause cracking.

Then I'd mount it on an old hard disk spindle. This has several advantages. First, it's a very high precision bearing assembly, which would hold the spinning groundglass in a plane flat enough for optical consistency. Also, it's mounted to a sturdy cast aluminium chassis, which you could drill and tap to take the lens mounts. You could also use the hard disk's motor to spin the shaft; it runs on 12V and it's reasonably quiet, although possibly not quite quiet enough.

Both the mounts need to be on jackscrews so you can fine-tune the backfocus. Experience photographing very very small objects with machine vision cameras informs me that you could probably get away with a CCTV-camera style lens as the optical component between the groundglass and the camera, although the optical quality of those is such that if I was making a piece of art, I probably wouldn't want my piece of art to go through it. I'm not sure what you would do here, but I would consider it reasonably likely that a suitable short field condenser would be available off the shelf.

Good luck, you'll need it.

Phil

January 5, 2006

I did some research and want to build one myself. I have an old GL1 which has a busted lens. I want to remove the lens and use a relay lens to put the image directly on the chip. could be difficult but I will share what I have found with the group.

Heres what I found when I searched for info on view cameras and other items:

1. Ground Glass. Ground glass can be purchased from any photographic store that sells parts for view cameras. From what I understand though, acid washed ground glass tend to be less contrasty and less bright than a homemade GG (dont know how accurate that is, but since homemade is cheap, I will start there)

to make a homemade GG the site recomended using thin glass to reduce refraction, color shift and increase brightness, which made sense. They recomended glass from a picture frame, which I do not agree with. They advocated it because it was the right size for a veiw camera (way to big for our needs) and I think buying 2 4x4 UV glass filters made for matte boxes would work much better and give me a good sense of opticle clarity.

You need 2 because of the method used. Basicly you place the glass on a flat surface (they mentioned glass can bend, good advice) and you put an abrasive, aluminumn oxide was what they recomended at 600gritt. put that and a bit of water on the glass and put the next piece on top, forming a sandwich. Now for the next 10-20 minutes make random oscilating, turning motions on the glass (I assume the pattern you do this will affect the pattern of 'grain') This should give you a good bright GG (and a spare in case one breaks)

as for the mount.

The whole thing would best be made out of steal or aluminumn and should have provision for a support system for larger lenses. Somebody please remind me what heavy weight rods are. I believe 17mm but I am not certian. I know lightweight support is 15mm.

I am building mine with an EOS mount, as I have a lot of canon lenses laying around. If it works I can rebuild with a PL mount, but EOS sounds cheap.

I found extension tubes on B+H for under 30 bucks. I ordered one and am waiting for it arrive and will buy some 1/2 or 3/8" steal or aluminum, depending on what the tube is made of. Here comes the expense of this operation. I will take it to a machinist to drill a hole to match the outer diameter of the tube. I also plan to have them drill the adjustment holes (1 in each corner to accept a large machine screw) so I can adjust the focal flange depth (thanks smith..john, I dont know what I was thinking, brain fart) You will need at least 3 screws to adjust this because not only do you have to adjust the flange depth, you have to make sure the GG is not skewed, which would make part of the screen sharp and part soft.

I am looking for a good motor to use, but that shouldnt be too hard to find. one thing I would like to do is put an opticle sensor on the gg and a circut to control the RPM of the GG. I want to have a push button setting with LED readout (so press a button for faster, press a button for slower, and a little LED screen will show you what setting you are at) Assuming I get that done I will post a scematic so yall can build one too.

I am trying to find a way to get the glass to oscilate effectively. I imagine it will take 2 motors, 1 to turn the glass and 1 to make that assembly go back and forth to hide the center spot.

now all that is left to figure out is how to make a good quality relay lens to put that image on the CCDs

January 5, 2006

I made progress on the relay lens. these look good:

3CCD lens

They have a minimum focus distance of .07 meters (7cm) I assume this is from the front element, because the site claims the 5.3mm lens can focus to 7cm, but its 7.2cm long from the C-mount, so that is not including the flange depth, so it cant be from the prisms plane.

Also does anyone have any reliable data for how these focus? Should I aim for a sharp picture on the face of the prism? or should I (more likely IMHO) aim to focus somewhere behind the prisms face so the focus comes together when it hits the CCD.

I hope to be able to calculate the distances so I am not guessing, but I am thinking I will have to focus the lens on the GG using a jewlers loop to ensure that the focus is as sharp as it can be, then set the relay lens using a sharpness chart (making sure to set the cameras set up menu to full detail to ensure best calibration)

I also looked up a way to spin the GG. the best way to mount it seems to be to set it up so the center of the GG is the center of the frame. I found what are called radial bearings (probably what we are all used to seeing) at <bearings> My plan is to mount a drum containing a mount for the ground glass into the center of the bearing. cut into the bearing will be a channel to accept a rubber band to spin the drum and GG in turn. This drum will need to be machined in 2 parts. a drum with the channel cut for the drive band, and a square cut to let light through, along with a lip so the GG wont slip through the drum, and a plate to go over and hold the GG in the drum tightly. I believe this will make the GG spin in one plane securely. The GG cannot move forward or back more than a few mm if that, otherwise soft image will be the result. this drum will be machined a few thousands of an inch wider than the bearing, then the bearings will be placed in the oven while the drum is placed in the fridge. the two will then be pressed together. it might also be spot welded.

That drum will be machined in town by a machinist with a lathe and basic machining tools. I am not a machinist and do not have any tools to make this drum, but I have been in contact with a machinist friend who has advised me on the best design to make machining easy.

Roadblocks:

On my lens there is no provisions for setting my apeture. once I remove my lens from the GL1 it will no longer have an apeture setting. The relay lens I am getting will have an iris, but that does not help me in regard to depth of feild control, which is my aim (I dont need a wide open DOF all the time) should I go with a different lens other than modern EOS? I can definatley put a nikon or minolta mount on the addaptor, then get a stepup ring to put my EOS if I want to later, I have yet to find an adaptor that allows for a nikon lens on an EOS, and I also have yet to find an EOS lens that also has a manual iris. most are set through menu on the camera, and I have yet to find a way to manually control that.

If anyone wants a drawing to see what this drum would look like I can get one on request by next monday (still on vacation) i dont know if I described it well.