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follow focus gears

 

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Follow focus gears for stills lenses, semi permenent, film style gear rings...

for GH1, GH2, AF101, Canon 5D etc

&.. back to hacked GH1 with PL mount..

Panasonic GH1 with PL mount adapter

4/3 sensor myths....
You can use C-mount lenses but, Does the lens cover the sensor? -No, probably not if it's under 30mm. Nearlly all old c-mount lenses were designed for 16 to 8mm film gates, on M43 sensors you see far more outside this area than the designer intended. Eg Bell & Howell Super Comat 25mm vignettes in corners, Wollensak Raptar 25mm & SOM Cinor B 25mm vignette the edge of frame considerably, wider lenses fare much worse.
" .. full size stills lenses -Yes, but but wide angle, say under 20mm, are generally slow, difficult to find and expensive. They may lose contrast with internal light bounce.
" .. 16mm Arri/zeiss mk1/2 super speeds: 25mm and above ok, but 9 to 16mm vignette too much.. And much the same for all 16mm lenses. example pics here
" .. Tega 5.7mm -No, vignettes. example pic here
" .. 8mm (f3.5) Pelang fish-eye -Yes! OK and no vignetting. example pics here
" .. Pentax 110 -Yes! and no vignetting. But no iris control, set at max, f2.8 they are not at thier best. example here
" .. Half frame or 35mm movie lenses -Yes, all of them.

   

The brief was to put proffessional follow focus gears on a set of Nikon and Konica stills lenses without modifying or damaging the lenses..

Arri style follow focus gears

Arri style follow focus ring, for mk1 primes.
standard "film" pitch = .8 (also known as 32 tpi).

internal dia = 61.5mm approx
screw centres dia = 66.5mm approx
overall size = 85mm (dia) approx, 102 teeth
width = 7mm approx

usually these are machined in aluminium or more commonly Delrin or polyester.

I'll add more instructions later on how to do this, and links to arri bars conversions for GH1/GH2 if anyone's interested.

Barrel dia for 50mm f1.4 AI is bigger than "standard" mk1 FF gears, but easy enough to modify the gear ring.
The lens' original rubber grip sits in groove in the lens barrel, so, (as to not modify the lens) the adaptor is a solid plastic replacement for the rubber grip, and it sits slightly proud of the groove. The follow focus gear slips over this and compresses the plastic ring. This compression might be enough to hold the gear ring firmly, but I put double sided tape between the ring and lens just to make sure. The original gear mounting threads are used to connect the 3 screws to corresponding "nicks" cut out for the screw heads, this prevents the gear ring rotating over the plastic adapter or sliding back towards camera. .

35mm AI is somewhat easier, as the lens barrel diameter is about 1mm smaller than internal dia of the gear ring. The rubber grip width is wider, giving more alternatives for mounting screws, though either the screw heads must be larger or use washers to connect with the adapter ring.

The white area is the double sided tape, white tape used on this occasion for clarity! This is not to hold the gear wheel on, simply to stop the ring slipping.
Alternativly you could use grub screws hidden under the gear ring as per the original Arri fixings.

The adapter ring, from camera side (with slot cut for washer) & typical screw/washer arrangement, although these vary slightly depending on the lens. Here, extra screw holes have been made to the gear ring, but it is just as effective using a nut on the rear of screw seen on the front view. Obviously black screws look neater!
The adapter is a split ring of plastic. I use 2mm thick shim of polypropylene, it is easy to saw/cut and sand.
For a tight fit, the centre of the gear is sanded or machined out to this new diameter. There are several ways of securing the gear without resorting to glue!
(1) use a washer and clamp arrangement as in the photo on the left.
(2) Drill a 2mm dia hole between adapter and gear contact, once assembled, put a small screw in the hole and they won't slip. It may need to be a grub screw to clear the lens parts.

(3) think of a better way and let me know!

alternative (2)

drilling a 2mm hole across the gear/shim boundary

actually it's wiser to do it off the lens...

(2) continued

example 2½mm screw in the hole after cutting thread..
either use a countersunk or grub screw on the lens, so it clears the metal parts of the lens.

   



(4)

Alternatives:

Redrock gears - on ebay
Zip/zacuto - http://store.zacuto.com
Cinevate - http://www.bhphotovideo.com

see also: GH1 50mm lens shootout , lenses with personality page, SR2 Hire

last updated:22 June 2011