Barlows and colour shift

[ct71]

I've been frustrated by all of the clouds and rain recently so did a bit of daylight testing of my eyepieces.  I've got a basic skywatcher refractor 90/910 and the supplied MA eyepieces in 10mm and 25mm.  Without question the best images I get of Jupiter are with my skywatcher deluxe x2 Barlow and a 15mm Celestron omni Plossl I've bought as extras.  Nothing big budget but I see it as a challenge to get the best out of the kit I have.

I was surprised by my daylight observations of a distant tree as this didn't translate to my day time test.

1) MAs not too bad at all - obvious blurring at the edges with a bit of purple/blue but sharp and good colour rendition in the majority of the field.  

2) Plossl not that sharper in daytime but does seem to do better at night compared to the 10mm MA.  Colour rendition good.

3) The Barlow made all of the images less sharp and introduced a blue/violet colour cast no matter the eyepiece.  Maybe magnification and daytime "viewing" coming into play but also more glass for the light to go through?  Cheaper anti reflective coating causing the colour cast?  I understand the blue and red shift as a result of the refractor but does the same happen in a Barlow?

 

Anyone has similar experiences?  Based on those I'm tempted to keep an eye out for a second hand 8mm and 12mm BST starguider and leave the Barlow behind...  Also, any ideas why the 10mm MA is less good in the night?  I love the 25mm - advertised on the EP as "ultra wide and long eye relief" - cleary all relative but it is a nice one to use and pan around the sky with.

[Elp]

A Barlow will magnify any chromatic aberration produced by the scope so yes it will get worse unless you use a Televue powermate I believe, the powermate will not correct the original aberration though.

Usually any "better" eyepieces will be an upgrade from the supplied with scope ones. The bsts are quite decent, so are the vixen npls and don't cost too much. I haven't tried it myself but a Baader fringe killer filter may help with the CA.

[Louis D]

Blue/violet color fringing is classic achromat chromatic aberration.  Observing at higher powers will reveal it more clearly.

As for why the MA looks worse at night, stars are the absolute acid test of optics.  Any aberration anywhere in the field will be seen with stars.  Even aberrations in your observing eye will be seen.  Extended objects seen in the daytime are much more forgiving than stars because your brain is forgiving of blurred objects, but not of aberrated stars.

[NGC 1502]

Plus 1 for BST Starguiders, great value.  If it were me, I’d go that route rather than a barlow.

[ct71]

Cheers all. Interesting main factor is Barlow magnifying chromatic aberration 👍