Fresnel magnifier lens frame & handle

Credit-card sized 3x Fresnel magnifier lenses are plentiful, affordable, and surprisingly useful. At a nominal size of about 55mm x 85mm, with negligible thickness, it can fit in a wallet, to be whipped out at a moment's notice when there is fine print to be read, or mischief to be committed. 

BUT: Thou shalt not touch thine optical surfaces, especially not the finely grooved back surface of the Fresnel lens, which is really difficult to clean without damaging it. This is exacerbated when the user actually needs visual help and probably has compromised motor skills too. Soon the lens is icky, and this saddens me.

So, find herewith a one-piece handle into which the lens can be clipped, to make it easier to use for those who need moderate visual assistance on a regular basis, while protecting the lens by keeping fumbling fingers far from fragile faces. Of course, this means you cannot carry it in your wallet any longer: the target audience is geriatric, and at home. There is a hole in the handle, for hanging on a hook, or perhaps a lanyard. Or just leave several scattered around the house: they are dirt cheap, so one can saturate the environment.

Some notes on the lens: for optimal image quality the smooth side should be facing the user.  (and fingers should never touch any of the faces, neither the smooth, nor the grooved.) The frame is symmetrical - this means that for left-handed use the lens can be popped out and inserted the other way round, to ensure this desired orientation.

The lenses have a focal length of about 80mm: optical magnification is defined as 250mm divided by the focal length (in mm), hence the approximate 3x magnification rating.

Printing

Printed in PETG, without supports. PLA will work too, unless the user is apt to leave it lying in the sun, which is not only likely to result in a warped handle, but may even result in fire. Do try to avoid this.

The two long edges of the rectangular aperture are grooved on the inside. The lens should clip easily into these grooves and fit slightly loosely (i.e. it should not be bent after insertion, but neither should it fall out easily). If this is not the case the entire frame can be scaled by a suitable percentage - independently in X and Y, if you prefer. Few of the dimensions are critical. However, I have bought scores of these lenses, from various vendors, and they all measure 54.3mm x 85.5mm. It is highly likely that they were all made in the same factory. On my Prusa Mk4 I can mount the lens as the handle comes off the plate, without any post-processing required, neither to the handle, nor to the lens.