My way:
Set the power wheel to (absolute) plano (0.00D)
Focus the eyepiece to make the target (absolutely) sharp.
Read the power.
(forget the recticle...you only really need it for prism measurement anyway).
Any thoughts on this departure from the accepted textbook methods?
Barry Santini, ABOM
Originally Posted by Barry Santini
You're kidding, right ?
What true need is there for the recticle besides prism (and, of course), target centering (which is related to prism)?
Help me understand you're viewpoint about "...kidding...?)
Barry
There is about a half diopter of available adjustment in the reticle. While it might read plano for you in its current position it might not for me. That is why they have some focusing ability built into it. As an ABOM I know you already know that.
The key to your comment is that you said you check for plano before starting to read lenses. What if during your check it doesn't read plano? Do you read the lens and then compensate for the power difference in the reticle? The trouble really is when a lensmeter is shared by several Opticians. An Optician I work with has to adjust the reticle more than a .25 diopter different from the setting that works for me.
Again, the key is just making sure the plano setting on the power wheel reads plano for you, if not then adjust.
I was taught to turn the reticle all the way counter-clockwise till it stops. At this point the prism lines should be out of focus. Then turn the reticle clockwise slowly untill the prism lines and ultimately the mires are clear. The other key is to stop where it first comes into focus. Don't go past clear focus then start going back and forth either or your visual system might start accomodation. I also typically do it with the lensmeter off and a piece of white paper where the lens would be. The white paper just makes the lines easier to see.
Is that what your looking for Barry?
Well, I think the reticle procedure is mistargeted. When you said "plano should be plano", that I agree with. I think my method allows the same amount of operator-to-operator telescope/eyepiece focus compensation, but the method I use means no operator has to remember a *read-compensating* factor, which the recticle system will demand (if the instrument is not *perfectly* calibrated.
Hope this helps
Barry Santini, ABOM
The purpose of focusing the reticle is to prevent you from having to use your own accomodation to see the target clearly. It really has nothing to do with getting the wrong readings on the power drum. By eliminating accomodation, it prevents eye fatigue when looking through the eyepiece (for long periods of time)
The reticle should be focused (wearing your distance correction if any) by turning the eyepiece all the way counter clockwise. Then turning it slowly clockwise while you look at the reticle. You should stop as soon as the reticle reaches maximum clarity.
fjpod is right on the money with this.
Oh my God!
double post
Barry,
It was the "forget it" part that made me think you were joking. If you don't take prism into consideration when "neuting" a lens, focusing the eyepiece wouldn't be too crucial either. I was taught the same way fjpod was.
Focussing the eyepiece the *correct* way (From out to in, i.e., fogging the eye) is, as you point out, the way to remove accomoidation from the process. My way differs not from the traditional in this manner.
however, an inaccurately assembled traditional instrument error is compensated using my way, without the need for an operator to carry a corrective amount in his/her head.
I'm thinkin' most of us may have little experience with poor "lab" lensometers. I've had quite a bit, and found my method eliminates problems with these instruments.
Thanks
Barry Santini, ABOM
The way I learned to focus a lensometer is to put white paper over the receptacle (where the eyeglass lens rests) and to look into the eyepiece. Turn the eyepiece all the way to the left so prism lines blur. Slowly turn eyepiece to the right until prism mires are sharp. I never use the optical mires for focusing. Correct me if I am wrong please.
thats what Ive been taught...anyone else agree?
This is exactly how Bausch & Lomb instructed users to focus their old Model 70.The way I learned to focus a lensometer is to put white paper over the receptacle (where the eyeglass lens rests) and to look into the eyepiece. Turn the eyepiece all the way to the left so prism lines blur. Slowly turn eyepiece to the right until prism mires are sharp. I never use the optical mires for focusing. Correct me if I am wrong please.
Darryl J. Meister, ABOM
Darryl, you are 100 percent correct, these other methods are wrong, what is confusing people today is they are getting slightly different readings , due to all the different indexes available
1. Put acard or paper on hte lens stop
2. Turn eyepiece counter clockwise to the stop
3. Look through eyepiece and turn eyepiece slowly clockwise until the reticle is clear and sharp
Adjust eyepiece every time you use the instrument if you are not the only person in the office. If you are the only user check daily
To verify power and axis accuracy use a Gaugemaster lacking that power can be checked with a series of trial case lenses +/- 6 and +/- 12
1. With eyepiece adjusted set power drum to Plano verify power drum reads 0 with the meiers sharp
2. check with +/- 6 if not sharp adjust the lens stop in or out until meiers are sharp with both + and- lens if not equalize the difference between + and - lens
3. repeat process with+/- 12
This is a reasonably accurate way to calibrate the instrument
Ed
Ed
MSEd, BBA, AAS Ophthalmic Dispensing
ABOC NCLC FNAO FOAA
There are currently 1 users browsing this thread. (0 members and 1 guests)
Posting Permissions
Reply With Quote
Bookmarks