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Refractors on M31: 5" F5 achro vs 5" F9 ED/apo

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#1 revans

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Posted 21 October 2019 - 06:55 PM

Got two telescopes out of mothballs... an old Meade 127 mm F9 ED/apo doublet on an LXD75 tracking mount, and an Orion 5" F5 achromat on an equatorial mount without a drive. I viewed M31 in both using two widefield eyepieces.... a 20 mm and a 45 mm.  The 20 mm gives 57x in the ED/apo and 31x in the achromat.... the 45 mm gives 25x in the ED/APO and 14x in the achromat.  I found the view in the achromat to be superior in the achromat using either eyepiece as compared to what I saw in the more expensive scope.  I also found it lighter and easier to use star hopping.  I'm sure that when I compare the two scopes on the moon and on Jupiter my opinion will be just the reverse.  But for deep sky observing, give me the 5 inch F5 achromat.  Rick


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#2 Mitrovarr

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Posted 21 October 2019 - 07:04 PM

The ST120 is hard to beat on those very large objects where you really need it's fast focal ratio and ability to use 2" eyepieces. Did you know you can fit the entire Veil nebula (yes, both sides) in the eyepiece?


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#3 revans

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Posted 21 October 2019 - 09:11 PM

It was an interesting comparison of these two scopes.  I put my 9.25 inch F10 SCT on the LXD75 mount instead of the refractor.  Although I had tinkered with the optics/collimation of the SCT some years ago, I guess over the years I compensated for most of the damage I had done,  Anyway, at 52x using a 45 mm eyepiece (widefield) I had really spectacular views of M33 and M57 that were obviously very superior to anything I saw in the 5 inch refractors. The stars were pinpoint and the nebulosity bright.  M57 was bright and almost greenish grey with the donut hole just visible at 52x.  This is a nice deep sky scope for a medium aperture instrument.  Lucky for me the mount drive still worked after all these years.  For things like the Veil nebula I have used just a 200 mm telephoto lens on my camera without using a telescope but using the drive by mounting the camera to telescope body and I got some decent photos of that and the North American Nebula etc.  That was some years ago now.




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