Monday, January 07, 2013

12" Zhumell Dobsonian Review and First Light

Pardon the rope, the Telrad was not permanently
attached at the time fo the photo!
This post will serve both as a review of the new telescope as well as a report on the previous two nights of viewing with it. So, yes, unexpectedly I purchased a new scope. I'd planned to purchase a 16" this spring/summer but upon seeing the current prices of the Z12 I decided that, based on my budget, spending $750 now would be much wiser than $2,000 later. As much as I would appreciate the added light gathering of the 16" the 12" is a substantial upgrade from the 8" and should be enough for now.

The scope arrived in good shape in undamaged boxes. I had it put together in an hour and that was taking my time. This is a huge scope for one person to safely maneuver. I'll be happy to have it in a permanent location with shed that will get rolled back during use.

Collimation before first light was a bit tricky. I'd read that the laser collimators that ship with these are out of collimation themselves and are of no use until they are collimated first. I set about doing that but adjustment screws are of a size (allen wrench) I do not have. Luckily my observing buddy Russ had his. Getting the secondary aligned was easy enough. The primary mirror, on the other hand, not so much. It seems that the tension springs in the adjustment bolts are pretty weak. As I turned them this way and that it became clear that I was going to have a hard time getting the mirror where it needed to go. Then it occurred to me that the lock screws, while not intended for adjustment, often do effect the mirror when tightened down so I tried turning a them a bit and presto, I had a collimated mirror.

This is a big mirror that will often need cooling down which is why they include a fan. I have not used it yet because I had it out in the shade on the first day and in the well house the second day so it was cooled off and ready to go at dark.

A few words about the hardware on the scope before I delve into what I saw with it. Everything seems very solid.  I've not used the finder scope yet because I ordered a Telrad and have used it both nights. That said, the finder seems decent in terms of construction. The big plastic cover for the OTA (optical tube assembly) is a pretty loose fit so I'll have to do something about that. Of course the stand is particle board like all of these mass production units but seems solid enough for now. Movement of the scope is very smooth and it is very well balanced. I WILL upgrade to a home built birch plywood stand at some point. All in all, the scope seems very well built. I've encountered no problem other than the above mentioned weak tension springs on the collimation screws that I'll replace and the loose cover.  As you can see from the photo, this is a huge scope and not something I want to move much.

The dual-speed Crayford focuser is very smooth and a nice upgrade over the focuser on the XT8. Being able to fine tune the adjustment is a very nice benefit of this focuser.

First Light for the new scope was Friday night and it was perfectly clear for it! My intent was to spend some time just getting familiar with the bigger scope and compare some of the views with what I've seen with the 8". There's no doubt it is impressive.

First object viewed was Jupiter and it looked great. The main difference, given good seeing conditions, is a sharper image. The 8" struggles with the 5mm EP but provides a fairly crisp image with really good seeing conditions. The 12" provides an even sharper image with a few more details  in the cloud bands and also seems to have a little more tolerance of poorer conditions though I won't know for certain until I've used it more. Of course the same eyepieces also provide higher magnification due to the different focal length. The 5mm needed for detailed planetary viewing gives me 240x in 8", but 300x in the 12". So, not only is it a sharper image but it is also more magnified. Even better, I could, push it to even higher magnification if given the right eyepieces/barlow whereas 240x is the upward limit for the 8".

Next up for comparison was M31, M32, M110: The Andromeda Galaxy and it's satellites. This is a big and very bright object so what I was hoping for was some detail. With the 8" I get a big and beautiful view but no detail. With the 12" I am seeing some structure. It is especially noticeable with the 11mm Explore Scientific 82 degree (provides a wider field of view than standard lenses). At that level of magnification I am seeing a smaller picture but I do see the dust lanes which I don't think I'm seeing at lower magnification. In all the EPs the 3 objects are beautiful and the more faint M110 is much more defined and easy to see.

Next on the list, the Orion Nebula which never disappoints! In the 8" the nebula presents a fantastic view and in the 12" it is a fantastic view. More detail is visible and some of the dark areas are more pronounced. I'll have to spend more time observing before I can offer any more detail.

Now we are getting closer to those things which I expect will really benefit from the 12". Specifically, globular clusters, faint nebula, and distant galaxies. A great example would be something like NGC 2158 which is very rich open cluster in Gemini which almost seems like a loose globular cluster. In the 8" it presents as a nebulous sphere with little to no resolution of stars. In my first attempt to see it back in September I failed with the 8" due to deteriorating atmospheric conditions. The second attempt the next night was a success but the view provided little detail. By contrast, the 12" presented  this cluster as very easy to see and with much greater detail as many stars are resolved. Through the 12" this cluster of stars is now exactly that, a cluster of stars and not just a nebulous sphere.

My next target was the Pacman Nebula, NGC 281 in Cassiopeia. With the 8"  I had no success finding it even with the NPB nebula filter. With the 12" it was easy to see.

After that, a trip to Bode's Nebulae, two easily visible galaxies in Ursa Major. These are easy to find, I was hoping for greater detail. Unfortunately I didn't get much but more than likely that was due to my not taking the time. The night was getting on and I wanted to get some of my remaining Herschel 400 so this is by no means conclusive. I fully suspect that when I revisit and spend more time on these I will indeed see some new structure.

Last on the list were my remaining Herschel 400 galaxies in Ursa Major, 11 to 12 magnitude. While the 8" would make these visible they are often incredibly faint. With the 12" they were easy to find with little to no effort... it was so easy I almost felt like I was cheating! They don't provide much in the way of detail but certainly more than is visible with the smaller scope. I'm sure I'll have more to say about viewing these fainter objects as I spend more time with the Z12. Suffice it to say that the light gathering capability of a 12" scope is fantastic.

I'd intended to offer up the second night's viewing but I'm going to save it for the next post as this is getting quite long! Stay tuned.


1 comment:

jiffycoil said...

Hi Denny,
Thanks for the detailed review and the wonderful tour of the sky. I very excited, my Z12 arrives this Thursday. I was wondering if you could steer me to the instructions you used to adjust your laser contaminator? I was also curious if you replaced your adjustment springs and if so what did you use and where did you get them. Thanks again and clear skys to you.