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Koni & Rapid Omega Stuff
by Bob Hutchinson

These are responses to email about KO and RO items I have sold on ebay.

Let's face it Rapid folks, the Rapid grip is really not very good. Wrong shape, wrong angle. The "fix" cable release installation for use with thumb is crap too.

I just finished a custom installation of a like new Mamiya Press grip to a Rapid Omega model 200.  What a big difference!. Here's how. I cut off about 1/2" of the tapered grip mounting stud and filled the big stub flat. I then made two cuts in the big nut with hacksaw 180 degrees apart and removed the nut (last cuts were with side cutters).

I removed the Rapid grip mounting plate and stripped it.  Using small compass I drew a .055" circle where I wanted the stub to mount, center punched four places and drilled and countersunk to clear #4 x 1/4" FH SS machine screw. I set the angle to the same as I use for an XL Graflex, about 40 degrees rearward. Then I used the mounting plate as template to mark, punch and drill the grip stub. I drilled 5/16" to 3/8" deep, tapped #4-40. I cut excess mounting plate away, debured, finished with file and sandpaper and assembled. A real grip for the Rapid. It's even better that the XL grip.

I have a koni omega 220 back that looks brand new. I got it as part of a bad deal on ebay. If you ever bid on stuff don't bid on anything that comes from the 1900 block on Hollywood Blvd. Anyway, the back looks new. The light trap felt was gooey and some of it had to be replaced. The problem now is that unless I grab the winding handle with a claw hammer or something I can't advance the film. Without the film in the back, the action is smooth and easy. The pressure plate seems to retract. Any suggestions?

Thanks, Matt Baker

Hello Matt,

First, what light trap felt are you speaking of? Most Rapid backs have foam or felt only on the ends of the back, not on the long sides. This may have been put there later. If you can get it out with acetone, leave it out.

Second, the spooling gearing is probably he source of the problem. If there is an ill fit  or no lube in the bearing the action without film may be appear to be easy and get uneasy with film or a load on the spool gearing and bearing.

With rack pulled out, hold the back in your left hand and twist the knob end of the rack while observing the fit between the rack and the pinion. Just a slight twist should separate the two indicating that there is no radial pressure on the pinion from a too tight fit between the two parts. Heavy radial pressure on the pinion, especially with inadequate lubrication, will make the back unusable.

At the film feed roller there is a pressure tab to keep film tight across the film plane. If this tab is applies too much pressure on the film it too can cause problems. For 120 backs, if necessary, remove it and straighten it so it applies less pressure. Some remove it entirely. For 220 backs similar measures might be taken.

The bearing probably needs to be taken apart and greased, not oiled, greased. Every back I have used that was really smooth and easy with film had light grease in the bearing, not on the rack or the pinion gear teeth, but inside the bearing and a loose fit between the rack and pinion.

This is all great advice, but also great advice is this: Obtain some cheap out of date film for back testing and seek another back.  Rapid backs are not expensive and there are plenty of them.  You can sometimes find auction at ebay for several backs at one time. If you haven't read my other stuff about Rapid backs go to http://bigcamera.com

Thanks and best regards,
Bob Hutchinson


Here are too many words in answer to your inquiry, but other will read this also.

Koni Omega model M and Rapid Omega model 200 uses a standard Koni or Rapid Omega "film back", 120 or 220. The "film back" attached to the "magazine/dark slide" assembly". Many properly refer to this assembly as a "Rapid magazine". The magazine system was develop when Konica started making the "M" model and carried over to the 200 model as made by Mamiya. The M and 200 use the same film backs and procedures.

A film back/magazine combo will fit a model 100 by just by eliminating the magazine from the film back. The film back clips up to the 100 just as it does to the magazine for the 200.

One of my auctions is for a new "120 film back", the other for a new "magazine/dark slide" assembly. For a model M or model 200 you will need the film back/magazine combination.

Because 220 film does not have a paper backing and other cameras have to change the pressure plate setting to compensate for two different thickness' of film, many wrongly think that the Rapid must use two different magazines for the same purpose. During film advance with a Rapid back the first 1/8 inch of handle or knob movement retracts the film pressure plate away from the film and film plane about 1/16" before the film moves. This avoids scratches on the film altogether. At the end of the cycle, the last 1/8 inch or so, the pressure plate presses the film back to the magazine film plane ready for exposure. No adjustments are necessary for different thickness' of film. One magazine for both 120 and 220 film backs. Of course, one must complete the film advance/shutter cocking cycle completely to make sure the pressure plate is in proper battery. I used to watch one photographer that had a habit of bumping the knob with his palm unconsciously before each shot.

Click the background webs at my Rapid auctions for more about. "Oh, I love my Rapid" stuff.


Koni & Rapid Omega Backs, Seals
I stick to ebay for equipment sales and will have a couple of good used Rapid backs there soon.

The roll back part of the Rapid back/magazine assembly sometimes fails to properly space the film. It is difficult to detect a bad back by operating it without film. As I had mentioned in other information, too many of the bad ones have good paint on them. The best way to test one without actually taking pictures is to load film, remove dark slide, operated to exposure 1, reach through magazine opening with felt tip pen and make vertical marks on left and right edges of film plane, operate to exposure 2, ditto, etc., etc. Remove film and examine for proper spacing, with no overlaps, etc.

I test all roll backs like this with out of date or junk film bought for peanuts, but it is no guarantee of perfect operation of a Rapid back. If operation of the film advance slide is stiff, or becomes stiff after a few exposures, the slide may not be cycled completely. This can throw the spacing off. It is important that the advance slide operate completely, so I always suggest that the user be able to describe his Rapid film advance technique as: "very positive" or "aggressive" on the pull stroke and just "firm" or "positive" on the push to battery stroke. The battery push stroke does no work until the last 1/8 or 3/16 inch, which returns the film pressure plate to the battery position. See info about this at http://bigcamera.com/market/index.htm

If anyone produces a magazine light seal kit with precut foam, I don't know about it. The only seal areas are: lens to mount, which is rubber and gives little trouble, the dark slide seal, little trouble, and the magazine seal, which needs replacement from time to time. If the seal is complete and not melted away, and you have no evidence of leaks, leave it alone. I have replaced 8 or so of these and it is time consuming. Local camera repair folks perform the magazine seal replacement regularly. Cost is $40.00 to $80.00. If you want to try it yourself the quality foam is available in 10 or 11 inch square adhesive backed sheets, from Fargo: http://www.fargo-ent.com . A metal straight edge, razor sharp something to cut foam about 3/32 inch wide, good light, good eyes and some time - new foam seal that will out last the old one.

No seals are used for magazine/back assembly but the seal areas need to be very black. A small bottle of the very black paint is really handy, I use it all the time. Get it from Fargo also. The assembly fit should be tight and can be adjusted to be tight by placing the magazine on a flat surface, large opening up and doing this: Place drift punch or screwdriver in center of the locking tabs for the back and tap lightly with small hammer to bend them slightly until back fits to magazine snugly. If you bend them too much use screwdriver to lever them up a bit. The assembly will be tight and should never need adjustment unless you mix and match magazines and backs.


Click Here to contact Bob Hutchinson.