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Meade ETX-LS Review - Part Two - Optics

Posted by John Kramer   11/24/2009 00:00:AM

This is a summary of the optical performance of the Meade ETX-LS, and second part of a 3 part review I'm dedicating to the Meade ETX-LS.

Part one focused on my initial impressions, which included my opinion on the physical characteristics and the initial go to capabilities of the ETX-LS. For the purpose of this review, I am going to give you my impression of the scope's optics, and my experiences with this telescope that I had during my 8 observing sessions so far under the stars.

Of the 8 observing sessions I have had with the ETX-LS, 4 of them included a side-by-side comparison to my excellent Orion 6" Intelliscope Dobsonian, on a variety of objects. Due to personal considerations and sky conditions, a true dark-sky site was not used for these observing sessions.

So, how did it perform?

It appears the ETX-LS arrived in good shape, and as collimated about as good as it can be based my initial star test. Inside and outside focus did not quite match during my first star test, however from what I read this may or may not affect optical performance when you're talking about the focused image, it only means a degree spherical aberration of the optics, caused by either under or over correction. I want to come back and revisit this, since I tested this without ensuring it reached thermal equilibrium, so currents may affect this result as well.

ACF - The visual impression of the ACF optics were nothing to blow me away, but stars were pin-points and very nice for a SCT. Stars seemed to hold up very well under different magnifications too, and better than I can recall to my 8" SCT, so this may indeed be an effect of the ACF optics, not really sure. I really need an opportunity to compare the ETX-LS ACF optics to a similar aperture non-ACF SCT optic, I just haven't had that opportunity yet. When viewing stars close to the edge of the field of view, I wasn't surprised by anything, there was still some sea-gull effects, but using a variety of eyepiece designs, wide-angle vs plossl for instance, reduced those effects. Were stars pin-points all the way to the edge of the field of view? Depends on eyepiece. Were stars more pin-point overall? Yes.

Bottom line on ACF, there may indeed be a slight visual difference, it did appear that stars were less "bloated" to me then I recall from SCT views in general, and it did appear more pin-point. So are the ACF optics worth it for the "slight" difference? Yes, if it were me I'd spring the extra cash for ACF anytime, just to have the piece of mind that I have the best possible optics.

Jupiter - The ETX-LS obviously needs more cool down time then the Newtonian, but when cool down was achieved, there were sharp views at the eyepiece yielding nice detail when the seeing permitted. One night in particular, I had 7 belts/bands visible in moments of good seeing, a fantastic view indeed in the ETX-LS. The separation of the North and South components of the South Equatorial Belt was a bit more clear to make out in the Newtonian then in the ETX-LS, but we are talking about a larger central obstruction in the SCT compared to a Newtonian, so not bad at all in my opinion. The North Polar Region had darker tinge to it in ETX-LS vs the Newtonian, and thus stood out a bit more in the ETX-LS. One thing I didn't quite like, and perhaps this is what is affecting my overall opinion here, is the color of the planet. In the Newtonian, whites of the zones were a bright white, and the belts were a light tan color. In the ETX-LS, Jupiter was not as bright, and the whites were more off-white, and the tans were a darker tan. You would think that darker tans would help with detail, but it didn't since they were offset by the off-white of the zones. Whether or not this is an effect of the f10 of the ETX-LS vs the f8 of the Newtonian, I don't know. I kept neutral by ensuring I swapped out the same eyepieces back and forth, and utilized mainly a 18mm in the ETX-LS and an 15mm in the dob, to give 98x and 102x respectively. I have researched and asked for opinions on this within the forums, and no clear consensus has yet to be found. I suspect that its a combination of the SCT larger central obstruction, a bit of light loss do to a non-dielectric diagonal, and perhaps simply an effect of more optical surfaces on the SCT. I think its only fair to say that I only noticed this as a result of the side-by-side nature of my review, and if the Newtonian wasn't present, I would never notice any thing at all besides a sharp, well detailed view of Jupiter. Comparing to the Newtonian however, I still have to say there was sharper views on the Newtonian then in the ETX-LS, as far as Jupiter goes. Detail was about the same, but the sharpness of that detail, and how it was a tad bit easier to see in the Newtonian then in ETX-LS pushed it ahead of the LS. Still, very, very good views were achieved in the ETX-LS. I just don't have an explanation on the difference in the brightness, and that's kind of driving this details-oriented person a bit crazy as I seek an explanation. It could be the coatings, or a combination of both focal length and central obstruction. I guess I'm reserved to think it was probably a combination of all the previous possibilities, but I think its safe to say that its nothing that is wrong with ETX-LS, it's just the difference you will notice from a SCT to a Newtonian.

Moon - The difference in color or brightness, as described above, proved to be the only factor with this target. Mare stood out nicely, and the bright ejecta blankets of craters were clearly contrasted against the Lunar surface. I pumped up magnifications in both scopes, and I could not see any detail in one that wasn't present in the other. One thing I noticed here in the ETX-LS, was apparent presences of more "floaters" in a given eyepiece then in the dob. I noticed this as well on Jupiter, using the 12.5mm between the scopes would present more of a floaters issue in the ETX-LS then in the dob. This is not a ding against the ETX-LS optically, it seems to be a cause of the longer focal length of the f10 scope vs an f8, but thought I would throw that out there. I prefer the brightness of the Newtonian, but again, it was the same amount of detail in both scopes and it was great that I could track the Moon with medium to high power.

Deep Sky - From my suburban site, my deep-sky targets consisted of the following, with a brief impression.

M31 - Andromeda Galaxy was bright and nicely framed, about mid-way in the field of view of the 26mm PL. Switching to a 18 mm SWA, M31 filled the whole eyepiece. I noticed stars were very pin-point in the ETX-LS, and the sky background was a bit darker, but not by much. I preferred the low power view of this, and using a 40mm PL in the ETX-LS, gave me a view of M31, M110 all in the same field of view.

M57 - Ring Nebula - The go to put this object just about center in my field of view using the 26mm PL. The image was great in both scopes, I really could not see any thing in the dob that I couldn't see the ETX-LS or vice versa. Again, a slightly darker background in the ETX-LS, but I really couldn't make out if there were any contrast gained on the nebula itself.

Double Cluster - A great site in the 40mm. Star and more stars. Go to put this object almost center of FOV as well of 26mm, I put in the 40mm to take in the whole view. It's hard not to have a great view of this object, and the ETX-LS had both clusters within the field of view. I can't wait to view this with a nice 2" eyepiece and 2" diagonal in the ETX-LS.

M42 - The Great Orion Nebula - Excellent view in the ETX-LS. The nebula looked slightly different in the ETX-LS vs the dob, with the ETX-LS having a bit more detail in the nebula itself, wisps were a tad more defined, but the dob had permitted the nebula to have more contrast at its edges. Trapezium stars were easier to make out and thus sharper, then the dob. In fact, E and F were clearer to see in the ETX then in the dob.

M2 - This was a bit of a surprise, it was quite bright and I thought I could see just a bit more resolution on the fringes in the ETX-LS then in the Newtonian. This globular was very good even from this suburban observing location, its one I will have to visit with my friends 10" LX200 next time we are out at our dark sky site.

NGC 7009 and 7662- These small, bright planetary nebula were easy in either scope. I actually prefer the narrower field of view in the ETX-LS on these planetary nebula.

Double Stars/Multiple Stars

Epsilon Lyra - The ETX-LS, once I switch out the included 1.25 prism diagonal with my 2" GSO Mirror diagonal, held its own very nicely against the newtonian. A lovely view. Being that it has a larger central obstruction then the dob, I could see that the ETX-LS had larger diffraction rings around the airy disk that made for a bit less black between the stars then did the dob.

Theta Orionis - I touched on this earlier, but this was better in the ETX-LS then in the Newtonian. F was simply easier to pick out, and E was clearer in the ETX-LS then in the dob. That impressed me.

Sigma Orionis - Fantastic multiple star in Orion, dead center in the ETX-LS. Wonderful colors, nice pin-points. Oh how I'm looking forward to double-stars with the ETX-LS. I synchronized the Autostar on a couple of different objects, and one this was done, I was placing double-stars in the center field of view of a 15mm eyepiece with a great feature call "Walk the Stars" in the Autostar. I went through 6 other doubles, and all were dead center of the 15mm eyepiece. That impressed and delighted me, since double-stars are becoming my favorite observing targets.


The ETX-LS is going to be one fun telescope. The views it gave were very good to excellent, and I'm very happy with it optically. When you combine very good optics with the go to and automatic alignment functions of the ETX-LS, you have a great combination and a well rounded telescope.

But speaking of go to, how has it performed with the automatic alignments? Well, that's next up in part 3, the final installment of this review, so please be sure to check back.