Does anyone produce a reasonably-priced mounting, with the ability
both to pan to desired altitude and azimuth, and to track the motion
of the stars accurately enough to keep star images as points at say
200mm focal length, on which you could mount a normal camera (say 3kg
if I'm using a heavy lens) by the standard tripod screw fitting?

I've got some lovely, though comatic at the corners, images with an
old Nikon 50mm/1.4 lens wide-open on a static tripod, see
http://www.chiark.greenend.org.uk/~twomack/orion-starry.png for an
example; on the other hand, with any longer lens the stars trail very
quickly, and with the very fast lens a thirty-second exposure is
saturated by the sky brightness around here. Darker skies are always
a possibility, but I live in the middle of Cambridge and can't drive,
so tracking, and going for longer focal length and smaller aperture to
dim the sky while keeping the stars, starts feeling like a better
option. There's an obvious contradiction in wanting a dark-sky site
reachable by public transport, and public transport networks tend not
to be running well at midnight.

Are there any lenses to be particularly recommended or particularly
avoided for this sort of work? I have an old Hoya 135/2.8 which works
quite nicely, and a 170-500 Sigma birding lens which takes reasonable
pictures of the Moon if only I can get it to focus accurately at
infinity, and looks as if with tracking it could get great photos of
the larger Messier open clusters. The daytime lens I use is Nikon's
18-200 VR, but that's f/5.6 for most of its range and gave pretty
disappointing results when I tried it out on stars. I've a friend
who's lucky enough to have a Noct-Nikkor, which is a coma-compensated
60mm f/1.2 and absolutely perfect for star images, but those appear
only once every couple of months on ebay, and go for thousands of
pounds.

The figure-of-merit is focal length / (f-number)^2, which means I'm
looking out for a reasonable-price second-hand photojournalist's
70-200 f/2.8 (as, given how fast and for how much they go, is every
other photographer on ebay); but I don't know how good those are at
getting pinpoint stars wide open. I've read at least one scathing
report about the performance on stars of the very long, very fast
lenses aimed at sports photographers, but those are wildly outside my
budget.

Tom

Does anyone produce a reasonably-priced mounting, with the ability
both to pan to desired altitude and azimuth, and to track the motion
of the stars accurately enough to keep star images as points at say
200mm focal length, on which you could mount a normal camera (say 3kg
if I'm using a heavy lens) by the standard tripod screw fitting?

On Jan 30, 3:04 pm, Thomas Womack <twom...@chiark.greenend.org.uk
wrote:
Does anyone produce a reasonably-priced mounting, with the ability
both to pan to desired altitude and azimuth, and to track the motion
of the stars accurately enough to keep star images as points at say
200mm focal length, on which you could mount a normal camera (say 3kg
if I'm using a heavy lens) by the standard tripod screw fitting?

Maybe the Takahashi Teegul SkyPatrol V2 would do what you want. It's
an equatorial mount which you really need to track stars for long
exposure photography because an alt/az one will give you field
rotation. It's about $760 or there abouts which might be more than you
want to pay.

Bill

Consider also a Vixen star-tracker or even a Vixen GP german equatorial

Does anyone produce a reasonably-priced mounting, with the ability
both to pan to desired altitude and azimuth, and to track the motion
of the stars accurately enough to keep star images as points at say
200mm focal length, on which you could mount a normal camera (say 3kg
if I'm using a heavy lens) by the standard tripod screw fitting?

I've got some lovely, though comatic at the corners, images with an
old Nikon 50mm/1.4 lens wide-open on a static tripod, seehttp://www.chiark.greenend.org.uk/~twomack/orion-starry.pngfor an
example; on the other hand, with any longer lens the stars trail very
quickly, and with the very fast lens a thirty-second exposure is
saturated by the sky brightness around here. Darker skies are always
a possibility, but I live in the middle of Cambridge and can't drive,
so tracking, and going for longer focal length and smaller aperture to
dim the sky while keeping the stars, starts feeling like a better
option. There's an obvious contradiction in wanting a dark-sky site
reachable by public transport, and public transport networks tend not
to be running well at midnight.

Are there any lenses to be particularly recommended or particularly
avoided for this sort of work? I have an old Hoya 135/2.8 which works
quite nicely, and a 170-500 Sigma birding lens which takes reasonable
pictures of the Moon if only I can get it to focus accurately at
infinity, and looks as if with tracking it could get great photos of
the larger Messier open clusters. The daytime lens I use is Nikon's
18-200 VR, but that's f/5.6 for most of its range and gave pretty
disappointing results when I tried it out on stars. I've a friend
who's lucky enough to have a Noct-Nikkor, which is a coma-compensated
60mm f/1.2 and absolutely perfect for star images, but those appear
only once every couple of months on ebay, and go for thousands of
pounds.

The figure-of-merit is focal length / (f-number)^2, which means I'm
looking out for a reasonable-price second-hand photojournalist's
70-200 f/2.8 (as, given how fast and for how much they go, is every
other photographer on ebay); but I don't know how good those are at
getting pinpoint stars wide open. I've read at least one scathing
report about the performance on stars of the very long, very fast
lenses aimed at sports photographers, but those are wildly outside my
budget.

Tom