In answer to the following letter by Mr C.D. Wood:
>
> In the last mail Johannes Helm said:
 
etc. etc.
 
>
> I read this with interest because we've had a lamp installed onto our
> Zeiss Axiovert135TV recently, by the Zeiss trained installer, who
> specifically pointed out me that there was absolutely no reason for
> the two images not to be aligned.  He said that this was the "newest
> research" and that all the talk of it blowing up lamps was nonsense.
>
> I'm not saying anyone is right or wrong here, I'm just a little bit worried
> about the lamp on our 'scope being wrongly fitted.  Is this guy from Zeiss
> wide of the mark?  Should I go a realign the two images right away?  Or do
> I trust that he knows what he's talking about, it being his job and all that?
>
> Any advice (in any tone of voice :-> ) gratefully received.
>
> Thanks
>
> Chris Wood
 
 
Dear Chris Wood and all the other interested readers,
 
unfortunately, it was about 3 o'clock in the afternoon when I send this
letter, so I was in my afternoon-being-tired hour and sent the letter to the
public (instead of to Dr. Levy as private response).
Now it is done and I cannot change it any longer; usually I prefer to
not write to the net.
 
The information about the possible reason for the bulb explosions which I
had written is essentially what I had learnt several years ago from a
Zeiss engineer in southern Germany. This information (as far as the alignment
procedure is concerned) also can be found in the manuals, e.g. by Zeiss, on these
Xe- or Hg-lamps.
Also, when recently talking about halogen lamps as installed in microscopes
(12V, 100W), I was discussing a similar point with a friend of mine in southern
Germany who is employed as an optical engineer in a factory distributing and
producing all kinds of lamps in which they use, e.g., these 12V/100W bulbs.
In newer arrangements, spherical mirrors often are used to help to heat up the
wire in the 12V/100W lamp (in order to save energy).
 
Now, there is no wire in an arc-lamp, but, unless the retroreflective spherical
mirror would be wavelength selective and NOT reflect heat (and as far as I know
these mirrors are not suppressing IR reflection), the energy which would
simply escape backwards without the mirror is reflected by the mirror and
refocussed directly into the arc where the energy is partly absorbed if the
retroreflective mirror is aligned in this way. It sounds
reasonable, that this could lead to a temperature in the arc region which
exceeds the temperature which would be there without any mirror.
I do not know, whether ALL the power supplies for arc lamps compensate for this
effect. At least in those power supplies which are made as highly stabilized
DC sources for quantitative fluroescence microscopic measurements, i.e. mainly
the 100W Hg and 75W Xe-lamps, such feedback controls regulating current so as
to stabilize light output should be present.
On the normal 50W Hg-lamps, which are AC driven, I suppose that such controls
are not present.
 
Paul Johannes Helm
 
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Paul Johannes Helm
 
Mailadress:     Department Physics 4
                The Royal Insitute of Technology
                S-100 44 Stockholm
                Sweden
 
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                The Royal Institute of Technology
                Teknikringen 14/4tr.
                S-100 44 Stockholm
                Sweden
 
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