Medium format idea

[Paolo Rudelli]

Jesse yours resoult hare impressiv ....

Just to know if my way ok tinking is ok ;)

for 6X6 format

you need digonal of 84,85mm

so in as circle of diameter of 84,85mm

you can put one frame of 67mmX50,25mm (4/3 ratio) maximum size...

[Paolo Rudelli]

i think i go for mini 6x6 ....

look at this thechnical sheet i made

READ

[Joe Holt]

Images look great Jesse! I can see some minor vignetting in the shots with the truck and the fence. Are you using a condenser lens? There is definately no grain in the shots (none that I can see). Could you give a break down of your rig?
Focal Length and F# of the Medium format lens?
Type of ground glass (how fine grind? WAO 9,5 etc?)
Condenser lens type(PCX or DCX, F.L. and diameter)
Can you post a pic of the rig attached to your video camera? I'm curious how big it really is. Finally, it is also helpful to know what video camera you were using. Great job!

Joe

[Jesse Rosten]

Joe,

First, let me say that the whole thing was held together with tape. Wanted to see if it would work before building something more permanent. I used it on the front of an xl1s with the standard IS II automatic lens. To get an idea of size, think of an XL1 with another 10 inches sticking off the front.

I ground the flat side of a huge PCX condeser with 1000grit AO. The final grind had quite a few scratches in it, but I was so excited to start shooting with the adapter I couldn't sit and grind anymore. Yes, there is some vignetting. I zoomed in on the image until most of it was gone. I'm afraid my condenser lens was just too big to be effective. I found it in an old overhead projector. It's about the size of a CD. Don't know what the F.L. is on it. But I'm pretty sure I'd get better results from a smaller condenser.

The medium format camera I used was a Kiev 88 with an 80mm 2.8 lens. Do a search for it on ebay and you can find them for relatively cheap. . I took the film back off the camera and taped the shutter down on bulb so the shutter curtains would stay open, then afixed my GroundPCX right where the film would normally be.

BTW this camera is an SLR so you could build a vertical mount system with it. Or maybe there is a big fat prism out there that would flip the whole image?

-jesse

[Joe Holt]

<<<-- Originally posted by Jesse Rosten : Joe,

First, let me say that the whole thing was held together with tape. Wanted to see if it would work before building something more permanent. I used it on the front of an xl1s with the standard IS II automatic lens. To get an idea of size, think of an XL1 with another 10 inches sticking off the front.

I ground the flat side of a huge PCX condeser with 1000grit AO. The final grind had quite a few scratches in it, but I was so excited to start shooting with the adapter I couldn't sit and grind anymore. Yes, there is some vignetting. I zoomed in on the image until most of it was gone. I'm afraid my condenser lens was just too big to be effective. I found it in an old overhead projector. It's about the size of a CD. Don't know what the F.L. is on it. But I'm pretty sure I'd get better results from a smaller condenser.

The medium format camera I used was a Kiev 88 with an 80mm 2.8 lens. Do a search for it on ebay and you can find them for relatively cheap. . I took the film back off the camera and taped the shutter down on bulb so the shutter curtains would stay open, then afixed my GroundPCX right where the film would normally be.

BTW this camera is an SLR so you could build a vertical mount system with it. Or maybe there is a big fat prism out there that would flip the whole image?

-jesse -->>>

Thanks for the info. It gives more meaning to your grabs. Brett Erskine posted in one of these threads (I can't remember where and when or I'd just give you a link) about how to do a crude measurement of the focal length of a lens. I'll try to duplicate it now.
Take your lens outside on a sunny day and hold it perpendicular to the direction the sun's rays are coming from. Project the sun's rays onto a sheet of paper and move your lens up and down until you get the smallest spot possible. Meassure the distance from the spot on the paper to the lens. This will give you a rough estimate of the focal length. It would be most efficient to do this at noon with the sun at its highest in the sky. You can then measure your diameter and then you'll have a baseline standard for making future lens aquirements for testing. Brett also posted that you want to find a condenser with an F1 rating which means the F.L. is equal to the diameter. Based on your images, I'd guess that you either need a shorter focal length condenser (to spread the light out more to the edges) or you need to zoom in until the vignetting is gone.

For grinding, be sure to use white aluminum oxide. Stay away from the grey stuff (they call it blue).

I'm just imagining the size of your rig! I don't think a vertical mount would be very practical for the XL1S. You'd need a step ladder to operate it :>)
Also be sure not to go into war zones with an extra 10 inches sticking out of the end of your camera. You might get shot as a combatant. Keep us posted. As far as I know, you're the first pioneer with medium format lenses. I would think that the HD guys would be very interested in your progress.

Joe

[Jay Silver]

Joe,

When you say the 'white stuff' versus the 'grey stuff', would that be the same as the 'polish' versus the '1000 Grit' on this page (halfway down)?


-j

[Joe Holt]

Jay,
Don't bother with rock shed. They are great but their products no longer serve our needs. We've evolved! Instead check out:
http://www.gotgrit.com/product_info.php/products_id/60


You only need 1/4 lb of each as it goes a long way.
I'd get 9 micron WAO and 5 micron WAO. You'll have better results in your fine grinding with these products. I also ordered Cerium Oxide which is a polishing agent. Some here would advise against the CEO but I've had some luck with it when used sparingly at the end of my grinding process to "finish" the fine grind. If you use the CEO too long, you'll begin to polish your lens again. If you find a source for 3 micron WAO buy it and post it as I'm sure there's a bunch of people who are interested in it. (including me!) As far as how to grind, there are many posts within the Aldu35 thread that give tips and links to step by step instructions. Just do a search for "grinding glass". I hope this helps. Good Luck!

Joe

[Wayne Morellini]

Hi guys, I'm interested in an medium format adapter for HD, but don't know much about the format, can you help?

I have seen Imax, and it does look impressive. What range of film sizes does medium format cover and what matches Imax? How do I tell what I'm buying? Where can I get them cheap?

As I said, Imax looks impressive, how much better is the depth of feild, converging verticals, and angle of veiw of MF over 35mm film, and how does it compare to human vision?

What is the range of focal length for a standard (feild of veiw) prime lense?

The aperature f ratio of the prime lenses, how low do they go? How does the aperature f ratio work?

I also am interested in getting the brightest image, any suggestions? I was thinking of maybe a wide fast Large format lense image downsized to medium format (same dof as medium format).

I have seen items advertised, called Directors Veiwfinders. Are there any veiwfinders with sufficent resolution to use as an HD adaptor?

Thanks

Wayne.

[Rob Belics]

You are mixing apples and oranges. Imax is a 70mm film. How you would ever adapt that to HD, I don't know. You are kind of trying to compare the Hubble to an amateur telescope.

[Wayne Morellini]

I'm asking what is the range of film sizes medium format covers, I understand that Imax is a medium motion format. I am asking what I would need to match the image characteristics (convergent verticals, angle of veiw, depth of feild) of the Imax film format (which medium format lense most closely resembles it). I am not looking to get Imax lense or adapt lesne to Imax camera. Just a bit of Imax look (without Imax resolution, or films sensitivity).

[Bob Hart]

A bit of practical info on the glass groundglass.
I found when polishing that I seemed to get less gouging and scratching when the flat glass sheet I was dressing the groundglass upon had been roughened with 120 grade grey emery then cleaned carefully.

I also tried a tip from an amateur telescope article of using some liquid soap to asssit lubrication. It seemed to help a little.

With the roughened base glass sheet, here was less inclination for the groundglass to stick and gouge. It's been a very frustrating learning curve. The first disk has been hopelessly scratched on the clear front face.

I tried using a piece of thick machined aluminium plate to dress the groundglass on but this did not seem to do anything except make me tired. The prescription lens makers use iron as a dressing surface on the machines.

[Wayne Morellini]

On the other adapter threads I think they have gone to a chemical GG process, also somebody remarked that he saw metal plate being ued to grind the glass professionally.

[Patrick Falls]

hello everyon, i have been sitting around waiting for all of the technical folks to come up with a working adapter for the xl1 for quite some time. i've been keeping track of the aldu. have someone come up with an advanced medium format model yet?

how much would something like this cost to put together?

[Jacob Ehrichs]

Just wanted to ressurect this thread from the bottom. I'm very interested in seeing where this type of adapter could take us. That it's projecting a bigger image for the cam to record is a major plus in my book and for my situation, negates the 'large' size of the adapter.

[Dietmar Zonewicz]

have a look at: http://arco.acromedia.de/ than go to projekte and select mini60 - filmlookadapter

Tell me what is your opinion about the system - except of that the last shot was much too dark.
Also watch the focus pulls.

The bosscreen did reduce the light that much, but I think I can reduce this an the vignetting by using a fresnel or a condensor behind it.
The groundglass was a mediumformat gg from Mamyia, the markers on it where removeable with aceton. It isn't as fine as the self grided may be, but at this big size it really doesn't matter. Remember the gg is 6x6cm!
Basis for the project was a Prakti six which is the simple version of the Pentacon six.


dietmar