Evostar 90 Vs SW 200P

[oceanheadted]

I did some lunar observation on Saturday night and took the opportunity to compare my cheapie Evostar 90 with a Skywatcher 200P (with a flocked tube).

I used a Pentax xf 8.5mm (117x) in the 200P and Nagler 7mm in the Evostar (128x). Now if you would ask me I would guess the 200P would beat the Evostar with all that extra aperture.

On the night the seeing wasn't that great both telescopes suffered from the image jumping around, but the 200P seemed to be much more affected. This agrees with what you read as standard opinion although I'm not convinced by the "atmospheric convection cells" argument. The evostar also seemed slightly to have the edge on contrast but that was negated to a certain extent by the chromatic abberation which it exhibited. Once you got past that however it turned out to be the better telescope on the night for looking at the moon.

One final point. When I swapped the Pentax XF into the Evostar the chromatic abberation seemed a bit worse. Is it possible that the eyepiece can help in the control of abberation?

I seem to remember reading in the S@N magazine that you don't see any benefits in resolutions in apertures above 110mm for most conditions in the UK. Any comments?

cheers

Alan

[essex sky]

hi alan

there is some truth in the convection cell theory

i.e the smaller aperture only looks through say one cell

where as the larger aperture has to look through many more

i think the 110mm theory is also sort of true , but on steady nights more aperture will always win.

the other night i observed saturn with both my 200mm sct and my 100mm refractor. the refractor gave the best steady image,

as the seeing was poor due to the fact saturn was rising above my next door neighbours house. and was affected by local warm air currents, but in steady skies the sct will always win. despite its contrast robbing central obstruction.

clear skies

lance