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#1 derekdann30

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Posted 26 March 2013 - 03:42 PM

It's probably posted somewhere here in the forum, but has anyone had any good experiences with this type of scope? Aside from the CA, how well does it perform on the planets? How is the construction quality? I have an XT8, but there is something about refractors that always gets my attention. Would the image quality rival a well collimated dob? Thanks

#2 vct123

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Posted 26 March 2013 - 04:08 PM

The detail on planets should be nice in the ar127 and similar to what you will see in the 8" dob, just a little dimmer.
The problem is the color of the moon and the planets instead of white or a cream color will be green and purple.
The faster the focal ratio, the worse the color will be in general and that has been my experience. Of course there are filters you can get like the Baadar semi apo, fringe killer, contrast booster, tried all those. I like refractors too but no more achro's for me.

#3 Mark Costello

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Posted 26 March 2013 - 04:23 PM

Hello derekdann30. As you can see from my "signature," I have one of these ES AR127s and since it's my only telescope, I use it as a "general purpose" telescope. That includes long observing sessions involving the moon, Jupiter, Saturn, and Mars.

As VCT mentions, the details on the planets and moon are nice. But don't discount the impact of the chromatic aberration. My recent experience with Jupiter is that I'm seeing a fair amount of detail on it at 236X, including up to four "dark" bands, and some splitting in one of them. The image of Jupiter is actually a cream color, maybe a tad yellowish. The chromatic aberration shows as a purple halo around the image. Also, there seems to be a slight softening of the edges of Jove's bands, maybe the seeing contributes to that, maybe the blue color going where it shouldn't is doing some of that. The lunar images are much better, it appears that the moon is more forgiving of chromatic aberration than small bright targets like the planets....

Are you looking for a second telescope to go along with your Dob or looking to replace it? The ES AR127 might be a good complement to your Dob (use for lower power and wider field views) but unless it has bad mirrors in it, it should serve up better images of the planets....

As I mentioned, I have one as my only scope and I'm delighted with it, but I tolerate and work with its design limits, including the false color. I sometimes think about going the other direction, adding a reflector 7-11" (might be a Newt, SCT, or even MCT) to complement it. :lol:

All success in making a winning choice....

#4 derekdann30

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Posted 26 March 2013 - 07:21 PM

Yeah, this would be used as a compliment to my 8 inch dob. Looking for something a little more grab-n-go. Still deciding between the AR127 or the 80mm triplet from the same company. The 80mm triplet being considerably smaller and color free or a larger Achro with purple halos. :question: Have you tried any filters to suppress the CA? How portable is it? thanks

#5 t.r.

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Posted 27 March 2013 - 06:51 AM

Mark, if you can run that up to 236x it must indeed be a performer. For average seeing at my locale, I run about 165x in my 130 apo and still see quite abit of detail. Only in the summer months can I run mags over 200x with any reliability. If you could, next time you are out, try to run that magnification(165ish) on Jupiter or Saturn and post what you think about CA and sharpness. All of the details should still be resolved and the image should be sharper yet and less colorful.

#6 Thomas Karpf

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Posted 28 March 2013 - 07:13 AM

The chromatic aberration shows as a purple halo around the image. Also, there seems to be a slight softening of the edges of Jove's bands, maybe the seeing contributes to that, maybe the blue color going where it shouldn't is doing some of that.


Yes, absolutely, the softening of the edges of the bands is due to chromatic aberration. Chromatic aberration blurs any object that is not monochromatic.

Consider a single star being focused by a refractor onto an array of pixels (a camera sensor). Blue comes to focus closer to the objective than red does. If green (in the middle of the spectrum) is in focus, then blue was in focus before it got to the sensor and red would be coming to focus past the sensor. The green forms a single dot (ignoring diffraction for these purposes), and blue and red both form tiny circles around that green dot (perhaps still falling onto the same pixel on the detector if it's a REALLY well corrected APO, perhaps extending several pixels out from the center for a really poorly corrected achromat).

Now consider a line of white on the moon falling on that detector horizontally (perhaps a rill). On the sensor, you have the line of green falling on row 100, red and blue falling on lines 98-99 and 101-102 and ALSO to the left and right on top of the line of green.

If all chromatic aberration did was add colored halos around bright targets, everyone would just Photoshop out the halos and be happy about it. Chromatic aberration blurs detail.

The only way to eliminate it entirely using a poorly corrected refractor is to use very narrow-band colored filters in front of the sensor and focus carefully for each color individually.

#7 PatHolland

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Posted 28 March 2013 - 09:48 AM

Thank you Thomas. That is an excellent explanation of CA.






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