Spoiled

It had to end up this way at last. A friend of mine finally completed his 18-inch Dob project, and yesterday night I had the chance to look through it for the first time. I have never looked through anything bigger than my own 12.5-inch before, and until now I have considered this to be a pretty large aperture. The leap to 18 inches gives a gain of one step on the magnitude scale, and of course it was very exiting to make the first views with it.

Of course such a large beast takes some effort to set up, and a ladder is often needed to reach the eyepiece. But still I found it surprisingly easy to use, and it was smooth and stable.

We observed quite a few objects, and I'll mention just a few ones here.

M51 appeared as on a photograph with this aperture, the only difference being that the direct view through the telescope is much more thrilling. The amount of detail is significantly larger than what can be made out with the 12.5-inch.

M101 was even more beautiful with several foreground stars, and with the emission nebulae in the spiral arms very bright and clear.

I have always paid much attention to the NGC3190 group in Leo. With an 8-inch scope NGC3190 and 3193 are not difficult to see. NGC3185 is quite difficult and NGC3187 is hardly visible with 12.5-inches of aperture. In the 18-inch all galaxies were clearly visible, the orientation of 3190 and 3187 being almost equal.

I have tried to make out the spiral structure of M99 with my 12.5-inch, but without success. In the 18-inch the spiral arms were easy to see.

In the Coma cluster the two giant ellipticals in the centre are within range for 8- and 12.5-inch scopes. Seeing more is very difficult. With the 18-inch an enormous number of faint smudges were distributed over the field of view. It is very facinating to contemplate over the real nature of those faint light spots. Hard to imagine, really.

We also observed some of the great star clusters. M13 was, of course, awesome. M37 was a very beautiful view, and seeing individual stars in distant NGC2158 (edge of M35) was not difficult at all.

I'm a bit worried about how it will be to return to the 12.5-inch after this. The drawback of the big scope is, of course, its size and weight. But the direct view of a galaxy like M101 with such an aperture is to die for. And I positively know that there are bigger scopes out there....

Inge S

Hello:
I think that I understand what you mean. But I also think that I am much more spoiled. I also have a 12.5" scope, and really enjoy using it. But, on 2 occasions, I have been able to look through a 88" scope at anything I wanted for a few hours. I do wish that more people could see what I have seen. It's truely remarkable what the universe looks like through a really large scope. The field of view is kind of small. The main difference isn't how faint you can see, but the details and colors. Now, everything looks so small and pale. We could resolve M15 to the core, and see the colors of all of the stars. NGC 6543 (Cat's Eye nebula) looked like a brillliant green rose with a bright orange star in the center. Now and again, I thought I could see surface detail on Neptune (the seeing wasn't that good). A friend of mine, however, got to look through a 315" (8m) telescope. Now that would really be something!

Cheers
Mike Connelley
-who's also thinking about building a larger dob...

Inge,

I enjoyed the descriptions of your observations. I am particularly moved by your comment about the real nature of the enormous number of faint smudges of light in the Coma galaxy cluster. Each a separate GALAXY, with billions of stars. What can be out there among them?

This feeling alone could make getting a bigger scope a necessity.

Ahh, aperture fever . . .

Perhaps you can gain a little consolation about going back to your 12.5” in some of your earlier threads. Recall your goal – you like to see something new every session. If you get an 18” scope, there will be infinitely more new things to see, and maybe then you could never “make it around the sky”.

You recall I wrote that I do the same as you with the 12.5” with my 3.5” and 4.5” scopes, only on brighter objects. “It is just as fun and rewarding with my smaller aperture scopes - until I run out of new things to discover.” I don’t know how many years it will take to run out of new things to discover with a 4.5”.

“The direct view through the telescope is much more thrilling” than photographs. Also a wonderful comment. I tend to see long-exposure astrophotos as beautiful but somewhat unreal and inaccessable.

One last idea to think about: how does increasing aperture affect your concept of closely spaced isophotes? I think increasing aperture does the same thing as exaggerating the vertical scale on a relief map or graph. But increased aperture also raises the background light level a bit to flood over some of the lowest isophotes.

Regards,
Rick Wiseman

Last night we made a second session with the 18-inch. The optics (f/5 Swayze mirror) were carefully collimated. Observing conditions were considerably better than the previous night, and around midnight seeing was superb.

We trained the telescope on many different types of objects. Among the galaxies were both bright ones with much detail (M51, M61, M64, M65, M66, M104 and M100) and faint smudges (Copelands septet). M104 is very low in our skies, but it was awesome in this scope, and one of the objects making the strongest impression on me this night. Also the black eye was a grand sight.

The Eskimo nebula in Gemini with a 9mm Nagler and an O-III filter was another highly impressive sight. Now, at last the real "Eskimo shape" was plainly visible, with much of the fine structure in the nebula very sharp and clear.

For me as an avid double star observer, Zeta Cancri, represented the ultimate moment of truth. At a magnification of 380x (6mm Radian) the scope showed a perfectly sharp image. The gap between the stellar discs was wide enough for another disc in between, indicating that this scope would happily handle a 0.4" double at these seeing conditions.

The scope also proved superb on Jupiter and Saturn. Images were sharp with great contrast on both planets, and intricate detail could be seen in the bands of Jupiter.

I do not plan to acquire a big Dob for myself after this. The drawback of such a scope is, of course, size and weight, and even though it was home made, it is a considerable investment. But this experience may influence my future way of practicing amateur astronomy. Fortunately the owner of the 18-inch is a member of our local astronomy club, and I look forward to many sessions where we cooperate. Travelling and trying other people's scopes is another option. And I'm still the happy owner of a grab-and-go 12.5-inch Portaball which is a winner when comes to efficiency and ease-of-use. But the images in the big scope are worth to die for....

Inge S