Equipment Testing: Meade 8 ACF, APM/TMB 80/600 & Equinox 66ED

The past few days were in real rush! Setting S4, S5 and S7 Physics test papers were exhausting. I don’t know what was going on. Everything seemed came out at once. So many things tempted me to go away from my school duties! The sky condition seemed fairly good, replacing equipment, chance of getting new telescope, chance of trying different telescopes, chance of getting a used top class telescope etc. Finally I squeezed some time for hobby!
The long waited Meade 8” SCT AFC was finally settled! The order has been delayed for many times and I’ve disappointingly waited for half years. Finally I got an offer from a local stargazer who bought this telescope in a special offer given by the local dealer half years ago. The reason that he sold this M8 was that he got another extremely cheap LX200 offer. The M8 ACF he sold to me was very new. It has been used in field, Pak Tam Chung, for once only. I was lucky enough to get it because another stargazer told me about this and I responded fast enough to it, or the chance would go! It is very hard to get a used M8 ACF in Hong Kong. Although he sold me at the same price he paid half years ago, it was still a good price and it healed my pain at once! Last night, the sky condition was so so. The transparency was ok, but the seeing was bad. With clouds running around, I could hardly catch a few moments to look at Jupiter. Nothing could be concluded, but the M8 worked. The maximum magnification I tried was 2000/9 = 222X.
Another encounter was the trial of the APM/TMB 80/600 APO. I went to the Sky-watcher dealer and replaced the long tripod with a short tripod for the EQ3Pro. Sky-watcher is certainly a homely-made like manufacturer. Their product specifications change from time to time and even their dealer doesn’t know it! Their product specifications can be modified according to requests! This is odd, but flexible right! I am an efficient guy. I know the dealer got a used APM/TBM 80/600. It would be nice if I can have a look at it before it was sold to somebody else. I deliberately arranged the tripod replacement and the glance of the APM/TBM APO in one go. Ha Ha! In fact the main course was the APO… Well, it was daytime, I did the terrestrial observations only. The first eyepiece I tried on the APM/TMB 80/600 was 25mm Aspheric Orthoscopic. When you look through the eyepiece, the feeling was WOW! The image was so sharp and the contrast was so high. The image was sharp to the edge of the field. This telescope was the best I’ve ever seen for terrestrial observation! I cannot imagine what will happen if I use the APM/TBM 203 to do terrestrial observations! The color tone was warm. The Aspheric Orthoscopic gave good eye relief and the field was reasonably wide. The viewing was so pleasing and comfortable. When I put the 16mm TBM Super Monocentric, which is supposed to be a top planetary eyepiece, the off-axis image was a bit blur. However, the image around the principal axis was extremely sharp and of very high contrast. The color of the Mono was not as warm as Orthoscopic. I didn’t have the chance to compare these two eyepieces on viewing stars side by side that day. I couldn’t comment which one was better for stargazing. It would be nice to do it later. Finally I tried the 13mm Ethos. There is no need to mention about its field of view. The viewing was very comfortable. The image was sharp and the contrast was high. I couldn’t tell the difference in sharpness between Aspheric Orthoscopic and Ethos. Both are very good eyepieces, which need longer observation and being tested to differentiate. Again I was in a rush to go! So try again next time.
I borrowed the Equinox 66ED from the dealer for a short period of time. I tried it in daytime recently. A first look at this little scope, it inherited the beauty build of Equinox series. I have tried Equinox 80ED and 120ED, now the 66ED. The only Equinox I didn’t try is the 100ED. Well, the optic of this scope was good. I used Skywatcher eyepieces and Tele Vue 2.5X and 5X Powermates in the entire testing. For daytime terrestrial observation, if the magnification was below or equal to 400/5 = 80, the color, sharpness and contrast are very good. It doesn’t mean it will breakdown when the magnification goes beyond 80, but will not be too promising to use it for birding or other terrestrial observations as the contrast and the brightness are low. I tried to boost the magnification to 400/8*2.5 = 125X and 400/15*5 = 133X respectively. I was able to see the price tag of a fruit store. I guess the characters’ size was about 5cm and the store was about 1.5km apart. A quick estimated resolution to achieve such an observation is 5X10^-2/1.5X10^3 = 3.3X10^-5. The Rayleigh resolution, theoretical maximum, is 1.2X550X10^-9/66X10^-3 = 1.0X10^-5. It is not bad right! However, if it is used for stargazing, the magnification can be boosted further since the background is much darker. It all depends on what celestial objects you are going to watch. For the 200X, I tried in different settings, 400/2 = 200X and 400/5X2.5 = 200X. The 400/2 = 200X gave a slightly better performance in terms of sharpness and contrast. At such magnification, the contrast was very low. However, the image didn’t breakdown completely. One could still see some details. The corresponding magnification per inch is above 70X. It is a good figure already. I owned a small achromatic refractor, Meade ETX 80. Its optical performance cannot be compared with Equinox 66ED in terms of chromatic aberration and resolution. To be fair, the price of ETX70 was just a few hundred. Although optically it is a loser, it is a best buy.

No comments:

Post a Comment