Author Topic: First Light with Zhumell Z10 10” DOB  (Read 1219 times)

pmethinxlamna

  • Active Astronomer
  • ***
  • Posts: 109
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: First Light with Zhumell Z10 10” DOB
« Reply #15 on: January 25, 2018, 02:46:47 PM »
Quote

This normal. Your finder is a small, very fast telescope. Telescopes to that are as sharp in outer half as they are in the center are very expensive, particularly when they're fast.

Why your telescope is F/5: If it were F/6, it would be 60 inches long instead of 50 inches..

Jon

Mark Patterson

  • Active Astronomer
  • ***
  • Posts: 117
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: First Light with Zhumell Z10 10” DOB
« Reply #16 on: January 26, 2018, 12:44:08 AM »
Great first reportMithrasTheArcher, always love reading the first light reports. I am not expert in any thing in particular and a lot of experts have covered everything you need to know, all I can say is just have fun with it, and see if your family wants to get involved in it.

calfkommomu

  • Active Astronomer
  • ***
  • Posts: 130
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: First Light with Zhumell Z10 10” DOB
« Reply #17 on: January 26, 2018, 06:31:46 AM »
Another point regarding the 30mm widefield that comes with the scope: a coma corrector will
not fix the astigmatism in it that causes the view to be soft away from the center. Only higher
quality eyepieces will be noticeably improved by a coma corrector. Coma is the least of your
concerns right now. The eyepiece would definitely work better at a higher focal ratio but the f/5
scope is worth the disadvantages it has by the offsetting advantages of reduced length, weight,
bigger light grasp, and wider field of view.

Nassim Zaragoza

  • Active Astronomer
  • ***
  • Posts: 119
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: First Light with Zhumell Z10 10” DOB
« Reply #18 on: January 30, 2018, 06:53:25 AM »
Quote
Quote
Many thanks for the helpful and welcoming responses thus far! I've really enjoyed reading your thoughts and suggestions. I've taken some of them to heart – well, to wallet – already and ordered a Starbound observing chair and Telrad finder with a 4" riser. I'm looking forward to adding those pieces to my stargazing kit, with hopefully some eyepiece purchases to come once I do a little more homework.

I can't shake the feeling that I am about to spend a ton of money on this hobby. 

Actually, tamping down my excitement and holding off on spending money has been a theme from the get-go. After getting "starstruck" back in August, it was very hard to not rush out and buy a telescope right away. With all of the options available and competing philosophies on how best to start, it was actually pretty overwhelming. I'm glad I took my time and waited, as it sounds like I really did get a good deal on this Z10 and it is a scope I can grow into.

I spent some time yesterday afternoon on YouTube learning how to collimate. This process loomed large in my mind and sounded like a real chore – a "reflector tax" – but in practice it was actually kind of fun to try and get the red dots to line up. I know that the really serious folks here collimate their collimators, but for my first time I just decided to let the factory-default laser do the work. Whoever had done this process before me really tightened the screws on the secondary mirror. I was afraid I was going to twist it right off - eep! - but they eventually came loose enough to adjust. Tweaking the primary took some fiddling, but I think I did it correctly. The stars looked a bit sharper to me, though I corrected the secondary first and the primary second and I've read in the interim that you're supposed to collimate Primary > Secondary > Primary. I'll try again ahead of my next observation.

With young children and a full-time job, I've got limited time/energy for setting up equipment, which is why I'm trying to make this scope as grab-n-go as possible. I'm keeping the scope covered in a shed in the backyard (including a shower cap around the bottom of the OTA to keep out spiders because ew). I do worry a bit about rust and dust, but the shed is about 15ft from the best observing spot in the yard and the scope is protected from the elements but not climate controlled. I think for right now this is the best solution to eliminating cool down time, reducing the distance I have to carry the scope, and also keeping it where my kids can't turn the steel OTA into a steel drum and spin it around on its base as fast as they can (see also: why I'm collimating it again ).

Question: Do eyepieces need cool down time too, or just the telescope mirrors? I've been keeping the eyepieces in a case in the house.

Regarding the finder scope, I took the telescope out last night and specifically looked for reduced quality in the outer half of the FOV. To my eyes, the stars on the outer half of the finder scope are less clear than the ones in the center. I did fuss with the focus of it and got things usably sharp in the center, but my general experience with the finder has been pretty frustrating overall. I'm eager for the Telrad to arrive.

Quote
[snip]

I trained myself to move the telescope by these phrases: Aiming the finder, move the telescope so that the cross-hair covers your target. Aiming the telescope, push on the telescope in the same direction that you want the target object to move. It's normal for the inverted image to slow one down at first. Remember, when looking through the eyepiece, push the telescope tube in the direction you want the object to move.

[snip] " ....True enough, taking my glasses off let me see the whole FOV in the eyepiece, but I couldn’t get the stars sharp. .."..[snip]

Regarding sharp stars...
<ul class="bbc">On a large telescope like your Z10, heat retained in the mirror during storage roils the cool night air surrounding your primary mirror outside. It will always cause frizzy star images early in the session until the heat dissipates. Using your fan will shorten the length of the frizzy period. You can't really judge the telescope's image fidelity until it has cooled almost to ambient temperature.
On a large telescope like your Z10, scintillation of star images is more noticeable. That can contribute to those ugly star images. The term 'seeing' is given to the phenomenon. Scintillation is induced by the atmosphere itself. Some nights, scintillation (seeing) is bad; some nights it's almost undetectable (good seeing). Nights of good seeing are a joy to behold.
Do an optical telescope test of the telescope. Do it only after the telescope has cooled to ambient temp (like just before you are ready to put it away for the night).

Here is the test:
<ul class="bbc bbcol decimal">point the telescope to a bright star, Polaris for instance.
Center the star in your 9mm eyepiece.
Defocus Polaris until you see concentric rings form around the star. You want to be able to see only three or four of these rings.. More than that, you've defocused too much.
Look at the ring structure that has formed (remember to keep Polaris centered in the eyepiece the whole time). Do the rings form a complete circle around the central bright zone?
Look at the image both with your glasses on and off. Do the rings appear round? Oval? Triangular? Is there a difference with your glasses on?

Sometimes the telescopes ship from the factory with the mirror clips too tight and the pressure from the clips will affect the shape of the rings. If that's noticeable in your test, it is something that you can fix yourself.
----------
C

All of these posts have been helpful, and I found this one to be especially so. "Push the telescope in the direction you want the object to move" was a GAME-CHANGER last night. Thank you! It was much easier to move around in the sky with this advice in mind. I even had another airliner fly into my FOV and tracked it for 15 seconds before it passed the zenith.

I did attempt to perform this star test as described. I centered Algol in the eyepiece and defocused it. Instead of seeing concentric rings, however, I saw what can only be described as a psychedelic display of pulsing colors and swirling currents. Is this the "scintillation" you're referring to? The defocused image was large and round, with four little indents on each of the poles of the star. It was, frankly, beautiful. I could have watched it for an hour. I'm not sure what it says about the optics, as this sounds like it has more to do with seeing conditions. I'll try it again on a star a bit higher in the sky next time.

<p class="citation">Jon Isaacs, on 03 Oct 2017 - 11:03 AM, said:<a href="https://www.cloudynights.com/index.php?app=forums&amp;module=forums&amp;section=findpost&amp;pid=8136685" rel="citation">[/url]<blockquote class="ipsBlockquote built" data-author="Jon Isaacs" data-cid="8136685" data-time="1507021433">
MithrasTheArcher:

Great write up.. And congratulations on your new scope..

My 10 inch F/5 Dob is a 15 year old version of the same scope. It's been a good scope.. A few thoughts and experiences:

- Chair: An adjustable chair is very nice but a simple folding chair works quite well. Saves a lot of bending.

- Astigmatism and sharp stars: There's a lot to think about here, your eyes, the telescope, the eyepiece.

Before discussing this, the important question is this:. Without your glasses, were you able to achieve relatively sharp focus on stars in the very center of the field? if so, that means your eyes are not the problem. Here's how it works:

The astigmatism in your eyes affects the entire field of view, the center out to the edge. If you are seeing sharp stars in the center, that means your eyes are not the problem.

Your 30 mm 2 inch eyepiece is a nice finder eyepiece and an entry level 2 inch wide field. It's reasonably sharp in the center of the field but away from the center of the field it shows more and more off-axis astigmatism. This is typical in an F/5 scope. In an F/10 scope the outer field would be relatively clean but at F/5, it suffers.

Wide field eyepieces that are relatively free of off-axis astigmatism at F/5 are expensive. Prior to TeleVue and the first Naglers, such eyepieces did not exist. TeleVue eyepieces are still the best in this regard but there are others that are quite good that are more affordable but don't expect a $100 2 inch wide field to be much better than what you have.

I think the best attitude is just accept the view for what it is, sharp in the center, not so sharp away from the center and just enjoy the view.

An F/5 Newtonian also has a noticeable amount of coma, tiny comet like tails on stars towards the edge of the field. Compared to the eyepiece's off-axis astigmatism, the coma is relatively minor.

- Finders:. The 50 mm RACI finder is nice because it agrees with a chart but it's difficult to line up on that first star, to get into the right area. I find a Telrad to be ideal for this and under darker skies whether there's plenty of stars visible naked eye, often the object can be placed in the field of view the main eyepiece without using the magnifying finder.

- Tracking: Soon enough it will be second nature and you will move the scope the right way without thinking about it. Your Dob is a left handed Dob, you track with your left hand..

Bottom line, you got yourself a winner, enjoy it, there's a lot to learn.. at lot to see.. a lot of fun ahead..

Jon
I tried observing last night with glasses on and off to get some more data points on what is actually happening with the glasses/eyepieces. I learned that without my glasses on, I'm unable to get the stars sharp in the center of the 30mm eyepiece. (The view is slightly better with my right eye than with my left, though.) With my glasses on, I can get some of the image sharp, but as you all noted the stars in the outer 1/3rd of the eyepiece all have little comet trails no matter what I do. I don't entirely understand the reason my scope has such a fast focal ratio, but I do understand from this thread that it will take some premium components – coma corrector, really good eyepieces – to maximize the quality of the view.

Happily, the 9mm is much sharper, even with my glasses off. The recommended Baader or Televue 1.25" zoom eyepiece with a Dioptrx sounds like it might be a great place to start.

One thing I am wondering: In the 30mm, depending on the angle I'm looking into the eyepiece, some of the brighter stars in the center have a little comet trail that appears either on the right or left side of the star depending on how I move my head. Is this an indication that the collimation is out? I know the importance of collimation from reading, but I don't actually know what a poorly collimated scope looks like through the eyepiece.

All that said, I did manage to take in some wonderful views despite a blindingly bright Moon in the sky last night.

First, I looked at the Moon because, well, it was omnipresent. I made the mistake of training on it with the 30mm eyepiece and no moon filter. Holy Blinding Light, Batman, that thing is LIT UP. A few seconds of that and it occurred to me I might actually be damaging my retina. 10" of light gathering on an object illuminated by the sun is WAY too much. Oof. For the next 10 minutes one of my eyes was night-corrected and the other was ready to stand on the beach in Miami. I switched out for the 9mm with the included moon filter, which was much more pleasant, although I couldn't get over how fast the Moon fled the FOV. It just moves shockingly fast. I couldn't get over it. That thing really books it across the sky in a way that is totally unnoticed in regular life.

The rest of the night was spent hunting down the Hyades and Pleiades, both of which offered sparkling (albeit not very sharp) views in the 30mm. I even managed to stumble on the Double Cluster in Perseus, which was thrilling. So many stars! The telescope resolved a lot of individual ones, which was lovely. I was a little disappointed by how light the background was, but I think that was the Moon's doing.

All in all, it was a very satisfying second night out. Still lots to learn. I spent a ton of time fighting with the finder and just pushing the telescope around trying to find things, but once I relaxed and tried to enjoy the wandering, I had a great time.

The astigmatism in your eyes will affect the view the most at lower powers, and less as you move up in power. It is based on your scope's exit pupil with a given eyepiece. Do you know what the CYL is on your prescription?

Freddy Banks

  • Active Astronomer
  • ***
  • Posts: 110
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: First Light with Zhumell Z10 10” DOB
« Reply #19 on: January 31, 2018, 06:54:01 AM »
MithrasTheArcher, I'm glad if I was able to help. We all have benefited from our collaboration on Cloudynights over the years. We owe a debt of gratitude to Astronomics, the gracious sponsor of the CN website and forums.  A few more of my thoughts...

Collimating: Always secondary mirror first; then the primary last. It's okay to repeat the sequence but always primary last.

Star test: From the picture you described, you may have defocused too much - Test wasn't valid. Use a 9mm eyepiece or less. Wait for the telescope to dissipate the heat from storage. Begin with a tightly focused star. Slowly defocus until you see only three or four maybe 5 rings at most. Take it slow. The star image will gradually dissolve into more or less concentric rings. The ring pattern may take a while for you to notice it. Keep the star centered in the FOV. Note the continuity and shape of the ring pattern - glasses off, glasses on. Write down every thing you see - maybe make a little sketch.

Psychedelic show last time may have been a combination of scintillation, tube currents and heat plumes from the roiling air in front of the mirror.

Keep your eyepieces warmer than the outside air. Otherwise, the lens will form a layer of dew that won't go away until the eyepiece warms up higher than the dew point.

Shed storage: Even if you did not use the telescope the night before -- Depending on where you live and the season, your primary mirror may develop a layer of dew on the shiny surface by mid-morning. The mirror cools at night. Then, as the warm, saturated air of the morning wafts across the mirror in the shed, the dew layer forms. Over time. the daily dewing may corrode the mirror coating. I would inspect your Z10 in the shed on a morning after it had sat in the shed all night, undisturbed. The dew, if any, should be noticeable between approx 9 and 10 AM. If dew is a problem, I have heard that placing a low wattage light bulb under the telescope may keep the mirror from cooling excessively at night.
--------
C

My 2 cents on buying stuff: Everything you buy has a learning curve. The stuff you have already took me quite a while to master -- before the telescope and I were functioning as an effective unit. I view my telescope as only tool that that expands what I can do with my naked eyes or binocular. You and the telescope working seamlessly together -- like an appendage to your body is what makes the magic happen. A lot of the other stuff can wait.

A dim, red reading light, a nice beginner's atlas, and eventually a chair. Lots of chair time under the stars -- growing more proficient each observing session by repetition and experimentation. Best wishes on your astronomy adventures.

ichpezafi

  • Active Astronomer
  • ***
  • Posts: 106
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: First Light with Zhumell Z10 10” DOB
« Reply #20 on: January 31, 2018, 08:53:48 AM »
Quote
Quote

[snip]

The astigmatism in your eyes will affect the view the most at lower powers, and less as you move up in power. It is based on your scope's exit pupil with a given eyepiece. Do you know what the CYL is on your prescription?
Thanks for the reply! The CYL for my left eye is -1.75 and right eye is -1.25. Is there a way to figure out at which exit pupil my particular astigmatism will no longer affect the image?

Waka Belcher

  • Active Astronomer
  • ***
  • Posts: 131
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: First Light with Zhumell Z10 10” DOB
« Reply #21 on: February 02, 2018, 09:32:01 PM »
Quote
Another point regarding the 30mm widefield that comes with the scope: a coma corrector will
not fix the astigmatism in it that causes the view to be soft away from the center. Only higher
quality eyepieces will be noticeably improved by a coma corrector. Coma is the least of your
concerns right now. The eyepiece would definitely work better at a higher focal ratio but the f/5
scope is worth the disadvantages it has by the offsetting advantages of reduced length, weight,
bigger light grasp, and wider field of view.

Thanks for this! I've got some sticker shock at the cost of coma correctors, so I think my next purchase after I get used to the existing kit is going to be a couple high-quality eyepieces, with the coma corrector to be purchased down the road once I've gotten more confident with the scope.

vichanettgrif

  • Active Astronomer
  • ***
  • Posts: 120
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: First Light with Zhumell Z10 10” DOB
« Reply #22 on: February 03, 2018, 02:58:26 AM »
Quote
MithrasTheArcher, I'm glad if I was able to help. We all have benefited from our collaboration on Cloudynights over the years. We owe a debt of gratitude to Astronomics, the gracious sponsor of the CN website and forums.  A few more of my thoughts...

Collimating: Always secondary mirror first; then the primary last. It's okay to repeat the sequence but always primary last.

Star test: From the picture you described, you may have defocused too much - Test wasn't valid. Use a 9mm eyepiece or less. Wait for the telescope to dissipate the heat from storage. Begin with a tightly focused star. Slowly defocus until you see only three or four maybe 5 rings at most. Take it slow. The star image will gradually dissolve into more or less concentric rings. The ring pattern may take a while for you to notice it. Keep the star centered in the FOV. Note the continuity and shape of the ring pattern - glasses off, glasses on. Write down every thing you see - maybe make a little sketch.

Psychedelic show last time may have been a combination of scintillation, tube currents and heat plumes from the roiling air in front of the mirror.

Keep your eyepieces warmer than the outside air. Otherwise, the lens will form a layer of dew that won't go away until the eyepiece warms up higher than the dew point.

Shed storage: Even if you did not use the telescope the night before -- Depending on where you live and the season, your primary mirror may develop a layer of dew on the shiny surface by mid-morning. The mirror cools at night. Then, as the warm, saturated air of the morning wafts across the mirror in the shed, the dew layer forms. Over time. the daily dewing may corrode the mirror coating. I would inspect your Z10 in the shed on a morning after it had sat in the shed all night, undisturbed. The dew, if any, should be noticeable between approx 9 and 10 AM. If dew is a problem, I have heard that placing a low wattage light bulb under the telescope may keep the mirror from cooling excessively at night.
--------
C

My 2 cents on buying stuff: Everything you buy has a learning curve. The stuff you have already took me quite a while to master -- before the telescope and I were functioning as an effective unit. I view my telescope as only tool that that expands what I can do with my naked eyes or binocular. You and the telescope working seamlessly together -- like an appendage to your body is what makes the magic happen. A lot of the other stuff can wait.

A dim, red reading light, a nice beginner's atlas, and eventually a chair. Lots of chair time under the stars -- growing more proficient each observing session by repetition and experimentation. Best wishes on your astronomy adventures.

Thank you so much! I will conduct the star test again, hopefully tonight if it's clear, and report back. And I'll heed the advice to go slow with the purchases. I'm going to start with the observing chair and Telrad, and once I get better at using the scope I'll hopefully start adding eyepieces. Some of the recommended ones in this thread cost twice what I paid for the scope, so I'll really have to budget for and plan those purchases!

Jason Kaltwasser

  • Active Astronomer
  • ***
  • Posts: 109
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: First Light with Zhumell Z10 10” DOB
« Reply #23 on: February 03, 2018, 03:02:05 AM »
Coma? Who cares? You are going to focus on the center 75% of the view anyway. What's outside that is for context or drift time.

Look!
Enjoy!

Unless you have some money for more expensive eyepieces and a coma corrector, don't worry about it. So you have a little coma in the outer rim. Ignore it.

John Trujillo

  • Active Astronomer
  • ***
  • Posts: 122
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: First Light with Zhumell Z10 10” DOB
« Reply #24 on: February 03, 2018, 03:20:05 AM »
Quote
Quote

Quote

[snip]

The astigmatism in your eyes will affect the view the most at lower powers, and less as you move up in power. It is based on your scope's exit pupil with a given eyepiece. Do you know what the CYL is on your prescription?
Thanks for the reply! The CYL for my left eye is -1.75 and right eye is -1.25. Is there a way to figure out at which exit pupil my particular astigmatism will no longer affect the image?
Yes - see chart below.
With your scope, you will startto see astigmatism in your left at at an exit pupil of 1.25 mm, and worse at larger exit pupils.
You will start to see astigmatism in your right eye at an exit pupil of 1.75 mm, and worse at larger exit pupils.

This translates to needing astigmatism correction using any eyepiece of about 9 mm and above, through your better corrected right eye. Keep in mind that the numbers change when you move to a different scope.

I use Dioptrx on my 2 lowest power eyepieces. Mine isn't as bad as yours (1.0), so I can skip Dioptrx (or glasses) at about 14 mm and below.


ecidjapa

  • Active Astronomer
  • ***
  • Posts: 126
  • Activity:
    0%
  • Reputation: +0/-0
    • View Profile
Re: First Light with Zhumell Z10 10” DOB
« Reply #25 on: February 09, 2018, 11:13:11 AM »
On using the RAF and Telrad; I picked up a "2-spot shoe" from Orion, along with the 4" extension for the Telrad, and have them mounted side-by-side, and love how it works.