help!!!!Nikon lensometer

[sparky]

I have a question the old time optigods may be able to help me with. I recently came in contact with a VERY old nikon lensometer. The problem is--- I can't figure the #**# out!! Instead of lines for the sphere and cyl-it has dots which are in a circle. I kind of got the gist of using it for spheres but i can't figure out how to get the darn axis there's no dial I can see and its driving me nuts!! Any help or instruction would be greatly appreciated! Thanks in advance! :D

[Steve Machol]

Is there a model number for this lensometer?

[sparky]

i think its 21450- that's the only # I saw on the machine

[shanbaum]

Isn't there a plastic ring with a reeded edge protruding from the front center of the machine at the bottom? This would rotate the target - as I recall, the axis is read on the reticle itself.

If there's no such ring, is there an opening? Perhaps the ring broke off.

When measuring cylinders, dots become lines; axis is determined by turning the aforementioned knob until these lines are parallel to the longer of the mires.

[John R]

Does it look anything like this.....

[John R]

Lets try again dodgy conection tonite.....
Does it look like this........

[Maria]

I know the style you mean, as we are cheap enough to still have them! Personally, I find it difficult to get the axis spot on with them, but I learnt on a line one. I think Robert explained it right (but I didn't understand), so here it is for stupid folks like me :)

When you turn the power wheel (or whatever it's called), the dots, that are in a circle, all blur out into lines. When the lines are all straight, you are on the correct power. (I have difficulty determining whether or not they are straight, they always look fine within a diopter either way to me!)
When you have the power that you will take the axis from, twiddle the dial up at the eyepiece that turns the axis stick around inside the lensometer until it runs parallel to the lines made of dots. You may then have some rough notion of the lens Rx, and an inclination to buy a good old line one.

PS Some have the axis protactor thingy inside, some have it on the outside, at the bottom of the barrel. If it's not either of those places, it has fell off/out. It is possible to find the axis using a fitting cross and a pen, but that's a whole other post :)

[sparky]

yes it does have that dial under the eye piece to rotate the axis.So basically when I have the correct sphere, it will be a circle of dots, find the axis by turning the dial till everything is in focus,then rotate the power till I get the cyl,which will go from a circle to an oblong line? I had a lab tech trying it out today along with a couple of old time dr. and they were all stumped and gave up! I think I prefer my good ole A.O. to this thing. I hope I understood everything correctly. Thanks for the help.

[shanbaum]

When you insert a compound lens into the instrument, the dots become lines. They will be lines while measuring both the sphere and cylinder powers. The axis is measured by rotating the target until the lines produced from the dots are parallel to the mires. The sphere and cylinder mires are similar (as I recall), the main difference being that the sphere lines are longer.

[David Wilson]

Sparky,
You have a ring-of-dots or corona target. Also known as a European target. Like all lensmeters it will work on the principle of the astigmatic pencil (Stum's conoid) for cyl lenses. Here is a method that will work for any lensometer (including crossed-line targets).
Step 1: Your first reading is your sphere. That is when the dots stretch into clear lines. Make this the strongest plus or weakest minus to get a minus cyl.
Step 2: Subtract the first reading from the second reading to obtain the cyl power. Or simply say I have turned the power drum so far towards the minus direction.
Step 3: The direction of the target (the way the dots are stretched) at the second reading is the axis. You use the graticule to line up with the dotd. A true ring-of-dots focimeter (lensmeter) has no axis drum because it would be redundant.

Hope this helps Sparky.
Regards
David Wilson

[sparky]

Thanks for the input everyone. I practiced with it today, and feel i can now use it with a degree of accuracy. This piece of equipment came from a dr. which has retired and sold his practice. Do you wonder-should he have retired that lensometer too?

[Lucasdad]

Does anyone know where I can get replacement inking pins for nikon lensometers? I would really appreciate the help. Thanks.:D