Mini35 Oscillating Ground Glass Idea

[Jim Lafferty]

You gotta work on your coding skillz, Richard :D

[Brett Erskine]

All these Thorlab parts and great quality and affordable. Its probably the way to go for most people but its important to keep in mind two things when using these parts:

1)Your no longer using a 15mm rail system so your missing out on important parts you will need later like a follow focus, powered zoom motor, etc.

2)Because the largest tube is only 2" wide you will not be able to make a adapter that works with medium format lenses. As mentioned before using medium format lenses has two benifits. One the GG is much larger and so is the projected image so the grain and softness of the image is greatly reduced. Second - You dont need to zoom in on your video cameras built in lens to frame up the picture on the GG so this means your shooting with a wider f/stop (brighter and better in low light - already a problem with these adapters). You also should be able to get away with not using a close up diopter which means you save some money there and have a even sharper picture yet again.

Of coarse if you plan on only shooting with cine lenses for their focus ability then a medium format adapter is a waste of time and your better off in many ways to use the great parts from Thorlab but if you want the ability and benifits of using any format lens from a cine lens, 35mm still and even a medium format lens then a medium format adapter is the way to go but keep in mind most of these Thorlab parts wont be useable.

Personally I've noticed what I feel is too much softness in most of the clips posted on here. Thats just me though. Never the less thats why I've been looking into doing a medium format adapter. Just laying out the options for everyone. Anyways things are looking good. The quality of the adapters are looking great now. Lets keep this going.

-Brett Erskine
www.CinematographerReels.com

[Richard Mellor]

hi brett I sent away some time ago for the demo dvd from ps teknik and they tested there system on the three major hd cameras
and all the great lenses they did ab testing with and without the mini35,and that is when I wanted to make one of these. rai orz has given us drawings that layout a design, that promises to be as good as the device I saw in the test dvd. we are so close. the parts in thorlabs must be 90 % of what is needed to finish this.
if you have any parts that you could recomend for the vibrating plate: counter balance, offset bearings I think we could finish this . I think the key is the machined tolerences of the thorlab parts . the tube from the camera lens to the slr lens must be perfect . that can be done . we just need to ocillate a ground glass plate in the middle of this system. I spoke to thorlabs
customer service ,and they said making the part do what we wanted to do was no problem. I explained the indie camera market. and hope they will return my call .

[Brett Erskine]

I have the same DVD. They make a demo DVD for their HD setup and another DVD shows off the MiniDV adapter.

There is no doubt that P+S Technik shows the highest sharpness of all the adapters - homemade or not. At the same time its a fact that you loose apparent resolution whenever you use any mini35. The homemade adapters can be close to the mini35 at best and at the same time I've heard HD shooters make a choice not to use a Pro35 due to the overly soft footage. I think the softness issue is one of those things that generally goes unnoticed because we dont know what were missing. But then again maybe Im being just too picky.

[Les Dit]

How many of you want to use the adapter for HD ? For SD, I think my previous video sample of my oscillating adapter clearly showed that it maintains pretty much all of the 720P HD resolution. It certainly would not decrease the sharpness of SD because the limiting factor with SD is the SD format itself ( 720 pixels across ).

Just some observations from my first version!

-Les

[Daniel Moloko]

i really need this adaptor for HD shooting with my HD10U

bye les, good work, and try to give us info about it as soon as possible

thanks

ciao

[Brett Erskine]

Again I dont want to force any bias or step on any toes. Instead just throwing out an alternative to consider. I've been working on this project since the beginning of these threads (and then some). In doing so I've gone down many paths (some great and some very costly) - always posting the good and bad here for everyone to benefit from. Very early on I first turn people towards using things like achromat diopters, focus tubes, PCX lenses and filter rings as parts so before you discount what I say this time lets instead post some unaltered "with" and "without adapter" screen shots of the same scene. It's all about the characteristics of the GG one chooses to use. They are all different. Grains not the only factor. How much it diffuses the light is important too. Too much and the image becomes softer and the highlights tend to glow noticeably. One thing is for sure though. Any short comings of your GG will be reduced by a factor of about 4 times if you step up to a piece of GG that is 4 times as large.

[Les Dit]

Absolutely Bret.
Grain is only one factor. The diffusion of the light, due to scattering, can reduce the sharpness of the image.
Grain is a non issue for moving GG systems.

A simple test for sharpness, lets say for HD: Resize the HD video to SD resolution, then upsize it back to HD . If the result is looking the same as the original HD , then you had no detail in the HD sized image that was actually at the HD detail level.

In other words, if you are able to re-sample the HD to a lower res, and effectively cut the potential high frequency detail out, and size it up again, it should look softer than the original HD.

These concepts are hard to describe in words, I think.

If anyone mistakes the test video I shot for SD , then I'd like to see that SD video camera! While it may loose a bit of detail on HD, those high frequency details don't even exist in SD.

A more extreme example: If we make an adapter for an IMAX camera, and it looses a very tiny bit of detail on the IMAX screen, the same adapter used with a SD video camera ( SD = web cam in my book ) , it won't show any loss of detail in the SD world. ( assume same GG image plane size used for intermediate image )

GG for moving adapters should have minimal diffusion. Bigger GG is always better for that. The engineering question is where the diminishing returns are.

Next time I test my setup, I'll shoot a res chart, with and without. Both in SD and HD.
-Les

[Brett Erskine]

Les do you have a HD camera or a HDV camera. I want to know how compressed the example we look at will be. Anyways thanks for checking into the GG issue. Look forward to seeing them.

[Richard Mellor]

well the mini35 is a product that gives and takes at the same time. you get shallow depth of field but lose some sharpness
when 35mm ccd chip become the norm no one will use any of these devices. but for the next three years the current options.

use nothing. and have no ability
to create a shallow depth of field .

buy a$10,000 ps tecknik.


finish project and have a under $500 ps tecknik clone .

people that have not seen the test dvd from ps technik. can judge for there selves. here are some still from there first model
http://www.pstechnik.de/sheets/downloads/focus_pull.pdf


this project is 90% complete with a source for the ocillating plate fitted in this cage it will be finished. we will have grainless capture up to hi def , and the members here will have a parts list to build one of there own , from thorlabs cage system and tubes.





I think the look that it gives to video is well worth it.

[Richard Mellor]

this whole category {alternative imaging} started with towards a film look that is what brought most of us here .how to help video look more like film . one of the last components of this was

the holy film look, shallow depth of field. the only device that
could do this was $10,000 . people would pay it to create .
bokeh.bokeh is sometimes an addiction in the art world , and
I agree .I see more and more tv using the film looks and I think it's getting better. our 50mm canon and nikon normal lenses are considered the best lenses to capture this look . I think this is a worthwhile project and worthy of our efforts.

http://www.photo.net/mjohnston/column49/


I am most interested in the trees.

tough bikers against a green velvet blanket

http://www.dvinfo.net/media/mellor/PDVD_540.BMP

[Brett Erskine]

Richard-
Very interesting link! I completely understand and a big fan of the Boken approach to photography. At the same time I know I want to at least start each project with a clean slate. In other words work with a camera that starts with images that are (for the lack of better words) "irreversibly bias". If I want a soft look for one project I'll throw a filter on the front of the lens and take it off for another - instead of working with a camera as if that same filter is permanently mounted inside the camera. Again thats just me being picky. I think for anyone thats doent feel its wourth the extra effort to go after that last 10% in quality I would say that the Thorlab/static adapter is the best design so far. Its made up of tough, precision parts that are easy and quick to build so definately the way to go.

[Les Dit]

Brett: It's a JVC HDV camera. It's video holds up well at about 8 megabit media 9 compression.

Richard: How much is Thor charging for the eccentric shafts ?

Brett: You mention the tough, precision parts that Thor makes. Maybe I missed it, but where are the parts that.... ummm .... move ? ( the heart of the matter, as you know ! )

-Les

[Brett Erskine]

Les-
You must have misunderstood. What I meant by tough precision parts was not moving (ie. oscillating parts) but parts that are strong and accurately made parts. ;-)

Sorry I had to say it. Im only messing with you. Seriously though these parts like the focus tube are precision pieces (unlike the PVC plastic tubes used before). Its important to keep things from shaking around at all because flange focal lengths are measured in fractions of a mm.

As far as the current issue with the oscillating parts I'm still using the micro offset shafts that I told you about awhile back. Its posted a few pages back. They are basically two small threaded shafts spot welded together to create one offset shaft. I'm still trying to find the same part ready made though. No luck. Beyond that my oscillating mechanism looks and acts the same as the P+S Technik. Variable speed control, tally light and camera battery powered. Im having a optical engineer look over my setup to make a calibrated field lens right now. Its a lot like your first one. Have you made some changes? Well thats about it. Let me know if you have any questions.

[Dogus Aslan]

hi.. i have also been studying for a while now..i have come to production level..i have made protypes pf the mills..and the metal parts of the tool are now being cut with laser cutters...this is the second protype we have made the first was very big and the design had faults..this one is improved..it has a 2.5 milimeter radius of the revolving ground glass..i thought that the multiple of the daimeter and speed of revolution is stable..so i increased the diameter to 2.5 milimeter, this was i will increase the revoltion speed and with it decreasing the sound..the bearing and mills where produced with a 0,001 +- mm sensitivty..this way decreasing vibration...i am expecting vibration in levels of not recognizing..but if there will be noticible vibration..counter weights will be added...i have tested the system stablely with a large format and a medium format beatie screen..i have found that the medium format gives better sharpness due to its finer structure...as soon as i compile the tool i will test with both..i have tried dozens of other galss but all seem to reduce f-stops in a great amount..the beatie screens are a miracle..(many thanx to mr.fresnel)..i will plan th motor power and speed later, it is easier to do than to calculate weights and friction..of course i have not entered the subject of turning the image around...i belive using to many parts other than gg will decrease quality, and increase the number of paramteres of a perfect image..i am planing to get an external lcd screen and simply rotate it..of course post production will fix what is on the tape...i have done some stable shots with the screen and pentax 1.1.2 lens.....since i have not put the thing together yet i have not been able to take mobile shots...the lens will be screwed on with a premounted c-mount, and will be screwed on to the camera (trv-940) with the 37mm diameter screw..of course we have designed the
platform which holds the whole thing which is aprox. 1.5 kilograms in maxiumum...

here are some links to the process:

http://www.tumgorsel.com/dosealas/dodo35/dodo.jpg
http://www.tumgorsel.com/dosealas/dodo35/dodo2.jpg
http://www.tumgorsel.com/dosealas/dodo35/dodo3.jpg
http://www.tumgorsel.com/dosealas/dodo35/dodo4.jpg
http://www.tumgorsel.com/dosealas/dodo35/dodo5.jpg
http://www.tumgorsel.com/dosealas/dodo35/dodo35-1.jpg
http://www.tumgorsel.com/dosealas/dodo35/dodo35-2.jpg
http://www.tumgorsel.com/dosealas/dodo35/dodo35-3.jpg
http://www.tumgorsel.com/dosealas/dodo35/dodo35-4.jpg