Medium format idea

[Jay Silver]

Advance apology #1: I'm sorry if this has come up before.

Advance apology #2: I'm no kind of optics whiz.

The idea:

In a previous thread (http://www.dvinfo.net/conf/showthrea...threadid=22416) it was agreed that a larger projected image on the GG would result in a better picture overall, but argued that putting any sort of magnifier between the 35mm lens and the GG would destroy the DOF we're after.

I wanted to toss out the idea of using a medium format lens on the front of the adapter and a magnifier between it and the GG to "correct" the DOF to a more 35mm look but with a bigger image.

Is this based in any sort of reality or is it just fairy dust?

And while I'm here, I was also considering another alternative: bouncing the 35mm image off a two-way mirror onto a piece of that super-reflective material from 3M and then shooting that image with the DV camera through the mirror. The idea was how to get an image off the same side of a surface as the projection, rather than going through the surface and shooting from the back.

If nothing else, a few more ideas for the pot.


-j

[Brett Erskine]

1) If your going to go thru the trouble of using a medium format lens then you better not use a magnifier to reduce the target size because it will kill all of the len's characteristic advantages such as less noticeabe grain and even shallower DOF than 35mm.

2)I brought up and made a diagram for this idea awhile back. Its a promising design with only two disadvantages: The heavy light loss due to a two way mirror and the fact that it doesnt correct the image for left to right (just up and down). Its likely however to create a crisper image because its not being difused by GG and will likely be grainless.

-Brett Erskine
www.CinematographerReels.com

[Joe Holt]

Jay,
Keep the ideas coming. Here are my thoughts...

1). A medium format lens would work to increase the image size and hence would reduce the grain (static adapter) I agree with Brett about the magnifyer. I don't know of anyone who has made an adapter based on Medium format lenses though. My guess why is because these lenses are much more expensive and harder to come by than 35mm lenses. If you have one laying around, I'd love to see some images with a medium format rig.

2). Why use a two way mirror at all? Couldn't you use an optic quality surface coated mirror? The mirror would be mounted at an angle that would project the image directly onto the 3M reflective surface mounted just above the opening for the SLR lens. The video camera would be mounted on a higher plane than the SLR lens. The 3M surface could be mounted at a parallel angle with the mirror keeping everything in the same focal plane. The problem I see is the video camera's need to be perpendicular to the reflective surface for proper focus. This would probably require the video camera to be mounted at an angle perpendicular to the 3M surface. This would work with smaller video cameras but would be quite challenging with larger models like an XL1.



.......3M/.......[]Video Lens
SLR[ ]...../mirror

This might be a nice grainless option for the new prosumer HD cams just now hitting the market. Let me know what you think. Joe

[Jay Silver]

Thanks for the responses. I agree that the medium format lens idea isn't very cost-effective but it might not be a total dead-end - I think I didn't explain myself very well in that first post, so here's another go.

Click for a diagram:
Medium Format Idea


And in the meantime I've had another thought along the lines of my two-way mirror/3M tape idea.

Another handy diagram:
Idea 3


More for the pot.


-j

[Joe Holt]

Hey Jay, or anyone one else interested. I found this Med. Format lens on ebay. It might be ok for adapter making. It's currently at $12 and ends in 2 days. Just in case you wanted a lens for testing your design. Joe

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=3807726700&category=3352&sspagename=STRK%3AMEBWA%3AIT&rd=1

Description
This is a Mamiya No. 27972 lens 1:3.5 C series 645mount lens,it is being sold as a parts lens only, the iris is sluggish and is not guauanteed to work. The lens is being sold as is and buyer pays 5.00 shipping in the lower 48, please use paypal if you want the fastest shipment.

[Nicholi Brossia]

I'd thought about this idea too, but don't know anything about medium format cameras other than the film being 6cm x 6cm. A 60mm frame would cover a lot more area (grain) than a 35mm without having to be magnified, therefore preserving the medium format's DOF. That would be pretty neat (granted I don't know the difference between 35mm and medium format DOF... from your description it sounds too shallow?).

Currently, with 35mm, a 4:3 frame requires a 50mm diameter focusing screen (ground glass) and 16:9 requires 42mm diameter. That's just about perfect for these prosumer camcorders. A 6x6 frame would require an 80mm diameter focusing screen at 4:3 and 70mm for 16:9. That would be great as far as overall grain coverage, but the adapter would end up huge. Although it may work out super well with the DVX100's 72mm threads, which would be awesome. Any ideas Brett?

Joe, I also like the prism block idea that you've drawn in your Idea 3 design. I'm not optical engineering inclined, but it sure looks like a good idea from my standpoint. The only thing I'd be worried about is splitting the colors up... like the "Dark Side of the Moon" album cover. Again, that may or may not apply.

[Joe Holt]

Jay gets credit for the drawings. They're great by the way. Could you do one explaining your two way mirror idea? I'm still a little confused on how the two way mirror works. Thanks, Joe

[Nicholi Brossia]

Oops, sorry about that Jay.

[Brett Erskine]

What type of prism as you showing there in your diagram? Let me know and I'll do my best to try and figure out if it will work. Good design by the way. My design is totally different and while it makes sure everything stays perfectly on axis it uses a two way mirror. This one doesnt so potentially it could be a better design. Let me know.

I'll look over the other drawings tomorrow. I'll tell you one thing right now though. Using a magnifing lens to increase the target size will also kill the brightness of the image. For example if you make the image twice as big it will be 1/4 as bright.

-Brett

[Jay Silver]

Here's a drawing of Idea 2. The more I look at it, the less workable I think it is.

As for the prism idea, I didn't have any particular prism in mind when I drew it and I can see how it could very well be a Dark Side of the Moon result. I went quickly looking through Edmond Optics and was surprised that there's only one sort of prism that bends light to 45° - a Schmidt prism. I wasn't surprised that they were really expensive.

Apparently Schmidt prisms show up in eyepieces for telescopes and binoculars so it might be possible to find them in the surplus market, although they probably wouldn't be big enough.

I really like the idea of capturing the image from the positive side of a surface, rather than from the back. It solves those 'transparent yet not transparent' issues. I'll keep thinking about it.


-j

[Joe Holt]

Jay,
I don't think your two way mirror idea would work in the configuration you are showing. I believe that a two way mirror requires one side of the mirror to be in darkness to create the reflective properties on one surface. You show light passing through the mirror from the SLR lens and then being reflected off the opposite surface to the video camera. The light from the SLR lens would reduce the reflective property of your two way mirror. Just like when someone turns on the light in the observation room durring a police lineup and the vicious criminal sees the hapless witness trying to make the ID.

I thought you were putting the video camera behind the two way mirror as in a tele-promtper. The light comes in from the SLR lens, is reflected in the two way mirror onto the 3M surface mounted above the opening for the SLR lens. The video camera, behind the two way, shoots the image reflected on the 3M surface.

I have an idea I'd like to try with the 3M reflective surface material you mentioned earlier. Do you have a link to s supplier of that material? Joe

[Jay Silver]

Like I said, the more I look at it, the less workable I think it is. Maybe there's something to your design, though.

I don't have a supplier link. I picked up a roll of 1" tape at a hardware store. Unfortunately it's got a waterproof coating on it that would probably interfere with the image. I do know it's possible to use this stuff for image applications like front screen projection so maybe it's possible to find it uncoated.


-j

[Joe Holt]

Is this the 3M reflective surface you were refering to?

http://multimedia.mmm.com/mws/mediawebserver.dyn?cccccc4jvorcx2DcQ2DcccsOPOy1yFR6-


Joe

[Jay Silver]

No, but that stuff looks even better.


-j

[Jesse Rosten]

Joe -

I have one laying around. A medium format camera that is. I've done a few tests using it on the front of my xl1s. The upside is you don't need a macro lens to get a frame-filling image. The downside is that the whole setup is still quite big. The DOF is noticably shallower than 35mm, but that's the effect we're going for here right? I'm going to try to post some stills from my footage but forgive me if this link doesn't work
http://www.savvyproductions.com/newELEMENTS/static/static.htm