It's just a collar that fits around the lens barrel. There's short stalk attached at a 90 degree angle. Makes focusing faster since you're using it and not the smaller focus ring. Kinda useful--worth grabbing for a few bucks. Most MF camera systems with helical focusing lenses had them. Mamiya TLR and RB/RZ cameras used a plus-sized knob that slipped over the standard focus knob for the same effect.
i'll drop my 2 cents about 6x4,5 systems,
recently, a year ago i was looking for the ultimate portable camera, something to shoot fast and with much better image quality than 35mm, like you i narrow my decision between mamiyas af, contax 645 and also pentax 645N; to resume it i ended with a contax i chose it for its better ergonomics and superb build quality. I have spent few months now with my contax and i've been shooting quite a few rolls and i still think is the ultimate 645 camera system, but if i was right now on the market again for 645 af camera i would look elsewhere. Why?
-money: for the same price of a nice shape contax kit, you can get a mamiya or a pentax plus 3 lenses. I rarely shoot wider or longer than 50mm equivalents but knowing that you have them in your bag is nice.
-reliability: i must say that my contax is my very first camera that hasn't had any problem at all, seriously, not even one, i can't say that for any other system i shoot with, but now i want to build nice outfit (extra body, extra lenses) and that is quite a few money to put on something that has not any future.
-lenses: everyone on the net raves about zeiss glass and how good it is, yes i confirm that, it is super sharp, but after making some side by side with a mamiya anything upper than f-5.6 is a tie and i guess it's the same with pentax. If you look for the boring wide-open look all time yes contax wins but i found that you need a f-5.6 to get good image quality with 645, and then a mamiya performs equal, zeiss colors? you mimic that later at printing.
My final thought is about 6x4,5 film size in general, i've been a heavily 6x7 shooter myself and i try to compare everything to that, to me the quality gap between those film formats is evident not so much but you can really see it, i must admit i didn't expect it, but i don't mean that 6x4,5 is a nonsense it's still a quality format and steps ahead to any 35mm camera. I'm saying this because i don't know what you expect from a 6x4,5, anyway, there is not any af reflex 6x7 camera or bigger. If you have any doubts between cameras you can always rent them and see it yourself.
Last edited by peri24; 09-20-2010 at 06:05 PM. Click to view previous post history.
What CGW said about the focus assist lever.
The big advantage for me is that with my right hand I cannot reliably grab and turn the focus ring on most lenses, but I can grab and adjust a lever that sticks out from the barrel.
It works really well - in fact, I'll even use it with my much more dexterous left hand when the camera is on the tripod.
Unfortunately, it won't fit on all the lenses, because some of them (like the 45mm) have barrels that are too large.
“Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”
Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2