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!
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.
1190630
More strength? If you could explain I might be able to answer. This is a standard adapter for your camera-specific T-ring. You need both to mount/use a camera with a telescope (unless you get real lucky shooting through an eyepiece) - I've used them with heavy film cameras with no problem - on a decent telescope. If the 'scope is lightweight it's probably not good for astrophotography anyway. But the "strength" issue is unclear - are you planning on some other kind of use?
187867
I also noticed the "200" and assumed that it meant 2.00. Turns out that it did: the glasses are indeed a +2.0 correction. I'm not sure whether they just left out the decimal point after the 2, or maybe "200" is just what they call it.
187865
I bought these for my husband who normally uses a 2.00 strength. I've borrowed them and can see great (I usually use a 2.50). I don't know what 200 means per the description of the maker--maybe a typo?
57695
The goggles only come with a negative value which is for near-sighted. Mine were totally useless, terrible distortion, I could not use them and was given bad information by customer service. When I complained, iI was treated rudely. They offered no positive numbers for far-sighted
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
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.
1074584
Refractometer is really easy to use. If you have DI water source u can use it to calibrate. If not the calibration solutions are inexpensive.
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.
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!
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
4681
Actually I am not aware of anywhere online that shows measurement. I use the eye dropper bottle that comes with the order and basically do the math myself.I always drink a full glass or cup of distilled water whether I am adding adding 3 drops or 23 drops.
1799592
You don't have to order separate goggles. The VPS500A Parts Kit will fit to your separate lenses. That is the idea of the kit - so that you can use different strength lenses for each eye. If your prescriptions are the same in each eye, you can just buy other prescription swim goggles. But with different strength lenses, you purchase the lenses and the parts kit separately. Has been working great for me - over one year - no problem. Anti Fog has worn off- I just purchased an anti fogger here on Amazon. The link for the parts kit is: Tusa Strap, Nose Bridge & Side Clip Kit For V-500A (Blue) You don't have to order separate goggles. The VPS500A Parts Kit will fit to your separate lenses. That is the idea of the kit - so that you can use different strength lenses for each eye. If your prescriptions are the same in each eye, you can just buy other prescription swim goggles. But with different strength lenses, you purchase the lenses and the parts kit separately. Has been working great for me - over one year - no problem. Anti Fog has worn off- I just purchased an anti fogger here on Amazon. The link for the parts kit is: Tusa... » Read More You don't have to order separate goggles. The VPS500A Parts Kit will fit to your separate lenses. That is the idea of the kit - so that you can use different strength lenses for each eye. If your prescriptions are the same in each eye, you can just buy other prescription swim goggles. But with different strength lenses, you purchase the lenses and the parts kit separately. Has been working great for me - over one year - no problem. Anti Fog has worn off- I just purchased an anti fogger here on Amazon. The link for the parts kit is: Tusa Strap, Nose Bridge & Side Clip Kit For V-500A (Blue) « Show Less
1747
These numbers refer to the strength (magnification) of the lenses. Higher numbers magnify more.
282298
I do not know what 'cyl' and 'axis' measurements are, but, here is what we did:1. when ordering Speedo goggles, we got the +/- number, from our opthomologist.2. when ordering the ProMate snorkeling mask, we selected the the color and then selected the appropriate eye-adjustment (my son is nearsighted) from the "size" pull-down menu on the ProMate scuba options.3. My 13 year-old son loves the mask and was our family underwater photographer in Cozumel.
1515978
I have found no differences between the different diffraction glasses that I have purchased from Amazon. I have been buying large quantities for a couple years now to pass out to 8th grade science students in an Expanding Your Horizons project that I volunteered for. We use them to describe how Optical Emission Spectroscopy works in our lecture called "Chemistry of Light" I have never even tried them under black light, but will look into that for future reference. Not sure about the actual diffraction grating sizes being used but we are just looking to get the children's interest sparked so we haven't been very scientific about it. I have found no differences between the different diffraction glasses that I have purchased from Amazon. I have been buying large quantities for a couple years now to pass out to 8th grade science students in an Expanding Your Horizons project that I volunteered for. We use them to describe how Optical Emission Spectroscopy works in our lecture called "Chemistry of Light" I have never even tried them under black light, but will look into that for future reference. Not sure about the actual diffraction grating sizes being used but we are just looking to get the children's interest... » Read More I have found no differences between the different diffraction glasses that I have purchased from Amazon. I have been buying large quantities for a couple years now to pass out to 8th grade science students in an Expanding Your Horizons project that I volunteered for. We use them to describe how Optical Emission Spectroscopy works in our lecture called "Chemistry of Light" I have never even tried them under black light, but will look into that for future reference. Not sure about the actual diffraction grating sizes being used but we are just looking to get the children's interest sparked so we haven't been very scientific about it. « Show Less