ASTROPHOTOGRAPHY
EQUIPMENT
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1. Camera, Lenses & Tripod
My
main film SLR camera is a Pentax ME Super. It's a very under rated
camera for astrophotography. There are a wide range of quality second
hand Pentax lenses available in the PK bayonet and M42 screw mount.
Some of the older Takumar lenses are very sharp and can be obtained
second hand for modest prices. Two of my favourites are an SMC Takumar
300mm f4 and SMC Takumar 85mm f1.9.
The tripod shown opposite is a Manfrotto
075 which is excellent for astrophotography.
After weighing up the pros and cons
of the various DSLRs I decided to stay with Pentax and buy a K10D.
Link to more on
Pentax K10D.
Link to more on lenses.
2. Tracker Mk 1
I
originally wanted to make a 'Scotch Mount' tracker. However I was concerned
with the tracking errors from the tangent arm approach. At that time I was
not aware of the more highly developed Scotch Mount's, that give improved
correction, so I decided to try and make a worm gear arrangement. My aim was
to try and make a tracker from readily available parts. This drove me to try
out a car windscreen wiper worm gearbox. A very obliging car scrap yard owner
let me look at a whole range of wiper motors and I picked one that had minimum
backlash and adjustment screws for play. Surprisingly this was an AC Delco
unit from a Mini Metro! Once I had explained what I was trying to make, the
owner generously gave me two for £4.
Link to more information
on Tracker Mk1.
After
having reasonable success with my first star tracker, it wasn't long before
I had the urge to try and make a 'bigger and better' one. This got off to
a good start when I had the opportunity to buy a surplus two axis alignment
table for testing inertial quality gyroscopes. Each axis of the table had
large bronze worm gears with 180 teeth, which were driven directly by 1.8
degree stepper motors. I stripped down the table and kept the gears and one
of the end castings. The parts lay unused for many months, until I bought
a Pentax SMC 500mm f4.5 lens. This lens weighes 3.4kg which was far too heavy
for my original tracker, so the 'Mk2 ' project began!
Link to more information on Tracker
Mk2.
4. Binoculars
Binoculars
are necessary if you are going to try and take photos of very faint objects
and those that are invisble to the naked eye. Used in conjunction with a good
sky atlas, they enable you to star hop accurately to locate the areas of interest.
This can be important if you want to centre largish nebula or find faint comet's
with a 300mm lens.
Most astronomy literature will recommend 7x50 binoculars
for observing. These give good light gathering capacity, with a 50mm diameter
objective lens. The magnification is x7, which can be held reasonably steady
by hand. The light gathering capability of the binoculars is related primarily
to the area of the objective lens, so increases with the square of the diameter.
The cone of light that enters the eye, through the binocular's exit pupil,
is equal to the objective diameter divided by the magnification. For 7x50's
this gives 7mm. The pupil in the human eye opens to approximately 7mm in 
dark
conditions, so these binoculars match the capability of the human eye. As
you reach middle age the maximum pupil diameter that is achievable reduces,
so much so that it will not open to 7mm. Thus the full light gathering capability
of certain binoculars cannot be realised. All is not lost though, as the central
part of the cone of light will have lower levels of optical aberations, much
in the same way as a lens will provide a sharper image in the centre as opposed
to the outer edges.
For astrophotography it is not necessary to have the ultimate
binoculars. Most binoculars, from reputable manufacturers will provide stunning
views of the night sky, especially star fields. Below is a comparison of three
common binocular sizes; 8x30, 7x50 & 9x63. Each of these has its own merits
and all perform perfectly well.
|
Front to back ;
Carl Zeiss Jena 8x30
Carl Zeiss Jena 7x50
Charles Frank 9x63
|
Objective Lenses |
Exit Pupils
|
5. Right Angle Finders
A
right angle view finder, or ref converter, is a must if you want to take overhead
pictures. They can be expensive, especially the ones that give a 'correct'
image. Many give a left to right image reversal, this is the case for the
two I have. They are a Pentax Refconverter and an Olympus Varimagni Finder,
left and right respectively in the images below. The ME Super should use a
Refconverter M type or type II, however these are quite rare and expensive,
so I have modified a finder for the Spotmatic range of cameras, by making
a new mounting plate. I find the Pentax finder is better than the Olympus,
eventhough it is sells secondhand for a quarter of the price. The right hand
image below shows the superior exit pupil on the Pentax (X1) compared to the
Olympus on X1.2.
6. Miscellaneous
One item that is very useful is a light pen, for obvious
reasons. Another is an 'illuminator' watch. This Casio watch is excellent
for astrophotographer's. It has a countdown timer which gives audible beeps
as it passes set times on the countdown; at 10, 5, 4, 3, 2 and 1 minute marks
and on the 50, 40, 30, 20, 10, 5, 4, 3, 2 and 1 second marks. This gives you
the reassurance that the timer is actually running and plenty notice to prepare
to end the exposure.
Top
My
main film SLR camera is a Pentax ME Super. It's a very under rated
camera for astrophotography. There are a wide range of quality second
hand Pentax lenses available in the PK bayonet and M42 screw mount.
Some of the older Takumar lenses are very sharp and can be obtained
second hand for modest prices. Two of my favourites are an SMC Takumar
300mm f4 and SMC Takumar 85mm f1.9.
