Question about Bronica 220 film backs

Hi,

Can one use a 120 roll film within a Bronica SQ 220 film back ?

If not, why ?

glamoute wrote:

Hi,

Can one use a 120 roll film within a Bronica SQ 220 film back ?

If not, why ?


You can if you are prepare to gamble on depth of focus to keep the image
sharp when it is not on the preset image plane of a 220 film. An
exception is pinhole images. In this case, you definitely can use the
220 back for 120 film.

I don't have a 220 SQ back to verify this but if I am not mistaken, the
only difference between 220 and 120 in the SQ backs is the position of
the pressure plate (where the image plane is) on the 120 and 220 insert.
220 has no backing paper so it's some fractions of a millimeter thinner...

If you know the difference between the thickness of a 220 film and a 120
film (without the paper backing), you may be able to compensate the 220
plate to give the correct image plane offset. Alternatively, it may be
possible to set the plate to the 120 position by some "hacking". I
suspect that the outer casing (with the frame counter) may be universal,
as the 120 label is on the insert and not on the housing. I will have a
look at my 120 back tonight. You got me curious about "hacking" the
plate position :-)

To draw some similarities, on the original Mamiya 645 220 insert, my
naked eye can just about distinguish the difference in "elevation" of
the pressure plate between a 120 and 220 insert. In fact, on the M645,
frame counting is on the body so the 220 insert merely adds a latch
(screwed onto the insert) to allow the counter to go twice the 120
count. I wasted half a 220 row because the previous owner has detached
the latch...

In most of the cases with mechanical parts, machining costs are
relatively high so most of the parts are engineered to be identical to
reduce the costs. As the only difference between 220 and 120 are (1)
film thickness and (2) frame count, you can bet the engineers will
exploit all similarities and just add or remove parts to make up for the
differences.

In article . com,
"glamoute" wrote:

Hi,

Can one use a 120 roll film within a Bronica SQ 220 film back ?

If not, why ?

You can use the back but not the insert. You have to have a
120 insert. I use the 220 backs with 120 inserts all the time. No
issues except when near the end of the 120 roll it gets a little snug
but then releases the film.
--
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