2/3" lens on Sony F3 via homebrew adapter

[Alister Chapman]

OK folks. I wanted to see just how well a 2/3" broadcast lens would work on an F3, but don't have $5.5k to fork out on one of the Abel adapters. So with a bit of head scratching, a few, lowish cost lens purchases and a few hours in the workshop I cobbled together my own adapter. At first I tried a 2x magnifier but this didn't quite give me full sensor coverage and was soft out in the corners. With a little more work I took the magnification up to 2.5x and I have clean corners. I'm really pleased with the performance, although one lens element needs changing for a higher quality element to combat some softness when the iris is fully open.

My old Canon J16x8 f1.8 becomes a 24 to 320mm f4(ish) par-focal lens which is actually quite handy. Next step is to make up a power cable for the lens so I can use the zoom servo.

I'm considering trying to find a manufacturer that can make these up for me properly, the converter should cost a lot less than $5.5k

[Leonard Levy]

Way to go Alister. I'll be looking for that.
How do you find time to work on shoots though?

[Brian Drysdale]

You really need a batch, my experience is that one off items have high machining costs.

Just checked and I don't know about the price, but Abakus now have their 260 Converter, which covers Super 35,

http://www.abakus.co.uk/Format_Converters.htm

[Alister Chapman]

£1,940 + VAT for the 260 B4 to super 35.

[Dustin Moore]

Is the softness in the corners a coma/astigmatism or a chromatic abberation?

Are you just using a doublet?

[Alister Chapman]

The corner softness looked like astigmatism. The adapter contains a pair of doublets.

[Greg Penetrante]

Originally Posted by Alister Chapman

£1,940 + VAT for the 260 B4 to super 35.

This is around $3200.00. ZGC wants $4200 for the Abakus. Might be cheaper to go directly from Abakus if anyone's thinking of purchasing one.

[Brian Drysdale]

Originally Posted by Alister Chapman

The corner softness looked like astigmatism. The adapter contains a pair of doublets.

How are you correcting for standard colour offsets built into the video camera optical block?

[Alister Chapman]

I'm not correcting for the colour path lengths and I doubt that Abekas or CineAble are either. So far my test shots show minimal CA, certainly no more than I get with the same lens on a prism camera. Don't forget the prisms introduce a ton of aberrations so the cleaner optical path of a single chip camera really helps get good performance from broadcast lenses.

[Brian Drysdale]

Nothing like Venetian blinds to show those colours. Although, if you're designing from the optics from scratch it shouldn't be a big problem to apply some correction, but I gather it isn't as noticeable on a 35 mm sensor compared to 2/3" HD.

[Dustin Moore]

With two doublets you have six curvatures, four indexes of refraction and four abbe numbers,
you ought to be able to remove the spherical abberation or sphero-chromatism (different spherical
per color) that is already baked into the 2/3" lens to compensate for the prism. Toss in an
asphere and it should be very good. It might be hard to use just off the shelf components
though without having a design plan and then making it fit to off the shelf stuff.

Is there a standards document that describes what optical properties a 2/3" lens must have
to properly work on a 3-CCD camera? I would imagine it would specify axial color and the
amount of spherical abberation per color needed to make it through the prism in focus.

IANALDBITSC...

(I am not a lens designer but I took some classes...)

[Ola Christoffersson]

Jesus, the things you guys know!! And I thought I was a camera nerd.

[Brian Drysdale]

Originally Posted by Dustin Moore

Is there a standards document that describes what optical properties a 2/3" lens must have to properly work on a 3-CCD camera?

Just be totally geeky: BTA S-1005-A HDTV Standard.

Canon have a good range of white papers:

http://www.usa.canon.com/CUSA/assets...WhitePaper.pdf

http://www.usa.canon.com/CUSA/assets...riImager08.pdf

[Tim Polster]

Originally Posted by Ola Christoffersson

Jesus, the things you guys know!! And I thought I was a camera nerd.

I agree! One question - Is there a way to make an adapter with less than two stops of light loss? Since the F3 has power it would be quite a tool to have ENG & EFP in one camera but having your ENG end at F4 is kind of a drawback. F2.8 would be fine.

[Brian Drysdale]

This is basically a range extender and it's the size of the Super 35 sensor which will dictate the magnification required, therefore how brightly the light is spread across the sensor.

It's an old trick, the best known example being the modification of the 16mm 12-240mm zoom into a 35mm 24-480mm using a x 2 range extender. It was about T9, so not a lens for interiors.