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Old April 20th, 2007, 04:32 PM   #91
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Yeah, that's what i hear... i'm glad to know that there is hope for this type of solution...

To me it's worth the headache and time of coming up with the perfect thickness if that means a working static solution...

Anything you can point me to where people have been trying this recently with any luck? Thanks so much...

Dale

Oh and one more question - i've noticed when people do attempt to use a static GG, there are often condensors involved? Why is this necessary for the static method? It the rotating method it's usuall Lens > GG > Achromat > Camera - but it seems people are adding condensor (or replacing achromat), or sometimes sandwiching the GG between two condensors - why is this?
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Old April 20th, 2007, 05:08 PM   #92
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The use of a condenser is independant on weather you use static, vibrating or spinning GG.

The purpose of the condenser lens is to eliminate vignetting, which will be the same problem regardless of static or moving GG.
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Last edited by Wayne Kinney; April 21st, 2007 at 05:03 AM.
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Old April 21st, 2007, 01:10 AM   #93
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Interesting - thanks Wayne.

I looked at condensor lenses a bit - and it seems in most cases condensor lenses are used back to back causing the paralleling rays, then the focusing of rays - in this application would you need both or just one between the SLR lens and GG? It seems you'd just want one condensor in front to parallel the rays and eliminate the vignetting and throw the un-vignetted image from the SLR lens on the GG for the camera to pick up - is this correct?

Lens < Condensor < GG < Achromat < Camera?

One other question and it's probably dumb, but do achromats magnify the image? I know for instance on the Letus35 Flip his final image is 1.9x the actual size, and i'm not sure if that's due to the way it's flipping the image internally or the achromat...

Thanks

D
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Old April 21st, 2007, 09:29 PM   #94
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Dale,

Your idea of how the condenser works is correct; It basically distributes or "spreads" the light/image over the diffuser, whether it be static, virbrating, rotating, etc. as Wayne mentioned.

As far as using two of them, I'm not sure that it's necessary. I've gotten good results with only one, on the front. I've tried using two but didn't see a difference big enough to warrant using a second one.


Quote:
Dale Backus: ... do achromats magnify the image?
Correct - they are used to magnify the diffused image so that the camera can pick it up. An achromat is used to prevent chromatic aberration / color fringing whereas a regular macro lens would possibly show these problems. (This occurs due to light wavelengths having different refractive indexes, causing the various colors to have different focal lengths. Achromats use more than one element to refocus them and keep them closer together. This usually shows up on the outer parts of the frame.)
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Old April 22nd, 2007, 02:06 PM   #95
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Very good, thanks so much for your help with this...

I wasn't clear on one thing though - so the achromat magnifies the image so the camera can focus on it, and it eliminates the chromatic abberation. Does this mean that if i'm shooting with a 55mm Nikon lens, that it will appear as though i'm shooting with a 100mm lens or something similar? I know that's what the letus does, and i'm not sure if that's because of the achromat specifically, or something else inside involving the image flipping.

Dale
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Old April 23rd, 2007, 12:54 PM   #96
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Good question, Dale.

In the case of a standard non-flip adapter, the lens' viewing angle, focal length, etc. aren't affected by the adapter, because the diffuser is basically just catching a projected image of whatever comes from the back of the lens.
So your 100 mm lens should look the same in your video camera as it does in your regular still camera.

Again, that's with the regular non-flips. I'm not totally sure what optics are in the flip versions to change that.
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Old April 23rd, 2007, 02:03 PM   #97
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That's what you'd think - we were actually messing with our today and we found it very strange - we were basically trying to figure out why our magnifies the image...

Our adapter goes - Lens < GG < Macro (58mm) < Mirrors (to flip the image) < Achromat < Backfocus Lens (49mm f1.7 Minolta) < Body

For the heck of it we removed the Macro just to see what it did - and we couldn't tell a difference whatsoever - very strange.

We're thinking, because the image that falls on the GG fits the exact size of the GG, that it was positioned to the camera would only see a portion of the image to eliminate the ragged edges of the glued piece of GG - that's the best we can tell. (BTW, our adapter flips the image and adapts straight to the body of our HD100)

If we were to make our own, using a static microcrystalline GG - am i still correct in saying it should go: Lens < Condenser < GG < Achromat?
I'm guessing the Backfocus lens that's on ours is required because it's adapting straight to the body, right?

Dale

Oh Frank, thanks for pointing me to your old tests - i checked out as much as i could and i was very impressed at the lack of grain, how was your system set up? I noticed a little vignetting and hotspotting, were you using a condenser? Thanks
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Old April 23rd, 2007, 09:11 PM   #98
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How does it come that the Redrock M2 spinning adapter does not use a condenser lens? I saw only that the spinning disc is thicker than normal gg's.

Daniel
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Old April 23rd, 2007, 10:19 PM   #99
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Dale.

As far as I have been able to work out, your combination will yield an approximately 22mm - 24mm, maybe bigger, maybe smaller, patch imaged off the groundglass. A relay lens with a wider field of view, a shorter focal length, would give you more but then you might find the corners going dark.

There is a bit of a trade-off. Condensers enable a larger evenly lit area off the groundglass at expense of more complicated construction and adding one or two more pieces of glass into the path which might degrade the image.

Larger means potentially sharper images as the size of the individual groundglass texture pits relative to the image size is smaller. Your SLR lenses on front will yield a wider field-of-view.

If the centres are not right you might find chromatic abberation (rainbows) towards one edge or sharpness going off in a radial stretchy sort of way towards one edge.

The whole condenser thing is a bit of a dark art for me as I don't know the math and the theory and don't have a junk box of various lenses to try out.

The 1/3" width of your CCDs in your camera set the limit for the field of view for the relay lens you are using. You may find you can do without an achromat if you position your relay lens forward of its normal flange position.

If you eyematched through the camera viewfinder when you set yours up, this is what will have happened. In this position the effects of an achromat on front of your relay lens may be more subtle as to be not noticeable.

If the results on a definition chart are no worse without the acromat, I would be inclined to take it out as there is one less optical process to add flare and diminish the great contrast which is a signature of the JVC. The downside is your appliance may become longer.

To get a larger area off the groundglass, you might need a relay lens in the ballpark of 35mm to 40mm. These in wider apertures and of acceptable quality are not so easy or cheap to find.

The 35mm motion picture image frame is 24mm wide. If you want to be faithful to the motion picture film look, then this is as big an area off the groundglass as you need.

A simple test is to cut a 24mm x 18mm rectangle out of a piece of paper, place this in the path on your groundglass and see if you camera is picking up all of the image area. You may find you are shooting inside of it by about 2mm.

Last edited by Bob Hart; April 23rd, 2007 at 10:22 PM. Reason: errors
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Old April 24th, 2007, 04:54 AM   #100
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Quote:
Originally Posted by Daniel Schaumberger View Post
How does it come that the Redrock M2 spinning adapter does not use a condenser lens? I saw only that the spinning disc is thicker than normal gg's.

Daniel
The M2 does use a condenser lens, they place it between 35mm lens and GG. The condenser is actually fixed inside the lens mounts.
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Old April 24th, 2007, 08:47 AM   #101
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Quote:
Dale Backus: Oh Frank, thanks for pointing me to your old tests - i checked out as much as i could and i was very impressed at the lack of grain, how was your system set up? I noticed a little vignetting and hotspotting, were you using a condenser?
Actually, I don't think any of those had a condenser except the one that mentions it in the file name. ("MicrowaxAdapter_Test_Condenser.mpg") So they could have actually been better as far as not having the vignetting if I had a condenser on them.

Later on I built one (held together with tape) that used a condenser from some magnifying glasses (the kind you would use in fly-tying or jewelry making). It worked well. http://70.147.193.182:81/mwtest/adapter_pic_05.jpg
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Old April 24th, 2007, 09:59 AM   #102
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Quote:
Originally Posted by Bob Hart View Post
Dale.
The 35mm motion picture image frame is 24mm wide. If you want to be faithful to the motion picture film look, then this is as big an area off the groundglass as you need.

A simple test is to cut a 24mm x 18mm rectangle out of a piece of paper, place this in the path on your groundglass and see if you camera is picking up all of the image area. You may find you are shooting inside of it by about 2mm.
Hey Bob
Great information.


Just to expand a little on this, let's not forget that the 35mm frame you mention is a movie frame, or what we know in stills photography as a half frame.

The 135 stills format is 24x36mm, since film passes though a 35mm stills (135) camera (and certain movie cameras) horizontally, not vertically, as in a regular 35mm movie camera.

So, if you're going to use 35mm movie lenses (in PL, Arri, BNCR or OCT-19 mounts or similar), you're going to want the movie 24x18 frame, but if you're going to use 35mm stills lenses (in Nikon, Canon, Pentax etc mounts) then you're going to want the 18x36 sized gate/frame.

If you use a stills lens in a movie gate (which you can, a lot of cinematographers do), then your lenses are going to turn out twice as narrow in angle of coverage and you'll be looking at twice the magnification on your focussing screen. Every stills lens turns out twice as tele when mounted on a movie gate or half frame camera. Which also means the potential for twice as much grain on the screen if you're using a fixed screen converter, etc..

Your typical movie lenses are very expensive, because to take a half frame 35mm gate and blow it up to the size of a cinema screen demands a lot higher optical engineering standards and build quality than a full frame stills lens does, just blowing up to a 16x20 print.

Here are a few more differences: movie lenses usually come with gears built in for follow focus, no click stops on their apertures (i.e. smooth aperture pulling), and a focussing helix designed for movies (focus pulling) and not for stills.

This means that one would typically have to rotate the focus ring on a stills lens some 270 degrees or more to get from infinity to nearest focus, whereas a typical movie lens would half that rotation amount.


HTH
Cheers
Chris
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Old April 24th, 2007, 07:21 PM   #103
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Thanks a lot for your awesome replies, guys. One question though, for Bob.

After reading your post several times i was tryin to figure something out... a relay lens (macro?) is necessary to potentially sharpen the image? Using my proposed lens layout: Lens < Condensor < GG < Achromat, would you still agree with this? OR do i need to put a Macro between the achromat and the GG? Does the achromat not act as a macro as well?

As for the Back Focus, the Letus35 HD100 comes with a backfocus lens that mounts directly to the HD100 body... is that completely necessary? My tiny little brain tells me if we just got everything at the perfect distance away to match the focal length of the JVC's imager, than we wouldn't need it? Thanks guys... really appreciate it
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Old April 26th, 2007, 02:25 PM   #104
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Guys you gotta help me!

I'm really getting down the the point where i'm starting to order stuff, and (due to my very limited cashflow right now) don't have a lot of room for screwing up. I read another post saying that with a 50mm 100FL Condensor, that would yield good results. Is there something wrong with using a condensor of shorter FL?

I really would like to know whether or not the Backfocus lens that comes with the Letus for the JVC HD100 is necessary or not.

Also, if i put a condensor in front of the GG, does the achromat need to placed at the FL of the condenser? It seems like something does, just not sure what.

Any help would be greatly appreciated. Thanks guys...
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Old April 26th, 2007, 04:23 PM   #105
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Dale

Chris Leong here
I'm building a DOF adaptor as well.

So what I figure is this:

Firstly, if your camera can focus down to within a couple of inches from its front element, then you can get started without anything.

Now I know you're buying commercial and I'm building, but the principles are the same, so check this out, please. I promise to be brief, but thorough.

Just in the design phase, I got a Nikon extension tube set, an old portable CD player that didn't work any more, a project box from Radio Shack, some of those milky CDs from the ends of those bulk CD packets, a battery holder, switch and potentiometer.

I think the most expensive things for me were the tube set (with Nikon mounts) and the potentiometer. Everything else was next to zero. (i.e. I had lying around the house anyway).

Okay, so then there follows a period of fooling around with actual construction vs what looks good on paper.

Mainly it was, for me, getting the motor that spins the CD mounted solidly enough not to lose focus, yet also isolated from the rest of the system so it would not vibrate/shake the rest of the system and not be too noisy. I ended up with a double mount design, one sturdy one with rubber shock mounts to isolate the entire motor/CD assembly, and one fine adjustment mount, also shock mounted but less so, since this stage is where I'm carrying the fine back focus settings, and has to stay where it's put.

At this stage, if your camera can focus on a 24x36mm rectangle at around 2" away or less, you can simply set the box with the mount and the Nikon lens up, spin the GG, and shoot the GG image as is.

Eventually you're going to have to find some way to fix the assembly to the front of the lens. I just ordered a Cavision 15mm rod system, but you can do what you want, as long as it's steady and won't fall apart before you're done shooting.

Now comes the fun part.

When the image is projected by the stills camera lens onto the spinning GG,
there's no frame, or gate on it. It's just a circular image on the GG.

You can frame as much of it as you want to, even have the corners fall off (vignette) by zooming out. Or you can zoon in and get just the center part of the GG image.

Now most zoom lenses will focus closer the wider they're zoomed out.
A lot of camera lenses won't actually focus down to 2" in front of the lens unless they're zoomed out.

So you're stuck with using the wider part of your lens.

Which is where CA (chromatic abberation) typically lives, at the edges of the lens.

So, in order to get rid of that part, and also to enable a more macro setting altogether, you add a glass/glass (achromat) lens doublet in between your camera and the GG so you can a) focus closer and b) reduce or eliminate the CA at the fringes of your image.

Also, if you find that your image isn't uniformly bright across your screen (i.e. is fading or falling off at the edges, then that's a sign that some kind of condensor may be required.

Now, what strengths to use? What diameter glass?

Well, that depends. What you really have to do is to learn your camera's lens.
By this, I mean that each lens has its own design compromises, construction cost being one of them.

A certain lens will not be super sharp at certain distances and at certain focal lengths (zoom settings).
At others, however, it kicks optical butt.

What you have to do is to get your camera working in those optical sweet spots, , where everything's at its sharpest and least distorted, and bring that sweet spot down to focus on your GG.

The catch-all setting for that seems to be a 10x macro achromat doublet, which is what most of the commercial DOF vendors are supplying.

If you'll notice, most high end 10x macro filters for stills cameras are, in fact, two element achromats, BTW.

What diameter? Well, that depends on your camera's front lens size and the size of the part of the GG you're shooting.

If you have a smaller video camera with only a 48mm front end, like an HC1 of the new Canon, then you'll not need to go much wider than a 52mm macro. And there are plenty of 48mm achromats available to you as well.

If your lens is wider, then probably a 72mm achromat would be useful.
Step up or step down rings (from 82mm to 72mm, for instance) can be used to adapt your particular camera lens to the 52mm or 72mm achromat sizes.
They're very inexpensive too, and not completely necessary, per se, for setting up purposes.

I'll say this again, so you're clear - the rings aren't necessary, you can just hold the macro filter up on front of the camera, or tape it there. You'll still get an image. Then you can refine it, fool with, set it to your own camera's sweet spot.

If you can get focus, an achromat isn't necessary either, . Just get one of those cheapo sets of +1 +2 +3 +10 closeup sets for your camera, available from eBay all day long, then fool with them and find the sweet spot on your camera's lens.

Obviously if you're starting with a larger achromat, you won't be using the edges of the achromat, so CA will be reduced compared to if you were zoomed full out and using the edges of the achromat.

Once you're clearer (after taping and screening several times) which settings are best for your camera, then you can sell the lower cost stuff back on eBay and substitute the higher priced elements.

It may be that you only need a +3 your lens to get its sweetest zoom setting to frame nicely on the image in the GG. Maybe with that +3, you're zoomed, maybye a third of the way wide, close enough to get by most all of the CA in your camera lens and in the +3 adaptor.

Maybe it's a +5. Whatever.

Point is, every lens design is different and so you've got to do a little hunting and pecking to get the best combination for your own camera combination.

To sum up - start off with the stuff you know you're going to need that's common to all DOF boxes - a box, a stills lens, a stills mount for that lens, some kind of GG.

If you need a macro set to help focus your camera on the GG image, then get one of those cheapo everything-in-it sets, and start experimenting with all of the various diopter strengths (maybe it will end up by being a +5, then a +1, for instance, that seems sharpest to you).

Get everything working, tape stuff, watch it. Change one thing at a time and shoot some more stuff. Better? Worse? Check the colors at the edges, the brightness at the corners. Any distortion at the edges? Keystoning? Barrel distortion? CA?

Settle down on the best combination of video lens focus, video focal length / macro lens length / GG to camera distance (the GG to stills lens distance will, of course, be fixed). Then upgrade your components and build it out nice.

Quite Easily Done.

HTH, YMMV, etc.

Cheers
Chris
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