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 - Jacob Julian

Pages: [1] 2 3 ... 10
Quote still falls far short of the mark of what a true monolithic worm block design should be.

You mean expensive? The Ovision block costs $540 whereas the one-piece solution from Losmandy goes for $175. There's probably some future risk that components will loosen up in the Losmandy block, like you've mentioned, but in an almost 0 vibration environment like a GEM axis we're probably talking about decades.

Regarding disassembling and mis-aligning things, that was the biggest issue with the two-piece block. This resulted in the infamous 76s error. I've personally taken apart the previous OPWB several times (I do like to tinker) and have yet to see a 76s error bump in my PE analysis. This tells me that it's very difficult to throw out of alignment. I'm 100% confident that even if things did loosen up over time, simply tightening them will be all that's needed to restore it to factory performance.

Personally, I'd rather have the extra $365 to put towards a new eyepiece or other astro gear.

I am not talking about expense and I am not advocating for Ovision. I posted the link to the photo to demonstrate the difference between the two and to make it clear what a monolithic worm block actually looks like.

Of the 3 eyepieces in the original post, I'd pick the 15mm Omni Plossl over Wide Angle Kellner. Wide Angle Kellner's don't work well in my f/4 scope. I've never tried a Sterling Plossl, but $25 seems like very good price.

Nem pense duas vezes. Mach1 sem dúvidas.

Reflectors Telescopes Forum / Re: Help me move to a large dob?
« on: February 02, 2018, 04:56:06 PM »
Well, I think I can only say a few things here which haven't been said. I'm very grateful for the comments some have made above.

1) In my opinion, you get what you pay for. Less expensive is less expensive for a reason.

2) I find that one gets the best performance from the thinnest high-quality mirror that you can buy. This means quartz if possible, but otherwise a well-annealed piece of good borosilicate glass figured properly to a smooth, accurate figure. Thin is good because it cools more quickly, and this pays big dividends if the optic is made properly. Proper cooling of the optic is also very important for the best performance.

3) A good mirror cell is very important for a thin mirror, and my recommendations can be found in my mirror cell article. The telescope structure should be on par with the quality of the cell.

You're welcome to contact me if you have questions.

ATM, Optics and DIY Forum / Re: A compact Dall/Kirkham
« on: February 02, 2018, 04:46:44 PM »
Well-put, Mike.
Thanks for explaning for me:

In this particular case, the figures I arrive at are the following ones (modulo errors in handling the pocket calculator, knots in the slide rule, or the usual problem between keyboard and chair):

For the elliptical primary mirror in question, the first focus is on the axis 1124.1 mm from the mirror surface. Any object placed here is imaged to the second focus, at 16648.0 mm from the surface on the optical axis. These values strongly depend on the conic constant, in this case: C = -0.763, and the radius of curvature, in this case R = -2106 mm.

If one were to construct a null test from this, the sensitivity of the setup with regard to the foci is very high, indeed: A shift of the source by 1 mm (which is 1/1000 of the absolute value) will change the position of the image by 220 mm and introduce 1 wave of spherical aberration at only .7 mm from the axis.

On the other hand, this means that any mirror which can image, say, the end of an optical fibre, sharply from 16648 mm, to 1124 mm from the mirror surface, where it can be checked with a microscope, must be in the right ballpark.
So, with two tests, one to check for smoothness of figure, and the second one for finding the foci can help determining the figure of a mirror, the figure can be checked. But, again, the task if placing the light source at an exact distance from the mirror.

I also know fully well that trying to figure a conic constant to three decimal places is very much an impossible task.
Nonetheless, this is the designed value I am aiming for.

The conic constant I achieve in the end will be measured interferometrically and the coma corrector fabricated and placed accordingly.
To facilitate this, I chose a coma corrector with only one radius: it consists of a plano-convex lens which will fit into a plano-concave lens.
The two surfaces can be fabricated and tested against each other, plus the radius can be controlled with a spherometer.

All the best,

Beginners Forum / Re: Thinking about a 2" Barlow - your opinion
« on: February 02, 2018, 04:27:06 PM »
Ed, you have beautifully summarized what I've been saying on these boards for many months. There are those in this hobby who want or "need" that last 10 or 15% of performance, and they truly have all my best wishes. With their expenditures, they drive the hobby to achieve greater things, and eventually, this greater performance becomes less expensive as it gets adopted by more and more. They are the ones, as you sort of put it yourself, buying the 70" 3D TVs now so that in 5 years or so, we can all enjoy inexpensive 70" 3D TVs. That's a benefit both for themselves and for everyone else.

And there are those among that group who will recommend this top-of-the-line equipment, but do it in a helpful way that says, "Yeah, I know this stuff is expensive, but it is the best. Don't end up buying stuff twice - buy this once and be done with it forever."

And then there are those among that group who snobbishly look down their noses at anything less than absolute perfection. Those who not only say that your $10 Barlow is an absolute unmitigated piece of junk, but who will go out of their way to climb up on the rooftops to shout it out to all who pass by. Unfortunately, you encounter people like that all too often in this hobby, both on these boards and on others.

Why can't we all live and let live? If someone is enjoying themselves with supposedly "lesser" equipment, as Tony just mentioned, let them enjoy their smileage. As long as they are out there under the stars, having fun, that's all that really matters. To paraphrase the old saw we throw around, the best equipment is the equipment you use. If you're using a $10 Barlow and it's doing enough of the job for you, who is anyone to say otherwise?

It would be like your saying that you love to listen to Bieber, and someone else's saying, "No, not only does he suck, it is a known and proveable fact that he sucks, and not only that, but you obviously suck too because of that." You would never let anyone tell you your taste in music was inferior, would you? As long as you enjoy it, that is what counts.

But really, no one should love to listen to Bieber. Ever.

Beginners Forum / Re: Any help? Tasco Luminova... mount with the tremors
« on: February 02, 2018, 04:08:04 PM »
My 60mm refractor's worst enemy is...

It would provide most the parts I would need to refurbish and update the 60 for less than the price of the parts sold separately, if I could find them.

Another of its enemies are those $99 4-inch table-top Dobsonians.

I'm building a 16 "Dobson and it's time to look for the 16" F4.5 optics and I do not want to ruin myself by buying very good optics that are worth a lot of money and more than I can afford.
That is why I ask those who have the optics of 16 "F4.5 GSO.
 How is the optical quality of these GSO mirrors?
Greetings and I hope you help me choose well.J.Tapioles

Most I've tested have been average--not horrible, just not great.
1 Meade 16" (GSO) was the closest to perfect I've seen in a production scope. Simply stunning and no errors of any size in the intra- and extra-focal star images.
It was easily better than 1/8 wave on the wavefront.
That's NOT usual.
The mirrors are thick, slow to cool, and made with lower-end BK glass.

--ask if you can return a mirror that isn't good enough for you to keep.
--design the scope so you have boundary layer fan(s) and fans behind the mirror. Don't test until two hours outside with fans running.
Even then, if you see thermals in the images, wait to test later.
--the scope in the picture, with one small fan, will not be adequate for cooling.

Mounts Questions & Expirience / Re: Polemaster problems?
« on: January 31, 2018, 12:34:45 PM »
I'll take the liberty to join this thread, because I am having Polemaster-problems too.
I have been using the Polemaster on a MacbookPro in OSX (once a stable version was available) and with Parallels VM win7 and win10.
No problem so far.
Because most AP software is for windows, I bought a Dell Precision M6600 i7-16Gb Win10
But on this machine the Polemaster software behaves very strange. As soon as I connect the camera and move my mouse, the window starts to flicker. The whole window or the left column starts to jump and flash.
I tried all their drivers, stable and beta. Different screen resolutions. USB2 and USB3.
All the same.
I guess this a typical Dell issue.

Statisticly there must be life in the universe . . .
So statisticly there must be someone out there with a Polemaster running it on a Dell, reading my question


ATM, Optics and DIY Forum / Re: DIY goto mount advice needed
« on: January 31, 2018, 06:01:50 AM »
I would double check that issue was the main control board and not the hand controller. A common mode of failure is that the hand controller will be plugged into the scope with the scope powered up. This can damage the IC(s) that are used to communicate on the hand controller to the main control board.
  If the hand controller is ruled out I would find out that you have voltage in the correct places. The first place to look is U1. That looks to be a voltage regulator. So it most likely takes what ever voltage from the power supply and drops down to most likely at least 5 volts or lower. It looks like the PIC are happy running between 2 to 5.5 volts so usually those IC would run somewhere between these values. So I would try to find the specs on U1 and see what its suppose to be doing and seeing if the output is correct. My guess is that regulator is 3.3 volt unit.
 See if the voltage is correct coming from U1 and if you have that voltage at the input and ground pins on the PIC IC's with the motors not plugged into the board. Try if the hand controller now sees the main board. If it does then the problem is the one of the motor modules.

     - Dave


 Check U1 on the board . That looks to be a low dropout voltage regulator. The PIC IC's want a voltage between 2 to 5.5 volts so that voltage regulator might be supplying 3.3 volts to the PIC's. It's a common failure to have them go bad and if it is the PIC's aren't running and that would give you the errors your seeing.

         - Dave

Thanks Dave I'll try this out and see post back what I find.

Light Pollution Topics / Re: What to look for when buying a new House?
« on: January 31, 2018, 12:09:14 AM »
<p class="citation">Quote<p class="citation">QuoteAlso keep in mind that trees grow. That view you had a few years ago might just be lost due to tree growth. Many trees can grow several feet a year.

Yes, but that is why there are chainsaws!!!  Remember a tree is just a wannabe stump. [/quote]

If they are your neighbors trees they may not be amused! [/quote]

No they were not amused. However, coming from southern California trees were unique and rather special to them!!

Then the trees fell in their driveway just missing their house.

Now they sneak across MY property line to cut trees that they think might endanger their home!!! 

Common comes to people based on experience!!

Eyepieces Questions & Recommendations / Re: Delos 14mm vs Ethos 13mm
« on: January 30, 2018, 11:52:02 PM »
Hi I'm looking to buy one or the other.  I have a 35mm Pan, a 22mm Pan and a 2" Powermate 2x.  I think either of these eyepieces could replace my CZJ orthos.  I have a TEC 7 f/15 Mak and a C14 (not in use right now), so both relative slow scopes.


This is an easy one for me. I have never been partial to the 80 degree plus Televue line, not the 82s, not the 100s. The only &gt;70 degree eyepiece I really like is the Leitz 88. It's largely a question of blackout and that to place my eye where there's no blackout I don't get the full field.

I've liked the Delos line very much. If the XWs weren't out there (horrors!) the Delos is the OCULAR line I would get. I suspect in any case the Delos line was introduced to compete directly with the XWs as TV must have noticed a certain number of defectors from the more-fov-is-always-better philosophy. Greg N

Reflectors Telescopes Forum / Re: Just purchased an Orion XX16G!
« on: January 30, 2018, 06:26:13 AM »
My mistake, it's a 14.5" NightSky w/ Argo Navis DSCs. Unfortunately, I think it's not close to you.


Reflectors Telescopes Forum / Re: Aluminum ramps for large dob
« on: January 30, 2018, 01:40:38 AM »
I walk between the two. Will depend on your scope's wheel spacing.The cargo flow of the pathfinder is raised a little. The long ramp fingers with the red plastic coating are long enough to reach the cargo floor.Teeter installed a lock pin to keep the mirror and rocker boxes together for transport. Inside the car the scope sits on a cardboard box. This allows me to slide the scope forward in the carpeted cargo area. The side seatbelts slip thru the bearings to keep it upright in case of sharp turns or accident.If your cargo area is lower, maybe a couple of 2x12 or plywood square to make it level?

Beginners Forum / Re: Star Party Etiquette
« on: January 29, 2018, 09:48:29 PM »
Where did this take place? Looks like a lot of fun.

This was Astronomy at the Beach, put on by the Great Lakes Association of Astronomy Clubs, at Island Lake Recreation Area, in Brighton. Here is a link to the info page at GLAAC:


If you click on the "Home" tab, you will see logos of all the members of GLAAC, which include a number of astronomy clubs. Clicking on any of their logos will take you to their respective home pages, in case you're looking for aclub to join.

Pages: [1] 2 3 ... 10