I read on another site that: 1/2 the cylinder measurement + the sphere measurement = diopter strength. Because I have a lot of astigmatism this changes the measurements quite a bit (-3.25 cylinder, -3 sphere). Has anybody else used this equation to determine the strength in buying goggles? I read on another site that: 1/2 the cylinder measurement + the sphere measurement = diopter strength. Because I have a lot of astigmatism this changes the measurements quite a bit (-3.25... » Read More I read on another site that: 1/2 the cylinder measurement + the sphere measurement = diopter strength. Because I have a lot of astigmatism this changes the measurements quite a bit (-3.25 cylinder, -3 sphere). Has anybody else used this equation to determine the strength in buying goggles? « Show Less
107802
That equation is correct... it is called spherical equivalent. With a -3.00 sphere and -3.25 cylinder, your spherical equivalent is -4.50. Keep in mind this will give you pretty decent vision - good enough to see at a reasonable distance, but this will not be equal to a full spectacle prescription. I am an optometrist.
40139
That's the method we used when buying my daughter's goggles. She ended up with -3.625 (R) and -4.25 (L) so we split the difference with a -4 prescription. She says they work well enough for her, and she has to be read a white board to get her workout during swim practice.
107803
hi, none of us are opticians. I'd give them a call and ask. That way you'll get a pair of goggles that you can use to read underwater - haha - but seriously, I was thrilled when I could see clearly underwater. It's worth the effort!
2071543
I physically measured mine using a digital caliper, it can only hold lenses with diameter 65mm safely.
21876
goggles dont come in sizes but in styles. Its wathever feel more conmfortable to you, the adjustment is done thru the strap. If you are talking about prescription it is usually what your glasses prescription is if its different on both eyes go with the lowest prescription. otherwise you will feel disoriented.
614136
Some people with an astigmatism will see more than one dot or the dot will seem out of round. I am one of those people and you just get use to it over time. My aimpont and delta point do the same thing.
2030132
Hello Joyce, The "mm" measurement refers to the size lens the filter is meant to fit. Most lenses should have this measurement written on them, and it refers to the diameter of the end of the lens where the filter screws on, not the "35mm equivalent" of the zoom, so it is important that you get the right size for your lens and there is only one correct size. This specification should be listed under the specs for the lens as well, and is specific to that particular lens..other lenses will have different diameters...Hope that helps!
998685
It says"Magnifier 2 5x ...". I believe the 2 is just part of the product name, there is no decimal point. A 4" lens diameter can't be 5x, they just can't make them. I even asked my eye doctor about ordering one from him. So I think the lens is a 1.5x with a 3x inset as the lower information on the page description says,. I sent mine back as the one I bought at a fabric store was better. I think you could find a 2x or 2.5x in a large lens with a 6x inset somewhere else. The around the neck batteries wear out very fast so you need rechargeable batteries for cost reasons.
315445
I have held a ring with the stone facing down against the measuring opening. I get a reading but it fluctuates if I move the stone. With a faceted surface it's easier but I have gotten readings for cabochons. It's a good tool but of course not definitive. There are different stones that have the same refractive range...for example...quartz, amethyst, onyx, aventurine, citrine...so I think you have to make a judgment on the stone using other info too. I am not a professional gemologist. I use this tool as additional confirmation of what I think the stone is. I also like the presidium Gem tester. There's a lot of glass on the market...even set in gold! I have held a ring with the stone facing down against the measuring opening. I get a reading but it fluctuates if I move the stone. With a faceted surface it's easier but I have gotten readings for cabochons. It's a good tool but of course not definitive. There are different stones that have the same refractive range...for example...quartz, amethyst, onyx, aventurine, citrine...so I think you have to make a judgment on the stone using other info too. I am not a professional gemologist. I use this tool as additional confirmation of what I think the stone is. I also like the presidium Gem... » Read More I have held a ring with the stone facing down against the measuring opening. I get a reading but it fluctuates if I move the stone. With a faceted surface it's easier but I have gotten readings for cabochons. It's a good tool but of course not definitive. There are different stones that have the same refractive range...for example...quartz, amethyst, onyx, aventurine, citrine...so I think you have to make a judgment on the stone using other info too. I am not a professional gemologist. I use this tool as additional confirmation of what I think the stone is. I also like the presidium Gem tester. There's a lot of glass on the market...even set in gold! « Show Less
377710
I not sure what you mean by 'strength'. I certainly do not have a spectrum analyzer or light meter to measure intensity and wave lengths from a specification perspective. What I can tell you is that I have prior experience with UV light in water supply systems and air vent systems and the results I have achieved with this device are consistent with these other better known systems/applications. Furthermore, like I posted, this is not a toy and should be handled as a tool. I also bought the UV glasses for eye protection, keep my skin out of the light ray, and keep me kids away when in use. One really good indication of it working is the 'ozone' smell associated with disinfected area. It is the same smell you get after a lightning strike. To find out how it works, I would suggest looking into water supply UV light systems. It takes very little exposure to UV light to kill bacteria that can be found in well water. I would be happy to share specific details if know the application for which you are considering this purchase.
1679463
Its infinitely variable as far as I can tell. Its like twisting a knob.I don't use this very often, only on one particular lens. I almost forgot about it. Thanks for reminding.No issues with this at all. Just guesstimate only for aperatures.
814584
Hey you properly calibrated it by using RODI water. You must put RODI water where you use it for the saltwater then just above it is a black cap an under the cap is a screw to calibrate it. So look into the eye part then adjust it to zero then it should work fine
21264
Honestly there isn't a big deal between -3.50 and -3.00 and you can get either one and you will see grate. But if you are still not satisfied go for 2 pairs of one -3.00 and -3.50 and just switch lenses and this way you have to pairs with perfect match
1379828
I am just guessing but I assume it is 2 and 1/2 magnification; I have one of these and the cord that you put around your neck can be adjusted to bring your work into focus so I wouldn't worry about it. I love mine! Well worth the money!
1870387
Using another spyglass viewing a yardstick and doing a little math I came up with 145' at 1000 ft which would be 450' at 1000 yds. A quick test against my Mom's similar $135 device, including the 10" focus ability, showed no visible difference to me. I do wish it had a rubber eye cup, though.
882730
When I look through a eo tech with its red dot and circle they are very fuzzy to me. The triangle reticle is sharp with no blur and comes to a nice fine point which I use for aiming. I really don't know how a astigmatism would effect it but for my eyes it's great.
47633
So you have the option to have a different strength for each eye? I did not when getting swim goggles and went with something in the middle, so in your case, either 2 or 2.5. I have one eye too strong, one not enough, but that does not seem to be a problem.
2263148
with out the 3x magnifier I wanted the two dot easy to see . with out the 3x magnifier over two dots hard to see them . yeah with 4 dots and no &#9726;3x magnifier looks like a straight line. I dint want the weight and pay the extra cash. my friend has the 4 dot and 3x magnifier really nice set up. hope this helped you :)
21877
They are adult size with different nose pieces to make a more custom size. If you mean correction strength ask your eye doctor. My son is nearsighted, he needs a negative correction I got him -2.0