For those of you interested in a static 35mm adapter that produce upright image, see the following design (not meant to be pretty other than functional).

http://f2.pg.photos.yahoo.com/ph/louisfeng@sbcglobal.net/album?.dir=/35mm+Adapter

You can see full size image (look for the button above/blow the image).

You are authorized to use this design for personal use.

Hi Vendible.
Shouldn't that be a roof pentaprism? I think that if you use a plain pentaprism (as you appear to show) the image will be laterally inverted.
Best,
Helen

"Shouldn't that be a roof pentaprism? I think that if you use a plain pentaprism (as you appear to show) the image will be laterally inverted."

I have carefully check and rechecked (see the ray trace). The design is very similar to the viewfinder on a SLR camera, except the order is reversed.

The penta prism does not invert the image, it only redirects the image 90 degree. Then the mirror does the inversion. A roof prism by itself will invert the image, but you will have to shoot at a right angle.

I'll just mention the dove prism. To get a 24x36 or 36x36mm dove prism will require a length of at least 150mm, just by itself. Mirror and penta prism is still the best combination.

Vendible,

I am referring to a roof pentaprism, not a roof prism. Nearly all SLR cameras use a roof pentaprism - a plain pentaprism (as you have shown, which is not like the ones in most SLR cameras) leaves the image laterally inverted. That's why SLRs use roof pentaprisms. If you don't believe me, look at the shape of the top of an SLR.


Best,
Helen

Helen,

http://f2.pg.photos.yahoo.com/ph/louisfeng@sbcglobal.net/detail?.dir=/35mm+Adapter&.dnm=DSC00140.jpg

Thanks for pointing that out. I'll recheck and make sure what exactly it is.

If you could draw or refer me to a picture, that would help.

Helen,
After some reading I think you are right, roof pentaprism. Thanks again.

Yes, Helen is correct.

Thank you Helen!

- don

i have two roof pentaprism, one from SLR 35mm camera and one from 6x6 camera. i'm not expert on physics, but i think that ROOF makes the difference here. in BOTH cases (35 and 6x6) the ROOF exist, not just ordinary penta prism.
if you look closer inside the prism - you will see almost invisible thin line which is the uppermost part of that roof, but when you look through eyepiece it looks flat. no splited image, no visible left and right half, but whole image.

in my opinion, just in that ROOF part the image changes the position - left goes to right, right to left, and then after that transition goes to your eyepiece.

and before that (in SLR cameras - or - in your project) finally the miror makes it upside down, so we see it normally.

again - i'm not physics guru, but in my opinion WITHOUT that ROOF image will be still wrong.

i can send to certain e-mail my photos of this roof pentaprism, to show in more visible way what i'm talking about. so anyone can see it. (or if someone has possibility to put it on his server... and make a link in this thread?)

filip

p.s.
i know that this sounds like almost a coinsidence, but i bought the pentaprism (roofprism) just because of that - to use it in agus35 modyfied project and have proper position of the image.

Hi Filip,

Send the file to me taylor@moorefilms and I will post for you.

Taylor

Clarification:

Pentaprism will deflect image 90 degrees without any inverting(up/down) or reverting (left/right) to the image.

Roof Pentaprism will deflect image 90 degrees and revert (left/right) the image, but does not invert (up/down) the image.

Using a pentaprism with a mirror will invert the image but not revert.

Using a roof pentaprism with a mirror will invert and revert the image.

Problem solved.

http://f2.pg.photos.yahoo.com/ph/louisfeng@sbcglobal.net/detail?.dir=/35mm+Adapter&.dnm=img13.jpg

yes, that's it!

penta roof+mirror=success!

taylor,

i just sent the pictures of my pentaprism to you.

thanks

This roof pentaprism introduces some more design problems because the outgoing surface is smaller than the incoming surface. That's OK for a camera view finder, but in this case, the bigger projected area, the better (more detail is preserved).

Dove doesn't work because it only inverts the image, doesn't revert it.

I'm looking for another solution.

For what it is worth, you may find the following Optics FAQ handy:
http://www.edmundoptics.com/TechSupport/optics.cfm

Optics:
http://www.edmundoptics.com/IOD/Browse.cfm?catid=10

Fresnel Lenses:
http://www.edmundoptics.com/IOD/DisplayProduct.cfm?Productid=2039

Ohhhhh! (this looks very familiar)
http://www.edmundoptics.com/IOD/DisplayProduct.cfm?productid=1966

T-Mount Adaptors (hmmmm...):
http://www.edmundoptics.com/IOD/DisplayProduct.cfm?productid=1460

More Lens Adaptors:
http://www.edmundoptics.com/IOD/DisplayProduct.cfm?productid=1459

Video Lenses?:
http://www.edmundoptics.com/Catalog/Custom/218.cfm

Cool!!!:
http://www.nightowloptics.com/addframe.asp?main=http://www.nightowloptics.com/products/modeldetails.asp?product=NOCA42

- don

Ok, I have verified that with a normal penta prism and a roof prism, you can create a correct inverted and reverted image.

More info about Prisms:
http://www.edmundoptics.com/IOD/Browse.cfm?catid=38&FromCatID=10

Image Inversion:
http://www.edmundoptics.com/IOD/DisplayProduct.cfm?Productid=2057

Mounted Penta Prism:
http://www.edmundoptics.com/IOD/DisplayProduct.cfm?productid=2086

Ground Glass:
http://www.edmundoptics.com/IOD/DisplayProduct.cfm?Productid=1935

Sandblasted Glass:
http://www.edmundoptics.com/IOD/DisplayProduct.cfm?Productid=2356

Opal Glass:
http://www.edmundoptics.com/IOD/DisplayProduct.cfm?productid=1671

- don

Vendible,
I know I'm a little late in the game here, but I've been researching this stuff since Agus started the first thread. Like yourself, I have been experimenting with taking it a step further by producing an upright image by reverse-engineering an SLR camera and using its parts. Its actually strange how synchronized our ideas seem to be. Anyway, I was just wondering about how finely ground glass you've used. I planned on using 3 micron aluminum-oxide grinding dust to achieve the equivalent of 3000 grit. I've read that you tried 1000 grit and didn't like the results, and I agree 100%. I was just wondering if you'd gone all the way down to 3 micron (it sounds like you have). If you weren't satisfied with that product, then I know I won't be.
Also, I'm very curious about your non-ground glass idea. I've been reading about large format cameras (same technology) and see that many photographers use brightscreens (Bosscreen) with a fresnel. Is this the approach you're taking? or is it more of a coating like flashed opal diffusers?

Helen,
I'd also like to thank you for pointing out the difference between pentaprisms and roof-pentaprisms. I knew that SLR prism looked a little goofy, I just didn't know why.
I know this is age old technology and I'm basically just discovering for myself what people have known for years, but I am excited about making this adaptor and hope I can contribute to the final idea.

Don: Edmund's is a fascinating place. As a kid growing up in the Midwest I used to save my allowance to order cool stuff from the Edmund Scientific catalog. If you're interested in this type of thing and are ever in the Philadelphia area, their factory store is just across the river in New Jersey. Very cool, especially the surplus room with bins full of wierd stuff at low prices. A real must see for any of you tinkerers! You'll find directions on their website.

Hey everyone I got hooked as well. Trying to make an adapter. So far I've torn apart an old 35mm Minolta and a twin lens yashica medium format camera searching for a solution. I think I have one which may work but only half way.

http://www.visionengine.com/projects/mini35concepts5.gif

Once I had the roof pentaprism off my minolta and was able to look down at the 45 degree slanted mirror I noticed the image was upright. Although reversed horizontally. Even so an improvement on the original Agus35 design.

The above (badly hand drawn) diagram above shows the camera mounted up top pointing down through a spinning ground CD or ground glass. Below that is the mirror and then the lens at a 90 degree angle to it all.

If anybody sees any error in it please specify. Thanks

I personally feel the BosScreen option would most likely work, as there is no grain structure in parraffin, which would also have no colourisation problems either.


Zac

is it possible to use parts from a medium format camera, as the oversized prisms and stuff would allow the fumm 35mm frame though?

Zac

Hi Mike,
That idea might be easier to shoot visually than the Agus35, not having to mentally rotate the image while taping, but you'd still have to reflect the footage in post (which you already know). It will be difficult at first getting used to the right-is-left, left-is-right property of your current design. But you'll get used to it eventually, just like the weatherman does (that's how they see themselves in the monitor while pointing around at the green screen).
It is definately a possible approach and could be usable depending on your preference. I actually read about and saw pictures of an adaptor similar to yours quite some time ago (it may have even been before Agus posted on the spinning glass experiment... its been a while) but can't remember where. It had the same layout with the camera at a 90 degree angle in relation to the 35mm lens. Everything seemed to work okay if I remember correctly, but it sure was awkward and goofy looking. Of course that could be due to all the duct tape ;).
One thing to think about is your audio. The on-board omni-directional mic might work just fine, but you'd probably have to go handheld for a shotgun mic. Its worth some experimenting.
Also, make sure you take into account the size of the spinning ground glass/cd. You're trying to project a rectangle image (35mm x 25mm) onto a round object, so you'll have to make sure the corners are inside the curve. To get a visual idea of that, take the pentaprism and viewfinder "cradle" off of the SLR to expose the mirror. Now put a cd above the hole until it covers the entire rectangle. On my Minolta, its a very tight squeeze and I don't think the cd would be able to spin. Normally, you could move the mirror further from the lens and compensate by moving the ground glass closer to the mirror, but it looks like the SLR ground glass is sitting right on the top of the mirror. If you tried just moving the mirror back, you could still accomplish a good picure, but you'd lose a lot of your focus range. Try this: take the pentaprism off the SLR body again, leaving the ground glass in place. Point the camera at an object about 5 feet away, then set the focus to infinity. The picture should be fuzzy. Now slowly lift up the ground glass. After about 1cm, the image will come into focus. That means that the lens will only focus on objects as far away as 5 feet at that setting... or provide a really nice close-up lens. By moving the glass further, you can focus on objects much closer than the original setting. So maybe you could move the mirror back and just use a longer lens? That might be worth a try too.
Fortunately, there are numerous designs that can accomplish the same "film-look" end result. Basically its a personal preference. If you're satisfied with the result of your design, then by all means go for it. Yours won't cost much at all because you don't have to deal with the prisms, which is a definate advantage. I, on the other hand, plan to go all the way to achieve an upright image mainly for the challenge... and its going to cost me :).

Nicholi,
It's great to know you are working on a similar solution. Yes, I have made GG from very coarse GG to the 3 micron aluminum oxide dust.

The coarse ones are good for diffusing the light to all the corners, but they leave those obvious noises on top of the video. The very fine ones like 3 and 5 microns, they have much less noticeable noise, but there appears to be a "hot spot" in the middle. This hot spot may become less obvious when you have them in a black box. But something else must be done to remove that. Maybe a fresnel lens would help.

Bosscreen could be another solution and probably won't make any visible noises. But I don't know where I can get hold of a small piece. Plus it probably will have the same "hot spot" problem.

Roof pentaprisms are hard to find by itself. Large roof prisms are expensive too. Pentaprisms are a lot easier to get. I have asked some optics companies, they can make custmized ones if ordered with large numbers (50+).

As you know, fresnel lenses are common in large format camera photography. That would cause me to view that as a possible solution. However, we are dealing with a much different scale in the sense that we'll be blowing up a tiny object to the size of a television. Just like you said in an earlier post, this will greatly exaggerate any imperfections in the glass, prisms, or any other part. My question is... would the grooves be visible after being blown up? It seems as though many people have different views on how the fresnel should be located relative to the ground glass. I have a feeling that this may come into play, even though I have seen a couple Agus35s that incorporated the fresnel and looked good... at least at the 320 pixel resolution on the computer.

Zac,
I also like the sound of Bosscreen's lack of grain, but has anyone blown it up on a television? I'm curious to see if imperfections are still non-existant. I'm also concerned with temperatures. During the summer, car interiors will reach 130+ degrees F. I don't plan on leaving any equipment in the car at that temperature, but if cars get that hot... will the inside of my adaptor? And if so, I'm sure the wax will melt/run. Also, just like Vendible said, Bosscreen is expensive and you can only get huge pieces... and you'd have to use a fresnel to diffuse that hot spot. Hopefully someone will run accross something worthy of a test.

As far as custom prisms, maybe we can get some kind of group buy going. I'm sure there are 50 people that will jump in on purchasing custom made prisms once the plans are tested and readily available. Also, I've found a company that could end up helping a lot. www.surplusshed.com has some great lenses and prisms that could be perfect for this project, and would most certainly provide a less expensive prototype. I actually just purchased items from them, and they've treated me very well. Currently, they have a 35mm x 25mm pentaprism, coated and aluminized (which just happens to be the perfect size for this project) www.surplusshed.com/pages/item/l2159.html
and a scope assembly that contains a 45mm long amici "roof" prism that could work as well http://www.surplusshed.com/pages/item/l3082.html
although it looks like that prism is not aluminized.

I'm curious to hear the results on your static diffusion screen tests, Vendible. Any variable that can be eliminated from this ultra-precise adaptor would help very much, especially that crazy spinning glass.

Nicholi yeah I've tried that. Moving the elements around. As you say in the minolta camera the ground glass (plastic) sits right above the reflex mirror. It's all such a pain. :)

Perhaps we are all going about this wrong. In the old world dealing with prisms mirrors were needed becasue film was a fixed format. However in the digital world things are different and we are dealing with digital cameras in teh end here. Maybe we can all petition some electronics manufacturer to build a battery powered box that has a firewire input and output along with an analog output. Where we can throw a switch and it will digitally flip and reverse the image to be recorded by a second DV deck.

That's a long shot considering the cost of R&D on such a device and it's limited market potential. But they could always market it to the masses as a firewire to analog convertor with that extra added bonus to it for us.

Even so it's along shot. But it would result in the best image as we wouldn't have bounce the light around losing stops and possibly degrading the image more.

Another idea (for people who already use 1 chip cameras) is to get a small Apple iSight camera and mount it upside down in the casing. Firewire it out to the camera to be used as the record deck. You would still later have to flip the image horizontally. But once again you'd get an image that is right side up and wouldn't have to bounce the light around.

Just some ideas.

Mike, I see you're imagination has been running :).

I agree that it would be best to avoid the prisms entirely. However, it seems that, in the adaptor's infancy, prisms provide the most effective means of accomplishing an upright image. You make a very good point saying that we're in the digital age and anything can be easily manipulated.
I think your firewire method may be a bit overkill, but you're on the right track. If this adaptor catches on, eventually the camcorder manufacturers will produce a camera that electronically rotates the image before recording onto the tape. That way, the 35mm lens could project directly onto a static "ground glass" and the camera would cover rotating the image 180 degrees.
I'm certainly not an expert on the subject, but it seems like that could basically be an in-camera menu setting, much like frame mode or any of the effects. I'm sure it wouldn't be too tasking, because they've already accomplished that exact idea with the on-board lcd screen (rotate 180 degrees and the image flips, then you can even mirror the image with a menu setting on some cameras).

As far as the iSight goes, there are a couple big hang ups with that idea. According to the stats, iSights can handle up to 640x480 resolution. However, it looks substantially lower in resolution. Many users claim that it just records a 320x240 resolution image and blows it up to 640x480. Even at that, NTSC is the equivalent to 720x480 resolution on a VGA monitor, so it would still be a degredation even at its highest setting (not as wide of a picture). Also, the iSight recieves its power from the firewire connection. I can't say for sure, but I'm guessing digital camcorders only send/recieve video and audio signals over firewire, not power.
Just as a side note, if you plan to make small web videos, the iSight is a neat little camera. Great low light abilities and close focus range makes it a great camera for smaller scale productions. Here are a couple sites to check out regarding "aftermarket" iSight software and accessories http://www.macdevcenter.com/pub/a/mac/2003/09/23/more_isight.html and www.kaidan.com/pdf/iSight_Kit.pdf.

I doubt 35mm lens adaptors will ever become prominant in the consumer community (too much to fiddle with), but filmmaking is a different story. Hopefully, the camera manufacturers will notice filmmakers interest in such a device and even see how simple it is to produce, then supply proper equipment to fill that demand. If they would just hurry up and come out with 2 inch, 16x9 ratio, ultra-high definition ccd's, then we wouldn't have to deal with all this ground glass nonsense ;).

Nicholi, thanks for posting the links. I already ordered both prism from them. Although I'm not sure about their quality (in a very picky sense), they are great for experiment.

I'm pretty confident that with the two prisms, a correct image will be produced. All my calculations and simulations confirm that. Although I would prefer a roof pentaprism/mirror combo over a roof prism/pantaprism combo (in terms of effeciency and cost), but for experiment, the minor loss of light in these reflection/refraction can be ignored.

In SLR camera, the Fresnel lens are used in between the ground glass and the condenser lens. My understanding is it will reduce the diffusion of light from the ground glass before it's passed onto the prisms. I still have to work out how the Fresnel lens' magnifying effect applies to the image, especially when there isn't a condenser lens in my design.

The way other people have used it is quite interesting, that is between the 35mm lens and the ground glass. I plan to get a cheap one to experiment first and try simulation to confirm the theory.

All this is so much fun to work out.

Yes, its a lot of fun... that will hopefully produce something :).

I've taken apart an SLR camera and plan to make my first prototype using salvaged parts. Of course, I will need to buy a close-up lens/diopter in order to view through the prism though.

I have a question about the 3 micron ground glass that you experimented with. You noted that there was much less noticeable noise with the downside being the hotspot. It seems as though, when enclosed in a box, the hotspot would become even more pronounced due to the lack of light "pollution" surrounding the area. My question is, was it the grain or the hotspot you didn't like about the fine grind? If it was the grain, then another solution should be found. If it was the hotspot, then hopefully the fresnel will turn out helpful. I'm sure that's exactly what you're in the process of experimenting with... and I plan to as well.

You may have already read this article, but I'll point it out anyway. http://www.wisner.com/viewing.htm has a good couple paragraphs describing the upside, downside, and proper placement of a fresnel lens. According to this site, the fresnel will create a full frame without hotspot (which we already knew), but will also reduce detail. This is what has always concerned me about using a fresnel. I guess I just need to experiment and see it for myself :).

Anyway... good luck with the experiments and have fun.

The article you posted were very helpful. I bought one of these pocket fresnel magnifiers from officemax. It does reduce the hot spot, but didn't completely remove it. Maybe a bigger fresnel lens with higher magnifying power is needed. The circles were barely noticeable. I think the one I have probably has 100 lines/inch, I saw Edmund sell ones with 200 lines/inch.

Regarding the 3 micron ground glass, all I can say it's at the border line. If it's very close to the video camera, then yes, the grain is noticeable, but barely. When it's about 2 inch away from the camera, then the grain seems to disappear. I can't tell you for sure because I haven't tried it in a fixure, my hand shakes. If this is true, then it may work out because the light is going to tavel in the prisms for at least a few inches. I think it's farely promissing and certainly worth a try. I'm still testing other materials to give better light transmission. It seems the hot spot problem can be fixed with a fresnel lens.

I will be testing a new material in a few days, it's coming in the mail. It's not cheap. If it doesn't make any grain, then I think we'll have a winner.

i'm not good in math, but maybe someone can find the answer...

can anyone tell the proper "size" of GG grain?

i mean - if we shoot with 1/3" or 1/4" CCD cameras, that means - we have specific measures of CCD - right?

1/3" is 4.8mm x 3.6mm

1/4" is 3.62 x 2.7mm

so that means that we can calculate the "size" of the grain and know which size will be visible and which NOT.

if the resolution is (in PAL countries) 720x576, we can calculate the SIZE of one pixel.
if the grain is SMALLER that pixel - it's invisible....

... or i am wrong?

any thoughts?

filip

Here is for my Sony PC101,

690K effective video pixels

that's 830x830 pixels, which is bigger than 720x480, but I think they use the extra pixels for stablization etc.

CCD chip width = chip height = 1/4.7 inch
= 0.212766 inch = 5.40426mm (1 inch = 25.4mm)
=5404.26 micron


size of each pixel = 5404.26/830 = 6.50596 micron

It may seem logical to concluded that 3 micron ground glass should appear to be pure white to the camera, but that's not the case. It's very close to that. I think there are more complex factors involved since the image to CCD translation is not 1:1. The actual image is much larger, and the lens shink it to that 1/4.7 inch area.

One of the problems is the little surface relief of the coarse surface can create shadows and reflect lights. In certain conditions these little shadow can become big enough to be visible. Also the reflections at some points of the surface can create small "sparks" that's brighter than its neighbors. Even if its smaller than 6 micron, it still contributes more light than its neigbor pixels. All of these little problems becomes less obvious when the ground glass is farther (a few inches) away from the camera.

Just to let you know in advance, I think I know what I'm saying... but I don't think I know how to say it. So please forgive my babbling.

The goal is to fit as much of the projected image into the video frame as possible. When you move the glass far enough away from the camera for the grain to disappear, don't you then have to zoom in to fill the video frame with the image? Since its an optical zoom, wouldn't zooming in look identical to moving closer, and thus the grains would appear to be the same size?
The grain size vs. pixel size calculation does make sense, but you have to take into effect how many grains are visible in the video frame (zooming in and out will effect the orientation between grain size and ccd pixel size). My understanding is that it isn't so much how many grains per area of the glass as it is the number of grains per area of the projected image relative to the ccd area. Both a 35mm and 25mm projected image would be identically composed on the video recording due to filling as much of the video frame as possible. However, using the same 3 micron ground glass, a 35mm image would appear to be less grainy than a 25mm image due to the 35mm image containing a higher concentration of grains.
Instead of calculating the 3 micron grains against the 6.5 micron pixels, it would be more accurate to calculate the number of "grains" in a 35mm x 25mm area (when viewed full frame) against the number of pixels in a 5.4mm x 5.4mm area ccd (which provides the actual full recorded frame).
That would be difficult. Technically we're not dealing with an exact grid of particles (grains) as much as tiny scratches and gouges in the glass. Honestly, I have no idea how to calculate scratches because they're so absolutely random. I considered calculating each grain as 3 micron x 3 micron (9 square micron) but don't think that would provide a realistic number due to the nature of the glass texture.

Hopefully that made some sort of sense.

Honestly, I'm still hoping for the best with Vendible's non-grain solution. Considering the upcoming market for higher resolution 720p camcorders, it would be a shame to have to totally reconstruct the adaptor to accomodate new camera's ability to see more detail and thus more grain. It sounds like, so far, you've been able to distinguish the grain on the on-board lcd/viewfinder which aren't very high resolution. If grain is visible there, it will most likely be even more pronounced on a 500 line resolution monitor.

I probably should have mentioned that since I still don't have a housing for the setup, for most of my tests I put the GG right in front of the lens of the camera (literally touching each other). In this case the grains are visible. However, since my camcorder has a small lens, even when fully zoomed out, it still needs to be at least 2 inches apart from the GG to view the full 24x36mm image area. Whether the grains are still visible or not in this case I can not tell for sure untill I can have them fixed in a box.

On another front, I have figured out how to fix the hot spot problem. I know people used fresnel lens. But I understand the theory now and what it takes to have it completely removed. So I feel much more comfortable with more tranparent (less coarse) materials. That also means if the 3 micron GG doesn't make visible noise at 2 inches away, then we should have solved all the technical problems, and I can start prototyping it on computer and building it. If the other materials I'm getting work better than GG, then we are going to have something superb.

I know it only makes things more complex, but a condenser lens is also needed in addition to the fresnel lens to completely remove the hot spot. Here is some reading if anyone is interested: http://topcontechnotes.home.att.net/viewingsystem/index.html.

If there is one high power fresnel lens exists (I don't know how much power yet), then we may not need additional condenser lens. If not, then condenser lens is needed to completely get rid of the hot spot. To get really high quality you can go with double lens etc. But there are math must worked out here to make sure we'll buy the right lens with right focal length etc.

I bought rotary tools that can cut and drill. Won't be here till a week later. I plan to build my first one with hard board and super glue.

Ok, with a fresnel lens and a magnifying glass, I'm able to completely remove the hot spot. I'm still not sure what focal length the condenser lens should be.

I can't wait for this to be perfected since it is much simpler and more manigable in size. Since the focal length must be adjusted using distance of the lense I thought some sort of system with a pull focus like nob could work. Maybe we could adapt something like in this rig http://homebuiltstabilizers.com/stop%20motion%20camera%20dolly.doc

I was thinking the same thing, Noah. The ability to fine tune the ground glass distance would basically be like adjusting back focus. Honestly, the picture is too small to accurately eyeball-focus it on the ground glass. The best focus won't be available until the adaptor has been assembled and the image is viewed on a high resolution monitor. The screw method would provide an excellent external adjuster.

As far as the 2 inches away thing... that's great. That means the picture is covering a larger number of "grains" and thus less will be visible on the video picture. I was afraid that the image would be so small that, even with the ground glass right up against the camcorder lens, it wouldn't cover the entire video frame. I have a GL2 which sees a 4cm x 3cm frame when placed right up against the lens - so I'll have to get a close-up lens to get a proper shot of the ground glass image.

The website you listed is great. Its about time someone actually explains how a fresnel works rather than just saying it works. I had a feeling that the ground glass (actually plastic) on my SLR camera is ground on one side, fresnel on the other because there was such a noticible difference in image quality when I flipped it over (could have also been due to the slightly longer distance from the 35mm lens to the actual ground glass face?). Are you considering getting a real glass fresnel from Edmunds and grinding the flat side with 3 micron? If that works, that would be a great space saver and you wouldn't have to align nearly as much.

I definately like the idea of a double condenser lens and by-passing the need for a fresnel. I'd like to preserve as much detail as possible, again, considering the 720 and 1080 resolution (NTSC) cameras that are being released. I will read the information on that website again and try to use the formulas to come up with a proper combination of condener lens. I haven't done any physics related projects in years, so I may not accomplish anything... but I'll try.

Another thing I wanted to mention... on the SLR camera that I took apart, there is a thin piece of metal (almost a frame) between the ground glass/fresnel and the condenser lens. Basically the condenser lens stands just slightly off the ground glass. Just thought I'd mention that.

Yeah... its been way way too long since physics class.

The fresnel lens is used only to reduce the size of the condenser lens. So it can be replaced by pure glass lens if size is not an issue. Since you have a condenser lens, could you measure the thickness of the lens, and post it here? I'm guessing without the fresnel lens, you need two pieces of 6mm thick plano-convex lens, each with focal length of 100mm.

i just thought about something which is suitable for GG but not mechanically added on the surface, but organic. on the agus 35 thread there is an idea to use eggnog "film" to cover the GG, but maybe there is something more controlable on the market?
some time ago i saw on the discovery channel that some guys are producing kind of "jelly" glass which is controlable by (if i remember that properly) small amount of electricity. the key issue there was not the transparency, but the thermo isolation etc. (those glases will be used in homes instead of mormal glass)
BUT, there were examples of how that "glass" behaves - and in, say "state 0" it was fully transparent, and in "state 1" -semi transparent - "milked".

so, to make long story short - maybe there is another solution for that STATIC GG in organic world around us...

(since the atoms are probably smaller than pixels - joke:))

just a thought.

Okay, I just made a quick measurement of the condenser lens from my SLR camera. So far, I've made the most accurate measurement I can with a ruler (not very accurate), but I will get some calipers tomorrow to get a precise measurement.

The lens is 35mm wide x 24.5mm tall, with a 1mm "standoff" area between the flat side and the curve. The deepest part of the curve (center of the lens) is approximately 3mm.

Here's a quick drawing of the lens with measurements:
http://f1.pg.photos.yahoo.com/ph/nicholossia/detail?.dir=/35mm+adaptor&.dnm=condenser.jpg

I have some calipers, I just have to figure out where they are. I will find them tomorrow and post more accurate information.

Something else I've noticed with my SLR is that in the center of the ground glass, there are two concentric circles. Of course, these areas aide in focusing, each providing a more detailed/precise focusing area. The inner most area is by far more detailed than the outside, but makes diagonal lines look jagged, much like the "stairstep" appearence of interlaced video on a computer monitor. This is due to some type of coating/film used as a substitute for the grind. After viewing the area with a magnifying glass, I can see that the film is made up of numerous tiny "cells" almost resembling honeycomb... hence the jagged/pixelized appearance. I don't think that would look good on a television.

The middle area provides slightly less detail for a slightly softer picture, yet the diagonal lines are very smooth and natural. This provides an acceptable image.
The outer area is by far the worst quality both in detail and brightness... unacceptable in my opinion.

Okay, so what does this lead to? Exactly what was pointed out earlier today considering fresnel vs. double condenser lens. The innermost circle is the only one that contains the honeycomb looking film that I spoke of. The other two areas have been ground identically (same grit). However, the fresnel is only existant in the outermost layer (I can see the concentric circles with the magnifying glass... they're tiny) where the detail is much worse. The catch is that the middle area contains a very small bubble in the glass... in other words, the very peak of a second (technically the first in series) condenser lens. This tells me that the only acceptable layout is a double condensor lens. This will get rid of the hotspot (if you set it flat side down on a piece of paper, you can actually see it working... there is a shadowed circle in the center of the lens) AND sustain the most accurate detail. Honestly, there is a huge difference between the quality of the two.

If everything works out right (considering I know nothing of mother nature) we should be able to derive the focal length for two identical, thin condensor lenses to be aligned in sequence after the ground glass.

Here's a drawing I threw together to illustrate that last post.
http://f1.pg.photos.yahoo.com/ph/nicholossia/detail?.dir=/35mm+adaptor&.dnm=SLR_gg.jpg

hello there,

when i read about the solution WITHOUT GG, i was very sceptical, but anyhow ...
i just checked the option WITHOUT moving parts and WITHOUT GG.
here is the list of things used:

- camera sony PD 100 (52mm front filter diameter)
- macro lens +10 (single lens) from Hama (52mm diameter)
- cake CD box (for 50psc)
- zenit PHOTO camera lens 58mm/f2.0

i zoomed into the zenit's lens picture to avoid vignieting and that's all. no prism, no nothing exept macro lens with 10x power, and cake box with zenit 58mm lens on it. so it looks really simple. i did the tests with the camera, but cake box was not so stabile, so i kept that in my hands which results in vignieting, but this is due to my shaky hand. focusing is in this case really difficult. i changed focus here and there to see how it looks.

for me it looks really good:
- it HAS proper DOF,
- for some reason, colors are bit different (read: subjectively better)

also, because of low light conditions (just one table lamp on the begining and two ceiling lamps (2x 75W) + christmas tree lamps) i used 18dB image gain BUT with -3dB offset in main menu settings).

these gives me interesting video (grain) noise, which probably helps to see everything more "filmic".

maybe i'm too subjective, so please tell me - do you see what i see - or this is just my illusion?

maybe i'm fascinated with it, but to me it has something common with proper film feeling.


i can send my "filmeo" (film+video) tests today to you via taylor (with his kind permission) if you want to see it. should i send them?

excuse my ignorance, but wouldn't just zooming into the back of another lens cause the 7.2 magnification we are trying to avoid?

Zac

I agree with you Zac, but just in case, I've posted an experiment on Agus's thread that hopefully others will participate in.

I got my first Job with the COLONIA35MM

the adapter i just made myself.

go to the site www.bobflash.com.br

choose the city RECIFE-PE

on the site theres a session called BOBCAM, where i go to parties and film everything.

check out the two last clips from a xmas party. i made the two with the 35mm lens, 50mm, 1.4.

it is wonderful, altought i had some problems to focus, with the light of the place, etc. im still learning. and i was drunk too, etc...anyway, tell me what you think of it.

im just waiting your review.

thanks

ciao

all static is the way.!!!!!

ciao

Daniel Looks good. Please post pix of your setup and rig.

You BR have too much fun.

T

it isnt just great because of my cheap trv18...

ive said before all the setup...

look at the pic of the Colonia35mm

http://www.bobflash.com.br/franquias/recife/locais/barrozoclub/eventos/24-12-2003_3146/fotos/124170.jpg

http://www.bobflash.com.br/franquias/recife/locais/barrozoclub/eventos/24-12-2003_3147/fotos/124306.jpg

<<<-- Originally posted by Filip Kovcin : hello there,
i can send my "filmeo" (film+video) tests today to you via taylor (with his kind permission) if you want to see it. should i send them? -->>>

You can also send it to me. I'll post it in my yahoo briefcase.

What you described is possible, I think I know the underlying optical physics. The problems with it is not the image, but the way to use it. I'll try to come up with a diagram to explain why it works.