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Low powered ep


HaiXing

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Hi I have skywatcher 8" classic dob. I was wondering what 35mm to 40mm ep would be nice to buy for viewing dso I'm willing to probably dish out $300 CAD for one. Or should I just go for a 2nd hand Pentax xl21 guy selling for $250.  Was also considering the vixen lwv 42mm

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A good low power eyepiece for that scope could be 24mm +/- 2mm, i.e. 22-26mm.

For a very low power eyepiece, usable primarily only in truly dark skies due to the brightness of the background sky in the eyepiece, would be a 36mm +/- 2mm.

I don't think you would use that low a power very often because most objects would be very small in the eyepiece, but having an eyepiece in that range for low power, dark sky, observing isn't a bad thing.

I still think you would use the 22-26mm more.

One very good example of a superb lower cost eyepiece would be the APM 30mm 70° Ultra Flat Field.  That sort of bridges the gap between those eyepiece focal lengths, and then you could easily

skip straight to something like the 17.5mm 76° Baader Morpheus or a 17mm Astromania SWA 70° (a true bargain)[In the EU, the Omegon Redline] for the next magnification up.

The APM is a lot better eyepiece than any of the Pentax XLs, and I think you'd use the 42mm only once in a blue moon.

Assuming a 1200mm focal length, 30mm is 40x, and 17.5mm is 69x, not a very big step up in magnification.

You could even have a 15mm be the next eyepiece up (80x).

 

 

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1 minute ago, Don Pensack said:

The APM is a lot better eyepiece than any of the Pentax XLs

That's a pretty broad generalization there.  Do you mean relative to the 21mm, 28mm, and 40mm XLs or relative to all of them down to the 5.2mm XL?

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I haven't used the 5.2mm, but I did use the other Pentax XLs for several years.

In my f/5-f/6 scopes, they suffered from lateral astigmatism.  The XWs improved that, and even with a wider field.

I view the XWs as a step up from the XLs.

The 30mm APM has no astigmatism in the outer field at all at f/5.

Comparing the 30mm APM to the 30mm XW, the APM was better-corrected at f/5.75, so if A > B, and B > C, then A > C.

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