Monday, August 17, 2009

Found Pease 1! And tested some nice eyepieces (16 August 2009)

Again a nice & clear sky, the 3rd in a row. I don’t need to work tomorrow so no worrying about staying late.

I have tonight also the opportunity to test some eyepieces (thanks to Hubert). I have an Astrolan ultrawide 30mm (80°) which provides me with a FOV of 1,2°, as well as a 9mm Nagler T6 and 4.8mm Nagler (the discontinued version) 

It’s not totally dark when I’m starting to test them. But that’s ok as I’m doing some side by side comparison. 

1. The first object was M13:

Astrolan 30mm (68x) vs. Pan 24mm (84x)
- A great FOV with this Astrolan (1,2°), much larger than the Pan (46’). But of course at the expense of a smaller magnification
- I have astigmatism with the Pan, but even more with the Astrolan. However, it disappears completely when I’m putting my glasses on.
- A bit of (vignetting). Don’t know how to translate in English 
- Good eyepiece for starhopping (see later in this report)

9mm Nagler vs. 9mm Celestron Plossl (225x)
- Nagler is providing sharper stars than the Plossl
- But the Plossl  goes slightly fainter!
- The FOV of 35' is just great

9mm Nagler vs. 9mm Celestron Plossl combined with Powermate 2,5 (563x)
The Nagler provides again sharper stars, but also here the Plossl goes fainter.

4,8mm Nagler (422x) (not compared with another eyepiece)
Sharp images, even at this power! Comfortable FOV of 20'. This is a great eyepiece!

Note 1: while testing I did not know this was a discontinued version and that the 5mm Nagler T5 provided a twice as large FOV. In fact, it's good I did not know, because it provides an unbiased opinion on this 4.8mm eyepiece. 

Note 2: I found on Cloudy Nights quite some remarks on the short eye relieve of this eyepiece. I don't recall having been confronted with this issue during my testing. It's true however it's impossible to observe through this eyepiece with glasses.

4,8mm Nagler with Powermate 2,5x (1055x)
Stars are small discs.

2. Next test was to find Pease 1 in M15
I have found Pease 1 (with Blinking Technique!) with the following eyepieces:

Celestron 9mm + Powermate 2,5x: blinking worked well because I do not have reflections on the filter as I can bring it real close to the eyepiece.

Nagler 9mm + Powermate 2,5: blinking more difficult as with this eyepiece I cannot bring the filter close to its edge, due to the firm eyecaps. I have reflections on the filter which makes it difficult to blink. I had only success when putting a dark cloth over my head.

Nagler 4,8mm: “easy” (everything is relative, so I mean in fact easier than with the 9mm and Powermate) 

3. Ringnebula (M57):
Nice image at 422x (4,8mm Nagler). Still able to observe it at 1055x but it becomes more difficult due to inaccurate tracking. Stars are little discs. Could see a star of mag 15.6 close to the edge (not visible at 422x) and maybe the central star. 

4. Little Dumbell (M76)
Here the 9mm Nagler gives a better view than the 9mm Celestron Plossl. I can see a bit more details on the nebula, and this time I see also a fainter star, which is not viewed with the Plossl. The 9mm Nagler (225x) gives a better view than the 16mm with Powermate (316x). 

5. Starhopping with Telrad and Astrolan 30mm 82°
I’m not used to starhop, so I admit I’m not good at it. However, I also know it’s always a little moment of joy when you found a DSO by your own means. I decided to give it a try by using the Telrad and the Astrolan with it’s 1,2° FOV. Without finder it’s of course a bit harder, reason why I limit myself to the obvious Messiers.  

I did not use starhop charts or an Atlas, only the constellation charts in the “Nigh sky observers guide” have been used. 

I have been able to find M13 (that’s really not difficult), M92, M56, M57, M29, and M15. I had to cheat a bit with M92 and M15: I did not found it immediately, so I used the ArgoNavis to locate, and then looked at the Telrad to find its position (aha, it's there!). Then I tried again only with the Telrad, and it worked. I repeated it a few times to save it well in my memory. I intend to try it during my next observation session.

So here is my eyepiece conclusion: 
- Astrolan 30mm (82°): fine eyepiece if you don' suffer from astigmatism. Otherwise it's OK when wearing glasses (which is not always possible when there is a lot of humidity in the air). It’s also a great eyepiece to starhop. 
- the cheap Celestron 9mm eyepiece is not bad compared to the Nagler 9mm. The Nagler is a bit sharper and provide some more details on a nebula. But the real “plus” of the Nagler is the field of view of 35'. Replacing the Celestron Plossl just for the quality of the image is maybe not worthwhile, unless you’re aim is to get the larger FOV or when you are obsessed by pinpoint stars.
- The 4,8mm Nagler is a great eyepiece. Unfortunately I have not been able to benchmark it with another one so I cannot judge if the premium price is justified. But I can imagine that at that power a larger FOV of 20' is real advantage and worthwhile over a traditional eyepiece. As stated previously I did not had an issue with the short eye relieve. If I have the opportunity I should compare this 4.8mm Nagler with the still active 5mm Nagler T5.  But honnestly, not knowing this 4.8mm was an discontinued version I was pleased with the view it gave me.

Great evening, and I can add Pease 1 to my observation list!

Addendum: observed the folllowing night once more with the 4.8mm Nagler, and indeed, it's a short eyerelief. Not really an issue when there is no condensation, which is  quite rare in our regions.

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