primes

[Charles Papert]

I'm onboard with Nick H. on this one.

For the realistic price of a set of 1/3" primes you could buy into a 2/3" camera...

[Jon Bickford]

I still think there's a bigger market for 1/3" primes than there for new 16mm buyers, but how many companies build 16mm lenses? but i don't know very many people that own 16mm and certainly not that are in the market to buy brand new (i still have a worked over arri-s non sync but haven't used it in over a year and a half) that said, someone could find a fairly nice used 16mm package for the price of an H1

[Tom Hardwick]

Canon had a Super-8 camera (the 310XL) that had a 3x zoom with an aperture of f/1.0. I have one of these and can confirm that the f/1.0 aperture was constant throughout the zoom range. Of course the Super-8 image area - at 4.1 x 5.7 mm - is the same size as a half inch camcorder chip, so making such a fast zoom for 1/3" chipped camcorders should be easy.

tom.

[Michael Maier]

I thought super 8 was closer to 1/3" than to 1/2".

[Tom Hardwick]

1/3" chips measure 4.4 mm x 3.3 mm for their effective area, considerably smaller than the Super-8 frame.

[Jean-Philippe Archibald]

And why it should be easy? A lot of threads recently talked about the fact that it is more a challenge to make a good lens for a smaller chip than a bigger one. since the chip is smaller, the lens must resolve more pixel with a small area of glass.

[Michael Maier]

Originally Posted by Tom Hardwick

1/3" chips measure 4.4 mm x 3.3 mm for their effective area, considerably smaller than the Super-8 frame.

Close enough. Closer to 1/3" than to 1/2".

[Bill Turner]

One thing to keep in mind is that these cameras typically use 3 sensors with the light divided via prisms and coatings. The prisms have a limiting f number (typically around f1.6) that means no matter how fast a lens one used the the image reaching the sensor will not be faster than the limiting value -- so an f 1.0 lens is no faster than an f 1.6 zoom.

Also the small target size allows the design of zooms whose performance rivals the best primes-- it is unlikely one would see a significant improvement in image quality over a well designed and manufactured zoom.

The one caveat is that the zooms for these small (1/3" ) camcorders typically "ramp" aperature (slow down) as you approach the tele end- to f2.8 or more. But the depth of field is a problem at the wide end not the tele for the most part.

[Tom Hardwick]

Interesting post Bill - I'd not thought that the beam splitting prisms would limit the maximum aperture value.

You say:
But the depth of field is a problem at the wide end not the tele for the most part.

but do you mean depth of focus rather than field?

tom.

[Bill Turner]

Tom:

I meant depth of field but may not have been clear why. In reading thru this thread, as well as many others, it seems there is a very strong desire to acheive a shallow depth of field for the purpose of isolating the object in the frame that one desires to focus the viewers attention on.

The tremendous depth of field present in these small camcorders (compared to 35mm Cine formats, or even 2/3" video) at the shorter focal lengths required to achieve comparable fields of view, seems to be one of the motivating factors in the expressed desire in this thread for fast primes for cameras like the Canon H1 or the JVC 100 HDV cameras that do allow for interchangeable lenses.

It was my expressed opinion that the fact that the zoom lens might be only f 2.8 at the tele-end, as opposed to f 1.6 at the wide was not a significant problem in the quest for the "shallow depth of field" look.

And yes the prisms limit the f number. The prisms also create abberations and other problems unless the lens is specifically designed for the type and thickness of glass used in the prism system. Because these issues are most evident at short focal lengths and high apertures, they tend to be less noticeable when using 35mm SLR lenses on a camera as the focal lengths are relatively long in video terms.

In most cases the zoom lenses designed for the camera have an aperture very close to the maximum the prism design will allow, at least at the wide angle end.

[Yi Fong Yu]

interesting discussion,

what's a prime?

[Bill Turner]

Prime lens is a term used to denote a fixed focal length (non-zoom) lens.

example the lens on the Canon XL2 might be a 5.4mm-108mm focal length zoom. One could via an adapter use a 50mm f 1.8 Canon 35mm SLR lens ( a prime or fixed focal length lens) on the camera instead.

[Yi Fong Yu]

so prime is basically a lens that you can't use for zooming. it's focal length is "locked"?