Ordered the Zuhmell Dobsonian 10inch scope. Questions?

Question

I have ordered the Zuhmell Dobsonian 10inch telescope along with an extra 4mm eyepiece [it comes with a 9mm and a 25mm which I am familiar with] and I plan to download stellarium and practice finding things until the Dobsonian gets here on the 5th. Also am going to look into loal astronomy clubs/star watches to possibly visit and check out.

Any recommendations of what to purchase in the future for this telescope?

I have getting a 2x barlow in mind but which brand would suit me best?

and what other accesories would be a good idea to get once I have found my way around this telescope?

This is not related to the Dob 10 but should I sell/send my Meade ETX-80 back eve after geting my Dob 10? I have been told that it is still good to have an easier scope to carry around easier and it is a decent refractor. The only other scope I have i an old 50mm refractor scope with a 9mm a 12mm and a 25mm eye piece along with a 3xbarlow eye piece. I sure could use the money that selling the ETX-80 could give me but getting your guys opinons is always worth a listen.

Thanks for your time.

Answer 1

I'd second the opinion that the 4mm EP is a mistake. That gives 313x which needs very steady skies to be worthwhile even at the best of times. Added to that it is really pushing what is practical for a Dob which are much better suited to low power, wide field imaging. This is without even considering the practical problems - if you bought that from Zhumell as well it will be a Plossl and Plossls are completely useless at such short focal lengths because of the lack of eye relief. More advanced optical designs represent far better value for money because they will actually get used, even if they are more expensive to purchase. I'm a great fan of the Baader Genuine Orthos at that kind of focal length although the Clestron X-Cels will give you a slightly wider field of view.



As for accessories, I would wait until you are actually using the scope. I suspect that my initial purchase would be a good mid-power eyepiece, perhaps 15mm. Next would be a low power wide field eyepiece, probably a two incher in the 40-48mm range. Finally I would ditch that 9mm Plossl in favour of something with better eye relief.



As for Barlows, Televue are the best in my opinion. The best Barlows are pretty much invisible in use - you can't tell they are there, you just have extra magnification. This is something never even approached by budget brands. However, given the eyepieces at your disposal I would not regard it as a priority.



Finally, I would keep hold of the ETX. You may well still have a use for it, particularly under light polluted skies - star hopping is fine under dark skies but forget it in the city. In any case I suspect you will be unpleasantly surprised how much it is worth on the open market. On a bad day it may be worth less than $100 so personally I'd rather keep the scope.



Update: I equally strongly disagree with Search firsts... rebuttal of my wide field EP suggestions which strike me as an overly simplistic analysis. The problem is that he is calculates the exit pupil with a straight aperture divided by magnification calculation which only holds when there are no other optical limits, something rarely true on Newtonians at low power.



From the published specs we can determine that wide field performance becomes barrel limited at 1.66°, and secondary mirror limited at only 0.58°. For anything above those fields a simplistic calculation such as performed here breaks down and real exit pupil will always be smaller than the calculated figure. The field will not be fully illuminated for any of the wide field EPs under discussion (even the 30mm), so the edges of the field will be dimmer than the centre (although you will probably not notice the effect). What you will notice is the wider field and higher surface brightness of the lower power EP making things a lot easier to find - remember you have no setting circles or computer at your disposal.

Answer 2

Ozzrya -



I would skip the barlow. You are already pushing the magnification at over 300x with the 4 mm eyepiece. Anything higher than that will be very difficult to use and will not be worth the effort. I have a good barlow for my 11 in. SCT, but I never use it. If you have the high mag eyepiece, which you have ordered, then the barlow just puts more glass in the light path. Based on my quick review of this scope on the internet, it looks like it only has a pretty marginal finder scope that will be difficult to use. So I would use the barlow funds to buy a 1x finder, like a Telrad. You will be glad you did. Much of your time will be spent in the effort to actually find the objects that you are seeking. Without a decent 1x finder, you will certainly encounter some serious frustration in that effort. With a 1x finder, you will find the task much easier. (ADDED: You will also encounter much less frustration if you stick with the 25 mm eyepiece until you get used to the scope. You will find that the 4 mm is frankly too high. Magnification is not important for most amateur astronomy).



Personally, I would return the ETX-80 and take along a good binocular. It will do the same thing for less trouble. Good Luck and Clear Skies.



ADDED (2): The finder scope in this case is basically a small refractor with a cross hair. Remember that the image in this will be inverted, so when you slew the scope (to find a target), the image will move the opposite way that you think it will. The advantage to a 1x finder is that you can stand back a bit, aim the scope in the right region of the sky (you see the sky in a normal view with a lighted sight and with no magnification - much less confusing) , then use the 8 x 50 to actually see the target (perhaps faintly) and get it centered for the eyepiece view. You don't need a barlow, and you don't need another eyepiece (until you're ready to spend a lot and get a good one). You definitely need a better finder. I suspect you will really want to buy one once you try to use the scope, so you may want to think about it now.

Answer 3

Please wait until the scope arrives and you have had a chance to use it before deciding what else you might buy. Personally, I'd say the 4mm eyepiece is a mistake. The usual next eyepiece is a good wide field eyepiece, 40mm or longer. Most interesting objects are viewed at relatively low magnifications. Except for planets. This isn't the best scope for them, though aperture is always good. Saturn through Tina's 18" was a memorable experience...



What are you using for star charts? They are always a worthwhile purchase. I like Pocket Sky Atlas for most observing.



Your 50mm refractor sounds like a Christmas Trash scope - the 3x barlow is a dead giveaway. It's not worth anything at all.



A Dob in this size range is a good scope and is highly recommended. Have fun!

Answer 4

A good long focal length eyepiece is what uses a Dob to best effect. I wouldn't worry too much about the exit pupil - if it is larger than your pupil than simply makes it more practical in that you can look around the image. As has been noted the calculated figure is often nonsense since limitations are further up the optical system anyway. It is nice to see someone with a thorough understanding of the subject in the round.

Answer 5

After joining a club, the next thing you should get is a case for your optical tube. It will help to keep the dust off the mirror and help protect it in transport. After that try a 40mm eyepiece.



Keep the 80mm scope.



Give the 50mm scope to a kid or donate to the new club for them to use as a door prize.



The 3x barlow might work on the 10 inch but not on the others. I really don't care for barlows because they add a lot of distortion.

Answer 6

Congrats on your decision. You'll appreciate a good quality barlow, and you will prefer it with a 9mm over using the 4mm alone as the 4mm eyepiece will have uncomfortably tight eye-relief if it is a standard Plossl.



My recommended barlows would be either an Antares or Celestron Ultima 2x barlow which are around $60-$80. Don't go cheap with barlows (and there are a lot out there much cheaper), you do get what you pay for and you will be using them for years with all types of eyepieces.



For 12mm and shorter I much prefer Orthoscopic eyepieces to Plossls as they are noticeably sharper in their views. And eye-relief while tight is not as tight as Plossls.



Speaking of sharpness, learn how to collimate your telescope. It's not difficult, but may take a little patience at first. The manual should give basic instructions, and there are others online. If you have a little money left over you could purchase a "Cheshire" style collimator (though the scope may come with a more or less adequate collimation "cap"). If the scope came with a laser collimator or you are thinking of getting one, you should shelve it, because the lasers themselves are frequently misaligned and will not give you as accurate a result as you will by your own eye.



When you tire of just the solar system you might consider buying 2" eyepieces in the 26-34mm range for those extra-wide "rich-field" views of the Milky Way and extended objects like the Andromeda galaxy. Or nebulae like the Veil.



If you are mostly viewing from the city (or other light-polluted environment) you will want to keep your low power eyepiece no longer than 30mm or even a little shorter. Under light polluted skies a nebula filter such as an "Ultra___" (usually "high contrast") type filter or Oxygen3 line filter can help with nebular objects.



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ADDED: I'll have to STRONGLY disagree with Andrew_S's recommendation of a 2" in the 40-48mm range for this particular telescope (focal length 1250mm). This will result in an exit pupil of 8.2mm with a 40mm and an exit pupil of 9.8mm with a 48mm. Under the darkest skies, your own eye's pupils will not expand beyond 7mm or so, and even less under light polluted skies or if you are middle aged. Any exit pupil larger than your own eye will be light lost and wasted. Plus at below practical magnifications the telescope's secondary casts a shadow at the eyepiece that results in "blackouts".



I noticed on the site describing the telescope that it doesn't come with dust covers. Go buy a pair of inexpensive shower caps with the elastic around the edge from the drug store so you can cover the ends of the telescope when not in use.

Answer 7

You have done enough,study the sky and spend much time with your telescope...you need no upgrades now

Wally