View Full Version here: : Dob sweet spot

13-06-2007, 05:28 PM
is thier such a thing as a sweet spot eyepiece for my 8 inch dob,i like 9mm but im also partial to 12mm,most of my time im doing planetary observations,im only using normal plosells,any 8 inchers out thier with an opinion?regards

13-06-2007, 10:03 PM
Its often said that the sweet spot magnification will give you a 2mm exit pupil, or in the case of an 8 inch scope, a magnification of 100x.

A 2mm exit pupil is said to give the greatest visual acuity.

13-06-2007, 11:21 PM
I'd agree, and that's also optimum for extracting all you can out of a deep sky image too. Below 2 mm pupil the eye loses its ability to differentiate subtle colourations , which is often overlooked issue in planetary observing.

I remember comparing a view of Jupiter between an 18" and 10" in les than perfect seeing. The image in the 18" at X180 though somehat soft was a wealth of detail that were dilineated only by the various pastel colour shades of the features, whilst the 10" at similar power was not much sharper but the features, all in shades of grey, were much harder to see.


14-06-2007, 08:45 AM
Yep, I would say that my 12.4mm and 9.7mm lenses get the most use out of them all. Very pleasant viewing with them :)