Telescope Reviews: Small refractor vs Larger Aperture Results: M104

For newbies and those just interested, I am providing links to sketches in this post with 2 different setups to give folks an idea what can be observed and enjoyed but also to see the advantages/disadvantages of aperture (or lack therof). First, realize that small aperture with astro-video cameras is delightful and portable, so we use it. But larger aperture does magnify detail and give you lots to look at--albeit with a narrower field of view. I use both, but the explanation and the sketches may give readers some comparative idea of what can be enjoyed for typical Messier objects. Last introductory note: the small aperture example in this case was under conditions when most EP folks close up shop because the detail of what they want to see is too washed out by haze and clouds. But, that is the joy of using astro video: if the conditions are marginal, one just keeps on truckin'.

SETUP #1: SV102ED (4 inch ref); MallinCAM Pro Dob Video Camera with focal reducer and extension but zoom on (net Mag: 132X); 14 s integration with AGC @ 40% scale; poor viewing conditions
SKETCH: M104 June 2008

SETUP #2: 12.5 inch f4.5 Dob with platform; MallinCAM Hyper Color with focal reducer and set at 14 s integration; AGC not recorded but probably 1/3 scale
SKETCH: M104 Sketch - Spring 07

Notes:

1. Note that the images are inverted relative to each other. Note the star just above the 104 nucleus on #1 and the star seemingly partially immersed in the nucleus glow in #2. This is the same star so it gives you an idea of the difference in the extent of the galaxy that is pulled out. While the cameras and setups are different, the Pro Dob chip is pretty sensitive so it is comparable in sensitivity. Since I was using 14 s integration with nearly 1/2 scale gain, the galaxy is still nicely pulled through the sky conditions. The basic shape and dust lane could easily be seen in both. In short, 4 inches does pretty well with the camera; 12.5 inches of aperture (I remember the night) nearly blows you socks off with more detail and a bigger image. With 12.5 inches aperture (and a bit better camera--the Hyper Color) I could see a much more robust galaxy shape and extent.

2. The width of the dust lane widens at the east end of the galaxy (our "eye" point of view). The widening is detectable with both setups. In contrast, this is hard to see using eyes and a good EP with 4 inches of aperture. See O'Meara's description in his wonderful book on Messier objects. He is a better observer than I am and provides an excellent description of what he can see with his 4 inch f/5 Genesis refractor and good EPs. The dust lane is hard to define with eyes alone with a decent amount of contrast.

3. If you look closely, you can see "knots" in the brighter side on either side of the nucleus of my sketch with the 4 inch setup. O'Meara makes note of them; I can see them easily with Setup #1 but they were almost washed out (too much integration) on Setup #2. I was not as experienced sketching in Spring 07 so I am sure I could have found them and studied/sketched them if I could do the observation period again. Suffice it to say, however, that the 4 inch does respectably well -- especially under the conditions of high clouds that were reducing the camera's ability to deliver an image I could study and sketch.

4. Aperture helps detail; small aperture provides lesser detail but a nicer field. So, no surprise, which setup you use depends on which object you want to chase down. It was enjoyable to see 104 hanging among the stars; the view is not possible with my 12.5 f4.5 setup.

4. Note the M13 sketch at the bottom of the top sketch (done with the 4 inch refractor). With poor conditions, I consider the view pretty good. On a good night last year with the Pro Dob on M13 and using the 12.5 Dob, we could count over 900 stars. When we did that, 4 people counted 1/4 of the clock area, we averaged, and multiplied by 4. To me, that is really good. Again, aperture delivers resolution ability and the camera captures the advantage. Of course, 4 inch does good too and provides better field of view (see the first sketch). I did not see near as many stars, but still saw a pleasing view and was able to "map" the surrounding field. With the 12.5 Dob, the field is much reduced.

None of these comments should be a real surprise, but it serves as a reminder that the heavens can be enjoyed under reasonably wide conditions with astro video tools using nearly any aperture. There are advantages to small and large aperture depend on the object one wants to examine. This summer, I will choose the 4 inch refractor to map and sketch the big nebula in Sag. but use the 12.5 to get details of the dark lanes and features in certain places in the object.

Enjoy your video cameras. In case anyone wonders how this much detail can be seen, I recommend getting a sketch pad and start sketching because it encourages more than a glance at these wonderful sky objects.

Clear skies.

Roland