Let's say you have refined the axis by straddling the JCC over the axis and all looks good. My question is this: if you now change the cylinder power and again straddle the established axis, won't...
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Let's say you have refined the axis by straddling the JCC over the axis and all looks good. My question is this: if you now change the cylinder power and again straddle the established axis, won't...
OP here. Yes, I think my question was answered, thank you everyone for the help.
Robert, original poster back here - so just to put it to rest in my mind, I think I understand that if someone handed you a pair of specs and asked you to determine the amount of prism, it would be...
Thank you.
I think I am getting what you are saying. Sounds like the exact same set of glasses could be considered to have prism or no prism strictly depending on the reference point assumed. Am I finally...
That makes sense, I understand what you're saying. What still gets me though is how a lensometer can deduce prism, since prism varies at different PD's (or DBC's to be correct).
I'm digesting what you guys are telling me okay. Let's say you don't know the desired PD or desired prism, and you check an unknown pair of glasses on the lensometer - won't you always get "some"...
I am trying to visualize this better and could use some help please. Let's say you have 2 identical spherical lens blanks. In one, you grind the back to produce a conventional plus lens. On the...
Well this is a FT bifocal with minus cylinder, so I guess I will have to be satisfied that it was ground correctly from a good blank, and must have warped at some point. Thanks a lot for the help.
Hi Robert, you mentioned the warpage might have come right out of the box. If that were the case, would the back curves be ground to match the irregular front curve (or in this case front curves...
The lens is a small oval shaped lens and there is just enough room above the seg to place the 3 points of the clock. That is where I am taking the 90 degree reading. I also took the 90 degree...
Thanks for the reply. I understand what you are saying about the 1.53 index the clock is calibrated to vs. the lower index of CR39 and that definitely would sway my results. BUT the anomaly I am...
Finished center thickness is about 3.5mm.
Dick, I took the lens out of the frame after your post and rechecked it. Also checked the mating lens while I was at it, and it has a purely spherical front curve. No difference, but good...
This lens was purchased online pretty cheaply so I am pretty sure it is not anything sophisticated like a free form lens. I would guess just spherical, maybe an aspheric at best.
I was trying to identify several pairs of spectacle lenses and came across an unusual one. The supposed prescription of the lens is 1.25-1.75@175 with a 1.5 FT add. I don't know if the front curve...
I would like to get a set if possible so I can use them like trial lenses. That way I could try different ones side by side.
In doing some aniseikonia testing, I would like to try what I have seen referred to as "SIZE LENSES". These are lenses which magnify but do not refract. For the life of me I have not been able to...
Would an aspheric design in this case eliminate, or at least decrease significantly, the off axis distortion?
Hi everyone. I have a lens here that is a +3.50 / -3.50 @ 180 with a base curve of 6. My question is this: assuming the same rx, the same base curve, same lens material, etc., would decreasing the...
Okay, assuming that anisokeonia, differing image sizes, etc. is NOT an issue and we are only interested in best distortion free vision, then here is the question>>> If each eye has a different...
This topic caught my attention and I was hoping someone could clear this up for me since it's on the subject. I understand that decentration will not work in some cases such as high prism and low...
Thanks for that info, it really helps my understanding. Thanks to everyone else too that helped me out.
Yeah, I think you're right on that one. I think maybe what I was describing might even act like a Maddox rod since it would just be stacked prisms... Thanks for the info.
Yes, that helps. I wonder if you took two large regular prisms joined base to base, and looked through the pair directly through the junction, whether any "correction" would occur. You would be...