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Old February 18th, 2004, 08:28 PM   #196
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aspherical lenses

The ever present and 'expensive-but-worth-it' Edmund Optics (no association) carries them (as well as just about anything else you'd ever want for lenses, mounting, focus tubes, etc... as long as you have money to burn).

http://www.edmundoptics.com/IOD/Disp...productid=2454

I've also seen here and there odd little things on ebay that might do... its always hard to tell. Here's an example:

http://cgi.ebay.com/ws/eBayISAPI.dll...category=30059

I could swear that in reading specs for one of the higher-end dv camcorders... that's it: the Sony DCR-VX2100 describes itself as having:
"Aspherical Ground Glass 58mm Lens: Larger diameter allows more light to strike the Advanced HAD™ CCD imagers for greater detail and clarity, while the aspherical lens reduces optical distortion, and provide better corner-to-corner focus." Not sure where the aspherical ground glass lens is positioned in the mechanism. I'd think the condensor would be placed right up against the ccd, but I don't see why they'd need ground glass at that point as the collimated image would just project right onto the imagers. Like I said, I'm new to this, just reading.

Usual disclaimers apply - just throwing out info I thought was interesting. Take it or leave it :)
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Old February 18th, 2004, 11:37 PM   #197
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xl1 version aldu35

Eric,
As for what i've discovered with the xl1s. there is some good news and bad news as far as converting this aldu35 version. i'm close to finishing the agus35 rotating gg version and am trying to take my lessons and move forward on a static aldu35 version very soon, as i think it will be more efficent in the long run. the good news is once a version for the xl1 is done it will work well because of it's low light sensitivity, you can also flip the viewfinder to right side the image by just unbolting and flipping to the other side. it's a bit awkward at first but your finally able to see the controls better. and the final reason, because the lens adapter will fit nicely along the xl1 body, as it's made for lens change outs as you know.

on the neg side, it will be a bit more costly because it doesn't have a built in lens to act as a relay lens and you'll want to move from the canon lenses and shift to nikon because they are abundant, cheap and fast. first things first you may want to consider, picking up a canon to nikon adapter. i found a relatively cheap one at www.lesbocher.com, in england, for 180.00 USD (only 100 pounds for them), a nikon/nikkor lens $25-$200(right now i'm using a 55mm f1.2 Nikkor-but there could be better-i don't think the mm make too much of a difference because the ccds shoot straight regardless), a +10 macro close-up lens $30 (this i am not sure about but i'll keep the group posted once i have the magic formula-as i am still having problems), your pipe extension-50¢ worth of 2inch pvc, your gg- another $30 or so, another pipe extension-another 50¢ worth of 2inch pvc, a plain nikon lens connector - $30, attached to the pipe and out to your nikon lens of choice $25-$200. i'm kinda guestimating on the cost, but there is also going to be much effort in there as well...

that's kind of my blueprint i'm aiming for now, as everyone says, it's a lot of testing and perfecting as well as trying to discover new optical tricks and technics. stay tuned....
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Old February 18th, 2004, 11:53 PM   #198
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almost done with my Static35, but I keep getting a hotspot in the center of the gg, I installed a fresnel but it only helped slightly. Im using a 50mm Olympus OM.

How do I get rid of the hotspot? More grinding? or less?

oh yea, im using a glass Skylight filter, ground with 1000 grit alum oxide, and I gotta tell ya it looks great, except for the hotspot!
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Old February 19th, 2004, 01:03 AM   #199
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John RMPP. Dont use fresnels. In Normal SLR viewing system theres a fresnel and a condenser. SLR's need one to solve the hot spot problem and use both for achromatic abberation reasons. Replace fresnel with same power condenser lens.

When you RMPP you will find out what condensers are exactly doing for you and why you cant just grab any old condenser or fresnel (ie cheap ruler with fresnel magnifing glass) and expect it to work. Not only should you not use a fresnel in the first place but my guess is that your not using one from a camera and thus its probably the wrong power. Its not just plug and play. Were are dealing with optics here not legos. Learning the basic of light and lenses will end up saving you alot of money, time and make your adapter better than the rest out there.
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Old February 19th, 2004, 09:05 AM   #200
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Fresnels, Asphericals and Achromatic Distortion

So to summarize Brett's previous (it's way back there... somewhere):

Condenser lenses and fresnel lenses do the same thing. They 'collimate' light, which means that light comes in one side from a whole bunch of different angles, but leaves the other side parallel. This helps for our purposes, because we want the image to focus from the 35mm lens onto our hard-earned ground glass in a completely flat and even plane of light.

The difference between a condensor and a fresnel is the shape. A condenser lens (also called an aspherical lens) is like a normal lens which has been cut in half and you throw away one side: it's rounded on one side and flat on the other.

A fresnel isn't much of a 'lens' at all, but a sheet. It's almost like a 'collapsed-telescope' version of a condenser lens - giving you (just like a collapsed telescope) a set of rings inside one another, flattened to a plane.

Unfortunately, where the 'cuts' are, you can see visible affects to the light. This is why a true condenser will give a better result than a fresnel, unless its just a camera viewfinder and not the 'actual image.' Fresnels are often used in the viewfinder of cameras, but never in the actual optics which hit the film.

Both condensors and fresnels, however, reducing or eliminate optical distortion: in which the center of the image is sharp and bright, but the corners are fuzzier and darker. The 'hotspot' is a perfect example of optical distortion.

Achromatic distortion, is less a factor of the shape, and more a factor of the glass quality itself. Achromatic distortion happens when the glass doesn't transmit all color spectrums equally, which puts the focal points for different colors at different locations. This has the troubling effect of causing the image to look slightly colored, because some of the color spectrum is out of focus at your chosen focal point. If you're experiencing this, the shape of the lense won't help, you'll need a higher quality lens. And when I use the word 'lens' I really mean any of the glass through which the light is passing. It could be the 35mm lens (unlikely), the condensor or fresnel, any prisms that may be involved, or (unlikely) your built-in camcorder lens.
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Old February 19th, 2004, 10:03 AM   #201
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Jonathon:

Thanks for your explanation.

There's a new short film made with a static solution, and it's found here.

It's a big d/l at 52mb, but it goes a long way to demonstrate what the visuals can be like. Shot with the PAL GL-2 (XM-2).

Here are stills.

The two most notable issues in the short are dust and a minor case of "blooming" in some of the shots (or, "hot spot" as it's being called.)

I'm hoping to make mine this coming week -- I've got all sorts of parts on order. Yesterday, at Home Depot, I found 2" plumbing couplers that are thick PVC, and pressure fit over the Century Optics achromatic diopter perfectly, so perfectly, in fact, that I doubt I'll need some sort of secondary clasp/support system to hold the adapter up and on.

The hot-spot issue will be an interesting challenge :/ Keep us all posted on your progress (this is directed at everyone, BTW), and I'll be sure to do the same.


edit: I've just put up this revised tutorial on building a static solution. It's incomplete, but I'm sure you could infer the rest of the steps necessary. I'll put pics up of the finished product once my new F-mount arrives.

Thanks,

- jim
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Old February 19th, 2004, 02:46 PM   #202
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Johnathan thanks for explaining what I've grown tired of repeating over and over and over. You can do a search for anyones past post guys. Anyways I would like to add something that you didnt touch on. As you know we need achromat macros for this project. And as you also know achromats are two elements commercially cemented together to correct for chroma aberrations. Well guess what. Condensers need the same help. You need TWO condensers to fix the chroma aberration problem at the condenser stage. In a SLR viewfinder they do this by having a fresnel AND a condenser. For our purposes we need to find the curvature/power of that fresnel lens and match it with a replacing condenser lens. You keep the other condeser and use it as the second. Done. BTW the reason why they didnt use two fresnels in SLR's instead...? Moire'

-B
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Old February 19th, 2004, 08:23 PM   #203
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here is some pics of my Alain35-Static solution. Its made of a 1-1/2" plumbing Union. I did have to put it on a lathe to make it all fit. Its very strong and tight and is a great solution for the body, the GG is a Skylight filter ground down w/1000 Alum Oxide. Im still trying to solve my Blooming/hotspot problem.

Here are some pics:

Body http://aequantum.com/del2.JPG
innards http://aequantum.com/del1.JPG

stills:
Alain35 image http://aequantum.com/test23.jpg dirty GG and low light, also zoomed in 2x due to hotspot
regular video http://aequantum.com/test24.jpg
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Old February 19th, 2004, 08:54 PM   #204
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John Gaspain

Good , I am happy to see the work of somebody else.

What did you use for Achromatic Diopter?

Alain
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Old February 19th, 2004, 09:23 PM   #205
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I took apart a $25 Sima .5 Wideangle lens, and used the first lens which happens to be a achromatic/macro lens.
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Old February 19th, 2004, 09:48 PM   #206
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Interesting read

Nice work, John. These models are getting nicer and nicer...

I came across this interesting article which you all may find interesting. It's more aimed at the 'viewing/focusing screens' in cameras which use a fresnel and ground glass. The one point which I picked up which I hadn't yet gathered here, is to be sure and insert the ground glass with the textured side away from the camcorder lens and toward the 35mm lens. Then any fresnel (not) or condenser (yes) would be pressed right up against the ground glass - right on the textured face. In the event of a fresnel, as described in this article, you put the textured side of the fresnel right up against the textured side of the ground glass. This creates a single focusing plane right where the two textured surfaces meet. Perhaps a no-op because I won't be using a fresnel... but anyway. Read and enjoy, if you like...

http://www.wisner.com/viewing.htm

Brett - Yes, I've been looking at lots of diagrams which all have two condensers, one on either side of the focusing plane (which is actually a reticle in many of the diagrams I've seen). So that makes sense... However - doesn't our diopter somewhat fulfill the role of the second condensor, or am I losing it?
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Old February 20th, 2004, 02:01 AM   #207
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jonathon- You bring up a good point because I too have seen the two condensers split and placed on both sides of the ground glass. You would think you would need to keep them together in order for them to work together on correcting the chroma aberration. I'll look into why they have it setup this way.
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Old February 20th, 2004, 02:43 AM   #208
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so it goes:

slr lense < spacer < condenser < ground glass (set at proper focal flange distance) < spacer < macro adapter of +7 or greater power < dv cam.

How do you figure out what the proper condenser for your situation is? I read through the posts but couldn't figure that part out.
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Old February 20th, 2004, 03:35 AM   #209
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Your ordering looks right to me.

From my understanding, the working models that Alain and John have built don't have the condensor. They both show images that look awfully good, but still exhibit varying degress of a little darkening and fuzziness of the corners and/or a hotspot in the center. Some believe this to be 'spherical abberation.' There has been a lot of information indicating that condensor(s) are a way to help with this. However, I'm unsure at this point the exact implementation of it - whether you just need one on the SLR side of the ground glass, or if you need a second one facing the opposite way on the other side of the glass. Also unknown is whether the condensor changes the focal flange distance from the SLR in any way. (I would think not). Hard to say. We'll just have to experiment a bit or read some more.

I'm still collecting basic parts, so far - have SLR lens(es) and my SLR lens mount point, built like Alain on the little plastic protective cap they give you for the backs of your unused lenses. I'm off to the Hardware Store for some kind of piping tomorrow - and need to get my hands on the grit for grinding... and glass blanks, and condensors... and ... well - they say "Patience is a Virtue."

Did some yucky first tests with, get this: a cardboard tube cut to focal flange distance - some of that 'satin' scotch tape on a skylight filter as crummy replacement for ground glass... Pretty gross, but enough to prove that the concept will work with my lenses/camcorder. :) Enough to justify spending some money for better parts. Also enough to learn that the upside down image is a pain in the neck... Any agreement on a 'best' solution for that?
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Old February 20th, 2004, 03:37 AM   #210
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Has anyone considered using a Kodak Ektanar lens from a 35mm slide projector? You can find these on ebay for under $50. You'd just need a mitre box and a hack saw to cut off the extented length on the back.

This may work for smaller cameras but I doubt for cameras with larger lenses.

I was reading this article:
http://www.rit.edu/~andpph/text-agfa-1280.html

Where the guy is talking about making a slide copy stand for his digicam and using the Ektanar lenses as his macro lens because of the higher quality. I have one of these lenses and tested it out with my digicam and indeed he is right the image is nicely sharp and appears correct. But I didn't go hacking away at my lens yet. I'm still using my two tiffen screw on macros for the DV cam.

I think the condenser lens issue is the biggest one right now. All of our test footage has the same flaws (uneven exposure over the film plane). I found a condenser or what I think is a condenser in the back of my Kodak slide projector and tried that out. It improved it but only by a fraction and it curved the edges of my subject. What do they call that? So I think Brett is right we need two condensers. Then again I may not have actually had a condenser I was testing.
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