Eyepiece for sw250 F4.7

[Adam Barnsley]

Thank you for your help. As always, your opinions are invaluable. I wonder how John's test came out.

Regards

[John]

Just now, Adam Barnsley said:

Thank you for your help. As always, your opinions are invaluable. I wonder how John's test came out.

Regards

I didn't use the 7mm XW much last night I'm afraid plus I was using a long refractor rather than my dobsonian.

I'll try again another time.

[Adam Barnsley]

3 minutes ago, John said:

I didn't use the 7mm XW much last night I'm afraid plus I was using a long refractor rather than my dobsonian.

I'll try again another time.

Ok. No problem😉

[Adam Barnsley]

My new, green  friend🤩

[John]

Very nice !

[Adam Barnsley]

19 minutes ago, John said:

Very nice !

Thanks John. I cant wait for first view. 

[Louis D]

On 20/01/2020 at 13:06, Louis D said:

As I recall, on bright stars, the 7mm XW would develop color smearing as the stars got to the last 15% of the field.  If I turned my head and eye just right to align everything perfectly, I could minimize it.  I'll have to get it out again and look for it to characterize what I saw in the past better.

The eyepiece was frustrating enough after having owned the 14mm and 5.2mm XLs for years, which did not exhibit such color issues, that I seriously considered returning it.  I've slowly warmed to it as long as I keep objects centered and not use the outer regions of the field.

I think I'm seeing something similar to what this CN reviewer saw in his 2004 comparison of the 10mm XW to the 10.5mm XL.  He consistently noted color issues farther in from the edge and of greater magnitude in the XW than in the XL.  Apparently, compromises were made to extend the field 5 degrees.

I went back looking for this lateral color, and it is there but very slight.  It's a bit of a purple smear pointing toward the center.  The 5mm XL showed it as well, but to a lesser extent.  I guess it's not as big a deal as I remember from when I first got the eyepiece.

I also compared them to the 4.5mm and 6.5mm Meade HD-60s and 5mm and 8mm AstroTech Paradigms, and there wasn't much to choose between them.  These budget eyepieces are basically flat of field and sharp to the edge with lateral color no worse than the Pentaxes.  The eye relief with eyeglasses was just a bit challenging on the Paradigms and the 4.5mm HD-60 to a lesser extent.  The 6.5mm was nearly as nice as the 7mm Pentax XW in all respects except apparent field size.

The 25mm HD-60 was indeed better than the 25mm Paradigm from 50% out to 75% out, but both were left in the dust by the 24mm APM UFF.  All were similarly easy to use with eyeglasses.

I compared them against the moon, Pleiades, and various Orion targets in my 90mm TS Triplet APO with and without the TSFLAT2 using a couple of GSO dielectric 2" diagonals (quartz and non-quartz).