|
|
Thread Tools | Display Modes |
#17
|
|||
|
|||
Let's Photograph Comet 46P Wirtanen
On Mon, 31 Dec 2018 09:26:42 -0700, Chris L Peterson
wrote: Don't you see the beauty in performing that division? Nope. It discards useful information. It's like characterizing a aperture telescope by focal ratio, and not providing the focal length and aperture. If all telescopes always had the same focal length it would be practical to do that. Then the aperture could easily be calculated from the focal ratio and the implicit focal length. Now, this is not the case of course, but in the case of visual acuity tests the Snellen chart is always at the same standard distance. A patient with 6/6 vision and one with 3/3 vision may have significantly different visual acuity; if you normalize them to 1.0, you lose that distinction. Did you ever see any visual acuity report giving the result 3/3? (is that in feet or meters btw?) The standard procedure for that would be to still use the standard distance but to insert correction lenses in front of the patient's eye. The strength of that lens must then of course be given in the report. In the rare case that the visual acuity test actually is performed at a distance of 3, this is easily handled by adding a note to the report. E.g. "acuity 1.0 at distance 3". If the "at distance" note is absent, the standard distance will be implied. Btw, how do American eye doctors give the strength of corrective lenses, or of any lenses? In metric diopters like in Europe? Or do they have their own diopter scale based on feet instead of meters? Or do they just give the focal length in feet? |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Can't see the comet 46P/Wirtanen because it's like winter 1986 here | RichA[_6_] | Amateur Astronomy | 4 | December 14th 18 12:22 AM |
Would like to photograph the Perseids | Paul Ciszek | Amateur Astronomy | 1 | August 10th 12 11:26 PM |
Best Lunar Photograph I Have Ever Seen | Davoud[_1_] | Amateur Astronomy | 27 | December 3rd 08 05:47 PM |
Interesting photograph. | Thomas Lee Elifritz | Policy | 2 | March 15th 04 06:27 AM |
Interesting photograph. | jacob navia | Astronomy Misc | 4 | March 15th 04 06:27 AM |