Re: [ATM] Extended Object Brightness

[tkrajci@san.osd.mil]

>From: Daniel Reinders <danreind@shaw.ca>

>My question was how to theoretically reconcile the well known hazard of
>looking at the sun through a scope with the idea (see archives under "More
>photons in my eye? ") that extended objects cannot be made brighter by
>passive means to the eye, due to exit pupil effects - unlike stars which 
are
>point sources.  Note that this is not true were one to place the eye at
>prime focus where it is clear that aperature does matter for extended
>objects.  Is this a case where a small "spot" of radiation heat flux can 
be
>tolerated very briefly (again NOT a recommendation to do so!) as per the
>naked eye case, but that same heat flux applied over the entire retina
>cannot be tolerated because it raises the "global" temperature of the
>eyeball more than the eye can stand (i.e. humours/retina get hot and cool
>down too slowly).  Is the answer here in the anatomy and pathophysiology 
of
>retinal burns, and not in the optics of extended objects?

I am in the proces of translating Dmitry Maksutov's first book 
(Astronomical Optics) from Russian to English.  He spends a good amount of 
time talking about the inhomogeneities of the eye.  In one section, if I 
recall corretly, he points out that glancing at the sun with the unaided 
eye is not instantly damaging because (among other things) the eye's 
imperfections will spread out this small image of the sun 
somewhat...lowering the energy level somewhat.  (Also, and I don't 
remember if Maksutov mentions this or not...our eyes are in constant 
motion...we don't stare fixedly like a frog's eye...and with a small image 
this 'image jitter' also helps reduce the sun's potential damage to a 
naked eye observer because the image jitter is, roughly, on similar scale 
with the size of the sun when viewing with the naked eye.)  

However if you were to look at the sun through a telescope...where the sun 
has a large apparent size...the amount of 'spreading' of this image by the 
eye's imperfections (and eye motion/image jitter) is insignificatnly small 
compared to the image size...so these factors will not help reduce the 
energy level to the central parts of the retina.

I hope this helps a bit.

BTW.  Maksutov went so far in his studies of the inhomogeneities of the 
eye as to make drawings and to map out the inhomogeneities in one of his 
eye.  Makes us amateurs look like a bunch of slouches, eh?  ;-)

Tom Krajci
Tashkent, Uzbekistan

PS.  Speaking of solar cooking...a short drive outside of Tashkent is one 
of the largest, most modern solar furnaces in the world...still in 
operation in this country.  I can't quote figures or directly compare it 
with the (French?) solar furnace...but the US Embassy science and 
technology officer tells me it's 'world class'.



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