There is one way to increase DOF without a ground glass (or anything else diffusing). You have to increase the entrance pupil.

The F-stop measures DOF at a certain focal length. It is the ratio between entrance pupil and focal length. If you are able to increase the entrance pupil by making your optical system (lens) far more complex adding 10ish lenses of the Zeiss prime and lets say 5 lenses of the additional setup to the already 13 lenses of your video cam ...

I think it may be possible to end up with an optical system that has a larger entrance pupil (hence lower F-stop) at the same focal length than the video camera stock lens. If you are very carefull in your construction it may even provide you with a sharp image.

I tried that with my FX 1 and a few lenses I bought. I even simulated in WinLens. But I was not able to create the desired results. Yet someone with more potent tools and more knowledge of optics might (I just regularly annoy my PHD friend who does laser optics).

Hi Jim,

I am getting the picture now. I read someone talked about this before in this forum or some other forum and they mentioned that the CCD only captures a small portion of the larger CCD. If you place the SLR lens at flange distance. Although you get DOF, but the angle of view is way too small or too large (which ever one it is). Its basically like zooming all the way onto a GG with your camcorder instead of just 3x time zoom.

So, wait a second. Would you need to remove the stock lens of the camera, or does it work if you just get the flange-to-CCD distance correct? Just curious about this because it seems very intriguing. I've been looking into holographic options and they seem very good, except for the grain. So if anyone (Jim, etc) has information about this "purely optical" option I'd love to hear it. Now I'm off to search for any more info on this.

It'd be cool to mod my hvx and put an interchangeable lens mount at flange distance from the ccd. Of course, it'd be at the permanent expense of other things... autofocus, zoom controls, warranties...

I believe the situation is, a condenser in between the Lens and the sensor fixes FOV while keeping DOF and a number of stops light gain. I have heard of an Canon SLR lens adaptor for the XL1s that did this. If you look for an very old thread on it with me in, the guy that had one is there. Just add filter to make more film like. The thread would be older than the 35mm adaptor threads, but my reply would be early on in the 35mm adaptor projects.

I would imagine that if you made it yourself, you would need a triplet tuned to the visible color frequencies we want to cut down chroma distortion. I understand these are expensive, as most are tuned to IR or UV for one of the primaries.

Canon XL and Letus Relay Lens
 

Hi,

Anyone knows how the Letus relay lens works? The one that bolt on to the Canon XL. You have to take out the canon own lens so you can fit the Letus relay lens. How can the Canon's CCD capture the image on the GG if there is no lens in front of the GG. Basically you are talking about having a GG right in front of the CCD. Am I right or am I missing something here? Thanks.

In the Letus adaptor models which entirely replace the camcorder lens, like Canon XL or JVC HD100, there is a real camera lens (Minolta (Rokkor?) f2 50mm, used for a relay lens in back of the Letus with the special camcorder mount fitted onto it.

There is also a added doublet on front of this lens to enable closer focus on the GG.

Thanks for the info.

Alex, you are missing, there is no GG, there is no need for gg, the adaptor is simply relay lens which SLR lens attach to it. The relay resizes, there is no need for GG for this, and you get normal SLR FOV and DOF. The problem you will find though, is that 3 chip prism blocks, and sensor microlens, have a limit of aperture before it starts to interfere with image, and wash out. Limit id somewhere around 1.6 to 14 aperture. The relay would allow an aperture to be converted down to below F1.0.

In digital cinema cameras we found a sensor that could do without micro-lens to focus light onto pads, as it also absorbed light falling off the pad. Rai was able to use super fast 16mm cinema lens with aperture below 1.0. Unfortunately nobody uses this design in normal pro cameras.

I think this thread derailed a few posts back. Holographic diffusers are basically the same as a focusing screen like the Beattie Intenscreen.

Made here...
http://www.poc.com/lsd/default.asp?p...ew&sub=lsdkits

Sold Here...
http://www.edmundoptics.com/onlineca...=1363&search=1

If you're capturing the aerial image or using a relay lens without diffuser, you will not get 35mm DOF.

angels
 

Donnie,

What are the different types of angles for? There are 9different kinds. Which angle does what?

The different angles refer the angle of refraction.

There is a crude illustration here...

http://www.anchoroptics.com/catalog/product.cfm?id=283

I am not advocating the holographic diffusers made by POC and sold by Edmund, they are way to expnesive and can only be used in a virbrating or spinning design because of the very heavy grain.

that link goes to some part about sand blasted diffusers.
here's an image of the angles and they're performance. What's the one everyone would pick to get the best overall image. I have a vibrathing adapter and can rid the grain.

http://www.edmundoptics.com/images/catalog/4269.gif

I'm guess the 15 or 20 degree would have the best bokeh results. Just by looking at the diagram it looks like it stands in the middle.

What they found with Holographic diffusers originally (back in original slr adaptor threads) is that when the angle was below a certain point it would get darker towards the outside.

No explanation was given about this darkness, but I believe it was probably because the angle was so low that light from the larger 35mm target was either missing the lens, or not being picked up as well by the lens at it's extremities. I believe the Beattie lens (though I did not follow progress) had a focal point that compensated for this. The solution would obviously be to put a relay lens in between to take the size of the target down to the sensor.

I can't remember but when I looked at some holographic diffusers, I found that they had a mishmash of grain, rather than a regular lensing system. Is this the case?

Rich,
"that link goes to some part about sand blasted diffusers"
I know, it was just the first picture I came across that showed diffusing angle.

On the POC holographic diffusers...
I found 20 degrees to be the best. I have some left over, email me your address and I'll cut a ~30mmX40mm piece and send it to you.


Wayne,
I'm not sure what you meant by relay lens? The dark edges that you described are the same old hot-spot problem, lower angle diffusers dont diffuse as much so you get a hot-spot. If the holographic diffuser had a fresnel lens it would fix that issue, or I guess you could try and mount a condensor behind it. Problem there is you are introducing a lens that is not achromatic. adapters that use plano convex condensers to fix the hot-spot are going to have some level of added chromatic aberration.

I am a minimalist, I think there should be as little as possible between the diffuser and the camera lens.

The image produced on the holographic diffuser is the best I've seen, if it were'nt for the major grain issue. I posted this a while back, shot with Letus35 with POC 20 degree diffuser, condesor removed from letus...

http://media.putfile.com/Modified-Letus35-