Category Archives: Astrophotography

Astrophotography Equipment Follow Up

Steven Christenson: New &emdash; Castles on High

New Equipment vs Old

In the years since I began writing about astrophotography techniques and equipment (including review of the Polarie, pointing tips, and processing techniques) things have obviously changed for me.  For one, I’m not working at astrophotography as hardcore as I expected.  The reality of managing an informative website (this one!), creating publishing and supporting tools, conducting fairly frequent expeditions and workshops, writing and improving content for webinars *AND* having a day job means I have to temper my enthusiasm. Or to say it more plainly, have my enthusiasm tempered by reality.

However a student asked me this question and I felt it was a good topic. The question:

I read your review suggesting the Orion Astroview EQ mount with optional dual axis motors. I’ve been looking for a cheap way to do decent tracking and have considered making a homemade Barn-door mechanical tracker to something more reliable (motor driven).

On Orion’s website, I find their Astroview EQ mount (#09822) and the dual axis motors for the Astroview (07828).

Soooo, my question is this: Since you wrote that article, is that still the most bang for your buck, or have you found something better/bigger/cheaper?
— Bruce L.

As I noted in my article, there are definitely bigger and better and significantly more expensive things … though nothing cheaper that I’d recommend. The Polarie is in the same price league.  After I made my recommendation my Astroview suffered a series of blows to the declination drive that rendered the drive useless.  The first blow was that the locking nut fell off in the dark and was lost. Once I replaced the lost piece (at about $35) the next blow was quite literal and it bent the drive axis rendering the motor useless. The truth, however, is I really didn’t need the second axis at all and I’d have saved a few bucks by only buying the single drive motor to begin with.  The Astroview is just beefy enough to carry the weight of my Orion 80ED refractor and a camera.  And to be quite honest since it is lighter and not a “GoTo” mount it’s actually easier to set up and take down than it’s bigger cousin, the Sirius mount. But the Astroview is nowhere nearly as well made.  So yes, I’d still recommend an Astroview as a minimum viable solution… provided you stick with a camera and telephoto / normal lens to do imaging.  Most telescopes worth mounting on the Astroview will cross the boundary of what the Astroview is designed to carry and will be too heavy for good operation.

Automating Focus – Two Steps Forward, One Step Back

I had upgraded the focuser on my 80ED to one sold by ScopeStuff (#RNFR) – a $320 motorized focuser. That focuser proved easier to use and more versatile, but I later found it coming apart and it required some heavy tinkering and investigation to get it working again.  I also realized that the system was not that well thought out – it was designed to have the motor base mounted to the focus TENSIONING screw rather than attached to a fixed screw on the focuser.  That’s probably in part why when I got it, the tube would not travel all the way through the almost 4 inches of focus. I’ve restored it to operation but it still won’t travel in the final 3/4 of an inch… that’s fine, however as I have never needed that much in-focus – I’m usually working with the focus tube nearly fully extended.

In focus - moving the camera inward, toward the front element of the telescope, thus shortening the overall length.
Out focus (aka back focus) - moving the camera outward from the front element lengthening the apparatus.

Is A Barn Door Tracker A Good Solution?

Let me address the question about a Barn Door Tracker.  There are no places that I have found to buy barn door trackers, it’s strictly a home-built type of thing. As I explain in the Astrophotography 101 webinar, a barn door tracker is a form of an equatorial mount that has been simplified to drive only one axis (the right ascension) and with a limited tracking time.  Various designs like the double arm version improve tracking accuracy while complicating assembly. My personal bias is that even though I’m pretty handy with tools I’d rather spend $400 on a fully built system than $80 on parts and 10-20 hours of my own labor building and perfecting the system.  I suppose if someone handed me a robust kit for $100 and told me I could assemble a motor driven barn-door tracker in an hour or less, I’d give it a try.  But at much more cost in time or money the barn door tracker starts bumping into fully built solutions like the Orion Astroview and the Vixen Polarie or the iOptron SkyTracker.

One of the principle impediments with all things astrophography – and part of the reason I created the Astrophotography 101 course is that there is a LOT of language used that is foreign to most people. And, there are legion of difficult choices to make. For example, I recently bought a William Optics Telescope. It is a well built, heavier than expected, refracting telescope that features a power focuser. Perhaps as a surprise to the uninitiated the “power focuser” is not actually powered (motor driven), it is an improved version of the manual Dual speed Crayford focuser and the term “power” implies it’s ability to hold focus without slop or creep – even if the other end of the focus mechanism is a pretty substantial camera.

I had hoped my existing finder scope and guide scopes would easily attach to the new William Optics telescope, but they won’t. The fittings are all different. For the most part astronomy and astrophotography equipment is a wild west of non-compatible, non-interchangeable components.  Much like you see if you try to use a Nikon lens on a Canon camera.  Or an intervalometer built for a Sony on a Lumix camera.  The difference, at least to my way of thinking, is that the compatibility of components is much better spelled out in the camera world than the astronomy world.

What about the Polarie?

The Polarie will work well with normal lenses. When I mounted my 70-200 with a 1.4x and the Canon 5D Mark II (or 40D) on the Polarie, tracking accuracy was pretty bad – but not directly because of the Polarie. The problem is that the systems is not balanced and there are three different points around which the apparatus gets sloppy: at the connection between the ring-collar of the lens and the head mounted on the Polarie. At the point where the head is attached to the Polarie screw, and where the “collet” with it’s two thumb screws attaches to the Polarie.  Invariably one of those would become loose enough that it would slip.  I found that putting a counter weight at the end of the lens reduced slipping and improved the tracking – but it’s a hassle and highly dependent on where you aim.  A true equatorial mount is easier to balance. The Polarie system works better when there isn’t a lot of torque around those attachment points.

In summary, I like and use the Polarie because it’s compact, light, not bulky and easy to take with me literally anywhere I go. But I would not use it to take serious astro images.  The Polarie best fits Landscape astrophotography.  For example, below is a 63 second exposure using a Canon 40D at 1000 ISO, f/2.8 at 16mm.  Using the 500 rule, star streaking would become apparent at about 12 seconds.  In this small size there is nothing at all visible, but do notice how the foreground head frame at Bodie State Historical Park is blurred – that’s because the Polarie was tracking the sky at 1/2 sidereal (star) rate. The photo has been exposure enhanced (brightened) to see details, and noise reduced a bit.

B_180-002309_sm

 


I realize the photo at the top has nothing to do with any of the subjects… it was taken in daylight. But, hey I like it. In my defense, the “Phantom Ship” structure seen in the first photo is the oldest rock at Crater Lake.

Here is an exposure that is a bit more germane. Two exposures, actually. One focused for the hand-lit tree, the other focused on the stars and both were combined in Photoshop.

Heaven Bound [C_075698+701]

Flat Frames

Please, no giggles. And yes, flat frames are a widely used astrophotography technique. But like many tricks that astrophotographers use, you can make use of flat frames yourself to do some clever things.  If you’re impatient you can skip ahead and discover how Flat Frames can be used below and decide if it’s worth reading the rest of this article.

What Is a Flat Frame?

A flat frame is a normally exposed image with the entire field of view of the image lit as uniformly as possible.  Like dark frames, flat frames are rather dull and uninteresting things to look at. They are visually white or gray and quite boring.

A typical flat frame

Flat Frame: Canon 5D II with 16-35mm f/2.8 L II lens at 20mm

How Do I Create a Flat Frame?

There are many ways to create a flat frame, let me quickly run through a few. First make sure your zoom, aperture and focus are as you will be using them because vignetting and center of field brightness change as you adjust the zoom, aperture or focus. I usually set my camera on aperture priority mode and let the camera meter for me.

But how should I take a flat frame image?

  1. Is your sky cloudless (or uniformly gray)?  If so, point the focused camera at the sky (and only sky) and take a couple of normally exposed images.  Because it’s probably not as uniform as you think, try rotating the camera and pointing it differently to get a good average flat frame. If you are using a very wide-angle lens, it may be hard to get “only sky”.
  2. Take a clean white t-shirt. Drape it over the lens or lens hood. Smooth it out. Shoot a few frames, rotate the shirt, shoot a few more. Obviously if you’re doing this at night, you’ll need a uniform light source – the good news is the color temperature doesn’t matter much.
  3. Select a uniform white or gray display on your iPad, iPhone, Mac or laptop computer. Hold the tablet up against the lens – making sure the lens is completely covered by the display and take several exposures. Rotate the camera or light source to avoid hot spots.

For optimum effectiveness, shoot the flat frames immediately before or after taking your normal shots and do not change the focus, aperture or zoom. Take your flat frames – you should have six to ten of them, and average them. Do not adjust your flat frames. That is, do not brighten, darken or contrast enhance them.

What Can I Do with a Flat Frame?

Did you read this far hoping that flat frames could in fact be useful somehow? Well then, here is the good news. With flat frames you can:

  1. Remove Dust – since dust tends to move around having taken flat frames very near to the same time you took your normal shots increases the effectiveness of the dust removal.
  2. Remove smudges on the sensor
  3. Reduce or eliminate vignetting.

To effectively use a flatframe, however, you must be able to use layers.

Using a flat frame you can get this result

Flat

 

Even though you started with this:

NoFlat

Notice how the bright center of the field has been normalized. You may not think of the center of a lens as being brighter, but you are probably quite familiar with the outer edges being darker, that is, vignetting. Because these images have been cropped the bright area is not centered as you would expect.

What about Dark Frames – Are They Related?

Flat frames and dark frames are not related at all and are used for very different things. Astrophotographers will normally take Dark, Flat, Offset and Light frames… all of which  serve different purposes.  We do recommend taking dark frames for night or low light photography.

How Do I USE a Flat Frame

You’re welcome to look up how to use Flat Frames in any of the references below, but we will be providing a “part two” article with the details.  We’ll also cover Flat Frames both in the next Astrophotography 101 and Photo Manipulation webinars.  If you want to be in the next webinar, please join our subscription list and we’ll let you know when we schedule it!

References:

 

Theory vs Reality in Photography

Several topics in this BLOG have provoked impassioned debate. We really appreciate that. Steven is a Software Engineer by training. Eric is a Molecular Biologist, and Harold is a jack of all trades. In addition to being an author and professional photographer, Harold’s background includes being an Attorney at Law and a Software Engineer. We do “geek” like nobody’s business!

I, Steven am raising the geek card just to let you know that we do care about precision – but we care MORE about great photography and applying real-world principles to real-world problems.

Streaking Or Not?

The biggest debate has been about what factors lead to streaking (trailing) in Night Photography shots of the stars. Shots of the night sky may produce noticeable streaks if the exposure length exceeds certain bounds with specific camera factors (focal length, sensor size and sensor geometry). But there are a huge set of assumptions behind the visibility of those streaks that are often overlooked. One assumption is that the finished image sizes are proportional to the size of the sensor used to create them – when does that happen in real life? Another assumption is that the viewing distance is proportionally related to the finished image size. These sound like they are reasonable, but in the real world, a print from a crop camera and a full-frame camera are extremely likely to  be made in the same finished sized and viewed from whatever distance the viewer chooses!

In the desire to get the math exactly right, many people trip over one or more of those assumptions. Our article about why the 600 Rule is a misguided way to determine the proper exposure length has had many proponents and opponents espousing the “inerrancy of the mathematics” and all the missing factors we may not have included. I love math, but: my assertion is that Reality beats theory when producing an image.  And that’s why the conclusion of the article is that the proper exposure length is an aesthetic decision more than a mathematical one.  The mathematics guide, but do not govern what the best choice(s) may be.

All Photography Involves Tradeoffs

I really enjoyed my Physics classes, especially mechanics. But I also remember all those exercises that included clauses like “neglecting friction”… In the real world friction with the the air and from tire contact on the ground is why a car on a flat road comes to a stop even though no brakes are applied.  Air friction (drag) is why it takes eight times as much power for a plane to fly twice as fast.

The reality of physic is why a lens, or sensor is always a tradeoff of something for something else. Perfect optics or a perfect sensor behavior is not possible at any cost. In the same way, a photographic exposure is always a tradeoff of one thing for another. If you need a faster exposure with a given amount of light you can: increase the exposure time, increase the sensitivity, or admit more light by opening the aperture. Of course you can also change more than one thing at a time. Indeed you MUST change more than one thing. Any change to one of the three factors requires a corresponding change to one or more of the other factors.

What Exposure Settings Should I Use?

If you ask me this question, I apologize in advance for rolling my eyes (it has been known to happen). I can give you a STARTING point, but remember that a starting point involves tradeoffs and conditions that can not be entirely foreseen. How warm is it? How much moisture, dust or particulates are in the air? How much turbulence in the atmosphere? How much artificial (or natural light)? What are the predominate colors of the light (white balance)? How efficient is your sensor? How sharp are your optics? How far away is your foreground from your background? What is that largest aperture available? How sharp is your lens at that aperture and at that zoom? What is important to you in the scene you’re trying to capture? And what are you trying to accomplish?

My best advice: try an exposure and see what you get. When all there was was film, precision was a lot more important than it is now in the digital world where you can immediately see the result with a histogram and a myriad of other data to help you decide what to try next.

In fact, here is your assignment.  Go out when it is dark and shoot a photo of the moon.  How dark is entirely up to you. Your photo MUST show the same kind of detail that you can see with your eye – the craters and the gradations from light to dark areas.  Use a telephoto lens – notice I am not telling you how telephoto, that’s also your choice. If the moon is “blown out” – and it probably will be, decrease the exposure. Keep taking photos until you get as much detail as you can.  You will almost certainly need to use manual mode to set your exposures.

What settings did you come up with?  In our “Catching the Moon” webinars we provide starting settings and also advice about how those settings may need to be changed.

For an extra challenge… see if you can get the moon AND stars in the same shot. What settings did that require?**

4 Moons 4 U [B_049969] Composite

**In retrospect, it was evil of me to suggest this. In only the most extraordinary circumstances is it possible with current technology to get a featured moon AND stars.  The example above required 3 separate exposures.

 

Hunting Comets and other faint objects in not-dark skies

AirGlow Comet [5_070386]

It turns out the much hyped PanSTARRS C/2011L4 Comet is not living up to the hype. Unfortunately failure to meet the over exhuberant expectations  is common since predicting brightness and visibility of an object like a comet is a difficult science. In fact, it’s part science, part black art and part good guessing – mostly the latter.

The photo above was taken on March 12 when the moon and PanSTARRS nestled closely together. The close quarters made finding the comet much easier despite the bands of clouds passing by.  The strategy for finding the comet in that case was simple: use a telephoto lens, put the moon at the right edge of the photo and take different exposures periodically and at different settings (e.g. +2, 0, and -2 stops). Then hunt for smudges.

The IDEAL telephoto lens would be one that was a few angular degrees wider than the difference between the moon’s position and the comet’s position. How to determine the position of each is discussed in the last section below. Figuring out the angular view of your lens is easy using online tools like this one from Tawbaware, makers of Image Stacker (like that program!). If you know the field of view at your minimum and maximum zoom, you can use that information to your advantage.

Finding the Comet with a Nearby Moon

The point at the moon strategy made finding the comet easy because:

  1. There is no way you’d be able to see the comet if you were not able to find the much brighter moon nearby.
  2. On that one night, the comet and the moon were within 4 degrees of one another.  That’s quite close.

I know some people tried to find the comet using wide angle lenses. That strategy might work, but the comet is such a tiny thing and it’s visibility is so tenuous based on the atmosphere, light pollution, and sky brightness that you may only realize – as many did – that you captured the comet after carefully inspecting your photos at home.

Contrails and Comet Tails [B_050938]

The truth is you are unlikely to see PanSTARRS by eye or in your camera’s view finder unless your conditions are nearly ideal.  Hopefully ISON which is coming in December will be brighter and better.

Finding the Comet when the Moon is Farther Away

The following night, both the comet and the moon had moved relative to the sky. On March 13, the moon was 12.5 degrees above the comet and about 4 degrees farther west (again, how I knew this is coming in just a minute).  So one simple strategy for finding the comet would be to zoom your telephoto lens so that it has a field of view of about 14 to 15 degrees in the long direction which for me, is 80 millimeters focal length on a 1.6 crop factor camera.

On a tripod with the camera in portrait orientation adjust the view so that the the moon is in the upper left of the frame. Shoot bracketed shots. Check the lower right corner of each one for the tell-tale comet smudge.  Keep readjusting the view so the moon remains in the upper left for each shot. Zoom out a little bit too, in case your geometry is a little off. Eventually as it gets dark enough or the sky clear enough you should find it.

In fact the way I found the comet last night without using my camera but by using my telescope. The program Clinometer (on my iPhone) measures angles. I sighted the moon with my 8″ Dobsonian telescope and measured the angle along the telescope barrel using the inclinometer program. I then lowered the altitude (elevation angle) of the telescope by 12 degrees to match the altitude of the comet. Then I slowly rotated the telescope northward until I found the comet.  It wasn’t easy from my urban location, but it wasn’t impossible either.  By the time I was able to find the comet it was only about 6 degrees high in the sky – that’s way too low if you have trees, hills, and houses nearby to deal with.  In theory, this strategy would work with a telephoto lens or with binoculars, however, binoculars need to be steady and where I spied from last night had streetlights in the distance and the flare and glare from those streetlights made finding the faint comet nigh impossible.

What if there is no Moon to Find the Comet With?

Unfortunately starting on March 14th, the moon will be quite far from the comet, so the opposite strategy is required:  Use a landmark in a known direction as the starting point and look “upward” from the horizon.  In other words, zoom your telephoto lens so that the field of view covers the angle from the horizon to the comets altitude (angle) above the horizon.  Don’t forget that as the earth spins this angle changes every minute! Orient you camera in landscape mode and point it as close as you can to the correct direction (azimuth). Look along the top of the frame to see if you’ve captured the comet.

IMG_1622.PNG

SpyGlass’s view shows the direction the camera is facing (Azimuth) and the elevation angle (Altitude)

But what direction should you point your lens or telescope? Use a compass application or actual compass. BEWARE however as the compass applications have lots of gotchas and are only accurate to about 5-10 degrees.  And if you aren’t sure how to use a real compass your local magnetic declination might bite you. Better would be a GPS with a built-in calibrate-able compass.  And perhaps even better still would be to use an application like TPE (which I discuss in my Catching the Moon Webinars) to calculate the correct azimuth from the location you plan to stand.  An application that might help a lot is “SpyGlass
however don’t forget that I found the directional accuracy of my iPhone and iPad to be pretty poor.  Being off by 5 degrees may mean looking in the wrong place.

How Do I Know the Altitude and Azimuth for the Comet?

Stellarium_MoonMarch14

Unfortunately, that’s a tough one.  I use the free program Stellarium. I then added the comet to the “Solar System Data Base” (search around on the web and you’ll find instructions). I selected my viewing location, dialed in the time, did a search for good ‘ol C/2011 L4 and let it tell me the azimuth and altitude.

PanStarrs_March14

Above I’ve dialed up the time and clicked the moon. The highlighted line shows me the azimuth (direction) and altitude (angle above the horizon) for the moon which at that time are 264 degrees or just a little south of west, and 30.5 degrees high.  Clicking on the comet shows 272 degrees – a tiny bit north of west and 9.5 degrees.  So now we know that the comet will be 8 degrees north and 21 degrees south of the moon – and that won’t change significantly for the rest of the night.

Since we also know the direction for the comet is about due west at this time, we can apply the telephoto-lens horizon trick I described earlier.

Another way you can find the azimuth and altitude is by checking my animation HERE – note that the animation is correct for San Francisco  (and most places nearby).  There is also a table of the azimuth and elevation in the text of the Flickr post.

 

By the way, one way to find the right spot on the horizon is to use the sunset location as a guide.

CometIllustration