The Framers Forum

Or my eyesight.
I've done a double mount 6mm showing and when put it against the wall arghh - it looked 6 at the top but less at the bottom. Turned it upside down and blow me down the thinner bit stayed at te bottom. Time for glasses.

Somebody will correct me I'm sure, but I believe it's parallax. I've spent minutes chasing mounts round 90 degrees at a time convinced something was wrong.

Dave

Chopping device or an illness Dave?

Familiar feature to shooters, things appearing different relative to each other when viewed from different angles. Imagine looking at a row of telegraph poles whilst driving past them. They stay where they are but appear to move relative to each other as your viewing angle changes.

Dave

It's a well known illusion. All to do with how we perceive things as 'stable' and therefore safe. Ask someone to draw a triangle for you. 99.9% of the time they will do it apex-up. Apex-down is unstable and therefore gives you a subconscious feeling of instability.

Same reason for bottom-weighting mount borders. Do them equal and the top will always look wider. In theory we should also bottom-weight double mount reveals, but no one does.

Bottom should be approx; 10 per cent greater than top margin. 6mm at top, about7mm at bottom solves the illusion.

The trouble is with that idea, Kevin, is that not everyone sees things in the same way...

A lot depends on the nature of the mount and the lighting conditions. How extreme the difference in tone/colour between top mount and bottom etc.

Spot on Prospero, it was a dark brown bottom layer and cream top, which did accentuate it.

kevin wrote:Bottom should be approx; 10 per cent greater than top margin. 6mm at top, about7mm at bottom solves the illusion.

I've never noticed this phonominium with double mounts, having said that I never go above 4mm.

I have however encountered that 'slipped down' look with mounts/matts but have always allowed for it by making the bottom slightly wider.

Is 10% a calculated amount, perhaps devised by an ancient Greek scholar or is it a figure generally agreed by framers? or neither!

guzzijim wrote:[quote="kevin"

Is 10% a calculated amount, perhaps devised by an ancient Greek scholar or is it a figure generally agreed by framers? or neither!

This was a serious question.