Quote:

---

Several of my friends have commented at different times that at a similar magnification an eyepiece and barlow combo will show some Planetary's central stars much more clearly than an eyepiece by itself. I've seen this myself too a couple of years back, switching back and forth enough to say it was not atmospheric.

What makes this apparently work, does the barlow, by making an effectively longer FL system, reduce coma and therefore produce tighter star images, or what? Have others seen this?

Steven

---

Barlows have little if any effect on coma. They do help reduce the off-axis astigmatism which some eyepieces generate when used in the steep light cones of short f/ratio instruments, but otherwise, they don't do anything for coma. On-axis, I have never really noticed much of a difference between Barlowed and unBarlowed systems as far as central stars are concerned, but I generally work at f/10, so the light cones are pretty shallow to begin with. Clear skies to you.

--------------------
David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info

Post Extras