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!
98633
Its actually not bad. I sighted in at 25yds and at 50yds. At 50 it was a little faint but you could definitely see it.. make sure you're not using a bright white paper to sight though as it will wash out. I really wasnt even expecting that for the price. It's worth the 12 bucks.
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
2071543
I physically measured mine using a digital caliper, it can only hold lenses with diameter 65mm safely.
1683132
It depends on what you'd eyeglass prescription is. You should check with you Optomotridt and find out what your prescription is and then get the diopter closest to that.Rich Signorelli
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.
1503374
The 25 and 36 refer to the size of the lens opposite the eyepiece in mm. The larger the lens the more light it gathers. This of course makes for a heavier monocular and a larger one. I have a 10x25 and it is fine. You have to have a steady hand though in using the devise.
1238980
The equation for the volume of a sphere is: V=4/3 &#960;r^3 (that weird n should be "pie" as in 3.14159) Thus, the volume of a 60-inch in diameter (30-inch radius) sphere is as follows: V=4/3 &#960;&#12310;(30 in)&#12311;^3((&#12310;2.54 cm)&#12311;^3)/&#12310;(1 inch)&#12311;^3 (1 mL)/&#12310;(1 cm)&#12311;^3 (1 L)/(1000 mL)=1853 Liters But, the volume of the balloon will depend on the pressure required to fill the balloon because the recoil force of the balloon will increase as the diameter increases. Basically, the pressure inside the balloon will be much higher than the surrounding air pressure. And the balloon pressure will increase significantly as the balloon diameter increases and approaches its burst pressure. So, the equation will be: (P1 (at sea level))/(P2 (needed to fill the balloon) )=V2/(V1(at sea level)) I work with angioplasty balloons (those used to treat blood vessel narrowings) daily and the burst pressure in those balloons is between 8 and 25 atmospheres for compliant and non-compliant balloons. This balloon is a compliant balloon (meaning that it changes shape with various pressures), so I would guess that the burst pressure is less than 8 atmospheres - probably more like 4 atmospheres. Thus: Volume =(4 atm)/(1 atm) x 1853 L=7,400 Liters (at atmospheric pressure) But, no fear, you don't have to fill the balloons to full capacity. By filling the balloons to only 40 inches in diameter, the volume and pressure will be substantially less. By my calculations, only 1100 Liters. As far as this information, you know what they say about experts: They know more and more about less and less until they know everything about nothing.
743771
It's not a graduated cylinder that's for sure. Based on the overall diameter of the location you are taking a measurement I imagine it would be very hard to get consistent readings, just due to parallax. If you're looking for something super accurate, this isn't the right tool.
2224926
I have no way to exactly measure the darkness or lightness of these goggles however, because I bought these for working in the shop, both grinding and welding, I felt compelled to answer. The seem dark enough for using a torch and grinding however I would not weld with them as they seem too light. Also, the little chain that holds the two eye cups together is really poorly designed. I can no longer use mine because I need to figure out a new middle connector or just throw them away... I honestly got really frustrated with the middle pc falling apart every time I tried to put them on!
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.
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
1253935
After using it, you can inspect it with a magnifier. I saw no problem and continued to use it on my lenses and filters. I'm happy with mine.
457479
I'm not sure of your question.. Li means nothing to me unless "light index" or something like that. RI is the standard term for "refractive index" which is what this device measures. Older testers used a very nasty and short lived chemical to bond a gem to the tester, and they had an analog readout. The accuracy of this is at least as good as the older machines.
834168
The first number is the magnification and the second number is the lens diameter. The larger the numbers the more magnification and light gathering potential.
1190631
As per previous answer it is just standard adapter for a camera specific T ring so you can attach camera to telescope that has 1.25 eyepiece It will not give more "strength" (I assume you mean magnification).
1216096
I have different sizes for different areas. I have been using the 1.0 for my face, 0.5 for around the eyes and 2.0 for body areas. I hope this helps. I actually did my face last night.