condenser placement help for agus35 adapter

[Jamie Roberts]

Hi all

I have just made a 35mm adapter based on the agus35 and I was wondering about the use of condenser lenses.

As I am getting a bit of light fallout around edges, I want to try one.

1. Does the condenser go between the 35mm lense and the gg...is that right?

2. What size and type will i need (or most likely be suitable)?

3. How do i actually fix it into the adapter housing?(in simple terms!)

I appreciate any help/advice you can offer.

I have been blown away though by how effective they are and how simple they are to make (and believe me I am NOT handy when it comes to making stuff!)

Thanks

Jamie

[Bob Hart]

Jamie.

I shall be watching this post as I may have to bite the bullet and use a condensor arrangement as well. I am getting some falloff when trying to use 16:9 cameras. At present I zoom in closer to avoid the falloff. This comes at a resolution penalty.

I was able to do without with 4:3 on a PD150. The image size I was taking off the groundglass was the 24mm x 18mm (35mm motion picture frame size).

With 16:9, if you stay with the same 18mm image height, then the width of the image area picks up the edges of the hot spot I previously avoided. I have also made life a little harder for myself with prisms.

Ben Gurvich, who is relatively near to where you are, got a non-erecting AGUS35 up and running, based on the project box design which was published awhile back. My own uses PVC pipe and pipe caps for the case. I didn't observe any hotspot or falloff on his tests but I think his was 4:3 as well.

The SLR camera lenses you use on the front matter a lot. Prime lenses with f1.8 aperture are pretty much mandatory if you want ideal results.

As for placement of condensers, ny understanding is that two, one either side of the groundglass is preferable and aparently as close to the groundglass as you can position them. The flat faces go toward the groundglass which is positioned between them.

I = groundglass
(| or |) = condenser.

The order of things looks something like this :-

SLR lens >> (| I |) >> close-up or macro lens >> camcorder.

There's better brains than mind working in this area so pay little heed to my comments.

[Jamie Roberts]

Thanks Bob

I am using 16:9 as well and have a couple of slr lenses, one being a canon 50mm f2 and the other a 130mm f2.8

I have managed to minimise the fallout for now by using a 10x PLUS a 4x macro (i know i know!) so i can get close up and get good focus and minimal fallout vignetting, and when I am securing the adapter on to the camera, I first turn everything on with the camera facing a well lit plain white wall(or similar) and adjusting the position of the adapter (with lens on) so that the fall out is largely out of shot. This seems to work pretty well for now but i would like to try some condensers and see if this can give me a bit more room to move so to speak.

I will just have to figure out how to secure the condesers into the housing. Was hoping someone may have already done it and been able to share how they did it???

Jamie

[Bob Hart]

By Agus35 I assume you have made a spinning disk version.

My own construction method for the Agus has been to borrow a little on what the Aldu style builders have been doing but instead of using stacks of flter rings to create a tube, have used plumber's PVC pipe and caps for both a non-erecting and erecting version. It is easy stuff to cut and shape. If you've got the tools you can get good precision with it.

For the non-erecting version, getting the centres right is dead easy. Axis alignment is a little harder as the pipe caps have an internal taper. The prism version is a far more difficult beast.

For the non-erector, I used a narrow piece of pipe, about 2" or 50mm. This runs the full distance between camcorder and SLR lens. A cap on back and front provide the camcorder and SLR lens mounts. I chose to mount my dioptre to the camera filter mount and the appliance itself separately to the lens hood bayonet fitting plus some reinforcement to the camera base via the tripod screw.

There is a gap cut out of the bottom side of the tube for the disk to run in plus some space for backfocus adjustment. I move the whole motor and disk as one for this. I used two big sewer pipe caps to make an enclosure for the motor and disk and for the non-erector, the pipe goes right though it.

For the erecting version I had to use 100mm tube and caps to find enough space for the prisms and leave enough cut-out space on the caps for the offset centres for the SLR lens mount and camcorder mount. It is a tight fit within 100mm diameter but it can be done. This tube fits sideways into a cut-out in the edge of the disk enclosure and is not a feed-through like the non-erector.

To secure the condensor or condensors in the non-erector, I would probably, choose condensers which went closest in undersize to clearing the internal diameter of the tube. I might have to make paper sleeves to take up any looseness in the fit.

I would cut very thin rings from the same PVC pipe materal, cut across one edge and trim out enough for these rings to fit inside the tube. - Like a piston ring in a cylinder bore. - Come to think of it, some old motorcycle or lawnmower piston rings might be about right except for the risk of chipping the glass.

I would then glue them as base stops into the pipe closest to the disk as I could get them. Then I would cut broader pieces, slot them out so they also fit inside the tube to be able to shove them in. If they are broad enough, there should be enough spring in the plastic to make them stay in place and secure the condensers long enough for testing, trimming and cutting the rings until I get the spacing right.

For a permanent arrangement I might try to make metal mounts on a lathe or drill holes through both tubes and lock them in place with screws.

The close-up lens I ended up choosing for the non-erector was out of a telescope eyepiece. This lens consists of three pieces of glass, two glued together as a compound element and one, which because it sits 18mm away from the groundglass, acts both as a magnifier and as a condenser, but is not a true plano-convex lens. I had to make my own brass tube on a lathe. This has the 58mm filter thread on one end for fitting to the camera

The lens set comes out at about 24+ but I am only guessing at this. From front of this lens to groundglass is 18mm, which is excellent for making a short device. I get a good light spread for the 24mm x 18mm frame but for 16:9, it is totally useless as the lens diameter is only 44mm. Whilst it can be arranged with the FX1 so that it does not vignette, there is a distinct out-of-focus ring within the overall image, then the corners are sharp again - very peculiar.

The erecting version is a whole more diffcult thing. My prism arrangement has the front of the rear prism within about 4mm of the disk and the overhanging bottom edge of the front prism only 1.5mm clearance from the disk edge. I have chosen a +7 dioptre to keep the whole thing as short as I can have it. This leaves me with little room to innovate with condensers and a whole new redesign, remake, new dioptre would be needed, hence my reluctance to experiment with condensers.

If you have used the project box enclosure design you might be able to make tube mounts up for the condensers by fitting them inside a single piece or pieces of tube if they have to be separated because of the disk position.

The method would be to use the internal rings as I describe, but to also use a pipe cap with centre cut out, glued to the tube, or a plastic flange which can be had from hardware to fit 50mm tube. The wide face of the cap or flange would have drillholes in it for screwing to the internal faces of the project box.

[Bob Hart]

A correction to the above post. I could not get the editing function to work.

The tube diameter should be 65mm ID not the 50mm quoted above. In a project box design, smaller diameter tube to closely match the diameter of available condensers would be okay.

[Jamie Roberts]

I have made the spinning version inside a 25 cd container as first used in the agus post.

I think I will use the screw idea and try and get 2 x 50mm pcx lenses roughly around 50mm diameter, mount them in a thin piece of pvc as u described, and screw them into place.

Now, I work in the education system so stopped in at a local high school science dept today to see if I could get hold of some plano convex lens but unfortunately they didnt have exactly what I was looking for. In one of their suppliers brochures though, i saw that they could get 'acrylic' plano convex lenses. I am presuming 'acrylic' wont be good enough and I will need glass?

I see you are in Australia Bob, where did you get your prisms, glass optic lenses from? ie where can i get pcx lenses from in oz?

Thanks

Jamie

[Bob Hart]

James.

If the acrylics are cheap enough it wouldn't hurt to experiment with them and use good glass later on.

I got my prisms from Francis Lord Optics in NSW.

sales@flo.com.au - email to Attention "Glenn"

I am getting a special order of four made up. I'm prototyping again to fune tune the 16:9 arrangement. This time the prisms are 45mm x 45mm x 65mm hypotenuse with 32mm common thickness across all faces. - uncoated as I don't know how well the arrangement will work.

My own jury on condensers is still out.

The 4:3 academy motion picture frame is 24mm x 18mm. The widescreen version is actually a top and bottom cropped version of that as far as I know from being a projector operator.

We simply used a wider projection lens and put crop masks in the gates to stop the overspill onto the floor and ceiling. For the anamorpic, the full 4:3 masks had to be put back in.

It's quite intriguing actually. If the original movie has not been masked in-camera or in post, the full 4:3 image is there, complete with boompoles and shaggydog mike covers. In that event you have to be careful to get the projector registration right.

The condensers appear to enable you to take a larger image off the groundglass. That wider image is not faithful to the true 35mm motion picture frame.

The cropped widescreen image is less height and same width. My only reason for trying to keep the same height and correspondingly more width is to preserve the resolution I have. I can afford to give away a little.

My existing prism arrangement with the 40mm prisms is a bit tight even for the 24mm x 18mm but good enough for 4:3. But for 16:9 there is a straight edge falloff on one side caused by being too close to the front prism apex.

If I move the frame area across, I then pick up the corner falloff on the opposite side. I think another 2mm in the prism path will give me what I want.

If you want to do prisms I'll send the updated design if you want it. It is not easy however. I have a lot of respect for Quyen and his mirrors. Having gone there before I went with prisms, I know what a b---- it is to initially set up.

[Bob Hart]

Edit problem again. I'm doing something wrong but I know not what.

I have not looked for sources of condensers within Australia yet. The published locations such as surplus shed are probably the best bet for these.

The Century Optics 7+ I got in through AV Central. (authorised Sony pro dealership.

There was probably a mark-up on it but by the time you pay import duties and sales taxes doing it yourself direct from overseas vendors, there may not be a lot of diffence in the final cost, including petrol to the airport post office to get the parcel out of customs and GST hock.

If you can't get five micron AO to grind your own disks, FLO helped me out previously when I got the first prisms.

I'm also using optical glass disks which are a b---- to make.

I actually got a softer but nicer filmlike image once using a DVD+R retail pack spacer but the disk chafed against the prism block and got a groove in it. I have not successfully remade one since, so I am back on the glass.

[Jamie Roberts]

Hi again

well Ive ordered two 40mm condensers from FLO which they gave me at a good price cos they arent cosmetically perfect ($25 each). They havent arrived yet but apparently have a 70-80mm focal length, and are quite thin as a result. I wanted 50mm but they would have had to order them in and would have cost more so i settled for what they had.

Once I get them, the next question I will have is about how they are tuned? I have no idea how you are supposed to do that but like everything else, Im sure I will soon learn!

Im using a clear sanded cd as gg and it looks pretty good.

Jamie