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Messages - juskemenbo

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1
Eyepieces Questions & Recommendations / Re: Eyepiece question
« on: February 09, 2018, 11:07:31 AM »
OK, let me explain about eyepieces as afocal devices.

As you move your eye back from the eyepiece, the field gets smaller, but stays in focus.
That's because, once the focal plane of the eyepiece is coincident with the focal plane of the scope, the eyepiece is essentially afocal.
No matter what distance you are from the eyepiece, the field is in focus.

Nonetheless, as you back away from the eyepiece, the pupil of your eye becomes smaller than the size of the image
formed by the eyepiece (which becomes wider). You see less of the field because the edge of the eyepiece barrel is literally occulting the image.
You can move your eye back and forth laterally and see different parts of the image, and it stays in focus.
But the body of the eyepiece itself occults the edge of the field.
This sounds suspiciously similar to your description of drifting back and forth and having the edge of the field get occulted.

This only occurs when you are too far from the eyepiece, however, to see the actual field stop completely all the way around
(which occurs at the exit pupil).

Now, if you are at the exit pupil, you see the entire field to the field stop and, if the exit pupil is smaller than your eye's pupil, all the light from the eyepiece goes into the eye.

If you are too close, however, the light from the eyepiece becomes larger than the pupil of the eye and your iris starts occulting the image.
If you move back and forth, first one side, then the other, blacks out as the rays are intercepted by the iris and you get what are termed "black-outs".
This happens a lot with long eye relief eyepieces used by non-glasses wearers, or people who stand to observe or even just when you drift a bit too close to
an eyepiece. I can induce the blackouts on nearly every eyepiece that's made unless the eyepiece has such a short eye relief I automatically hold back
to preserve my eye.

So what it looks like at the eyepiece is dependent on where your eye is relative to the exit pupil.

If the eyepiece has spherical aberration of the exit pupil, however, then the exit pupil itself is not all at the same distance from the eyepiece, and moving in toward the eyepiece may make either the
center or edges of the field black out in an alternating way that resembles large kidney-bean-shaped shadows in the outer parts of the field. This is termed "kidney bean blackouts" or simply
"kidney-beaning". It is found in (primarily) widefield eyepieces without a flat exit pupil. This doesn't have to be severe (like the original 13mm Nagler)--it can be slight, but still result in an eyepiece
being sensitive to eye placement. I have run into many of these over the years.
http://www.handprint...O/ae4.html#SAEP

So, traditional "blackouts" are caused by the observer's eye position relative to the exit pupil.
"Kidney bean blackouts" are caused by SAEP in the eyepiece.
Other than cataracts or macular degeneration, those are the two sources of blackouts in eyepieces as I understand it.

The "walking past a keyhole" look simply indicates the observer is farther away from the eyepiece than the exit pupil.

2
Beginners Forum / Re: Question about green lasers
« on: February 09, 2018, 08:25:58 AM »
Quote
Quote

Thanks for all your replies. I didn't think I would get so many varied answers! The reason I asked the question is because I'm about to acquire a small scope without goto abilities and wanted some way to aim it at the planets and moon. I have an extra Telrad and some other look through finders but would prefer some other way to accomplish this without bending over. I'm getting a little long in the tooth and contorting my body to look through a finder scope isn't my favorite thing to do! I was hoping a green laser would do this for me without me stooping over. Again, thanks for your replies.
Don
p.s. ....too bad I can't mount my StarSense on it!! LOL

I use a laser extensively for the same reasons, and I absolutely love it.

You can buy a quality laser that is tested and guaranteed to work in cold weather from Howie Glatter. They're expensive, but worth the money spent when they work every time.

In my Seattle suburb, I can see the beam on any night unless it's pointing directly at the moon.
Steve, the Glatter lasers are superbly machined but the standard laser pointer he sells is powered by alkaline batteries. (not good for temps below freezing) And, his collimators are machined as 1 1/4 inch or 2 inch eyepieces, so although they use CR 123A lithium batteries (good down to about -5 deg F), they cannot be easily mounted to work use as a pointer. (after all, they are collimators, not pointers)

3
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Gary:

When I'm faced with this issue, as Ed suggested, I just pull the eyepiece out of the focuser, there still should be plenty of barrel in the focuser for stability.

It's simple enough and costs nothing and adds no weight. Why not?
Jon

Jon,

I know it would work, but I am FAR too anal-retentive for this field expedient solution. The visual back of this scope secures the EP with set screws that mar their barrels, so I have fitted the safety undercuts of all my EPs with a protective strip of heavy vinyl tape to protect the barrel as wells give the screws something to bite into for a more secure hold than set screws normally provide. See photo. I have EPs that are 25 years old that are still in pristine condition.

Also, to get the maximum precision and performance out of inexpensive gear, I try to ensure that every optical and mechanical component registers in exactly the same place every time its used. Playing around with my laser collimator has shown me how to use the slop in one component to compensate for the slop in another and get the most precise alignment. For example, I have a pencil mark on the focuser that marks the height at which my EPs come to focus, and I raise the focuser to this position when I collimate the scope. Collimating at one height and focusing at another doesn't work quite as well. Without a hard registration stop, the EP would never be in the same place twice.

Attached Thumbnails


4
Why doesn't everyone get more expensive wider FOV?  Yes the price is a consideration.

Why doesn't everyone drive Mercedes?  Because Ford will get you there in reasonable comfort at a fraction of the cost.

5
Mounts Questions & Expirience / Re: Realistic AVX unguided times?
« on: February 09, 2018, 04:00:24 AM »
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It really depends. Is your AVX in good shape? Have you gotten your polar alignment right? Is it windy? How much weight do you have on it? What area of the sky are you tracking?

And also on your focal length. That is the really big deal. At 400 - 500mm, it's easy. Almost every sub will be good at 30-seconds. At 1-minute, you'll be throwing out the occasional frame, but not too bad. At more than that things continue to go downhill.

Best bet? If you need to expose for longer than about 1-minute, or you need more focal length, just guide.

6
Reflectors Telescopes Forum / Re: My new Dob is ruined....
« on: February 09, 2018, 03:27:25 AM »
I'm an ex Naval Aviator, and airline pilot, I can't even imagine sitting in a car or plane and NOT strapping in.

I had a young enlisted woman in my squadron in Maine, she was a single parent of a 6yr old daughter, not wearing a seat belt and hit an ice patch and then a tree at an estimated 25mph, died at the scene. AND ON TOP OF THAT, the life insurance wouldn't pay SINCE SHE WASN'T WEARING THE SEAT BELT!!!

It might not save YOUR life, but might save your families!!!!

PS-check out dobstuff.com have lots for you to consider with your parts.

Glad YOU are OK.

7
Quote
BrooksObs wrote:
<p class="citation">QuoteI have to agree wholeheartedly with brother Sketcher's take on the question in his post #3 of this thread. More than anything else, solar filter failures are a result of the user's lack of reading and following manufacturers' instructions, not the product's inability to perform as intended safely. Most of the posts that appear in this thread are just "...well, I read/heard that these filters are very dangerous and should never be used." Just more hobby old wives tales as seen so often on this forum in regard to countless subjects.

Sorry old boy, but it definitely isn't "old wives tales". The risk of eyepiece "SUN" filter failure *is* there (and has always been there). A good friend of mine (Rick Johnson, who often posts to the imaging forums) had one of the eyepiece "SUN" filters properly installed in his early 1960's vintage 2.4 inch refractor and was observing the sun out his living room window when he lived in Lincoln, Nebraska many years ago. The doorbell rang, and he went to answer it. It was the UPS man delivering something for Rick, and once he got done with the transaction, Rick went back towards the telescope and noted something unusual. There was a brilliant beam of light coming out of the telescope and something dark was now embedded in his ceiling. The sun filter had shattered and one small shard had blown out and gone up to be stuck overhead permanently. As Rick often puts it, "The UPS man saved my sight". Now I too had used my little SUN filter that came with my 2.4 inch Sears "Discoverer" (60mm f/11.67) for many years in the late 1960's and early 1970's, but when I heard about what happened to Rick, I threw the filter away and advised anyone who would listen that while they reduced the sunlight to a low enough level, even the smallest defect in the near-focus solar filter material could possibly result in a failure with terrible consequences.  From that point on, it was either use projection or full-aperture filters out in front (that is, until Ricky got me firmly hooked into solar H-alpha viewing in the late 1980s). Thankfully, these little eyepiece SUN filters seem to have vanished from the 2.4 inch refractors we now seen marketed, but if anyone I see ends up with one, I will give the same advice to them: THROW IT AWAY! Clear skies to you.

8
Quote
Hola Danny,

I believe that this may have been the mirror that we purchased from Carl to compare the mirror that
we made with his method, as the time period is correct and it was the same size and F ratio...

I also remember him working the kink...

Ours turned out just a smooth and we then sold his mirror.

Best Regards,

Preston


I've seen your name in Cal's collection of CZ's writings in the zambutousergroup.

and that pdf is a great record of how as he says, "it takes a lot of technique"

not just simply hit this, hit that bam your done. lots of testing and adjusting.

9
ATM, Optics and DIY Forum / Re: Delmarva Mirror Making Seminar
« on: February 03, 2018, 09:13:36 AM »
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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

Dave,
I will be bringing three 8 inch mirrors: two f/5 and one f/4. One of the f/5 is a mirror I did over 40 years ago which I'm sure I can improve it's figure. The other two will be fully polished to a sphere. If time allows I hope to have all three parabolized before the end of the workshop.

10
Quote
Quote

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As for the 8.8mm Meade UWA - very sharp on the Moon, but the field is easier to take in with the 9mm Lunt and the 6mm Ethos despite the larger AFOV. This is purely a matter of the optical design characteristics of the 8.8mm Meade.

Dave

Dave,

Would you say that the AFOV of the 8.8mm could not be taken in because of inadequate eye relief or something else that happened to notice? Mine is in the mail anyway, but it's good to know what you think of it as far as eye placement and eye relief go.

George

George,

There are some eyepieces that I describe as "self-vignetting". What I mean by this is based upon the exit pupil and eye relief characteristics it is not possible to see the field stop cleanly because there are significant blackouts when you bring the eye close enough that the field stop is visible. I find the 8.8mm Meade UWA is of this sort. I can see a nice sharp view if I have my head back at the correct spot for the exit pupil. But at that distance the field stop cannot be seen.  Now the 5.5mm Meade UWAis not like that at all. Neither is the 9mm Lunt XWA or the 6mm Ethos.

It is possible that my sample has a misplaced field stop - and in general this effect is much more obvious when looking at the Moon. For DSO it is less noticeable although I do still notice more issues with blackouts than with other eyepieces. The 5.5mm Meade UWA is very comfortable and finding the field stop is easy with no blackouts.

Dave

Dave &amp; George,

The 8.8mm is a diff beast than the 5.5mm. I asked someone at an astro store to see how the FS was in the 8.8mm and the 14mm Meade Series 5000 WP UWA and he said that they were both hard to see the FS and said that the 5.5mm was the easiest of the three to take in the views.

I wonder why Meade made them all different in that regard?

11
Reflectors Telescopes Forum / Re: First Light Review of Orion XX14g
« on: February 02, 2018, 09:11:37 PM »
Quote
santafe retiree wrote:
<p class="citation">QuoteSo the optics are as good as advertised, i.e. diffraction limited i.e. 1/4 wave PV, and the mechanics are sound

Well, in the case of my XX14i, based on the above definition, mine were not diffraction limited at all despite after sending the primary back to Orion for testing and Orion then saying the primary "is within our expected (and advertised) quality". My primary was 1/3.1 wave p-v on the wavefront and 1/12.8 wave RMS on the wavefront, neither satisfying both the Rayleigh and the Marechal criteria. The effect of this degree of wavefront error was easily visible on objects like the moons of Jupiter, so even errors down close to the Rayleigh limit are not insignificant. Orion has played a bit fast and loose with their definition of "diffraction limited", which is in general a somewhat less than useful term. Now, of course (after some time at Lockwood Custom Optics), I do have mirrors which are far better than the common error standards (and it *really* shows at the eyepiece). As for the mechanics, while the scope is reasonably stable, the design remains flawed in a number of ways, so if I had to do so again, I would not have purchased anything this big from Orion. They clearly do not yet know how to produce a good quality instrument (only how to just sell a big one). Clear skies to you.

[/quote]I remember your experience when I was in the market for the G-12"(at least I think it was your story).

Based on that, I had budgeted enough money to have the mirrors refigured because even with the refiguring price, I still thought that it was a great deal for a Go-To telescopes.

I was fully expecting to pull it out of the box and find a mirror on the very edge of acceptability.

First time I pointed it to a star and tested it, optics seemed quite good. Very smooth, no turned edge, and if there was a zone, it was under the secondary (and that is why I mentioned this to the OP. A zone under the secondary will lower the Strehl if the mirror is tested on a bench but if it is under the secondary, it has zero affect on the image).

Anyway, I was pretty happy. It took about six months before I got around to making a 33% obstrction and doing an SA test, but when I did, test was excellent. Almost perfect secondary shadow breakout on either side of focus. The level of SA correction was as best I could tell no more than 1/8th wave. I had to struggle to see any difference in the breakout.

This last two weeks, I have had pretty regular 400x seeing and the views of Jupiter and Ganymede have been outstanding.

This is always a concern with mass produced optics though.. Are some people lucky and just get a great sample, or did a review where somone found a serios problem cause Orion to complain to their manufacterer and maybe they tightened up tolerances? Maybe until no one was looking again?

I don't know. Just happy my mirror was a really nice mirror.

I saw one other thread here were someone had their 12" mirror tested and Strehl was over .95.

Seems to be variable, but there do appear to be some excellent ones out there.

12
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So, just finished flocking my TS planetary, and it doesn't look too bad!

Assuming that this is totally unnecessary in expensive, well made eyepieces, I'm wondering how often it might be a good idea to use flocking or matte paint to reduce reflections in relatively cheap eyepieces.

Have any of you done this, and with what kind of results?

I got the idea of doing this from the many posts about a glare issue with the Burgess/TMB planetary.
This led me to the instructions given here: https://www.cloudyni.../Burgesstmb.pdf

Of course I'm also just using this post as an excuse to show off my own handiwork, so please do that too if you have any pics TS / TMB planetary with flocking

Is a simple solution for this, can one just use black felt marker and do the inside barrel and the filter threads?

13
ATM, Optics and DIY Forum / Re: Velvet lining of reflector
« on: February 02, 2018, 01:50:49 PM »
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Why not just buy Scope Stuff flocking paper?


I have the Edmund's stuff, very similar if not the same-same. I hate the glue on the back. I had to contact cement over it.

but the black is really really really black.

and all you really need to do is behind the 2ndry and around the sides of the mirror.


14
Thanks for clarifying Aleksandar. I think I might investigate this a little further. I also had the impression that the brightness in the stopped down Schief was a bit higher than in the refractor. Strange, since I eliminated internal reflexions in the lens by using the gel and especially since the Schief has 2 mirrors, one correction lens and a diagonal prism in the optical train. But the difference, if there was any, was quite subtle. When I compared the chief to several 8" SCT's in the past, the Schief always lost as far as image brightness was concerned, even though it has no central obstruction. I think it has to do with the high reflectivity coatings of modern SCT's versus the standard aluminum coatings of the Schief.

15
Reflectors Telescopes Forum / Re: how to get the most out of your dob
« on: January 31, 2018, 12:34:02 PM »
I like the knob. Maybe its personal preference, but I use it all the time. Plus if your not using gloves it is not as cold as the steel/aluminum tube when its cold outside. My guide knob I ordered from optics mart is made out of a rubbery material.

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