Friday, March 21, 2025

Converting Bronica ETRS 135N Film Back to 135W



This is my journey of converting a Bronica ETRS 135N film back to panoramic.  Almost like the 135W back.  The Bronica ETRS camera is often overlooked because it shoots 6x4.5.  The smallest medium format size, but it is really nice camera to shoot with.  I have been shooting with it for over 4 years without any problem.  Over the years, I have shot 120, 220 and 35mm films with the appropriate backs.  Shooting 35mm films results in 24x43mm images and it also expose the sprockets as well.



I love panoramic images which I started shooting with a Horizon 202 (a swing lens panoramic camera).  That camera was sold when I started shooting digital.  In the last few years, I started to shoot film again and really want to shoot panoramic again.  Since I was already shooting with a Bronica ETRS it makes sense to use that to shoot panoramic with the 135W film back.  It produces 24x55mm images (2.3:1 ratio).  The cost is the only draw back, costing more the camera itself.  Currently the cost of a 135W film back is about £600 (GBP).  Not the amount I am willing to pay as it is not what I shoot all the time.

I have seen various posts on the internet on how to convert a 135N film back (cost around £150 currently) to 135W.  It involves removing the film mask to and fitting a 3D printed wide mask, moving the film transport roller to the wide position.  There is one drawback though.  Film spacing will not be correct for the wide format.  The 135W back uses a different gear ratio to move the correct amount of film forward.  The 135N film back will not do that.  The work around is shoot a blank frame with the lens cap on after shooting a photo.   Not the most efficient use of film but at least you do not get overlap images.   This is the draw back of converting a 135N back to 135W back.  I have heard you can 3D print a new gear with 14 instead of 21 teeth to achieve the correct film spacing.  That is something for me to do in the future.

Now onto the modification.

Step 1: Remove the standard 35mm mask.  There are 4 small screws holding it.



Film masked removed and the 3D printed wide mask next to it.


Standard and 3D printed wide mask.

Step 2: Remove the metal plate on the side held by 4 screws.





Step 3:  Remove the roller pin and remove the roller.  Watch out for the ball bearings on the sides of the rollers.

This photo shows the location the roller needs to needs to be moved to.

Roller removed, note the ball bearings.


There are 7 ball bearings on each side.

Step 4: Use 2mm ID, 5mm OD, 2mm width bearings to replace the ball bearings.  Then move the roller to the outer position.

Fitting the bearings will fill out the space for the new roller position.


Roller moved to the outer position.


Step 5: Put everything back together.  You need to counter sink the 3D printed mask of the screw holes.  The screws are not long enough and the screw heads should be flushed with the surface.  Note the standard pressure plate is not wide enough to cover the wider area.  I may look into a wider pressure plate in future.

The wide mask fitted.  I will paint the mask with black paint before using it.


This is the image spacing using the blank frame method (shooting a blank image at 1/500s at F22 with the lens cap on).  Else you will get frame overlap.


Test images from the first time using the modified film back.

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