leaky frame corners on new-to-me Pro-SD back

[Wayne]

I'm getting a corner leak effect with this back, which is a 220 back. Several frames had the leaky look at the location shown in the left frame below. But not all frames. Only one frame had the leak in the location shown in the lower right frame. Film was Pan F 120.

As I mentioned elsewhere I found the tension on the winder to be worrisome. despite many people using 120 in 220 RB backs with no troubles, I wonder if they got lucky or I got unlucky. This seems like a possible film flatness issue, which would jibe with my feeling the film was not advancing as freely as it should have.

I'm going to have to run some backing paper or a sacrificial roll through this back and see if that extreme tension happens again. This was not a mild increase in tension, which I fully expected. I was afraid something would break as I advanced it.

 

[shutterfinger]

That looks like something is blocking light from the film in the corners, a light leak would look much different.
Backing paper is .006 inch thick. Kodak and Ilford films in 120 format are .0045 inch thick. Fuji films are .0035 thick. 22o film has paper at the lead and trail edges of the film and none along the length. A pressure plate on a 220 insert is closer to the guide rails than a 120 insert. You may have misloaded the insert.

 

[Wayne]

Of course you're right. Darned negatives got everything reversed in my stupid head. I'm not sure how I could have misloaded the insert but I am good at finding new ways to screw up.

 

[shutterfinger]

I'm not sure how I could have misloaded the insert but I am good at finding new ways to screw up.

When starting the paper on the take up spool its easy to off center it which results in the paper being being forced against one end of the spool. This will be obvious as the backing paper will be crimped on one side. Another possibility is the backing paper was loose across the pressure plate and pinched between the pressure plate and the outer guide rail. The guide rails are the flat, polished metal strips across the top and bottom of the film opening. The outer ones guide the paper, the inner ones help keep the film flat. Look at the take up spool, transport rollers, pressure plate, and supply spool and verify that the backing paper is centered and taunt from supply to take up before putting the insert into the shell. Correct if it is not.

 

[Wayne]

I checked the edges of the paper when the roll was done, because I thought that may have been a problem but I could see no signs of edge buckling or misalignment. I'm going to run a sacrificial roll of 20 year old Velvia through it in daylight to see if I can reproduce the tension issue.

 

[shutterfinger]

Do you take the darkslide out when making an exposure or just pull it out enough to clear the film plane?

 

[Wayne]

I always pull it all the way out.

They are replacing the back for me, so hopefully that will take care of the several issues I've had.

 

[itsdoable]

Those look a lot like vignetting from a filter or lens hood that is too deep...

 

[Wayne]

Those look a lot like vignetting from a filter or lens hood that is too deep...

That's a possibility. I actually remembered to extend the hood on that roll of film, something I quite often forget. You'd expect it to vignette all 4 corners equally but my hood is a bit compromised so it's quite possible it vignettes unevenly. Good thought...