the bosscreen did reduce the light that much, but I think I can reduce this an the vignetting by usung a fresnel or a condensor behind it.
The groundglass was a mediumformat gg from Mamyia, the markers on it where removeable with aceton. It isn't as fine as your self grided may be, but at this big size it really doesn't matter. Remember the gg is 6x6cm!

dietmar

<<<-- Originally posted by Bob Hart : Obin

Sanding off the top layer. That option works fine except for the disk having a green tint which has to be manually white-balanced out. Not a big deal but it is there.

Pat.


it's not green it's clear

Hello all...

I'm just popping my head in here to note a finished adapter that works very well.

I did a tutorial on building the Agus35 originally, and then followed it up with an Aldu35 tutorial shortly thereafter, and then got submerged in life's distractions and demands. I finished the adapter recently and took it to NYC for some random tests.

Here are the images (http://ideaspora.net/aldu35/images/screengrabs/). I'm currently working on encoding some footage as well.

This adapter is built from instructions in this tutorial (http://ideaspora.net/aldu35), for the GL-1. It's not the cheapest adapter, but it is simple and effective. The only notable exception to the instructions -- as they currently stand -- is that in the most recent iteration I ground one side of the GG by moving the GG ontop of the grinding glass, instead of the other way around. By doing so, it was easier to ensure that the side that was to remain free of scratches would do so.

The main problems I'm having to overcome now surround keeping dust off the elements, and keeping my shots steady while pulling focus handheld. I sometimes worry that spray paint might be flaking off the interior and settling on the glass -- in the future, I'm going to see if I can dye the plastic of the PVC tube instead of painting it.

When proper time and care is given to callibrating the adapter I've built, there's no vingetting/blooming of the image. I don't use any condensor lenses, and attribute the image quality of my adapter largely to the use of the Century Optics achromat.

I've taken note of James Ball's acid-etching instructions and have ordered etching cream -- thanks for the extensive notes, James. As it stands I'm not sure if I do or don't like the grain I see in footage, but there's always room for improvement and it's nice to have a choice.

Thanks for everyone's who has been contributing!

Anyone know what's up with Agus these days? He had stills back in the day from a short using his adapter that I've wanted to see...

- jim

Obin

Good news if there are clear ones around. Could you advise which brand of CD-R it was.

not sure jsut some random disk at work :) I will look today and tell you

Bob the color in many CDR discs is from the foil on the top. You are grinding the top off anyway; therefore you will end up with a clear disc.

Yes, John that is/was the deal with mine

<<<-- Originally posted by Obin Olson : FYI I just took a normal cd-r NOT the spacer type and sanded the top layer off...now it's a better then spacer-type GG because the cd-r is a higher quality then the cd-r spacer! I took my small orbit sander and did away with the top coating..works great -->>>

I got a cheap obital sander some time ago for this pupose too (only about $10US) but have yet to get around to it. How much better is it than hand grinding, or chemical etching?

It's not better than grinding with AOx -- I don't understand why people are regressing to the original project -- the results simply aren't there.

I've got an original Agus35 that hasn't left the shelf since I made the static solution pioneered by Aldus -- and while it's a nice relic, and has some aesthetic potential, the investment needed to get it working properly outweighs the benefits.

- jim

Jim you really have to change your tutorial to say "grind only ONE side of the UV filter's glass" not BOTH. If they do both they are sure to have very soft images. Not to mention it take twice as long to gind both sides. I only mention it because I know you agree but havent changed the tutorial yet.

Actually, Brett, quoting the tutorial:

You may find it to your benefit to cover one side of your filter with strips of scotch tape in order to avoid scratching, while still allowing you to see through it completely. Ideally, you're going to want to frost only one side of the glass, but if you scratch both sides, grinding them until they're uniformly frosted will be your only recourse.

I've since placed some emphasis on this part of the tutorial, but it's been there for a while now.

In the future, once I get the time to grab more shots of myself grinding, I will change this area of the tutorial to demonstrate grinding by moving the GG over the grinding glass, rather than how it's currently demonstrated...in this way I found it easy to keep one side free of accidental scratches.

Still waiting on my etching cream :D

- jim

Hi all,

I've been reading this forum with great interest for the past few weeks. While I start putting together the components for an Aldu35, I'm also waiting for the design to "settle".

I'd like to help out, so I've done a little more research into optics and home-made cameras and have dug up some useful stuff, I believe. (It's hard to read every post, so apologies for repeating and any wheel re-inventing).

I think it's also important to start identifying the trade-offs so we can make our own choices and learn how to better use the adapter. There are LOTS, especially with regard to:

Peripheral Illumination Loss
=================

After reading up, I'm learning that there are a lot of sources for the loss around the edges. Please correct/add on to these.

a) angle of view
Your choice of lens might contribute to this problem. The wider the angle of lens you mount, the greater the light loss on the periphery relative to the center. No escaping this because it's physics. Unfortunately, choosing a longer lens means losing a few stops.

b) aperture setting
At f2.8, the illumination at the edge of a 35mm image is 40% less bright than the center. At f8, the image edges are 90% as bright. By keeping our lenses wide open, we'll get more light onto the GG but we'll contribute to periphery loss. (I'm guessing this is also why people have reduced peripheral vision at night.)

c) coarseness of GG
Hand-made camera makers seem to find that, all other things being equal, the coarser the GG (ie, less scattering) the brighter it is; however, the more the edges of it will be dimmer compared with the center. Everyone here seems to be going for a fine grain, which helps keeps the GG evenly but not as bright overall, which causes us to want to open up the 35mm lens as much as possible, which contributes to light uneveness! Ugghh!

d) off-axis condenser mounting
This is the principle behind those traffic lights you can only see straight on. If you mount a condenser and it's not right on the optical axis of the adapter, you'll make a real mess around the edges of your images.

e) mis-specified condenser lens
Condensers can sometimes contribute to peripheral illumination loss. There are at least three ways: the wrong focal length, wrong position and/or the wrong orientation. More in the next section.

Condenser Lens Issues
==============

Whether or not to put in a condenser has been debated quite a bit. I'm putting myself in the must-have-condenser camp. I found this to be a really good discussion of condenser/fresnel issues for home-made medium-format camera makers: http://medfmt.8k.com/bronfresnel.html

a) focal length of condenser
Hand-made box-camera makers (who place a GG as a focus screen on the film plane before replacing with film and exposing) suggest a focal length for the condenser that is a little longer than the focal length of the prime lens assembly. This makes sense, because that's the only way to get the condenser to focus on the same point that the front lens is working on (aka, the lens's "rear principal point"). Note, though, it's not possible to get it perfect since that point shifts (and the focal length of any 35mm lens changes from its specified focal length) as you move it away from infinity focus.
The worse thing you can do, I'm reading, is use a condenser lens whose focal length is much longer than your 35mm lens, ie "overshoot" the rear principal point. In other words, if you've got a condenser whose FL matches your standard lens (say ~50mm) and you use your 28mm WA lens insteads.
But it seems to me that it should also be bad if you "undershoot" the rear principal point. Think of a Fresnel light: when you move the bulb away from the lens, it goes from flood (wide, less light in center, gentle falloff) to spot (narrow, more light in center, hard fall off). Flooding the light is like the focal point has "overshot" the light bulb. Spotting the light is like the focal point has "undershot" the light. It leads to a spotlight effect and hard edges.
Both types of peripheral illumination falloff show up in some of the test images I've seen so far. Using the wrong focal length for the condenser can sometimes be worse than having no condenser at all. This might explain why some people have ignored the condenser. I think that before you give up you should try to get focal length and position right at the same time. If you can't get one with a focal length approximately the same as the 35mm lens and position it butt up against the GG, then get another condenser whose difference in focal length makes up for the difference in position.
Re an earlier post, where Jonathan measured the focal length of a condenser element from this Canon AE-1. His was 155mm; but it was actually part of a multiple thin lens element (with a GG/fresnel combo). If that fresnel's focal length was 70 or 80mm, then the combined focal length would be about 50mm, which would sound right. It's the combined focal length that counts and where the condenser is relative to the front lens.

b) orientation of condenser
If you use a planar-convex condenser, the orientation matters. The flat side should ideally face the 35mm lens, the convex should face the direction of convergence. If you put it in backwards, you introduce spherical aberrations or over-convergence. That over-convergence might even contribute to peripheral image loss. I haven't read that specifically however. (Check out this website for a good applet that shows it: http://www-optics.unine.ch/education/optics_tutorials/plano_convex_lens_aberration.html

c) condenser position relative to GG
Putting the condenser after the GG seems most practical for us home-brewers. But, in theory, it's supposed to be better to get the light rays to converge just before they become diffuse as they strike the GG. Getting them to come in parallel helps to reduce diffusion (relative to the coarseness of the grain) and thus loss of brightness, apparently. This might be why in some SLR cameras, the designers put a condenser lens before the GG. But it also adds a little to the light path and means the GG has to be placed a little further back. (Apparently, it needs to be pushed back about 1/3 the thickness of the condenser if it's glass). Getting this right might be tricky if you're building a rigid assembly and you don't have a caliper to measure the thickness of the lens. If you've got a variable spacer between your lens and your GG, it shouldn't be a problem to make this adjustment.


Sorry for the length. Hope it's useful, especially to the people who are trying to catch up.

thank you kaushik for your informations on lens .


I have a link to my finished aldu35 . I wonder if you could look at the design and give recommendations to design changes.

I t was made with 52mm lens filters, 1500 grit ground glass, from opto sigma, and a plcx lens


www.dvinfo.net/media/mellor

Richard,

How do you like the 1500 grit ground glass form Opto Sigma? I was going to order some but they never called me back.

the agus 35 was made with 52mm lens filters the 50mm piece of ground glass fits perfectly. the filters threaded spacers allow fine tuning of focal length. as to the ground glass I,ts the best I have found or made so far. the part numer is 009-0160

http://www.optosigma.com/miva/merchant.mv?Screen=PROD&Store_Code=OS&Product_Code=pg211&Category_Code=Filters+%26+Apertures

<<<-- Originally posted by Richard Mellor :
I have a link to my finished aldu35...

It was made with 52mm lens filters, 1500 grit ground glass, from opto sigma, and a plcx lens


www.dvinfo.net/media/mellor -->>>

Sorry, Richard. I didn't see a jpg for an aldu35. First question I think is if you know the focal length of your PCX lens and how close is it to the length of your 35mm lens.

kaushik- the first three files ,35mm lens adapter are the aldu35
- need to rename them - the pclx lens is 50mm with a focal
length of 50

richard -- i wish had the knowledge to do more than take a stab, but i'll take a humble stab:

i take it your pclx is not up against the GG. i would think that having a condenser with approximately the same FL as your 35mm lens also requires it to be as close as possible to the GG. if it's far back from the GG (a 6mm spacer ring is already a hefty 12% of the FL), then its focal point will also be short of the lens "rear principal point" (the imaginary point inside the lens that we want to stay targeted on).

thinking back to the fresnel light analogy, if the light bulb is moved beyond the focal point (ie, the focal point falls short of the source), then it acts like a spot light. this might explain why your peripheral illumination loss has such a hard edge to it (to my eyes).

i guess you have two options: use a pcx lens in the same position but with a slightly longer focal length. or get your current pcx lens right up against the GG.

the other source might be the aperture. if you've got it wide open, light from sources that are off-axis have a greater chance of getting lost compared to light from sources in the center. stop the lens down and you'll get less light overall, but there won't be as much waste of off-axis light sources compared with the center.

I've been busy with school and other things lately, but I've got back on track with my adapter, and I now have a working prototype.
(large image files)
www.edwardflinch.com/images/mini35.htm

I also have a short clip here: (2.6MB)
www.edwardflinch.com/images/testshot.mov

The ground glass is ground with 5 micron grit, and the condenser lenses are from Surplus Shed. All of the components fit together very snugly. I chose the two condenser lens approach after doing some experimenting. I found that it reduced some spherical distortion I was getting.

Michael: Nice images!

I too am using a GL2 w/ my adapter so I am glad you posted your prototype design for us to check out.

I notice a small amount of grain and maybe some color fringing on the sides, but the frames look good.

By the way, about how much do those PCX lenses run?

Thanks!

kaushik thank you for your help. I will try the changes.

The PCX lenses are fairly cheap:
http://www.surplusshed.com/pages/item/l2119.html

Now that I have a working assembly, I can do a good comparison between the bosscreen and the ground glass. I will post the results soon.

I also had an idea the other day about an alternative GG. I was reading the thread about microcrystalline wax, and I wondered if some other material could be sandwiched between filters to get that effect. My eyes fell upon a bottle of Elmer's glue, and I grabbed two "junk" 50mm sky filters and proceeded to put a glob between them and squeezed out any bubbles and as much glue as I could. The funny thing is that it works pretty well, with no apperance of grain. I lost several stops, though, but the glue on the outer rim appears to have sealed the glue between the filters to keep it from drying. I will add it to my comparison.

Nice idea on the glue Michael. I had an idea to use some of that non-reflective frame glass. The two I tried, however, were too transparant to work.

Are people using a 35mm movie camera image size on the GG, ( 4 perf 35mm size ) or a full 35mm still image size ( 35mm vista vision, 8 perf ) ?

I think the mini35 product does the movie camera size, but is that what guys using 35mm still lens's actually want?

I see a dilemma here.

-Les

I don´t use a stacic adapter, i use vibration (micro circulation), but 35mm movie frame size or 35mm still image size, that is the same question. If you have original movie camera lenses, you will use movie size. These lenses are very, very expensive and in addition, very bright (mostly 1:1,2 to 1:1,4). If you have the $ for movie lenses, you have it also for use a P+S Adapter. But DOF is not only a question of picture size. Remember: More bright (more open iris) = more DOF. But, more framesize = more DOF too. So if you use a still camera lense with and full size frame, for example 1:2,2 instead of a 1:1,2 lense with movie size, the DOF will the same. The other way is, you can still camera size zoom in, or you can use each size between them, so you can play with different DOF. (But if you zoom, you can see more grid on a STACIC GG and you have a problem with wide angle)

Thanks Rai,
I am going to build a micro circulation adapter for my JVC HD10, I don't think a static screen will ever work with my camera.
I think I'll make it big enough for an 8 perf frame.
-Les

Looking for some advice...

I'm building a static adapter out of 55mm filter rings. I'm looking for a condenser lens that will fit inside the the 55mm tube I've created. I'm curious to know what you guys think about any of the 50mm lenses listed on the link below. Or do you have another suggestion for where to find a 50-54mm condenser?


www.edmundoptics.com/onlinecatalog/displayproduct.cfm?productID=2032&search=1

I've finally finished reading this HUGE thread, and I've started building an adapter for the Xl1s. I heard Dino was building an adapter, but he seems to have disappeared lately. Anyone else trying to figure this thing out for the xl1s? Id love to hear what others have had trouble with and solutions they have found.


I've made some progress, but I have a few problems/questions, maybe someone can give me some suggestions.

1. Condensor lenses:
Im having hot spot problems, and want to add a condensor to my setup to see if that will fix the problem. Where and what to buy? I dont know enough about optics to understand what exactly I need, or even where to get it. At the moment, Im working with 2" pvc pipe and all my filter rings are 52mm. The focal length of my 35mm lens is 50mm. suggestions? links? How are you mounting them on the inside of your adapter? Whatever happened to the idea of putting one on both sides of the gg, has anyone tried that yet?

2. Ground Glass:
At the moment, Im simply using Hollywood frost gel as a substitute ground glass element, as it is much cheaper and faster than actually grinding my own glass, and works pretty decently. although I will be upgrading to reall gg in a later version of my adapter. What is the latest consensus on best option for GG element? I've seen posts about buying ground glass already made, seen about DIY gg, and I've seen posts about alternatives. Whats the latest scoop?

3. Relay lens:
For those of you who own an xl1 or xl1s, you know that its simply not practical to try to add an adapter to the end of the any of the lenses. Their just too long. I currently own a manual 16x and a manual 14x and neither of them will to the job i need it to. So, ive decided to build some sort of relay lense to capture the correctly sized image on the GG (which I havent had much success with yet). I've tried a 1' 16mm motion lens, but it had a very strange effect. I could focus between 1 and 3 inches from the lense (not film plane) but that was it. no more range. even at infinity, it was 3 inches away. So, I was looking at a rectangle (roughly) about 2mm across. definately not big enough, although it was conveniant that it focused so close. I dont know enough about 16mm lenses to keep trying them, so i've decided to try a ultra wide 35mm still lens and see how that would do. The reason i think it would work is because even though it is going to have a major tele effect because of the 7x magnification, its an ultra wide, so I can focus relatively close, and it just might be wide enough to get the 36x24mm image. If anyone has any suggestions, feel free. i really want to get this adapter in a more advanced prototype stage, but im stuck on more than one issue, and dont know where to go.

Stephen Birdsong
by the way, since there are a few threads that have nearly 100 pages of posts, wouldnt it be beneficial to be able to search a single thread, rather than just a category? Who could we recommend that to?

Stephen,
jears ago, i made three kinds of working adapters. One of the camaras it works with, was the Canon L1 / L2. As you know, it is the model before XL1 and had similarly changeable lenses (the only optical diffents are focal length, because: L1/L2 = 1/2" CCD, XL1 = 1/3"CCD). So i think it work also with the XL1. Next week i will test it.
One of my adapters come with static GG (i tested 100s of them, some selfmade all the way are posted here, but no one was satisfyingly) . Finally i found a manufacturer and we developed together a high quality GG (See my posts on Microcrystalline Wax). But unfortunately, another company have a patent on this way. The next two models have moving GG (micro circulation). Moving GG improves the picture always, also if you use the best GG. All modells hase aspheric lenses on both sides of the gg (each with flat side face to the GG). My first and most inexpensive way to focus on the GG with the L1/L2 was that: Apart a old, not working camcorder with smal lenses (with macro) make a connector and took it in place of original Canon lenses.
All my models are supported with a cameraplate, so there is no load on the lenses. (Without this you can destroy your camara body.
Next days, i will post a link to detail informations, with parts, pictures and sources of supply, etc.

Has anyone acid-etched their glass successfully?

Based on James Ball's advice, I purchased acid etching cream. I've copied his directions and looked over them carefully, but haven't had the time to set them to use (I'm in the middle of a big move at the moment...)

I'm writing wondering if James or anyone for that matter has had success with his method, or if the lack of updates is evidence of an idea gone wrong?

Thanks,

- jim

Rai, have you considered microlens array focus screen as GG?

It is totally grainless even to my hi-res HDV camera.

Please see here for the detailed discussion and pitfalls:

microlens focus screen discussion (http://www.dvinfo.net/conf/showthread.php?s=&threadid=22456&perpage=15&pagenumber=4#post180505)

Hi everyone I would like to ask for some help

I am looking for a part for my agus 35. I would like to find a way
to adjust the distance between the slr lens and the ground glass the agus 35 is made with 52mm filter rings. I found some things on a telescope site that almost work this would also help with my anamorphic lens ------- thanks in advance

Alex,
>...have you considered microlens array focus screen as GG?
>It is totally grainless even to my hi-res HDV camera.

You say it is totally grainless. Did you really test that? That can not be. It does not exist any grainless GG. A GG must even have grain, but it is just a way you look at them. A GG for a still camera is make for human eyes, and not for HDTV. You cant see any grain, but the cam see it. And microlenses are a bad way, because they have a repetition stuktur, as a lattice, and with a videocam it will produce moree´. Test it out, you will see, but if you find it work nevertheless, let me know details...

Richard.

Your enquiry says Agus35 so I presume your device is a spinner. I used a plate in the enclosure with three holes arranged in a triangle layout. Three threaded pillars face backwards and fit these holes. On those pillars are small hard coil springs. On top of each is a washer. (I used brass because it is easier to turn the adjustment by hand.) The plate goes on top of the washers. More washers go on top of the plate. A nut pulls down onto each washer. This gives adjustment in two axes relative to the lens centerline and distance adjustment from the lens. The pillar layout looks thus ---

----O-----Disc Centre-----O----




---------------O---------------

If your device is the Aldu version made of stacks of adaptor rings leading to a fixed groundglass, then I don't have an answer except perhaps to keep taking rings out or adding them until your backfocus is close, then taking one out, then cheating a half turn on each segment to lengthen until backfocus is correct, measuring the total of the added length, then dressing the contact face of each ring including the ring you took out, shorter so they all together make that length.

The other option is to make thin shims out of food foil which fit the screw hole pattern of your SLR lens mount and spacing the mount away from the focal plane with them until the backfocus is correct. You may be able to get some adjustment of your fixed groundglass inside its holder by the same means.

thanks bob your right .I was talking about aldu 35 . the problem is the filter spacer won,t get me to the adjustment I need. close but not a sharp focus


something like this http://www.harlequinastronomics.com/otheradapters.html

Rai, regarding microlens GG you wrote:

> You say it is totally grainless. Did you really test that?

Tested and re-tested.

Seems that because there's about 2 million micro lenses in the 24x36mm field, each lens element is therefore too small for even HD cam to resolve - but yet they do the job as a great ground glass with very little loss of light, too.

See here:

http://www.dvinfo.net/conf/showthread.php?s=&threadid=22456&perpage=15&pagenumber=4 (http://www.dvinfo.net/conf/showthread.php?s=&threadid=22456&perpage=15&pagenumber=4#post180505)

Alex,
>Seems that because there's about 2 million micro lenses in the 24x36mm field, each lens element is therefore too small for even HD cam to resolve...

This does not convince me yet, because 2 million micro lenses on 24x36mm. That´s 2315 lenses each mm², but only 48/mm (on a string).
24x36 is a 3:2 format. A camcorder works with 4:3 or 16:9. Therefore a 16:9 picture is max. 24x13,5mm. If your HD cam works with 720 lines, the cam "see" 53 lines/mm, but there only 48 mirco lenses/mm. That cannot be invisible.
In order to make it invisible, it would have 2 ore more lenses each line. With a 720 line HD cam your GG would have 106 or more lenses on a 1 mm string. That means 11236 each mm² or approx.. 10 million for the GG. With a 1080 line HD cam your GG would have 160 lenses on 1 mm = 25600 each mm² or approx.. 22 million for the GG.
I had tested many GG, also Minolta, also with micro lenses, but i never found a grainless one.
Tell me the part no and i will test your GG on a optical bank and with a HD Cam, because i am open for all working 35mm parts

Rai, part number and a link to the store that sells it is in the thread I referred you too. See my previous post.

Regarding your doubts: I see what I see. Every other GG produces grain. Minolta does not. Period.

Alex, I believe you, but i would also like to see it. In the thread, they talk about minolt GG Type G and Type C. Which exact you mean?

Could anyone post a sample pic of this ground glass from Minolta?
How do you manage the problem with the markings?

hi everyone this is a link from the other thread

http://www.bhphotovideo.com/bnh/con...=minolta+screen

Posting a still image from a GG setup proves little. A slow image pan with parts of the image out of focus is the test I'd want to see. You see, the grain will only show up as being static if there is motion.
A media9 video of 8mbps would let you see it.
-Les

Les is right.
Also the link is useless.

Richard.

Sorry I cannot be of any help. In setting up are you attempting to work both the camcorder to groundglass focus and groundglass to SLR lens backfocus at the same time.

The only other suggestion I can make is that you make up a target, whiteboard marker lines on the groundglass to intially get that focus at optimum, then direct your SLR lens to a cardboard target, (beer carton or whatever with sharp printing on it) at a measured distance from the groundglass, set your SLR lens by the focus numbers on the lens barrel to the same, then adjust the space between the SLR lens and the groundglass until you get your sharpest image. If you measure from your groundglass to the lens mount face, it should now be in the ballpark of 46.7mm for Nikon. What the others are I don't know.

You've probably done all this stuff already but there it is anyway. Good luck.

Rai, here's the link to the GG. It's Maxxum type G.

http://www.bhphotovideo.com/bnh/controller/home?O=productlist&A=details&Q=&sku=173377&is=REG

The picture does not show any markings but unfortunately they are there. Plus, there's a very faint but still visible small circle right in the middle. Markings appear carved on the flat side while, while circle is on the curved side. Makes this lens unusable.

GG Minolta Type G, Maxxum: I found a GG with the same smal grain, but without "circles" and without marks. Read this:

Alex, thanks, but it is so: I have tested this GG type last year. And it is, like i said it before, this GG is not grainless. Okay, it is one of the best, and you must exact focus on it to see the grain. But than most (PAL version) cams see the grain. There are also some circles on it (not only one, like you say) but this is because this GG has a fresnel lens inside.

My company work with 35mm solutions since many years, so we have tested every GG we found. For my requirements this Minolta GG with this grain was too bad. Maybe it work with NTSC. But i can say we have a GG with exact the same grain like this Minolta Type G. The different is, it is without fresnel(=circles) and without marks.

So, what are the results?
What GG is the correct one?
Do they have Fresnell or Microlens? They are not the same.

Juan, the Minota GG Type G is a sandwich Type: fresnel + GG + (one-side-flat)lens. The fresnel lens kill the hot spot, but produce also the circles. And that´s why it in not unusable.
If the GG itself came with microlens or not, i dont know.

We use a optical bank to test groundglasses. A (still photo) pojektor with a high def testpicture on one side, the GG in the middle, and a microscope on the other side. For a good GG, there are 4 importantly points: low light loss, small grid, hight scharpness, and very even (no clouds or shadows).

So you still recommend the Wax/Parafin compound way?

Brett.

Is your email address as posted still current. I have a comparison test pattern split-image .jpg of the Agus35 (5 micron oharadisk)into PD150 plus a .jpg of the 5 micron machine-finished oharadisk while stationary which might offer some comparison with the other hand-finished 5 micron Aldu35 versions. I'm still using the SW5042 lens set which is inferior to the setups others here are using.

ADDENDUM TO THIS POST:

The comparison image is at www.dvinfo.net/media/hart and titled "oharcomp.jpg" There is also another image with the 5 micron AO dressed disk stationary, ie., fixed groundglass titled "oharatp1.jpg".