Jonathon:

Thanks for your explanation.

There's a new short film made with a static solution, and it's found here (http://www.anotherstateofmind.be/temp/marla.mov).

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

Here are stills (http://www.anotherstateofmind.be/temp/marla.jpg).

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

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

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


edit: I've just put up this revised tutorial on building a static solution (http://ideaspora.net/aldu35/). It's incomplete, but I'm sure you could infer the rest of the steps necessary. I'll put pics up of the finished product once my new F-mount arrives.

Thanks,

- jim

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

-B

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

Here are some pics:

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

stills:
Alain35 image http://aequantum.com/test23.jpg dirty GG and low light, also zoomed in 2x due to hotspot
regular video http://aequantum.com/test24.jpg

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

What did you use for Achromatic Diopter?

Alain

I took apart a $25 Sima .5 Wideangle lens, and used the first lens which happens to be a achromatic/macro lens.

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

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

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

Brett - Yes, I've been looking at lots of diagrams which all have two condensers, one on either side of the focusing plane (which is actually a reticle in many of the diagrams I've seen). So that makes sense... However - doesn't our diopter somewhat fulfill the role of the second condensor, or am I losing it?

jonathon- You bring up a good point because I too have seen the two condensers split and placed on both sides of the ground glass. You would think you would need to keep them together in order for them to work together on correcting the chroma aberration. I'll look into why they have it setup this way.

so it goes:

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

How do you figure out what the proper condenser for your situation is? I read through the posts but couldn't figure that part out.

Your ordering looks right to me.

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

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

Did some yucky first tests with, get this: a cardboard tube cut to focal flange distance - some of that 'satin' scotch tape on a skylight filter as crummy replacement for ground glass... Pretty gross, but enough to prove that the concept will work with my lenses/camcorder. :) Enough to justify spending some money for better parts. Also enough to learn that the upside down image is a pain in the neck... Any agreement on a 'best' solution for that?

Has anyone considered using a Kodak Ektanar lens from a 35mm slide projector? You can find these on ebay for under $50. You'd just need a mitre box and a hack saw to cut off the extented length on the back.

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

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

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

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

Good article on EdmundOptics describing in 'Application Primer 3' the effective use of achromats around the ground glass. They even use the words "This is the same type of four element configuration used in relay lens systems" which is what we're building.

http://www.edmundoptics.com/TechSupport/DisplayArticle.cfm?articleid=267

Great link. I recomend everyone to read and learn what its teaching because it sums just about everything up all on one page. Thanks.

okay so if i read that article correctly then it should go like this:

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

I'm not sure exactly what formula to use to get the proper Achromat Lens System, or even where you would get one

I know very little about lens types. So please bear with me on this. I'm trying to accumulate the needed items for the static adapter.

I almost hate to even ask, being it has probably been ask before, but I cannot find a definitive answer.

Must a close up lens state it is Achromatic or is that just a Century designation? Would a Macro +10 close up NU filter work?

Something like this:
B+W 58mm Macro Close-up +10 (NL10) Lens
http://www.bhphotovideo.com/bnh/controller/home?O=productlist&A=details&Q=&sku=11209&is=REG


Thank you very much for the help.

Tavis, the only thing I'd suggest is when you say 'Achromat Lens System,' that actually incorporates the ground glass. In other words, I'd list the whole sequence more like this: (top to bottom this time)

SLR LENS
SPACER
ACHROMAT 1 (curved side towards ground glass)
GROUND GLASS (at proper ff)
ACHROMAT 2 (curved side towards ground glass)
SPACER
MACRO +7 (or acceptable for your cam to focus)
DV CAM

After having run through the Achromats described above, your light should be 'color correct' with all wavelengths focusing to a single point. All that's required at this point is to 'keep it correct' not fix anything more. So... generally, I'd think that any macro adapter for a camera would strive to stay 'color correct' - there's probably degrees of this, but in general, I'd say: don't worry about requiring the label at the macro.

This also means that if you don't include the achromat system to 'repair' color abberations than your macro won't help and you'll still have color abberations.

At least that's my best guess at the moment :)

now, do the ACHROMAT's vary from setup to setup depending on the slr and flange distance required, or is there a generaly funtional pair of achromats that could conceivably be used in more than one differing setup?

This would be a really bitchin setup with the chromatic aberrations and hotspots fixed.

Hey, Hello, yo there,

So, does that mean the Century Achromatic x7 negates the need for the achromat(curved lens) on both sides of the GG? But, if I only use a macro on camera I would need the achromat GG setup?

Interesting... My initial reaction was, "No, because the achromats also repair 'spherical abberation'". However, I also recently read that spherical abberation is a distortion in which certain parts of the image are geometrically presented in the wrong place, but the information is not lost. This (theoretically) means that you can correct spherical abberation at any point prior to hitting the CCD... This doesn't "feel" right to me, but according to what I've read, you could skip the achromats around the ground glass, in exchange for an achromatic macro... who will repair chroma and spherical abberation as the very last step before sending it to the ccd.

The part that doesn't feel right: Part of the way in which the achromats fix spherical abberation is to more evenly present light across the entire surface of the ground glass. If you skip this, than there are simply places on the ground glass that don't see as much light... I don't think you can ever 'put that light back' with an achromat later in the path...

I'm really talking out of my butt here, based on the articles I've read. In this case, I'd have to say I wouldn't trust myself :) Practical experience would be a better measure. Try it and see if it works. My gut reaction is that the double achromats around the GG would work better.. but you might get some relief with only the achromatic macro. Good luck!

Yeah, the more I think about it the more convinced I become. The Chroma and Spherical abberation must be fixed prior to the ground glass.

Our ground glass is really a type of 'intermediate' CCD which forms a particular focused image. This is the 'relay' concept. We image the 35mm SLR lens image onto the ground glass and then we shoot another picture of that focused image with our camcorders.

It's very analogous to making a video of some film that's been projected on a wall.

If you have a crappy projection onto the wall (with bad color and rounded corners) there's no way to fix it with fancy lenses in your camcorder.

In a way that is good news, . . . I think. I can get a 10+ macro lens for around $25-$50 where as the Achromatic Century 7+ is over $200.

Now, where and how do I go about getting the two lenses to make the achromat/GG sandwich?

here is actually a illustration i put together for the standard dv version (not the xl1). This should be close to what your saying johnathon.

http://www.dinoreyes.com/images/lens_standard_dv.jpg

thoughts?

Where to get the achromat indeed?

I definately agree that the chroma and spherical aberration have to be fixed prior to the GG, or else the image will not be evenly focused on the Ground.

I'm still unsure about the order, Jonathon, are you sure that there is an achromat on each side of the GG?

As an aside, i thought it'd be great to build it as a setup where the spacer between the SLR and the GG was adjustable and marked so you could use different brand lenses and get the right focal flange for them.

Nice design, but am I missing something here? Did Alain have anything nearly that complex? I thought his was just:

SLR lens -> housing with ground glass inside at proper flange focal length -> macro/achromatic lens/filter -> dv camera.

Why the added steps allathesudden?

- jim

Gorgeous, Dino :)

You can be in charge of illustrations for the technical manual, when it comes out...

Tavis... take a look at Dino's picture. Pretty much nails it. Except - I completely agree (Dino, care to do an update?)... having an adjustable-length spacer between the SLR and the first achromat would provide flexibility of using different SLR lenses. It also is likely to be something that's hard to get exactly perfect when cutting and mounting... so the adjustment would likely be required no matter how many lenses you've got.It doesn't need to be something easy to adjust - more analogous to the 'back-focus' of a zoom lens. You kind of get it set for what you're using... and then lock it down.

It would be huge aid in properly setting the SLR lens to Ground Glass focus. I think you would likely set the SLR infinity... then you use the adjustable flange length to correctly focus the inifinty setting on the ground glass with some distance object. Then as you require SLR focus on nearer objects - it will still properly place it's focal distance on the ground glass.

I don't think you're missing anything, Jim... as we keep thinking about this, we can't help but notice little things here and there that it would be nice to fix. The ground glass is a big improvement over the scratched CD, for example. Currently, we're just investigating ways to get light more evenly and strongly onto the ground glass for an even better image. When all is said and done, there's a complexity/price-to-feature decision where adding more and more complexity doesn't add a corresponding equitable benefit. Everyone needs to make their own decision about where on that continuum they want to exist. Personally, I haven't built mine yet, and am willing to give the achromats a try if they'll improve even further. I can always take 'em out :)

Plus, I think at least half of the fun of a project like this is the research and attempts at improvement. If you've got one that works well enough for your needs, then by all means - enjoy it and don't look back!

so how many Degrees Apparent Field of View do the achromat's need to be? Has anyone found a source for these sucka's yet?

Great diagram Dino!

okay, here's in keeping with some of the creations so far. for those keeping score at home, to the best of my knowledge the deluxe version has not been created yet but most likely would be the one that would yield the best results do the the color correction capabilities of the achromat lens. in a nutshell the lens makes the light shoot in a straight direction. the deluxe design also includes a collar for adjustment when you use other primary lenses-this is also has yet to be proven. Another question would be could you make the system with a single (just achromat lens 1) and allow it to function properly? anyone have an answer? so check the links below and if need be i can do some tweeking. i have also included what might be considered a standard concept (with the fresnel lens) already proven to be quite amazing in proof of concept.

for miniDV

http://www.dinoreyes.com/images/miniDV_standard_aldu35.jpg

http://www.dinoreyes.com/images/miniDV_deluxe_aldu35.jpg

for xl1/xl1s

http://www.dinoreyes.com/images/xl1_standard_aldu35.jpg

http://www.dinoreyes.com/images/xl1_deluxe_aldu35.jpg

keep in mind folks, the standard is cheaper to develop and inconcept the deluxe version would be the ultimate in optical quality. also, just as a reminder, what we are doing here on this thread is HUGE and may very well shake up the status quo-or at least, wake them up.

enjoy

nice work once again!

Sorry to ask this, I don't know if this as been discussed before (this thread is too big to search) but,

what is the advantage about using a nikon lens as a relay lens instead of the stock 16X XL lens with the XL1 ?

does the direction of the fresnel make a difference of the image on the gg? that is, should the "ribbed" side face the ground glass or should the smooth side?

I believe i read that the ribbed side should be facing the gg.

I'm not fully convinced that we need a second achromat behind the ground glass... muddled logic follows...

What we're really building here is a tiny little projection system. We 'project' the 35mm SLR image onto a surface (our ground glass) as accurately and brightly as possible (the need for the first achromat).

However, we then photograph this projected image as if it were a new image. The way the camcorder focuses on this very near image is through the use of the macro adapter. Quite simply... the macro adapter places focus of the camcorder right on the plane of the ground glass. I think that the second achromat behind the ground glass would just screw things up.

It is helpful to think of all of this using the 'projector' metaphor:

Let's say we built our little device differently:

Imagine that I had a hypothetical 35mm camera, which instead of a viewfinder, had an overhead projector which, lets say, shoots out some contraption on the side of the camera onto a big screen. So... whatever I aim the camera at shows up on this big movie screen to my left. It accurately portrays what the 35mm lens sees... if I change the focus on the lens... the big projected image comes into and out of focus, etc...

This movie screen is effectively the same thing as our ground glass. Movie projectors all have various ways of increasing the light and reducing spherical abberations to make a 'flat' image on the screen... this is the same thing as what our first achromat is doing.

Now - stop there for a second... the projection of what the 35mm lens 'sees' onto a projection surface (the ground glass) is one complete problem... which is solved, in our case by the 35mm lens image getting corrected by and achromat and focused onto a screen (ground glass).

Now - the second and completely separate problem...

We want to make a camcorder recording of this screen. Falling back to the movie projector metaphor... I take my camcorder and walk right up to the screen which is projecting the 35mm camera image. Lets make an assumption that I have to be 3 feet from the movie screen. (Assuming I'm transparent <grin>) I try to make a recording of the screen. However, the screen is too big - so I change my camcorder lens to be wide-angle enough that I can get the whole thing into my viewfinder.

This is analogous to our use of a special 'macro' lens on our camcorder in order to record the ground glass, which would normally be way to close to focus on. Once I have the macro and can correctly focus on the ground glass... I'm done.

Does this make sense to anyone but me?

Jean-Phillipe,
the built in 16x lens would make any lens adapter on this thread stick out over almost 1.5 ft. (1/2 a meter?) i'm guessing. not usable under any situation. i reccomend the nikon adapter out of experience building the Agus35. the lenses are cheaper, faster, and abundant for testing and using. in the diagram above i also noted a pl lens mount, but that would be for movie lenses, you could easly do with an inexpensive nikon mount, about $30 USD, and once again with any fast nikon/nikkor lens for your primary.

Jonathan, & Tavis,
in the article here, the graphic at the very bottom shows the "white light" hitting the curved side of the achromatic lens, straightening out the light, then hitting the image plain (the gg in our case)

http://www.edmundoptics.com/TechSupport/DisplayArticle.cfm?articleid=267

in the diagram i put together, could that be incorrect, should the curved side face out and the flat side of the achromat lens face the gg?

me confused still, but i do agree maybe only one achromat would be fine, the first one. thoughts?

I see what you're saying about the one achromat but i'm not entirely convinced, but i am unsure are we trying to do 1:1 imaging here? If you read here http://www.edmundoptics.com/TechSupport/DisplayArticle.cfm?articleid=267

It says:

we find that 1:1 imaging can be achieved with two lenses working at infinite conjugate distances. Using two achromats with convex crown surfaces facing each other, a far superior imaging system is obtained. Spherical aberration is negligible at large apertures, with the addition of color correction.

Also if you look at figure 3 on that webpage, you see the two achromats face to face, then the image plane, ie. our GG right? so it should go
SLR > Achromat1 > Achromat2 > GG...etc...

http://www.edmundoptics.com/IOD/DisplayProduct.cfm?productid=2008 at the bottom of that page there is a couple more diagrams, do they help anyone? now i'm wondering if you're right about only using one achromat. brain hurts...

Ok, Thanks Dino!

The first achromat bends the light and sends it straight down the barrel (ground glass).

The second achromat picks up that light and curves it a bit more (forming a diverging cone) and sends it straight at the ccd (point of cone).

The line and angle that the second achromat sends the light is perfectly in line with the angle at which the camera (with macro lens) is looking back at it. By perfectly matching you get the most effecient system. In other words the brightest and without any hot spots.

Remember the achromats, condensers, ext. all have to be match to the focal length of all the lenses you want to end up using.

Im so glad to see everyone working hard on this again.

Brett Erskine
Director of Photography
Premiere Visions
1761 W. La Palma Ave., Suite #302
Anaheim, CA 92801
www.CinematographerReels.com
BErskine@CinematographerReels.com

P.S. BTW good diagram Dino. Thanks for doing that. Fairly similar to my adapter. One of the changes I made was to make the barrel between the ground glass and the camera adjustable as well so its works with more than one miniDV camera. Cant forget about the DVCAM's and HD as well. On the otherside it has quick change mounts to take any still, PL, or medium format lens. There are other things too but we should focus on the achromat issue first then move on.

PremiereVisions35 adapter...coming soon.

Ack - like Tavis said: "Brain Hurts". Wish I had taken the time to go and get the masters in optics :)

Makes sense, Brett. Hard to know without experimentation. Anyone who builds one... and has learns something about the effects of abberation - good or bad - drop a note here ... I'm hoping to grab my achromats and ground glass in the next week or so, and spend some serious time with them in different positions trying to find the right combination. I've been reading too much and I can't really find a definitive answer, so I'm just going to try some things. Will post results as I have them. Looking forward to having a working model, though - the footage from others looks so nice...

Sounds like you've got one built, Brett? How's it working and what was your design?

anybody have a cheap place for acromats?

I'm new to this film-look 'hobby', but not entirely new to optics and such. Here's a couple of points:

1. By putting an achromat or ANY other lens between the photo lens and GG, you're altering an arrangement that's already perfect, i.e. a photo lens positioned at the flange length from the film in a 35mm camera (GG in our case) will do it's job better if you don't mess with that part of the system, unless you think that you can beat lens manufacturers at their game, and design a better lens. If so - good luck!

2. The image formed on the GG IS the object for whatever imaging system will follow. If you get vignetting/halos, you may want to put a so-called 'field lens' (already discussed in this thread?) right AFTER (ideally, at zero distance) the GG. A Fresnel, when used as described elsewhere in SLR viewfinder systems, is a cheap version of field lens. The trick is to find a thin field lens with little chromatic aberration.

3. Using an achromat as a macro makes perfect sense unless your DVcam can focus close enough without one (my Sony PC100 can). Using a 35mm projector lens for that purpose is another great idea.

Brett, what kind of quick change mounts are you referring to? I'd be very interested. Do you have a link? The only solution I see so far is purchasing a c-mount for $30 and removing the lens adapter part, but this is hardly universal. A reverse t-mount would do the job, but I cannot find any.

A note on inverting and reverting the image. Looking at Pro35, I believe they're using a porro prism, the same one used in binoculars and spotting scopes. I can't figure out the proper size. The one widely available for telescopes is 1.25", and would be too small for a 35mm image. The next 'standard' diameter is 2", which would be ideal, but I can't find any manufacturers that produce it. The cost of a 2" porro would be pretty high. Another alternative would be to use a diagonal upright (Amici prism, I believe). These do exist in 2" size, but are expensive as well. Also, you'd have to put the camcorder at a 45degree angle.

http://www.solarobjects.com/product.asp?catID=61&productID=283
would this have a prisim we could use

Rhoman Shafro,
I have been in a search for such a mount myself well i found a reverse t mount if you are interested.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2989251818&category=30059
I am too trying to figure out what adapter to get for my Minolta Md f/1.7 lense. I looked at a few c mounts and since i never had one i asked the guys if the bolex thread mount comes off, didn't get an answer yet.
good progress everyone!

2 Richard Mellor: Yes, that's the kind I'm talking about. I'm guessing, however, that the one inside 16X50 binoculars may be too small. Having a porro that's used in telescopes, with 1.25" OD, will be better, but may also not be enough. You could get a Swift or Bausch&Lomb 1.25" porro for about $50-60, and a TeleVue or Astro-Physics for just over $100, but I've yet to find a 2" porro. Here's an example of 1.25":

http://www.bhphotovideo.com/bnh/controller/home?A=ShowProduct&kw=SWEP864&Q=&O=&sku=219216

Overall, a porro gives a better image than a diagonal prism, so that would be my preferred choice.

2 Dmitri Henry: This is EXACTLY what I was looking for! Thank you so much! However, the one I need is for the Nikon F-mount. Since there's plenty of T extension rings available, you won't have to make your own adapter out of PVC or what not. You're guaranteed perfect lens alignment, and it'll look better.

I have a Nikon brand F-to-C. This is a $160 item, but someone gave it to me ages ago. The bayonet mount part comes off, there are 4 tiny #0 philips screws. I'm trying to adapt that to a 1.5" female PVC connector, but would much prefer to save the F-to-C and get a reverse T-mount instead. Like most of us, I don't have a shop to manufacture mounts, cut threads, etc.

Makes perfect sense, Roman... and welcome to the discussion!

Roman-
Welcome to the thread. Its great to have you. Let me answer some of your questions.

1)Reverse mounts normally are a problem because you loose the ablity to focus at infinity but my adapter has a adjustable flange tube so the issue would be resolved and multiple mounts would be possible. Never the less I decided not to go with reverse mounts. Im using straight PL and Nikon mounts (but just about any mount you want will work). Each is attached flush against the face of a filter stacker with a hole in the center. Simply twist on/off any given mount.

2)These guys will fabricate just any adapter piece to your specs.
http://www.srbfilm.co.uk/index1.html

3)Field lenses are the same as condensers.

4)The second lens is probably a good idea to have because the image on the ground glass is not the same as say for example the same image were printed out and viewed by your camera. The reason being is that when the camera is viewing a image projected on ground glass, the image becomes increasingly brighter the more inline you are to the incoming light. Thats why everything from rear projection tvs to the hot spots on our adapter are brighter when your looking straight at it. Your example about film planes/condensers is not valid. Film (or CCDs)dont need any type of condenser because its much much more forgiving on this issue. This is why you dont see a condenser in front of the film gate of a SLR camera.

Thanks for the info about the prisms. I wasnt aware that B&H had something like that. The two prisms you mentioned and a few more that will work can be found in a link I posted here awhile back. You shoud check it out because it has diagrams explaining just how each prism effects light. Heres the link:
http://www.dvinfo.net/conf/showthread.php?s=&threadid=17195&perpage=15&pagenumber=58

Roman-
When your talking about the measurement "1.25" for the porro prism is that dimension representative of the viewable distance across a image circle, square or rectangle?

The reason why I ask is because we need to fit a 36mm by 24mm image within the above image area. 1.25" comes out to just about 31mm.

If it wont fit at least the motion picture film gate at 24mm by 18mm will.

2 Brett: I believe that the 1.25" reference is for the outside diameter of the eyepiece, that's why this porro prism (or 1.25" diagonal prism) will be too small, and the next 'standard' size as far as scopes go is 2".

Reverse mounts are not a problem unless they extend the overall flange distance beyond the standard one (like 46.5mm for Nikon, 42.1 for Canon FD, etc.), that's when you can no longer focus at infinity. I'm trying to avoid manufacturing connections as much as possible, not just for aestetics, but also to have a standard solution anyone could use. Thanks for the link, I haven't studied it yet, but it looks like a goldmine!

The difference between a GG and film is this: any incident light that falls onto film will cause the desired photochemical reaction. The GG scatters light in all directions, and that's why you get a hotspot in the center and vignetting on the periphery due to off-axis light beams. The field lens corrects that. In SLR viewfinders, the Fresnel right before or right after the GG IS the field lens. Fresnel is very thin, and that allows it to be placed right next to the GG, i.e. in the focal plane of the objective. Having the field lens in the focal plane is the key: this placement does not change the principal planes of the overall system, it only helps to collect off-axis light beams.

The difference between a field lens and a condensor is (mostly) semantics, but usually condensors are used to create a collimated light beam (like between a light bulb and the slide in a slide projector), and field lens is used to condition the intermediate image.

The bottom line, IMHO, is that you do need a field lens right behind the GG, but you do not need anything between the objective lens and GG.

Roman,

Just for clarity, when you say "behind" the ground glass, do you mean on the camcorder side?

Yes Justin, always follow the path of light rays. What I mean is this order:
Objective lens -> GG -> Field lens -> Macro Lens -> Camcorder.