Optical conversion

Apologies for straying off-topic, but I know there are a lot of clever people here who might know the answer.

A friend of mine wears glasses and has difficulty doing her eye make-up because she can't reach her eyes with the glasses on and can't see her reflection with them off.

She can't readily find a magnifying mirror that's powerful enough, but knows of some expensive mail order ones that claim to be stronger than usual.

I know that if she uses a 3 dipotre magnifying glass on a plain mirror, she can see OK, but the problem is that a mirror will be labelled as 3X or 5X, whereas a lens gets categorised by dioptres or focal length.

Is there a way to convert the preceived magnification as seen through the lens & mirror t( n dioptre ) o get an equivalent rating as defined for mirrors ( n times ) ?

Reply to
Roly
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She'd be better off with contact lenses.

Reply to
The3rd Earl Of Derby

She's tried contacts but can't get on with them.

She's also tried glasses where each lens individually flips down and she's tried a monacle too.

Each of those solutions causes further problems for her, but the mirror & magnifying glass solution has worked well for more than ten years. However it's inconvenient to hold it all together, so a stronger magnifying mirror appears to be the ideal answer.

Boots do a Tweezer mirror that's very powerful ( 10X ), but it's only 3" across and too small to be used conveniently for eye make up.

Reply to
Roly

This type should make her eyeballs huge. :-)

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Reply to
The3rd Earl Of Derby

Suggest you post this on sci.optics - it may be a better bet.

Reply to
dave

wants is a reasonably strong magnifying mirror as it's much simpler to use.

But interestingly, the Maplin's description says that it has a 3 dioptre lens, 1.75 X magnification.

That's the first time I've seen a reference that correlates the two ways of measuring magnification.

Is it appropriate to extrapolate those figures ?

I assume that by holding a lens to a mirror, a 3 dioptre lens effectively becomes a 6, due to the light passing through twice. Therefore as she knows that a 3 dioptre lens and a mirror work for her, then presumably we can assume that the magnification is 2 x 1.75 = 3.5, so a 5X mirror should be suitable as she has found that a 3X doesn't do the job.

Is there an obvious flaw in this reasoning ?

My intuition suggests that the difference between 3 X and 3.5 X is not particularly obvious, but she has no joy with the 3 X mirror, but good results with the flat mirror and lens ( which in reality is just a little under 2.8 dioptre ) which should provide a little under 3.5 X. That leads me to believe that the formula doesn't work quite in the way that I am assuming.

Reply to
Roly

How about trying a fresnel magnifier, or two, in contact with the mirror ~5" x4" types are available at about £3 each post paid

e.g. the Midi Sheet magnifier on the page below.

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've used them as low priced fresnel lenses for my LF cameras' ground glass screens. )

Reply to
Malcolm Stewart

Oh! bugger, ok try this for size :-) get a surveilance camera and 22" TV, put the camera on top of the TV,point the camera at her face and zoom in close enough to her eye...hey presto eyeball on TV.

Stop blinding me with optics equations.

Reply to
The3rd Earl Of Derby

Another thought has she tried a mans shaving mirror? you can get these with some magnification.

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Reply to
The3rd Earl Of Derby

the dioptre measurment is the reciprocol of the focal length expressed in meters.

For a simple lens like a magnifing glass, the magnification will be given by f/f-s f is the focal length and s is the lens to object distance.

Reply to
John Rumm

the dioptre measurment is the reciprocol of the focal length expressed in meters.

For a simple lens like a magnifing glass, the magnification will be given by f/f-s f is the focal length and s is the lens to object distance.

Reply to
John Rumm

snipped-for-privacy@NTLworld.com (Roly) wrote in news:1hd39ab.1w6hbgd1dbj1huN% snipped-for-privacy@NTLworld.com:

I don't know if either of these will help.

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My other suggestion is that you post this query in

uk.sci.astronomy

What they don't know about mirrors and lenses (reflectors and refractors)

prolly isn't worth knowing ;)

mike

Reply to
mike

I know of someone in a similar position who uses one of these:-

They have it taped to a mirror and it gives magnifying mirror with a "working distance" of about 6" and enough magnification. Maplin appear to do one for about GBP6

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Reply to
Peter Parry

Some links from my bookmarks may be of interest.

Practical optics info and FAQs at Edmund Optics

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Optics Reference Guide, has loads of optics formulae.
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Mirrors by the ton
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and Optics Tutorials (Uni of Florida)
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of Maryland demonstrations
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uk.d-i-y FAQ is at
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Google uk.d-i-y archive is at
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NOSPAM from address to email me

Reply to
Phil Addison

I'm in the same boat. I bought a mirror recently from Lidl which is much better than any I've had before, don't know the magnification though. It is about 6" across and has a suction pad on the back. I stick it to a window where the light is good. It might or might not be good enough for your friend but it was only about 7 euro I think so would be worth a try. Keep any eye on the Lidl newsletters :-) HTH

-- Holly, in France Gite to let in Dordogne, now with pool.

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Reply to
Holly, in France

|Apologies for straying off-topic, but I know there are a lot of clever |people here who might know the answer. | |A friend of mine wears glasses and has difficulty doing her eye make-up |because she can't reach her eyes with the glasses on and can't see her |reflection with them off. | |She can't readily find a magnifying mirror that's powerful enough, but |knows of some expensive mail order ones that claim to be stronger than |usual. | |I know that if she uses a 3 dipotre magnifying glass on a plain mirror, |she can see OK, but the problem is that a mirror will be labelled as 3X |or 5X, whereas a lens gets categorised by dioptres or focal length. | |Is there a way to convert the preceived magnification as seen through |the lens & mirror t( n dioptre ) o get an equivalent rating as defined |for mirrors ( n times )

I have the same problem at the opticians, can't see what the new frames look like without proper lenses in them. He took a photo of me with one of these fancy mobile phones which I could view with my real glasses :-)

I am sure that something could be rigged up with a webcam.

Reply to
Dave Fawthrop

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