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!
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
571851
no, it measures the light reaching the subject which is independent of the lens used. It gives you accurate light measurements either in e.v. units, or in f stops. f stops as a measurement of light are equivalent. Differing lenses will affect the depth of field, but the amount of light will be constant and not vary with the lens. Thus, f/1.4 on a 50mm lens will give you the same exposure as it would on a 100mm lens.
2071543
I physically measured mine using a digital caliper, it can only hold lenses with diameter 65mm safely.
1951961
There are three lenses which can be stacked for greater magnification. Using the first lens only it's about 8-8.5 inches. Add the second lens and that drops to about 4 - 4.5 inches. Add the circular lens (for the right eye only) and it drops to about 3/4 - 1 inch. Hope this helps.
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.
439838
It is variable, from 1.75 to 5 - it depends on how far away the lamp is from the item: 1.75 if up close to the glass, 5x if a foot away - more than a foot away and focus begins to be lost. I use it for modelling and its about as good as it gets.
866403
I haven't used it, bought it for a professional guide in Africa. Has a little square in the center to center the target with. Is 6x magnification, if I recall right, so does magnify the target. with that magnification, I'd put 400 yds, in a real steady hold, hand braced on something at 400 yds..maybe a bit less. everything is fog proof these days, and probably water proof,if you're talking rain..don't know about scuba diving with it. you might want to go to the Optics Planet site, as they have the breakdown on those things on their site.
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.
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.
518034
1/2 a cup exactly then subtract 3 1/2 tsp. I use a syringe type dropper made for oral medicine to measure. Your results may be a little different... but this is a really good place to start. For me this makes round death stars. If you add too much you get fun house mirror death stars shaped all cone like on the top. (which is the bottom of the mold)
1025376
Sorry, but I don't have an expert answer. Here's what I did. I simply measured, with a very accurate ruler the exact outside center cross distance on the lens. No matter if it measures in inches or metric, just Google the number for a conversion. Worked perfect for me on the first and subsequent orders.. The covers fit perfect, are very well made and I'm very happy to have this protection for all of my lenses. Hope this "grass-roots" method works for you. Bob D., Maine
1165242
Wow, that answer isnt listed ANYWHERE, not even their website. This sight is identical in width to the one I just took off, that was a .100, so it appears to be just a standard general width sight.
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?
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
1652323
Her is two thoughts, 1st you can use a minus 1 and that may give you the rsange you want but I took the 2nd way which I purchased a -2, that way I can use the plus adjustment to get the proper adjust. Don't to purchase an eye cup for the corrective lens.
1746
That is the strength of the reading glass. The higher the number the greater the magnification. It is not at all about the size as it will fit your head.