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Messages - pesorramidd

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Reflectors Telescopes Forum / Re: Bomber Bob Going DOB?
« on: February 08, 2018, 06:44:08 PM »
Say it ain't so...

Yes, the old refractor dude has lost his mind: I'm working a barter deal for an Orion 12.5" Newtonian on a motorized Dobson mount. Gonna drive out and star test it tomorrow night. It will be the largest scope I've ever owned.

As punishment for your transgression, you must send me the Goto-Hy-Score 452.

Eyepieces Questions & Recommendations / Re: Edmund 28mm RKE
« on: February 04, 2018, 09:30:39 AM »
Eye placement wasn't the problem it was the image...there are plenty of better eyepieces to choose. The pair of 25mm UOVT Orthos I have give a better image. I tried the rubber eye guards on the RKE 28's....just awful.

Sounds like you may have got a bad sample. Not saying these are Naglers, but they in general are nice eyepieces. The 21.5mm is very nice also. I got it pretty new though. I'm sure quality control is a bit up and down on these. Although I've had three 28mms and all of them were equally nice.

Still, they would not be my choice for binoviewing. Rather have 2 24mm panoptics or 2 plossls.

General Astronomy & Observing / Re: Observe planets and Moon.
« on: February 02, 2018, 04:19:57 PM »
One could say, then, that in order of importance and in relation to planetary observation would be ....:
-The quality of the mirrors
-The focal length (in this case the more the better ..)
- The aperture of the telescope
I imagine, that the collimation and the proper cooldown are very important factors that are above the three characteristics mentioned above ..

I like 1-1.2 degrees for observing the observable lunar disk: the moon's full height is about half the diameter of the field of view, so you get half a moon-width's space around the moon.  Cropping closer can provide an initial "oh wow,": but seeing the moon in some context is more satisfying for me.  So, yes, the 26mm would be better than the 32 for observing the moon, but as I said above, I still think a lower power is better yet.  I wouldn't go so far as to say that the 26mm is a waste, but I surely don't think it is a priority given that you have a 32mm plossl.

At 26, 32, and 38mm, these 70 degree eyepieces sound like clones of the Orion Q70 and Agena Astro SWA lines (sold under other names, too). I have all three, and my 26mm doesn't seem as sharp as the other two. Furthermore, the Explore Scientific 24mm 68 is a much better eyepiece.

Yes, a 24mm 68 will max out your view in your little Mak, but so will your 32mm plossl. Extended objects in the plossl will be brighter, so I'd probably use the plossl as my finder eyepiece with the Mak. The 24mm should work nicely with the moon in both scopes, though.

The 38mm (or a 40mm) would make for a big exit pupil in an F/6 scope, but you'd still be under 7mm. That may or may not be too much for you.  Or you may like the extra field enough regardless.  I'd say the 32mm 70 is probably more useful on a day-to-day basis.  A 30-32mm 82 could be better yet, but a good one costs as much as-- or even more than-- your scope.

Also, that 38mm is REALLY big and heavy.  You may need to use a counterweight (or bungee-cord) to preserve your dob's balance.

As far as sizes of things...
Pleiades-- a little under 2 degrees, but you need a little more than 2 to really appreciate them.
Beehive-- about a degree and a half
Orion nebula-- about a degree, but you probably won't see that much visually unless you are under really dark skies. Plus you'll want higher powers to look at the core, Trapezium, etc.
Big Dipper and Orion-- Huge-- way too big to fit in your scopes field of view (e.g., I think the Dipper is about 10 degrees across)
A max field eyepiece is also extremely valuable in FINDING smaller objects and very helpful in star hopping.  You may want to skip to higher powers once you located the object, but the widest possible field is extremely important in locating objects to observe in the first place.
Very good information all around; thank you everyone!

So I think I'm gonna stick with the 32mm 2-inch 70° SWA. I actually bought one mere days after acquiring my Dob. After looking at other eyepiece options, I was wondering if I got the right one, but after all these discussions, I think I did.

As far as the even wider EPs costing more than the scope, this one almost costs as much as the scope, as I bought it used. So it fits well with my budget.

As time goes on, I'll look at adding something like the 24mm 68° or other similar pieces as I work my way down the focal length stack.

I do actually like the way the moon looks in the 32mm 2-inch, but I'm even more looking forward to seeing some DSOs with it. I'll be able to take it to a dark sky star party in a couple of weeks, so I'm really looking forward to that. So far, it's just been big city backyard, which means the moon, Jupiter and Saturn.

Again, thank you to everyone for helping to educate me about some considerations in picking eyepieces. The televue link really helped me to compare all the different combinations that are out there.

I'm sure I'll have more newbie questions soon enough.

Happy Friday everyone!

ATM, Optics and DIY Forum / Re: Stuck at!
« on: February 02, 2018, 03:13:44 PM »
My way of establishing the F/D ratio:
Multiply the diameter of the mirror by 1/16th. (or divide by 16--- in this case, 6" would be .375)
Divide that result by the sag you measured----presto, there you are. I do this on the fly all the time. The moderate focal length ATMs generally deal with, this works fine.

.375/.058 = F/D-6.466 (rounded off)
PS If I was concerned about coma, I'd keep in mind an F/8 should be fairly free of it over the central half of the field of view at lowest mags. Some ATMs, and even pros will remark how fast an F/8 will change during correcting the initial sphere. An F/6.5 will change quite a bit slower. Some things to consider---

Cool trick, thank you.


Reading the original post I noticed you're rather concerned that the mirror is now f/6.5 and not f/8. Don't be. It's not going to be much harder to figure, and you'll be able to get a wider field now.

Yeah thinking f/6.5 might be the way to go now. I am concerned that I'll have to make a taller stand now though...

<p class="citation">Oregon-raybender, on 12 Dec 2017 - 06:29 AM, said:<a href=";module=forums&amp;section=findpost&amp;pid=8267409" rel="citation">[/url]<blockquote class="ipsBlockquote built" data-author="Oregon-raybender" data-cid="8267409" data-time="1513052953">

If you can, find a copy of "All About Telescopes" by Sam Brown. We used it in the Telescope Makers Workshop for decades. We found it to be the best all round, simple book on explaining all of above. It is a great resource for someone going on his own without the support of a local club. The drawings and the details of explaining and design of simple test could be of service to you.

I think it's wonderful for you as a family project. Is your daughter helping you? It would be a good STEM project for her.


Starry Nights

Yes she's helping me, though she's lost some interest as I'm taking much longer on this project that I originally proposed - good motivation to see it through. I'm looking forward to moving on to polishing and testing...

I appreciate the book suggestion! I'm thankful this hobby has a timeless quality to it - great to read stuff from the 'old masters' and put it to good use. I'll find a copy.

<p class="citation">ccaissie, on 12 Dec 2017 - 05:41 AM, said:<a href=";module=forums&amp;section=findpost&amp;pid=8267292" rel="citation">[/url]<blockquote class="ipsBlockquote built" data-author="ccaissie" data-cid="8267292" data-time="1513050083">

Sometimes when aggressively hogging, you get a hyperboloid..."v" shape...very deep center, not much else. Then it takes a lot of grind to get a smooth curve, even TOT might take a while to smooth enough to get back to true readings. If you think you can make it with the qty of grit, go back and smooth it w/ 80.

You can scrape up all the glop, throw it in a glass of water and pour off the fine stuff and reclaim the unused grains. Not necessary to wash after each wet, try flushing most off by adding water and work the tool a few strokes, repeat until fairly clean of mud, then sprinkle grit on and resume. Not too much grit, each grain needs to do its own work, not be crowded and create mud.

Marking the tool with a sharpie all over then test-rubbing the dry tool/mirror will show you the contact, and likely the center is not in contact from the hogging. So more smoothing/mating/lengthening the radius. The sharpie test is useful throughout grinding.

Try the spit test described in the ATM I book from the 30's. Wet the mirror, stand it up safely. Hold a flashlight next to your eye and catch the reflection of it in the mirror from a couple feet away Bob your head, and watch the reflection. If it moves in the same direction as your head, you're inside the radius of curvature, so back up, if it moves opposite, you're outside. When you find the point where you can't tell, drop a gob of spit on the floor. Get out the tape measure and find your radius.

Don't let your wife see it.

Also you can wet the mirror and find the image of the sun to measure the focal length. Shine it under the eave of your garage, maybe using a stick to record the distance. A spray bottle of water helps to renew the wetting.

First time? You're doing good. You'll probably grind past the bubble or 'seed'. If not, just make sure when changing grit that it doesn't harbor any of the old size.

Thank for the encouragement and advice  I'm also going to get started on that mirror stand / tester. So much to do...

We're talking on the order of a millionth of an inch!

General Astronomy & Observing / Re: Erroneous Weather Forecasts
« on: January 31, 2018, 08:23:16 AM »
I forecast that it will be clear whenever the moon is near full. Seems to be correct 90% of the time. Also, I forecast that it will be cloudy when there's a special event happening in the skies that I want to observe.

« on: January 31, 2018, 08:15:35 AM »
You will be more confused at the end of this topic than before.

ATM, Optics and DIY Forum / Re: Polishing a 6" f8
« on: January 31, 2018, 05:34:10 AM »
  The W stroke uses about 1/3 of the diameter. Go slow and test after about 5 minutes since it works quickly. If you don't have a copy of Sam Brown's All About Telescopes I high recommend you get a copy. It shows just about every type of error one can get and how to fix it.

             - Dave

To be perfectly frank, there is significant diminishing returns with eyepieces. When people say that a 250 dollar Nagler Type 6 looks "better" than a 100 dollar Explore Scientific 82 degree piece, what they really mean is "in a few really small ways that my highly trained eyes can look for, the Nagler is a tiny bit better". If someone gave you a case full of eyepieces ranging from 75 bucks to 500 bucks, I think you would probably be surprised just how tiny the differences were (with exception of physical traits like how wide the field of view is and how much eye relief there is). I remember actually being disappointed the first time I looked through an Ethos 21mm because I had just looked through a 20mm ES 100 degree and I couldn't tell a difference.

Long story short, the diminishing returns on eyepiece quality vs cost is VERY steep.

Well said.  However, this ignores the psychology involved in eyepiece buying. Yep, that plossl may do the job, but those newer mega wide angle jobs are like buying a Ferrari next to a Pinto.

Please pass that 21mm Ethos!

t-shirt/memes suggestions:
dancing in the dark- totality awesome
i swapped daddy's eclipse glasses with his cinema 3-d glasses
stop trying to make solar eclipse happen- it's never going to happen

Or just cause the birds all stopped singing doesn't mean your safe looking up.

I don't have the decades of experience that some have. I think it terms of magnification as I use my eyepieces across 3 different scopes of 3 differnet focal lengths. When I am not using a zoom, which I usually am, then I am looking for a wider FOV eyepiece. I don't think of exit pupil at all.Maybe after more years of experience I will think about this more.

I don't think about exit pupil either. Maybe I should but I don't wear glasses so maybe it's not anything I would need to consider. I am somewhat red/green color blind though so odd tinges of color on bright objects has never really registered with me.

I'm getting up to speed with my new MX+ and can say that you will love it. SkyX really is fairly intuitive, but it takes a few replications to remember where the appropriate menu options are located. Those videos are more helpful than the manual to get started. The first thing you will want to do is get your imaging camera connected so you can use Image Link. It's helpful to know your camera's image scale: Scale = 205*pixel size/FL. Start with Rough Polar Align and then take an exposure with your camera. Once Image Link is able to successfully find an astrometric solution for the image, you are ready for the automated process of obtaining pointing samples for tpoint and Accurate Polar Alignment using 40-50 stars. That is covered nicely in the videos. After you have performed APA, you can follow the video for generating and fitting a PEC curve. Since you have a permanent installation, you can redo the automated tpoint run with a much larger number of stars, run Super Model, check APA one more time, activate protrack and you should be good to go. You will quickly learn to love Closed Loop Slew. I don't have a motorized focuser and my filters are not quite parfocal, so whenever I change filters, I slew to a bright star, put on the B-mask to refocus, then use Closed Loop Slew to get back to the exact same location the scope was at for the previous filters. And most of the time I remember to remove the B-mask before starting the next imaging run :-)

The main thing about the MX+ is that it gets out of the way and lets you concentrate on imaging rather than having to fight your mount to get it where you want it to be and tracking the way it needs to be tracking for your images. Enjoy!


Not really sure why it's called sixtests...

Sixtests was Jim's Foucault and similar test analysis program. His program for 2D hartman was called ? (maybe 2dhartman.)
Sixtests at one time had analysis for six different test methods.

I do think it would be better for the index to be sequential (NGC 1 - NGC 9999 as one sequence, for example) with symbols indicating the type of object. That way you wouldn't have to know the type of object in order to use the index. And sometimes the type of object has been disputed (e.g., M71).

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