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Old 16-04-2021, 09:40 AM
Tropo-Bob (Bob)
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Tropo-Bob is offline
Join Date: Sep 2013
Location: Cairns
Posts: 1,319
I was able to trial these last night on doubles, clusters, nebulae and the New Moon. I again used my 81mm F8.7 Vixen.

I thought the most sticking feature of these EPs was the lack of either Pincushion or Barrel Distortion. I could not detect any in the 15 & 18mm EPs, very little pincushion distortion in the 5 & 8 mms and a noticeable, but still small amount in the 12 & 25mms. I was able to sweep without any noticeable affects even with the 25mm EP. In this regard, it is much better than my 24mm Panoptic. This lack of distortion will also be helpful for terrestrial viewing. No more bent poles and lines!

Nor did the EPs suffer from field curvature. The 81mm scope only has a focal length of 625mm, so curvature was a possible issue. (As many are aware, curvature is greatest in smaller focal lengths and does not relate at all to the F ratio of the lens.)

The EPs showed details well on all objects, but the 5mm was hampered by the seeing conditions. I overcome this by barlowing the 12mm, so effectively obtaining a 6mm option, which I found more useful to split doubles. The EP/ Barlow (Celestron 2x shorty) combination came to focus only a 2 or 3 mms inside the EPs normal focal point.

The EPs performed well when viewing the Gem Cluster in Carina. The colours seemed particularly bright and striking.

In the daylight, I thought the larger 4 lengths were all parfocal. However, when viewing stars, I had to make very minor adjustments each time that I changed EPs.

The EPs did show some off-axis astigmatism but it was tolerable.

Another positive are the twist cups on the top of the Eps (as shown in the attached image). Together with the rubberised exterior, the Eps feel ergonomically easy to handle. Furthermore, as these are light Eps, there is no danger of my little refractor becoming unbalanced when they are being changed.

Edited: I meant to say that there was slight pincushion distortion, not barrel distortion.
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Last edited by Tropo-Bob; 16-04-2021 at 12:54 PM.
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