Tavis Shaver,

What a great link. For anyone interested in this subject the whole site should be required reading.

Starting at: http://topcontechnotes.home.att.net/viewingsystem/page3.html

all the way to page 16.

Paul
dvdof.com

<<<-- A fresnel 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, ... -->>>

This solution was chosen only for a matter of size...
2 low power condensers are better then one of high power to avoid spherical distortion.
And when u REALLY need space u can replace one condenser by a fresnel...but optically the fresnel MUST not be used in a system dedicated to record a sharp image...

is space really a limiting parameter in our equation?

what about coating some stuf on a regular glass.
For example if you already have used cyanoacrylate (instant glue) on glass, there is always a white haze around the glued parts.
You can try to heat some of this glue under a glass.
They do this for looking at fingerprint on glass.
<b>Caution: cyanoacrylate contains cyanure (lethal gaz), so it is good to take care of doing this outside and not let the gaz reach your skin, eyes or lungs.</b>

Alternatives to GG
 

Giroud-
Your talking about a similar technique as a product called a "Bosscreen". They are 4X5 and 8X10 focusing screens that are grainless. They achieve this buy melting and then hardening a very thin layer of wax sandwiched between to flat clear pieces of glass. The results are amazing!

Heres the bad news. Its going to be nearly impossible to not only find the ideal thickness of the layer of wax to use but having it lay down completely flat and even is a real feat that may only be possible by a commercially machined process. The other thing that there is a chance that Bosscreens will melt and be destroyed on a hot day. And dont even think about cutting down a commercially made one to size for the same reason. They are expensive too.

One interesting note though. Bosscreens advertise their product as having a microcrystaline layer (the wax). I know another company that says the same about their product...Movietube.

Good luck.

Just got off the phone with a highly recomended camera repair man. He confirmed that there is both a fresnel AND a condenser lens in a SLR as shown before here:

http://topcontechnotes.home.att.net/viewingsystem/page6.html

He also confirmed that without one of the two you will have chromatic abberation problems.

Bottom line is we are back to my idea of finding a replacement condenser lens for the fresnel and having two condensers working together to make a achromat field lens. This way we wont have any "pincushion" (barrel) distortion or chromatic abberation. Damn I wish we could of K.I.S.S. but that would be S.

-B

Thoughts on 'correct' grit size
 

Hey you glass grinders!

Those of you that chose to go with the 1000 grit - did you like the results? I've heard of people using 320, 600 and 1000. There was some speculation at some point that there was a point where you've gone 'too' fine and would start to lose the diffusive properties... You can go finer that 1000 grit Aluminum Oxide as well, wondering what the pros and cons of finer and finer grit are...

Any comments from the polishing among you?

Jonathon
 

I have mine done whit 9Y (9 micro bryte capsule) that is a bit smaller than 1000 and it's ok ,but after that ,there is something call Red pollishing that I have try ,but then I start losing the diffuse properties and I start to see thrue it , so ,no good.In fact it can reduce the grain more but I was not able to control the grinding enought so I start having some tranparent spot and this apend just in couple of second.

Alain

I did mine w/ 1000 alum ox, I just did a quick 1hr grind which I should do another 1hr final grind.

here is a pic, look at the top pic- notice a very small amount of grain in the edges where the light is less strong. I will do a final grind shortly to clean it up but overall I am pleased with the results of 1000.

http://aequantum.com/fresnel.jpg

Alright, here's a dumb question for Alain (or anyone with the answer):

I've got a Tiffen UV filter here and it has on both sides a raised ridge at the edge. How, if I'm supposed to have a piece of glass as my grinding implement, do I make contact with the UV filter's surface with the grit and the grinding tool?

My piece of grinding glass exceeds the diameter of the filter, and so the ridge prevents the two pieces of glass from touching. Did you use a smaller piece of glass to do your grinding? Or, did you remove the filter from its mounting ring? (and if so, how?)

Thanks...

- jim

yet another question about ground glass...

Is there anybody who really tried an holographic diffuser....
Theoretically they make the post condenser useless...

anybody with real tests?

thanks

Hi Jim
 

1-Shure you have to remove the glass from the ring.

2-That's why you have to start whit bigger grain , to make the surface of the glass even .Sometime you could put a bit of pressure in the center but not much.

That's the reason why you need two pieces of glass plus your filter, you grind on one for a time and then you change for the other one .Otherwise the surface of the glass you'r using for grinding start to become uneven .(concave)

Hope you understand, I am missing some english word to explain it more clearly.

By the way I whil send you some new image in 1 hrs.

Alain

Jim I was thinking of using the same thing - uv filter on a ring.

Here is what I was thinking of doing:
Get a small round mirror from a craft store, a small suction cup like one from a child’s toy dart, attach a shaft to the suction cup, the cup to the backside of the mirror and the shaft to a dremel, then buff away.

I have not done this yet, but that is my plan. Although I may have a hard time keeping it even.

Move the filter, not the tool
 

Hmmmm - I've always understood the grinding process as this (and I think this is what Alain is describing).

Take a large piece of glass - say 8x10. Put it down flat on a clean work area. Put your grit mixture onto this and smooth it out a bit. Then you take the glass from the UV filter (or whatever your real ground glass is going to be) and put it down on this 8x10. Space your fingers out evenly across the back of the filter and work it in circular motions on the much larger piece of glass. So you're moving the UV filter across some larger piece of glass... not putting some tool to the stationary uv filter.

This is what Alain means... after a while, the area of the 8x10 will get ground in under the pressure from your filter, and you either have to move to a different spot or get a different piece of glass

Alain: how did you remove the filter from the ring?

In your original image of the ground glass -- the close-up -- it's still in the ring after being ground. I'm confused :/

- jim

In order to remove it, you must have one of the filters that has a 'retaining ring' (not all do... my Hoya is completely unopenable). If it has a retaining ring, you'll usually see two slots across from one another on one side of the filter. You use something called a 'span wrench' which is like a double-headed screwdriver which stretches across the filter and when its in the slots, you turn it, lifting out the retaining ring.

Jim
 

Yes ,because I put it back on the ring so I can use it to screw on my other parts.
My adapter is made from aluminium tubing that screw on each other

Normaly the tiffen filter have a ring that you unscrew to remove the glass, but take care they are somtime hard to remove.Take care to not scracth you glass and not to scrap the screw or (filets in french)


Jonathon
That's it . But I normaly change from one glass to the other every
5 to 10 min.

Alain

Filter Removal
 

Jim, most of the filters I've seen have an inner ring that needs to be unscrewed from the outer ring, thus releasing the filter. Professionals use a spanner wrench to do it:

http://www.edmundoptics.com/IOD/DisplayProduct.cfm?productid=1457

Expensive stuff... Look at their Instruction Sheet )PDF file), you may want to make one...

P.S. You guys type too fast, I'm always late with my replies :).

Alain, what kind (size, source?) of tubing are you using? I'm still playing with PVC...

I have remove it whit a small screwdriver but whit precaution.
hold your filter whit something realy steady ,like a vice ,and that's it

Alain

Damn, this is an annoying detail I wish was included earlier.

My filter has these two notches seated opposite of eachother, so I'm assuming this is a retainer ring filter. The thing doesn't want to budge, though :/

edit: nevermind

- jim

---Alain, what kind (size, source?) of tubing are you using? I'm still playing with PVC...


I have use part's of len's that I have unmount to make my adapter.

I keep everything,and turn it to something else. :-)

Alain

theory to thoughts...
 

i'm just amazed at how addictive this project is for everyone. we are discussing lot's of different issues at once, it's crazy and great at the same time...

so here is what i've figured out so far... ideally you WILL affect the image quality using a FRESNEL lens, so optimally you want to go with a cheap and better CONDENSOR LENS like here, http://www.edmundoptics.com//IOD/DisplayProduct.cfm?productid=2032

secondly, you can use a GROUND GLASS or as a better quality alternative a HOLOGRAPHIC DIFFUSER-but they are expensive, unless your on the Euro...

so far the K.I.S.S. (keep it simple stupid) seems to be the ideal configuration, which goes as such for a standard DV cam:

PRIMARY LENS+spacer+GROUND GLASS or HOLOGRAPHIC DIFFUSER + CONDENSOR LENS+spacer+[if you need a +7 or greater macro]=mounted to the DV lens

at this moment i'm crawling up the walls trying to figure out a better method for xl1/xl1s version as it seems a bit tricker-you can almost put a lens right up to the CCDs themselves-so this creates much more complex optical arrangement that needs to be optimized.

comments, thoughts, quips?

back to work...
-D

Condenser Lens Specs?
 

Hey All,
This thread is amazing! I stumbled onto it accidentally and haven’t been able to leave it alone. I started building my Agus 35 when I found the separate Alain 35 thread and so I’m building both simultaneously. I’m at the point where I now need to install a condenser lens to help with the hot spot in the middle of the image. My first question is, what are the condenser lens specs others have used? Does it depend on my choice of SLR lens or are all of you using the same condenser lens? I followed the link to the Edmunds optics condensers but I have no idea which lens is right. I read in a thread earlier that a condenser from an old slide projector might work. Has anyone tried that?
Second, does the condenser lens really go between the GG and the camcorder’s lens? You are still focusing on the GG with the camcorder lens, right? So you focus through the condenser lens? This doesn’t make sense to me as I guessed that the condenser would spread the light more evenly across the GG as it does with a slide projector. Can anyone set me straight on this? You all are amazing. Thanks for a totally entertaining project.
Oh, BTW, can anyone provide a link on more info about the Hollographic Diffuser mentioned by Dino in the previous post?
Joe Holt

http://www.edmundoptics.com/IOD/Disp...productid=1363

That's Edmund's holographic diffusers - pretty expensive. In general, I've found most things available at Edmunds for up to 75% less in other places. Holographic diffusers, unfortunately, are not one of those items I've found anywhere else :-(

I've learned some interesting things messing around with the optics removed from my 35mm SLR.

All of the optics involved (other than the objective lens) are rectangular and exactly 36mm x 24mm -- the size of a 35mm film negative.

However, the round objective lens definitely 'sees' a circle - which is significantly larger than the 36mmx24mm footprint.

One thing I've noticed about my rectangular optics is that they seem to be completely covered, evenly, with image. I can't help but wonder if some of the corner distortion others have seen comes from not zooming in quite enough. With a circular image on a ground glass, I would think it would be hard to gauge where the 'true' 36x24 frame lies...

An Agus builder could theoretically draw a 36mmx24mm rectangle right onto the ground glass - and focus their camcorder on this rectangle. I'd bet they would find significantly less distortion within the boundaries of this frame (especially with a condensor or two). Alternatively (if you didn't want to mark up your hard-earned ground glass), you could insert another piece of glass with the marked frame.

Here's an (unfinished) article on the cropping I'm talking about... be sure to read pages one and two - the cropping is shown on the second page...

http://www.digitaldingus.com/articles/fov/fov.html

Nice article, Jonathon! Pardon my ignorance, but is having a 36X24mm GG image a kind of a 'Holy Grail' concept that cannot be altered? What if it's slightly smaller? Just wondering...

Anyway, to zoom in to the correct size (let's say 36X24), you can print a 36X24 square in a circle on a transparency sheet, and stick it right after the GG. Remove after zooming.

About Holo diffusers: well, I've tried them last night. Don't ask how I got them, that's a whole other story... I had 3 samples to play with, 5deg, 20deg, and 60deg diffusion angle:

1. 5deg is the brightest, but exibits a strong halo, and the texture is too rough for the DV lens not to notice. With the SLR lens fully open at 2.8, the out-of-focus objects looked like they have 'crawling ants' all around their edges. This could be also a 'feature' of my crap Sony PC100.

2. 20deg is OK, but just OK. Somewhat smallish halo is visible, but if you don't mind zooming in a bit, could be OK. Still, I think it would require a field lens. The results are NOTHING compared to what Alain had produced with his finely ground GG. With my camera (1/4.7 CCD size, what a joke!), you get a lot of digital noise.

3. 60deg is way too dark to be of any use. So dark, in fact, I couldn't even get a focus (manual, of course!).

After this fiasco, I started thinking: if Halo diffusers are so great, how come no manufacturer uses them for typical photo applications as a GG replacement? I'm sure they could spare $100 or so for a quick test :D

Bottom line: I think Alain's solution (lots of elbow grease) is the one. Unless, of course, we get hold of the supplier of this magic 'crystalline wax'. Since I'm lazy, I had high hopes for Holo diffusers, but...

Wow - good info on the holos... we'll all just assume that they "fell off the back of a truck." You make a good point about the photo applications not using them - and sticking with the tried-and-true ground glass. Once again, Alain finds the best solution first shot out of the gate, and then we all run around with our heads cut off trying other things only to learn he had it from the beginning :)

I certainly don't think that the 36x24 gg image is a holy grail. You can certainly focus your entire image on any size ground glass you can get and focus in to wherever you'd like. I just thought it was an interesting point of reference as 35mm cameras certainly are aimed at this size, so their focusing systems (mainly the viewfinder focusing system) would be aimed at minimizing optical distortion only to this size... not the entire circle. It would seem like we'd be pushing our luck to expect no optical distortion outside of this frame.

Speaking of focusing - this is another area of concern for me. Since our cams will be hard-focused to the ground glass, all of the actual image focusing will be done manually with the 35mm lens. I, for one, put little faith in the ability to consistently get good focus on my crappy (and at the moment, inverted) viewfinder. It is common practice in medium format photography to have a ground-glass 'focusing screen' which the photographer actually scopes with a magnified loupe to inspect for focus. There has also been specialized focusing screens that either line up two lines or their color evens out when in focus - a number of tricks which make focusing much more quantitative - less subjective. Given our manual focus situation, it'd be interesting to see what ideas might pop up for some kind of magnified or non-visual focusing systems.

I certainly noticed that much of the example footage I saw on the original thread had some pretty serious focus issues. If anyone ever intends to blow any of these shots up for projection, they'd better figure out how to have some hard focus :)

I agree with the focus issue and the first thing that poped in my head was the idea of taking the focusing aid circle, that you see often in the middle SLR viewfinders, and off setting it to the very top or bottom of the screen where it would hide behind the area where black letterbox lines normally are. You cant have the circle in the middle because it will ruin all your shots and since alot of us already shoot 4:3 and add our letterboxing in post anyways we would have the best of both worlds. Just a quick idea. I'll give it more thought.

Excellent idea... I wonder if we could stretch your idea even slightly more and place the focusing circle (I've got one from the SLR I just trashed for parts...) just outside the full 4:3 frame. One could zoom out with the camcorder and set the focus, then zoom back into the full frame. If you were good, you could use this technique multiple times to set a few focus marks somewhere on the 35mm lens for a follow focus shot... Of course, if the circle were in the shot the whole time, you could just keep your eye on it. Who needs 4:3 anyway ;)

microcrystalline focus screens & Hol diff's
 

http://www.stabitech.nl/Bosscreen.htm#top

The manufacturer was not easy to find, it took a bit of Sherlock Holmes-ing, but got there in the end!

They're expensive, (120 euro for a 6x6) - but hey, they have all the right properties,

- excellent light tranmission
- no hot spots
- good dynamic range
- no grain

You can specify no markings, however I would recommend asking for a 36x24mm frame guide to be printed in the middle.
They take around a week to make, and the company is based in Holland.

Ive persoanlly tried commercial fine GG, (6 micron), Holo diff, Opal Diff. The best out of these is by far the Hol diff, but as someone else noted, they don't transmit nearly as much light as GG.
Not tried Bosscreen yet, but contemplating it...

great article...
 

jonathan, great article on Field of View (FOV) effect it's VERY relevant to us XL1/XL1s guys. i also believe there may still be something in Halo Diffusers, and i know they come in a large variety of degrees (5, 10, 20, 30, 60, 80), but that requires testing. if anyone is interested, you can try going to www.poc.com, they will send out FREE samples of their goods to ONLY to "engineers" and "researchers," in, just by coincidence, 2"x2" diameters(!).

I suggest any "engineers" and "researchers" out there might inquire with them... ;)

onward,
D

Alain's got new footage and pics he'd like to share:

Footage

Pic 1

Pic 2

- jim

Ah.... isn't a little less DoF wonderful :)

Nice Alain. What's the music?

strangely, in the scene of the window with the red brick wall, there is some stuff in the top right corner that moves very fast like some spots on a 8mm movie.
amazing, no vignetting...
what kind of gg are you using ? is it moving ?

Looks great Alain, how did you get around the vignette?

Thank's again Jim.

Jonathon, I did the sound track.


Francois,( there is some stuff in the top right corner that moves very fast )
This is some drop of melting snow falling from the roof.Here the spring is comming. :-)
The gg is static , from alu oxyde 9Y( 9 micro Bryte capsule) it's a bit smaller than 1000 grit.

John ,(how did you get around the vignette) One condenser.

Alain

Bosscreens
 

Simon- Thanks for the link to the Bosscreens. For the longest time I wasnt able to find them in anything smalled than 4 X 5 with gridlines so I didnt plan on using them. But with this new info the plain 60mm X 60mm sounds very interesting to me and it looks like custom sizes can be made (at a price). As far as putting the 36mm by 24mm markings I can fully understand why you would want to do that but personally I would just leave it blank which opens me up to using medium format lenses as well. Another advantage is the ability to zoom back alittle with the video camera's lens which will give me the choice of having or not having some very beautiful vignettes. Now that they seem more practical for our designs Im going to go check one out first hand at a local camera store. The claim that these screens dont need a fresnel and at the same time are very bright seems to defy the laws of light and optics so I'll be checking on that and just how grainless these screens are. I've always thought that they relatively expensive but if this gets the job done right then thats what I'll do. Too bad we'll have to baby these screens on hot days because after all they are going to be sealed inside a flat black tube.

-B

Alain with that last video did you check to see that you were shooting a 36mm X 24mm frame?

Also when you say you used a single condenser is it a achromat? What camera did you get it out of?

Brett, for what its worth, I was reading a medium-format camera forum the other day (can't remember where it was), and they were debating the value of Bosscreens as focusing screens. Someone brought up the same issues about heat and possible damage (having heard that it can happen), but about 4 people immediately chimed in just after that, saying that they'd used them for a long time, never with any problems...

Bosscreens
 

Thanks John. Yeah I read the same forum (photo.net). It does seem a bit unlikely under normal use but you have to remember that on Medium and Large format camera the ground glass is mounted at the end of the camera and not trapped inside of a back tube thats likely to get alot hotter.