I need to strongly notify that existing most of telescopes may not have enough opportunity to obtain good images as the telescope's potential. This means, image of your telescope could be drastically improved by correct countermeasure described following against "tube current". The countermeasure may bring you amazing sharp & fine image with only A FEW DOLLARs investment.
See a Jupiter's photo which was taken as my just second trial result of planetary photographing with the countermeasure for the thermal disturbance error (tube current). The picture itself looks not so fine unfortunately because I'm just a beginner of planetary imaging so that I have only poor skill of photographing. But, I can assert that planetary visual on that day was clearly greater than the picture, and it was the best planetary visual which I had never seen.
Actually, that night was not the best seeing condition but a very usual night, so that I could see jet-stream fluctuation caused by air motion on the Jupiter's visual, however I could confirm that the countermeasure succeeded to remove the tube current. Therefore, as a result showed that, Jupiter’s visual image was distorted by jet-stream (seeing) but was SHARP and FINE. I felt my telescope has got 1-2 grade upper resolution compared with before the countermeasure. So that I could enjoy viewing very detailed structures around GRS on the Jupiter.
See the picture of my telescope with the countermeasure, that is very simple. It is that just wrapping the optical tube with silver foil like a space satellite equipment. The foil would have thin in its thickness to obtain better performance of temperature adaptation to ambient atmosphere.
Therefore, “survival insulation sheet” may be the best solution for this, which takes only a few dollars.
The purpose of this sheet is to avoid radiative heat transfer which probably induces strong thermal disturbance in optical tubes.
However my discovery is different. Surely, the heat from the primary mirror causes disturbance, but it is one of factors.
My point of view is radiative cooling effect on optical tube. According to a theory of heat radiation, heat going away to space can be calculated by Stephan-Boltzmann constant. I was awfully surprised by the calculated result of the radiative cooling, which said that over 200 watts(!!) energy was going away from my OTA to space would you believe! This means, it’s heat energy impact is same as putting 200W heater under my OTA. I cannot ignore this effect even though most of general theories on telescope optics ignored it. This effect may be larger than a effect induced by temperature gradient between mirror and air.
Therefore, describing usual case, an optical tube is cooled by radiation, then the tube cools air in it. This heat transfer induces convection flow with density fluctuation which means refractive index perturbation which brings image distortion.
This is a big problem, because 44% light of making image comes from outer thin ring area of main mirror with 1/8 of aperture width, in addition the ring contributes telescope’s resolution limit. In spite of this important principle, the outer ring area is disturbed by the 200W right radiative cooling induced air disturbance.
Therefore, the silver sheet has became one of my essential goods for planetary observation.
The discovery showed a fact that prevention of thermal interaction in an optical tube itself makes big improvement of image disturbance. Surely, turbulent jet-stream at sky altitude affects imaging, that is definitely true, but its influence is not of all.
RESULT
 |
| Jupiter image with the countermeasure 20cm/F5 with SR4 eyepiece, EOS60D DSLR |
The COUNTERMEASURE
 |
| OTA with silver sheet wrapping |
Therefore, “survival insulation sheet” may be the best solution for this, which takes only a few dollars.
The purpose of this sheet is to avoid radiative heat transfer which probably induces strong thermal disturbance in optical tubes.
MECHANISM - Why does your telescope bring distortion?
A very popular belief of thermal disturbance error is that it is induced by primary mirror which has warmer temperature than ambient air then induced convection flow makes the disturbance.However my discovery is different. Surely, the heat from the primary mirror causes disturbance, but it is one of factors.
My point of view is radiative cooling effect on optical tube. According to a theory of heat radiation, heat going away to space can be calculated by Stephan-Boltzmann constant. I was awfully surprised by the calculated result of the radiative cooling, which said that over 200 watts(!!) energy was going away from my OTA to space would you believe! This means, it’s heat energy impact is same as putting 200W heater under my OTA. I cannot ignore this effect even though most of general theories on telescope optics ignored it. This effect may be larger than a effect induced by temperature gradient between mirror and air.
Therefore, describing usual case, an optical tube is cooled by radiation, then the tube cools air in it. This heat transfer induces convection flow with density fluctuation which means refractive index perturbation which brings image distortion.
This is a big problem, because 44% light of making image comes from outer thin ring area of main mirror with 1/8 of aperture width, in addition the ring contributes telescope’s resolution limit. In spite of this important principle, the outer ring area is disturbed by the 200W right radiative cooling induced air disturbance.
Therefore, the silver sheet has became one of my essential goods for planetary observation.
コメント