# Thread: Image Magnification is different ?

1. ## Image Magnification is different ?

Hello all !

recently i order a pair of GLASS LENSES with the following powers :

RE -5.75 DS -1.00 DC AX 67
LE -5.25 DS -0.50 DC AX 55

when got the fitted lenses , i found two changes in the New Lenses ,like
1.They are of more weight
2.The image Magnification [ of lights of roof ] on the Front Surface of the lens [ in New Lenses the image apprears BIGGER then the OLD LENSES ].

the weight ,i understand ! coz i'v given him BIGGER FRAME & CHOOSE LOWER INDEX then old one .
but WHY THE IMAGES ARE BIGGER ? is it because The New Lenses are made of PLANO BASE ? or something else is causing this.
i'm afraid ,may be my client will not accept is or will have vision problems.

kindly help me !

kind regards !

2. What if any, is the difference in power from your old Rx and the new one?
If this changed, particularly to less minus, your image size would change.
Other things that can affect this are changes in vertex difference (do they sit closer or further away than old glasses?
Changes in base curve? Changes in material used?

Chip

3. ## image magnification !

Originally Posted by chip anderson
What if any, is the difference in power from your old Rx and the new one?
If this changed, particularly to less minus, your image size would change.
Other things that can affect this are changes in vertex difference (do they sit closer or further away than old glasses?
Changes in base curve? Changes in material used?

Chip
many thanks for reply MR Anderson !

no the powers of the both glasses are same ,only the change in BASE CURVE , INDEX .

4. The front curve and thickness of the lens will affect both magnification of images seen through the lens as well as the size of images reflected off the front surface of the lens.

For a given power, as either the center thickness or front curve of the lens increases, magnification through the lens increases, and vice versa.

The relative amount of spectacle magnification M due to the front curve and center thickness of the lens is given approximately by:

$M=F_1\times\frac{t}{n}$

where F1 is the front curve, t is the center thickness in centimeters, and n is the refractive index.

The convex front surface of the lens also acts like a convex mirror, which will make reflected images appear smaller.

Flattening the front curve will increase the size of reflected images, although this should not trouble the wearer as much as changes in the magnification of images seen through the lens.

5. Originally Posted by Darryl Meister
The front curve and thickness of the lens will affect both magnification of images seen through the lens as well as the size of images reflected off the front surface of the lens.

For a given power, as either the center thickness or front curve of the lens increases, magnification through the lens increases, and vice versa.

The relative amount of spectacle magnification M due to the front curve and center thickness of the lens is given approximately by:

$M=F_1\times\frac{t}{n}$

where F1 is the front curve, t is the center thickness in centimeters, and n is the refractive index.

The convex front surface of the lens also acts like a convex mirror, which will make reflected images appear smaller.

Flattening the front curve will increase the size of reflected images, although this should not trouble the wearer as much as changes in the magnification of images seen through the lens.
many thanks Mr Darryl ,
i'v done the same ( change the index from 1.8 to 1.9 & change the front curve from plano to 2 ) and the problem is solve !
i got the new lens thinner & good looking !

many thanks once again !

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