F-(<)1.0

[Gavin Greenwalt]

This could have done it, though it would have been tricky. It sounds like he would have needed something like a large format screen and find a way to vibrate it (just guessing required size here), or a ground glass disc about 2' in diameter and turn that into a massive spinning DoF adapter. If you didn't move it you would have had stationary "grain" from the GG. Not practical, but it would give great results. Right?

Haha, now I really want to build a specialty 2' diameter DOF adapter just for fun.

Then again the grain on that scale would probably be negligible. The real problem with 35mm adapters is that they are only 24mm across. If you had a 2' GG the grain would be subsubpixel I imagine; but horendously expensive.

"If I were a rich man... doobeedoobeedoobedoobeedoo...."

 

[Roberto Lequeux]

Hey, you'd probably only need one gyro if you actually used something like that... :0

 

[Gavin Greenwalt]

Btw Roberto, congrats on your '4k'th post.

 

[Matt W.]

Making a 4x5 ground glass is trivial; the issue would be finding an appropriate condenser lens. Modern 4x5 focusing screens use fresnels directly on top of the ground glass, and even the finest fresnels have a very noticeable pattern, while a spherical lens of similar size would be enormous. The best solution would probably be a 77mm center filter (easily available off the shelf), but these go for $600 new and would reduce sensitivity a couple stops.

If I somehow find a few hundred dollars lying around and my eBay skills are good I may build a 30mm/f0.49 Super35 equivalent large format adapter over the next few months and then add a center filter if it works.

 

[Roberto Lequeux]

What exactly is a condenser lens?

Btw Roberto, congrats on your '4k'th post.

Oh look at that, he he he... thanks Gavin.

I suppose I gotta hurry up and work my way up to 5k now :coolgleamA:

 

[Matt W.]

If you use a normal ground glass, the image that's formed in it will be very bright in the center and extremely dim at the edges, particularly with wide angle lenses, for two reasons. It's primarily because the rays toward the edges of simple wide lenses are oblique, and so hit the ground glass (or film, or sensor, or whatever) at slightly "off" angles. And so you have to look at the sides of the ground glass from a slight angle to see the image correctly, which is more an issue with brighter ground glass (as it has deeper ridges) than finer ground glass, I believe. I have a 4x5 camera with no fresnel and with a moderately wide lens there's a ridiculously pronounced hot spot so you have to move your eyes all over the ground glass to see the full image. With a long lens, the rays are much closer to parallel and so there's less fall-off. A condenser lens or fresnel straightens the rays a bit, so you can see everything from a straight-on angle. If you remove the ground glass from any modern SLR camera you'll notice it's ground in concentric ridges like the fresnel on a light. 35mm adapters had to emulate this without the ridges on a fresnel and so used a condenser lens near the ground glass (I think; I don't know much about how this really works). As a separate but related issue, there's also optical vignetting (with a simple lens, the fourth power of the cosine of the angle of the occluded ray) in addition, making the edges really dim.

So the condenser tries to correct for the dim edges, basically. (For what it's worth, the design of SLR and cinema lenses makes them mostly immune to this kind of severe fall-off, but large format and rangefinder--Leica--lenses are not immune at all.) But for a system built around one lens and a really "thick" ground glass (microwax, for instance), a strong center filter might be good enough to cancel out the dark edges. How I wish I had the money to put this rig together! I'm sure I could get it working really well with a bit of trial and error, though it would require a shit ton of light and the contrast would be....bad. Some day. I'll slowly collect the parts on ebay until then.