<<<-- Also - in current form the image that reaches the DVCam is still rotated 180 degrees. Makes it a little hard to use - would be nice if there were some way to view the image right-side-up while composing. -->>>

Hi everybody (new to this very interesting forum ),
a way to rotate the image is to add an other lens....like the SLR lense rotate the image an additional lense after the condenser will revert the image...

but that makes a lot of glass to go through...and considering that the amount of light is a problem...


but we are forced to add a macro adaptor....i think that the additional lense to re -rotate the image and the macro adaptor can be merged into one single lense that we are going to calculate the front and back focal length.... :)

i don't know if it's really possible but why not...

Malheureusement , ce n'est pas si simple.


Alain

Inverting prism eyepiece
 

Right, Alain. I wonder if the eyepiece has a built in lens that corrects for the entire added eyepiece's focal length difference.

here is some new motivation for you all, a short made with a static35'ish device.

This short is groundbreaking!
http://www.dvinfo.net/conf/showthrea...5&pagenumber=1

http://www.originalversion.net/temp/makingof01.jpg

What I don't understand, is why he had a hotspot in Marla. Was it the result of taping through the viewfinder.

I will start getting my parts in this week. I have high hopes, wish me luck.

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.

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

Dino, isnt the frenel supposed to be on the 35mm side of the GG?

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 :)

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 ?

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.

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

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?

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.

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

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

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.

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.

<<<-- 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

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?

Roman: I am using After Effects' native transform options to rotate the image 180 degrees. I'm sure you can do this in Premiere or Vegas.

I'm not sure about what kind of condenser. I was assuming they were all pretty much the same. I do not know for sure, though.

I just did a test, I put the fresnel on the camera side of the gg and it did smooth out the hotspot by making it about 20% larger, so it moved the light outward.

This is good for theory just proving that we need a good acromat. A fresnel has rings which are visible, not good but did well for experimenting.

I will have some acromats in a few days, to solidify the theory.

Thanks, Frank! John, just for the fun of it, could you try to put the Fresnel on the SLR lens side of the GG? I wonder what the results would be...

<<<-- Originally posted by Roman Shafro : So, my order would be:
SLR lens -> spacer -> GG -> Condenser -> spacer -> Macro (if needed) -> DV -->>>

But the probleme remains ... what's the best deal for the condenser part...

a field lens is a good choice but it gives a lot of distortion....2 identical field lenses is much better...but it's bigger...this is the reason why the first field lens is replaced by a fresnel just after the GG in all the SLR viewing system...

we have a lot of options
1- single field lens
2- 2 field lenses
3- 1 Fresnel (but a lot of ghosting effetcs)
4- 1 fresnel and a field lens
4- an achromatic

think that now, experimentation will be the key...

heres some pics of my fresnel placement test, as you can see the fresnel does its job best on the camera side of the gg, however the rings are visible, thus I will replace the fresnel with an acromat later this week.

http://aequantum.com/fresnel.jpg

cool john, that's great! can't wait to see what it looks like when you get your achromats.

Thanks, John! I guess the question of which side the condenser should be on is over... Olivier, I'd say a thin achromat field lens is your best choice, and the focal distance shouldn't matter...

ground glass and corrective lens(es)
 

The reason why I thought you needed two corrective lens (one on each side of the ground glass) is because I was under the understanding that in a traditional SLR viewfinder system the order was as follows:

35mm lens>mirror>FRESNEL>GROUND GLASS (sometimes the fresnel and ground glass was one piece with the fresnel on the 35mm lens side and the ground glass on the other)>followed by a condenser>and then the prism and eyepiece optics of coarse.

I'm going to call a local guy that repairs used cameras tomorrow so find out and finally put this issue to rest. In the mean time if someone wants to open their old SLR I would be very interested in what they find.

-B

Brett
 

I have done this, and the one I have is a glass whith fresnel on each side then the pantaprisme and eyepiece optics .

The mark on the fresnel, normaly a circle ,is a small circle on one side and a biger one on the oher side, so it look like when you are perfectly in focus the image that correspond to the film plane are in between the two fresnel .

Alain

Alain let me make sure I understand what your saying. The SLR you opened up had a piece of glass that had one fresnel pattern on one side and another on the other side and seperate from that was the ground glass?

Brett
 

No ,It's only one piece whit a fresnel on each side,apparently no ground glass.But it's realy hard to see.I have take a look at it whit my microscope and it look that they make a( ground fresnel )or maybe it's just the quality of the fresnel that look grainy.This is made from plastic also. Probably a cheap way to make this thing.

Alain

brilliant Giroud!
 

totally forgot about holographic diffusers in laptop LCD screens! that's VERY similiar or even the real a real holographic diffuser, this could very well be another key to improving high quality low-light transmition. possibly (yet another and possibly better?) alternative to ground glass (!). just a hunch, but great idea Giroud!

My old dusty Canon AE-1 which had previously been just sitting on a shelf collecting dust (since the purchase of my digital camera) contained ( in this order from behind the lens):

• nice mirror: 35mm film size
• real condenser - not fresnel right up against: 35mm size
• ground glass/focusing screen (reticle on glass): 35mm size
• very nice pentaprism 35mm entry - smaller exit
• viewfinder had small real lens to magnify - size of small exit

And of course, the real question - was the condenser on the lens or viewfinder side of the ground glass... answer:

"I DON'T KNOW!!" (it popped out as I removed the last screw and I didn't see which way it was. C'est la vie).

I didn't have any fresnels in there.

Thats alright Johnathon. I just wanted to know if it had both. Besides the condenser goes between the gg and the prism. Take a real close look at the profile of that condenser's glass. Is it two lenses cemented right on top of each other or a simple single lens. It will be hard to tell so look closely. If its two they are using a two element achromat condenser if not its a simple single element condenser.

Hmmmm... upon closer inspection - my ground glass/focusing screen must be a fresnel... because it magnifies as I move it closer and farther away from a subject... but its just very very very fine. I can't see the rings at all, even under magnification. It appears (can hardly tell - even under magnification) that the back of the fresnel has a sort of 'ground glass' finish. (plastic)

And as I look at the shapes of these things, I'm almost positive the condenser was on the lens side. with the 'ground glass' pressed against it, leaving the fresnel side of the focus screen pressed right up against the entrace plate of the prism. (It all seems to 'fit' together this way)... When I hold it all together and put my 35mm slr lens in front of it at the right distance... even with no light baffling, it completely and evenly fills the viewfinder with no obvious vignetting.

The condenser to the best of my magnified attempts appears to be a single element. Must not be an achromat.

(heh, Brett, I see you're awake on the CML threads too...)

See now we are back to what I was talking about before - the apparent fact that SLR's use BOTH a condenser AND a fresnel. We need to confirm the proper order of them including the GG. Once we have that its a matter of replacing the fresnel with the same power condenser. From what I've seen SLR viewfinders have a single piece of plastic (or glass) that has a very fine fresnel pattern pointing towards the 35mm lens and the ground glass texture on the otherside. Following that is a condenser lens.

A field lens with sufficient power to bend the edge rays into the DV cam lens results in a lens with great curvature.

Not only will a lens with such a short radius of curvature produce:
- a viewed image with unacceptable pincushion distortion
- a large amount of chromic aberrations.

Two thin lenses in series will give the same power as the thick lens with great curvature.
But each of the two lenses have less curvature, thereby greatly reducing the pincushion distortion and chromic aberrations.
But for a camera it has the disadvantage of taking up space, making the camera larger.
Camera designers realized that what they needed was a very thin lens with reasonable power.
Fortunately, such a device was available: The Fresnel Lens.


But are we really concerned by space problems here with this adapor...i don't think so...



http://topcontechnotes.home.att.net/viewingsystem/page5.html

http://www-optics.unine.ch/education/optics_tutorials/field_lens.html

What about using white frost lamp effect filter material. The stuff they hang in front of film lights to defuse it? This material is cheap in small amounts, durable and grainless.

Just an idea.

Great ideas here.

DK

a freasnel would be fine to use in the adapter, there are fresnels available that have rings fine enough that there's no way the dv's ccd would pick them up, but you need to combine a condenser WITH a fresnel, like this http://topcontechnotes.home.att.net/...tem/page6.html

<<<-- Originally posted by Daniel Kohl : What about using white frost lamp effect filter material. -->>>

I tryed with that. when you zoom in to find appropriate picture - the grain is visible. i checked different types, but the grain is always visible. the good side is that is very equally placed. so, maybe someone will like it.

filip