| Long Exposure DSO Photo Techniques |
It's an Expensive Hobby
Don't waste your time on a CGE/G11 class mount, go right for the Paramount, your astro life
will be much more enjoyable. With this quality mount, anything less than a large RCOS or
Tak FRC would be a waste. You'll need an optical train rotator, an adaptive optics unit, and
an OAG, go with the Van Slyke rotator and OAG, the SBIG or Starlight adaptive units will
work. You'll want good cameras, choose the SBIG STL, FLI Proline, or Apogee Alta series,
say the 6 to 9 Mpix series with a sizeable frame external guide head, filter wheel, and LRGB
and narrowband set of Astrodon filters. A good roll-off roof observatory building (avoid the
air current prone domes) and you'll have the basics for serious astro photography. Your
bank account will also be seriously depleted, but then what was all that money just laying
around for anyway, you were not planning on a near term retirement, kids college
expenses, other household requirements.......were you? You were,...Oh well, maybe you'll
win the next lottery drawing.
The point of the preceding paragraph was to illustrate that astrophotography can be an
expensive hobby. Sure you can buy a small, inexpensive mount, telescope, and camera (I
have one of those setups). You'll get small, recognizable photos of the brighter objects. If
this is your goal, go for it. If you are interested in creating moderate quality web images, a
medium sized/priced setup (mount, telescope/s, camera, computer, software, etc) should
do the job (I have one of those too). If you are looking for high end, magazine quality
imaging, and you want to be able to make credible (wall hanging) prints, you, at least, need
a large frame (expensive) camera. A high end mount, and high quality optics make sense in
that case, and you will pay dearly for those items. Decide what you want to do with your
equipment, research the available components, think ahead, plan and budget for your
acquisitions. Don't waste money on unnecessary "widget" purchases, you'll end up with a
setup that satisfies your imaging goals without wasting so much money/time.
Enough of the soapbox (I also support my ham radio and photography addictions, so there
are never the resources or time to go around). On with the methods I used to catch
photons, and process images.
A Balanced System
The three main elements of the imaging system are the mount, scope, and camera. There
are ancillary components, like filters, focuser, rotator, OAG, and/or AO unit. Most, if not all,
experienced imagers will agree that the mount is the single most important component,
required to achieve technically sound photos. Therefore, the largest portion of your
system expense will, or should be, in this element. Opinions vary as to whether the scope
or camera comes next. I suggest that it is the camera, the scope being close behind.
The Mount
You may not need a high end mount (like the Bisque Paramount, AP1200, Tak EM500, Mathis
500, Parallax HD200), but if you want tight round stars, not ovals, in your photo, and you
plan on using a scope/camera load appreciably greater than 50lb, it will certainly help. Be
sure to account for everything sitting on the mount when calculating the load! If your total
load is in the range of 40-50lb, a mid sized mount (like the AP900, Tak EM400, MI250,
Losmandy Titan) should take care of your needs. A total load in the range of 30-35lb should
be adequately carried by a low end Losmandy G11, Celestron CGE, or Tak EM200. If you plan
on a light load (20-25lb), the Orion or SkyWatcher EQ6 mounts may suffice. A very light load
(<15lb), like a small, short imaging refractor with an OAG, or a very light, short guide scope,
and a light camera may require nothing other than a EQ5, but for reasons mentioned
elsewhere in this site (high tracking error, backlash, stiction, etc), I'd not recommend the
EQ5 for imaging with a typical scope. Patience and persistence can result in acceptable
results, using the EQ5, if you use a coarse enough image scale (short focal length imaging
lens/scope) but your hobby time will be much more enjoyably spent if you are using one of
the higher capacity mounts. In short, derate any mount manufacturer's load claims to 50-60%,
and you'll be much happier with the results you routinely achieve.
The mount manufacturers are trying to sell mounts. Many of them will post load claims,
much like the gas mileage claims posted by auto manufacturers (remember the saying
"your mileage may vary"). Under typical visual use, many of the lower end mounts will
(marginally) suffice to put the subject into a "low" power eyepiece, and keep it there.
Astrophotographic requirements (guiding ability) are much more stringent. Go with a good,
or at least sufficient mount, for enjoyable astrophotography.
The Camera
Most people will select a camera that offers the greatest number of pixels that they can
afford. This is fine if your budget is umpteen thousand. If you are looking for a more
affordable solution, take a look at the smaller frame cooled cameras like the Starlight
Xpress H9, using the sensitive, yet low noise Sony 285 CCD. It has such low dark noise, that
"darks" are not required, or even desireable for exposures under 10 or 12 minutes. This
can save you some hassle. If you just don't mind spending the time, the SBIG ST2000 offers
a similar sized, though noisier CCD, for a similar price. If you can spend a little more, the
Starlight H16, or QSI 540. Both of these use the noisier Kodak CCD, but with the integral
40-45 degree TEC, dark noise on individual exposure, less than a few minutes is low.
"Darks" are required beyond a few minutes, but that's the price you pay for the larger
frame. Most scopes are of a focal length that will result in good spatial sampling with a
pixel size of 6-9um. Take a look at the pixel size of the CCD you are considering, don't go
for one with tiny pixels (4-5um) unless you are using a very short focal length scope. They
have lower (effective) dynamic range when used in the (standard) unbinned mode. The
Sony CCDs are generally lower noise with moderate sensitivity. The Kodak are generally
noiser. Their KAI series (interline) have lower sensitivity. The KAF series (frame transfer)
have higher sensitivity.
If you are willing to keep individual exposures below 4-5 minutes at ISO 800, 6-8 minutes at
ISO400 (NOT the best approach for many low surface brightness subjects), the latest DSLRs
may offer a good alternative. They are, at least, the only low priced alternative for full
(35mm) frame cameras. The APS-C sized sensors (CMOS tend to have lowest noise) are
even more affordable, but in this frame size, the TE cooled Starlight M-25 (using a low
noise Sony CCD) probably offers a better value for general astro imaging. DSLRs are
improving with every new generation, and I suspect that the next generation, or that
immediately following, will provide about as much performance as most imagers will
require, AND they don't cost a small fortune. Just be sure to have the bandpass filter
replaced with clear optical quality glass, or a wider filter so that you have a reasonable
response at deep red (650nm), were so many of the nebulas emit light.
Don't waste your time on a CGE/G11 class mount, go right for the Paramount, your astro life
will be much more enjoyable. With this quality mount, anything less than a large RCOS or
Tak FRC would be a waste. You'll need an optical train rotator, an adaptive optics unit, and
an OAG, go with the Van Slyke rotator and OAG, the SBIG or Starlight adaptive units will
work. You'll want good cameras, choose the SBIG STL, FLI Proline, or Apogee Alta series,
say the 6 to 9 Mpix series with a sizeable frame external guide head, filter wheel, and LRGB
and narrowband set of Astrodon filters. A good roll-off roof observatory building (avoid the
air current prone domes) and you'll have the basics for serious astro photography. Your
bank account will also be seriously depleted, but then what was all that money just laying
around for anyway, you were not planning on a near term retirement, kids college
expenses, other household requirements.......were you? You were,...Oh well, maybe you'll
win the next lottery drawing.
The point of the preceding paragraph was to illustrate that astrophotography can be an
expensive hobby. Sure you can buy a small, inexpensive mount, telescope, and camera (I
have one of those setups). You'll get small, recognizable photos of the brighter objects. If
this is your goal, go for it. If you are interested in creating moderate quality web images, a
medium sized/priced setup (mount, telescope/s, camera, computer, software, etc) should
do the job (I have one of those too). If you are looking for high end, magazine quality
imaging, and you want to be able to make credible (wall hanging) prints, you, at least, need
a large frame (expensive) camera. A high end mount, and high quality optics make sense in
that case, and you will pay dearly for those items. Decide what you want to do with your
equipment, research the available components, think ahead, plan and budget for your
acquisitions. Don't waste money on unnecessary "widget" purchases, you'll end up with a
setup that satisfies your imaging goals without wasting so much money/time.
Enough of the soapbox (I also support my ham radio and photography addictions, so there
are never the resources or time to go around). On with the methods I used to catch
photons, and process images.
A Balanced System
The three main elements of the imaging system are the mount, scope, and camera. There
are ancillary components, like filters, focuser, rotator, OAG, and/or AO unit. Most, if not all,
experienced imagers will agree that the mount is the single most important component,
required to achieve technically sound photos. Therefore, the largest portion of your
system expense will, or should be, in this element. Opinions vary as to whether the scope
or camera comes next. I suggest that it is the camera, the scope being close behind.
The Mount
You may not need a high end mount (like the Bisque Paramount, AP1200, Tak EM500, Mathis
500, Parallax HD200), but if you want tight round stars, not ovals, in your photo, and you
plan on using a scope/camera load appreciably greater than 50lb, it will certainly help. Be
sure to account for everything sitting on the mount when calculating the load! If your total
load is in the range of 40-50lb, a mid sized mount (like the AP900, Tak EM400, MI250,
Losmandy Titan) should take care of your needs. A total load in the range of 30-35lb should
be adequately carried by a low end Losmandy G11, Celestron CGE, or Tak EM200. If you plan
on a light load (20-25lb), the Orion or SkyWatcher EQ6 mounts may suffice. A very light load
(<15lb), like a small, short imaging refractor with an OAG, or a very light, short guide scope,
and a light camera may require nothing other than a EQ5, but for reasons mentioned
elsewhere in this site (high tracking error, backlash, stiction, etc), I'd not recommend the
EQ5 for imaging with a typical scope. Patience and persistence can result in acceptable
results, using the EQ5, if you use a coarse enough image scale (short focal length imaging
lens/scope) but your hobby time will be much more enjoyably spent if you are using one of
the higher capacity mounts. In short, derate any mount manufacturer's load claims to 50-60%,
and you'll be much happier with the results you routinely achieve.
The mount manufacturers are trying to sell mounts. Many of them will post load claims,
much like the gas mileage claims posted by auto manufacturers (remember the saying
"your mileage may vary"). Under typical visual use, many of the lower end mounts will
(marginally) suffice to put the subject into a "low" power eyepiece, and keep it there.
Astrophotographic requirements (guiding ability) are much more stringent. Go with a good,
or at least sufficient mount, for enjoyable astrophotography.
The Camera
Most people will select a camera that offers the greatest number of pixels that they can
afford. This is fine if your budget is umpteen thousand. If you are looking for a more
affordable solution, take a look at the smaller frame cooled cameras like the Starlight
Xpress H9, using the sensitive, yet low noise Sony 285 CCD. It has such low dark noise, that
"darks" are not required, or even desireable for exposures under 10 or 12 minutes. This
can save you some hassle. If you just don't mind spending the time, the SBIG ST2000 offers
a similar sized, though noisier CCD, for a similar price. If you can spend a little more, the
Starlight H16, or QSI 540. Both of these use the noisier Kodak CCD, but with the integral
40-45 degree TEC, dark noise on individual exposure, less than a few minutes is low.
"Darks" are required beyond a few minutes, but that's the price you pay for the larger
frame. Most scopes are of a focal length that will result in good spatial sampling with a
pixel size of 6-9um. Take a look at the pixel size of the CCD you are considering, don't go
for one with tiny pixels (4-5um) unless you are using a very short focal length scope. They
have lower (effective) dynamic range when used in the (standard) unbinned mode. The
Sony CCDs are generally lower noise with moderate sensitivity. The Kodak are generally
noiser. Their KAI series (interline) have lower sensitivity. The KAF series (frame transfer)
have higher sensitivity.
If you are willing to keep individual exposures below 4-5 minutes at ISO 800, 6-8 minutes at
ISO400 (NOT the best approach for many low surface brightness subjects), the latest DSLRs
may offer a good alternative. They are, at least, the only low priced alternative for full
(35mm) frame cameras. The APS-C sized sensors (CMOS tend to have lowest noise) are
even more affordable, but in this frame size, the TE cooled Starlight M-25 (using a low
noise Sony CCD) probably offers a better value for general astro imaging. DSLRs are
improving with every new generation, and I suspect that the next generation, or that
immediately following, will provide about as much performance as most imagers will
require, AND they don't cost a small fortune. Just be sure to have the bandpass filter
replaced with clear optical quality glass, or a wider filter so that you have a reasonable
response at deep red (650nm), were so many of the nebulas emit light.
