Briot ACCURA..... Accuracy???

[Clive Noble]

I'm interested to know the experience of other Accura users.

I'd like to start by saying this is the 3rd Patternless edger from Briot that I have owned over the last 12 years, and I am extremely happy with this present unit and even more happy with our local representatives, Dagil - Tel Aviv, who service and maintain it every time I call whatever the hour, whatever the reason.

However I have one big problem and am told by the service guys that nobody else has complained about this.

Let’s take an everyday situation, we want to edge a pair of PALS, Rx +5.50 with a +2.00 add. I’ve measured on the Pt. that we need 22mm height, no more.
The frame is scanned and PD is entered then the height, 22, is entered, the lens is edged and the PD is perfect but the height is around 23mm or more..... Patient problems.

When I glaze a high minus, the height drops, 22 becomes 20.5 or 21.

In the case of a high plus bifocal, say we need 16mm seg heights, the segment comes out lower, 14.5 or 15.

Prisms up and down are just a disaster.

After a year or so of having to replace lenses I’ve worked out my own system of compensating for this parallax problem, I can now glaze a pair of Progressives +7.00sph Right and a -7.00sph Left and get identical heights....but I do think Briot should have thought through this viewing and blocking method a little more carefully.

Am I really the only one?

Best to you all….. Clive

[DR.P]

Greetings from Houston:
I too own an Accura edger. I have not had your same problem. I will tell you that the more sophisticated these machines get, the more there is to go wrong, go wrong, go wrong.
They are fantastic about taking care of the problems, but they do need to be constantly tuned!
Sorry not to tell you of the same problem.
My biggest problem is the auto groove feature. I don't find it puts the groove where I would. Thank goodness for the override.

Dr.P

[shanbaum]

Originally posted by Clive Noble:

The frame is scanned and PD is entered then the height, 22, is entered, the lens is edged and the PD is perfect but the height is around 23mm or more..... Patient problems.

When I glaze a high minus, the height drops, 22 becomes 20.5 or 21.

In the case of a high plus bifocal, say we need 16mm seg heights, the segment comes out lower, 14.5 or 15.

Prisms up and down are just a disaster.

Most alignment methods used in blocking lenses have the same problem. Every mechanical blocker does. It's not parallax; it's largely through-power deviation. In order to project an image of the feature to be used as the Layout Reference Point (lensometer spots, ink markings, seg) onto a screen, light passes through the lens; the power of the lens (including prism power) will cause the image of the LRP to move in the direction of the angle of refraction at the LRP, unless the LRP is coincident with the Prism Reference Point and the prism is zero. There are other nasty effects that arise due to the projection of features residing on a curved surface onto a flat one.

In some designs, light doesn't pass through the lens, but the features on the reference surfaces (invariably the front) are aligned using reflected light; the problem with that approach is that the features - especially segs - are much harder to see than the projected silhouettes of the features.

Electronic blockers at least have the potential to solve these problems, but... I only know of two finish blockers, and one surface/finish blocker that actually do.

I should add, a similar effect occurs when viewing the alignment mask through the lens; in this case, the image of the mask is deviated.



[This message has been edited by shanbaum (edited 07-15-2000).]