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Messages - lodersconsharp

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Beginners Forum / Re: Considering 2 (used) reflectors for 1st scope
« on: February 09, 2018, 10:50:35 AM »
I can remember when I got interested and hit this forum off the bat. One of the first recommendations...and I still have get the book..."The Backyard Astromers Guide"...a little dated in terms of some equipment but very useful....

That said I asked like everyone else before me and will continue...what scope for x amount of $$$$$

That's the Million Dollar's sort of like asking..."What first car"......

The first thing...take baby steps is about the best advice. I cannot tell how many bought some wizard goto setup thinking all they had to do was plop it down, hit a button and expect to see dazzling display they saw in some takes learning, patience, desire, fun and some degree of work.

My firs scope was a used one, which thankfully that was good suggestion versus spending a lot of $$$$ on something new...again like a car...good first one used to get your feet wet. And like "Cars"....they come in all flavors, add-on, knobs, buttons, colors, hardware, etc...and you get what you pay for. Mine which to this day provided some excellent views was a used Orion XT8 Light bucket with some starter eye pieces. I researched on what more I could get out of it and lined the inside with Black self-adhesive felt which did improve it. Since then I moved on & up but that scope was real fun and helped me take "Baby Steps" without going over my head.....just my 2 cents worth....

General Astronomy & Observing / Re: Astronomy has me disappointed
« on: February 09, 2018, 09:07:28 AM »
Sizematters,  . Its a gift , not everyone GETS it. We do it ALONE mostly , gene


I agree that at least Gwacheon is quite better than Seoul. But it is not enough dark to observe deep sky objects. You can find how bright Gwacheon are at  Dark Sky Map .

Suwon also is not good to observe deep sky. Past two weeks, the sky condition was fairly good. A lot better than usual Korean sky.

Anyway, it will be good to have a car to do observations. Yonging Football Center that I said is placed in Kyunggi-do. Yangpyeong is placed in Kyunggi-do also. Gangwon-do has better sky but it is too far from Gwacheon or Suwon.

Reflectors Telescopes Forum / Re: Focus on focusing.
« on: February 04, 2018, 12:53:00 PM »

Mask is an inch away from the spider.

There's your reason. That difference of an inch.
One, or the other will be in focus.
But not bofus...
That doesn't make sense. Using either the mask or the spiders should give the exact same focus, because we're trying to focus on infinity here. The focus on infinity doesn't change, when we change focus methods...Clear skies!
Thomas, Denmark

Beginners Forum / Re: First Good Telescope
« on: February 03, 2018, 12:42:03 PM »
Celestron NexStar f/10 5SE Schmidt-Cassegrain Computerized Telescope = $700 ( https://www.celestro...rized-telescope ) -- comes with mount & tripod
45-Degree Erect Image Diagonal = $40 ( https://www.celestro...-image-diagonal )


Celestron C5 f/10 Spotting Scope = $600 ( https://www.celestro...-spotting-scope ) -- comes with 45-degree diagonal for erect image
Celestron NexStar SLT Computerized Mount = $320 ( https://www.celestro...puterized-mount )It would appear that the NexStar 5SE + 45-Degree Diagonal is the better deal.

Beginners Forum / Re: Dumb newbie question
« on: February 03, 2018, 01:29:03 AM »
All true, but the interesting thing is the OP stated his has a removable "center", which I take to mean it is centered over the central obstruction (i.e. secondary mirror). My Skywatcher dob has the same arrangement as in the link you provided above, in which the aperture stop is off-center, so it is not aligned with the central obstruction.
I did say center, and the cap is centered. This morning, I removed the center cap and took a look through the EP. The secondary mirror did not pose a problem. I didn't find that removing the center cap improved magnification over removing the entire tube cap (if that is the effect of increasing the focal ratio of the scope).

Thanks, all, for your answers.
Just for the sake of curiosity, I'd sure like to know the make and model of this scope.

Eyepieces Questions & Recommendations / Re: Eyepiece Fever
« on: February 02, 2018, 10:38:36 PM »
There is a rather sharp debate in our club among a group of wellcredentialed, well equipped observers who contend that any observing challenge can be well met by a kit of 3 well chosen eyepieces (commonly of antique design) and another group of generally less experienced observers with varying degrees of the fever. They are borderline civil in their contentious debate.

Obviously I think one group is making no sense but the argument does not interest me. It is pointless to argue about matters of faith and those folks have advanced their positions in that vein; that and their perceived superiority based on their experience and credentials. Silly boys. With silly hats on which they wear their pins like the colors on a mandrill's bottom.

The fever took me some time ago and I have enjoyed the illness. But my resistance to it is based in mycommitmentto avoid being aneyepiece collector. Collectors are fine but I'm just not one. For me the "cure" has been getting about all the eyepieces I can use and of about as good quality as I can see.

I think an observing challenge CAN be met with an optimized 3 ep kit. But I think it easier with a larger group of well chosen ep's.

Thank you very much, Jim!

Beginners Forum / Re: What do I buy after an 8 inch dob?
« on: January 31, 2018, 09:43:46 AM »
Storage in an unheated shed is mostly a win-win. Temp changes won't hurt the mirrors. Your mirrors will be closer to the outside temp than if they were inside with heat and A/C. All you need to do regarding spiders and dust is to be conscientious about dust caps. I use old sheets over my scopes as an extra layer of protection.

I own 3 different EQ platforms, the first bought new and the others bought used. The prices ranged from $300 used to $550 new.

ATM, Optics and DIY Forum / Re: Crossed Czerny–Turner spectrograph
« on: January 31, 2018, 03:08:47 AM »
Good paper, Lars! Another good reference is the book "Spectrograph Design Fundamentals" by John James, available from Amazon. Page 81-83 reference a paper by G. R. Rosendahl in JOSA 52 (1962), page 412 that discusses minimization of C-T aberrations. Termed the Rosendahl "cosine-cubed "condition, it describes a geometry for a C-T that eliminates tangential coma in the slit image at one wavelength and minimizes it across a spectrum. The resulting system is not symmetrical about the grating, with the grating being located closer to the slit/M1 input optical path by just the right distance and tilt. It also allows for the collimator mirror M1 and the re-imaging mirror M2 to have different focal lengths.
I chose to simplify the spectrometer for Benach to a centered system as shown here because (1) his telescope already has a central obscuration and costly unobstructed off-axis optics aren't needed, and (2) he's not working in the infrared spectrum where thermal emissions from the spider, diagonal holder and mirror cells act as out-of-focus stray light that can lower spectral contrast.
The corrected C-T spectrometer is certainly a do-able project for Benach, but it seems overly complex.

Beginners Forum / Re: Red light vs Dim white light
« on: January 31, 2018, 02:23:06 AM »
It's my understanding, and experience, that you need to be light adapted to get beyond 5mm exit pupil. I can't get the entire FOV in my 55mm at F10 (5.5 exit pupil) until I've been in the dark for about half an hour. Then my wife turns on the kitchen light and poof I'm back to square one.
That's because you're holding your eye too close to the eyepiece. A 55-mm Plossl has vast eye relief -- some people would say unusably long. You need to be roughly 2 inches back from the eyepiece to see through it properly. It's tricky to do that and still keep your eye centered. The best way is probably to build a guide from a piece of paper wrapped around the eyepiece.

When your eye is properly placed, you should be able to see the entire field of view regardless of the size of your pupil.

Generally, pupil size and dark adaptation aren't strongly related. Most people's pupils adjust fully to new light levels in a matter of seconds. Dark adaptation, which involves chemical changes in the retinal cells, takes much longer.

Light Pollution Topics / Re: Questions about light pollution
« on: January 31, 2018, 01:49:08 AM »
"Can I find a house that will stay in the same bortle sky scale class for at least 20 years. "

That is pretty near impossible; as you cannot control the land usage around your home for 1 year, let alone 20 years!

Thank for answer.

Given that we cannot maintain the same bortle class in a loaction is there a hope that I can find a house that at least stays reasonibliy dark through a long time period? Astrojensen mentioned that we can but the question is by how much the bortle rating will increase?

<p class="citation">Quote

Looks like it would be really hard in future to find a stable bortle 4-5 sky
It will only be hard if you MUST live close to major populations. There will still be vast tracts of land with dark skies, but they will be sparsely populated and often have a harsh climate.Clear skies!
Thomas, Denmark[/quote]
Thank you for answer.

<p class="citation">JHollJr, on 23 Jun 2017 - 9:02 PM, said:<a href=";module=forums&amp;section=findpost&amp;pid=7955749" rel="citation">[/url]<blockquote class="ipsBlockquote built" data-author="JHollJr" data-cid="7955749" data-time="1498244533">

I believe Prince William County, Virginia passed lighting ordinances years ago. I vaguely remember doing the research back in 2006. Nonetheless, the light pollution is considerably worse now than it was when I bought my house and first started observing here in 2005. The suburbs are growing by leaps and bounds and there appears to be no let up. Every new housing development, every new shopping center, every new stadium or park adds to the problem.

Today I heard an add on the radio asking whether or not listeners had the right video surveillance camera for their floodlights. That's what we are up against. Some just think implicitly that we all have floodlights.

Thanks for answer. I guess it is almost guaranteed to end up with brighter sky if you live in suburbs of a dynamic city. I'll hope that Istanbul wont devolop much in 5 years.

Reflectors Telescopes Forum / Re: Obsession 25 not listed any longer?
« on: January 30, 2018, 11:49:10 PM »
Somebody posted on the Obsession FaceBook page today that Dave recently said that the 25 is in deed gone. The remainder of his scopes will continue.

Eyepieces Questions & Recommendations / Re: Dust inside Leica ASPH Zoom
« on: January 30, 2018, 11:15:14 PM »
I don't think it's oil, if that was then case then you would expect it to leave streaks and move around, especially if you were to leave the eyepiece on its side. That doesn't happen. These are stationary specks on one of the internal lenses.
I also don't think it's dust either, as these particles are completely black and spherical, which isn't what dust looks like. It must be shavings off the inner side-walls that wear as the eyepiece gets used, that's the most logical explanation I've come across so far. But then you would expect this to be a far more common problem with this type of eyepiece, which also doesn't seem to be the case.
They are tiny oil droplets formed on one of the glass surface. They come from the lubricants of the zoom rail.
The oil or some debris from the complex mechanics of this eyepiece makes a lot of sense to me. I have never had, or seen, dust between lens groups. Actual dust would be visible between lenses. Oil, debris from the mechanical friction, or debris during assembly are the potential types and sources for what is being seen and called dust ime.


Drift aligning wouldn't help your problem. It is a technique that can be used to refine the polar alignment of any mount, but polar alignment is not your problem. The AVX's go-to should work even if the polar alignment is severely wrong.

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