Replacing my X-cel LX 5mm

[N3ptune]

I opened my 5mm XcelLX to clean the inside and ruined it instantly but it was a pleasant EP to use. I replaced it with a Explore Scientific 4.7mm after the incident.

[Louis D]

23 hours ago, TheLookingGlass said:

I've tried the 15mm Astro Tech Paradigm in the 15mm FL in a 10" reflector, (basically the same OEM EP). Not pretty around the edges, although in this comparo in the magazine, it went against others that will be far worse, I can see why it was rated better. Only thing I did like was the eye relief.

Yes, I noticed it was the only positive/negative design in the bunch.  It's almost guaranteed to have better performance across the field and for long eye relief.  However, many of the older, simpler designs like some of the Konig variants can be sublime in their sharpness and contrast in the center 30 degrees.  It really depends on the level of polish and quality of stray light control.  Pentax Kellners are highly sought after as one example of this.

 

22 hours ago, John said:

Some eyepiece ranges have stronger and weaker focal lengths and that might be the case with BST Starguiders ?.

I've found that the Meade HD-60 line is mediocre at the edge in the 25mm and 18mm, improves considerably in the 12mm, becomes basically perfect in the 9mm, and is nearly perfect in the 6.5mm and 4.5mm focal lengths in faster scopes.  Conversely, eye relief is best in the 25mm and 18mm and somewhat less in the rest, getting particularly tight in the 4.5mm.  Apparent field of view is less than 60 degrees in the 25mm and 18mm, but grows to over 60 degrees in the rest.  It's clear that the two longest ones are a different design from the four shortest ones.  In particular, the eyelens is 26mm in diameter on the 25 and 18 and 22mm on the rest.  My pick of the bunch would have to be the 9mm.  Nearly perfect to the edge, 63 degree apparent field of view, and 17mm of usable eye relief with the eyecup folded down.  I'm going to have to do a more detailed shootout when the weather cools off between it and my 9mm Vixen LV, 10mm Delos, and Celestron Regal zoom at about 40x.

[TheLookingGlass]

On 8/6/2017 at 15:17, Charic said:

I used to think it was better to avoid eyepieces that got worse towards the edge, but what we need to remember is that much of the aberration is inherent, caused by the design of the telescopes objective, not caused by the eyepiece itself. Just about any eyepiece in any scope should be great on axis, and even the best eyepieces can suffer at their edges, if correction is not applied ahead of the eyepiece on the faster scopes. 

I don't suffer coma on my scope? its probably there, but because I don't bother looking for it, its not an issue! I track constantly on axis, its something I just do, its natural.
No doubt I'd notice coma if I let my targets  drift, or when photographing, but otherwise, its not an issue for me at present. 

Ahhh, yes, somewhat true.

However.....take a 5mm Pentax XW, 4.5mm Delos, 10mm or 7mm XW  / 7mm Pentax XL and they are sharp right out to the edges...even in fast scopes w/o a coma corrector. Not always going to be inherent from the mirror. It all depends what you buy. Other EP's in the same FL's won't be quite so nice as these I mentioned. 

[TheLookingGlass]

Yep. 6.5mm Meade HD-60 is sharp to the edges in my scope as well.