When mounting the lens in pastinous and metal frames, the most important parameter to achieve a well-manufacturing, quality and aesthetics, is the shoulder that will make the lens.
requires a combination of technical knowledge, proper equipment and proper frame-lens choice before executing the recipe.
In summary we can say that the basic conditions to achieve a right shoulder and thus correct application of the lens are:
- Correct form from the frame which is to be built.
- Good condition of the wheel and especially the sharpening stone.
- Suitable (compatible) curvature of the lens relative to the frame and the recipe.
The form we get from our frame must be checked before proceeding to cut the lens. Any distortion-shaped lesions, called and "water" leading to irreparable damage to the lens after grinding and make it unsuitable for installation.
'All laboratory machines require frequent maintenance and in our case the grinding stone is very important. If the situation is not good, and that can make the result will be less than our expectations.
The correct "reading" of the recipe that we will do, help our customer to select an appropriate frame and the choice of a suitable lens, are important steps and if done correctly will lead to a perfect result.
In the case of negative lenses, our main aim is to hide the lateral thickness of the lens as much as possible. Also admittedly it is not acceptable to allow the lens to protrude substantially from the front side of the frame. Our modern grinding machines allow you to take measurements of the thickness that will result in any kind of rebate you choose. Generally pastinoi frames allow averaged around to 1.7 - 2.0 mm thick front without making that annoying felt, while in a thin metal frame should not exceed 1 mm, except in cases where the thickness of the lens leaves no other choice. In an effort to bring the thickness to the rear side of the frame are forced many times to reduce the curvature of the shoulder, especially in the case of high refractive index lenses.
In these cases there is a risk that the lens rests well and need to intervene in the frame itself by changing its curvature. This is good to avoid.
Looking from the prior frame and the curvature of knowing we are able to make the right choice at the base of the lens grinding and do not stray more than one point up or down. That is, if we have a backbone based on 5, it will be our shoulder is 4 to 6 and most preferably 5. For this reason, when we have many degrees negative lens must select frames with slight curvature.
Similarly, the positive lenses, the most common problem occurs when assemble lenses with several degrees crescent skeletons. In such cases it is important that proper selection of the base flange of the lens rather than the concealment of the thickness because the problems in implementing the frame will be audible. For this reason we choose the frame with a large curvature when we have a positive lens with several degrees.
