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Old March 30th, 2004, 01:39 PM   #16
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Technically, you only need a pentaprism with a 36mm x 24mm base, which is the standard size found in any SLR camera. That will invert/revert the entire projected image properly. The downfall is with the roof of the penta-prism. Check out the first couple pages of this thread, paying particular attention to Helen Bach's posts. Here you'll read about the important difference between pentaprisms and roof-pentaprisms.
It is possible to use the standard SLR pentaprism, but you'll have to have a very strong close-up lens/diopter and be very very careful to orient the prism correctly to get a full frame picture. You'll probably find that this is more hassle that its worth. As far as having one custom made, that's very expensive. I think that's spoken of in the posts as well.

If you want a deep depth of field, you can adjust the f stops accordingly (which will cause loss of light - you don't want that), or just take the adapter off entirely. Plain video has very deep, almost infinite, depth of field. You could always use the camcorders zoom to increase the focal length and shorten the depth of field to get it perfect.

I don't really understand your "interchangable lenses" question, but this sounds like one of those options that relies on personal preference. If you're talking about interchangable 35mm lenses, yes as long as you're careful to use the proper flange-film distance and the same brand/model lenses. If you're talking about changing the actual camcorder, you'll just have to make it adaptable.

Remember, this is your design. If there is something you'd like to include, test it. The Agus and Aldu models are not strict instructions or even guidelines that must be followed. They just provide a very solid foundation for you to begin your own experiments. Now it is up to you to decide what you want, how you want it, and how to test it.

Good luck with your design. I hope to see and read about your setup soon.
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Old March 30th, 2004, 05:03 PM   #17
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Well I'm slowly getting my supplies.

And there's a glass cutting place, that'll ground the glass as well but the draw back is that they can only do it on 3mm glass. And I don't think that is suitable.

So now I'm at an empass, Ground glass, or frosted CD?

I was planning on using a fresnel with both, which begs the question how much of a difference will it make to have the CD made out of glass.

Plus I have the choice of picking between a 35mm Pentax lens, a 50mm Canon lens and a 55mm Mamiya lens. Which do you guys think I should go with?

That is all for now.

Rock on with your projects people.

Trevor T
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Old March 30th, 2004, 06:48 PM   #18
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Trevor,

It sounds like you are where I was about 30 days ago. I have a Sony PD100A (I think your camera is the miniDV twin of mine) which I have built no less than three 35mm adapters for. I have an Agus 35 with the spinning CD, an Adlu35 with a static GG and a vertical mount 35 where I tore off the pentaprism of a Minolta SLR and shoot straight down onto the focus plane. Each one has its plusses and minusses.

The Agus35 (even with a plastic CD) doesn't show any grain in my images. The down side is that I have to change batteries and it's the same size as my camera. I also have to either get an external LCD monitor to mount upside down or try to frame shots with everything upside down. (I haven't gotten the monitor yet)

The Aldu35 is much smaller but I have to grind glass and it is hard to get a fine grain without scratches. This can be quite frustrating. I am seriously considering using the homemade bosscreen technique described in another thread here. Obviously, this adapter needs an external monitor mounted upside down too.

The vertical adapter has the poorest quality image but it is the easiest to shoot with because it is correct vertically. It is still backwards left to right, but with practice, i got pretty good at panning with a moving subject. You can see some photos of this adapter here. http://www.paddlefilms.com/vm35mmadapt.htm

Here are a few hints if you're interested.

1. If your Sony is like mine, You don't need a magnifying lens. (diopter) My PD100A zooms and focuses right up to and even smaller than the 36mmx28mm frame size on the GG. Once you zoom in and get your focus, be sure to turn your camera to manual focus.

2. Use a condenser lens instead of the fresnel. For my Agus 35, I found a rectangular Dual Convex Lens here for $3

http://www.surplusshed.com/pages/item/l1584.html

I made a mount for it and placed it as close to the video camera side of the spinning CD as possible without interfering with the spinning CD.

For the Aldu35 I have a 60mm dia. 60mm F.L. PCX (plano convex) from Surplus Shed. This does a great job in getting rid of the hotspots and I haven't noticed any other problems with the image. Verticals are good and color seems to be OK too.

For the vertical mount 35, I had to take out the fresnel focus screen and keep the stock rectangular PCX that is ground on the flat side. There was a slight central hotspot and some minor vignetting so I took a 52mm filter mount and placed a dual convex lens into it I don't know the focal length but the lens is quite thin I would guess over 100mm. I screwed this right onto my Sony and mounted the Sony as close to the focus screen as possible. This did the trick. The problem with this adapter is that the ground condenser has scratches and the grain isn't as fine as the other adapters.

3. Use fast SLR lenses. For my tests, I've found that F 3.5 is the absolute smallest you want your aperature set at. I am using minolta MD lenses and have 35MM F2.8, 45MM F2.0, 58MM F1.4 (this is by far the best lens for my adapters) 28mm-70mm F3.5 Zoom and a 70mm-200mm F3.5-4.0 Zoom. The zoom lenses have to be set wide open and can only be used in direct sunlight. If I stop down any more, the grain really jumps out at you.

4. I haven't used a "Frosted" CD but grinding a clear plastic CD with Aluminum Oxide works well. I placed my ground side towards the SLR lens.

Good Luck and I'm sorry you got mixed up in all of this. This can be really addictive. i look forward to reading about some of your discoveries. Joe
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Old March 31st, 2004, 04:17 PM   #19
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Thanks for the tips Joe, I'm taking in all this information and will try to process it into the best product I can.

As for Pentaprisms, I've e-mailed an optical component supplier who works out of Edmonton Alberta, they told me their pentaprism prices range from 10 dollars to 500 dollars. All depending on the parameters at which they make them.

The largest they can make their pentaprism faces are 200mm, roughly what size of pentaprism would I need for my adapter? Just a rough size mind you, I understand everyone's camera will be different, and it all depends on the components you use.

Also

How much light will I lose by using a pentaprism? Do you also lose light when reflected off a mirror, or because the light isn't passing through the mirror, you don't lose any. I kinda want all my bases covered before I opt for a constructed pentaprism.

If anyone's interested, here's the link.

http://www.euro-optics.com/

Trevor
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Old March 31st, 2004, 08:21 PM   #20
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<<<-- Originally posted by Trevor Trombley : Thanks for the tips Joe, I'm taking in all this information and will try to process it into the best product I can.

As for Pentaprisms, I've e-mailed an optical component supplier who works out of Edmonton Alberta, they told me their pentaprism prices range from 10 dollars to 500 dollars. All depending on the parameters at which they make them.

The largest they can make their pentaprism faces are 200mm, roughly what size of pentaprism would I need for my adapter? Just a rough size mind you, I understand everyone's camera will be different, and it all depends on the components you use.->>>


Trevor,
I'm really more of a hands on kind of guy so I probably won't get the technical terms right, but in my opinion, as far as a roof pentaprism goes... you want the opening face that would be looked through by the camcorder to be at least 40mm across and 30mm high. The roof pentaprism that came out of my Minolta camera only measured 20mm across and approx. 18mm high. This was sufficient for looking through with the naked eye with a magnifying eyepiece but not enough apperature for the video camera. I fear that any pentaprism designed for viewing with the eye will be too small for our use. Be sure to explain to the Optical Pros what you are trying to do with the Roof Pentaprism with your camera. The image you are trying to see is 36mm x 28mm (4:3). There are other people on this forum who know much, much more about this optics stuff and hopefully, someone with more knowledge than i will chime in.

As far as a mirror, be sure it is an optic quality surface coated mirror. Rear coated mirrors are too inefficient in transmitting light for our uses.
You will always loose some light when you reflect it or it passes through each plane of glass. In my humble opinion, I'm willing to loose some light to gain a correctly oriented image. please keep us informed on what you learn about the Roof Pentaprisms.
Oh, one last thing, be sure to look for a roof pentaprism, not just a pentaprism. There is a difference. The roof corrects the image left and right while the mirror corrects for up and down. Without the roof, you get a reversed image. Joe

<<<--Also

How much light will I lose by using a pentaprism? Do you also lose light when reflected off a mirror, or because the light isn't passing through the mirror, you don't lose any. I kinda want all my bases covered before I opt for a constructed pentaprism.

If anyone's interested, here's the link.

http://www.euro-optics.com/

Trevor -->>>
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