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Old February 20th, 2004, 03:59 AM   #211
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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/TechSupp...?articleid=267
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Old February 20th, 2004, 06:02 AM   #212
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Great link. I recomend everyone to read and learn what its teaching because it sums just about everything up all on one page. Thanks.
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Old February 20th, 2004, 08:26 AM   #213
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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
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Old February 20th, 2004, 10:30 AM   #214
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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.
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Old February 20th, 2004, 12:11 PM   #215
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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 :)
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Old February 20th, 2004, 12:22 PM   #216
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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.
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Old February 20th, 2004, 12:40 PM   #217
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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?
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Old February 20th, 2004, 01:12 PM   #218
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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!
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Old February 20th, 2004, 01:15 PM   #219
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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.
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Old February 20th, 2004, 01:23 PM   #220
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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?
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Old February 20th, 2004, 01:29 PM   #221
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something like this??

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?
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Old February 20th, 2004, 01:29 PM   #222
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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.
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Old February 20th, 2004, 01:37 PM   #223
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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
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Old February 20th, 2004, 01:40 PM   #224
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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.
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Old February 20th, 2004, 01:47 PM   #225
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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!
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