THE PRACTICAL MANIPULATION OF A LANTERN
Having now described the optical lantern in its various forms and the more
important accessories, we come to the question of practical manipulation.
In making arrangements for an exhibition the first thing to be seen to is
to ensure that every accessory that will be required will be there, and the
best plan is to make a complete list of all sundries to be provided. Such
items as string (for the sheet), lime tongs if limelight is used, pliers
for changing carbons if the arc is to be the illuminant, screw-driver,
matches, the _key of the lantern box_, and other similar items, are likely
to be left behind unless such a list is made and carefully checked. On
arriving at the hall, the first thing to be done as a rule is to get up the
sheet, after which the professional operator generally begins to feel happy
again.
The next thing, if it has not been done first, is to determine the position
of the lantern, and this, as has been explained in Chapter VII, is a matter
of the size of picture to be shown and the focus of the objective.
It is a mistake to show too large a picture; a little 'white' round the
edges is a good thing, and it is better to have a small disc well
illuminated than a large one less bright. Convenience, however, must also
be considered, and it is often justifiable to go back a few feet farther
than other considerations would dictate in order to place the lantern in a
gallery or other spot where it is out of the way.
Having fixed the position of the lantern, it should be got into place, the
cable or tubing connected or whatever else is necessary, according to the
illuminant to be used. It should then be lit up, the flasher of the lens
opened, and the light {83} centred sufficiently to produce some sort of
disc upon the screen. (It is, of course, presumed that the lenses, &c.,
have previously been cleaned.)
A carrier should now be placed in the stage and a slide inserted into it,
and the method of doing so requires a little explanation. The slide must be
placed in the carrier upside down, as will be obvious to anyone who has
studied Chapter VII, but in addition to this it must be turned the correct
way, otherwise the picture will be reversed from left to right. This in the
case of certain subjects, such as a copy of a picture, may not greatly
matter; but in slides depicting buildings or landscapes with which the
audience may be familiar, or worse still, printing or writing, is a serious
blunder.
Slides made by a commercial firm will usually be 'spotted,' that is to say,
will have two white spots on the face of the slide when the latter is
viewed in its correct position, and at the top. The slides should be turned
upside down and placed in the carrier with the spots, of course, now at the
bottom and _towards the condenser_.
If a slide is not spotted it should be viewed as it is to appear on the
screen, and then placed in the carrier with the face that was towards the
operator as he viewed it turned to the condenser, and of course inverted.
The above remarks apply only in cases where the image is thrown _on_ the
screen; in the comparatively rare instances where it is shown _through_ the
latter the slides must be turned round laterally, but of course still
inverted. The slide having been placed in the stage it should be 'focussed'
by racking the objective in or out, and if necessary pulling out the draw
tube as well until the image on the screen is sharply defined. So far the
light has only been roughly centred, sufficiently so to enable the slide to
be focussed, and to complete the operation both slide and carrier should
next be taken out of the lantern, leaving a clear disc on the screen, and
this disc may resemble any of the appearances shown in Fig. 50. {84}
If it resembles A the light must be moved to the left, if like B to the
right, like C it must be lowered, like D it must be raised, always moving
it to the side opposite to the dark shade until this is central on the
disc. If it now resembles E, the light must be moved nearer the condenser;
if, on the contrary, the centre is dark, it must be drawn back until
finally the circle should be as nearly as possible clear and bright all
over, as at F.
[Illustration: FIG. 50.--Adjustment of the Light.]
It is important to note that this adjustment _cannot_ be properly made
while a slide is in position, and neither can it be made until the lantern
has been focussed, so the above procedure is the only way to get a
satisfactory result. With some of the larger illuminants, such as a
paraffin-oil lamp, there are no centering adjustments, the size of the
radiant rendering exact centering unnecessary, and generally speaking the
smaller the luminous point, the more exact must the operation be.
In the case of such illuminants as acetylene or limelight {85} care must be
taken that they are turned fully on before centering, otherwise turning on
the fuller amount afterwards will raise the position of the luminous spot.
The centering achieved, the slide carrier may be replaced, the first slides
placed in position, the remainder arranged in their proper order, the
system of signalling with the lecturer determined, and all is ready.
If there is still an interval before commencing, the light may be switched
off or turned out, or in the case say of limelight, turned down very low
until wanted.
It is of extreme importance to see that all the slides are in their right
order, though the duty of seeing to this usually rests with the lecturer
rather than with the operator. I remember hearing of one lecture on the
life of Queen Victoria, when the lecturer announced, 'The next picture will
be a photograph of the Royal Prince who for many years shared the Throne
with our gracious Sovereign.' At the words the operator brought on the next
slide, which proved to be _a restored specimen of a prehistoric monster_
(tableaux!). Such mistakes 'bring down the house,' but in serious lectures,
and especially at religious services, cannot be too carefully guarded
against.
Mention has already been made of the liability of moisture to condense on
the surfaces of the condensers or slides, and to avoid this, so far as the
condensers are concerned, it is well to light up say ten minutes before the
lantern is actually wanted, or alternatively to take out the condensers and
thoroughly warm them in front of a stove, or to place them wrapped in a
cloth on hot-water pipes. The slides should in the same manner be warmed
before using and should be finally held above the lantern or placed on the
top, if this is flat, the last thing before being placed in the carrier. If
these precautions are omitted, on a cold night the first surface of the
condenser will become so covered with moisture as to almost obscure the
slide, and this will quickly disappear {86} with the heat of the lantern.
Next, the two inner surfaces of the condensers will behave in turn in the
same way, and will take considerably longer to clear, especially if the
ventilation of the condenser is poor; then the fourth surface will take up
the running, and finally, when the lanternist is congratulating himself
that the trouble is over, each successive slide will become affected in the
same way. With an operator who knows his business, none of these troubles
should occur.
ACCIDENTS.--These will occur sometimes, even in the best managed
exhibition; the rubber tubing feeding a limelight jet gets kinked or
trodden on, or a fuse melts if electric light is being used, &c., and out
goes the light. In such cases a loud request such as, 'Would you mind
turning up the light for a minute, please,' accompanied by a good-humoured
laugh, usually allays the fears of 'nervy' people. An operator must never
get 'nervy' himself. I have known of more than one fiasco because some
little hitch occurred, and two or three timid ladies crowded round and
asked anxious questions, till the lanternist lost his head. In one such
case the cautious superintendent at a children's entertainment decided that
it would be safer not to have the exhibition at all, simply because a
regulator was not screwed tightly enough into a cylinder to prevent an
escape of gas, only the operator (a somewhat youthful one) had been driven
to the verge of lunacy by continual questions of the standard type, 'Are
you sure it is safe?' 'Will it blow up?' 'Are you certain you understand
it?' &c., &c. More serious accidents, such as the entire lantern getting
upset, ought never to occur, and it is up to the lanternist to take
whatever precautions he deems necessary to safeguard his instrument. With a
juvenile audience, for example, it is often a good thing to arrange a
barricade of forms round the lantern and to see that no one comes within
it.
Finally, 'whatever is worth doing at all is worth doing well,' and this is
as true of lantern exhibiting as of anything {87} else. There are a
deplorable number of lantern exhibitions given with the sheet hanging in
creases, dirty lenses, light poorly adjusted and centred, and occasionally
slides shown upside down. A conscientious lanternist should see to _every_
detail; slipshod methods, as in everything else, mean poor results.
Printed by SPOTTISWOODE, BALLANTYNE & CO. LTD.
Colchester, London & Eton, England