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Topics - poithegepur

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This is for those who are always left out of the show me threads.  Any entries?

Hi community,

In search for dark sites, I found these two dark site map web pages:


If you look at the two maps, you will notice that they look very different from each other for any given region. If you search for Palos Verde, CA, for example, you will notice that lightpollutionmap is much more fine grained than darksitefinder. This begs the question: How come these maps are so different from each other?

Mounts Questions & Expirience / Celestron CGX Review & Problem
« on: December 31, 2017, 04:39:20 PM »
Hi Everyone -

I wanted to give a quick update on the Celestron CGX as well as ask the community for help in diagnosing a major "problem" with this mount.

In short, here is the review:

If the mount would track as promised, it would be a fantastic new mount! It is well designed, solid, and seems to handle a full load (C14 with imaging gear) with no problems (other than it has a serious tracking problem).   My only complaint and what I see as a flaw, is that it doesn't have a polar scope attachment. Celestron is counting on you using the "All Star Polar Align" instead of a polar scope. Other than that, it is extremely well designed and thought out.

Now onto the crux of the problem. I will hold off on a glowing and longer review until I can be shown that the mount actually works!

I've had the mount out 3 times now and the problem has occurred all 3 times, so i've been able to replicate and ensure it wasn't a setup issue. More importantly, on the 3rd time out, i took great pains to make sure all setup, polar alignment, balancing, etc were spot on.  I created a video showing how the mount performed and also detailing the problem.

The core problem is this: The mount keeps the object "centered" - i stopped after 15 minutes, but have reason to believe it would have kept on tracking just fine for another 15..... HOWEVER, as its tracking, the mount "wobbles" around excessively.... I've never seen this before on my AVX, CGEM or CGE Pro.

So my question to the community is: Is there a known reason for this or explanation of something i've missed? I am also going to open a ticket with Celestron on this as well.It also appears the mount fails to update properly with CFM.

Bottom line: As it is performing now, THIS MOUNT IS USELESS.

Greatly appreciate any help in getting to the bottom of this..... i'm hopeful that a firmware update will resolve this problem and allow this mount to live up to all the hype!Video overview:

- Showing how well it keeps an object (Beteleuse) centered over 15 mins
- Showing the "wobble" problem
- Showing PHD Guiding 2 graph and behaviors
- Showing update "failure"

Video on YouTube:

Thanks in advance,

Attached Thumbnails

Reflectors Telescopes Forum / OOUK VX6L 1/10pv ota arrives
« on: December 29, 2017, 03:29:37 PM »
My Orion Optics UK, 1/10pv 150mm-f/8 newtionian ota with rings/dovetail arrived about noon Tuesday 09/06/2016. Large box, well taped, ota inside well wrapped/braced for shipment. All appears to be in order. Well made scope imo.


The white ota is labeled only as VX6L with Orion Optics underneath. The additional raci is from Teleskop Service, I believe, marked TS. The OOUK ACU-2S dual speed crayford focuser is a low profile collapsible with a built in extender. Nicely machined. OOUK 9 point mirror cell with fan, included rca jacked plug. 2 plastic caps, top and bottom, for protection.

The Schott Suprax, Hilux coating mirror is center spotted. Included Zygo interferometer report,

Measurement controls wavelengrth out 632.5 nm. Profile Plot, Oblique Plot, graphs included. Synthetic fringe map shows lines straight up and down.

Strehl 0.988
PV wavefront 0.105 wave
PV 66.29 nm
RMS 0.018 wave
AstMag 0.004 wave

Don’t know what everything means exactly, but, from reading CN, sounds like a nice mirror!

My Astrozap gem manual lxd75 clone with 1.5 inch tubular tripod holds the ota sturdily with the tripod collapsed, not extended. The focuser is at a nice height for visual.

Cant wait to use the scope!

A very nice scope…shipping from UK to USA was about 45% of the base cost. EU VAT of 20% was NOT applicable to the shipment (0% VAT).

Good viewing,


Beginners Forum / Zhumell Z8 in The Gorge seeking nice EP setup!
« on: December 28, 2017, 01:51:02 AM »
Hi there,

Since this is my first post and I happened to skip the official Introduction page, I will simply ask my question(s) and briefly introduce myself here instead.

After much search and review (thanks in large part to this forum) I recently purchased my first "Real" telescope, a Zhumell Z8. The main purpose is not only for myself but to help excite my family's interest as well. At first I went back a forth between GoTo and PullTo scopes, leaning towards the PullTo due to thepreferred Dobsonian setup, but as many of you state to "Learn the Sky", and "Bang for your Buck"are actually great ideas when starting out and so I ultimately purchased as I did.

I currently reside in Hood River, OR and except for the current "Eagle Creek" fire happening in our area there really is not a lot of light pollution here in The Gorge. This can of course makefor some great viewings.

So you know, I am still very muchin the beginning stages, even though Ihave played around with generic telescopes since childhood. Anyway, I am really excited to be here to learn as much as I can, andalso excited to be finally divulging into a subject I should have seriously begana long time ago...

Now on to my question(s)...1.) As many of you know the Z8 comes with both a 30mm (2") and a 9mm (1.25") eyepiece. Like others I am looking to have the best EP setup related to this scope (FR - f/5.9, FL - 1200mm, A - 203mm). I am not going to place a max value of investment as I believe all EP's should be seriously considered, especially realizing these can always be transferred to additional equipment as I progress. What I will say is that I prefer to stay with 2" pieces which have as wide a viewing angle as possible... so Basically, whatare the best EP's for the money that will also allow me to enjoythe Z8 to its full potential?... Also, please keep in mind I do have the Zhumell 2x Barlow, and while maybe not the best in quality (will upgrade as I get more experienced) Iam hoping it allows me toonly need a few quality pieces for my setup.

2.) ...Ok, so I do have one more question to ask: The Z8 came with an 8x50 finder, I purchased an additional Telrad after reading many positive recommendations. My question is how and where do you mosteffectively place the Telrad onto the scope (I would like to make use of both the finder scope and Telrad)?... I have heard you can apply the Telrad directly to the scope, but where is best?... I have also seen an adapter online that can hold what appears to be two finder scopes, would this work in my case (finder and Telrad)?...

Please know I do appreciate any and all comments so thank you ahead of time!

- not so out there.

Mounts Questions & Expirience / CGX vs Atlas Pro AZ/EQ-G
« on: December 25, 2017, 09:21:06 AM »
I am trying to select between these two mounts.  Main use will be AP with OTAs ranging from 8lbs to 18lbs.

My worries are:
AP suitability
Software compatibility
Support when needed if something breaks

Without placing a great deal of my opinions on the market, I'd really like to understand what more seasoned AP folks think and what your choice is and why.

I have not completed any AP in a couple of decades now.  I used to use a CGEM with a Orion Newtonian Astrograph and got fine benefits but the mount was overloaded and I had some backlash and other issues as a result.  I'm a bit from practice and I'm trying to make the ideal choice for the ideal reasons.Thanks for the input and advice!

ATM, Optics and DIY Forum / Calculating the focal length of a compound lens
« on: December 24, 2017, 08:37:20 PM »
So I Have been using these formula's to calculate the focal length of a Straightforward 100mm F15 Fraunhofer achromat (specs at:
Since the elements are in contact.

When adding all the numbers (n = 1,5168 for N-BK7 and 1,62005 for N-F2 according to OSLO EDU), you get a focal length of 1503,649156mm (at I assume 0.58756 ??m, because that is the default main wavelength for OSLO EDU) .  I calculated this in Excel and in my graphing calculator and got exactly the very same results.

However, when I enter these numbers in OSLO EDU, it outputs a focal length of 1499,6mm

Can anybody tell me in my own method of calculating that the focal length manually is faulty?  How can OSLO develop another number?  Rounding errors?  An erroneous integrated Schott catalog with incorrect refractive indices connected to different wavelengths?

I'm also interested in calculating the focal length of a more complex compound lens with n >2 lenses.  How can one do that?

Edit: Is it perhaps because I didn't factor in the atmosphere lens in between the elements?

Beginners Forum / So my Z12 turned into a Z10
« on: December 24, 2017, 05:47:39 PM »
I recently responded to an internet ad for someone selling a Zhumell Z12 dob with numerous eyepieces for $350.

Being a newbie in this pastime, and suffering badly with my small dated 114mm newtonian, I contacted the vendor and told her I would be right over to take a look at the extent.  Upon arrival, she informed me that it had a 12" mirror and had only been out twice in the two years she owned it.  It seemed like it came right from the box.  Needless to say I was eager to pick up this kind of fine scope at such a great cost.

I scrutinized the eyepieces, took a fast glance down the tube (I can only imagine the twinkle in my eyes once I saw that large shiny main), checked out the alt/azi bearings and all were in perfect condition.  Even 3 of the 5 eyepieces were still in original packaging.  I handed over my money and loaded up the extent, anxious to receive it under the stars for some seeing.

Arriving at home prior to dusk, I put it up in the garden and was amazed at the wild views I had been becoming.  I spent hours in the dark only cruising the skies, hopping from Jupiter to Saturn, Vega to Arcturus, wide angle 30mm ep to tight 8mm, tried a few Messiers but had not really got down my star navigation nonetheless but I was hooked.  This totally blew away my small 114mm.  Money well spent.

I then began a few little mods.  Nothing big, just added a Telrad, moved the 8x50 finderscope over 3/4 inch to accommodate the Telrad, and inserted a bathtub cap dust cover into the bottom of the tube.  Then I chose to earn a lightshade at the end of the tube that, of course, required some dimensions.  Circumference = diameter x 3.14....but my tube diameter only measured a hair over 12".  What gives, I believed.  Looking down the tube, I noticed there was 3/4 inch gap on all sides of the main. . .how could this be a 12" mirror as promoted?  Then it dawned on me and my heart sank a small bit, just like 2 inches, then my Z12 had turned into a Z10.  In my haste to boost my aperture, I failed to take measurements before buying.  Taking the kind woman at her word about it being a 12" mirror, my eager newbie standing had little me in the hind quarters.

Do not get me wrong, I LOVE THIS SCOPE, and I got one hell of a deal on a practically new extent, but I would've much rather had the error in hauled go the OTHER way.

So today I find myself suffering from aperture envy yet again.  Wondering how much the amazing views I am getting with a 10 inch would improve with a 14 or even 16 inch dob.  At some stage I'd like to get to AP but that is years down the road for me because it's such a significant investment for proper gear.  So being merely a visual astro guy for the time being, I'd like to get into the biggest aperture I will manage.  A 12 inch seems a modest jump so I've been eyeballing the 14's and 16's.  I have noticed the Orion XX16 and the item is a monster but being that it collapses into manageable pieces, I believe it would fit my requirements and cure my aperture envy for visual observing.

I guess if there's a question in all this it would be is there a massive amount of difference in seeing power between a 10 inch and a 12 or 14 inch, or possibly a 16 inch?  Enough of a difference to justify the expense of a new king sized dob?

Aside from those queries, I only wanted to go off on a rant just a bit about my experience being new to the hobby and lessons learned concerning the 2nd hand market. . .buyer beware and always know that your dimensions and bring along your tape measure.

General Astronomy & Observing / Finder Scope
« on: December 23, 2017, 11:45:39 PM »
Any opinions of the Orion 6x30 RACI finder scope?  I enjoy the notion of a 7 degree field of view, in comparison to 5 degrees with all the 9x50 RACI finder.  I really don't need the crosshairs to be illuminated, since there's plenty of light pollution to do this for me.  The 6x30 is about 1/2 the weight too.  I can get a 3.2 level fov with my lowest power eyepiece.  A 32mm Plossl would give me a 3.5 level fov.  The 9x50 finder wouldn't give me much more fov than that.  The 6x30 finder would double the fov of a 32mm plossl within my scope and be about the same as the fov in binoculars.  Are there any good RACI finders that would give me a wider fov than that?  Any other tips or opinions?

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