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Old May 2nd, 2005, 02:16 PM   #376
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Sarena, you are right. Back focus is totally separate from focal length. And to answer your question, Mandy, the G35 pics show examples of three different mounts. I assume these are Nikon, Pentax, and Canon. I believe they said you can buy the mount separately and use your same tube.

These are all answered on the G35 forum.

I am not buying a G35 since my adapter works great, so I'm not shilling their product here, but I think it's funny that a lot of people have this cynical prejudice that the G35 guys are sitting there trying to hide grain, hoping to trick a bunch of people when the device first is available. I don't get that impression at all from watching those guys And that would be a pretty silly idea to attach one's name to or try to build a business around.

The real issue is whether the G35 guys' *opinion* of how much grain exists or is tolerable, compares favorably to other people's opinions.



Nice catapult, Dan! :) Anyone who has built anything complicated knows it takes many times longer than you think it will take, so 8 hours is very good!
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Old May 2nd, 2005, 04:29 PM   #377
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I've just gone roughly through this thread, so maybe this is asked before, but how does the catapult make a circular uniform motion? And do you think it is usable for MF lenses too?
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Old May 3rd, 2005, 11:09 AM   #378
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Oscar,
the catapult don't have nothn' to do with GG (yet, lol)
(It may come handy for the whole converter though...... rotf)
It was just what I had to built lately (son's school project) and Bill said:
"I'm always interested to see what you've built next." Zeat's all. (still rolln'...)
But I agree we should stick to the thread (although is sooo fun to slide at times...)
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Old May 3rd, 2005, 05:34 PM   #379
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Still a bit puzzled, are you going to fight a guerilla35 war with your sons catapult?
Stick to the thread...is the catapult finished? If he's really your son, why did he need your help?
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Old May 3rd, 2005, 05:35 PM   #380
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Heres some more facts:

1)Every model video camera (and thus its built in lens) has a different minimum focus distance it can achieve for a given field of view. Basically this means if your not using a diopter then your particular camera may or may not need a extension tube. And if you do need a extension tube it may only need to be short or you may need to make it very long. EACH CAMERA IS DIFFERENT - test your own to find out the facts.

2)Generally speaking if your not using some form of a condenser lens then the longer the extension tube the less you will notice light fall off in the edges of the frame (ie. hot spot). This happens because the scattered light from the GG doesnt have to bend as such a tight angle if your looking at the GG from a distance (ie extension tube). Just hold up your adapter close or far from one eye and see for yourself.

3)MF focusing screens are designed to fix both of these problems and thus your adapter will not need a long extension tube or a diopter anyways.

4)You also dont want to put the GG extremely close to the video camera either because you will get a distorted view of the GG AND your video camera will not be able to keep the entire GG in focus at one time.

5)Learning the basic in optics will reveal what is happening to light with different lenses and GG and you will not need to do nearly as much trial and error. Google the optical components that go into these adapters and make your adapter work like you want it to work.
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Old May 3rd, 2005, 05:44 PM   #381
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Speaking of getting off topic, by coincidence I got the chance to view the raw footage from the latest G35 demo. There really is no grain at all.

To answer Mandy's comment, "I wonder how they accomplished that," it was not done by compression as others have postulated. It was done by an expensive, labor-intensive screen made for them, and a lot of homework. They didn't just start a few months ago. I got the chance to talk to Jonathan of Guerilla35 and was surprised to learn how much thought and work was put into their deal.

The product is also not what I thought it was (I thought it was simple a GG and condenser on a long tube).

I spent $150-200 on my first tube and have revised it multiple times. I've probably spent another $50-100 on bits and pieces. I have some condensers for my GG on the way, and a Beattie as well, so that's another chunk. I derived a lot of enjoyment doing it but in retrospect I wish the G35 were available because $300-400 for an adapter with grain is not that far from $800-900 (i think) for an adapter with no grain whatsoever. Gotta save them pennies!
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Old May 3rd, 2005, 05:48 PM   #382
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Yeah Brett,

I am learning about the close to the GG thing. I am trying anytihng right now to get this thing working. I have put the GG and the camera very close, but I am still getting blurriness around the edges. Must be too close.

Also, how can one tell the strength of an achromat - for example, this one

http://www.surplusshed.com/pages/item/l1590.html

Last edited by Leo Mandy; May 3rd, 2005 at 06:04 PM.
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Old May 3rd, 2005, 07:18 PM   #383
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You can tell the power of an achromat paetly by its focal length. Genereally shorter the focal length the stronger the achromat. You want your achromat to have the proper focal length to send all light going thru it towards a common target at a specific distance (the CCD). Find the angle that the light must bend to hit that target and you have the means of finding the proper focal length for your achromat.

Or you could always just buy a Maxwell or Beattie screen.
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Old May 3rd, 2005, 07:40 PM   #384
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All I can comment on the achromatic is this: for that price, go for it (but it all adds up!)
and if you can get away with it... let us know...
but then again: if those would be a suitable replacement, how come Century is still in business ? just wondering...

(I bought mine from Century,(btw) the screen from Beattie, and some other parts of the best I could find....including US $ 80 for the motor itself! all this having "oriental replicas" on the table @ $0.25 each!)

here is another link I just found:
http://www.angelfire.com/ca/erker/closeups.html
They might work with some camcorders (as long as the diagonal exceeds the diagonal of the format).
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Old May 3rd, 2005, 07:47 PM   #385
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WEll, to do that, I would have to scrap all of my DOF machine plans at this point because I am using the spinning GG and going to a Maxwell or Beattie screen would cause me to go the oscillating machine route, which is a long long road. I still want to try this spinning GG until I can'ts tries no more! The achromat that I was looking at
http://www.surplusshed.com/pages/item/l2076.html

is starting to look good because the focal length is short 80mm FL ( I wonder the strength that would be) and it is clear coated - so this might be a winner for me. What do you think Brett?
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Old May 3rd, 2005, 08:01 PM   #386
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Here is another link:
http://shop.mellesgriot.com/products...=1034&mscssid=
It looks like it comes from the same manufacturer. z'got to be something "just about" with the $9 ones.... but at this price, you can't go wrong.

Last edited by Dan Diaconu; May 3rd, 2005 at 08:03 PM. Reason: forgot info
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Old May 3rd, 2005, 08:14 PM   #387
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Yep, I just found the exact same one at Melles Griot. There is something going on, definitely, probably a second, a scratch or some minor abberations or something. I want to spend the $9.00, but 31.5 mm is a small diameter for my camera - considering the thread is 43mm...hmmm...it makes me think. I wonder if it will matter?

If you check out
http://www.anchoroptics.com/catalog/...d=14&start=226
They also have the achromats, but they are graded as well - and more expensive, even for the Grade 3's.

I am still trying to find another source of lenses!
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Old May 3rd, 2005, 08:27 PM   #388
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I wish I could help you further but as explained before each camera is unique. Not to mention how you build your adapter is unique as well. I'll I can do is recomend that you follow some of the things I have listed above. After that only person that can answer your questions will be you because each project is unique.
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Old May 3rd, 2005, 08:58 PM   #389
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Of course I understand what you are saying Brett, that is why it makes creating a universal adapter sooo hard! I guess James Hurd has a way of making an achromatic lens, so it is possible, just how, I have no idea!
I think I am going to splurge and get the one at Surplusshed to see what it is like. After that, I am going to continue to test and see what the best distance for my camera is - and I am still unsure whether I need a condenser or not - there seems to be some question about if it is necessary or not.
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Old May 3rd, 2005, 11:34 PM   #390
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Hello all,
I had planned on starting this thing already, but I've been tied up trying to close a deal on a house. Hopefully in the next week or so I can get started.

But anyways, here's a link that I was most likely going to buy from: http://www.edmundoptics.com/onlineca...?categoryid=10

They have some high quality lenses and a few lines that are cheaper priced.

Here's one for achromats specifically: http://www.edmundoptics.com/onlineca...=1749&search=1

These are 35% off: http://www.edmundoptics.com/onlineca...=2396&search=1

These links may provide some help in determining what lens you need/want: http://www.physics.uq.edu.au/people/...r/achromat.htm

http://www.usa.canon.com/html/eflens...y/index_a.html



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