Mamiya RB Pro-SD with 6x8 power back - cropping line question

I just bought a Mamiya RB Pro-SD with a 6x8 power back.

Looking through WLF, I see the normal guide lines for vertical orientation.

Here's the question. As I understand it, these guidelines are for 6x7 film back. I have a 6x8 back. How do I know where my real guideline is for this back??

I am aware, I get full 6x8 on vertical position only.

Found my own answer.... TYPE-A focusing screen.

Hum....

According to this site http://rb67.helluin.org/accessories/

There is a type A and there is a type A for 6x8. How does this work? I have what appears to be a type A that came with my Pro-SD. But my back is 6x8 power back. So... what do I do??

tkamiya said:

Hum....

According to this site http://rb67.helluin.org/accessories/

There is a type A and there is a type A for 6x8. How does this work? I have what appears to be a type A that came with my Pro-SD. But my back is 6x8 power back. So... what do I do??

Click to expand...

Wasn't there a viewfinder mask for 6x8 that shipped with the 6x8 motorized back?

I've got a really incomplete understanding of this, but here goes ....

As I under stand this, you need to have a Pro-SD, a later Pro-S or a modified early Pro-S or modified Pro body to obtain a 6x8 image on your film.

None of the viewfinder screens will show the entire image - the viewing system isn't quite big enough. The movable guide lines are, however accurate, because they show where the short side edges (the 56mm dimension) are. What isn't shown accurately is where the ends of the long dimensions are - the viewfinder isn't big enough.

I surmise that the special 6x8 version of the A screen is slightly longer in the vertical dimension.

Have you seen this photo-net thread, with included chart?: http://photo.net/medium-format-photography-forum/00Y50b

So... there IS another type-A screen (why did they name it the same!) for 6x8.... Thank you for the pointer.

tkamiya said:

So... there IS another type-A screen (why did they name it the same!) for 6x8.... Thank you for the pointer.

Click to expand...

I think that Type A actually refers only to the type of screen (all matte with fresnel).

It is just that it comes in two slightly different layouts.