Re: LED illuminator

On Jun 26, 12:17 am, "helio" <forbid...@xxxxxxxxx> wrote:
"Peter" <peterplan...@xxxxxxxxxxxxxx> wrote in message

news:65deb1dc-0e84-4062-b12f-f7b4ab6aef7b@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

There is no point in getting all excited about cooling. The
newer LEDs work at a quantum efficiency of around 30% meaning that a
10W LED generates perhaps 6W of heat. That's nowhere near comparable
to the heat output of a multi-core overclocked CPU being thrashed by
some gaming freak. 6W is about what a mini-maglite flashlight bulb
generates.

It seems to me we were talking about my 20 W LED. I get not excited about
overdimensioning coolers, but as I project to try LEDs of increasing power
starting from the one I own, this I showed you seemed suitable to my needs.

Doesn't a diffuser introduce a lack of contrast? And isn't contrast
influencing the resolution?
There is no reason why a primary incoherent source should not be
replaced by a secondary incoherent source.

So, why to distinguish between primary and  secondary incoherent sources?

 >No difference isdiscernable  in the image. So contrast is unaffected; and
resolution
 >has nothing at all to do with contrast; it is purely a function of NA;
 >visibilty is something else and that's why we have DIC, oblique etc.

I repeat: my optical education is near to zero, so I fear that my intuitive
objections to your resolution-only-determined-by-NA criterion can be
promoting laughs. But I read on the Molecular Expressions website
(http://micro.magnet.fsu.edu/index.html) that 'any resolution criterion is
not an absolute indicator of resolution, but rather an arbitrary criterion
that is useful for comparing different imaging conditions. As an example,
'resolution in optical microscopy is often assessed by means of an optical
unit termed the Rayleigh criterion', but 'the Rayleigh criterion applies
specifically to the case in which two self-luminous objects must be
distinguished. In other contexts, such as differential interference contrast
(DIC), brightfield, or darkfield microscopy, other criteria will apply.' So,
it appears that the power to distinguish between two points depends on
infinite factors. In the Kohler illumination, 'the aperture diaphragm should
be adjusted to provide sufficient image contrast without being closed to the
point of introducing a loss of resolution and detail'. Now, if a simple
change in the aperture diaphragm can modify resolution, how can you say than
the insertion of a ground glass into the optical path does not modify it? I
read that in the Koheler settings 'If the ground glass diffuser screen has
not been (or can't be) removed, an evenly illuminated light disk should
appear in place of the filament coils', so rendering the Kohler adjustments
unfeasible. Now, if the removal of the ground glass is needed for correct
Kohler regulations, how can the insertion of a ground glass be ininfluent in
high power (to say, 100 x 10) observations? Finally, apart from this, my
eyes KNOW that when I lower the ground glass they see worse.

A 4 Ampere pulse is not bad for a phone battery.
The 4A is not from the phone battery, but from capacitors.

It seems every thing I saw in the thread was wrong; I hope to do better in
the
next reincarnation. It is obvious that the dual-cell capacitor has the merit
to surge the charge, but I was talking about a 4 Ampere pulse squeezed from
a two stylos battery. You can get too 1000V from some CMOS working at 5V and
few diodes and capacitors. In these cases, ordinarily, one focuses his
attention on the result, not on the trick. Have you ever heard: 'Wow, an
array of 100 x 1W LEDs?'. People say: 'Wow, a 100W LED'. And: 'Wow, a
voltage multiplier obtained with inverters and a handful of diodes and
capacitors' ? I suppose people say: 'Wow, 1000V from a 5V circuit'. So I
was pointing at the result, as ordinary people do.

I'm studying an easy-to-build flash strobe for LEDs.
Nothing wrong with strobing an LED for a
photomicrograph but it does seem a pointless exercise.

My idea to start the project was born when you said: 'But, how on earth to
make a control circuit? It would need to be a PWM controller with the
facility to produce a single full-intensity flash with a variable duration
of, perhaps, 100 microscecond to 10ms.' Now, I'm interested in this too, and
the flash strobe I'll like to build has a programmable duty-cycle so one can
obtain every type of squared wave, including single pulses. And, as you find
this a pointless exercise, I'll proceed alone on this route.

Best regards

Well, good luck! And above all, enjoy your microscopy!

Peter
.

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