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6 mm Vixen Lanthanum LV vs. 6 mm UO Ortho



I purchased a 6mm Vixen Lanthanum LV eyepiece along with my first telescope (a Tele Vue Ranger) about four years ago. I was buying the telescope primarily for birding, but having gotten the astronomy bug from scanning forHale-Bopp with binoculars early in its career, I decided to pick up some astronomical accessories at the same time. The Lanthanum was selected for its 20mm eye relief, since I wear glasses for nearsightedness and astigmatism.

This is a well-built eyepiece. The green and magenta multicoatings appear dark and uniform. The heavy chromed barrel has a safety undercut, similar to that on Tele Vue's eyepieces. The lower part of the body is nicely finished in satin black. The upper part of the body is covered in smooth gray rubber, that is extended to form a deep eyecup. This eyecup collapses to accommodate eyeglasses, albeit with some difficulty; the rubber is rather stiff.I have heard, though, that the Orion versions of these eyepieces have a more flexible eyecup.

Views through the LV were sharp and contrasty. I regularly used it on the gas giants with a 2x Tele Vue barlow with good results. As I got more experienced, I found that the eye relief was really not an important feature for me. I can see more detail if I remove my glasses and take advantage of the stray-light protection afforded by the eyecup. I find that with exit pupils of a millimeter or less, my astigmatism is negligible. Even with longer focal length eyepieces, I often find the astigmatism is less of a problem than the stray light that comes in behind my eyeglasses in my urban backyard. Having the eyecup extended also makes it easier for me to center my eye properly: despite the generous eyelens (about 0.8" diameter), the exit pupil is small and easy to miss.I can't quite bury my eyeball in the eyecup though, or the view blacks out.

About two years ago I purchased a 6mm University Optics ortho. For a while, I used both 6mm oculars about equally, trying all the while to see if one was clearly superior. Both have similar fields of view - 45° in the LV6 and 43° in the ortho. On-axis sharpness, edge sharpness, and contrast were very good in both eyepieces.The ortho, though, had a noticeable advantage in brightness.This was most obvious in faint open clusters, where the ortho would show some stars that were invisible in the LV. I also came to prefer the ortho for its lack of blackout problems - with its tiny eyelens and 5mm eye relief, there is no doubt as to where to put your eye. I know people who find the eye relief of short focal length orthoscopics and Plossls to be intolerable, so this is a matter of personal ergonomics that you will have to decide for yourself. The ortho stayed in my eyepiece case, while the Vixen LV went back into its box in the closet.

Recently, I acquired a 5" apo, and decided to reexamine the Vixen eyepiece. In the very well-corrected apo, eyepiece aberrations are easier to spot than they were in the Ranger. What I found was not significantly different from what I saw in the Ranger.The LV really is a very sharp, well-corrected eyepiece. My only target for planetary performance currently is Mars, which from Seattle's latitude, is almost always aswim this apparition. Therefore, I can't definitively say how the low-contrast performance of the LV compares. It still seems very close, but maybe a hair behind the ortho. Off-axis, the LV6 shows a little more astigmatism than the ortho, but this is hardly noticeable until about 80% of the way out.At the edge of the field, stars and planets are radially stretched maybe 25%. Despite what others have reported, I didn't see any lateral color in the LV6 until the very edge of the field. The aberrations of the LV6 are relatively minor; quite inconspicuous unless a bright star or planet is in the outer 25% of the field. Starfields in this eyepiece generally give the impression of being sharp to the edge.

On the moon the other night, the LV6 was surprising me by clearly beating the ortho on fine detail. But, after I blew the dust speck off the ortho's eyelens, they wound up in a dead heat. One weakness of the ortho is that its tiny eyelens can be nearly blotted out by a stray eyelash. This makes the LV6 a better choice for public star parties. Its large eyelens is less sensitive to contamination, and its long eye relief makes it less likely to pick up mascara and other contaminants.

One other difference between these two eyepieces that will be important to some people is the focus position. I had a borrowed 8" dob that had been set up for Tele Vue Radians, which did not have enough infocus for the ortho.The Vixen LV, however, worked fine.

Conclusion:

If you are looking for a planetary eyepiece, the 6mm Vixen LV offers sharp, contrasty views on a par with the University Optics orthoscopic. The decision between the two becomes a question of eye relief and price: the Vixen has 20 mm of eye relief and sells for $109, the ortho has 5mm but sells for $58. For double stars and deep space objects though, the Vixen suffers froma bit more light loss than the ortho.





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