Rittreck View 5x7 Roll Film Back

[Simon Benton]

I have just obtained a 6X9 roll film back for my Rittreck View 5x7 - it includes the ground glass and the roll film holder slides up to take the picture. I can open the back but I cannot work out how to remove the roll film holder part. It comes out part way but it looks like the rewind knob is preventing it from coming out the rest of the way. Can anyone help with this? Thank you!

[Math]

In most cases you can pull the rewind knob outwards, giving way to the holder to come out. Did you try that?

[Simon Benton]

Yes I tried pulling out the wind knob but it will not budge.