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Old April 19th, 2004, 09:30 PM   #691
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um...that's +1.
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Old April 20th, 2004, 04:06 AM   #692
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porro & roof prism??

Quote:
Porro Prisms are narrow right angle prisms used in pairs to make a system that erects and reverts an image from the objective lens of an optical system.
Some one know if porro prism act lick roof prism to revert image???

how to use ??? to "erects and reverts an image" ???
http://en.wikipedia.org/wiki/Porro_prism


link for porro prism maby "big" for for us
http://www.aosa.es/Ing/Catalogo/opti...orro2Class.htm
http://www.aosa.es/Ing/Catalogo/opti...mas/notpor.htm


and this look like p+S kit ;) ;)
http://hardinoptical.com/tvporro.html
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Old April 20th, 2004, 12:40 PM   #693
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Thanks everyone for answers to my questions.

Grain shows up at f4 on the SLR lens? What gives? It would make sense to me if the grain showed up when the camcorder was stopped down, but does anyone know why the grain shows up when the front lens is stopped down? I guess I have a lot more to learn about optics.

James:
I looked at the "Problem" page on your website. Did you ever figure out what was smearing the edge like that?

Ari:
Sounds like shipping across US-CAN border is too expensive. I hope someone can buy some of that off you to help offset your costs.

Anyone within the US have some left-over White Aluminum Oxide that they would like to part with? I would happily pay for the amount still in the container, and pay shipping and stuff like that. Or, I could pick it up if you are in my area. I'm in Olympia Washington, and I go to Seattle every week.
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Old April 20th, 2004, 03:23 PM   #694
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Justin-

I think the problem is with my SLR and not with any other part of my adapter. I took it all apart (again) and tested the image at various stages dismantled and I only see it after the lens is attached. Not sure if that's actually the problem though. It could be a problem with the adapter that's only apparent when the lens is attached! I haven't had the time to check it with another lens. And of course incorporating another lens will throw off the length of the adapter :(

I've seen this type problem to varying degrees before in images taken with other people's adapter.

Has this problem been dealt with before in this thread?

-J
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Old April 21st, 2004, 03:15 AM   #695
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Nice job James, and welcome to the 35 club
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Old April 22nd, 2004, 05:04 PM   #696
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Lenses with different focal lengths

Hello everyone! Reading these threads and brainstorming this concept has been some of the most fun I've had with coming up with guerilla filming tactics.

I'm a little confused about one thing though. With my 35mm still camera, the distance of any lens I put on it is always the same distance to the film plane; no adjustments of the lens to film place distance need to be made by me to use that lens. But if I'm collecting my knowledge correctly, you guys are saying that lenses of different focal lengths will need to be distanced differently from the ground glass to obtain a clear projection? If this is so, why don't I have to do that on my 35mm slr? and does that mean there's no way of being able to use one build for all of my nikon lenses?
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Old April 22nd, 2004, 05:46 PM   #697
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You're correct - the focal flange distance (the distance from the back of your SLR lens to the film) is the same for a particular camera body... which is why you can use any SLR lens which fits that body. The same is true for these adapters. You can build one adapter which will accept any of your Nikon lenses (which are for the same body style).

The focal length is hard to get exactly right, so many people building adapters have made this distance adjustable for fine tuning - or for the more adventurous, to support multiple body style lenses (Nikon and Canon for example). But for a particular body style, once its set it shouldn't change.

There has been a lot of discussion about the focal length of the condensor used. It doesn't seem to matter a ton because with a PCX condensor (flat one side, curved on the other), the flat side is right against the ground glass. If you've ever taken a regular magnifying glass or lens and looked through it at a piece of paper, you find that the closer you get the paper, the lower the magnification. When you're right on the paper, there's basically *no* magnification, which is what we want.

Now, this being said, the purpose of the condensor is to try and 'collect light'. We believe that the degree to which this is accomplished is a factor of the curvature of the lens. A long-focal length (very little curvature) doesn't collect as much light, but has less spherical abberation... and the inverse is true for a short-focal length. The ideal is right in the middle - collect as much as possible without curving up the edges. The general concensus is to use a focal length equal to the diameter of the lens - 52mm diameter/52mm focal length or thereabouts. But, to be honest, I don't think there have been a ton of experiments *other* than the diameter=focal length combo.

The key is that the condensor isn't really 'focusing' the light to a point, but collecting 'stray light' that wouldn't be in the direct path to the macro lens.

My two cents...
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Old April 23rd, 2004, 06:50 PM   #698
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Blurring on James's image edges

Hi everyone,

Glad I discovered this forum. I've been trying to design an adapter on and off for the last 18 months. Have recently switched to the DVX100 and, starting from scratch, will hopefully build something that doesn't have as much hotspot as my last attempt.

James, I think the edge blurring might be caused by the Hoyas. At such a close distance from the GG you are certainly using a significant portion (i.e. diameter) of the glass of both the Hoya diopters. Of course, lens quality decreases near the edges and having two of them back to back is sure to amplify any abberations the lens may have. Also, it sure would be nice if you didn't have to use 55mm lenses, but could use something larger.

I wish there was more selection in hi powered diopters, especially with a 72mm diameter. Century Optics makes two very low powered ones for the DVX100.

Still, your results are the best I've seen for the DVX100 so far. And Brett, your suggestions have been great.

Keep up the good work everyone. Hopefully I'll be able to contribute something useful.
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Old April 23rd, 2004, 09:58 PM   #699
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Actually, James, I'm just wondering if the edge blurring would still occur if you were to take out the condensor from your adapter?
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Old April 23rd, 2004, 10:38 PM   #700
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Thanks guys!

I've posted another test (along with captured still frames).
http://www.homepage.mac.com/dvx100/iMovieTheater6.html

Joel -
I first noticed the problem before I even incorporated the condensor. Though it seems logical that it is the (2) X10 Hoyas, from what I can tell they alone don't appear to be causing it. In fact I'll post an image to prove it ;) And I hope I'm wrong! I'm still looking at my SLR as the source of the problem. Don't know why it would exactly. And until I can disprove that assumption with another (good) lens, that's where I'm going to focus my attention...so-to-speak.
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Old April 23rd, 2004, 11:28 PM   #701
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James, that looks beautiful. What a nice record of the moment.

Hmm, it could be your Konica lens, but hopefully you can narrow down your problem, as the Hoyas seem to be the only way to go right now. Thanks for the reply.

For what it's worth to people researching different diopters, my first attempts were with a Sony VX2000E and a Century Optics +7 diopter (58mm). The Century Optics (Schneider) lens despite being an expensive piece of glass, still managed to show noticeable pincushion distortion when used in conjunction with my VX2000, though it stayed sharp even toward the edges.

I initially dropped the project because of the hotspot. I hadn't considered using a condenser before reading this thread. That seems to change this.

Anyone have any luck finding an Achromat PCX lens? Maybe an Achromat is overkill for the condenser, but might be worth it if they are out there.
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Old April 23rd, 2004, 11:41 PM   #702
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Just had a thought about testing the cause of the smearing. James, if you try to shoot a relatively uniform image source (like a bleached out sky or a bright wall) and stop down your Konica lens a bit until you can clearly see the grain pattern of your GG, then take a frame grab of that, you might be able to ascertain if the smearing is caused before the image hits the GG (i.e. by your SLR lens) or after the image hits the GG (i.e. by your diopter combo). If it is caused by your Konica lens, the grain pattern around the edges of the frame will still be consistent with the grain pattern in the rest of the frame. If the smearing is caused by your diopters, then the grain pattern around the edges of the frame will be disturbed (i.e. smoothed out).

Anyhow, great work!
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Old April 23rd, 2004, 11:55 PM   #703
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DAMN! Bad news. The Hoyas do appear to be causing the aberrations.
http://www.homepage.mac.com/dvx100/PhotoAlbum5.html

Although the test was less than exactly accurate, it does clearly show the problem.

Thanks for the push Joel and the compliment :)
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Old April 24th, 2004, 12:30 AM   #704
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Sorry to hear that, James. But at least you now know what's causing the blurring.

You could always try taking off one of the diopters. This would force you to zoom in more, which would also mean you'd be shooting through less of the diopter's edge area (i.e. through more of its sweet spot). The only hurdle could be that the DVX100 might not be able to zoom in enough to shoot a 24X36mm target full frame with only one diopter. You can certainly test this, though. You mentioned you were zoomed to about 60 as it is. I wonder if you have enough zoom left in the ol' camera to fill the frame.

On the downside, it would lengthen your adapter by 5cm, but might improve your results.
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Old April 24th, 2004, 03:39 AM   #705
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Hmm, by my pen and paper calculation you will probably not be able to zoom in down to 36mm across. If you are 60% zoomed in at +20, I think that with a +10, the tightest you can frame in will be around 40mm.

Though, I'm curious what the real world numbers are.
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