Toyo tv zoom lens 12.5-75mm 1/3-2/3 ccd

[marc]

I have Toyo tv zoom lens 12.5-75mm 1/3-2/3 ccd. I have read that a tv lens that is good for 1/3-2/3 ccd will cover the standard 16MM frame. But I have also read that tv lenses have to be kept above a certain f stop when used on film because of the different color coating methods used in manufacturing them. Does anybody here have any experience with this subject? Also, do any other adjustments need to be made to the lens before being used on a c mount movie camera?

[mattias]

2/3" covers 16mm, some of them even s16, but 1/3" doesn't. some still might but don't expect corner sharpness since they're designed for a frame the size of super 8. i don't quite see why the coating should matter, but there are other differences i guess, such as that ccd's only register light that hits them straight on while film doesn't care. this is certainly an issue at these short flange distances, at least if we're to trust manufacturers of 4/3 lenses, but I'm not sure what it means in reality (if anything it should be more of a problem the other way around, right?). no, you shouldn't have to modify the lenses. if they fit they fit, and if thry don't for example because of protruding rear elements interfering with mirrors and prisms, there's nothing you can do.

[mattias]

do you have a link to the coating info btw? would be interesting to hear.

[marc]

The manufacturing info says that it is good for 1/3-2/3 ccd. So, I guess that means both, which would cover standard 16mm. I don't have any technical info on the coating but I have gathered a few things from reading what others have said about the coating of TV(video) lenses. Apparently, these lenses are not coated the same that standard film lenses because each chip in a video camera picks up a different color depending where it is located behind the lens. Not being an expert in Video cameras, I cannot elaborate on that any further.

[mattias]

that may very well be true, but what I'm wondering is why it requires stopping down when shooting film. i wasn't asking for techical info per se, just a link so i can trace the information.

[marc]

Sorry to say, it has been a while since I have researched that info. I went back recently to look for similar discussions on this issue on photographic forums but did not have the same luck. From my extreme layman's perspective, what I have gathered is that stopping down the lens to a minimum F stop causes all the colors to converge so that you are not lacking in one or the other. Wide open, you have have a separation of colors. for example, if you shoot at the widest F stop, the outer edges will be lacking one of the primary colors and you will get a strange color cast. I have not yet tested the lens to compare it against a traditional film lens.
Apparently, this is why film lenses are more expensive than TV lenses; the manufacturing process involves a more thorough process in terms of color coating. This Toyo lens, I got for $25.00. Imaging getting a price like that on a zoom lens made for a 16mm movie camera.

I just found this:
http://webcache.googleusercontent.com/s ... =firefox-a

[mattias]

that's only a problem when using film lenses on digital, not vice versa. it's not the coating but the angle at which the light hits the ccd, as i mentioned above.

[marc]

Did you read the information in the link? It does mention problems with video lenses being used on film cameras at wide f stops. I was just wondering if anyone on this board had experiences using them an how wide an f stop they were able to get away with.

[mattias]

if the lens is meant to be used on a 3-ccd camera it definitely means trouble on film. there are a million reasons a lens might be less compatible with a certain format, i never wanted to imply that there weren't issues, i just never heard that coating would be an issue when using video lenses on film.

[marc]

What am I misreading here?:

"The second difference between video and film lenses is the color landing. This is (to my surprise) largely ignored/unknown among many cameramen.

Glass refracts light differently per color. In lenses this results in chromatical aberration. To make camera lenses that focus all colors to the same plane (= make it free of chromatical abberation) is difficult and expensive. It requires the use of complex lens combinations of different glass sorts. It is needed, however, for good quality film photography.

This you probably all know.

Now comes the story that some (apparently) don't know: In order to save money and produce cheaper lenses for video cameras, when color TV started, TV lens manufacturers sat together and asked video camera manufacturers for a favor. They accepted because it was also in their advantage.

They agreed to put the red, green, and blue tubes (now CCD's) at different focal distances. This is a clever idea for TV indeed, it allows to make the lenses much simpler and cheaper, obtaining a similar imaging result! These RGB distances where then standardised. Yes it is a trick!, A very clever
trick. You have to think of it! It saved the TV industry many $.

As such, lenses for color TV cameras are easier to make, and cheaper, than lenses for B/W TV cameras or film camera’s. So official TV lenses spec’s focus the red, green and blue images at slightly different distances. If you put a TV lens on a film camera, you will probably focus on your green image, but your blue and red film layers will not be optimally in focus. Again, stopping down will help. Again it works in both ways. Again, a simple mathematical fact, no mystery."

[mattias]

that sounds correct, but where does it mention coating?

[marc]

I guess it does not. Then is the color abberation a result of the curvature of the glass? On thing is clear, if this information is correct, you will not get equal color quality at all f stops using a TV lens on a film camera. According to the above information, the widest f stops will give a distorted color rendition on film with these lenses.

[mattias]

again it's only an issue if the lens is for 3-ccd cameras. do you have the full specs for your lens?

[marc]

No, I wish I did. Another issue that was brought to my attention is that the 2/3 ccd is a tad smaller than the standard 16mm frame and it will likely cause vigenetting around the corners.

[mattias]

if you get vignetting it usually goes away if you zoom in just a little bit. i've used 16mm lenses on s16 this way and i think that's a bigger difference in size. it only takes very little, but you have to shoot some tests and remember where the limit is.