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Old February 23rd, 2004, 08:00 AM   #286
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http://www.kauserinternational.com/Photography/Ohner/Copier/Ohnar%20Digital.htm

and

http://www.ephotozine.com/equipment/tests/testdetail.cfm?test_id=124

found on Ebay for 70$, very nice quality, fully dismountable.
tube diameter 52mm with 58mm ring adapter.
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Old February 23rd, 2004, 08:58 AM   #287
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updated schematics

so here is the k.i.s.s. (keep it simple stupid) updated version of the Aldu35 for standard DV cams, as i understand it.

http://www.dinoreyes.com/images/lens_standard_dv_simple.jpg

comments, corrections? i just want to get this right...

ideally both connecting tubes cound have an adjustable collar

nice link Giroud, so close...

-D
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Old February 23rd, 2004, 09:03 AM   #288
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Dino, isnt the frenel supposed to be on the 35mm side of the GG?
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Old February 23rd, 2004, 09:11 AM   #289
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That looks right, Dino. We're pretty sure that there should be nothing between the 35mm lens and the ground glass. The condensor helps more light more evenly reach the dv cam.

The only comment I have is on the macro - the requirements here will vary widely, depending on the needs of the DV cam. Mine has a built-in macro and doesn't even need it. Some need like a +7, some need more...

Conceptually, it breaks down to getting a macro that lets your dv cam focus on something that is only an inch or two away (distance from the dvcam to the ground glass).

Easy to test out: just take your plain ol' camcorder and put a photograph/newspaper about two inches in front of the lens. If you can sharply focus on it, you don't need a macro - if you can't... then you do :)
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Old February 23rd, 2004, 09:30 AM   #290
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why not to make de front part side of the fresnel sanded in way
to have de gg and the condenser lens in one piece ?
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Old February 23rd, 2004, 09:34 AM   #291
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if by any chance you already have dismantled an LCD screen (particularly on laptop) you will find many intersting layers made of plastic material that are ultra thin and looks either like gg or fresnel or even both.
cannot give a sample there, but it worth to give a try.
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Old February 23rd, 2004, 09:44 AM   #292
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if you got a sony VX2000 (no macro feature) , you can have a correct focus very close to the front lens on the camera, but unfortunately the zooming range to fill the screen is very short before you loose focus.
The trick would be to have the gg image bigger than the 24x36 size.
Is this a problem with a 35mm lens
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Old February 23rd, 2004, 09:46 AM   #293
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okay...

as always it would be nice to keep it simple, but could we have these scenarios?

1) if you use a fresnel lens, in order to avoid the appearance of the concentric circles, it would be placed IN FRONT of the gg

2a) if you have a condensor lens, you would place it IN BACK of the gg

2b) i also believe that a condensor lens may(?) have a indented back, but if it has a flat back you could possibly sand that also like a gg (a more radical approach to 2a)... and yet another question, would the curved part face the ccds or face the primary lens?

would the observations be correct for 1 or 2, anyone have an idea?
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Old February 23rd, 2004, 09:58 AM   #294
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Of course, the coolest thing about any built-it-yourself project is, you're free to do whatever you'd like. I'd recommend not using a fresnel anywhere because of the visible rings.

I believe it was Roman who correctly spoke of trying to keep the relationship between the SLR lens and the ground glass pristine. As he said, this is already a perfect relationship, and its unlikely that we will improve it. This is the reason for not having anything between the SLR lens and the gg.

I think that at least some of the condensers I've seen are flat on the 'intake' side - and could theoretically be turned into a ground glass... but it's a pretty radical step, especially considering that you can just place a normal ground glass right up against it for the same effect. I'm not sure what you'd gain by directly making the back of the condenser a diffusion surface.

I'm 99% sure that the curved side of the condenser is on the camcorder side... the flat side rests right against the back side of the ground glass.
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Old February 23rd, 2004, 10:38 AM   #295
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we should just rent a mini35 for a day- take it apart- take pictures- then put it back together

or become friends with an optics major
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Old February 23rd, 2004, 11:20 AM   #296
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John: Ha ha ha! That would be very helpful.

I took my GL2 and mini 35 static homebrew system out this weekend and played around with it a bit. I discovered that if I attached the ground glass directly to the front of my GL2 (it's a ground 58mm uv filter), the camera was able to focus on it. I shot some footage like this for a while and then removed the ground glass and put a spacer inbetween. With the later approach, I had to zoom in a bit.

This is all I had:

35mm lens (50mm) -> spacer -> ground glass -> spacer -> GL2

Overall, I really liked the look with the shallow DOF.
I have discovered how hard it is to keep ground glass free from dust and other bits of stuff. These things really show up in the image. Also, I think I need to grind the glass even more. Sometimes the grain isn't noticeable, depending on the light, but it should probably be more fine for the resolution. The picture looks low-rez / soft, overall. (I got used to looking through the adapter, and when I took it off and saw the regular camera image through the viewfinder, I thought it was HD. Not really, but I'm just saying how much sharper the regular image is. :-) )

It looks like I don't need an achromatic diopter, but I am still looking for a condenser from an old SLR camera. I think this will help out a lot. I don't see why an extra condenser is needed for the other side, though.

Forgive my ignorance to optical theory and explanation, but it seems that by having a single condenser between the 35mm lens and the ground glass (the flat side of the condenser being against the ground glass), the condenser is 'channeling' the incoming image in a more flat/uniform manner onto the ground glass, at which point the camera would pick up that image - which should have no hotspots or vignetting, but an even distribution across the ground glass. However, I then think about how SLR cameras basically have a mirror that lifts to expose the film in the back of the camera, which (to my knowledge) has nothing inbetween it (the film) and the lens out front. Is that correct?

btw, I did all my shooting in Frame Mode, which made it easier to flip in post without having to mess with the field order. Thought I'd mention that as an incentive for you guys with this feature.

Thanks for all the posting. This has been the most enjoyable thread.


,Frank
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Old February 23rd, 2004, 01:30 PM   #297
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Okay, are you guys 100% sure that the condenser or fresnel or whatever lense you use to distribute the light more evenly goes behind the GG?

Doesn't the hotspotting and chromatic aberration come from light hitting the GG unevenly? If this is the case wouldn't you want to put the fresnel, or whatever in front of the GG?

The GG becomes your Object to shoot with your macro adapter on your DV cam right? So shouldn't the image be colour and light corrected before it becomes the object on the GG?

SLR > Spacer > Condenser > GG > Spacer > Macro > DV

Please correct me if i'm wrong as i'm just trying to figure out what would work the best.
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Old February 23rd, 2004, 01:40 PM   #298
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We thought that for a while :)

But if you think about it... if you just had a plain old 35mm SLR camera, the light coming into the lens gets focused onto the film, which reacts to the incoming light, making a purty picture. There's no fresnel or condenser in the middle of that interaction.

Our ground glass is right where the film would be, so it gets exactly the same light as film would get.

The hotspotting comes from how we then consequently view the ground glass... from behind with a macro, which is basically an intense wide-angle lens. Have you ever noticed that whenever you use a wide-angle lens (fisheye, for example) there is some pretty serious distortion around the edges? Our macro puts us in a similar situation.
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Old February 23rd, 2004, 03:13 PM   #299
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<<<-- But if you think about it... if you just had a plain old 35mm SLR camera, the light coming into the lens gets focused onto the film, which reacts to the incoming light, making a purty picture. There's no fresnel or condenser in the middle of that interaction. -->>>

Yes but we can't compare a ground glass to a film... the ground glass is much more efficient with a light coming perpendicularly...but the risk is to ruin an optical system (the slr lens) with a poor lens ...the film is not really sensitive to direction of the light comming to it because it's near to 100% absorbing the light....


correct me if i'm wrong
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Old February 23rd, 2004, 03:15 PM   #300
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2 Giroud Francois: you can make the GG image bigger, but the brightness will be lower: you only have so much light coming through the SLR lens. Also, try to think of a qualty lens for the condenser, Fresnels are no good. Thanks for the LCD screen tip, I'm going to take my old IBM screen apart & see what I find!

2 Dino Reyes: diffused light is scattered in a cone pattern; say, a 20 degree diffuser makes a 20 degree cone of light out of every incident ray that hits it. The periferal part of the diffuser will appear darker than the centre because some fo the diffused light will not hit the next optical element (macro or DV lens). That's why you want the condenser lens to follow the diffuser, not the other way around. The curved part should face the CCD, just like Jonathon Wilson said. As for grounding the flat part of the condensor: if it's a quality lens, it would be multi-coated to increase light transmission. If you grind that coating away, you may not like the results :D.

2 Frank Ladner: I'm with you 100% on the film analogy. What kind of condenser can you get from an SLR? Wouldn't that be a Fresnel? Also, what software do you use for flipping & left-right correction in post?

2 Tavis Shaver: Yes, pretty sure ;)... BTW, chromatic aberration is non-existent in reflective or diffusive components, it affects only lenses (prisms too, I believe), because the index of refraction of the lens material depends on the wavelength of light going through that lens. Au contrare, the hotspotting is found only in diffusers. Yes, GG (together with the condenser!) is your object, so if the condenser is an achromat lens, you're OK. So, my order would be:
SLR lens -> spacer -> GG -> Condenser -> spacer -> Macro (if needed) -> DV

2 Jonathon Wilson: the higher the power of your macro lens, the more barrelling (sp?) you'll observe. I'd say, go with the macro of lowest power taht allows you to focus on the image with your DV.

Last night, I finished fabricating & painting my 'adapter', and now trying to find a suitable condensor lens. Also, I'm going to Efston Science store, to play with diagonal and porro erecting attachements they may have. I also need to think about the support (bridge plate, support rods, etc.) to put the whole thing together. Unfortunately, a router and a Dremel are the most high-tech tools I have. I may try to rout the baseplate out of a phenolic sheet. Anyone got ideas (or links?) for an adjustable support?
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