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Mika Luostarinen - Instruments
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My current set of observing equipment is shown in this page. I do majority of my observing with my old (1999 model) Meade 10 inch SCT telescope but I also use a smaller 6 inch Maksutov-Cassegrain and even smaller Scopos 66mm ED-APO refractor in my observing. This set of three telescopes complement each other quite well and I usually select the instrument based on the target I am observing.
The small 66mm refractor has a wide field of view (FOV) and it serves me well when I want to observe relatively bright binocular targets ie those variables which comparison stars are relatively far away from the variable. The SCT is the best instrument when I need to observer dim targets (lets say below 12-13 magnitudes) and the Maksutov is a good instrument for mid-range targets. Optically all these telescopes are either good (SCT) or very good (Maksutov, ED APO). I have noticed that the limiting factor for image quality is not the optics but the atmosphere that usually causes the image distortions during observing.
 My old Meade 10 inch SCT telescope with the new mount. The new SBIG ST402ME CCD-camera and f3.3 focal reducer is seen in the end of the tube. The mount is computer controlled. |
I recently (summer 2007) decided to "upgrade" from visual observering to CCD-observing. For this reason I purchased a SBIG ST402ME CCD-camera with photometric BVI-filters. During july-september 2007 timeframe I took about 4500 CCD-photos. CCD-observing (especially variable star CCD-observing) can be done even in the middle of light polluted city.
 My old (2003-2004) "city observatory" with the white wooden plates that were meant to block the street lights. I later painted the inside of the plates black to minimize the reflections. These plates became obsolete when I moved to CCD-observing. The telescope was positioned low because it needed to be in the shadow created by the plates (there is one street light _right_ in front of our terrace!). |
One problem I always had with my old 10" is that its not very suitable to be used as a travelscope due to its weight. For this reason I purchased a smaller ED-APO refractor (SCOPOS 66mm/400 ED-APO) and mounted it to a HEQ-5 computer controlled GO-TO mount. This small telescope has very good optics and it fits perfectly for observing variables visually in the 2-11 magnitude range. With a CCD camera you can easily reach into 14 magnitudes with a relatively short exposure times.
 This is my smallest telescope, the Scopos 66mm ED-APO. Its small but it has very good optics and with the CCD-camera it provides a very nice 1 degree FOV. |
The SCOPOS 66mm is ED-APO refractor. ED means Extra low Dispersion and APO stands for Apochromatic. Apochromatic means that there is no false color in the image the observer is seeing. Normal achromatic objective lenses that are used in most entry level and affordable refractors can't correct the false color very well.
The term False Color refers to the problem that when the observer is watching -lets say- a white star the star color is not seen as white but instead the white star has some small amount of blueish or reddish tint in it. Basically this means that you do not see the colors of the object as they should be but instead there is some False Color present in the image. In addition to the False Color problem the typical achromatic lens can not show good contrast compared to well made APO refractor.
The reason why the False Color is seen in the image is because a typical achromatic lens can not bend all the wavelenghts of light to the same focus point in the end of telescopic tube. This means that red light compared to blue light has different focus point in the optical axis. Using the focuser in the telescope does not help because the lens can not bring all the wavelenghts to the same focus.
In the old times telescope manufacturers tried to keep the false color under control by making telescopes with very long focal lengths. Long focal lenght means that the lens has to bend the light less (in degrees) compared to the optical axis and thus there was less false color but the tube lengths were horribly long. The shorter the tube then the more the lens has to bend the light and the more obvious the false color became.
Usually APO refractors have three lens elements that can correct this problem so that all wavelenghts are focused in the same focus point in the optical axis (or lets say that the distance difference is so small that it is practically impossible to see any false color). This means that the image contrast is very good and objects real color is shown to the observer. The images that the APO lens can create are more pleasing and can reveal more details. This is especially true when doing lunar or planetary observing where small details and colors can really make the difference.
The SCOPOS 66/400 is ED APO which means that it is not really a true APO. In some places this type of optical system is called semi-APO. It has only two lens elements just like achromatic lenses but the other lens is made of ED glass.
Despite of having only two lens elements the Scopos produces really good images in my tests. With low and mid power the color correction is very good. I have not yet tried to use this telescope with truly high powers (I dont have a good ocular for that currently).
The SCOPOS 66mm ED-APO is a superior quality compared to the price. It is also excellent travelscope that can be taken to star trips and taken out with a moments notice to have a quick look at something interesting on the sky. It also complements my bigger and heavier Meade telescope very well.