Planetary Observing with 5mm Eyepieces: Pentax 5mm XO; Baader 5mm Orthoscopic; University Optics 5mm Abbe Orthoscopic and 4.8mm Super Abbe Orthoscopic Review

   Four 5mm eyepieces that are readily available from US astronomy equipment suppliers were evaluated and reviewed for their performance in planetary observing with 4 and 5 inch refractor telescopes.  Going into the tests, I assumed that the orthoscopic eyepieces would provide excellent on axis viewing of planetary detail based on a wide array of reviews on this classic simple eyepiece design.
The main questions I was interested in addressing in the tests were:

• Does a premium quality eyepiece (i.e., Pentax 5mm XO) provide noticeably better views of planets than a good quality Abbe orthoscopic eyepiece when viewing through a top quality refractor?
• If the premium quality eyepiece does provide a better planetary view than other eyepieces with a top quality refractor, are similar benefits obtained with midlevel and entry level refractors?
• Does use of a binoviewer provide improved planetary viewing to monocular viewing?

Figure 1 (From left to right): Pentax 5mm XO; Baader Planetarium 5mm Genuine Orthoscopic; University Optics 5mm Abbe Orthoscopic ; University Optics 4.8mm Super Abbe Orthoscopic

5mm Eyepieces Evaluated/ Reviewed

• Pentax 5mm XO – 44 degree field, 3.6mm eye relief.  5 elements includes low dispersion lanthium glass, SMC coatings.  Manufactured in Japan.  Cost new $359 USD (Abbreviated as Pentax 5mm XO or Pentax XO)
• University Optics 5mm Abbe Orthoscopic – 45 degree field; estimated 4mm eye relief.  4 elements.  Reported on several websites to be manufactured by Kokusai Kohki in Japan.  Cost new $76 (Abbreviated as UO 5mm Abbe ortho or UO ortho)
• Baader Planetarium 5mm Genuine Orthoscopic – Abbe orthoscopic design.  40 degree field, 5.5 mm eye relief.  4 elements in 2 groups.  Reported by distributor to be manufactured in Japan.  Cost new $109 (Abbreviated as Baader 5mm ortho or Baader ortho)
• University Optics 4.8mm Super Abbe Orthoscopic  - This eyepiece is reported by posters on cloudynights.com to be made in China and appears to be identical to the 4.8mm orthoscopic eyepiece made by Kson Optics in China.   Specifications are not provided by the supplier.  Cost new $48. (Abbreviated as UO 4.8mm super Abbe or UO super Abbe)

Other eyepieces were used in the tests with the 5mm eyepieces including:  Televue 3.5mm Nagler type 6, University Optics 4mm Abbe Orthoscopic, University Optics 7mm Abbe orthoscopic and Televue 7mm Nagler type 6.  In addition, I compared performance of the  5mm eyepieces with quality of viewing through a binoviewer (William Optics binoviewer with Televue 8mm Plossl eyepieces and 1.6X Barlow nosepiece lens or with 5mm University Optic Abbe Orthoscopic eyepieces and no nosepiece lens).

Refractors Used for Evaluations

• Takahashi TOA-130S  130mm triplet f/7.7, 1000mm focal length (TOA-130)
• Takahashi TSA-102S  102mm triplet f/8, 816mm focal length (TSA-102)
• Televue 102  102mm doublet f/8.6, 880mm focal length (TV102)
• Vixen ED100SF:  100mm f/9,  900mm focal length (ED100)

Evaluation procedures
   Jupiter and Saturn were observed during early morning and evening periods between June 29 and July 30, 2011 from Gainesville Florida.  Conditions were very humid and sky transparency was low. However, seeing was generally good to excellent. Saturn in early evening was occasionally observed under only fair seeing conditions after rain storms passed through. Observations were made with 2 to 3 telescope at a time using all four 5mm eyepieces switching between telescopes mounted on Losmandy G11 and GM-8 equatorial mounts.  At each time period, all four eyepieces were switched between the three telescopes being tested at that time using the same diagonal (usually a 2-inch Astro-Physics Max Bright).  Image sharpness, color saturation and contrast and light scatter pattern (glare around point light source) were compared. 

Note on light scatter patterns:  Light scatter was estimated by comparing the outer border of the glare around Jupiter or Saturn relative to a bright outer moon (e.g., Titan for Saturn and usually Io for Jupiter).  The amount of perceived light scatter around a bright planet is the result of several variable factors including:  1) scatter of reflected light from the planet in Earth's atmosphere due to atmospheric moisture and particulates; 2) telescopic front element and tube internal reflections and scatter; 3) diagonal reflectivity and scatter; and 3) eyepiece scatter and internal reflections.   When generating the light scatter patterns for the four eyepieces, they were done in a period of a few minutes using the same telescope and diagonal so that all factors except the eyepiece were as constant as possible.

Results
Three of the four 5mm eyepieces tested provided sharp planetary views at the 163 to 200X magnification viewing with the four refractors. The Pentax XO, Baader ortho and UO ortho provided sharper, more detailed planetary than any of the other eyepieces tested. Seeing was generally not good enough to get optimal views with either the 4mm UO orthoscopic or 3.5mm Televue Nagler type 6. Very sharp views of Jupiter and Saturn were obtained with the 7mm UO orthoscopic and 7mm Televue Nagler type 6. However, the 5mm eyepieces provided more planetary detail.

	Figure 2: Visible light scatter pattern for 5mm eyepieces viewing Saturn with TSA-102 on July 30, 2011 at about 1:00 UT

• Pentax 5mm XO:  This eyepiece produced the highest quality planetary views with least light scatter (Figure 2) and greatest contrast, color saturation and sharpness.  Performance was only slightly, but noticeably better than that for the Baader and UO orthos.    Occasionally, under less than optimal seeing condition, this eyepiece made the difference between seeing objects and not.
  
  For instance, on several evenings when viewing Saturn with the entry level refractor, Vixen ED100SF, it was not possible to see the Cassini division with most of the eyepieces. At the time of the test, the Cassini division was a difficult feature to see clearly with a 4 inch refractor with the rings tilted at only a 7 or 8 degrees North from the axis of view from Earth. While it was possible to see the Cassini division with all of the eyepieces when using the other two 4 inch refractors, (TSA-102 and TV102), it was only possible to see the Cassini division with the ED100SF when using the Pentax XO.

• Baader Planetarium 5mm Genuine Orthoscopic and University Optics 5mm Abbe Orthoscopic:  These two eyepieces performed identically as far as light scatter, contrast, sharpness and color saturation. If the Pentax XO performance were rated at 100%, the Baader and UO orthoscopics easily performed at the 90-95% level.

• University Optics 4.8mm Super Abbe Orthoscopic (Kson Optics):  This was the least expensive of the eyepieces tested and was intended to be the "negative control" in the tests. It performed as anticipated with light scatter being the greatest of the 4 eyepieces (Figure 2) and sharpness, contrast and color saturation being the weakest of the eyepieces tested. If the Pentax XO performance were rated at 100%, the performace of the UO 4.8mm super Abbe was at the 80-85% level.

Binoviewer performance compared to single eyepiece viewing:  The binoviewer allowed viewing using binocular vision for detection of subtler cloud surface details and tonal changes that were especially beneficial when viewing bands and cloud patterns on Jupiter with all 4 telescopes tested. On the other hand, the images were less bright due to noticeable light drop off, had greater light scatter and had corresponding decreases in contrast and color saturation. Views of Saturn with an entry level refractor (ED100SF), where details such as the Cassini division were already difficult to see, were not improved by the binoviewer. However, when viewing Saturn with the top class TOA-130, views were enhanced by the binoviewer.

Answers to questions asked:

• Does a premium quality eyepiece (i.e., Pentax 5mm XO) provide noticeably better views of planets than a good quality Abbe orthoscopic eyepiece when viewing through a top quality refractor?
  • Answer: Yes, but only very slightly and at a much greater cost.
• If the premium quality eyepiece does provide a better planetary view than other eyepieces with a top quality refractor, are similar benefits obtained with midlevel and entry level refractors?
  • Answer: Yes, but only slight benefits result at very high cost relative to the cost of the entry level refractor.
• Does use of a binoviewer provide improved planetary viewing to monocular viewing?
  • Yes, binocular viewing allows detection of subtler surface detail and color due to the benefits of binocular vision. However, binocular viewers decrease light transmission, increase light scatter and lower contrast and color saturation. While there are beneficial planetary viewing results with binoviewers, benefits are greatest with a high performance refractor and are of minimal benefit with an entry level refractor.

	Vixen ED100SF (left) and Takahashi TOA-130 (right) on Losmandy GM-8 and G11 mounts, respectively after an early morning session viewing Jupiter. Eyepieces are laid out in the white box for shifting between eyepieces on each telescope. A William Optics binoviewer is mounted on the TOA-130
Eyepieces laid out in box for comparison viewing	William Optics Binoviewer on TOA-130 with Televue 8mm Plossl eyepieces. A 1.6X Barlow is mounted on the nosepiece for comparable magnification of planets to the 5mm eyepieces tested.

Index

Date posted: 31 July 2011, Updated 09 August 2011