BirdForum is the net's largest birding community dedicated to wild birds and birding, and is absolutely FREE!

Register for an account to take part in lively discussions in the forum, post your pictures in the gallery and more.

Reply to thread

Message: <blockquote data-quote="Can Popper" data-source="post: 604430" data-attributes="member: 39163">Siebert 24mm UltraOne of the most unusual eyepiece in Harry Siebert's eyepiece offerings is the Siebert 24mm Ultra.  What makes it different from other eyepieces is that it offers a wide field of view (65 degrees), long eyerelief (20mm), and a flat field by using only 3 lenses.Those who are familiar with eyepieces know that on the surface, having such a combination of features seems to be mutually exclusive.  Other 3 lens eyepiece designs such as the Kellner or Edmund RKE have narrow fields of 35 to 45 degrees.  Typically, most of today's eyepieces use 5, 6, or 7 lenses to provide the three features in the same eyepiece.  However, using so many lenses has its own drawbacks, namely the loss of light and contrast.In a test done by Cloudy Nights (<a href="http://www.cloudynights.com/documents/planetaryeyepieces.pdf" target="_blank">http://www.cloudynights.com/documents/planetaryeyepieces.pdf</a>), the three to four element eyepieces ruled the field over the fancier, more expensive eyepieces (such as the Televue Panoptic and Pentax) when it came to unveiling the fine details of planets.Recently I was in the market for an eyepiece that would provide the lowest magnification and the widest field of view on my Pentax 100ED.  Such an eyepiece would be useful for digiscoping because I wouldn't need to use as much camera zoom and it would result in fast shutter speeds due to its large exit pupil.  Doing some research on Cloudy Nights, Televue's website, and Harry Siebert's website, I found that for the 1.25 inch eyepieces, 24mm was the lowest power one can go and still have a field of view in the mid 60's and higher.  Beyond 24mm, one starts to trade field of view for a lower magnification due to the limitation of the 1.25 inch barrel size.The two widest field 24mm eyepieces are the Televue Panoptic 24mm and the Siebert 24mm Ultra.  On the Siebert website, some comparisons were made between the Siebert 24mm and the Panoptic 24mm (<a href="http://www.siebertoptics.com/SiebertOptics-eyepiececomparisons.html#24mm%20compare" target="_blank">http://www.siebertoptics.com/SiebertOptics-eyepiececomparisons.html#24mm compare</a>).  The Siebert 24mm seems to compare well with the Pano at F6 or above which is where the Pentax spotters are.  Reading Siebert's findings and knowing the result of the Cloudy Night review, I decided to go with the Siebert Ultra.First, I called up Harry and asked him what his secret sauce was out of curiosity.  I asked Harry if he used fancy glass elements made of lanthanum or flourite to achieve the same features of the Panoptic with half the glass.  Harry laughed and told me that wasn't the case.  He achieved the features through the clever design trick of moving the chromatic aberration to the edge.  I could tell from the tone of Harry's voice that he was proud of his 24mm Ultra eyepieces.From the five attached pictures below, one can see that the Ultra 24mm provides wide, sharp, and flat views.  And if one looks closely at the image edge, one can also see the chromatic aberration that Harry Siebert intentionally moved to achieve the three features using only 3 lenses.</blockquote>

Verification