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first saturn images of the season

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19 years 9 months ago #5186 by John OBrien
Replied by John OBrien on topic Re: first saturn images of the season

Bad news, it says that this is due to a decentering (sideways shift) of the optical compenents in the scope !!

He was talking about refractors.


Sorry to butt in but I have noticed this with my 70mm refractor. Does he say how fix it? I have a Celestron Firstscope 70 btw.

Thanks - John

"We are the music makers ... and we are the dreamers of dreams." - W.W.

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19 years 9 months ago #5187 by michaeloconnell
Replied by michaeloconnell on topic Re: first saturn images of the season
Dave,
Here's a link you may be interested in re. your image of M33.
You'd need to take some short exposures and some long ones and combine them soa s not to lose the detail.
www.astropix.com/HTML/J_DIGIT/COMP2.HTM

John,
I could be wrong, but what you're seeing could be the result of the refractor having an achromatic lens i.e it's in the design of the lens rather than the scope having a "fault" as such. I think what Dave is suggesting is something that may only be picked up with large apo refractors which should have no false colour inhirent in their design. Hopefully Dave can clarify a bit more.

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19 years 8 months ago #5199 by dave_lillis
Replied by dave_lillis on topic Re: first saturn images of the season
Guys,
Do not confuse what I'm describing above with colour fringes and rings around abjects. Those cases usually have the same colour around the entire object at any one time, although the colour is different when the inside and outsides of the focus images are compared. If this is what you're getting, there is nothing you can do about it, its called chromatic abberation.


What I'm describing above is something different, its seeing a red tinge on one side of the object and at the same time seeing a blue tinge on the other side of the object (eg jupiters edges), at the same time.
From what I read, this is due to missaligned optics, in a SCT, you might be(in my case was) able to fix it, in a small refracter, this is also the case.

Dave L. on facebook , See my images in flickr
Chairman. Shannonside Astronomy Club (Limerick)

Carrying around my 20" obsession is going to kill me,
but what a way to go. :)
+ 12"LX200, MK67, Meade2045, 4"refractor

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19 years 8 months ago #5200 by John OBrien
Replied by John OBrien on topic Re: first saturn images of the season
I'm used to CA from my photography experience and what I'm getting is as you describe, red and blue separations. I usually just try and realign the three R G B channels in Photoshop and that helps but if I can, I would rather do this optically.

Now that you have pointed out that it can be fixed I'll have a search around the net and see what I can find, though if anyone has any pointers that would be great.

"We are the music makers ... and we are the dreamers of dreams." - W.W.

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19 years 8 months ago #5201 by albertw
Replied by albertw on topic Re: first saturn images of the season

What I'm describing above is something different, its seeing a red tinge on one side of the object and at the same time seeing a blue tinge on the other side of the object (eg jupiters edges), at the same time.
From what I read, this is due to missaligned optics, in a SCT, you might be(in my case was) able to fix it, in a small refracter, this is also the case.


Sounds a lot like atmospheric refraction. In which case there is not much you can do about it other than to separate the image into Red Green and Blue and re-align those components.

This, first attempt of mine of Saturn last year shows it up nicley:


Cheers,
~Al

Albert White MSc FRAS
Chairperson, International Dark Sky Association - Irish Section
www.darksky.ie/

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19 years 8 months ago #5203 by dave_lillis
Replied by dave_lillis on topic Re: first saturn images of the season
Good point Albert, but I also noticed it when Jupiter was very high, much higher then atmospheric refraction alone could cause.

BUT if you looking at saturn these days, it is fairly low in the sky until well into early morning, so maybe thats what Johns seeing ??

If it is misalligned optics, then I dont know what you can do with a small refractor, big high end refractors allow for lens collimation etc.

Have you tried rotating your eyepiece to see if its the eyepiece causing the problem, i've seen scopes with average optics only to be destroyed by crap eyepieces.. a bad star diagonal might also introduce odd abberations.

Dave L. on facebook , See my images in flickr
Chairman. Shannonside Astronomy Club (Limerick)

Carrying around my 20" obsession is going to kill me,
but what a way to go. :)
+ 12"LX200, MK67, Meade2045, 4"refractor

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