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Does SkyTools Prefer Barlows?
Newbie Alert!  I have a question about the "Ideal Eyepiece" column on the nightly planner screen.  I have profiled my telescope in the software with several lenses (30mm. 20mm, 12.5mm, 10mm and 8mm).  When I load a filter class (i.e. Planetary Nebula) the resulting list contains 2 nebulae that are best viewed with my 10mm eyepiece but also lists 16 nebulae ideally viewed with my 20mm plus a 2x barlow. 

Can someone explain why the software seems to prefer a barlow'ed 20 to a straight 10mm.  Wouldn't these provide equal magnification?

If it matters, both eyepieces are from the same series and have the same field of view.


For faint extended objects that are more difficult to detect, the algorithm maximizes contrast, but for obvious or easy objects, contrast doesn't really matter, so it attempts to pick the eyepiece that presents the most pleasing view, which depends on the size of the object. A small planetary will look better with higher magnification, but a large one may require a wider field of view to fit.

In your case of the two similar magnifications, the eyepieces are probably not truly identical. For example, the exit pupil may be different. So the algorithm is picking the one that optimizes contrast or field of view, although in practice there may be little difference.
Clear skies,
Head Dude at Skyhound
It's also probable that the 20 mm eyepiece has longer eye relief than the 10 mm, so it's easier to get your eye into the proper position. Eyeglass wearers are especially aware of this.

Phil S.

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