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15mm Plossls Shootout
Beginner or advance astronomer, we all contemplate whether buying premium really worth it. Plossls in particular can be purchased between $10 and $100 a piece; and one can’t help but wonder if 10x increase in price really results in 10x performance gain. At one point I had a good selection of 15mm Plossls on my hand and decided to see for myself.
Equipment: I have a few scopes but Explore Scientific 127mm F7.5 APO triplet refractor was particularly well suited, since 15mm EP delivers 2mm exit pupil in it. The scope was equipped with Explore Scientific 2” dielectric mirror diagonal and Baader Q-turret which allows easy and fast switching between 4 EPs.
15mm Plossl selection consisted of entry level Meade 4000 yellow letter ($20-30 new), Vixen NPL ($50), TeleVue modern version ($90) and Vixen SLV ($169). The first three are true 4 elements, symmetrical design Plossls. SLV has a more complex 7 elements design. However, since it has 50 deg FOV, many treat them as soaped up Plossls. :)
As in my previous 32mm Plossls shootout I used Orion Nebula complex as a target. M42 presented a great view. Nebula brightness was a bit subdued whether because of the Moon or smaller aperture. Still, there were enough structure and dark and half-tone features to make the testing effective.
Overall view: At first glance, all 4 EPs did very good job. I was looking through Meade Plossl thinking how one can improve on this: sharp stars, nice nebula details, but then I switched to the Vixen SLV – and view improvement was obviuos and considerable. Image just got refined in all aspects: sharpness, contrast, level of details. Thus, the first place was easy to assign. The other three took a while to sort out. As with 32mm Plossls, 15mm TV was a bit behind the other two in nebula brightness. Meade had a bit softer focus than other two. At the end overall second place went to Vixen NPL, TV was neck to neck with NPL in sharpness and contrast, but lost a bit in transmittance. Meade took the last place mainly because it was somewhat less sharp than other two and had a bit less contrast.
Field of View: There were no noticeable differences in AFV. However, Vixen SLV was better corrected: the stars were sharp almost all the way to the edge, except maybe last 5%, where they got slightly out of focus. All three Plossls showed more edge softness than SLV, but about equal amount. Meade appeared to have blurrier stars at the edge than other two; most likely because it had softer focus overall. Still, this field curvature was relatively mild, in no way distracting from the views.
Sharpness: Sharpness was judged from how sharp and pinpoint like the stars are. I have my 127mm APO for about a year and had plenty of sharp views, but I never saw stars as sharp as with Vixen SLV. The moment I switched to SLV I spotted E component in the Trapezium, right away, at 60x, and not as flitting glimpses, but as a sharp dot just sitting there. :) To achieve that you do not just need sharpness, but also good contrast and light scatter control. TV and NPL had similar good sharpness, but a tad less than SLV. Once I knew where to look I found E component to, a bit fuzzier and less obvious. I don’t believe Meade Plossl had enough sharpness to spot E. I don’t blame it. :) I had plenty views with much fancier EPs in the past and never manage to split E at 60x.
Light-scatter: Looking at the glow of bright stars, and also placing them just beyond FOV I could not tell any obvious differences between 4 EPs. All had about the same (very good) light scatter control.
Contrast: Two Vixens and TV showed about the same level of contrast, highlighting nicely structure details within the nebula body and thin filaments coming from the wings. Meade views had somewhat less contrast. In fact some of the thing filaments were not visible.
Brightness/transmittance: Meade was the winner showing the most of central area of M42 and most of M43. Vixens had very similar transmittance, somewhat behind Meade. TV was a ted darker yet, in fact M43 nebulosity was visible only with averted vision in TV.
Colors: Vixens had the neutral palette, which I liked the most. TV had warmer tones and Meade was on the colder side. SLV showed a bit more, while Meade a bit less color saturation, with TV and NPL in the middle.
Ergonomics: SLV was clear winner with plenty of eye relief (20mm) and screw-type eye cap which you can place at comfortable level whether you observe with glasses or not. TV had the least ER. It felt tight before but now comparing to NPL and Meade, it became obvious. I did not apreciate NPL design at first, but then I realized that it uses the most of eye relief. In fact I can just yet see the field stop with my glasses on. Not possible with other two Plossls. With that in mind I assign second place to NPL. But I can see why some may prefer traditional design of TV and Meade.
Value: While there are winners and runners up in this shootout, there are no losers. I won’t hesitate to recommend all 4, in particular because they come at different price tags.
SLV has the highest price tag, but also overall the best performer. In fact I would strongly recommend it to owners of telescopes with premium optics and planetary and double stars enthusiasts.
At ~$50 new /~$30 used NPL is the best value as far as performance vs price goes. TV are good quality Plossls but pricewise less atractive. Finally, Meade with excellent light transmittance is an attractive option for faint DSO hunters and those who look for inexpensive but well performing EPs.
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