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Old June 30th, 2005, 12:16 PM   #16
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I think it may well be your monitor on the fritz. There is no loss of resolution, obviously the web version is heavily compressed and these artefacts do degrade the image considerably. I have checked this on broadcast montors, and my monitors have recently been calibrated so I am pretty sure its ok, but if anyone else notices this, please let me know, so I can do my best to resolve the problem. The camera is an XL1s and the movie was shot in frame mode 25fps. For all those who are wondering how the system works, I will do my best to explain more clearly. I will try to get some pics uploaded, but I am a bit busy at the moment. Think simple, ok here goes.

1. Take a big ass bearing with an internal diameter of about 55mm
2. Fix it into something, i used a piece of MDF with a hole in it, for weight reasons.
3. the outer wall is now fixed and the inner wall spinning freely and accuratly.
4. Fix you glass into the inner wall of the bearing.
5. Get a machine shop to make you a groved pully which also attaches to the inner wall of the bearing.
6. Fix your motor into a box, along with the unit i have just described.
5. Get a pully belt, and wrap it around the motor pully and around the pully which is now attached to your bearing.
7.Switch it on, and your inner bearing wall will begin to rotate.
Tinker, and Job done, you should have a rotating piece of ground glass.

Hope this helps.
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Old June 30th, 2005, 02:30 PM   #17
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cyclone effect

Nicholas....

nice work....

i tried to dl the larger mov directly, but the link is messed up,,, ie it only goes to stream on the large file.... (you can dl the small version)...


the design that you used had a theoretcial flaw of spinning fast in the center and much slower on the outside edge....

i did not see this effect in the resolution that you provided... did you experience this at all at certian rpm's of the motor?? or was it noticeable with the better monitors???

thanks
skv
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Old June 30th, 2005, 02:50 PM   #18
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Sorry about that, I have sorted those links now, so you can download a larger version if you wish. It all works.

The problem you mention did not occur at any shutter speed. This is not an artifact present in the film. I am very particular about stuff like that. I used an excellent quality optical ground glass, which is paramount in making these things from my experiance. Diffusion paper, and sanded glass in my opinion can't provide the level of acuracy achievable with a good quality optical GG. I used a motor from a video player with 12v of power. Seemed to work very well indeed. The artifacts you mentioned were present having initially constructed the device, but with a bit of lubricant on the bearings and having left it on for an hour to break it in, the rpm was hig enough to not have any artifacts at all.

Hope that answers your question.

Nick
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Old June 30th, 2005, 03:17 PM   #19
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Quote:
1. Take a big ass bearing with an internal diameter of about 55mm
damn you beat me to it...about a week ago I started looking for the parts to do just that. I was going to use a Pillar block bearing...but that might be to heavy. Have a source for the bearing you used or was it a local source?

Quote:
the design that you used had a theoretcial flaw of spinning fast in the center and much slower on the outside edge....
Even if you do come across this problem shooting off center should solve it (only the center in essense does not move...the difference in speeds on good glass shouldn't be noticable)
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Old June 30th, 2005, 03:32 PM   #20
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It is a very robust and simple design.
For the bearings, Local source, I don't know about the states, but over here in the uk, there are hundreds of bearing suppliers. Give one a ring, tell them what you are looking for and 'bob's your uncle', Job done.
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Old June 30th, 2005, 06:52 PM   #21
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Cool!, thanks for the reply,

Have you thought about using an XL2 on your next project? (or maybe sony FX1/Z1 that would be great for blow ups!)
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Old June 30th, 2005, 07:44 PM   #22
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>>>>1. Take a big ass bearing with an internal diameter of about 55mm
<<<<<
Should I check the doctor for that?

Besides the technical part, which is great, the film and story have high quality.
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Old June 30th, 2005, 08:51 PM   #23
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gg

thanks for fixing the links.....
i wanted to dl it and burn to dvd and see it on the bigger tv screen.....



""""I used an excellent quality optical ground glass"""""


could you expound on that just a tad as to the grain or ????

thanks ,
skv
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Old July 1st, 2005, 12:07 AM   #24
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Very nice. I also would like to know the details about the ground glass you used. Where did you get it? What are the specs of the glass?

And how'd you avoid having a hotspot?
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Old July 1st, 2005, 02:02 AM   #25
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Excellent video, very impressive and very inspiring!

I did a search for Nick's other posts and it looks like he's using a Knight Optical 40 micron GG and a macro to get rid of the hotspot? I ordered a GG from Knight Optical, it was only 5 micron finish, too much grain, but the annoying thing was it came with a flaw in it. Not impressed. I recommend Optosigma.

Cheers
Andy
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Old July 1st, 2005, 04:16 AM   #26
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Thanks Andy, for your kind comments.

I am using a ground glass from knight optical. I have to say, if you want a custom job, give them a call and they will try to get you whatever you need. They also replaced a 40.00 gg, free of charge, because it cracked duiring heavy use. Just to clear things up for people, a macro will not get rid of the hotspot, the macro is merely to allow your camera lens to focus on the screen which is very close to the camera.

A condenser, much like the ones used on focussing screens can be used to help eliminate a hotspot, however it will reduce your image size. I have done numerous tests with this, it seems the main way in which this works is by utallising the brighter cental part of the image, and essentially magnifying it in size. If you take a nikon viewing screen apart, you will see this is the case. i.e, if you buy a 28mm lens, you won't see all of your fov.

The best way, to eliminate the hotspot, which is incidently what I have had to to, it to use a gg without any condenser, and buy very good quality fast lenses. I have been using nikons. I made the mistake of buying a fast vivitar, 24mm, and thought i had a bargin. Next to my nikon 28mm with the same apeture, the vignetting was incredible. The apeture on the vivitar, f2 was about 3mm wheras on the nikon at f2 it is about 40mm. I'm sure someone knows the reason for this on here, and this could be causing a problem for some people.

It doesn't matter how good your adapter is, without good lenses, it will always look crappy.

Hope this helps
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Old July 1st, 2005, 08:38 AM   #27
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Thanks for the info, but I found what you say not to be necessarily true. Using my Canon 50mm 1:1.8, hotspots during the day and there is not a step down mechanism on it, so I am stuck with that aperature. BUT on my SEARS cheap 1:2.0 lens, there is a step down and I get the same hotspot with it. So maybe the condenser is a necessary evil?

BTW, I have a couple of extra lenses lying around that when looked through make the image smaller - are these condensers?

Last edited by Leo Mandy; July 1st, 2005 at 08:53 AM.
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Old July 1st, 2005, 09:27 AM   #28
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I can not really comment on your design or the issues you are having, as I havn't seen it first hand. The fact that you are comparing 2 questionable lenses with eacholer, will of course lead you to draw your own conclusions, and without looking at your GG, lenses etc, i couldn't really comment on your hotspot problem. It may well not be the lens in your case, it could be the GG etc.

I am however comparing a 28mm nikon 1.4 lens, with an 800 retail value with that of a 24mm f.2 vivitar with a 80.00 retail value, both set to F2 and I can assure you, there is no hotspot with my setup using the quality lenses, where there is with the lesser ones. Again, this is with a well built adapter. I am not sugguesting buying an 800.00 lens for your rig, as your problem may well lie elsewhere. Therefore, the condenser is only really a necessary evil, if you are to use cheaper lenses, or you have a problem elsewhere in your design, and I can assure everyone from my own experiance, that this is the case. If you have seen my film, and feel that a condenser is a necessary evil, than you are sugguesting that I have a hotspot on my short, which doesn't appear to be the case, this why I am confused with your argument.

I appreciate your opinion, and can understand the appeal of using a condenser, for ease. I would however also not choose to use a condenser for another reason, as it does blur the image towards the edge of the 35mm image plane. This i would imagine is due to the different focal distance between the center of the condenser, which is closer to the macro lens and the outer edge of the condenser, which is further away.

Hope this helps make my point a little clearer. I'm sure there are numerous different designs which all work equally well, however this is the best result I have found, and as I have said can only talk from my own experiance.

Nick
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Old July 1st, 2005, 09:47 AM   #29
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Nick,
You are right about the cost of the lenses. I am using a charity shop cheap lens that I found with a Canon EOS 750, so I think it is not in the range of $800.00, so in that case, you point is well taken.

And no, I didn't see any hotspot on your film, it looked great (as I stated earlier), the dark shots looked great, with lots of brightness.
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Old July 2nd, 2005, 12:53 PM   #30
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Hi Nicholas,
Firstly, great short, very inspiring. Been through all your website as well, very nice stuff.

I am also from the UK (Brighton in the South East), so finding a good source for ground glass is hard.

I see you got ya ground glass from Knight Optical. Could you tell me which type you used from them?

http://www.knightoptical.co.uk/acata...ssDiffuser.htm

they have Ground-LEGB, Ground-B270 and Ground-UV fused silica

Do you think they would be able to custom cut a cd shape for me? I emailed them but get no reply.

Cheers,
Wayne.
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