Lensometer question

[Conoid of Sturm]

I'm competent with a lensometer, but admittedly didn't use ours much at LC because I was a retail manager and the lab guys verified for us. I probably wouldn't have used it at all except for just wanting to learn it. So I'm far from an expert.
Anyway, where I work now we have a Reichert lensometer, and I can't tell a difference with or without a quarter diopter of cylinder. For example, I checked a +2.00 -.25 the other day and it looked exactly the same to me whether I dialed in the cylinder or not. An employee told me this is because our lensometer sucks. It's new, though, so I don't know. I'm careful about focusing it to my eye, etc. Any advice/thoughts? Do I just suck at lensometry?

[For-Life]

Well if you turn it off axis by 45 degrees, play around and see if you can tell a difference between the cyl and sphere. Otherwise, I bet the lens either has no cyl or is weak on it.

[Conoid of Sturm]

True, it could be the lens, but it worries me. I want to know that I'm doing my job right. Suppose it were an eighth of a diopter off--should I be able to see that? I looked at other lenses and the same thing applied, I could not tell a .25 difference. The most likely explanation is that I suck, since as I said I have not really spent enough time to become a master at it, but I do things in the right way as better people have told me so I wonder...Does my lensometer suck, or am I doing something wrong? Just so you know what I'm doing, I'll explain my approach...
I first focus to my eye (no need for detail here I'm textbook on that), then I put the power wheel to waaaay minus, and move up until the cylinder lines come into focus. If the sphere lines come into focus first, I assume I'm off axis and move cyl wheel 90 degrees...and so on...That's probably way wrong, and if someone will teach me the right way I will remember you in my prayers. Thanks.

[Framebender]

You should be able to tell an eighth. I'm not familiar with the lensometer you're using. Its manual or digital? I use a Model 70, so you set the axis and the sphere power and use your fingers to roll the lens for centration and axis. Then you check cylinder for power and spot it up. At least that's how I learned.

Order yourself a stock glass lens with cyl. That will give you a good idea of if your're off. Good luck to you!

[chip anderson]

If you work for a doctor or doctor located nearby facilty, borrow some of the lenses from his trial set and check them.
Chip

[dcarew]

The lens you were checking may also have poor optics. If a sphere lens is distorted, it may look like it has cyl.

Also, I agree if the compound lens looks like a sphere, it probably has weak cyl.

[Samuel Jong]

Is it true that most lensometers are designed and set for measuring lenses with index 1.5 with abbe number 58?

[EyeFitWell]

When I was first using a lensometer, I had the same sort of experience. Soon, though, I learned a difference between kinda clear and dead-on clear in those lines. Also, if you want a quick way to see if there is any cyl in the lens, dial in the sphere power and rotate the axis wheel. If there is any cylinder, you should see the three little lines loose focus and the fat lines come into focus (or whatever type of lines are on your lensometer). That's a good quick trick if you're in a hurry.

It's possible that the lensometer you're using isn't very sensative, but my guess is that you're not yet noticing when the lines are visible versus when the lines are *bingo crystal clear* (that's my term-you must quote your source!) :D
Good luck!!

[EyeFitWell]

I noticed that you worked at LC, and I'm guessing that's where you learned. When I started in this field, I worked at a high-end shop with premo lenses. Working with those lenses (frequently stock lenses) things were really crystal clear. I later worked at LC for a short time and I quickly noticed that many lenses ground were within tolerance (I was used to things being exact) and they were often kind of fuzzy in the lensometer. I'm not saying they were wrong, but they weren't *bingo crystal clear* if you know what I mean. Try getting your hands on some stock lenses with cylinder and check it out. Often times stock lenses are more dead-on than a ground lens.

[Dave Nelson]

you may also find resolution can be an issue with some types of polycarbonate lenses, and may make it difficult to obtain a crisp target on the machine, which, in turn, would make it difficult to resolve a .25 cyl.

[Conoid of Sturm]

Thanks so much EyeFitWell, Dave, and everyone else. I have largely resolved the problem by focusing the lensometer as people here have suggested and practicing nearly constantly at work, which has indeed helped me better tell the difference between "crystal clear" and "kinda-sorta."
The tip for checking for cyl is much appreciated, I'll pass that along. Same with the tip on poly.
I think it came down to me being inexperienced, the lensometer not being the best, and half our lenses coming in wrong. Speaking of lenses coming in wrong, I'm posting with a question about that and just want to say how lucky I feel to have you guys and gals around to help!