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!
897742
I have been satisfied with my refractometer so far. I previously had one that came in a gem lab I purchased 25 years ago and it wasnt nearly as easy to read as this one. No complaints to this point.
1632329
Hi, The focusing distance is always measured from the sensor. Therefore, subtract the distance from the sensor to the front of the lens barrel (approximately 3 inches), and you are left with actual "working distance" of about an inch. Hope that helps.
21263
i would get the -3 that way you don't cause disorientation, because water as is does have refraction, so i would go with the lowest diopter.
49300
You need to know your glasses prescription. If you're nearsighted, (need correction for distance sight your rx will be a negative number. The lenses come in 0.5 increments. For example I have a -3.75 correction. Since it is in between correction options I ordered a -3.50. (If your in between order the lesser strength). If you are far sighted the correction will be a +.(ie reading glasses). Hope that helps.
1576951
There was no strength specified in the description. After the order was placed, the vendor emailed me to check whether I wanted strength 2.0 (he said that is what I ordered even though I was not able to specify a strength at time of order). That gave me the opportunity to let him know that I wanted 1.75 and that is what they sent. BTW, we love the glasses because it is the small compact size my husband was looking for.
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.
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.
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.
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.
1177290
It depends on what your eyeglass prescription is. I spoke to my optometrist to see Whart general range is.
2263147
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 ◾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 :)
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.
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).
1990075
you will notice the top of the clear ring starts lined up with zero at the top of the scale. You want to use the top of the ring to get your measurement from. You have to slide the ring back up for each measure. You should measure 3 times or more and average the reads. For a pistol hold the gun down on a table or sturdy surface as just holding it in your hand introduces errors. I found doing that usually caused it to read as much as a pound more than when the guns held butt down on my bench.
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
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.