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 - Nick Ellis

Pages: [1] 2 3 ... 10
ATM, Optics and DIY Forum / Re: Looking for a 10" F8 mirror
« on: February 09, 2018, 11:28:00 AM »
Doggone- I never spent that much, not even close on any scope except my 7.1" Mak-Cass !?!?
(only reason, I couldn't buy all parts and substrates for less than what I paid)

That Heidenhain has 5000ppr. It is not accurate to +/- 0.125" - physics prevents it.

(I have this from the Heidenhain reps themselves) the actual physical accuracy is in the +/- 10" range, and interpolation is used to get the smaller figure.

This is not to say that the interpolation is not accurate: but there always will be interpolation error and SDE (subdivisional error).

I understand Orly, that is accuracy, not precision. The incremental rate calculation relies on a precise incremental measurement, not an accurate position measurement. The sidereal rate is about 15 arc-sec/second so that if you are measuring the rate 5 times per second you would be measuring the elapsed counts from the encoder and getting a value of (15 arcsec/sec x 0.2 seconds x 8 counts/arc-sec) = 24 counts.

If the incremental precision is based on the error you stated, +/- 10 arc-sec which is a linearity error, and the per cycle increment is 259.2 arc-sec (360 deg / 5000 cycles) then the linearity percent error is +/- 3.85 %. If we apply that to the expected counts then the error in counts measured every 0.2 seconds would equal to 24 x 0.0385 or +/- 0.92 counts, or about +/- 1 count.

So if we add the two errors, interpolation and linearity, then we get 24 counts +/- 2 counts. so the measured incremental rate error will vary about +/- 0.25 arc-seconds (we should actually add these errors in quadrature since these are random errors, no systematic errors). Since this is a random error and not a systematic error this error gets averaged out over time as you correct the rate so it amounts to nothing to worry about.

This analysis ignores other errors with the mechanical coupling causing other non-linearity in the incremental rate measurement, but the total measured random rate error for my EQ6 mount,including all the mechanical, electrical, and other errors involved, was about +/- 0.7 arc-seconds/sec (2 sigma, 95%) which is equivalent to an RMS error of 0.35 arc-seconds.

This is proven with the results that I have obtained when using the TDM. The paper I wrote back in 2011 identified a systematic error in the TDM which has been corrected since.
If there is another way to analyze the behavior of using an incremental rate encoder, then I would welcome your analysis.


Eyepieces Questions & Recommendations / Re: Eyepiece upgrade ?
« on: February 09, 2018, 09:20:21 AM »
Eyepieces will make a difference, but not as much as you might think from reading these forums.

Get to your "destination" scope. It may not be your final scope. Probably won't be in fact. But it will have optics good enough to qualify.

Then worry about eyepieces.

The June/July issue of "Garden and Gun" (yes there us a periodical by that name) has an article titled 10 Great Escapes. Some these like Davidson NC, Ellijay GA, Middleburg VA and Water Valley MS may meet some of your criteria. Davidson is a college town for example so may more easily assimilate a Yankee. Do know that when we stay in the Deep South, we become "[email protected] yankees"

Actually the people down here are great. Most all are willing to help a person in need. Aside from bigger cities like Hotlanta and Nashville, the slower pace is very refreshing. My place is so rural that drivers still "wave" to those going in the opposite drection. This necessitates keeping one hand on the wheel at 12 O'clock just to be at the ready.

Best of luck in your new start. Might even find a lovely southern lady.

Goto all the way! I even use Starsense. My observing time is rare and precious. I focus on developing my observing skill.
I'll play the star hopping rally game later on once I buy my second scope, which will be a smaller grab and go setup but also a nice one for open star clusters, asterisms and planets (no appearture fever for me, I plan to go between my 8" sct  and a 4" apo refractor on manual mounth).

Mounts Questions & Expirience / Re: How do I update my Starsense Firmware?
« on: February 03, 2018, 11:51:43 AM »
I've tried everything I could think so and it stops in the middle of 2/6 around 6%, then when starting up it of course says BOOT LOADER Serial Invalid Pkg:0008. Any suggestions would greatly be appreciated! Yes, I've got the correct mount selected and everything connected like the Celestron diagram. Everything download correctly and connects correctly. Log files says memory corrupt. Please help!


Beginners Forum / Re: Need to pull eyepiece out just a little to focus
« on: February 02, 2018, 07:22:10 PM »
Hello, Is it normal to have to pull en eyepiece out of the holder just a little bit (and then tighten it down slightly out of its normal position) in order for it to be able to focus? I have an 8" Dob and I was trying out a wide FOV 12mm eyepiece, and it wouldn't focus unless It was a few mm out from being fully seated. Thanks!

Actually this seems a bit unusual to me for a 12mm eyepiece.Many modern1.25" widefield eyepieces in this range typically have focal planes that are positioned around the same point in the barrel relative to the rim and therefore the primary mirror. Is it a dual 1.25/2" barrel eyepiece by any chance? Some of those like the 12mm T4 Nagler have field stops (focal planes) much lower in the barrel as do some of the longer focal length Plossls (e.g. 1.25"40 and 2"55mm). Looks like the 6 and 8mm Ethos have their focal planes rather low as well.

For non-dual barrel eyepieces there are some 1.25" adapters that have higher profiles than others. Typically these are labeled "high hat" adapters. My older TeleVue high hat appears to be several mm taller than the current version. By comparison standard adapters stick up about half as high, and a flush mount adapter I have specific to a low profile JMI focuser sticks up only ~1mm above the focuser rim.

So if you can't trim the effect out by adjusting the primary collimation position or releasing any restricting screws, another option would be considering a different adapter that better matches the characteristics of your scope and eyepieces.


As far as I understand, by convention field curvature is referenced always to object space such that when the field is concave toward the object it is considered positive

This seems odd, Glenn. Field curvature follows the same convention as do surface curvatures. When they are concave to the object (sky) they have a negative sign. Also, by convention, the light comes from the left.


By convention, retractors have a positive field curvature and we know from experience that focusing the outer field requires moving the focal plane inward so that curvature towards the objective is positive.

By convention, light travels in the positive direction from left to right. Any movement or curvature in the same direction is positive. Any movement or curvature in the opposite direction is negative. Refractors have field curvature concave to the sky, which gives them a negative sign. For systems with objects at infinity the sign changes relative to the object/sky and not the objective.

Mladen, that's exactly how I read it in simulations. Refractor field sags in negative direction.

Jon, here's what isn't in collision with convention that I see in the software:
At the focuser, you need to subtract from the focal length of the telescope to find the best focus for outer field. It's adding the negative value of curvature to the value of FL, thus moving the focuser inward.

For a square base, the degree wheel can be a disk attached to ground board and just barely peek out beyond the square rocker box. The pointer attaches to the rocker box.

One can also have a distorted degree wheel that fits around a square base. That's what I have on my 13", drawn using some custom PDF-generating code.

I do think it's a good idea, though, to combine degree wheels with some alignment. Back in the day, AstroInfo for PalmOS had a feature where you could do N-star/object alignment (with a minimum of two objects, but better precision with more) with degree wheels, and then would show you the wheel coordinates for each object. It had that feature, because I programmed that feature. :-) I don't know if there is any app for modern hardware that has that feature. (I miss various features of AstroInfo, though I appreciate the much greater speed of modern hardware.) It might not be hard to make an add-on for Sky Safari that reads its configuration files to find out which object you were looking at and shows wheel coordinates for it, using the same technique as my old proof-of-concept Astro Surveys app.


There are lots of good choices for planetary scopes and a tracking mount can be an advantage.. But some scopes track better manually than others, some observers actually enjoy tracking manually.. the more you do it the better you get.. last night I was thinking about a similar thread, I ran my big scope up to 805x, it was stable and smooth tracking by hand.. most scopes are not that good.. but many are.

One general suggestion, the moon and planets are interesting targets but they are often not visible and when they are visible, conditions may not be favorable for their observation. Currently Jupiter is rising about sunset and is not well placed until late in the evening. Saturn rises about midnight and won't be well positioned for a few hours..Mars is very small right now. And the stability of the atmosphere s often and issue, particularly at more northly latitudes.

My point: Amateur Astronomers have to be opportunists. If your interests include binary stars and deep space objects, you will have many more opportunities to enjoy the night sky than if you stick with only lunar- planetary. Consider your purchase in the context of observing everything there is to see. This not only provides more opportunities but you will discover aspects to the night sky that you might never imagine..

There's a lot of magic out there just waiting for you to look at.


ATM, Optics and DIY Forum / Re: Coring Zerodur
« on: January 31, 2018, 07:50:04 AM »


<p class="citation">Mike Spooner, on 03 Nov 2016 - 3:04 PM, said:<a href=";module=forums&amp;section=findpost&amp;pid=7517563" rel="citation">[/url]<blockquote class="ipsBlockquote built" data-author="Mike Spooner" data-cid="7517563" data-time="1478178297">
Thanks for the replies. I'm not worried about a little edge effect around the hole (1.5 - 2") but would hate to crack the flat. My Pyrex 10" flat was cored with no visible effects but thought I'd approach the procedure on a large flat with due diligence and caution.

Thanks again,
waterjet it. it doesn't add to any possible stress by raising the temp.

Its still an abrasive cutting process subject to the Twyman effect.

If an f/6 doesn't get more out of Naglers, Delites etc

That is a matter of opinion that is certainly arguable. Testing your conditions is the best plan. Then you can narrow down the focal length you're after.
The Meade Series 5000 82<sup>o</sup> 5.5mmis a top performer and definite best buy. I think the 5mm T6 Nagler is a really fine ep and it can be bought from the classifieds on AstroMart or this forum pretty regularly for $210/220. Those wide FOV's will be handy. The Delites get good press but not all like 'em and the FOV is significantly narrower. They show up in classifieds now &amp; then too.



iif you are wanting ultra compact and somewhat ultra light then I would suggest the Obsession UC 15 or the Sumerian Alkaid.
I wouldn't suggest the alkaid.

Would you mind expanding your thoughts on this? I am curious why you dislike it. It was at the top of my list when I was looking around at large Dobs...

Beginners Forum / Re: Star Party Etiquette
« on: January 31, 2018, 01:18:25 AM »
Droe, in my earlier post, I referred to you as a guy. I'm sure you would have corrected me if I was wrong. I don't know why I made that assumption. I happen to be a female, and I know I'm not the only one here on the board.  Oftentimes, it's hard to know gender based on our screen names.

Anyway, sorry for the back to topic! I am close enough that I will probably go both nights. Saturday does seem to have the best prospects for clear skies, though.

But not when your signiture sez "Cheri". Kind of a give away.

Yep. I was considering joining the local club where I live.
A friend of mine invited me to one of their star parties. I was looking forward to meeting them.
Then I mentioned to my friend me and Speedy, my little dog, would see him there.....
"Uh, no dogs allowed."
In a public campground? in a National Forest? where the only requirement is a leash (State Law)....
Yep. I can understand if a dog was a big lumux.
So me and my 13 pound chihuahua stayed home.
No rules, and no dues.

The filter feels like it wants to start cross threading about half way. Is this normal? It also will hit my baader prism so I had to 3d print a 7mm shim for it. CN won't let me upload STL files so here's a link to the 3d model if anyone wants it:
https://www.thingive...m/thing:2702830Attached Thumbnails

Pages: [1] 2 3 ... 10