Blur mires in lensometer

[Mivec]

Can anyone enlighten why i just can't get a sharp mires on the manual lensometer for some lenses like Polycarbonate?

[Wes]

I find that to be the case as well with higher powered lenses with low abbe values. Also high abbe progressives with a couple diopters of prism thinning and lenses with prescribed prism.

[rdcoach5]

Can anyone enlighten why i just can't get a sharp mires on the manual lensometer for some lenses like Polycarbonate?

Any material can be poorly or well ground. There is good or poor quality poly as well. Try a different lab and you will see a difference. If you don't, try another. I get sharp optics or I return the lenses.

[OpticalMessiah]

The other way to approach this question is with a question: Do you get a crisp, clear image of the reticle after adjusting the eyepiece, while blocking your light source? While this question may seem pedantic, I've noticed that a lot of people don't make the eyepiece adjustment before reading a lens, resulting in a slightly blurry image.

If your problem is only with polycarbonate, then the lenses weren't made well, or are inferior, as rdcoach5 suggests.
In addition, some lensometers don't read high plus or high minus lenses very well, particularly in the rare case that the lenses are spherical.

wss2020 is correct as well. With some lensometers, any movement away from the optical center will yield a faulty reading.
Having a prism compensator on the unit makes reading prism much easier, and more accurate.

Hope this was helpful.

[RT]

If the lens is a lined bifocal like ST28, it could be due to aberrations from the lens hard coat just above the seg. Many labs will raise the OC above the seg on ST28 higher in polycarbonate than other materials. Poly lenses tend to have more problems getting an even hard coat just above the seg.

[OpticalMessiah]

If the lens is a lined bifocal like ST28, it could be due to aberrations from the lens hard coat just above the seg. Many labs will raise the OC above the seg on ST28 higher in polycarbonate than other materials. Poly lenses tend to have more problems getting an even hard coat just above the seg.

Wanted to thank you, RT. I haven't seen "ST28" in many years, and there it is, in your post. When I first started my journey in this job/profession/craft, I cut my teeth on ST28s. That's the only bifocal term I used for the first three years of my optical life. At the time, it sounded very "medical" to me; it still does. Even with the other two bifocal terms, ST28 remained the Alpha Male. Then FT28 and D28 moved ahead in popularity, and our hero was relegated to third place. But, thanks to RT, ST28 is back, and looks stronger than ever. Congratulations, ST28, and thanks again, RT.

[QDO1]

if the eyepiece is correctly focused for YOU, then the explanation is that the lenses you are looking at are poorly ground, or poorly coated

[OpticalMessiah]

Thanks, QD01, you got me back on point. I appreciate it.

[One science]

Go in another place. It might be the lab's problem and if in another place you'll have the same problem it means that is the Polycarbonate's lenses fault.