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Messages - Jon Beckner

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Beginners Forum / Re: How do you deal with the frustration of Weather
« on: February 09, 2018, 05:23:42 AM »

If I need an astronomy fix and its crappy out I usually do something related to it.

Related to drinking....?
Drinking and women...they both kill ya.
Its a good way to go

ATM, Optics and DIY Forum / Re: Oversized Secondary Mirror
« on: February 08, 2018, 07:11:05 PM »
Im re-working a 17.5 " DOB that I bought used. It was a rebuilt coulter, and I was a bit wary, but the seller assured me the optics were above average. However, they were not - they were abysmal. Ed Jones tested the primary and it came back WAYYYY under corrected - I think it was by 2 waves ???

Whazzup with these very incorrect commercial mirrors? Bad testing techniques at the works or they just don't spec it very closely?
Our Meade 16" mirrors came with very bad figures. Star tests were poor, and bench tests showed way over 1 wave error.

I'm not much of an optician, but I can hit 1/4 wave....I guess it's like imported goods, they are often low quality because nobody asked/paid them to do better.

General Astronomy & Observing / Re: Kite Mosquito Patch - will they work?
« on: February 08, 2018, 06:38:49 PM »
Thermacell works reasonably well for me as long as it's no too breezy out.

You might also consider pre-treating some of your clothing with Permethrin, available in spray form from Sawyer. It's effective and odorless once it dries (to me at least) without leaving your skin feeling yucky. It lasts through several wash cycles (with line drying being the best way to maintain a treated item).

edit: i'm bad at typing =)

Just to clarify, the Starguider isn't an Ortho eyepiece. Its a type of 5 element eyepiece with 2 ED elements that it advertises itself on.


I do not think that the Orion 38mm is the best fit for your two f/5 (?) reflectors (nor you f/6.25 refractor). First of all, the exit pupil might be on the large side (depending on your eye and your observing conditions). The secondary shadow might show up in the field, the sky might look washed-out, and the exit pupil might be larger than your eyes entrance pupil – thereby reducing the effective aperture of your scope. Note also that this eyepiece is specified as having a focal length of 40mm by other re-branders, so exit pupil might be 8mm in your telescopes.

Secondly, it will not show a well corrected field in your fast telescopes.

Since this is meant to be the primary low power eyepiece in all your telescopes I will advise you stay around the 30mm mark. To the degree that your budget is flexible I would suggest getting an eyepiece that will show a well-corrected field in your fast telescopes. You might find the Explore Scientific 68° 28mm ($ 179 new) within your budget on the used marked. The 24mm version costs $129 and it might be all you need (depending on your sky conditions, pupil diameter and viewing preferences).

<p class="citation">Jon Isaacs, on 07 May 2017 - 12:16 PM, said:<a href=";module=forums&amp;section=findpost&amp;pid=7868440" rel="citation">[/url]<blockquote class="ipsBlockquote built" data-author="Jon Isaacs" data-cid="7868440" data-time="1494152187">

I agree with dufay, the Orion Q70 is not a good fit for F/5 Newtonians and F/6 refractors, it's sharp enough on axis, not sharp off axis. At some point it's likely that you would want to upgrade it..

As far as of this and the planets, I consider myself to be a "serious" planetary observer. I've n a fast scope, orthos don't have enough eye relief in the short focal lengths required. Planetary observing is about two things: a good telescope with enough aperture to push the seeing and excellent seeing.  Whether an eyepiece has 4 elements or 7 elements, I look for good to correction across the field and decent eye relief..

Best thing to do, look through some eyepieces that belong to someone else..


I've decided on bumping up the budget and getting the Explore Scientific 28mm 68 degree AFOV new.


Hi! I'm an astrophysics major and an avid amateur astronomer. As a student, I don't have a ton of income, but I'm scraping up funds for my first equatorial mount. I've been doing lots of imaging on my Nexstar 8SE and ALTAZ mount, but the field rotation really starts to show quickly. I am trying to decide, primarily between:

1) Celestron CGEM II (on sale for $1439)
2) Sky-Watcher AZ-EQ5 (1350. I was a bit skeptical of the az-eq mix, but I keep hearing good things!)
3) Sky-Watcher EQ6 (1400)

I currently have a Nexstar 8SE SCT and an Orionshorttube80mm. I image with a canon 1100D DSLR, mostly milky way and deep sky stuff. In the future (read: once I hear back from job apps, haha) I plan on getting a modest apo or Newtonianastrograph.

I was hoping people would have recommendationsfor which to choose. There seemed to be sparse reviews for the CGEM II, has anyone had experience with it?

Thank you!

Go with # 3, the EQ6.
Better yet, wait for the newer EQ6-R to come out. Oh...and welcome to Cloudy Nights.

Mounts Questions & Expirience / Re: Bresser EXOS-2 German GoTo
« on: February 03, 2018, 03:17:55 AM »
Any updates on this mount's performance? I am contemplating picking one up, price seems too good to be true!



I wonder, though, how much of the astigmatism seen in his 40mm Meade SWA was in the center of the field. If it was only lateral field, it was likely in the eyepiece.
Astigmatism from the eye is seen dead center as well.

Don, it is the outer field astigmatism that bothers me. On axis, I found the Meade SWA 40 to be just fine, out to maybe 60-70% of the field stop on my 8" f5.8 Newtonian. And the problm I had with the 40mm f/l was that I could tell my pupil was cutting off and throwing away light.
What size secondary do you have and what is the distance from secondary to focal plane?

Could be light loss on the edges due to your 70% illuminated field being considerably smaller than your field stop diameter of your eyepiece. See (The 70% refers to an amount that below which definite light loss is detected by most people. e.g. if you are a variable star observer you want the diameter of your 100% illuminated field to match the diameter of your field stop in the eyepiece you intend on using, hence an oversized secondary for such work). The f ratio also comes into play as this determines how steep the light fall off is. Most Newtonian telescopes used to be and many still are designed for a 0.5" diameterfully illuminated field which isfine for general purpose use but one can fine tune any such telescope within reason to give optimised viewing to suit ones needs.

Note too less corrected eyepieces often suffer from significant field curvature in the outer 30% so refocusing for the edge is needed especially when used in a Newtonian similar to your specs. Small stars at the edge can be much fainter and often 'disappear', (galaxies definitely do) unless the edge is focused and not the middle.
Now that is something I didn't consider. I built my scope ~30 years ago, and I wasn't exactly planning for a fully illuminated 46mm field aperture. I remember thinking more along the lines of reducing the amount of light to the primary mirror that was obstructed by the secondary, and a compromise between planetary and deep sky viewing.

So this Newtonian scope is the following:
8" primary mirror
47.6" focal length
1.5" secondary mirror
39" measured center to center from the primary to the secondary, or about 7.7" from diagonal to focal plane.

Beginners Forum / Re: What did Santa get you for Christmas?
« on: February 02, 2018, 03:11:37 PM »
Well I just joined in hopes of getting some advice on last year's major Christmas score, a Celestron Advanced VX mount with 8" Newt, SSA, t-ring adapters and filter set. We were living in a rental in town, so the viewing was not great and then of course the weather was not cooperative. (Next severe drought, I'm buying a new OTA -- guarantees weeks of rain.) Then we finally closed on our new home and moved, and the telescope stayed in storage until November. We got it out again over Thanksgiving while the kids were home had some great viewing.

This year my son gave me a new eyepiece and my wife gave me the Skyportal wifi deal. Rain. Rain.

Last night it was beautiful and I was proud of how organized I was getting things setup to play with the new "toys," and the AVX failed. More on that in a separate post. But on the bright side, I keep the telescope in my home office in hopes people will think I'm smart or something.

Eyepieces Questions & Recommendations / Re: Eye relief of 11mm TV Plossl
« on: January 31, 2018, 10:58:27 AM »
I agree that the 9 or 11mm TeleVue DeLite would be the way to go. It offers the kind of eye relief you will need, an über sharp view, and a little extra TFOV compared to anybody's plossl. The TV Plossls are, indeed, amazingly good, but so are the DeLites, so you don't have to worry about missing anything. The TV Plossls represent the pinnacle in simple eyepiece design, for their time (1980's ?). Simply fantastic, and they still produce one fantastic view that can't be beat, perhaps, until one gets to the astronomically priced simple models (like the Burgess Optical Supermonos or Zeiss ortho options). But the Planetary Eyepiece Comparison article you mention by Mounsey, tho a classic here on CN, was written in 2006, before PaulDellechiaie had made even an Ethos, and well before the DeLites. The eyepiece world has changed since 2006. If you can't afford that, I'd go with the Baader Classic Ortho 10mm, but compared to the DeLites, they're relatively primitive, technologically, and comfort-wise.

Mounts Questions & Expirience / Re: GOTO mount for 8" Meade Starfinder
« on: January 31, 2018, 09:43:10 AM »

I weighed mine last night at it tips the scales at about 18# without an EP.

It looks like the iOptron IEQ45GT would be a good choice.... though the Orion is a bit more budget friendly. Is the Sirius Pro the replacement for the Atlas? It appears so...

This is the Atlas:http://www.telescope...36/p/116277.uts

There are also some used ones in the classifieds here on CN.
Sweet. Thanks!!

ATM, Optics and DIY Forum / Re: Mirror making workshop in Toronto
« on: January 31, 2018, 06:20:35 AM »
Ed, Marc: you are such enablers. I will be aiming for f/12.

Beginners Forum / Re: What straps to help carry 10 inch dobsonian?
« on: January 30, 2018, 04:00:22 AM »
I like a single dorsal longitudinal handle so I can carry the ota with my right hand and base with my left hand and carry it a long ways. Carrying just the ota with 2 hands is so easy no handle is needed. I am tempted now to skip the handle and just pick up the whole unit in front of me, though handles are more comfortable.

I just picked the whole thing up again. Very doable, but it digs into my fingers. Also bumps the front on my legs, reducing step size, and blocks my view.

Wheels are another option but just feel silly for an 8". I'll add them anyway.

The fine focusers on both eyepiece holders worked well for me, but I often wasn't using them to achieve critical close planetary focus; more often to fine-adjust system back focus in conjunction with Baader's spacers, which I described here a while back...

Glad you re-emphasized this; it's always useful to have additional means of controlling backfocus!

As others have said, I would think long and hard about your focal ratio. The generally accepted (dare I say) conclusion is that added aperture will make a bigger difference than a smaller central obstruction so long as you are below ~20% CO. As long as you are below 20% CO, I would consider either larger aperture or shorter focal ratio, since the visual performance will be negligibly different. Given that you don't need to fully illuminate the entire field, getting down to a 20% CO should be very, very easy.  A conventional 12.5" F/5 with a ~2.1" secondary would be fine, and would be a ~17% CO. You would be very hard pressed to see any difference between it and an F/9 in terms of planetary performance. Increasing the aperture by just 2" or 4" would have a significantly more noticeable effect, when seeing allows of course.

Reflectors Telescopes Forum / Re: Dobson 10" for planets/moon ?
« on: January 25, 2018, 10:54:03 PM »
Not sure if your SC and/or the 10" dob you are contemplatinghas tracking. If you have tracking on the SC but do not have tracking on the dob (I mention it since they do tend to be manual) you may find it does not matter that the dob can go to 200x, 300x, or whatever if you cannot keep the planet in the FOV at those higher magnifications.

Tracking by hand is a skill to be learned and some observers are better at it than others. Some find it bothersome, some enjoy it. And some Scopes definitely track better than others.

I think 200x is not a problem for most observers, for most Scopes.  At 200 x, the difference in the view will be quite apparent.

But even then, it may not be fun..


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