Photographing the
Transit of Venus
On
13/5/2004, Peter Adderley posted:
I'm interested in taking pics of the transit of Venus. I believe this
will happen for us Sydney people, from 3pm onwards on the 8th June -
World Oceans Day.
I have a very simple digiscoping setup, and I wonder if it would be
safer or advantageous to put the sun filter in front of the main
telescope lens, or between the scope eyepiece and the camera lens.
Concerns are as such:
1. Could the filter, being between the scope eyepiece and the camera,
present a heat damage problem?
2. Supposing the filter(s) I use are 3mm tinted perspex. Which location
will present least distortion?
3. Will the same density work for both locations? My intuiton tells me
it will.
4. What is the best material to use? I'm looking at perspex as it's
easily available and cheap, but I may need to use more than one layer
(assuming 3mm and available densities not known as yet).
My setup is fairly primitive:
http://www.acay.com.au/~adderley/mars/telescopy
As you can see there is no physical connection between the scope and
the camera.
Ian
Musgrave replied:
3:07:10 pm to be exact (for Sydney
that is). My transit of Venus page should go up this weekend.
>I have a
very simple digiscoping setup, and I wonder if it would be safer or
>advantageous to put the sun filter in front of the main telescope
lens, or
>between the scope eyepiece and the camera lens.
FRONT of the main telescope lens,
FRONT (too much heat gets focused on the filter when it is between the
eyepiece and the lens with catastrophic results)
>Concerns are
as such:
>1. Could the filter, being between the scope eyepiece and the
camera,
>present a heat damage problem?
YES
>2. Supposing
the filter(s) I use are 3mm tinted perspex. Which location will
>present least distortion?
DON'T, use only aluminum plated
Mylar or a similar specific solar filter material (available through
all good telescope shops), everything else will let too much light (and
heat) through.
>3. Will the
same density work for both locations? My intuiton tells me it
>will.
Do NOT put filters between the
eyepiece and lens
>4. What is
the best material to use? I'm looking at perspex as it's easily
>available and cheap, but I may need to use more than one layer
(assuming 3mm
>and available densities not known as yet).
DON'T use perspex, use solar
filter rated materials only. Aluminium coated Mylar is fairly cheap.
Otherwise use solar projection and
video the projected image.
Daya Papalkar queried:
Maybe a series of really basic & silly questions:
Why can't the telescopic lens be fitted directly into the camera? Or an
adaptor used?
Wouldn't you lose a lot of the image quality by putting the camera lens
up against the eyepiece of the telescope?
Is it a matter of cost ie a telescopic camera lens is much more
expensive?
Are there any good basic astronomy websites that describe photography
as well?
Ian
Musgrave replied:
>Why can't
the telescopic lens be fitted directly into the camera? Or an
>adaptor used?
No, the focal lengths are
incompatible. For my astrophotography, I use a Pentax SLR or a webcam.
In these cases the cameras lens's are removed entirely, and the camera
body fitted to the telescope with a special
adaptor. This is not applicable to
Peters video camera as you can't disassemble the front lenses (at least
and the be able to use it as a normal video camera later) .
>Wouldn't you
lose a lot of the image quality by putting the camera lens up
>against the eyepiece of the telescope?
Some, but for the sort of imaging
Peter is doing, the loss of quality is minimal.
>Is it a
matter of cost ie a telescopic camera lens is much more expensive?
Partly, they are very expensive
and they are just not available for Peter's camera. Also, you need to
mount the system on a mount that can easily track the object in
question, at high magnification, the rotation of the earth
becomes significant, and you constantly have to adjust the mounting to
keep the object in view. Telescope mounts are designed for this, camera
mounts aren't
>Are there
any good basic astronomy websites that describe photography as
>well?
Yes, you will find some in the
meteor and links section of my website.
http://home.mia.net/~reynella/skywatch/ssky.htm
and:
At 09:51
17/05/04 -0700, Peter wrote:
>Ian,
>A retired survey recommended using a welding mask filter.
>Any coments on this?
Number 14 welders filters are
acceptable. I'm not sure if you can get one big enough to put over the
front of your telescope. NEVER put it between the telescope lens and
the video camera, even welders glass will crack.
Stephen Berry added:
You might be able to get a larger size from a welding supply
specialist such as CIG,WIA ,Liquid Arc or Lincoln Welders.I have seen
some in use on automatic welders where the operator can not wear
a normal helmet. These were about 150mm x 150mm.
Peter
Adderley replied to Daya:
> Why can't
the telescopic lens be fitted directly into the camera? Or an
> adaptor used?
I'd be surprised if an adaptor
exists as the lens is very wide.
> Wouldn't
you lose a lot of the image quality by putting the camera lens up
> against the eyepiece of the telescope?
Yes, the field of view is a circle.
> Is it a
matter of cost ie a telescopic camera lens is much more expensive?
I wouldn't have done it this way
if I'd bought the scope myself, as I acquired it from my father many
years ago.
> Are there
any good basic astronomy websites that describe photography as
> well?
Ian will have more on that, but if
it's methods of connecting a telescope to a camera, do a search on
"digiscoping".
BTW, every man and his dog claims
to have invented digiscoping, including myself ;-)
Here's a list of digiscoping
egroups:
http://www.md.ucl.ac.be/peca/test/Egroups.html
Robin commented:
Welding filters and tech specs
http://www.aussieweld.com/product_pages/xelux/active_welding_filters.htm
http://users.hunterlink.net.au/~deamt/welding.html
Email
karen.fox@nohsc.gov.au
at the General Standards Team, NOHSC and ask for the Australian
Standard for welding filters.
Good luck with the construction.
Daya
Papalkar added:
Sorry to go off on a tangent...
We had a really beautiful moonset
here in Sydney & with the naked eye you could make out reasonable
detail. However, trying to photograph this & capture the same
detail (for me at least) was impossible. Either underexposed, or
slightly overexposed - and the moon looked like a white half-blob in
the sky.
I was using a digital SLR (Canon
300D) with the kit lens (18-55mm, which is supposed to be equivalent to
28-80mm). I tried shutter speeds from 1/30 to 20 sec, and aperture from
f5.6 (max) to about f11. All no good compared to the naked eye.
Any tips?
Peter Adderley wrote:
To photograph the transit of Venus through a small field telescope I
bought a number 13 welding lens filter.
This is as as high (or dark) as they go. However the filter is 50mm
wide and 105mm long, whereas the main lens of the scope is 60mm
diameter, leaving a gap on either side.
When the sun finally made an appearance this morning I tried the setup.
It seemed to work just fine except for one thing. I had a slight
image distortion in the form of astigmatism. I thought this may be due
to the gaps, so I cut a cardboard ring to correct for it. This had the
effect of cutting down the field of view too much, but I still
experienced the aberration to the same degree. I proved it was coming
from the filter because rotating it also rotated the axis of the
astigmatism. I can only think that the material used in the glass
compound to make the
filter is the cause, so I now wonder if it's worth buying a larger
filter. (oils ain't oils?)
Also thinking of cheating, by bribing or name-dropping my way into the
CSIRO labs at West Lindfield in Sydney. They have a great sun
telescope. oops
Thanks also to Stephen Berry who's been trying to dig up standards. He,
as I too, has found there's not a great deal of kinship between the
sciences of welding and astronomy.
Although I could also solve the problem by ordering a proper astro solar
filter from the web, I find gerry-built solutions far more challenging
and
personally satisfying. Even if I could afford all the good gear I
reckon I
probably wouldn't bother with the transit event.
Goodness, some people used to sail the oceans of the world to witness
such
an event, making all kinds of interesting discoveries along the way ;-).
Ian
Musgrave replied to Daya:
>I was using
a digital SLR (Canon 300D) with the kit lens (18-55mm, which is
>supposed to be equivalent to 28-80mm). I tried shutter speeds from
1/30 to
>20 sec, and aperture from f5.6 (max) to about f11. All no good
compared to
>the naked eye.
What is your effective ASA? For
film cameras, and are you using the camera on a tripod or fixed surface
with cable release or remote?
With exposure longer than 1/125 of
a second for astronomical objects, some solid mounting is important,
you can't do hand held. Cable release is also fairly helpful.
With my pentax KM using F2.8 and
ASA 400 film, I found the best results in the range of 1/15 to 1/4 of a
second, depending on the phase of the moon, crescent phases needed
longer exposure than full phases.
Try exploring the range between
1/8 to 1/15 over the next few days, using your fmax and a solidly
supported camera.
Cheers! Ian (also, see some of the
links in my web site for astrophotography)
and to Peter:
> I
proved it was coming from
>the filter because rotating it also rotated the axis of the
astigmatism.
>I can only think that the material used in the glass compound to
make the
>filter is the cause, so I now wonder if it's worth buying a larger
filter.
>(oils ain't oils?)
Possibly, welding filters aren't
made to astronomical smoothness, so molding or cutting the glass slabs
welding glass is made from may produce asymmetry, a larger slab may get
the distorted sections away from the lens (unless the distortion is
through the entire slab, can you check this).
>Also
thinking of cheating, by bribing or name-dropping my way into the CSIRO
>labs at West Lindfield in Sydney. They have a great sun telescope.
oops
I LIKE that idea.
>Thanks also
to Stephen Berry who's been trying to dig up standards. He, as I
>too, has found there's not a great deal of kinship between the
sciences of
>welding and astronomy.
No, really?
>Although I
could also solve the problem by ordering a proper astro solar
>filter from the web, I find gerry-built solutions far more
challenging and
>personally satisfying.
The video system is the key bit
that you have made, why muck it up for the sake of a proper filter?
>Even if I
could afford all the good gear I reckon I
>probably wouldn't bother with the transit event.
>Goodness, some people used to sail the oceans of the world to
witness such
>an event, making all kinds of interesting discoveries along the way
;-).
I wouldn't mind being in the South
Pacific for this.
Daya Papalkar responded:
> What is your effective ASA? For
film cameras, and are you using the camera
> on a tripod or fixed surface with cable release or remote?
My ISO was 100. I was using a fixed surface but not the cable release
(don't have my tripod at the moment & have to hold on to the camera
- don't want it to fall off!). I imagine the results will be better
when I get my tripod
back. However, I can tell from building lights etc whether or not the
camera was stable during the shot.
Last night I tried again and got much better results by using a small
aperture (f36 with an exposure of around 2.5s). The whole shot is very
underexposed (including building lights), but at least you can see some
detail in the moon eg the terminator & the sea of tranquillity (is
this the correct name??). I didn't realise that the moon was so much
brighter than the city lights. An exposure time of 10s at f36 exposes
the moon adequately, but there is a loss of detail. This may be due to
the stability of the camera.
> With my pentax KM using F2.8 and
ASA 400 film, I found the best results in
> the range of 1/15 to 1/4 of a second, depending on the phase of
the moon,
> crescent phases needed longer exposure than full phases.
>
> Try exploring the range between 1/8 to 1/15 over the next few
days, using
> your fmax and a solidly supported camera.
When I try with the largest aperture, the moon gets totally washed out
with light & I lose detail (this is not due to image stability). I
discovered how to change the ISO settings after moonset & there is
an ISO 1600 setting, so
I will experiment with that too (& I will have my tripod back!!!).
Another problem is the small image, but I can't really fix that without
getting a telephoto lens.
Gerald
Cairns responded:
I don't get time to indulge in
this thread but thought the following info may be of interest.
I received an update from a
company which claims to have a 21 mpixel video camera for microscopy
and that the software permits variable depth of focusing so that
brilliant 3d images are achieved. I have yet to find out
if the 21 mpixel chips are real or
simply software enhancements but if it is real I wonder why still
cameras have not got them first? I want one for my microscope but
what's the price........
I reckon this might provide
everyone with a new dimension in photography. I will try to get the
details and pass them on.
Ian Musgrave answered:
>Last night I tried again and got
much better results by using a small
>aperture (f36 with an exposure of around 2.5s). The whole shot is
very
>underexposed (including building lights), but at least you can see
some
>detail in the moon eg the terminator & the sea of tranquillity
(is this the
>correct name??).
Getting the Moon AND the buildings right is very tricky, film
photographers often do this by exposing the moon adequately, and when
developing, develop for the right time for the moon, then mask the moon
and develop the lights.
>I didn't realise that the moon was
so much brighter than
>the city lights. An exposure time of 10s at f36 exposes the moon
adequately,
>but there is a loss of detail. This may be due to the stability of
the
>camera.
At exposures of 10s and greater, the rotation of the earth becomes an
issue (yes, really), and you might get slight trailing of the lunar
image.
> > With my pentax KM using F2.8
and ASA 400 film, I found the best results in
> > the range of 1/15 to 1/4 of a second, depending on the phase
of the moon,
> > crescent phases needed longer exposure than full phases.
> >
> > Try exploring the range between 1/8 to 1/15 over the next few
days, using
> > your fmax and a solidly supported camera.
>
>When I try with the largest aperture, the moon gets totally washed
out with
>light & I lose detail (this is not due to image stability). I
discovered how
>to change the ISO settings after moonset & there is an ISO 1600
setting, so
>I will experiment with that too (& I will have my tripod
back!!!).
Let me know how it goes, I am eyeing off digital SLR's with envy.
>Another problem is the small image,
but I can't really fix that without
>getting a telephoto lens.
:-)
Daya
Papalkar wrote:
> Getting the
Moon AND the buildings right is very tricky, film photographers
> often do this by exposing the moon adequately, and when
developing, develop
> for the right time for the moon, then mask the moon and develop
the lights.
I
was thinking that there must be a way to replicate darkroom exposure
techniques using digital images (like in Photoshop - but I would know
about 1% of its functions). I did photography in Yr 11 at school -
great fun & I really liked the ability to manipulate the image in
the dark room.
> At exposures of 10s and greater,
the rotation of the earth becomes an
> issue
> (yes, really), and you might get slight trailing of the lunar
image.
I was wondering about this. The
moon seems to set a lot quicker if you are trying to photograph it! :)
> Let me know
how it goes, I am eyeing off digital SLR's with envy.
I used to have a Pentax film SLR
& used to love it. I gave it to my uncle along with a telephoto
lens (don't ask). So, I was without a decent camera for about 8 years
(until I got this).
I love this camera. With a 1G
card, I can take about 300 photos at hi-res - which is basically
unlimited because it's not too difficult to download them to computer.
You can view the images straight away from the LCD (including an
impressive zoom function) & delete if you like. It means that you
can make adjustments as you go and perfect the image. It even records
all the camera settings in the file, so you can see how you took the
photo. The camera gives you an exposure graph for the photo too.
I got my tripod back yesterday and
took some group family photos. With a remote, I just took a whole
series of photos. I would never do that with a film camera - because
you have to pay for processing every single photo.
This way, I can just pick out the
one photo where (almost) everyone is actually smiling for the photo!
> >Another
problem is the small image, but I can't really fix that without
> >getting a telephoto lens.
>
> :-)
Cost factor :-(
Constellations
for Small Kids
On 29/5/2004, Kirsten wrote:
Can anyone point me at a website to show kids the easiest
constellations to look for in the Australian sky?
Tony
Hyland replied:
A good page to start with is:
http://www.heavens-above.com
You can enter your city name, and
it will show the sky for your latitude/longitude, correct for the
current time, with constellations clearly marked.
You can also see lots of other
things, like the track of the International Space Station, and other
satellites that are visible from time to time.
Ian Musgrave responded:
[SFX: polite cough]
Ah, what about
http://home.mira.net/~reynella/skywatch/ssky.htm
And the maps, descriptions and links (specifically to kids sites in the
links section) therein
Cheers! Ian (who is trying to finish the June page now)
