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Messages - Mark Dominguez

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Beginners Forum / Re: OIII or UHC Filter?
« on: February 09, 2018, 09:15:39 AM »

I was told by some more experienced folks that UHC or like Orion Ultranlock are best for 8" aperture, OIII coming into better use at higher apertures.

I agree. Most people who say O-III filters aren't "too dark' are using scopes 10 inches or larger.
No most people who say this know exactly how to use an OIII filter in a smaller scope. One of my favorite views of the North American Nebula is in my 100mm f/6 refractor at 15x and 25x using the Lumicon OIII filter. You have to use the right power range, get fully dark adapted, and use averted vision, but an OIII filter can be effectively used in apertures smaller than eight inches. Clear skies to you.

Since this photo was taken I have gotten all the SPLs save the 4 mm, and added a Leica ASPH to the stable.Herd Thinning will happen some time this year, although I am still open to more Super Monocentrics.

Attached Thumbnails

The Orion Nebula always reminds me of a ghostly bird in flight lit by stars. Even in a 3 inch glass it is impressive. There is something about viewing it in the predawn hush, when all the world's asleep in their comfy, comfy beds, that somehow intensifies the experience. Makes it all the more memorable. Making lasting memories is arguably the most normal thing in the world.

Hi everyone,

I've been looking around the internet trying to find an answer to a question I have regarding GOTO equatorial mounts. I own an iOptron SmartEQ Pro with a small, light refractor typically mounted on it. This mount comes with two alignment procedures, a "one star align" and a "multi-star align". The former only uses one star to align the mount, while the latter can use many stars. I believe, in doing my research prior to making my purchase, that many GOTO mounts feature similar routines.

What I would like to know is this: how does the use of one star and multi-star alignment impact GOTO pointing (the ability to accurately slew to and point at a target in the sky) and tracking performance (the ability to keep the target centered in the eye piece)? Or, put another way, how does using more stars impact GOTO and tracking performance? Assume a "normal" amount of polar alignment error for a beginner. My instinct is that the more stars added to the mount's internal pointing model, the more accurate the GOTOs will be. I have no intuition yet on how it would impact tracking, though.

This leads to a few more follow up questions:
What is the purpose of a one star alignment if two (or more) star alignment is naturally better (assuming it is)?
Does the quality of the internal pointing model impact the tracking performance (the ability to stay centered on a target) on a GEM?
Can a high quality pointing model (with, say, six well-centered stars) compensate for less than stellar polar alignment or collimation of the scope and the mount's polar axis? Either w.r.t. GOTO accuracy or tracking performance?

Reflectors Telescopes Forum / Re: Ebony Star Azimuth Kits...
« on: February 02, 2018, 05:05:22 PM »
FWIW, a 4x8 sheet of anything is enough for several scopes, so if you're making just one, it's kind of a waste. I was able to locate a small amount of Wilson Art #42 finish, it happened to be in "Jamocha Almond" (not a bad color at all...matches well with stained or natural baltic birch) from a local kitchen cabinet/millwork shop. They had it laying around as scrap. It only took three or four phone calls to various shops around the area before I got a hit.

Beginners Forum / Re: Maksutov? Schmidt?
« on: January 31, 2018, 12:49:01 PM »
Thanks, Sky Muse. That was seriously helpful, and probably prevented a mistake in buying a mount and Newtonian. The Celestron Omni XLT 6" is clearly a better instrument, plus it has a 2" focuser. The user reviews were generally positive. I am slowly but surely gravitating toward the belief that a 6" Newt is probably a better-than-average starting point. I am unsure of the GEM ratings (EQ-5, EQ-3, etc.) but will research that as soon as I post this. I can't tell you how helpful this thread has been. Thanks to all.

Boy, I see those hand warmers and am so thankful that I live (and have lived) in low humidity places. Bad enough to deal with cold weather but add dampness and I'd find another hobby. :-(

ATM, Optics and DIY Forum / Re: Delmarva Mirror Making Seminar
« on: January 31, 2018, 10:23:02 AM »
If you come with a fully polished mirrors ready to parabolize, you might want to have another project as a back up. Using the test methods we use it doesn't take long to parabolize a mirror even an F/4 one. In the 16 years I have been helping teach the class, those fully polished mirrors usually take a day to finish and the class goes over three days. A couple of years ago I null refigured two 12" f/7 in between teaching during the three days.
 Looking forward to see all my old friends and meeting new ones.

               - Dave

I'm wondering what would happen if the primary mirror's center marker were a few millimeters away from the center?
Has that ever been checked?

Light Pollution Topics / Re: Light pollution and aperture
« on: January 30, 2018, 11:07:25 PM »
my 8"sct was frustrating in my area...its go to wasn't that great either I couldn't see much and I couldn't star hop to things because I couldn't see enough stars on many nights. When I switched to a 14" dob it's like the sky opened up for me here. It may not be the best view compared to anywhere dark, but it gets me out feeling that wonder again! Honestly the sky glow doesn't seem worse at alL  I can enjoy finding just about anything now, especially during a new moon in the winter, things seem to be a bit better sky wise.

ATM, Optics and DIY Forum / Re: Building a 4" F15 Dall-Kirkham Cassegrain
« on: January 30, 2018, 03:37:28 AM »
3B Certification

Strange that it's not dated...

ATM, Optics and DIY Forum / Re: Cutting thin steel tubing
« on: January 26, 2018, 06:36:16 AM »

Chain pipe cutter? Rotary pipe cutter? This is thin walled tubing, not pipe. You'll crush it in a heartbeat. I would say your approach is wrong. Add the struts at one end. There is nothing magic about the ends of the tube that requires you to split it.


He never said size or gauge so how do we know

He mentioned cutting the tube for a 3" refractor. Not very likely to be heavy walled.

Mounts Questions & Expirience / Re: EXOS2-GT
« on: January 26, 2018, 03:54:00 AM »

The $500 Explore Scientific FirstLight FL-EXOS-2 GoTo EQ Mount - FL-EXOS2GT ( https://explorescien...2-goto-eq-mount ) has a recent video review: and a Cloudy Nights Forum topic https://www.cloudyni...153-fl-exos2gt/ .

The video review is for the PMC-Eight controller version of the mount which costs $899 not the $499 version used in the FirstLight series.
if you have any details about the EXOS2-GT the 499$ please share it[/quote]
I started this thread a while back to kind of keep the standard EXOS2-GT mount information a little more centralized. I'm only starting to get into AP and I'm only a beginner with a lot to learn. Unguided, I can do about 2 minutes max (and easily do 90 seconds unguided) and the stars stay round. I think if you kept the exposures under that, this mount would do fine. Over that maybe the ST-4 guide port is the route to go. I'm not into guiding yet.
These were taken with my OMNI XLT 150mm reflector and my DSLR on my EXOS2-GT. I'm just experimenting with exposures, stacking, etc. from a very light polluted backyard. These pics below aren't stacked.These are just single 30 second exposures of M31 and M57. Obviously I'm a newbie to AP, but these pics only reflect my photography skills, not the mount. I've taken 90 second and two minute exposures (of just stars) just to see how long the mount could track without the stars being affected.
M31 - not near enough exposure time, and I really need far more subs and stack them. Still learning...
Besides my heavy light pollution, the moon was out which didn't help, so I took a few pics of that too...

which telescope did you use for those pics? amazing job, my expectation was much lesser then what you showed me, any other pics you would like to share?

good job

ATM, Optics and DIY Forum / Re: Adaptive Optics
« on: January 26, 2018, 02:27:56 AM »

Here's a couple. There are newer just google "Adaptive Optics." If you want to roll your own, look at the papers from
the late 1990s. These are a little easier to copy.

If you decide to really go after it, PM me, I have some PZT disks I can part with.


Adaptive Optics in Astronomy by Fran├žois Roddier (Amazon and others)

The optical bench... fairly simple

Interferagram of theUnimorph (semipassice-bimorph) with 1 section energized.Attached Thumbnails

Beginners Forum / Re: Vixen a80mf acquisition - what do you think?
« on: January 26, 2018, 02:15:03 AM »
The "off the cuff" calculation is much simpler.

The scope is 910mm long and 80mm wide. The focal point is zero mm wide. So its a simple linear relationship.

Halfway down the scope the light cone will be 40mm in diameter and this will occur 455mm from the focal point.

1.25" is appx 32 mm and the light cone will be this diameter somewherevery close to 364mm from the focal point. That's over a foot from the eyepiece.

So, no I still think its not worth it to upgrade to 2".

And yes, I know there are 2" eyepieces that will not use all 2 inches of diameter. It depends on the focal length of the eyepiece and its apparent field of view. But even if there are a few EP's out there that can squeeze a tiny bit of extra FOV out of the scope, is it seriously worth it? For all practical purposes, the same FOV can be had by getting a large 1.25" plossl for a lot less money, less hassle and zero risk of damaging the scope by retrofitting it with a 2" focuser.

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