220 back

[wishingwellphotos]

I have a rb67 220 back. Can i load 120 film in it ?

[paul ron]

<p>You can use 120 in a 220 back just be sure to start the roll on the first turn of the leader to align the first frame to the start of the negative strip. If you have a 120 paper backing to run through, mark each frame as it passes the gate, you will see what I mean.<br>

As far as some of the fire storm this will create, I already know all the arguments against doing this will be preasure placte issues... NOT TRUE! The only difference in a 220 back n a 120 back is the counter n frame metering to compensate for the differnence in roll diameter... the rpeasure plates are exactly the same spring loaded plates adjusted to 1mm off the front mask.... THAT IS IT!<br>

So let the games begin...</p>

 

[jeff_livacich]

<p>All I'm gonna say, is it's "pressure plate".</p>

[LenMarriott]

<p>John, Years ago when I was doing weddings I often (slow learner) inadvertently loaded a 120 film in one of my 220 backs. (Bronica SQ Ai) I nearly always caught the error after I finished loading the film and so remembered to stop shooting after frame 12. Never had any problems with the images. Other factors, subject movement or inattention, distracting backgrounds, camera shake, exposure or focusing errors, flash errors etc. were more likely to degrade my images than the occasional loading error. Not to worry! Best, LM.</p>

[erie_patsellis]

<p>Jeff, no offense, but my decades long experience (and knowing Paul's attention to detail) tell me otherwise. works just fine, as long as you load properly and stop at 10. These days, I just have a pile of backs, but in the day when a back cost hundreds, I couldn't justify having a dozen backs like I do now.</p>

[jeff_livacich]

<p>Sorry, I was just clarifying 'preasure placte' and 'rpeasure plates'.</p>

[ondebanks]

<blockquote>

<p>the rpeasure plates are exactly the same spring loaded plates adjusted to 1mm off the front mask.... THAT IS IT!</p>

</blockquote>

<p>That surprises me - not that I know anything about the RB67 backs, but just because in the case of the old M645 series, there IS a difference between the pressure plates of the 120 and 220 inserts. The 120 pressure plate is completely flat from edge to edge, whereas the 220 plate has a slightly milled edge on both sides, allowing the central flat part to sit fractionally deeper into the body, taking up the space where the 120 backing paper would lie.</p>

<p>(And one would think that positioning the pressure plate just right would matter more for the larger film area of the 6x7 format.)</p>

[wishingwellphotos]

Thanks for all your help. i loaded a roll, wound it to # 1, pulled the dark slide and i see film and it looks fine. Thanks again. JB

[q.g._de_bakker]

<p>Pressure plates work (guess...?) by applying pressure. They push the film against the edges of the film gate.<br>

They can't do that when designed to stop short of 'against the edges of the film gate'.</p>

<p>The film or film + paper backing resists the pressure applied by the pressure plate (in well designed backs, that is). The interaction keeps the film where it should be. <br>

The film or film + paper can do that, because there is absolutely no need for a spring behind the pressure plate so stiff that it would be necessary to leave somewhere for the film or film + paper to go.</p>

<p>I do know there indeed are designs that do form such a channel, i.e. don't really press. But though they seem to work, they are rather 'strange' (to put it politely).</p>

[wishingwellphotos]

So QG- are you telling me it will work or not work ?

[ondebanks]

 

<blockquote>

<p>So QG- are you telling me it will work or not work ?</p>

</blockquote>

 

<p>Yes, QG, I'm not sure either what your overall point is? That it is unnecessary for 120 and 220 pressure plates to <em></em>be different? But then, why would so many respected MF camera manufacturers use different types of plates/inserts, rotating plates, or reversible plates?</p>

[wishingwellphotos]

I am sorry. I made a double post. didnt know you couldnt do that. Sorry elves. Wont do it again. Thanks for

everyones help. JB

[q.g._de_bakker]

<p>Joh, and Ray,</p>

<p>Yes, i'm telling you that it is completely unnecessary to have different pressure plate positions for 120 and 220 film.<br />That, Ray, is why so many respected MF manufacturers do <strong>not</strong> use different types of plates or inserts.<br />Just different frame spacing and counter mechanisms.</p>

<p>Why do some others?<br>

Maybe to fool you into believing you need to spend more money than necessary? Maybe what you think are switchable pressure plates are in fact plates acting as switches, switching between two settings of the spacing and counter mechanisms?</p>

<p>But it certainly is not because you would need two separate width channels for 120 and 220 film. On the contrary; you only need one fixed film position (the edge of the film gate) and something pushing the film against it (a pressure plate allowed to push the film, and not the edge of some silly channel).</p>

<p>Whether it works using this particular back? Probably. If not, it will, as Paul already said in the first reply in this thread, not be because of pressure plate position.</p>

[yefei_he1]

<p>Don't know about 120 vs. 220, but one time I used the 35mm film panoramic adapter on a Mamiya 7 rangefinder, and forgot to set the pressure plate accordingly, and all my images came out blurry. I think I needed to set it to 220 for 35mm film but I kept it at 120.</p>

[yefei_he1]

<p>Reading the Mamiya 7 panoramic adapter confirmed my memory. One needs to switch the pressure plate from 120 to 220/135 setting. Other rangefinder type cameras such as Bronica RF645, Fujica G690, CV Bessa III 667/Fuji GF670, and the M backs for Mamiya Press cameras all have switchable pressure plate settings. Some TLRs do, too. And at least in the case for Mamiya 7, it does make a difference. And it makes sense that 220 and 135 are grouped together against 120, since neither 220 or 135 have paper backing, but 120 does. Still, this doesn't mean the modular film holders from SLRs can't have the same pressure plate setting for both types of films. The difference may be that in a rangefinder camera or similar the start and end of the roll do not bend back behind the pressure plate, and there's little wiggle room, so the pressure plate position needs to be exact.</p>

[q.g._de_bakker]

<p>There you go!<br>

Now you know from personal experience how silly it is to have a pressure plate that doesn't press. <br>

A completely unnecessary, counterproducive arrangement.</p>

<p>A pressure plate does not need to be "exact". On the contrary. "Exact" to what standard would that be? How does a non-pressing pressure plate, a preset channel width arrangement, deal with different film base thickness?<br>

The answer is: "Not".</p>

<p>I don't know what they were thinking when they came up with such arrangements, but it would have been better if they had taken the day off instead. It's plain stupidity.</p>

[ondebanks]

<p>OTOH, I once tried an experiment where I set the pressure plate in a Kiev 6C (one of those cameras where there is a channel difference and a 2-position plate) to 220, loaded 120 film, and took astrophotos at wide apertures (one of the most demanding tests of film flatness). The results were terrible - the film had clearly bulged out in the centre of every frame, throwing the stars out of focus.</p>

<p>Now before you laugh and say "what did you expect, with a crappy Kiev?" - this 6C (not 60) was a camera which gave excellent images when set to the appropriate pressure plate setting and used with the best German P6 lenses.</p>

<p>So what went wrong? The 220 pressure plate should merely have applied pressure to the 120 film, rather than channelling it, as QG says. But that pressure completely screwed up the flatness. I am inclined to think that Yefei He is onto something when he surmises that the straight-across film path could be a factor (this was a 35mm-shaped camera).<a href="../photodb/user?user_id=3801011"><br /></a></p>

 

[q.g._de_bakker]

<p>The curl of the film is what causes film flatness problems when using rolled up film (beit 120/220 or 35 mm or 70 mm film).<br />The pressure plate serves two purposes: putting the film the correct distance behind the lens (and for that all it needs to do is push it against the edge of the film gate; and countering the curl of the film.<br />That curl will push the film to the rear, away from the film gate. What the pressure plate must do is resist that movement, supply a flat surface the film then has to conform it's shape to.<br />The correct position of that plane is again set by the edges of the film gate. The film being pressed against those, squeezed between plate and edges, sets the correct channel width, i.e. ensures that the entire plate sits at the right distance to keep the film in the correct position everywhere.</p>

<p>Such an arrangement automatically corrects for different film or film+paper pack thicknesses.<br />An arrangement in which the plate sets a channel of predetermined width obviously can not. Where the film enters and leaves the film gate, the position will be set by how it does that, the interaction of rollers, and such. In the middle however, there's nothing but luck to help the film sit in the right position.</p>

<p>So am i surprised that you run into such problems?<br />;-)</p>

[q.g._de_bakker]

<p>But yes: wat you describe is the 'opposite' of the above, and should not happen.<br>

I don't know yet why it did.</p>

<p>Unless the pressure plate has a bulge in the middle (a Kiev it is, you say ;-)), there is no way it could cause the film to bulge.<br>

Except if the preset channel is too narrow, and the film gets really squeezed. Then, it could be possible for the film to turn up and create a bulge.<br>

If that's what happens, also a result of that extremely silly preset width design 'idea'.</p>

[paul ron]

<p>Are these spring loaded plates doing this? There is absolutely no reason a spring loaded plate will not push the film flat against the film mask.</p>

[q.g._de_bakker]

<p>Absolutely.<br>

Unless (and that's what these last posts in the thread are about) the plate is not designed nor made to push the film flat against the gate.</p>

 

[yefei_he1]

<p>I'm thinking that the design of those rangefinder type cameras or backs leaves little room for a singular spring mechanism that's durable enough, strong enough but also flexible enough to press both types of films against the gate, without adding too much stress to the film advance mechanism due to friction. The latter is probably the key issue. </p>

[q.g._de_bakker]

<p>The force needed to push the film into position isn't big, so i don't think friction should be a problem.<br>

There is no need for a huge construction. And it's so simple that a sprung pressure plate probably is one of, if not the most durable moving part in cameras.<br>

So i don't really share that thought.</p>

[yefei_he1]

<p>I certainly have experienced film slipping partly due to too much friction between the film and the pressure plate, on a Bessa II to be exact. The take up spool will be pulled out of position, and I can't get the film to advance at all after 7 shots. I think it is a real concern for the camera designers.</p>

[paul ron]

<p>The over tensioning you are refering to might not be the preasure plate, it is more likeley the spool is not running freely enough on it's end pins or thte spool tension springs are too tight against the roll of film. If the preasure plate is too hard on the film you can just unbend the springs a tad n your problem will be cured.<br />.<br />BTW preasure plates are polished coated plates which were designed for the passing of alot of film with the least amount of vacumn build up, thus the small holes or channels, to reduce friction. It has nothing to do with 120 vs 220 it works as designed for both equally as well.<br />.<br />The rails should be clean and the end rollers of the film gate should be running freely not jammed down to the mask as I have seen in most old cameras. <br />.<br />Examine each componenet in the system and see what is wearing or has shinny wear points; not the good old preasure plate I'll bet?</p>