Sunday, March 10, 2013
Instamatic Astrophotography
No, I don’t
mean we’re literally going to use that
darling of 1960s snapshooters to take deep sky astrophotos, but almost,
muchachos, almost. If you’re interested in imaging the sky, that is, which some
amateurs are and some are not. Why ain't everybody an astrophotographer? Some
folks genuinely don’t like the idea. They’ve never tried taking pictures but
are pretty sure they wouldn’t like it. For them, contemplating the Universe through an eyepiece is fun and relaxing and that is enough and good on ‘em.
I suspect,
though, that a lot of amateurs who’ve actually tried
imaging and have dropped out of what Unk calls “The Difficult Art” have done so
not because they don’t like the idea of capturing the Universe, but because it
all seems too much. Too complicated.
Too expensive. No pretty color prints of M42 for them then, right? Nope, it’s
easy to take nice deep sky astrophotos from the get-go without a lot of fuss if
you keep it simple with Unk Rod’s
Instamatic Astrophotography System.
I know
you’ve been told how to get started in astrophotography: begin with star trails and move up to
piggybacking. That is still good advice. If nothing else, you get used to
taking a camera and its accessories into the field and begin to learn about
dew, light pollution gradients, and all the other gremlins. And I guess the
majority of new imagers still get started this way. But very few want to remain
with wide field vistas or star trails for long. Most aspiring deep sky imagers
want to take pictures through the
telescope as soon as possible.
Problem is,
going from star trails snapshots or piggyback astrophotography to through-the-scope
prime focus work is one heck of a big jump. Mainly because of the guiding part
of the long exposure equation. As you may know, the telescope mounts most of us
can afford are not capable of long exposure imaging—taking shots of more than a
minute or two in duration—without guiding. Small imperfections in gears mean
that if a “guide” star is not continuously monitored and small corrections made
to the mount’s aim, stars will wind up off-round, and no astro-imager wants
that.
Autoguiding
ups the gear factor and the aggravation factor several fold. If you, like most
folks in these latter days, want to guide automatically, you need a lot more
stuff than just a telescope, a mount, and a camera. You need a separate guide
camera (unless you are using an expensive CCD cam equipped with self-guiding),
and you need something for the guide camera to look through, a guide scope or
an off axis guider. Finally, you will probably need a computer. There are a few
guide cameras that don’t require a PC, but the more affordable ones don’t work
very well.
You also
need a lot of patience and experience. It sometimes takes months to get a
guiding system working reliably. You may luck out and get round stars the first
night out with the default settings in your guide software, but you may instead
find you need to spend plenty of nights fine-tuning everything from software to
the guide scope mounting. Luckily for enthusiastic imaging newbies, you can,
like Uncle Rod, cheat.
Well, you’re
not really cheating, but you are
making things easier on yourself. The secret to my approach is dispensing with
as much stuff as possible. Guide scope? Leave it at home. Guide camera? It
stays there too. Five thousand dollar CCD camera? Fuhgeddaboutit. You may even
be able to let the cotton-picking laptop PC sit in its case. This is Instamatic
Astrophotography, a way to get simple but attractive color snapshots of the
deep sky in minimalist fashion. The images us celestial tourists get this way are a lot like the snapshots taken by terrestrial tourists:
humble but loveable.
If you
haven’t guessed already, what I am talking about is unguided imaging. Yeah, I
know what some of the gurus on the dadgum Cloudynights.com will tell you: “Won’t work. Not unless you have an
Astro-Physics or Software Bisque Mount (to the tune of about 10k).” Lucky for
you greenhorns your old Unk is here to tell you ‘tain’t necessarily so.
What’s the
secret? There are several. First, you want to start out with the best-behaved
mount you can afford. No, you do not need a Mach 1, but you want something
better than a pea-picking EQ-1. If you have an Atlas EQ-6 or a CGEM or
iOptron’s iEQ-45, you are golden. Those lower middleclass mounts, though, a can
still be too much for a cash-strapped newbie who’s just invested in a camera,
an OTA, etc., etc. The answer is Celestron’s inexpensive CG5 (now being
replaced by the better but similarly priced VX). It’s not necessarily “the
best” for our purposes, but it is the “good enough.” Meade’s now-discontinued
LXD-75 will also do the trick, if not quite as reliably, and is even cheaper.
Quite a few
astrophotography beginners have alt-azimuth mode scopes like the basic
Celestron NexStars or the Meade LS. The Celestrons can be used in equatorial
fashion, but that requires a wedge that costs money. The Meade LS cannot be
used equatorially at all. The good news is that at the relatively short
exposures we will be using an alt-az can do OK, though a polar aligned mount
will do better. A GEM or fork on a wedge only has to track in one axis, not two
like an alt-az. Alt-azimuth tracking doubles the possibility of tracking error.
Next is the
scope. Tracking errors are magnified by long focal length, natch. What you want
is a telescope with a reasonably short focal length. Maybe 600 – 1200mm, with
something on the lower end being better if your camera has a small sensor chip.
If you have a telescope in that focal range, maybe a small ED refractor, cool. If
not, many, including SCTs, can be made to fill the bill with a focal reducer.
Then there
is set-up. There are two things to consider here: balance and polar alignment.
If your mount is to perform its best, balance is critical. That’s true for any
equatorial mount, but even moreso of those in the CG5 class. How do you
balance? Slightly EAST HEAVY. When the R.A. lock is disengaged, you want the
tube to slowly move to the east. If you
are a little east-heavy, the drive will pull
the telescope along; the gears will remain in contact with each other,
minimizing tracking errors.
Believe me,
campers, balance makes a big difference. Naturally, you will have to redo your
balance when you switch from imaging on the east side of the Meridian to the west,
so it’s usually best to confine the evening’s targets to one side of the sky or
the other. Also, let me emphasize that when I say “slightly east heavy,” I mean
slightly. Having the scope way out of
balance in R.A. will make tracking worse rather than better.
How about
declination balance? That is not as critical. If you were guiding the
telescope, you might want the balance slightly biased in one direction, north
or south. But you are not, so just balance well enough in declination the mount
doesn’t strain during go-to slews and don’t worry about it.
The last set
up consideration is polar alignment. If you don’t have a good polar alignment, stars will trail in declination
due to something called “field rotation” no matter how well the R.A. motor and
gears do their job. To minimize this declination drift, you want to achieve as
good a polar alignment as possible. Doing a full-blown drift alignment is best,
but if you are like Unk and don’t have the patience for that, some of the
“almost as good” alignment methods outlined in the linked blog post above work fine.
How about
exposure times? That is the crux of the matter. The key. The out. Stay at
30-seconds. Your mount may be able to go a little longer unguided—sometimes—but
30-seconds will ensure the greatest number of “keeper” sub-frames. You won’t
get too much detail in dimmer objects at 30-seconds, and the exposures will
look pretty noisy, but you can take lots of 30-second exposures and stack them
into a final picture that does show plenty of detail. It is always better to
expose subframes for as long as possible in the interest of keeping noise down,
but 30-second stacks will look right good to you in the beginning.
Finally,
there’s the question, “Which camera?” A DSLR is probably the best choice. And a
Canon DSLR is still what you pick if you’re into astro-imaging, all things being equal. The DSLR, no matter who
made it, has several important advantages for the beginning imager. It is
wonderful for terrestrial use if you decide astroimaging ain’t for you, and it
is easy to use in the field by itself without computers and a lot of support
gear.
Even more
importantly, it has a relatively large chip. The APS sized sensors found in the
lower cost DSLRs are as big as, or usually considerably bigger than, what’s in
all but the more expensive astronomical CCD cameras. In addition to giving you
a large field for framing big objects, a larger chip makes the camera more
forgiving of a mount’s go-to accuracy or lack thereof. Also, the
“magnification” factor of the chip is low. Smaller chips exaggerate guiding
errors. The image covers a smaller area of sky than with a larger chip, making even
slightly non-round stars look worse than they otherwise would.
Which
doesn’t mean you shouldn’t consider a CCD camera. If you don’t have much money
to spend and/or don’t need a camera for earthly shots, an inexpensive CCD might
be the way to go in the beginning. A
bottom-of-the-line CCD, Meade’s original DSI, is what Unk got started with eight
years ago when he decided to finally buckle down and learn astrophotography the
electronic way. In addition to being cheaper than DSLRs, these cameras have another
advantage: their imaging chips are
small, but they are more sensitive than those of DSLRs, particularly to red
light, which is very important if you fancy shooting nebulae.
What’s out
there in the (well) under-1000 dollar CCD camera range? There used to be a lot
more to choose from, but with Meade and a couple of others leaving this section
of the market, I am only aware to two widely available choices at the moment, Orion’s StarShoot G3 cameras, available in one
shot color or black and white for about 400 bucks, and Starlight
Xpress’ Lodestar for $699.00. One other possibility is the QHY-5II, which seems similar to the Lodestar. It
is quite inexpensive at $245.00, and appears to have promise, but I don’t have
any information beyond that.
Which would I choose? The Lodestar is capable of
producing nice pictures, but is intended more as a guide camera than an imager and
is not cooled. Same with the QHY. The Orion is cooled and produces smoother
looking, more noise free images without a lot of post-processing hoo-doo. Color
or black and white? Color, surely. Most novices want color and do not want to
fool with filter wheels and tricolor imaging to get it.
Novices
often ask if there ain’t a third way, a cheaper solution than a DSLR or a CCD
camera: “Unk, can I take astrophotos with my point and shoot camera?” You
can—of the Moon and planets. Just shoot into the eyepiece in afocal fashion and
you can get some nice pix in the beginning. Unfortunately, these cameras just
aren’t up to the task of deep sky imaging.
If your
wallet or purse is feeling light, be assured there is a cheaper way. Meade, as above, discontinued its DSI CCD cameras
a couple of years back. They made plenty of them, though, so they are common on
the used market. The Meade DSI and DSI II are inexpensive used, and while they
are not cooled, clever hardware design means they do a better job keeping
thermal noise at bay than you would think. The DSI III? It’s a goodie too, with
the difference between it and the earlier cams being a larger chip.
Unfortunately, it sold for considerably more than the early DSIs and still goes
for a fair amount used. Even the basic DSI I can do surprisingly well; all the
astro images in this blog entry were done with it.
What else do
you need? The Orion, the QHY, and the Lodestar all require a computer for
operation. Most DSLRs can take 30-second shots without even a remote (“cable”)
release, much less a computer, but having an inexpensive camera remote makes
DSLR shooting way easier and is practically a necessity. Without one, you’ll
have to fool with the self-timer so you don’t shake the scope when you take a
shot. The Orion cameras are powered by the USB bus, but their coolers require an
external 12-volt battery for operation.
Camera,
mount, and scope in hand, let’s set up on the observing field and do an Instamatic
run. With the scope balanced for whichever celestial hemisphere you will be
imaging in, the next step is polar alignment.
How you do that is up to you, whether by drift aligning or taking an easier way
out. I center Polaris in the hollow bore of the CG5’s RA axis (I did not buy
and don’t need or want a polar alignment borescope) and do Celestron’s AllStar
polar alignment, which is more than good enough for 30-second exposures.
How about
PEC, periodic error correction? If your mount has it, use it. Details will vary
with the scope model, but you pick a star, a reasonably bright star, in the
area of your target. Center it in an illuminated reticle eyepiece and start the
PEC recording process. Watch the star, and if it drifts in RA re-center it
using the hand control (which is set to “guide” speed). When the recording is
finished, begin playing it back, however your particular scope has you do that.
PEC will almost always result in a higher percentage of 30-second keepers.
Next item on
the menu is attaching camera to the telescope. How you do that depends on the
camera and the scope. If you are using a DSI or one of Orion’s CCDs, it’s easy.
Those cameras come with a 1.25-inch adapter that slides into a focuser or a
visual back. If you are using an SCT, that visual back will be screwed onto an
f/3.3 focal reducer. DSLR? You will need a widget called a “prime focus
adapter” and a T-ring that takes the place of your camera lens. The T-ring threads
onto the prime focus adapter, which then screws onto the (usually f/6.3) reducer
on an SCT or slides into the focuser of a Newtonian or refractor.
Fire up the
camera next, and make sure you have plenty of fire. The small CCD cameras are
powered by the computer over their USB cables, so you wouldn’t think that would
be a problem. Well, it is. Your computer supplies them with power, and can only
supply the amps they need if it has sufficient power available itself. Even if
your computer’s internal battery will furnish enough current to keep the PC
alive for the whole observing run, run it from an external 12vdc battery and an
inverter to ensure it has enough extra power to keep the camera going.
DSLR
batteries do pretty well—in the daytime when they are warm, anyhow. On a cold
observing field where they will have to hold the shutter open for 30-seconds exposure
after exposure? Not so much. My Canon Rebel’s battery will last a couple of
hours, but no more. Solution? An extra battery or a battery eliminator, which
most companies sell for their cameras. You will probably need a small inverter and
a battery to go with a battery eliminator, since most are designed to use AC
mains current.
Time to
start shooting. Well, start focusing,
anyway. That’s duck soup with the li’l CCD cams. Meade’s Envision software for the DSI and the programs shipped with other CCD
cameras, have focus utilities that allow you to get a star focused without a
hassle (I generally rough focus on the last go-to alignment star and fine-tune
on dimmer stars in its field). Focusing a DSLR that has “live view”—that presents
a constantly updating live image on its display screen—is not too bad. Focusing
a DSLR without live view is absolute murder
if you are not running the camera with a PC and a program like Nebulosity.
When you are
OK with focus, it’s rubber meets the road time. Go-to your first target. Most
current mounts won’t have any trouble putting it on the large chip of a DSLR.
The tiny chip of an inexpensive (or older) CCD? If your object is not visible
in the field when the scope stops no matter how you up the exposure, engage
“Precise Go-to.” Both Meade and Celestron mounts feature this utility, which
ensures you get on the target every time.
When you
select an object with Precise Go-to enabled, you will also be asked to choose a
bright star in the neighborhood of the DSO, usually from a list. Do that and
the scope goes to that star first. Center it, press the “go” button, and the
mount/scope proceeds to the target. You can be pretty much assured it will be
in the field of even the smallest chip every time; usually near the center.
Precise go-to would be a pain for normal observing, but when you are imaging,
you’ll usually only do a few objects per night, so it is not too much of an
annoyance, and is certainly easier than hunting around for your subjects.
Then you
start taking 30-second subframes. As many as possible. At least 25 for most
objects; more is better. The more subframes you have for stacking, the better
exposed and less noisy the finished image will look. Doing a lot of subs is
easy with a CCD or when you’re operating a DSLR with Nebulosity or a similar program; you just tell the software to
expose 25 shots and walk away. No Nebulosity?
You will have to manually trigger each DSLR shot. Once again, at least having a
remote/cable release “interval timer” makes DSLR shooting easier, much easier.
And so the
camera clicks off exposure after exposure of M13. What can you expect of ‘em
without guiding? If you’ve carefully balanced the telescope, you can expect
most of them to be pretty good. If you’ve got PEC running, a large majority
will have un-trailed stars. You cannot, however, expect every single one to be
OK with a CG5 class mount, or even with a mount in the next tier up. There will
always be some you have to throw out. An errant gust of wind, a bad spot in a
gear, or one of the numerous unidentifiable gremlins that plague astro-imagers
will always send some to the trash.
When you’re
back home cozy and warm, the next step comes: stacking and processing. That is
the subject for a whole blog entry some Sunday, I reckon. But modern programs
like the free Deep Sky Stacker and
the inexpensive Nebulously (which
does a hell of a lot more than just stack frames) make stacking and combining sub-frames
nearabout painless. A little tweaking of brightness/contrast/histogram using
the image processing part of your stacking program or a separate program like Photoshop and you are done.
As I warned
in the beginning, your pictures will not make Jason Ware or Robert Gendler
sweat, but they will be yours and you
will love them. Heck, even years and lots of imaging experience down the road,
some of my 30-seconders still look right nice to me, muchachos. If nothing
else, you’ll have leapt into those scary deep sky-imaging waters with both feet.
I’ve since gone on to autoguiding and all that stuff, but I still enjoy and use
the simpler way, good old Instamatic astrophotography.
Next Time: Comet Fever?
Comments:
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The lower middleclass mounts have a greater load capacity, and maybe more features, than the inexpensive ones. Are there other significant differences that affect performance even if one is careful about load?
Kendahl
Kendahl
# posted by 
: 6:09 PM
: 6:09 PM 
I have taken the plunge going from pure visual to instamatic astrophotograph and it is extremely addictive. http://darrenwastro.blogspot.com/2013/01/astrophotography-revisitedcmos-and-ccd.html?m=1. Love your articles...one of the things I look forward to every week
Rod -
My LXD 75 and Nikon 7000 work very well. One big thing is that the D7000 has an intervelometer, and I can have it take 3 or 4 hours (on one battery) without ever touching the the setup.
Very nice write up. BTW did 23herschel 400 Galxies Friday and Saturday with the club (21 degrees - it was cold).
My LXD 75 and Nikon 7000 work very well. One big thing is that the D7000 has an intervelometer, and I can have it take 3 or 4 hours (on one battery) without ever touching the the setup.
Very nice write up. BTW did 23herschel 400 Galxies Friday and Saturday with the club (21 degrees - it was cold).
Another great blog. Extremely informative and dead on!
With all the video cameras and CCD cams I have I do find myself going back to the simple days of digiscoping (A-focal). I have found the Lumix digital cameras go up to 60sec exposures and the quality of the optics and chips have made this fun to do again. Especially having the ability to mount eyepieces directly to the camera with readily available adapters. Shoot, I am even seeing reasonably good results from iPhones posted on the internet. It will be fun to see where all this technology leads to in the next few tears.
With all the video cameras and CCD cams I have I do find myself going back to the simple days of digiscoping (A-focal). I have found the Lumix digital cameras go up to 60sec exposures and the quality of the optics and chips have made this fun to do again. Especially having the ability to mount eyepieces directly to the camera with readily available adapters. Shoot, I am even seeing reasonably good results from iPhones posted on the internet. It will be fun to see where all this technology leads to in the next few tears.
Another great blog. Extremely informative and dead on!
With all the video cameras and CCD cams I have I do find myself going back to the simple days of digiscoping (A-focal). I have found the Lumix digital cameras go up to 60sec exposures and the quality of the optics and chips have made this fun to do again. Especially having the ability to mount eyepieces directly to the camera with readily available adapters. Shoot, I am even seeing reasonably good results from iPhones posted on the internet. It will be fun to see where all this technology leads to in the next few tears.
With all the video cameras and CCD cams I have I do find myself going back to the simple days of digiscoping (A-focal). I have found the Lumix digital cameras go up to 60sec exposures and the quality of the optics and chips have made this fun to do again. Especially having the ability to mount eyepieces directly to the camera with readily available adapters. Shoot, I am even seeing reasonably good results from iPhones posted on the internet. It will be fun to see where all this technology leads to in the next few tears.
Don't forget to look at BackyardEOS for managing your DSLR. It made all the difference for me. It makes imaging really simple, once you get the dad-blamed telescope pointing in the right direction!
Also have look at http://www.ideiki.com/astro/ .
This peace of software is real cool and has got a ton of features.
The only one i know that has a bahtinov focusing tool. Give it a try and kinda cheapo too.
This peace of software is real cool and has got a ton of features.
The only one i know that has a bahtinov focusing tool. Give it a try and kinda cheapo too.
Also have look at http://www.ideiki.com/astro/ .
This peace of software is real cool and has got a ton of features.
The only one i know that has a bahtinov focusing tool. Give it a try and kinda cheapo too.
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This peace of software is real cool and has got a ton of features.
The only one i know that has a bahtinov focusing tool. Give it a try and kinda cheapo too.
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