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Messages - rennlispuring

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It makes finding objects much easier. Looking at star charts, I can say "Find X star, then go north 5 degrees". I can turn one slow-motion knob to move my scope North, regardless of which part of the sky the object is in. With an alt-az mount, the action you take to move in a specific direction depends on which part of the sky you're pointing at.

Plus the usual advantages of tracking with one axis, imaging, etc.

Polar alignment is a non-issue (people blow this one out of proportion). For visual, (and even when doing planetary imaging), I never do more than eyeballing my polar alignment - I plop the mount on the ground, and shimmy it back and forth until it looks like the RA axis is pointing North. The alt adjustment is already close enough. I spend about 15 seconds on this. You don't need to expend any more effort than this for casual observing.

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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 you 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

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rmollise thanks for advice. Im not scared to open the HC and ill do it again. but you can see in photo i dont have anything on lcd. Im willing to buy another one just would prefer to buy a used one than new. Im looking at this one but wanted to confirm by some experts it would work.http://www.ebay.com/...0QAAOSw3ydV6K09

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The amount of complaining in the world has also roughly tripled, partly because people spend too much time online and not enough time observing.

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@highertheflyer: Do you want to know exactly?
If you download FlexPDE I can send you a model to play with. You can fill in any CTE you like.

Hi Arjan.
Would the student version of FlexPDE6 afford the unkeyed scripts a means for plugging in the Hayward C3 parameters, a glass that has an expansion coefficient (from what I have heard) twice that of Pyrex?
I'd enjoy experimenting with the basic version if the properties of the model will allow.
Thanks,
Jim

21
ATM, Optics and DIY Forum / Re: Fastest mirror for first-time grinder?
« on: January 23, 2018, 03:16:35 AM »
two issues IMHO.

1) Those related to the size, f/#, conic and material of the actual mirror
2) learning to work with glass. The sound, feel and process.

A small first mirror gets you through #2 saving a great deal of time on the larger mirror. The smaller mirror also absorbs most of the "Dang" moments saving the larger mirror those experiences.

I agree, if you've pushed any glass, go for the one you want.

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I looked at M45 last night with my 20 mm IP It looked pretty nice then I switched it to my 26 mm and it even look better then I put a 10 mm in and I can only see a handful of stars if that’s the case with the lower magnification eyepieces why would you ever use a seven or 10 mm?

You didn't mention what scope you were using or what magnification each of those eyepieces provided. What eyepiece I select depends on what I am observing, what telescope I am using and what magnification I want.  I have scopes with 400 mm FL, 1200 mm FL and 1900 mm FL.  A 10 mm eyepiece gives me 40X, 120X or 190X depending on what telescope I am using.  So I use whatever FL eyepiece is needed in that scope to give me the magnification I want or that the atmosphere will allow for that target.Sometimes I am working low power and may spend the entire evening under 100X.  Pleiades, other large clusters, Andromeda Galaxy ( if I am at a dark site ) perhaps the moon would typically be my targets.  I select my eyepiece accordingly

Most nights I spend more time in the 100 to 220X range. This would be double stars, globular clusters, details within a star cluster, planets and the moon. I select my eyepiece accordingly.

If the atmosphere will allow me to get above 220X then I can get closer on planets the moon and see more inside those globulars and open star clusters.  I pick the eyepiece that suits the condition and my goals.Using the example you posted, the Pleiades.  I may use my 10X or 15X binoculars if I want to see the overall beauty of the cluster. I think the Pleiades looks best in binoculars.  I can get down to 12X in one telescope but frankly I like it better in binoculars. 

Other times I want to dig into the Pleiades, investigating a select portion. I might be working at 100X or higher. I can't see the whole cluster but that is not what I am seeking.

For example, Alcyone - Say I want to split this into its component stars. I may be working at 150 to 300X to do this.
From Wikipedia:

The Catalog of Components of Double and Multiple Stars lists three companions: B is 24 Tau, a magnitude 6.28 A0 main sequence star 117" away; C is V647 Tau, a δ Sct variable star;[14] and D is a magnitude 9.15 F3 main sequence star.[15] V647 Tau varies from magnitude +8.25 to +8.30 over 1.13 hours.[16]
The Washington Double Star Catalog lists a further four companions, all fainter than 11th magnitude, and also describes component D as itself double with two nearly equal components separated by 0.30".[17]

The main star, Alcyone A, consists of three components, the brightest being a blue-white B-type giant similar to many of the other B-type stars in the Pleiades cluster. It has an apparent magnitude of +2.87 (absolute magnitude = −2.39), and a radius almost 10 times that of the Sun. Its temperature is approximately 13,000 K giving it a total luminosity that is 2,400 times solar. The spectral type of B7IIIe indicates that emission lines are present in its spectrum. Like many Be stars, Alcyone A has a high rotational velocity of 149 km/s, which has created a gaseous disk flung into orbit around the star from its equator.The closest companion has a very low mass and is less than 1 milli-arcsecond away, with a likely orbital period just over four days. The other star is about half the mass of the giant and they are separated by 0.031 arcseconds, or about the distance from the Sun to Jupiter, orbiting in about 830 days.[18]So eyepiece selection is based on what scope, what magnification, perhaps what field of view I want, and what I am after.

Frankly my most used eyepiece is a zoom so I am not really aware of the focal length, I just zoom in and out to get the best view for that target.

23
ATM, Optics and DIY Forum / Re: Designing A Planetary SCT
« on: January 21, 2018, 03:27:28 PM »
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Excellent idea! How do I figure out the angles and radii of the lenses and mirrors?
I am familar with OLSO LT and access to ZEMAX.
I have a 127mm fl=1000 spherical mirror and a 10" f.5.5 parabolic mirror that I could use for such a project.
I'd look for another primary, F/5.5 is not a good one to use. You really need Zemax to design a Chief.

Ed

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I am eagerly waiting on my AYOdigi II because it's supposed to just disappear when observing. That's one major reason I ordered it.

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Reflectors Telescopes Forum / Re: Boundary layer fan working or not?
« on: January 21, 2018, 11:36:28 AM »
First one has the fan, but the airflow is not entirely sufficient _or_ the baffle is a bit high above the mirror (or too narrow). Unless, of course, you did your best to make the temperature difference extra brutal.

But it's close, and it should already make images quite a bit better.

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FWIW, being east or west heavy makes a difference in the PE magnitude of my iEQ45 Pro. You may want to test PE in both situations.

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Eyepieces Questions & Recommendations / Re: Praise for the 3x TV barlow
« on: January 21, 2018, 04:05:06 AM »
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Mainly with the 2x barlow I felt as if edge performance was negatively impacted - not to the extent that the "look for something better" barlows were affected, but certainly noticeable. Sharpness at the edge seemed to suffer ....

I have noted this with mine as well.

Well that is reassuring for me. I've bought the 1.6x Antares barlow three times and each time I was less satisfied than the previous time. I guess I won't bother picking up another 2x TV barlow. Just about every time I give an eyepiece/barlow that I sold for performance reasons a 2nd chance, my original decision to sell the first sample gets confirmed. When I get another sample of an eyepiece/barlow that I sold for monetary reasons my regrets for having sold the first sample are also confirmed ... as is the case with my not too long ago aquired 3x TV barlow- the 2nd one I have owned. Never should have sold that 1st3x TV barlow- although the compression ring screwis a lot smoother on this one.

The performancedifference between the 3x and 2x TV barlows is an additional reason I heap praise on the 3x TV barlow. I'm not one of those people that thinks everything TV puts out is great. But when they nail it - they really nail it. They nailed it with the 3x TV barlow. People that have not been impressed with the 2x TV barlow should be aware that the 3x TV barlow is a better barlow (much better IMO but I know not everyone that has used both agrees so as always YMMV).

Dave

28
Beginners Forum / Re: Inexpensive table and chair
« on: January 21, 2018, 12:06:51 AM »
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I'm looking for something to take to dark sites, etc. Paint buckets won't work there
Sure they will, as long as you can put them in your car. It's also very easy to find standard folding chairs for around $20.
But as I said, building your own support is by far the best solution. All it needs is a scrap of plywood, a length of 2x2 or 2x4, an electric drill, and a decent saw.
I forgot to tell you I don't drive. I can't do this to somebody I'm riding with.

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Will there be a real discernable image difference between an F6.0 and an F7.0?

This is one of those possibly too-close-too-call things. Making your own mirror allows you to make it whatever FL you want at all, so it's better in the long run (my opinion) to first decide WHAT you want then make it that way, rather than letting chance determine it. When I made myself an 8", I wanted f/6, but eventually I got f/5.8. Is there a difference? Not really. But in the tube it fit in the backseat of the car we had at the time, so that was a big plus.

But I've been working on a mostly aluminum 14.7" truss (string) scope for quite a while, and I've actually made a couple different mirrors for it so far

30
General Astronomy & Observing / Re: What am I seeing?
« on: January 20, 2018, 03:38:23 PM »
Denis, in nearly all instances a meteor seen transiting the face of the moon as seen through a telescope would simply appear as a strikingly bright streak that would traverse the lunar disk in just a small fraction of a second. In contrast, an illuminated satellite would exhibit a distinctly slower rate of travel, requiring anywhere from perhaps 1/2 second up to a couple of seconds to cover the moon's 1/2 degree disk.

BrooksObs

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