Based on reports I have heard regarding telescopes pointed into the sun
I suspect that that an SLR (assuming focus at infinity) would first see
the focusing screen melted followed by cracking and/or separation of the
eyepiece behind the pentaprism. Telescopes eyepieces with elements
tightly constrained within metal cells may explode with some vigor due
to thermal expansion.
Chuck Norcutt
Dawid Loubser wrote:
> No, of course I didn't look through an 250mm f/2.0 lens and point it
> into the sun!
> That would result in instant retinal meltdown - and anybody apart from
> a complete
> amateur doing this would arguably deserve it.
>
> As I was sitting in the car waiting for the locksmith to fix the lock
> on our back gate (I was locked out due to a broken key) I was pretty
> bored... Nothing to photograph here that hadn't been done before...
> All alone.
>
> I decided to take the 250mm out of it's pretty metal case. I admire the
> heft, the craftsmanship. I turn the focus ring. Ahhh.... smooth internal
> focusing.
>
> *bash bash bash* - the locksmith is trying his best to open the gate.
>
> I take off the fine leather front cap (the back cap is still on). I
> hold the lens in the sun. I admire the fine 9 curved diaphragm blades
> that snap in place light as a feather.
>
> The Cicadas are noisy in the trees outside. It's 35ºC or something
> today.
>
> Just as I start to think "Hmm, there's a bit of dust in this lens" -
> and wondering
> what extent of dirt inside a lens like this would ever make it worth
> it to ship this
> hunk-of-glass back across the atlantic to let John disassemble and
> clean it -
> and briefly recalling something John wrote about his reluctance to
> disassemble this
> particular lens - the corner of my eye catches the smoke erupting from
> within my hands.
>
> WTF!? The rear lens cap was being set on fire! I quickly twist the
> rapidly melting
> rear cap off the lens and threw it to the ground. In literally 20
> seconds or so, this
> lens focused the sun's rays to such intensity to melt through a
> plastic rear cap.
>
> For some reason, I immediately thought of the ramblings of Michio
> Akiyama
> on his Red Book Nikkor Aid website, where he drools over his
> collection of
> Ultra-Micro Nikkor lenses. I quote:
>
>> "To put this lens, I obtained an old cloth. The pattern of old Japan
>> is woven to this cloth.
>> This cloth is a cultural asset preserved in the Shosoin.
>> No one can buy the real thing in an old age.
>> Because, the cloth was made in Japan of 1300 years ago. Then, I
>> bought the cloth of the replica made for the tea ceremony in Japan.
>> I put the graceful lens on the cloth of Shosoin.
>> The Far Eastern light was seen."
>
> I believe that, had one of Akiyama-san's precious Nikkor's spontaneously
> combusted in his hands like my Zuiko 250/2.0 did today, he would have
> had a
> real religious experience worth writing about.
>
>
> Addendum:
> My lens is fine - only the rear cap suffered. There was a bit of
> residue on the
> rearmost lens element, but because this was, in fact, the drop-in UV
> filter in the
> rear, it was easily removed and cleaned.
>
> This has me thinking though - if people burn holes in their Leica
> cloth shutters so
> easily with their teeny weeny ~39mm-diameter lenses, how quickly could
> one do it with
> this monster? Thank goodness there is a mirror in the optical pathway
> in an OM body,
> because what sort of damage could this inflict? Not that one would
> ever - I hope - have
> to point this lens into the sun like I have during actual photography,
> but it dawned upon
> me in a very real way how much light energy some lenses focus onto a
> single point.
>
> I wonder how long it would take to melt all the plastics (admittedly,
> there are very few)
> in an OM body if I were to set it up with this lens pointing into the
> sun?
>
> No, I wouldn't really do it (too afraid I could damage the lens) but
> it's an interesting
> though experiment.
>
> 20 seconds. That's all it took to make a rear lens cap smoke.
> Sheesh.
--
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