Eric Chesak's telescope thermal focus management system is made up of three main elements: the heater, the power and temperature control system, and the thermocouple for temperature feedback.
Well, it kind of looks funky, but it obviously works. This is such a simple and straightforward idea that you wonder why it hasn't been done before. I suspect that it is the way that the original problem was put.
Your're absolutely right. Not pretty, But... it really works well. It's dark, so nobody sees it anyway. I've been using this system for about 2 years with really stunning success. It works better than I imagined it would.
Those pictures really are amazing, and do you just use a normal telescope, or is it designed for deep-space photography? Either way, thats a really cool (er, warm) way to keep something the same temperature.
Hey thanks John. You can take deep sky images with many different telescopes. It's the equatorial mount that is probably most important. The scope I use is a Takahashi FSQ-106ED, which is used for imaging a lot, as it has a very large imaging circle (can use large imaging sensors) and top notch color correction. Thanks for the comment...
Eric, I would imagine that you're taking photos of objects that you can't see, even with a telescope. How do you identify where they are and what they are?
Absolutely correct, Rob. Most of the objects are very faint and not visible with the naked eye. In this case, there are many ways to find the objects. An older technique is to use setting circles, on the mount. This provides two corrdinates, Right ascension and declination). The night sky is well mapped, so the object will have their coordinates listed. However, most modern mounts are computerized and will slew to the object automatically, once properly initially aligned.
Before I had my GOTO mount, I used to spend hours locating difficult targets, exposing, framing and re-exposing - trying to get the target framed. These days, I can look-up the target, obtain the framing angle and coordinates. I adjust the scope and punch the target into the mount's computer and 99% of the time, it's framed and ready to go.
There's a lot more involved with long exposure imaging (accurate polar alignment, active guiding, cooling the imaging sensor, etc). But just having a GOTO mount will take a lot of the work out of imaging.
Rob, You got it. There are some mounts where you enter the coordinates and have to manually push the scope to the proper coordinates. But most modern mounts have some sort of GOTO option. It takes a lot of the time consuming work out of trying to find objects.
The mount I currently use is an Astrophysics Mach1GTO. The "computer" that it uses has over 17,000 objects in its database (stars, clusters, nebula, etc). Once the mount is aligned and calibrated, you can enter an object or coordinate, press GOTO, and it will slew to that object with superb accuracy. If you're interested, you can find details here:
http://tinyurl.com/2xkk3e
If you speak to any serious astrophotographer, the majority will say that the mount is the most important piece of equipment for getting good, long-exposure, deep sky images.
That's fascinating, Eric. So the GOTO already has the object you're seeking. The link you provided actually shows photos of the objects you may wish to capture. When you capture an object, do you submit it to the site (if you get a better shot than they're presenting)?
Rob, the GOTO library is usually just text based (M42, NGC 7822, IC1318, etc). So you have to know that you want to image and the name of it. I usually look through a sky atlas to see what large objects are in the sky, research them on the internet, check the size and fit into my field of view and then go from there.
I did send some of my images of Dark Nebula to the Barnard project at Georgia Tech (http://www.library.gatech.edu/barnard/links.html). I also submit my images to magazines and such. But I find that my images don't hold a candle to what others can produce.
What makes the difference in the quality of the images, Eric? Is it the telescope? The production of the image? The atmosphere at the time of capturing the image?
Rob, there are quite a few factors that make a good image (probably too many to list here). But here's a short list:
1. Telescope - Good optics with a large flat field and little/no chromatic abberation, coma or other optical issues. The scope also need a good focuser to be able to hold the imaging equipment.
2. Good Mount - very Stable, able to track accurately and accept feedback from an autoguider (separate camera used to help lock-on to a star). Also needs to be able to hold the weight of the scope and imaging equipment.
3. Good Camera - Many use spectrum-modified DSLR's, I use a cooled full-frame monochrome CCD with filters (RGB and narrowband). A CCD requires a laptop or computer.
3. Dark Skies - Light Pollution is the enemy of good image quality.
4. Good weather conditions - "Seeing" - atmospheric disturbance, Transparency - little dust or water vapor in the air. This becomes increasingly important as the magnification (focal length) increases. araasch commented on some of these issues below.
5. Lots of good image Acquisition and image processing software (MaximDL, Photoshop, Registar are the main ones that I use) and a good knowledge of their use and techniques - Image processing is where I'm the weakest and where I concentrate most of my time.
6. A lot of patience - acquiring the necessary equipment, climbing the learning curve and acquiring the necessary images.
7. Luck - with respect to weather, transparency and still & stable atmosphere. Also with respect to getting everything to work properly, which is always a challenge.
So there's a few of the things to consider. The is a partial list and is not necessarily in the order of importance.
What most folks don't realize is that the majority of deep sky, planetary and some other images are made from many single exposures. My deep sky images can be 20, 30 or more, single frames, shot over many nights. Planetary images, can be many thousands of individual images. These are digitally stacked to increase te signal-to-noise ratio. This also allows one to use other techniques to reduce the noise.
Altitude is most definitely a help. Just as you mentioned, the less atmosphere you need to look through, the better.
But all the images that you see on my site were shot from my back yard at about 3,000 ft, with light pollution and less than stellar "seeing". So good shots can still be had in less than ideal conditions, including light polution, and high humidity. A lot can also be done, on a tripod with a camera, Star trails, scenics and such.
Actually, This was the first time some of my astro buddies had heard of my system. I had eluded to it many times, but was still testing it. Since the GF article, I've since shared it. At least 2 of my astro friends are interested in giving it a try.
It may not be a catch-all solution, but for small f# refractors (where the critical focus zone is small), it really seems to help.
Well, this is a good forum to share your solution, Eric. Those who are interested get a video demonstration and full build instructions if they decide to give the solution a try.
The space photos are nice but as an Engineering Tech I am impressed by the workmanship on the little control box. Very well done. Although the red lion controllers are a little expensive. Automation Direct has controllers that work very well at about half the price of a Red Lion version.
Thanks Noswad. I love metalworking. I'm no pro, but enjoy it. You're right about the controller. There are many different units that will function identically.
Excelent analysis and perfect solution. That's what engineering is all about. This project, I would imagine could have mutiple applications, such as maintaining temperature in a birthing box or mainitain growth cultures, and so. Good workmanship!
Wow! Those images are breathtaking. We are big astronomy fans and have made many trips to Fort Davis to go to McDonald Observatory for their star parties. We took our son 2 years ago to look through their 109" telescope for his thirteenth birthday and Dr. Lambert, the director, allowed us to stay after the viewing and observe astronomy researchers at work - my son even got to help and log in on the official viewing sheet for that night's research.
We have been talking a lot on Design News about getting the next generation excited about science and astronomy is certainly a great way to do it! We have a Meade ETX-125 and have been toying around with the idea of astrophotography enough to buy a scope mount for our camera - but never got any further. After reading about this super cool gadget - it makes me want to go at it again. What a neat way to keep the scope temp regulated AND prevent condensation. Way cool gadget!
Thanks Nancy. I've wanted to get images like this since I first saw them in Grade school. Now, some 40 years later, I'm able to do it. I really enjoy the hobby.
About the initial temperature setting... so you start off with a setting that will maintain whatever the ambient temperature is at the beginning of a session? And the real point to my question... do you still need a dew heater on the primary?
I have made a dew heater for my Canon 20D because I do 2 min. max piggy back astrophotography. I'm upgrading in a year or so to a scope that will allow longer exposures and prime focus work. It would be great to skip the dew heaters for what you've shown us here.
Doing most of my astrophotography from a site near the Delaware Bay means that dew can be a big problem. At times the whole scope gets wet. This might even stop that.
For the starting temperature, I usually check the dew point at the start of the session. I set the temperature a little above this dew point, and go from there. I rarely need a dew heater, as I image from the desert Southwest. But on several occassions, there has been a nice layer of frost on my equipment cases, where the scope & objective are completely clear. As I mentioned in a post below, this system is not as advantageous on scopes with larger f#. It's also not needed on carbon fiber tubes, since the CF expansion coefficient is very small.
Thanks for your interest. I appreciate you taking a look.
As you stated, telescopes focus points change over temperature so one way to minimize this is to hold the telescope temperature constant over time. However, as the temperature drops during the exposures, this will cause thermal air currents of increasing strengths to be present around the telescope which are not desired.
This becomes more critical with longer focal length scopes, as they provide more magnification for any given imager.
A different solution to this problem is to use a micro focuser which actually makes minor focus adjustments that are intended to compensate for the shift in the focus point of the telescope. This way, the main body of the telescope is allowed to vary in temperature so it will be close to the ambient temperature and generate fewer thermal air currents.
As you are no doubt well aware, if the objective lens of the telescope is cooler than the dew point, moisture will soon form on the objective lens which is highly problematic. The addition of a heater which only heats the objective end of the telescope to that necessary to keep it just above the dewpoint allows imaging with minimal thermal air currents being generated.
You may find that you would get sharper images with such a setup, at the price of a more complex system.
Hi araasch, You're right about the degrading effects of thermal gradients. This was definitely a consideration during the initial though processes. But with an aluminum tube, and careful management of the temperature, the internal volume seems to come to thermal equilibrium fairly quickly. The key is to keep the temperature differential small. I typically keep the system just above dew point. Regardless, I get pinpoint stars from my first exposure through my last. So this leads me to believe that any thermal gradient effects must be less than the resolution of my system (3.5 arc-sec/pixel). I have no problem resolving single-pixel stars, all night long.
You also made a good point about the effects being magnified on tubes with longer length (larger f#). However, this focus management system would not be as advantageous on larger tubes. An f10 scope would have a CFZ 4x that of an f5 scope. So thermally-induced focus issues are much less of a problem. In the build instructions, I mentioned that I was having focus shift issues within the window of my 30 minute exposures. An f10 scope would be far less likely to experience this.
The larger the aperture, the more sensitive your system will be to thermal gradients.
This is becase the light rays entering the aperture of the telescope are essentially parallel with one another. So, you can think of the section of atmosphere that the telescope is looking through as a cylinder with a diameter equal to that of the telescope's aperture. The length of this cylinder extends to the limit of the Earth's atmosphere. If the refractive index of the air in this cylinder is uniformly distributed and remains constant for the duration of the exposure, you can expect a great photo.
Unfortunately, this will not happen due to two causes, either of which can be dominant. Firstly, the atmosphere can be turbulent due to weather conditions, local terrain, nearby heat sources that heat a portion of the cylinder of air like roofs of houses, etc. This is termed "seeing". And secondly, your telescope may be at a different temperature than the air close to the telescope. If the seeing is otherwise good, having the telescope at a much warmer temperature than ambient can cause the seeing to become poor, especially for large aperture telescopes. The effect of poor seeing from either of these sources is to have the atmosphere act as a time-varying lens which changes the direction a particular light ray enters the telescope by a small amount. If the shifts are uniform across the aperture, the telescope will likely act as if it was pointed in a slightly different location for an instant, if it is not uniform, the contrast of the image suffers as the telescope is effectively pointed in multiple locations simultaneously.
The higher the magnification that you are using a particular scope at, the worse this effect will be.
This leads to some interesting situations where on some nights when the atmosphere is especially turbulent, people using large telescopes want to pack their stuff up because what they see at the eyepiece is a jumbled mess, while those using smaller diameter scopes can still continue to observe, as they are sampling a smaller volume of turbulent air with their telescope.
For non-local seeing problems, adaptive optics have allowed ground based scopes to eliminate much of this atmospheric turbulence.
But it is still a good idea to minimize the temperature difference between your scope and the local ambient temperature.
I looked at your photos, and I agree that this is not a problem for your scope, however. The fact that your scope is a short focal length and has a small aperture allows this solution to work fine for you, and in that regard may be quite optimal.
Bottom line, if you are getting round stars that are point-like, you can't be too far off the mark!
P.S. If you want to see the effects of localized heat induced air currents, look through your telescope at a moderate to high power (150x or so) while observing a bright star well above the local horizon (45 degrees or so). Defocus the star a bit so you see a fat star, then place your warm hand near the telescope objective so the heat from it will rise through the air cylinder it is looking through. You should see the effect very clearly.
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