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Topics - Marvin Neboet

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Sorry for the long title but I wondered if anyone can confirm that this is true:
Comparing  a 6 inch F5 with a 80mm f7.5, the 80mm would require 8x more time to gather the same amount of light assuming they're both being used for astrophotography.
This is from dividing this ((6x24.5)^2/80^2) by this 5^2/7.5^2

Mounts Questions & Expirience / Tracking with equatorial mount
« on: December 29, 2017, 03:54:21 AM »
Hi, I apologize in advance if this seems like a dumb question but how does an equatorial mount track a planet across the sky? When I look at the path the planet takes it descriv
bes an arc across the sky from east to west. The equatorial mount as I understand it is set so that the angle matches the tilt of the Earth and accounts for one's latitude. But when the mount is pushed along to track an object wouldn't its path be an angled straight line while the planets path is curved?

ATM, Optics and DIY Forum / First ever build and some 3D printing
« on: December 28, 2017, 08:31:32 PM »
I live in a part of North America that has, in recent years, provided a lot of light pollution and cloud cover. I also travel to drier, darker and clearer parts of the continent fairly often though I rarely have a telescope with me. I’m also looking at a possible long stay in South America through work. All of this was in my mind when, one day, I came across a Cloudynights user called Pinbout. Pinbout posted about CAD sketches of travelscopes (and, indeed, a whole host of other interesting gizmos). I was intrigued and struck up a conversation with him via PM. One thing led to another and soon I had received a box full of laser-cut wood that could be fashioned together to make an 8” travel dob.To sum up: I used them to build a little travelscope. I write a lot about it below but if you want, skip ahead and look at the pictures.
Now, I bought cut pieces because I have next to no woodworking ability. Borrowing clamps and gluing the pieces together took me a few months. Of course, that wasn’t real work, it was just getting over the inertia and anxiety of not really knowing what I was doing. In the end, the pieces aren’t perfectly square but they’re close. It really is pretty cool when a bunch of disparate bits of wood start to look like something. But just to emphasize, I'm all thumbs. I never could put a model together. So don't expect art.As I began to think about actually getting the scope put together, I came up with this design parameter: make it just good enough. I had already glued the wood together in such manner that no one would mistake it as being constructed by a master. Moreover, this scope would not be my main scope. I figured I would only use it when travelling and, thus, much more forgiving of usability or maybe when I needed a really wide field of view. With all that in mind, I set about acquiring the rest of the material I would need and trying to put it together. In the process I learned a lot about Dobs and design. I no doubt have a lot more to learn.First, I needed an optical system and was fortunate to pick one up from a friend who had replaced the GSO 8” f/4 mirror in his imaging scope with an 8” Zambuto mirror. I bought a 70mm GSO secondary and, then, realized it was far too big (in terms of mass on the UTA), so downsized to a 52mm secondary. This was to be a recurring theme: if you’re building your first scope, be sure to budget in that you will buy lots of bits that don’t end up in the final product. They DO tell you this (as am I) but one always assumes one is smarter than everyone else. And, of course, I wasn’t.Anyway, having the optical system together, I lacked a focuser and poles. Pinbout (Danny from now on) had warned me to keep weight down on the UTA ring. However, he’d supplied a 1.25” focuser plate and I only own 2” eyepieces. Rather than buy new eyepieces (which may have been the sensible thing to do), I bought a Kineoptics HC-2 2” helical focuser. This is an excellent focuser and Joe LaCour was great to work with. He generously provided a .stl file for a focuser base and I was able to beg time on a colleague’s 3-D printer and soon had both a focuser and a light weight base.

For the poles, I wanted them to telescope. Though I’ve never built or owned a travel scope, it never made sense to me to go to such lengths to make most of the scope compact but then have these very long poles. I again used the 3-D printer to fashion pole clamps that would hold a 7/8” OD tube with a ¾” OD tube (both from Texas Towers). I installed ¼-20 threaded inserts into one end of each and, voila, had tubes that could vary from 16 to 29 inches and be very stiff with the clamps in place. They’ll now fit in a small suitcase or even in my backpack.

I printed two other pieces: guides to hold Teflon and act to keep the altitude bearings in line. The other is a laser finder bracket. The only other non-standard thing I did is to use a rough cabinet liner in place of Ebony Star on the altitude bearing. I couldn’t get narrow enough pieces of Ebony Star cut so I just went with the laminate thinking I’d replace it later. As it turned out, it works great so I’ll probably just leave it. If I do need to replace it, I was able to buy meters (x ½”) of the stuff for just a few dollars. Again, it fit the design parameters of “good enough to work”. You probably wouldn’t want to use that laminate on a premium scope but, well, look at this thing.

I bought a slim spider from 1800Destiny. It works but is clearly designed to be used in a compact or, less expensive, shall we say, scope. It really does fit the design parameters perfectly but it pretty tricky to get collimated. Once it is collimated, it holds. But it’s a painful process.I was finally ready to put it all together and I used a huge pile of screws, bolts, nuts and washers. It all goes together but there is too much. I plan to replace all the fastening hardware on the UTA either with nylon versions or, at least, shorter versions. The thumbscrews connecting the UTA ring and truss poles are 2” long which is at ¾” more than needed. Likewise the bolts holding the focuser on. But, for now, it works.
So, there it is. My first telescope build after over 30 years of astronomy. I had a lot of help and made a fair number of mistakes. In the end, I have a travelscope and it provides a nice image with nearly a 3 degree field of view using my 27mm Panoptic. The motion is smooth (even in altitude where I have a cheap cabinet laminate instead of Ebony Star, which is on the azimuth bearing). I expect I’ll really enjoy using this scope and continuing to poke and prod as I make improvements.Many thanks to Danny (Pinbout) and my friend Steve for their helpful guidance and encouragement along the way).

I'm going to post a whole bunch of pictures now. It will take several posts.Attached Thumbnails

ATM, Optics and DIY Forum / Altitude Bearings for solid tube
« on: December 28, 2017, 01:57:37 AM »

I am looking to make a dobsonian base for a solid tube OTA I am constructing out of sonotube, the optics are 10" f/4.5. I really love the teeter style base and I am looking to make one similar to it. My desire is to have a comfortable telescope where I can roll the tube to whatever angle I need and to be able slide the telescope in its rocker if I put a heavy eyepiece in the focuser so Ido not need to use counter weights, rather I just change the fulcrum of the OTA.

In order to best do this I would like some large altitude bearings. After doing some minor research I came upon this quote, "Based on our experience, we would recommend altitude bearing diameters of 1.2 to 1.8 time the tube outside diameter, with a bias towards the large size." This is from stellafane's website https://stellafane.o...ltbearings.html

I was hoping to get suggestions on the best way to meet my needs. Is there a cheap commercial product out there that I could use to serve this purpose rather than cutting my own? I have read a little about old metal film canisters and I know John Dobson used something military surplus on the sidewalk astronomers 18".

I am open to any and all suggestions, I just don't want to blow the bank on them.

Clear skies,


Considering that the finderscope in question is a RACI 50mm finderscope with a focal length of 208mm, which 1.25" eyepiece (no need for crosshair) would you recommend and why?

Some choices which I am considering:

ES 20mm 62°
TV 20mm Plossl 50°
Baader Genuine Ortho 18mm 52°
Skywatcher Silver Plossl 20mm52°
Skywatcher 20mm LET Eyepiece 50°
Vixen NPL 20mm 50°
Vixen NLV 20mm 50°

The ones highlighted seem suitable (but I am including others of course), but I am open to other suggestions. Basically which one would work best in a f4 doublet achromat RACI finderscope with amici prism in the mix obviously. I don't wear glasses and at those focal lengths eye relief is not an issue for me. I would like to stay with a minimum of50° AFOV and the key consideration is handling of the steep light cone - which one would do it better and present an overall more pleasing FOV.

Also any other eyepieces you would recommend - most welcome. Even a Pan 19mm despite not needing such a FOV. Keep in mind that the diameter of prisms in such finderscopes is 20.5mm and that obviously one would expect the edges of the prism to be something to avoid...


Light Pollution Topics / Interesting article
« on: December 27, 2017, 11:05:23 PM »

E.O.H.Chesmont Astronomical Society -
Galaxy Log -
Galaxy Log Blog -
Telekit (Swayze optics) 22" F/4.5 Dob
Homemade (Parks Optics) 12.5" F/4.8 Dob
Vixen 5.1" f/5 reflector
TMB/APM 8" f/9 Refractor”The Beast”. One great DEEP SKY achro
ES 6" f/6.5 achro. Good one
Celestron Omni XLT 102 refractor.
Celestron 10x60mm Binos

Hi all.

Been recently toying around again with an idea I first had a few decades hear me out.

A few points first, which will explain the why? of the idea.

Long focal ratio scopes have less abberations.

Eyepieces, particularly ones of a more modest nature/cost, work WAY better at something like F8 ish than F4 ish.

Field curvature can get irritating when you get older and or you get more optically picky.

If you want low power for milky way sweeping or the occasional nice comet you are looking at smaller scopes used at the lowest power possible.

Field curvature is proportional to focal length. Shorter focal length (which typically goes with smaller aperture) means more curvature, which is bad.

Refractors typically have field curvature roughly 1/3 of their focal length. Newtonians have a field curvature approximately equal their focal length.

And another thing or two I am too lazy to explain right now.So, my proposal is this. For a smaller aperture, low power scope you use an undersized secondary. A secondary such that when you are "at" any point in the field of view, you are only using a fraction of the mirror.

This allows you to have a small aperture scope with a lower f ratio (say F8 ish) using something along the lines of a 50mm plossl.

The "operating" aperture is the ratio of the diagonal to focus distance divided by the diagonal to mirror distance multiplied by the diagonal size.

This design also allows for some pretty effective baffling as well.

The downside is a primary mirror much larger than the operating aperture as well as much larger and longer tube than would be required for a normal equivalent scope.

Beginners Forum / telescope information for beginners
« on: December 27, 2017, 10:06:13 AM »
Hello everybody.  I just retired form military and wish to expand in my love of astronomy.  I started out a few years back with a very cheap mead 114 mm reflector with goto mount 25mm, and 9mm eye piece. .  While this mount holds steady and works ok.  I need something which will give me a larger and far better image.  Everything I look at is quite small occasionally I can focus and find a very clear thing but it's so small its disapointing.  If I were able to get state saturn at least 1/2 in. image I believe I would be quite pleased.  And who knows maybe my expectations might be to high in my own budget of maybe 500.   I would love to observe planets and some deep sky objects such as galaxies and nebulas.  Ok been thinking about getting a 8" dob such as orion xt8 or the skies watcher collapsable 8" dob.  But I read a lot regarding the collimation being wrong on these 2 scopes and if they try to correct it that the bolts are stuck and cannot collimate it correctly.  And that they are colour less.  So I want help from someone that has used these scopes before since there are no celebrity parties around where I am out of.  Maybe a refractor 3.5 or 4" or maybe a small mct such as theCelestron NexStar 4SE GoTo mct, orOrion StarSeeker III 90mm GoTo mct.  I have a golf course next to me with no lights at night a great spot to view.  Any help would be great I've been exploring for a few months now and feel fried together with all of the overload.  In case you have other suggestions that would be great.  Thank you for your ideas.

Lately I built a 16", f/4.35 dobsonian telescope which operates just great.
So now that acquired a better comprehension of woodworking I feel as building an equatorial platform for my telescope.
My latitude is 10 levels and I know this introduces a few challenges.
I'm a member of the yahoo group of EQ platforms and according to my understanding, provided my place the best layout in my case would be a classical cylindrical platform.  The one explained by Warren Peter.  I know a roller support has to be added to prevent the whole thing to fall northward due to my low latitude.
Am I in the right spot with this layout?
I intend to use one of those Celestron motors for immediate driving.

Beginners Forum / orion 8" dob vs. meade lx90 8"
« on: December 24, 2017, 08:18:18 PM »
Id love to know whether the meade has better optics than the dob.  I not quite good when it comes to optics.

Mounts Questions & Expirience / ZEQ25 Problem - Backlash?
« on: December 24, 2017, 06:57:07 PM »
Hello Everybody,
So my little IOptron ZEQ25 is coming up on a year old today for me.  I bought used so maybe it is a total of 3 years old.  In any case, I have noticed a problem that appears to have cropped up lately.  When I push on the left and right arrows on the hand control (now I can't recall which axis that controls!) , it will "leap" in the opposite direction before proceeding appropriately.  I guess this is possibly backlash?  The hand control does have the choice of anti backlash settings but I have never needed to alter them before.  Is this something that could maybe be addressed with Paul Chasse's ZEQ25 tuning video?  Or if I contact IOptron?  Following is a link to a quick video that I took tonight.  The first 18 seconds show the "great" axis moving correctly.  Starting around 22 seconds, you can see the jumping.  Sorry for your water mark on the movie too.   The original video had a loud high pitched wine when I listed it and that I did not everyone to go deaf listening so I muted the sound using a trial editing program.  Overall the mount is working great, it is just this one little issue about the one axis.  Thanks!


Beginners Forum / Eyepiece
« on: December 24, 2017, 09:34:41 AM »
Hello Forum. My name is Fergal from Ireland.  I got my hands on a Sky-Watcher 102 4" Refractor.  F500.

I'm brand new to Telescopes, but understand the Nightsky Fairly well.  Was seeing Jupiter last night with all the included 10mm Eyepiece (50x) and the 25mm Eyepiece (20*).  I dont have a Barrlow Lense.
Very Disapointed with the magnitude of the Planet, thought it would be far larger through a Telescope.  Naive!

Which brings me to my Question.  I want a lot more Magnification.  Sky master possess a range of Skywatcher Planetary 58?? UWA 1.25" Eyepiece Range.
They've a 2.5mm, (200x) 4mm (125x) plus a 5mm (100x).  I'm considering the 2.5mm one.  I know this is the very upper limit of the Telescope,
Would I be better using the 5mm, and purchase a Seperate 2x Barlow Lense, therefore if conditions are right I can use the 200x , or simply but the 2.5mm (200x) and await ideal conditiond.
Additionally the 25mm which is included with the extent is pointlesss.  Cant find a use for it.  I do a good deal of observing duiring daily as well, and also cant see any use for 20x Magnification.  It seems pointless.  A Finely Polished Jam Jar woud offer better Magnification.

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