Pushing C90 to the limit (7:15-7:45p,22-Oct-98)

After the purchase of the 6.3mm Celestron Plossl, I've just observed with the C90 for once only and on that night, my two favorite planets were gone from the night sky. Therefore, I've only used 159X that the 6.3mm offered on the moon, while it's breath taking already for a relatively
new amateur like me.

After getting my Ranger, I've put aside my C90 for the quality difference is quite large and people are likely to neglect their old lovers when they are having new ones. While several days ago, I've decided to place my C90 in my office so that I can go up to the roof when the weather is nice. Now, the C90 got its unique position.

Tonight, it's virtually the first observing session after the purchase of my Ranger. I always have an idea in my mind, and it is to use the 6.3mm with the barlow in my C90. I guess people always want to try higher power. With the 6.3mm with the Orion Shorty Barlow in the C90, I can get 317X which is far beyond the ability of the quality and the aperture of this small scope. The manual states that we can push it up to 210X, while I have no way to verify it. I've only a 12mm and it yield only 167X and the next step is 317X.

I tried the C90 on the Jupiter first. At 40X with the 25mm Celestron SMA, Jupiter is a little disc and all the Galileo Satellites are in the view. With more experience, I noticed that there're servere chromatic abberation. I guess the major source of this error, is from the eyepiece.

I tried to use 83X with the 12mm Celestron SMA, I could see two cloud bands, but they were not as contrasty as in the Ranger (76X with 6.3mm Celestron Plossl). Central obstruction? Less perfect opticals? I guess both.

Next, I tried out the 12mm Celestron SMA with the barlow. It yields 167X, and the view was alright, but again, not as contrasty as that with the Ranger at similar magnifications. Later, I tried to use the 6.3mm with the barlow, i.e. 317X. Oh! I got a fuzzy disc of light. I just couldn't improve the view by turning the focusing barrel. I would say there're two reasons: first of all, the limit for this little scope is exceeded; second, the focusing mechanism is bad. Okay, at least now I know what's meant by "the image is broken", and how blurry the view can be, if the optics is pushed too much.

My next target was the Saturn. At 40X, the view is so nice. The ring was clearly visible, and I could see the gap between the ring and the little disc. Then I tried it at 83X, great! The disc is larger and things seem to be clearly. By pushing it higher to 167X, no more detail could be detected, while again at 317X, I couldn't even obtain a clear image.

Now, I know that it takes better seeing to see if I could get 317X for the C90, however, I guess it's unlikely. Maybe I should proceed to use higher magnification on the Ranger, since Tele Vue tests each Ranger up to 300X, and people reported that they could push it up to 500X in good
night. My plan is to push the Ranger to 240X by purchasing a good 10mm eyepiece, with the 5X Tele Vue Powermate. One sad thing other than the confirmed fair optics of the C90 is that, I forgot to look at the Andromeda Galaxy, which was planned originally.

7:15-7:45p, 22-Oct-98, By So King Yan Oldfield