Incoming from Watchgecko

A place to discuss other watch-brands
JAFO
Senior Forumgod
Senior Forumgod
Posts: 4490
Joined: Wed Jul 15, 2020 3:59 pm

Re: Incoming from Watchgecko

Post by JAFO »

Bahnstormer_vRS wrote: Sat Mar 27, 2021 5:29 pm
exHowfener wrote:Does anyone here watch "The Repair Shop" on BBC1? There's a guy on the programme (a jeweller) who wears two pairs of glasses.
I've done that before now.

Taken an old pair of reading glasses and placed them in front of my regular Varifocal spectacles.

Guy

Sent from my Xperia 5 using Tapatalk
Yes two pairs of 5 dioptre glasses gives you 10 dioptres (maybe it's 5x5 so 25) doesn't it? I think that's getting to a decent magnification. Not sure exactly what power.
User avatar
H0rati0
Senior Forumgod
Senior Forumgod
Posts: 2314
Joined: Wed Jun 27, 2018 7:49 am
CW-watches: 4
Location: Alpenvorland

Re: Incoming from Watchgecko

Post by H0rati0 »

JAFO wrote: Sat Mar 27, 2021 11:14 pm

Yes two pairs of 5 dioptre glasses gives you 10 dioptres (maybe it's 5x5 so 25) doesn't it? I think that's getting to a decent magnification. Not sure exactly what power.
not quite 10 dioptres because you get diffraction across the air-gap but pretty close. At that power, focus is achieved at 10cm because a dioptre by definition is the reciprocal of the focal length. Times magnification (magnifying power as opposed to power of lens) is more difficult because it depends on the distances between a "typical" eye, magnifier and object but typically 3-4X for 10 dioptres.

Thus more power (in dioptres) means you have to shorten the viewing distance, narrowing the field of view and in practice the lens has to be more complex because aberration (distortion) increases and it all starts going sideways.....
"There is no beginning to enlightenment and no end to training" - Dogen Zenji (1200-1253)
JAFO
Senior Forumgod
Senior Forumgod
Posts: 4490
Joined: Wed Jul 15, 2020 3:59 pm

Re: Incoming from Watchgecko

Post by JAFO »

H0rati0 wrote: Sun Mar 28, 2021 3:18 pm
not quite 10 dioptres because you get diffraction across the air-gap but pretty close. At that power, focus is achieved at 10cm because a dioptre by definition is the reciprocal of the focal length. Times magnification (magnifying power as opposed to power of lens) is more difficult because it depends on the distances between a "typical" eye, magnifier and object but typically 3-4X for 10 dioptres.

Thus more power (in dioptres) means you have to shorten the viewing distance, narrowing the field of view and in practice the lens has to be more complex because aberration (distortion) increases and it all starts going sideways.....
I definitely find my 25x loupe set very hard to use. I get all types of aberration, and a very limited depth of field. I imagine that's the inexpensive lens design of my viewer. I notice a difference with binoculars. I have a lovely pair of 8x30 pentax binoculars, and the image is always crisp and clear. much more so than when I use other less expensive glasses.
User avatar
H0rati0
Senior Forumgod
Senior Forumgod
Posts: 2314
Joined: Wed Jun 27, 2018 7:49 am
CW-watches: 4
Location: Alpenvorland

Re: Incoming from Watchgecko

Post by H0rati0 »

JAFO wrote: Sun Mar 28, 2021 4:09 pm

I definitely find my 25x loupe set very hard to use. I get all types of aberration, and a very limited depth of field. I imagine that's the inexpensive lens design of my viewer. I notice a difference with binoculars. I have a lovely pair of 8x30 pentax binoculars, and the image is always crisp and clear. much more so than when I use other less expensive glasses.
Pentax do know what they are doing when it comes to lens design....though naturally the design of binoculars is a very different from a loup. For your 25x try holding it very close to your eye and then bring the object into focus. It will be very near the loup but that's how they are designed to be used - though as you say on a cheapo one the optics (aberrations) won't be anything to write home about.
"There is no beginning to enlightenment and no end to training" - Dogen Zenji (1200-1253)
  • Similar Topics
    Replies
    Views
    Last post