"Best of" Eyepieces Forum
Posted 30 November 2005 - 08:10 PM
Posted 30 November 2005 - 08:11 PM
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2014 Buyer's Guide to Eyepieces
AFOV vs. TFOV
Determining Eyepiece Focal Length
Eyepiece Designs, Aberrations, etc.: Links
Eyepiece Fieldstop Spreadsheet
Eyepiece FOV and POWER by star drift method....
Poll: How Many Eyepieces Do You Have?
How to measure/calculate Apparent Field of View.
Original Best of Thread
Planetary Eyepiece Comparison
Pupil dilation vs. sky darkness
So, What's in Your Eyepiece Case?
This is the original thread that has now been locked; but can still be read
So, What's in your Eyepiece Case, Restart
Useful Magnification Ranges
Threads about individual eyepiece models
Orion Stratus & Baader Hyperion
With possible variations in glass type and coatings, these appear to be very similar eyepieces.
An in depth comparison of these lines.
This shows that the structure of these lines is very similar, possibly identical at the shorter focal lengths. Shows conclusively that the coatings of the Hyperions and Stratus differ, though advantage was only seen in the longer focal lengths. Thanks to Sven and Amalia.
Masuyama Eyepiece Thread
Synopsis of the various Masuyama clones.
Pretoria Eyepiece thread (with pictures!)
These eyepieces were made in the 80's and are quite rare today.
Focal Ratio (F Number) = Telescope FL(mm)/Aperture(mm)
Magnification (Power) = Telescope FL(mm)/Eyepiece FL(mm)
Exit Pupil (mm) = Aperture(mm)/Magnification
Resolution (arc seconds)
Dawe's Limit (elongated double star) = 0.12/Aperture(meters)
Rayleigh Limit (split double star) = 0.13/Aperture(meters)
Field of View (degrees)
Measured F.O.V. = 15 X Time (seconds) X cosine(Declination)
Calculated F.O.V. = EP Apparent F.O.V./Magnification
EP=Eyepiece; F.O.V.=Field of View; FL=Focal Length
1m=1000mm=39.37 inches = 3.28 feet; 1"=25.4mm; 1mm=.039"
Posted 03 May 2008 - 03:23 PM
Televue EPs are not the best. No single eyepiece or eyepiece line is the "best." What TV's are, is a premium-level eyepeice combining excellent optics with excellent build/fit/finish. In the same league with them are many others such as Pentax, Takahashi, and yes Questar/Brandon. IMO, once you get to the premium levels, for the most part (there are always exceptions) what you now have is all of them having excellent optics, and the differences are now subtle as each company does soemthing a little different, accenting a different aspect of the optical performance realm. This now translates into satisfying the tastes of a subset of people. So TVs are warmer in tone, Brandons cooler, there are subtle differences in levels of scatter and contrast and of course the afov. So all these things add up to being able to please collectively, most of the people out there after top-shelf optics.
So bottom line is that there are several "Best" eyepieces out there. Your own personal preferences and tastes really define which of the group becomes best for you.
Posted 17 May 2010 - 11:07 PM
You didn't ask, but I am going to venture an explination of what this means in practical observing terms.
If you look at a star field in a telescope with pin-cushion distortion, you actually cannot SEE the distortion. The stars in the field will all still be bright and sharp at the edge of the field. Just by looking at a star field, it is almost impossible to SEE the pincushion distortion.
HOWEVER, the effect is that the angular seperation of stars at the edge of the field is larger than if you put those stars at the center of the field. If you put a double star at the center of the feild and let the star pair drift to the edge, what you will see is that the stars appear to get further apart. The field is literally being stretched like a rubber sheet you see in those gravity well pictures. It is usually subtle, but very real. Now stars remain more or less pinpoint, but if you put a PLANET near the edge of the field of an eyepiece with bad pinchshion, it actually gets stretched into an oval.
This though is not what bothers people.
What REALLY bothers people is that when you are sweeping the sky using an eyepiece with bad pinchshion distortion, the effect is a bit weird. Because angular magnificaiion is highest at the edge of the field, as stars come into view, they appear to be moving FAST. As they approach the center of the field, they appear to SLOW DOWN! LOL.. Is weird to see. And of course as the star to get near the opposite field stop, they ACCELERATE again.
Also, stars that do not cross the center of the field appear to move not in straight lines, but rather converging arcs as stars frome either side of the field pass close to the center and then start seperating as they move out of the opposite side.
I THINK (and I could be wrong) that this is the PRIMARY reason why some people are REALLY sensitive to pincushion distortion. If you never sweep your scope, for 99% of the targets, you will never know it is there. Keep your eye to the eyepiece while moving the scope though, and it can be a squiggly experience.
So, while the link above gave a technical description, I hope that my volenteering a practical observer's explanation is helpful.