ENG lenses are made for shooting video:

• large zoom ratio

• constant brightness (f-number) across the zoom range

• parfocal (holds focus distance across the zoom range)

• smooth controls

• gears, for a servo controller or follow focus

• back focus adjustment

It's a treat to shoot video with a good video zoom lens, instead of using lenses designed primarily for photography. Most of the SD and pre-HD 1/2-inch lenses can be had for less than $100 or $200 on eBay. Lenses are f/1.4 unless stated otherwise. (Note that the minimum f-number only applies to the first half or so of the zoom range. At the long end, the minimum f-number usually goes up by about a stop)

Canon SD and pre-HD models:

• H9ax3.8 I

• H15ax6 I (internal focus, doubler)

• H20ax6 I (internal focus, doubler)

• PH10x8B

• PH12x7.5B

• PH14AX6.6B I (internal focus, doubler)

• PH15x7B

• PH15x7B I (doubler)

• YH13x7.5

• YH14x7.3

• YH16x7 f/1.9 (internal focus)

• YH17x7

• YH18x6.7 K (internal focus)

• YH18x6.7 I (internal focus, doubler)

• YH19x6.7 K (internal focus)

• YH19x6.7 I (internal focus, doubler)

Fujinon SD and pre-HD models:

• S12x7.5 (older)

• S13x4.6 (newest) f/1.5

• S14x6.2 (older, doubler)

• S14x6.6 BERM (older, doubler)

• S14x6.6 BEVM (newer, doubler)

• S14x7.3 f/1.9

• S14X7.5 BRM-4 (newer)

• S15x6.1 (newest, internal focus, doubler)

• S16x6.7 (newer)

• S16x7 (older)

• S16x7.3 f/1.9 (newer)

• S16x7.3 f/1.9 (newer, internal focus)

• S17x6.6 f/1.5 (newest, internal focus)

• S18x6.7 (newer)

• S19x6.5 (newest, internal focus)

• S19x6.5 E (newest, internal focus, doubler)

• S20x6.4 (newest, internal focus)

eBay searches:

http://www.ebay.com/sch/i.html?_nkw=canon+%28ph%2Cyh%2Ch15%2Ch20%2Ch9%29+lens+-screw+-fisheye+-e1ph+-nikon&_sacat=0&_odkw=canon+%28ph%2Cyh%2Ch15%2Ch20%2Ch9%29+lens+-screw+-fisheye+-e1ph&_osacat=0&_from=R40

http://www.ebay.com/sch/i.html?_nkw=fujinon+%28s12%2Cs13%2Cs14%2Cs15%2Cs16%2Cs17%2Cs18%2Cs19%2Cs20%29&_sacat=0&_odkw=fujinon+%28s12%2Cs13%2Cs14%2Cs15%2Cs16%2Cs17%2Cs18%2Cs19%29&_osacat=0&_from=R40

Bayonet-mount ENG lenses, be they 2/3" B4 mount lenses or 1/2" lenses, are designed for cameras with prism optic beam splitters and 3 CCDs. Single sensor cameras like the GH2 and GH3 don't have that chunk of glass, so these lenses don't perform very well. You have to reduce the aperture size by several stops to get rid of the haziness. For that reason alone, I have no interest in the bayonet-mount ENG lenses. If you really don't need large aperture settings, the bayonet-mount ENG lenses are alright. A 2/3" lens can be used with a built-in 2x extender (on the lenses that have them) to cover the 4/3" sensor, though the performance of a 2x extender used this way is not excellent. The doublers are not designed to cover anything more than 2/3", so the picture gets soft outside of that central 2/3" portion of the image. You can always use a 2/3" or 1/2" lens in ETC mode, though, and get a sharper picture in the corners without any need for a 2x extender.

Employing a 2x extender doubles the f-number as well as the focal length. You don't get something for nothing. An extender doesn't make your lens bigger. It just magnifies and enlarges the image that it projects, which of course makes the image darker. Using 1080 ETC mode has a similar penalty for noise performance: on the GH2 it's equivalent to a 2.6x extender, and 2.4x on the GH3.

You can use a 2/3" B4 mount 3-CCD ENG lens with a converter that optically corrects for the missing prism. But those adapters cost $1500 and up. It's probably the best solution if you are dead set on using the GH2 or GH3 and you have more money than time.

C-mount lenses for single chip 1/2" or 2/3" sensors are another option. They need to be used with ETC mode. 1/2" format covers 1080 ETC mode 96% (i.e. close enough), and 2/3" format covers it 133% (i.e. more than enough, and your angle of view won't be quite as wide as it would be on an actual 2/3" camera) But the best performing C-mount zoom lenses require modification to fit in an m43 adapter. 1" zoom lenses will also work, but they don't fully cover the 4/3" sensor, so you will need to crop and lose some resolution. 1/3" lenses provide good coverage for 720 ETC mode, if you can live with the lower resolution.

There is no really good solution here. You need to spend some time or money, or think about a different kind of camera.

@Balazar, Thanks for this - very informative.

You said the standard 1/2" adapter being offered on eBay was 'wrong' - it what way was that, and do you know if this has been corrected now?

I picked up a Fujinon ENG lens with an extender, and comparing it to the Sony mount Canon lens we have at work, it's definitely different, so I guess I'm safe to assume this is a standard mount?

Lining it up on the bench with my AF101 it appears to fill most, if not all of the sensor, but having picked up the lens for £25, I'm not sure I want to spend nearly ten times that on an adapter until I'm sure it's going to be OK!

Does the fact that this Polish adapter seems to be the only one available suggest that using 1/2" lenses on M4/3 is maybe not such a good idea? And you say the 1/2" mount is quite close to the B4 2/3" standard - probably a silly question, but close enough to adapt? You can pick up the 2/3" adapters a lot cheaper than this 1/2" one…

The lens is a Fujinon Lynx III S18x6.4 BERM, btw.

Rather than risk nearly £200 on an adapter for a lens that might not be worth it, I bodged up my own, by cutting down a m4/3 macro tube. I had a cheap set of extension tubes kicking about and found that the bayonet flange from the lens almost fit inside. I took the flange off the lens to use as a pattern to cut slots for the lugs, then ground out the tube with a rotary file until it was a snug fit - not exactly precision engineering, but it worked better than I expected, and I've always got another section of tube left to take to my friendly machinist to make something a bit better. And of course that's a lot of weight, even with the zoom servo removed, to be hanging off an adapter with no lens support, so it's not a field-ready solution, just something for testing with.

Bearing in mind that there were almost certainly some leaks and internal reflections, the results were mixed, so I'm going to have to do some more testing before I pronounce judgement and post some footage. At the moment, I'm thinking it's more a 'character' lens than the practical jack-of-all-trades that you'd want from an ENG lens. There's some definite colour fringing when you're zoomed right in, it's a bit soft at wider apertures and it vignettes below about half-way, but there are areas where it performs quite well. Anyway, I wont be buying an adapter yet, if at all, but I think I'll get a better version of my home-made one machined and see how that works out.