John
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Posts posted by John
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Another vote for the 10mm Pentax XW here and the 10mm Delos is just as good as well. On a somewhat tighter budget I agree that it's hard to beat the 10mm Baader Classic Ortho for sheer optical quality. The Vixen SLV's are sharp and contrasty as well - rather like a 50 degree XW or Delos.
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6 minutes ago, johninderby said:
This article addresses just thiis issue of brightness and aperture.
https://medium.com/@phpdevster/how-telescope-aperture-affects-your-view-24507147d7fc
Good article that. Well worth a read
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Well I'm not surprised at that
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7 minutes ago, MarsG76 said:
Of course.. but ultimately the best zoom will not be as good as the best fixed fl ep... just like with camera lenses.. a prime lens will be better than a zoom lens of the same class.
Which zooms have you compared to which fixed fl eyepieces ?
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10 minutes ago, MarsG76 said:
Can't see the pic but a zoom eyepiece will always be of lesser quality than fixed focal length optics.....
Depends on the zoom.
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I think all the advice in this thread has been given in good faith and I'm sure recieved as such by the original poster
We can only post our experiences and these may well differ person to person. Eyepieces very much a matter of personal preferences I think. Sometimes you need to try a few types out to find out what suits you.
I hope @Gonko enjoys the eyepieces chosen and I'd be interested to hear back on how he/she finds them once a few sessions have been had (could be sometime given the weather we have been having
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Another interesting factoid about the XWs is that they use special coatings on the cemented lens surfaces as well as the multi-coatings on the glass to air surfaces. This was considered quite innovative when the XWs first came onto the astro scene because cemented lens surfaces were not usually coated back then. Maybe this technique is used by other manufacturers now ?
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When I'm trying to observe the faintest targets (eg: the Horsehead Nebula) I don't want any light at all near me for a good hour or so before attempting to see my target.
When I've been at a very dark site even the illuminated face of a watch seems glaring when the eyes are really dark adapted.
Coversely, when planetary observing, some exposure to light can actually improve the ability to pick out subtle detail. I've read that experienced planetary observers actually stare at an illuminated white surface for a few moments before putting their eye to the eyepiece.
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This is useful guidance on optical aberrations, both from the scope optics and from the eyepiece:
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I occasionally use a 40mm 70 degree eyepiece with my F/5.3 dob, but only very occasionally. It's just not as effective under my skies as the 31mm Nagler or, even better, the 21mm Ethos. I've not worked that out mathematically but found out by trying it out under the stars.
But with my slower refractors, the 40mm / 70 is much more useful
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9 minutes ago, Greymouser said:
.... Maybe it is me that is wrong here though...
My experience / understanding about Hyperions is the same as yours.
Not the first eyepiece range I'd consider for a F/5.9 scope.
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The 40mm would give you a 10mm exit pupil in your 20 inch dob. Might not be that effective ?
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3 hours ago, Anthony1979 said:
So in 2 hours it should have rotated 3 cm
Only if the circumference of your mount at the point you have marked it is 36cm. If it is different the rotation will be different. 36cm was just an example that @Waldemar was using.
I agree with Cosmic Geoff - get on and use the mount.
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8 hours ago, Stu said:
Any ideas why there is a difference John? Presumably they are all designed for similar scopes? The shorter focal lengths all have excellent reputations, seeming to imply negative FC is better in countering scope FC, but that must vary depending on scope type?
I don't honestly know Stu. It used to be said that the XWs in the 1.25 inch fittied were originally designed for spotting scopes but I'm not sure about that. I doubt that you would use the 2 inch XWs in a spotting scope. The XWs replaced the XL range so the origins of the XLs are relevant as well. Interesting piece here on these ranges:
@jetstream / Gerry - I find the 1.25 inch XW's have pretty low levels of light scatter given their optical complexity so I think there is a good chance that the 2 inch ones will score well in this department too. The 5mm and 7mm XW are now my "goto" eyepieces for splitting Sirius and for that you want as little scatter as possible.
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I think I have medium coloured eyes and I don't find that I need to use a lunar filter.
Who believes polls anyway ?
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I've no problem observing the Moon with my 12 inch dob and no filter. I do have a suitable ND filter but I keep it for outreach observing in case anyone else feels that they need it.
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3 hours ago, Mr Spock said:
Interesting design. Both the 30mm and 40mm are different from the rest of the range and from each other.
The XWs vary quite a bit in their optical design across the range of focal lengths. This chart includes the old 30mm and 40mm XWs but I think the optical design there is the same as the new release of those focal lengths:
Their optical characteristics show some variation across the range as well - some show negative field curvature and some positive:
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4x the price usually equates to a few % difference in performance once you get above mid priced / mid market eyepieces I reckon. A lot of folks still go for those last few % though. Fussy lot, we are
Personally I'd be interested to know how the 40mm XW-R compares with my Aero ED 40mm which cost me £50 used.
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17 minutes ago, Rob Sellent said:
Just speaking outloud for I have absolutely no idea but are Meade popular on SGL, or in the UK/Europe?.....
Where is that bag of popcorn icon ? - ah, there it is 🍿
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I've used both eyepiece types and agree with Robins assessment.
At low to medium magnifications the BST Starguiders are pretty good. I think you did the right thing in investing in a Vixen SLV 5mm for higher powers though.
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2 hours ago, DarkAntimatter said:
I wonder how they would compare with a TV panoptic. 70 vs 68 degree fov; 20 vs 24mm eye relief.
I have a 24mm Panoptic and some shorter focal length XW's. The 2 degree difference in AFoV is not really noticable to be honest with you. I have used a Pnetax XW 30mm and compared it with a Nagler 31mm and the UWAN/Nirvana 28mm. The Pentax was a really comfortable eyepiece to use and not as heavy as the others. Here is the report I compiled back then:
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The Pentax XW range seems to now include a 30mm and 40mm focal length in the 2 inch fitting again:
http://www.ricoh-imaging.co.jp/english/products/binoculars/scope/xw/index.html
In the US prices listed are $370 for the 30mm and $400 for the 40mm.
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The SWAN's are OK but do suffer from some distortions in the outer field of view when used in scopes faster than around F/8. At 40mm I use an Aero ED 40mm and that works really well in my F/6.5 102mm and F/7.5 120mm refractors. Stars are sharp pretty much right across the field of view plus the Aero ED 40mm is quite light for a 2 inch multi element wide angle eyepiece.
There are other options within your budget such as the Explore Scientific 68 degree 40mm if you are prepared to buy secondhand.
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Rigel B
in Observing - Reports
Posted
Good report - splitting Rigel is indeed good practice for splitting Sirius as the split between the primary and secondary star is about the same.
I find that I need above 200x to split Sirius. The "Pup" star trails behind the primary star as it drifts across an undrive field of view with that pair. It is somewhat more tricky than Rigel of course. The "Pup" glimmers faintly through the flaring around the primary star.