Part 3: Selecting a solar telescope

Before I purchased a solar telescope, I had seen images from them but knew nobody that could advise me of what to look for, how to choose or even offer advise on which scope to buy. So I searched far and wide for information, unfortunately there were very few good reference points to help me select a scope.

I did the best I could and chose the Coronado Solarmax II 90mm scope, it is a very nice telescope overall, good size / weight, great views,etc.

Sunspot and photosphere as viewed in the Solarmax

However, if I was to buy it all over again, I might have made some changes.

First I will start with important considerations:

To double-stack or not to double-stack, that is indeed the question:
- I purchased a single etalon (filter) on a 90mm aperture.
- A dual-stack (double etalon) will offer a lot more detail, based upon images I have seen, perhaps up to double the detail as you will get more contrast from the double stack. The contrast comes from the length of wavelength (angstrom) you allow in the scope. For instance my scope has a >.7 angstrom bandpass. Normally a double-stack scope allows in >.5 angstroms, so less light equals higher contrast as less energy is hitting your eye or the camera sensor.
- The double-stacked scopes are about double the cost as well, my suggestion is to trade aperture for double stacking! Spend as much as you can, but if you can get a smaller double-stacked scope, go for that one instead of the larger aperture single etalon scope.

Type of focuser:
This is an important one, that is very hard to get enough information about.
There are two types of focusers that come with solar telescopes:
- Dual-speed crayford types
a) these types of focusers can be used to obtain exact focus, simple and very intuitive to use.
b) they also have smaller focal travel, so you may have to add on extensions to increase the focus capability.
- Helical focusers
a) these types of focusers are much more difficult to use, requiring manipulation of two sliding focus tubes (one for course, one for medium focus) and then a circular focus knob for attaining fine focus.
b) they do have a longer image train, so you don't need to add extensions to the image train.
My suggestion is to find a scope with a dual-speed crayford style focuser, it is much simpler to adjust focus with these types of focusers. When your out in the Sun and covered by a sunscreen to block the sun so you can see your PC screen better, you will thank me for it.

Aperture: How much is enough?
This is a good question that many astronomers face constantly, this is commonly referred to as 'aperture fever' because it seems you never have enough and always want more. :-)

FOV of Solarmax II 90

For viewing the Sun, this becomes even more interesting as the Sun is a relatively close and very large target.
I find that I like to take my solar scope with me a lot, because as long as it is not cloudy outside, you can pretty much view from anywhere.
The question you need to answer is: are you primarily a visual or photographic user?
- If visual, larger apertures will offer amazing views and lots of detail.
- If photographic, the larger aperture will restrict your Field of View (FOV) to a small portion of the Sun.

Blocking Filter:
This is one that many people don't really consider (myself included). The Coronado offers many different model numbers of blocking filters, here is the difference:
- BF5 - this one is predominantly for visual use, it comes contained in a diagonal with a 1.5 in barrel
- BF10 - this one is ok for visual / ok for photographic, it also comes in a diagonal with a 1.5 in barrel
- BF15 - this one is ok for visual / great for photographic, it also comes in a diagonal with a 1.5 in barrel
- BF30 - this one is tuned for photography but is ok with visual as well. This blocking filter comes inside the telescope, with a 2 in opening. This allows you to either place a 2 in diagonal on the scope or use a camera with a 2 in aperture in prime focus mode.

Recommendations:
1) I would not buy the BF5 or 10 if you plan on doing any photography
2) I would buy the BF15 if I planned on doing 'web cam' photography (this is the one I have on my scope), I have found it difficult to find a way to mount my 2 in aperture camera on this 1.5 in diagonal.
3) This one is interesting in many ways, you have the flexibility of using 1.5 or 2 in aperture cameras and you have a larger blocking filter so more light will enter the camera. However, it appears that the blocking filter is inside the telescope inside the focuser, this may be problematic if you plan on moving from a helical focuser to a crayford style as you will have to find a way to remount the focuser (afaik).
I will likely stay with my BF15 as I look to modify my focuser to a crayford-style (as soon as the warranty expires) :-)

Well, there you have it, overall I am pretty happy with my scope. In the future I will buy a second etalon (double-stack it) to add contrast and detail and change the focuser to a crayford-style to make it simpler to focus.
After all, you cannot be in this hobby without continuing to dump cash into your setup. :-)

I am always happy to answer any questions or share my experiences on the subject.

Clear skies!

Part 2: Viewing the Sun safely

Continued;

In the previous post Part 1: Viewing the Sun Safely I offered information about viewing safely as well as inexpensively. This post will be nothing like the first, except a continued focus on safety. :-)

Here is where it gets more interesting, that is... if you have a telescope:
- Baader solar filters, these are somewhat inexpensive (as solar filters go) and fit over the front of your telescope objective lens. They offer views of white light, which is nice to view sunspots as well as an eclipse. Images captured of the Sun in white light look like the photo below (but this photo is extra cool, as they also captured an airplane transiting the Sun!)

 

Sun via a 'white light' filter

- In this same realm there are also glass solar filters, which fit over the front of your telescopes objective lens and offer similar views as found in the white light solar filters. Some of the glass filters have a tint to them that makes the Sun look orange-ish instead of purely white (or light blue).

Filters of these types normally run anywhere from $80.00 - $200.00.
Generally these filters are very safe as long as you follow these rules:
- check the filters before you put them on the telescope, by looking at the Sun with the filter, if you notice any spots of bright light (eg: a pinhole), take the following action, depending on your filter type:

1. If mylar, take a piece of small black electricians tape to cover the pinhole
2. If glass, take a black 'sharpie' and fill in the part that is scratched or otherwise damaged

Now it is about time to hit your wallet hard... be prepared! :-)

There are telescopes that are dedicated to viewing only the Sun, these scopes come in two major varieties:
- Hydrogen Alpha - tuned to the wavelength of 656.281 nanometers, this telescope is great for capturing surface features as well as prominence.
- Calcium Potassium - tuned to capture waves at 393.4 nanometers, this type of filter is really good for capturing magnetic phenomenon.
Both of these types of specialized telescopes come in various sizes and thereby prices. The Hydrogen Alpha (HA) scopes are easier to come by as they are the most popular.

I own a Coronado solar telescope (HA), which I used to take photos like this:

Solar Prominence

There are many vendors for these types of telescopes, the most prominent vendors are Meade (Coronado) and Lunt Systems. Both of these vendors make fine solar scopes, so you will not do bad with either.
 In part 3, I will offer my observations on Solar Telescopes and photography.

Clear Skies!

Viewing the Sun (safely): Part 1

With the on coming annular solar eclipse this weekend (May 20th 2012), I thought it would be good to write about the Sun.
I have been doing a lot of solar astronomy of late, that is viewing the sun through a telescope.
Many people ask me 'how do you look at the sun, isn't that dangerous?'

The answer is:
Yes and No... let me explain.

• Yes, it is dangerous if you do not have the proper equipment, just looking at the sun through a telescope without the proper filters is a good way to permanently and completely damage your eyes. Even with the proper filters, great care should be taken to ensure the filters are in good condition.
• No, it is not dangerous if you take the proper precautions and have the right gear.

So lets start with the gear:
There are many things to choose from, some very inexpensive and others well.. let's suffice to say that Astronomy can be (but doesn't have to be) a very expensive hobby. ;-)

Inexpensive items:
- Solar viewing goggles, the ones pictured here can be purchased at Amazon.com (albeit they are pretty expensive for what they are. Of note, these are not the most fashionable eyewear, however, they allow you to view for longer periods as they are 'hands-free'. (http://www.amazon.com/Eclipser-Viewing-Glasses-Double-Alumunized/dp/B007XKWL7U/ref=sr_1_2?ie=UTF8&qid=1337146524&sr=8-2)

Solar Viewing Goggles

- Solar viewing card, the card pictured below is actually quite inexpensive, but cards are harder to hold up for longer periods of time. (http://www.amazon.com/Eclipse-Viewing-Sunspots-Transit-Hand-held/dp/B007R7A4T6/ref=sr_1_1?ie=UTF8&qid=1337146697&sr=8-1)

Solar Viewing Card

Continued in part 2

DIY Coronado SolarMax mount plate

I have always been interested in viewing the sun, even with my first telescope I had filters that allowed me to see sunspots, but there is so much more to see with the sun. So, I recently purchased a Coronado SolarMax II 90 from OpticsPlanet.
The scope came with a nice case, several eyepieces, a barlow and a clamshell mount with a solranger spotter. What wasn't apparent at the time of purchase was how it would mount to my CGEM, there was no mention of anything outside of the clamshell mount.

So here is what I did to mount the scope:
Purchased the following:
- Aluminum door threshold ($9.99)
- a pair of knobs ($2.00 for the pair)

I measured the maximum width the CGEM mount would accomodate and decided that 3 inches would be about the right size for the width of the mount plate, to ensure that the mount head screws were firmly seated in the mount, you wouldn't want them to pop out or strip while your scope is mounted. ;-)

Next I cut and removed burs from the mount plate:

As you can see above, I also drilled out two small holes at each end to hold knobs used to secure the plate from accidental slippage off the CGEM mount head. You can also notice three holes I drilled to mount to the provided SolarMax clamshell.

Above is a side shot of the bottom half of the clamshell mounted on the new mounting plate and I inserted the safety knobs as well. Note: the safety knobs were installed on the bottom of the mount in the final procedure, this makes them act as a safety catch in case the mount slips from the CGEM mount head, keeping your scope off the pavement.

I painted the new mount plate a semi-gloss black to kind of match the CGEM as well as the black parts of the scope. In the image below you can see it mounted to the CGEM and scope mounted on it. You can also see the placement of the knobs and see how they might be helpful if the mount starts to slip from the mount head.

The image below shows the mount and scope as it is tracking the sun.

Here is a link to my first light video I got from the setup:

http://www.youtube.com/watch?v=MPKJ_DzhsVE

I used an Orion Starshoot Planetary imager for this image, I will be creating a way to mount my other cameras that should provide a greater level of detail than the 640p image provided in this imager. I found that the level of detail provided in the video is about 100x less than what you are able to see visually. If you have never looked through one of these scopes... it will take your breath away.

As a final note: I was initially somewhat concerned about the stability of the choice of materials, but after hours of visual use, tracking for 3 hours and my first video, I believe the mount plate will prove to be a very acceptable part of this setup and at about 6x less cost than a mass produced mount plate.

Happy Photon Hunting!



Bahtinov Mask and Imaging

One question that I get asked a lot is:
- How do you know when a star is perfectly focused?

When attempting to focus on a star, the range of focus can be somewhat large, meaning that the difference between perfect focus and out of focus can be very visually challenging to discerne. This is true of visual astronomy, but even more difficult and time consuming in astrophotography.

There are many ways to obtain a perfect focus, one of my favorites is to use a tool called a Bahtinov mask, which fits on the front of your telescope over the aperture.
If you are performing visual focusing with the mask, just point the telescope at a bright star and you will see diffraction spikes emanating from the star as you look into your objective lens. You can then adjust the focus of the telescope to create a perfect diffraction image, where the spikes are completely in alignment.
Here is an image of what the alignment should look like:

In the image above, you notice three diffraction spikes per side of the star, the objective is to align the center spike so it is equidistant from the two outer spikes. If it is closer to either side, then the image is out of focus. This is a very simple procedure if you are looking to focus for visual astronomy, however if you are attempting to perform this for astrophotography, this is where some challenges emerge.

Here are some tips that I use when attempting to focus with the mask on a live camera image:

Getting good diffraction spikes:
1) If you are attempting focus with a camera and Bahtinov mask, you will need to increase the time of the image to ensure that you capture enough photons to obtain a good view of the star and diffraction spikes. The image above was taken with 30 seconds of exposure, when I took images of 10 and 20 seconds, the diffraction spikes were almost not visible. Experiment to find the right time for your imaging setup to capture enough photons to enable you to see the diffraction spikes clearly, once you see them clearly, note the imaging time and move on. Spending more time per image than absolutely neccessary to see the diffraction spikes is not going to help you achieve better results.

Imaging focus:
2) If you choose a 'focus' routine in your imaging software (such as Maxim DL), the software will have the camera initiate a continuous loop of photos for the duration of imaging time you set (eg: 30 second images), spaced apart by a time roughly equal to the amount of time necessary to download the photo from the camera to the PC. I find this to be less than optimal in most cases as the loop doesn't allow enough time between photos and downloads to perform modifications to focusing. The lack of delay in focusing, may make you waste a bunch of time making 'blind' focus changes thereby increasing the time spent focusing.

Instead I choose to shoot a single photo, see what focus modifications need to be made, make the adjustments and shoot another single photo. I find that this process is generally much faster than trying to work within the 'focus' routine.
For example, using the 'focus' routine I will spend roughly 15 minutes attempting to gain perfect focus, when using the single shot method, I usually have focus within 5 minutes. (given 30 second image captures)

Reducing setup time:
3) Once you find great focus on your camera, you may want to remove the camera and insert an eyepiece with a focusing ring into the telescope. The concept here is to move the eyepiece around until you have a very clear picture of the stars without changing the actual focus of the telescope, essentially giving you the same image visually that you had while taking photos. Once you obtain focus, you then lock the focusing ring in place around the barrel of the eyepiece. This makes the eyepiece parfocal with the camera, allowing you to use your eyepiece to move between objects to image without having to repeat the focusing of your camera.
When you have a parfocal eyepiece, it can be used to gain an initial setup for your telescope without moving your focus, making it faster to get to the fun stuff and away from additional setup time.

In summary:
The Bahtinov mask can be a very effective tool for obtaining great focus, leaving you with very tight round stars and clear shots of your intended target. Taking the time to learn how to most effectively use it in your setup routine can shorten time to imaging, which is time well spent in my book.

Notes:
1) In order to facilitate removal of the mask after focusing and not getting fingerprints on the primary objective lens of my SCT, I placed a couple of small zip-ties on the edges of the mask, they are not in the light gathering path so they do not affect the images and they make the removal of the mask a very simple task in the dark. (Photo below)

Homebrew: Dew shield (day 1)

I decided to build a new dew shield for my telescope.
Why you ask? Because I thought it would be an interesting project and I didn't have one for my CGEM.
I plotted out what I would need to buy to complete the project, here was my shopping list:
- 24 inch wide aluminum flashing, this is a very light and flexible material (not sure if it will be rigid enough, but a good first try :-))
- flat black spray paint, for both the inside and outside of the dew shield
- pop rivet set (black pom / hand rivet tool)

At a minimum this should give me a very light, dew shield that will protrude about 24 inches from the primary objective lens. Offering a good amount of both dew and ambient light blockage.

I am a little worried about the rigidity of the aluminum, but getting it cut and formed will tell me a little bit more about the material and it's weaknesses.

Happy Photon Hunting!

Any night is a great night for Astronomy

Tonight is June 15th, the moon is in the Waining Gibbous phase, meaning that it is illuminated at about 99.73 (or so) percent, pretty much a full moon to most people. That means that there is so much light in the sky that you can only see a handful of stars. The moon is also so low on the horizon that it is pretty much unable to be viewed in my telescope.

About now you might be asking yourself, so why is Ken saying that any night is a great night for astronomy? He can't even see a thing through his telescope because of all the light of the moon and can't even see the moon due to tree coverage.

Let me let you in on a little secret... Shhh, don't tell anyone, but...

Astronomy is a hobby that requires instruments, some that are as in expensive as a set of binoculars, while other instruments may be as (or more) expensive than an automobile, but they are all instruments and just like musical instruments or other scientific instruments, they take practice and sometimes tuning to ensure optimal performance when you need them.

So being the boring guy that I am, I took this evening to do a couple of fun tuning activities for my scope, here is what I did:
1) I checked mechanical zero against my mounted optics to make sure that everything was aligned and operating as it should.

2) I tried out my brand new dew shield, one that I designed and fabricated myself out of lightweight aluminum (worked as expected, but saw some areas of improvement that I will work on this week).

3) tested my optics for collimation, which to my surprise was remarkably aligned, about as close as one could reasonably expect, can't ask more than that. :-)

4) tested the new bhatinov mask that I fabricated for this scope, the legs of the stars came out brightly, slowing for pinpoint focus of the stars.

So even though I wasn't able to see some of the skies wonders tonight, I was able to dial in my instruments to a fine level of precision, ensuring that when the moon and the atmosphere provide me more optimal viewing opportunities, I will be ready and able to take in the beauty of our universe, one object at a time.

Happy Photonic Hunting!