There are also two mirrors used, the first one is C8, Shika; the second one is the MEWLON210 on hand, Cassegrain. In spite of this, the adjustment of the optical axis of the catadioptric has been ineffective, and there is basically no adjustment. There’s nothing to do tonight. I calmed down and carefully experienced the adjustment of the optical axis. The result really made me adjusted to a relatively regular concentric circle at about 600 times. Now I have some experience and experience accumulated with the return mirror. Let’s share:
1. Adequate thermal balance must be performed to adjust the optical axis: I have never experienced the importance of thermal balance like today. Today the sky is not completely dark, and Jupiter is very bright at about 30 degrees above the horizon, so I lifted out 210 for observation. I have never seen such a bad Jupiter. It is basically the same as a hedgehog ball. It is almost in a defocused state. The cloud belt can only see the thickest one, and it also appears and disappears from time to time without any details. After careful analysis, the first reason is that Jupiter is too low and the airflow has a large influence. The second reason is that the optical axis may be inaccurate, causing the aperture to shrink and sharpness. The third reason is that the heat balance is not performed. To confirm this, I took out the TMB115 and looked at it again. Although it is not as spectacular as Jupiter at the zenith, it can at least be in sharp focus. After comparison, 210 really shouldn’t have such a bad performance. It seems that the main reason is the problem of thermal balance.
Today’s weather is cool and the wind is relatively strong. With the 210 open lens barrel, the heat balance is also fast. Before the heat balance, the star-point defocused diffraction circle is in the shape of five stars. It is impossible to see the concentric circles at all. It takes half an hour. Basically, the diffraction circle is relatively stable, but only the inner circle and the outer circle can be seen. The more thorough the thermal balance is done, the more stable the diffraction ring, and the more advantageous the adjustment of the optical axis. In the first half an hour of thermal equilibrium, I can barely distinguish the diffraction circle at 200 times, but it cannot be adjusted at 400 times. However, as I continued to toss, the final mirror thermal balance should be said to be quite sufficient, so I achieved a victory in the final stage of adjustment.
2. Choose a good goal: In the past, in order to save trouble, the lights on the ground were used to adjust. However, even if the light is a few kilometers away, the details can still be seen under the high magnification of the telescope, so this approach is very undesirable. Last time my 210 was adjusted with the help of the farthest ground light I could find. At that time, the diffraction circle was already very regular, but today, when I look at the real star points, it is obvious that they are not concentric. This also shows that if it is not a perfect ground For the light source, you must choose the real star point, otherwise you can only adjust the worse.
Also pay attention to the choice of star point. Through my repeated comparisons, I found that bright stars are inappropriate, and the beating of the diffraction circle of bright stars will be more obvious, which is very unfavorable for identification. The best effect should be faintly visible to the naked eye. The brightness in the finder mirror is moderate and there is no burr. Astral. The diffraction ring of this kind of star will be faint at high power, but it is much more stable, which is good for discrimination and adjustment.
refractor