Edging High Vertical Prism

[Oscar]

I have a FT35 with 8 up and 8 down prism. I am using an Optronics 3b blocker (lenses are blocked from the bottom). After blocking, I physically check the alignment based on the line on the chuck relative to the seg and it looks straight and spacing is even. After edging, the eye with up prism is too high and the eye with down prism is too low.

Where is this slipping up? Is it paralax in the blocker? or alignment in the edger? Is the only fix to block a little lower for the up prism and a little higher for the down prism?

Looking ahead, would this also affect horizontal prism / PD?

[Lensman11]

It is most likely not slippage but the prism causes misalignment in the blocking. Get some Plano prisms and counter the prism in the blocking process

[Oscar]

It is most likely not slippage but the prism causes misalignment in the blocking. Get some Plano prisms and counter the prism in the blocking process

My blocker blocks from the bottom with the front curve laying flat on the table. I thought this type of blocking is supposed to help prevent these types of issues?

[Lensman11]

You are referring to mechanical issues due to angle if the lens and yes you blocker will eliminate that i am referring to the prism displacing the image a causing the blocking problem.

[Oscar]

You are referring to mechanical issues due to angle if the lens and yes you blocker will eliminate that i am referring to the prism displacing the image a causing the blocking problem.

where would i place the plano prism? in between the lens and the blocking screen?

[Lensman11]

Place it where it will not interfere with the blocking of the lens

[DHawkes]

Make sure the lens is horizontal when you block. You may need props for a level playing field.