Shares and cherishes the gorgeous night sky, the everyone's property.
The diffraction pattern of the 8″ LX90AT with the broken corrector plate
The image of the Hadar (Beta Centauri) through the broken 8″ LX90AT. Look, the star image is no longer pinpoint.
Saturn delivered by the 8″ LX90AT with the broken corrector plate. It looks like the Saturn is being engulfed by a black hole.
Now, the main character~
Did you ever try to break your scope before? I doubt you dare. I maybe the first LX90AT user with the cracked corrector plate.
Here the story begins.
If anyone remembered my previous post about disassembling the LX90AT, you should know why I removed the corrector plate. Yes, I dropped a toothpick into the OTA from the visual back. All of the nightmare started from here. I bought a Purosol Optical (PO below) and their microfiber cloth as I planned to clean the corrector plate. In the end, I cleaned the primary mirror as well because the PO claimed that the solution was enzyme based and would not hurt the coating. That’s true, just that the microfiber cloth left quite a lot of fiber behind.
Galileoscope™ is now on sale at USD15 @ Galileoscope official website.
What’s a Galileoscope? In celebration of International Year of Astronomy 2009, a team of leading astronomers, optical engineers and science educators developed a high-quality but low-cost telescope kit. At just USD$15, you can own the Galileoscope which is even better than the one used by Galileo Galilei himself since 1609.
If you’re a computer enthusiast, you must be familiar with the benchmark score obtained from 3dMarks, PC Mark, Everest, PCMark, Prime 95 and so on. Is there anything similar to represent the performance of telescope? Well, there’s is and someone did it in the form of scores too.
Credits to Mr.Yoshida Hiroshi, he has done a review on 75 telescopes. He reviewed them visually and scored them. The photographic performance of the telescope is not taken into account. I would say this is just a reference for you but not solely the factor to consider a telescope.
Before buying a telescope, I suggest you read through the reviews posted at forums like cloudynights.com and most importantly, join a stargazing session with someone who already owned a telescope. You will know better what to expect.
Here you read the rankings, cz-telesco.bbs.coocan.jp
The content is in Japanese, you can use Google translator to translate into English or any other language you prefer.
Image shift and mirror flop are the common phenomena seen on mirror type telescope, especially SCT. When either of them happens, you can see the image through the eyepiece shifting. The reason for these phenomena is the not-so-perfect movement (slightly to left or right) of the mirror. What’s the difference between them?
While focusing, “Image Shift”.
While slewing, “Mirror Flop”.
Both are actually the same thing. When focusing, you are doing the shift of the mirror back and forth, thus you made the imperfect movement and the movement caused the image shift; when slewing, gravity is doing it and it causes the mirror flop.
Before anything starts, I want to explain AA. AA is my own abbreviation, it’s Amateur Astronomer in full.
What’s the common requirement of an AA’s scope? Unless you are a serious AA with deep pocket, you won’t have an observatory that allows you to mount a gigantic telescope inside. Some AA travels to the dark site with his scope or just move his scope from his house to the backyard. It can’t be too heavy. So, portability comes into one of the major considerations. We want to get the largest aperture within the portability.
8″ SCT has it all. For example, my fork mounted LX90 has an aperture of 203.2mm, 2000mm focal length and weights about 24kg. I can carry it around easily. (Not for a marathorn though)
Left: 8″ LX90 of Erwin Kats from Netherlands.
This is an interesting question, isn’t it? I only know about this today and I want to share it immediately.
Larger Newtonian (reflector) has a faster focal ratio. As you know, focal ratio is the value of focal length divided by diameter of primary mirror (aperture). So, that means faster focal ratio telescope has a relatively shorter focal length. Why does a large Newtonian (eg. 8″ Newtonian) have a fast focal ratio? The focal length of the Newtonian and refractor is almost nearly the length of the telescope. If a 10″ (250mm) Newtonian has a focal ratio of 10 (f/10), the length of the OTA is most likely over 2.5m. How can a single person handle such a bulky telescope? That’s why large Newtonians are always built to be “fast”.
What about the small aperture Newtonian? Manufacturer always made them slower and the secondary mirror is directly involved in this matter. When a Newtonian has a large secondary mirror, its focal ratio will be smaller in value. If a Newtonian has a small primary mirror but relatively big secondary mirror, the center obstruction (CO) is too great which will results in lower contrast images as well as observing. However, a large Newtonian won’t have much lower images because its center obstruction is relatively small.
The same theory applies to refractor too.
It’s so interesting to disassemble a telescope especially those have a very precise and big gears. I’ve disassembled my computer since I was 8 and 8 years later I disassembled my LX90. I will tell you how to do so step-by-step. However, take it at your own risk, I will not responsible for any damage done to the telescope. I suggest that you read all the procedures before you do anything. If possible, read one more before you start and it’s advisable to print this article with you or leave your monitor on when you are doing your work.
In the Part I, I’m going to tell you how to disassemble the corrector plate. The photos below are clickable for a larger version.
(1) First, unscrew every screw on the black housing in front of the OTA. There are 4 on the top and 3 at the bottom. The screws have to be unscrewed by Allen Wrench. I have 3 from Meade when I bought the scope.
(2) Afterthat, you have to remove the screws on the ring which have the specification of the telescope. Please make sure that you don’t point your scope down at this moment just in case the corrector plate fall down and result in severe damage.
(3) Caution! Although you have all the screws undone, don’t remove the corrector plate now or you will regret for life.
(4) Now, check whether the Meade engineer made a marking over the edge of the corrector plate and the black housing. If he did, continue to the next step. If not, you have to do your own marking. Make sure that it’s visible!
(5) Do you see 6 pieces of cork slices filled in the gap between the corrector plate and the housing? I suggest removing them before you proceed to remove the corrector plate. After removing them, hold your hand on the secondary mirror (the center obstruction) and turn the scope down. If the corrector plate doesn’t fall down at this moment, try the way below.
(6) You suppose to see 2 big gaps, don’t you? I used a knife which was small enough to fit into the gap and insert it to the maximum (the knife holder may touch the corrector plate now). Use the way that you open a tin with a spoon to remove the corrector plate. I heard a loud “boom” when I successfully remove it. Do you still have the secondary mirror mounted on the corrector plate? You better have it untouched because once it’s removed, you can’t put it back precisely. You have to call UPS and pickup the item back to Meade. Haha… Frankly speaking, I did remove it accidentally. Luckily, I made a marking on the screws that hold the secondary mirror. Luck really plays an important role. I was able to put it back almost the same as before.
(7) Okay, the corrector plate is removed. What shall I do next? I did cleaning of the corrector plate and removing of a toothpick which was ACCIDENTALLY dropped into the OTA via the baffle tube.
(8) Let me show you the back of the corrector plate which faces the primary mirror.
(9) No more, I am going to put the corrector plate back now. I restore the cork slices first. Wish you a happy removing! 
1200th comet discovery of SOHO (Solar and Heliospheric Observatory) spacecraft was found by a Chinese amateur astronomer, Bo Zhou. The SOHO No.1200 was a tiny, diffuse, and very faint object. It’s detected in images taken with the spacecraft’s LASCO C2 coronagraph which he downloaded.
From this, we know that we don’t have to own a telescope to do researches or findings. There are quite a number of “virtual telescope” among the internet. I will try to collect as much as possible to benefit those who can’t afford to buy a research grade telescope.
I will create a page of the collection and more virtual telescopes will be added.
The magnitude of faintest star you can see with the telescope is called Limiting Magnitude. The limiting magnitude is directly related to aperture, where larger apertures allow you to see fainter stars. The atmopheric condition often reduce the limiting magnitude.
Photographic limiting magnitude is approximately two or more magnitudes fainter than visual limiting magnitude.
M: Magnitude (constant)
D: Diameter of primary mirror (cm)
Bad Behavior has blocked 452 access attempts in the last 7 days.