Degree Prism Finder
 HASSELBLAD PME90 90 DEGREE METERED PRISM VIEW FINDER *EXC++* 412EE2043 US $749.95 
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 Hasselblad PM90 PM 9 90 Degree Non Meter Prism Viewfinder View Finder 42288 US $389.00
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how to say this is a good refractor telescope?
* Focal Length 1200mm (47.2”)
* Objective Lens Diameter 150mm (6”)
* Focal Ratio F6
* Optical tube: Seamless aluminum
* Objective lens: achromatic, air-spaced
* Focal length, Objective lens diameter, and Focal Ratio:
* Eyepieces: 25mm and 6.5mm Plossls, 1.25”
* Focuser: Rack and pinion
* Diagonal: 45 degree correct-image prism diagonal
* Finder scope: 10x magnification, 30mm aperture; crosshairs
* Mount: equatorial mount with polar axis finder scope
* Tripod: Aluminum
* Total Weight 21.4kg
thanks!
Probably not.
First of all the specifications are wrong. A 150 mm objective with a 1200 mm focal length makes it f/8, not f/6 as stated. This immediately makes me suspicious. Secondly, the 45° erecting prism. These are only found on cheap terrestrial refractors. Any serious astronomical refractor will have a 90° non-erecting mirror diagonal. Third, a 10x30 finder is not adequate for a scope this size; it should be at least 7x50. Fourthly, a total weight of 21.4 kg is too light for this size of scope, suggesting that the mount and tripod are too lightweight to support this size of scope.
In a more general way, any 150mm f/8 achromatic refractor will have severe chromatic aberration -- it should be at least f/15 to have acceptable colour correction. I owned a scope like this and found its colour fringing unbearable after a while. I also found it extremely difficult to mount adequately, because of its long heavy tube with a very heavy objective lens at the high end. If you want an achromatic refractor, I'd recommend a 120 mm f/8.3 or f/9.3 instead. Its colour correction is better, and it's much easier to mount.
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