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Old September 9th, 2009, 03:04 PM   #1
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Why do we need HD lenses?

Been looking seriously at buying myself a Letus or SGblade set up very soon. However iv'e got a few questions when it comes to lenses.
When shooting 2/3 inch XDCAM HD we've all been sold / told the fact you need to shoot with HD lenses.
What i wonder is..... what sort of quality is coming through a DOF adapter and a 35mm canon or nikon prime lens?
With a decent Fujinon wide angle retailing at around $25000 AUD or a complete LETUS kit with Zeiss 35mm primes at around $13000, what am i missing here?

Whats soooooo good about HD glass????????

Also..... if you had the 2/3 inch relay with your Letus , could you use a 2/3 inch to 1/2 inch step down adapter and use the same kit on an ex3 with no loss in angle of vision?


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Old September 9th, 2009, 08:50 PM   #2
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There's two separate issues.

HD lenses - A 1/3" sensor is smaller than a 2/3" sensor. A lens which delivers an image which is only just acceptably sharp across the whole image frame for 2/3" will produce a less acceptable image on 1/3".

There can be exceptions and escape clauses. Many lenses produce a sharper image in centre of their image area, so this sharper centre may cover the smaller area of the 1/3" sensor. When the pixel counts are the same for a 2/3" and 1/3" sensor, 1/3" lenses must deliver a sharper image and pass more light for equal results.

This aspect flows on to the relay stage of a 35mm groundglass adaptor

With groundglass image relay, Letus, Brevis etc., obviously the sharper the relay lens conveys the groundglass image to the camera, the better.

Then there is the quality of the image which is projected onto the groundglass by the 35mm lens for the camera to see.

Groundglass images tend to diminish the harshness of a video image, conferring the "film look" so coveted by users. The texture of the groundglass loses some detail.

A less sharp 35mm lens image on a groundglass may still be acceptable but due to the scatter effect of the groundglass texture, a soft image will become apparently more so, a sort of amplification effect. The blending of neighbouring detail points into each other also causes an apparent loss of contrast which we see as poorer clarity or sharpness.

So sharper lens images onto a groundglass are desirable perhaps not for sharpness itself but for apparent brilliance and contrast.

It is all a highly subjective and personal preference thing. Others may differ from me on this topic and please take heed of their comments.

In the making of the movie "Dear Wendy" in which a P+S Technik PRO35 adaptor was used, there were creative decisions made to slightly degrade the image quality and to use older cine lenses. The DVD "extras" are worth a look at. DP was Anthony Dod Mantle, more well known for his work on "Slumdog Millionaire".

Last edited by Bob Hart; September 9th, 2009 at 08:55 PM. Reason: error
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Old September 10th, 2009, 05:42 AM   #3
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Nobody says very much about image quality and ground glass based devices. Thinking about my physics lessons many years ago, there has to be both difraction and difusion taking place - so has anyone published any test chart images of the impact of these devices on image definition?

Logic is telling me that there must be a measurable change in image resolution that gets overshadowed by the soft background. How soft is the sharp image, if you see where I'm going?
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Old September 10th, 2009, 07:19 AM   #4
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Scroll down this linked page and you will find two images of a Lemac resolution chart shot with a Letus Extreme on SI2K via a hacked relay arrangement and a Sony PMW-EX1.


Last edited by Bob Hart; September 10th, 2009 at 07:23 AM. Reason: error
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