Cassiopeia Observatory

Review: 2" Explore Scientific 9mm 100° Eyepiece

Posted: 17 November 2012

I have enjoyed lunar terminator touring from my observatory, but I felt cramped with the limited field-of-view (FOV) of my 9.7mm eyepiece. I decided that the Explore Scientific 9mm 100° eyepiece would give me a nice expansive yet magnified view of the terminator. Since the moon was new when I received the eyepiece, I tried it first on some Deep Sky Objects (DSOs) and was pleasantly surprised by the views it provided.

"First Light" with the new eyepiece was on Tuesday, 13 November 2012, on the Double Cluster. Using my Meade 8" LX200-ACF, I first viewed the Double Cluster with a 1.25" Meade Series 5000 26mm (77X, 60° apparent field-of-view, 19mm eye relief). I then switched to the new 9mm eyepiece (222X, 100° apparent field-of-view, 9mm eye relief). The Explore Scientific 9mm eyepiece was nearly parfocal with the Meade 26mm eyepiece. The 9mm provided a very sharp view of the stars to edge of the FOV. And as expected, the larger apparent FOV with the 9mm showed more stars in each of the clusters in the FOV. While the true FOV with the 26mm was wider (lower magnification), the magnified view in the 9mm was impressive. I viewed the Double Cluster with a 1.25" Meade Series 4000 9.7mm eyepiece (206X, 52° apparent field-of-view, 4mm eye relief). Compared to the new 9mm eyepiece, I felt very restricted with the 9.7mm eyepiece due to its much narrower FOV.

Using the new 9mm eyepiece (222X), I then viewed M31. The galaxy was surprisingly bright at such a high magnification on the 8" telescope. The M32 and M110 companion galaxies even looked good. The best views of this first night with the 9mm was of M57 (Ring Nebula), M13 (Great Globular Cluster in Hercules), and M92 (globular cluster). In fact, the Explore Scientific eyepiece provided the best view I have ever had of M57 in the 8" telescope. The ring was bright and showed some structure. When I viewed M13 with the 9mm, my first reaction was that I was seeing way more stars than I had ever seen before in the globular cluster. The same applied to M92. The Explore Scientific 9mm 100° eyepiece is going to be my favorite eyepiece for viewing globular clusters.

Due to my having caught a cold at the Expo, I decided to cut the new eyepiece "first light" session short. And then, due to cloudy nights, I had to wait before using it again. Finally, on Friday, 16 November 2012, the observatory was opened at 1804 MST, 66°F. The sky was mostly clear, with some clouds low in the southwest. I was still fighting off the cold but it was less severe than it had been on the "first light" session.

At 1809 MST, viewed the crescent moon with Meade 8" LX200-ACF using the Meade 1.25" Meade Series 5000 26mm (77X, 60° apparent field-of-view). The entire lunar disk was visible within 26mm FOV. Switched to the 2" Explore Scientific 9mm 100° eyepiece (222X). About one quarter of the lunar disk was visible in the FOV. I compared the lunar FOV with the 9mm eyepiece to that of the 1.25" Meade Series 4000 9.7mm eyepiece, which only showed about a ninth (estimated) of the lunar disk. With the Explore Scientific 9mm eyepiece, viewing the moon was a delight. The lunar surface was sharp all the way to the edge of the FOV. I found that I would not slew to look at various areas on the moon, but would just move my eye around to look in different directions. That was a unique experience at a telescope and was very pleasant and natural.

I added the Antares f/6.3 Focal Reducer and viewed the moon with the 9mm 100° eyepiece. This would not be a normal use of the 9mm eyepiece but I wanted to know what the FOV would be. The lunar disk nearly filled the entire FOV, but was more a magnified view than what I would see with just a 26mm eyepiece alone.

I then slewed to the star Altair to make some true field-of-view measurements. I recorded the Declination values with Altair placed at the north and south edges of the FOV. The difference would be the true FOV. With the focal reducer, I determined that the Explore Scientific 9mm eyepiece has a true FOV of 46'36" on my 8" LX200-ACF when using the OPT 2" star diagonal. Without the focal reducer, the true FOV is 25'30". These actual measurements compare favorably to the values (27' and 42.9') shown in the AstroAid software on my iPhone:

I then did some more lunar observing with the 9mm 100° eyepiece. Simply lovely. It was great to have such an expansive view of the moon. I decided to do some iPhone afocal photography through the 9mm eyepiece. I don't have a 2" adapter for my MX-1 afocal adapter so I had to handhold the iPhone over the eyepiece. The short eye relief and wide FOV of the eyepiece made capturing a good image difficult, but I was able to get this one (which does not show the entire eyepiece FOV):

I ended this session early since I didn't want to make my cold worse. Closed the observatory at 1902 MST, 61°F.

How well did the 2" Explore Scientific 9mm 100° eyepiece meet my expectations? The wide FOV provided awesome views of the lunar surface. I expected that. What I did not expect was how well the eyepiece did when viewing DSOs with the 8" telescope. The high magnification and wide FOV yielded excellent views of the DSOs I observed during the "first light" session. The 9mm had a shorter eye relief than I had expected. To see the entire FOV, my eye had to be very close to the eyepiece. It felt like I was closer with the 9mm than I was with the 9.7mm although the 9.7mm has a much shorter eye relief in its specification. But once the entire FOV was visible to the eyepiece, stars and the lunar surface were sharp everywhere in the FOV. The eyepiece is waterproof (not tested) and comes with a 5 year warranty. It accepts 2" filters (although I don't have any to test). More details about the eyepiece are available on the OPT web site.

The 2" Explore Scientific 9mm 100° eyepiece is definitely a "keeper". It will be right at home on my Meade 8" LX200-ACF telescope:

I look forward to many nights of lunar terminator touring and DSO observing using the Explore Scientific 9mm 100° eyepiece. As I said earlier, the eyepiece will be my favorite for viewing globular clusters with the 8" telescope. If you want wide angle but magnified views of the moon and DSOs, you should definitely consider adding the 2" Explore Scientific 9mm 100° eyepiece to your collection.

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