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sixela

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About sixela

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  1. The barlow magnifies more in that position and the effective f/ratio of the system (scope+barlow) is increased dramatically, and that usually lowers eyepiece astigmatism significantly. Also, you're looking at a much more narrow field in which the LX90's field curvature is much less bothersome (to reduce the softness without the barlow, try to focus stars that are somewhat closer to the edge, and you might be surprised at how sharp the centre still is: your eye can accommodate for a different focus much easier in one direction than in the other).
  2. There's no need for them. That's something else than saying there's no benefit in them (especially if you have a fairly sizeable collection of simple ortho, Pentax XO and TMB Supermono eyepieces).
  3. Watch out: the Paracorr actually requires a bit of focuser in-travel, so count on using roughly 15mm less out-travel (it varies, because if the visual Paracorr tunable top is set correctly the Paracorr, unlike your eyepieces, always ends up in the same spot.) The Paracorr itself is pretty long. Can you install a 2" parfocalisation ring on its barrel so that you can just reach focus with the original focuser racked out? Try to see if you can make the partially inserted Paracorr work without extension tube (of course, ensure there's enough barrel left inserted for it to be stable!) You might also be able to win a centimetre or so by moving the primary forward on its collimation bolts (assuming the springs are firm enough not to render collimation less stable).
  4. a) things never look like they do on pictures, because you eye isn't sensitive enough. For them to look good (but different), dark adaptation, averted vision, experience and first and foremost a dark moonless sky (with little light pollution) are very important.
  5. If you are the DIY type, it's also not impossible to adapt a knob with Vernier caliper yourself to one of the two existing knobs. I did that with a few bits'n'pieces and a knob from Mentor Components. Here's one from someone who installed one after I did (I had two more components because the shaft diameters didn't match):
  6. The bearings won't work that way. The solution is to get an equatorial platform instead you can just about see my Tom O. platform under my scope in my avatar), but these are usually not very precise and can't be guided (unless you take one of Tom Osipowsky's dual axis platforms with ST4 guiding port, but they cost a bundle).
  7. It's the same thing. The effective focal length relates the entry angle for a light bundle and where it maps on the focal plane, so it directly (together with the focal length of an eyepiece) determines magnification. Yes. The catch is that 2" wide field eyepieces are usually especially recommended for the lowest power eyepieces, and a barlow by definition won't save you there (you can't replace a 31mm ES 82° eyepiece with a 4" barlow and a 4" 62mm 82° eyepiece). As great_bear also correctly points out, a barlow also won't correct problems present at the original focal plane of a scope indirectly related to f/ratio on a given design (a Newtonian f/5 scope with a barlow still has the coma of an f/5 Newtonian, an achromatic refractor short tube with a barlow still has the chromatic aberration of a short tube, etc.).
  8. It's the same thing. The effective focal length relates the entry angle for a light bundle and where it maps on the focal plane, so it directly (together with the focal length of an eyepiece) determines magnification. Yes. The catch is that 2" wide field eyepieces are usually especially recommended for the lowest power eyepieces, and a barlow by definition won't save you there (you can't replace a 31mm ES 82° eyepiece with a 4" barlow and a 4" 62mm 82° eyepiece).
  9. For something radically different: Sumerian Optics [Watch out, the price at the bottom of that page do not include optics and a focuser, see Sumerian Optics for full price list] Mind you, it's certainly not grab and go like a Starblast or small refractor on Alt/Az mount is, but it's eminently portable.
  10. To be honest, if you begin and you want to buy one filter I'd consider a narrow UHC filter (Lumicon, Omega Optical NPB, Orion Ultrablock) first. It isn't usable on all objects but it helps more dramatically on emission nebulae and you'll keep on using it even at dark skies. If you want something for more types of objects, I'd be tempted to pick a Lumicon Deepsky, a Baader UHC-S or an Omega Optical GCE; the Neodymium Baader filter is rather poor at suppressing light pollution and keeping the object intact (I still have one, but that's more as a planetary and moon filter).
  11. You do need some spare focuser in-travel, though (but less than the extension is long, fortunately).
  12. There's no reason to think Powermates are "better" than the plain TV barlows unless the specific features of the telecentric telextender are relevant (small insertion depth, relative independence of magnification factor and Powermate/eyepiece spacing, unchanged eye relief even for longer focal length eyepieces, lack of vignetting in some rare eyepieces, etc.). In fact, for planetary observation, I tend to prefer the 2x TV barlow by quite a margin (and I put my money where my mouth is and sold my 2.5x Powermate).
  13. A barlow and a simple eyepiece usually has "less glass" than many more complex eyepieces (for wider fields or for long eye relief). In fact, many eyepieces have a built-in lens group at the field end that functions pretty much like a barlow.
  14. Not really, but it doesn't have a tube, so its aspect ratio is never too narrow. If a collimation tool is too narrow, then it's possible that even if you rack the focuser in completely you can't see the whole of the primary reflection (and if you rack the focuser out, the secondary may clip the reflection of the primary before you can actually see all of it).
  15. No, because we don't know if the camera was centred, and if it wasn't, then the effects of that parallax dominates all the "errors" we see. And we also don't know what collimation tools you have, you haven't said whether there is a center spot on the primary (despite my question), etc. so we can't tell you how to fix it either. As I said, the one error we can see (a rotational error of the secondary) is the least relevant one, so I'd rather not make you chase red herrings if there are big fat tunas around. If you want to know what it has to look like, look up "Jason D"'s avatar. Or this thread: http://stargazerslounge.com/equipment-help/121989-centring-secondary.html
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