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Category: Maximizing Viewing Success
Eyepiece Selection
Posted on Apr 22, 2011, 12:26 am Author: Jen Winter

Eyepiece Selection

Question:   What Eyepiece do you recomend with my DayStar Filter? 

Answer:   Tele Vue Plossl series eyepieces of 32mm, 40mm and 55mm

Remember that at F/30, a high powered eyepiece can exceed Dawes' limit.  Observers will find best results with an eyepiece which is 32mm or greater to avoid this.    Eyepieces of higher power will result in a fuzzy disk without the ability to focus well.

We have tested a number of eyepieces over the years.  Most recently in the spring of 2011, we performed a comprehensive eyepiece comparison between various brand names and eyepiece styles.   Nagler, zooms, radians and other "fast" eyepieces typically perform very badly on DayStar applications. 

Other brands do offer Plossl eyepieces in 32-50mm and they can give a respectable performance in leiu of a Tele Vue.   We have also found some of the very old wide field "Erfle" eyepieces aren't bad for an experienced observer.  We are not aware of any manufacturers who currently offer an Erfle. 

Repeatedly in side-by-side tests, we found Tele Vue brand Plossl eyepieces to offer the highest contrast, most even view and widest exit pupil.  In Solar Observing, contrast is achieved by control of scattering. Tele Vue Plossls stand out in superior design.  Furthermore, the adjustable eye cup offers additional contrast by allowing the user to dark adapt during sunny days.  

Eyepiece features we found to increase performance include: 

- "Fully Multicoated" 
Of those eyepieces which did better than others, those marked "fully multicoated" offered better views from less internal scattering.

-  Blackened optical edges
Tele Vue and other eyepieces which performed better all had blackened edges of their optical elements. This also reduces internal scattering within the eyepiece.

- Internal Baffling
This is where Tele Vue seemed to stand out among other eyepieces.   Not only does Tele Vue thread their eyepiece ends, but they also thread and anodize the internal space components which separate individual elements.   This additional baffling seems to kill a great deal of potential scattered light and significantly improves contrast.

- Eye Cup
Good eye cups are also essential to high contrast solar observing.   Without a good eye cup, the observer must combat bright ambient light from the very sun he or she is trying to observe.  

- Wide exit aperture
Eyepieces with narrow exit apertures leave the observer with a narrow position in which the sun is actually visible at all. The need to wag one's head back and forth in order to observe really reduces customer satisfaction.  Also, in outreach environments, a poor exit pupil display can mean one child in line might never actually see the sun. 

We welcome the opportunity to test another eyepiece which might perform well.   This report may be updated if we find other well performing eyepiece choices.  

Tagged Keywords: plossl, Eyepiece, selection, length, choice, performance, contrast, observing, viewing, solar, hydrogen, daystar, focal

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Good info
Jen has done a great job putting out all this information for the Solar observer.
Posted by Randy Shivak on May 6, 2011, 11:24 pm

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