Show Posts

This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.


Messages - exvermabo

Pages: [1] 2 3 ... 8
1
Eyepieces Questions & Recommendations / Re: Barlow vs. PowerMate
« on: February 09, 2018, 10:24:41 AM »
I would use a regular barlow for shorter focal length eps, if you tend to barlow longer f.l. eyepieces I would go with telecentric, otherwise the eye relief can become too much. Eyeguards normally in the correct place are now in the wrong place which can be trouble.  Regular barlow is great for shorter ep's like orthos that can use a boost in eye relief.

btw Astro-Physics does tell you the focal length of their 2" barlow, the prior "Barcon" version was -127mm:

>>The Barlow focal length is -102 mm which is longer than conventional types

2
Beginners Forum / Re: How do you fight bugs?
« on: February 09, 2018, 06:58:29 AM »
Flame thrower. Here in Maine it is the only thing that works. Of course, if you don't have a flame thrower (or naplam), a commercial fogger works, pumping out pemethin, nuking your yard and surrounding area. Bad thing is, this kills all the bugs including the good ones so I don't usually use that method. Here deet is "come-thither #5" and if giving blood is your thing then have at. We use head nets too but darn hard to look through an eyepiece with a net on your head. My answer will be to wait until Fall-winter and the little Buggers freeze solid.

3
Reflectors Telescopes Forum / Re: Catseye triangle and the TuBlug
« on: February 09, 2018, 03:53:14 AM »
Quote
Don:

I'm not sure what that Template looks like, Jason's looks to be elliptical.

In any event, I'm out in the back country without resources to make a template or to accurately install a new center marker.  I've come to the realization that the accurate placement of the center marker is critical and only the star test is independent of the accuracy of the placement of the center marker.

This means any fine tuning of ones collimation is questionable because it is dependent on how precisely placed the center marker is.. 0.010" is difficult to achieve by hand.. Thus the machine shop with the travel dials on a mill. That should be good to 0.001".

Jon

Print the template and look at it at a 45° angle. The elliptical center is now circular. (see Jason's photo)
The shadow of the center marker is similarly distorted until you look at it at a 45° angle.
You can copy the template to your computer and print it at any % of size you want. Some printed size would make the center marker shadow perfectly sized to fit within the center oval (circle at 45°).
How large you print it would depend on the size of your center marker shadow.
It's a brilliant way to improve the view screen of the Tublug, since it's easier to center the shadow using its outer edges than its inner circular opening.
I use a barlow attachment on my Glatter laser from time to time to check during the night if I think something is amiss, but I far prefer to use a Farpoint or Catseye Cheshire.

Engraving the center of the mirror could be very very accurate (Mike Lockwood does this on his mirrors), and you're right that getting the marker on the mirror to 0.01" (0.25mm) would be difficult.
I have the plans to make a template device that can achieve that accuracy each and every time, but I've never had it made.
it's a circular piece of plexiglass with concentric circles marked on it for every popular mirror size from 10-18" (it could be made larger for larger mirrors). In the center is a spring-loaded plunger that plunges through
a tube that sticks up above the circular piece of plexiglass. You moisten the bottom of the plunger so the center marker sticks to the plunger (with the adhesive side facing out). You carefully place the plexiglass circle on the mirror
and line up the circular markings with the mirror, then press the plunger down until it contacts the mirror. The plunger presses the center marker down firmly so the adhesive sticks. The level of accuracy
would largely be determined by how well the spot placer managed to center the plexiglass on the mirror. I think 0.1mm accuracy could be achieved.
The device would cost some to make well, so it might primarily be mirror makers who'd be interested in the tool. I think it'd be a lot more accurate than an acetate template sagging into the mirror, though, even with
Jason's book technique to hold the acetate template steady.

4
General Astronomy & Observing / Re: Dark Skies
« on: February 09, 2018, 01:16:25 AM »
Dave, my question wasn't rhetorical. I sincerely wondered. I'm always amazed when people post on CN saying they just plunked down $1000 on a scope but have never seen the Milky Way. I definitely wouldn't have done that but I'm glad something grabbed you.

I recently took 30 college aged students out to a dark sky and 28 of them saw the Milky Way for the first time. They were all blown away but only a few (4-5) said it was something they'd hoped to do. To the rest it was just nothing that had ever popped up on their radar.

5
Reflectors Telescopes Forum / Re: Truss tube dob Finder placement
« on: February 02, 2018, 11:05:50 PM »
Quote
Quote
But it is very unlikely the most comfortable, most practical orientation of a finder on a Dob will result in the diagonal being oriented vertically, normally it would be at somewhere between 30 degrees and 45 degrees. This is not easy to deal with because the view is flipped at that angle, it's very difficult to figure out the orientation relative to a star chart or naked eye/Telrad view.


But the field will rotate on a Dob anyway; for practical purposes what you see in the eyepiece will appear randomly different to the orientation on the star chart, and thus equally difficult to figure out.

I am discussing the field of the finder.

Jon

6
Reflectors Telescopes Forum / Re: Suck or Blow? The fan on my Z8.
« on: February 02, 2018, 10:38:34 PM »
I'm on my own 10, installed a fan of 12v, to suck the air out of the pipe.
I installed two modes, the fan code runs at 12V cooling, and the second when I work at 6v during the observation. From my practice this method turned out to be the best.

Boris.

7
Beginners Forum / Re: Rich field vs. wide field
« on: February 02, 2018, 08:37:25 PM »
Hey, I thought this was a "Beginners" forum! I always thought they were interchangeble.  Learned something.  Great thread.

8
Beginners Forum / Re: Two nieces interested in astronomy
« on: February 02, 2018, 06:12:06 PM »
My Starblast 4.5 is my main scope. No autotracker though. At f/4 it's difficult to find wide angle eyepieces that are sharp to the edge of view. I like the small size, light weight and tabletop convenience of the Starblast 4.5, if you have a good solid table available at your viewing site. I agree with Augustus that an XT6 would be better. I'll probably upgrade to an XT6 after I retire and quit moving around every few years. But for now, the portability of the Starblast 4.5 is more important.

9
Be safe Keith.

10
At 1000$ or so the Celestron SE8 is imho a very good pick. Take note that the 6SE is not that smaller (mount is the same, and a C8 is not dramatically bigger than a C6), just somewhat less "powerful" but a bit more stable.
The Evolution is the nwer and improved model, has extra features (among them a built-in battery, which is in any case a better option than using alkaline batteries with the SE) but it is also heavier.
In my opinion neither setup is very apt to start deep sky astrophotography, but can be good for hi-res planetary astrophotography.

The C8+AVX package is probably better suited if plan to dip the toe into the pond of astrophotography (the c8 is still an hard toy to start with, but can place a DSLR plus its lens on the eq mount to get easily decent wide-field shots); from the perspective of long-term planning, the EdgeHD models have useful improvements over standard SCTs for what it concern long-exposure astrophotography, so may be worth the extra price. Besides, their larger corrected field is nice also for stargazing, if want to use 2" stuff.

As for thermal issues, these are a feature of all large telescopes. With Newtonian reflector it is probably easier to add (if have the skill, which is not my case) active cooling, or boundary layer aspiration, but it may be done even with SCT (e.g. a PC vent with 1.25" or 2" adapter, which may be fitted into the SCT visual back) to speed up the initial thermal stabilization.
Then there is the issue of air temperature dropping through the night, but IME the C8 can manage this quite well except in those cases of extreme variations between day and night (high altitude, deserts, etc...); on the bright side, due to the overall shape and ergonomics, the C8 has less to fear from your own body heat.

Collimtion of smaller SCTs is not very difficult, especially when using a tracking mount, since it can be done at the eyepiece on a star*; you may replace the screws with knobs, to avoid the use of screwdrivers. I did this with mine, but have noticed that dy doing so have increased the frequencies of small adjustments.

*good seeing, high power (I use a 5 or 6mm EP) and a thermally stable telescope are in my experience staple requirements. But since good seeing and acclimatized telescope are staple requirement for high-power observations, in the end you can always check and adjust the collimation when it truly matters

11
Quote
Cary,
Some early filters were sandwich construction because the filter surfaces were soft and the second piece of glass
was protection for the coatings. I personally owned some of these.
One might use the word "laminated" to describe them, but I preferred the term "sandwich".

Yes, this is exactly what I meant.

12
Light Pollution Topics / Re: It Never Hurts to try!!
« on: January 31, 2018, 07:14:27 AM »
Here's hoping that someone knows what to do this time.

13
ATM, Optics and DIY Forum / Re: Maksutov project
« on: January 31, 2018, 05:33:19 AM »
Majestic Optical Coatings in NJ will do the AR coating. A few years ago Surplus Shed was selling 6" uncoated Jaegers objective and at that time Majestic charged $250 to coat both surfaces of one the elements.http://www.majestic-...-coatings.com/
 I had the corrector for 1961 Quester redone at Cumberland. They stripped the old MgF2 coating, redid the aluminized spot and MgF2 coated both sides for $220.

          - Dave

14
Hi Karsten,

thanks for adding these Barlows to the discussion. Interestingly there seems to be a new 2'' coma correcting barlow with only 1.6x power factor. Would result in a nice 3.75 mm exit pupil when used with a 30 mm widefield eyepiece at f/5.

Unfortunately this barlow comes for a whopping 395 Euro: http://www.apm-teles...tml?info=181488

 

Cheers

Eric

15
ATM, Optics and DIY Forum / Re: Schief vs Newtonian comparison question
« on: January 30, 2018, 12:23:29 PM »
Quote
Sounds like a job for the experts in Zemax or Oslo to me......

I agree: Why I said "For the experts..."...but if a non-expert knows that's fine too...

Pages: [1] 2 3 ... 8