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The Siebert 36mm, a most unusual eyepiece.

Posted by Manuel Reyes   03/22/2006 12:00AM

The Siebert 36mm, a most unusual eyepiece.
I have been using the 36mm for several months now and I have always judged my eyepieces based on my tendency to grab them over others in my collection. Some eyepieces have that comfortable feel when you want a view you can count on. In my case it has to have the right amount of eye relief and I can't have the idea in my head that the eyepiece is not giving me my best view. This means it has to compare better then average to what is currently available. So this is what makes or breaks an eyepiece in my collection. Now, on to the review.

In the review below I do most on my comparing between the Siebert 36mm and the Panoptic 35mm. And the scopes were 8" f4.9 Dob and a friend's 12.5" f/5 Dob.

I have broken this review down into the objects I am viewing.

The Great Orion Nebula.

This jewel of the winter skies is something I look forward to each year. There is so much to see here that it's hard to take it all in. It is a big object as well and fits nice in an eyepiece of the 36mm size. On a very good night with good seeing and transparency the Siebert 36mm brings out subtle detail that I never noticed in some of my other eyepieces and even with my time using the Pan 35 it did not seem to do any better. This is not to say the Pan 35mm did not have any advantages on the 36mm but subtle detail and color shifts were not one of them. The Trapezium resolved into 4 stars very nicely in my 8" f/5.9 and in my friend's 12.5" f/5 Dobs. You could move those 4 stars anywhere in the FOV and they still resolved the same as the center which is not bad for any eyepiece. Of course the PAN was the same in this regard. So little time so many other thing to view and review so let's move on to Pleiades.

Pleiades: The Beautiful 7 sisters.

More like 9 bright stars mixed with a lot more dimmer stars. I did not see any difference in the Pan or Siebert on this. They both framed the whole cluster with lots of room to spare. There was one thing though. At the time I did not know Pleiades' had nebulosity but noticed some diffused glare around some of the stars. I thought I saw it in the Pan 35 but was sure it was there when I looked through the 36mm Observatory eyepiece. I later found out that it was a little nebulosity that does not usually come out without photographs. This said a lot about these eyepieces and the conditions of the night that I had the privilege of being out on. Next beautiful thing to look at: The double cluster in Perseus!!!!

The Great Double cluster in Perseus.

As important as it was for my eyepieces to be sharp and clear to the edge for the Pleiades, it is even more important for me to enjoy the Double Cluster. I like to plant my eyepiece in the center of the spectacle and look at my leisure. I am looking for subtle difference in the Clusters. Stars that are of different colors and are of different brightness and all this is spoiled if the field is not perfectly sharp. If the field is sharp enough it almost looks like some of the stars are in the foreground. This gives the Cluster a strange 3d effect and makes it come alive. And I can say in the two dobs this was the case with the Pan 35mm and the Observatory 36mm. The clusters were sharp, bright and very detailed. In truth, that night I had never seen them look better these clusters were almost too beautiful to bare.

Galaxy NGC 891 A small mention.

My best test for the light transmission for a low power eyepiece is if I can see NGC 891. This mag 10 on edge galaxy is hard to see in my 8" dob unless the conditions are very good where I do most of my best viewing in PA. There are some nice dark spots here and my spot has about mag 6 or better conditions on a good night. Every thing must come together to see it and the eyepiece must do its part. In this test the 36mm pasted very well.

Finally The Crab M1 nebula

The remnant of a star gone super nova in 1054 AD only shows me structure with a great eyepiece. And the 3 eyepieces I like to use for their different perspectives are the Nagler 13mm t6, the 2" Pan 27 and the 36mm OB. The subtle details in this nebula reluctantly show themselves with careful viewing and the right eyepiece selection. The 36mm distinguished itself on the Crab because of its exceptional contrast.

Barlowing: The 36mm takes barlowing very well in my x2 Orion barlow. The eye relief did not go up too high and the FOV was not reduced a lot. When used in conjunction with my Ultra x2 Telecentric barlow as shown in the picture above the barlow operated invisibly. A good example of this was with these 3 open clusters M36, M37and M38 in Auriga. These look great through the 36mm, sharp and bright but when you barlow it at x2 the brightness is supposed to be 4x less bright theoretically but with the Ultra barlow it was hard to tell. Things just looked bigger and still very bright. All the stars I could see unbarlowed in the 36mm I could see even better at x2. So even though the 36mm barlowed good in a regular barlow it was even better in the Telecentric style and the FOV and ER were not lost. So your results barlowing with the 36mm will depends to a larger extent on the barlow used.

Summary: The Observatory 36mm is an eyepiece that may be unmatched for it's price range. This is not to say there are no eyepieces that are it's match or better but none I could find at this price. It has a combination of characteristics that attracted me to it. It is light, It is compact, it does not have a tendency to black out or "kidney bean" , It barlows beautifully and it has nice eye relief as about 22mm which is not typical of an eyepiece at this low power. In short, I Like it.


Sharp in fast and slow scopes alike.
22mm ER with a wide FOV.
Light weight and compact.
All my filters threaded in well.


After it was mentioned to me by another CN user I tested the 36mm on Sirius to see if I could see a reflection on this bright star and the answer is yes. A dim reflection could be seen. I wish it had not been pointed out to me since I might have never noticed it. For most it is unlikely that this will be an issue except under the most extreme use.
It does not have a flashy look.

Manuel Reyes