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torchlight

Newbie questions

35 posts in this topic

3 hours ago, torchlight said:

Now I am starting to get an idea of size for sure.

Well to be fair there are some baby versions on a tiny Dobsonian style mount which I have seen pictures of and those most def. are designed for table tops, but anything with any substance is destined to stand on the floor like mine does - bear in mind that mine is relatively small (The first one they show in the video above, the 6", is I think a 150P on a Dobsonian mount NB.  it took me a few days before I realised that some telescopes can go either onto a tripod or onto a Dobsonian style mount like mine - don't forget mine is an 8" version - I think of it as a beginners telescope) - if you search the forum for 'Dob Mob' and check out some of the photos of how big a Dobsonian mounted reflecting telescope some people feel is err.....portable! your jaw will certainly drop!

Edited by JOC

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On 4/18/2017 at 14:37, torchlight said:

Hey fellow forum followers,

Complete and utter newb, decided that staring at the sky seemed like a good idea, having just moved and claiming a den for myself I have the room for a scope of some type. I have some questions though 🤔

I see mentioned in a lot of reviews "cool down on these is very good"? Why do they heat up?

We have skylights in the upstairs, is it realistic to watch through glass windows? Do you have to be outside away from light sources?

I have contacted my local astro group, they have an open night this Friday so I can see what it's all about.

What can I expect to reasonably see with say a £200 telescope and good conditions? Will I be amazed? Left jaw hanging?

Is a tripod essential? Table top telescopes are stable enough? Just seems to my mind a tripod that comes made for the telescope seems more logical?

Anyway thanks in advance.

 

Hi torchlight,

I've had a lot of fun with this: a 150mm f/5 Newtonian on an alt-azimuth...

58f80c42e1f79_6f5a.jpg.897c77c8798267f393e8d7ba0c8d3505.jpg

If you have considerable light-pollution in your area, each and every millimeter of a 150mm aperture would help.

This 130mm f/5 kit would be a bit of fun to tinker with...

https://www.firstlightoptics.com/reflectors/skywatcher-explorer-130p.html

Next size up on a tripod... https://www.firstlightoptics.com/reflectors/skywatcher-explorer-150p-eq3-2.html

With a 150mm F/5 Newtonian on an equatorial, the telescope would need to be rotated during the mount's revolutions, and a 150mm f/5 would be easy enough to do as it's not that bulky and heavy.  This is the same 150mm f/5, but on my EQ3-type equatorial similar to the one shown within the listing above...

58f810192fedf_6f5kit.jpg.3697264591720fd19f6184e601c03700.jpg


I wouldn't recommend a 200mm f/5 so much though, in so far as rotating it, although others do.  Users of same even make modifications to make rotation easier for the larger Newtonians.  A distinct advantage of an equatorial is its tracking capability, by using a slow-motion control, or a motor-drive.  It's quite difficult to track objects at the higher powers with manual mounts, other than an equatorial, but with a bit of practice it can eventually be mastered.

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@torchlight With 130mm telescope I had many jaw dropping experiences! It's a matter of observation and taking the time to carefully look at the objects, then, you can see subtle and really interesting things! :laugh: Now I use a 200mm and I don't regret the upgrade, it is worth the extra money.  8 inches is a good balance for portability (weight) and aperture to be able to see many many objects, it can last a lifetime.

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5 hours ago, Alan64 said:

Alan slight puzzlement here - as you probably know I don't have experience with these types of mounts - aren't they both on tripods???

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1 minute ago, JOC said:

Alan slight puzzlement here - as you probably know I don't have experience with these types of mounts - aren't they both on tripods???

The 130mm f/5 Newtonian is mounted on an EQ-2 equatorial, and the 150mm f/5 Newtonian is mounted on an EQ-3 equatorial.  Equatorial mount-heads are always attached to a tripod or pier.

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again thanks for all the help and replies. I think that it's going to be betwixt the 150P or the 130M in the sky watcher. or the dobsonian in whatever size I can reach 2nd hand I guess.


I know it does not make any difference but the look and asthetics of the sky watchers are more pleasing to me?!


the equatorial mounts are the more difficult to set up and swing on a curve rather than up, down, left right, am I right?

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I, too, prefer the Sky-Watcher kits over those branded Celestron.  Synta Optical of China makes both, incidentally.

You're right about the motions of the two types of mounts...

58f9819ec2925_mountmotions.jpg.df0f5ecdf5de0ea0dbfea06e5f23d742.jpg

An alt-azimuth is Earth-oriented, and often used during the day for land observations, as well as for stargazing at night.  An equatorial is sky-based, and designed only for stargazing; albeit during the day in one instance: solar observations, but only with a safe  solar-filter fitted over the front of the telescope.

I, too, am often drawn to the Sky-Watcher Explorer 130M whenever I see one online, as I tend to prefer the moderate-to-high powers myself.  But the tube is longer and would shake more on the EQ-2 mount, especially at the higher powers.  It also has a lesser, spherical primary mirror, however quite ample for good images at the f/7 focal-ratio of the Newtonian.  The motor-drive is certainly an incentive, and more on that to follow...

The Sky-Watcher Explorer 130P, at f/5, previously suggested, comes with a parabolic primary mirror, and a shorter tube which would not shake as much on the EQ-2, like when grabbing the focusser knob and turning it to focus on an object, or when the breezes or winds are blowing.

The difference between a spherical mirror and a parabolic mirror is this...

 sphericalaberration.jpg

On the left, the light rays reflected off of the parabolic mirror all meet at the same focal-point, and for sharp images, the sharpest they can be if the Newtonian is well collimated.  On the right, the spherical mirror is unable to reflect all of the light rays evenly and to one focus-point.  Note how the rays focus at different points, with the purple rays being behind the red rays, and the red rays behind the blue rays.  A parabola is more difficult to grind and figure there at the factory, and they cost a little more as a result, but the effort and minimal extra cost is well worth it, and for the sharpest images, especially at the higher powers.  The reason that the 130mm f/7, with the spherical mirror, is longer is because the spherical aberration is less noticeable at the longer focal-length(hence, a longer tube), but the aberration is still present; the staggered focus-points of the rays.

Among achromatic refractors, which use lenses instead of mirrors, chromatic aberration(or false-color when viewing brighter objects) is the main error to overcome.  The longer the focal-length of an achromat, the less false-colour is seen.  It's similar with a spherical mirror, in that, again, spherical aberration is noticed less at a longer focal-length.

Now, I know that the 130P doesn't come with a motor-drive, but tracking an object is still quite easy with an equatorial.  Once the RA-axis is set to your latitude, 34° N in my case...

58f99084b47ce_latitudescale5.jpg.5cae1c88aed6e0992d81b35cfa52d414.jpg

...and the RA-axis aimed at Polaris, the north star...

axes3.jpg.bb15055396c9bae28297da02cf7c36c8.jpg

...then all you'd have to do is twist the knob at the end of the RA-axis' slow-motion cable to track, and almost effortlessly.

Synta Optical overseas makes both the Sky-Watcher and Orion(U.S.) versions of the 130mm f/7 and 130mm f/5 kits; same kits, just a different name on the tubes is all.   

Here are a couple of videos demonstrating each, particularly the 130mm f/5...

The 130mm f/7... https://www.youtube.com/watch?v=VZbq5xfaSOg

The 130mm f/5... https://www.youtube.com/watch?v=Y2sIZGdL8Tc

In addition, you want the thinnest secondary spider-vanes for a Newtonian, and for improved contrast and sharpness.  Those of the 130mm f/7 are thick, and likely of plastic, like these of my 100mm f/4...

spider-vanes.jpg.6573317b543e10aae4cb7b5b8dc7e67f.jpg

The 130mm f/5, however, has much thinner vanes, of metal...

spider-vanes.jpg.3e4f404c8d85906100e4fa384304948a.jpg

...and almost invisible.  Ideally, we would like for the secondary mirror to float in mid-air right there in the centre.  Such is not possible, of course, and with the thinner vanes being the next best thing.

Each vane has an adjustment knob on the outside of the tube, and for helping to centre the secondary mirror under the focusser.  Only very slight adjustments would be required if needed...

Cheshire5a.jpg.f43d0c2b7f51053f49f9403f5edab5d5.jpg

With the 130mm f/7, however, the vanes are fixed, and you'd have to trust that the focusser was properly squared to the tube before it left the factory.  The adjustable vanes simply allow for a more precisely aligned optical system overall, and for the sharpest images.

The primary mirror of the 130M is not centre-spotted.  That of the 130P is.  Incidentally, the "P" stands for "parabolic" in that.  The primary having a centre-spot makes collimating the optical system that much easier, and more precise.  You can centre-spot that of the 130M easily enough, however.

The 130P may or may not come with a collimation-cap.  I would ask before ordering, and if not...

https://www.firstlightoptics.com/other-collimation-tools/rigel-aline-collimation-cap.html  

A primary centre-spot is needed to use the cap to its full potential.

Incidentally, I prefer this motor-drive over the one comes with the 130M.  It uses just a single 9V battery to power it...

https://www.firstlightoptics.com/skywatcher-mounts/ra-economy-motor-drive-for-eq1.html

It states "EQ-1" on the box, but it's also for the EQ-2 as well...

http://www.teleskop-express.de/shop/product_info.php/info/p395_Skywatcher-Tracking-motor-for-EQ-2-mount.html

Teleskop Service even uses the same image for the one for the EQ-1...

http://www.teleskop-express.de/shop/product_info.php/info/p394_Skywatcher-Tracking-Motor-for-EQ-1.html

It has a variable-speed control, right there on the front of the box.  With that, you can cause any object in the sky to stand perfectly still there in the center of the eyepiece.

The motor-drive that comes with the 130M, the speed is fixed, and not everything in the sky travels at the same exact speed.  Granted, you'd have to continuously observe a speedier or slower object for quite awhile before noticing the drift of an object.  In addition, the motor-drive uses a (4) "D" cell battery-pack; cumbersome, and potentially more costly to operate.  The battery-pack can be bypassed, however, and with a 6V, AC-to-DC adaptor.  Some use more advanced batteries even, like lithium-ion packs.

Hmm, I just saw this... https://www.firstlightoptics.com/clearance/clearance_skywatcher-explorer-130p_71314.html

You'd have to be careful there, and in calling first to inquire for more details.

The Sky-Watcher 150P Dobsonian is quite nice, I cannot deny...

https://www.firstlightoptics.com/dobsonians/skywatcher-skyliner-150p-dobsonian.html

It, too, has a parabolic primary mirror, and it would be a good bit brighter.  I know that my 150mm f/5 certainly is, but a 130mm f/5 is no slouch either.  Later, you'd want to change out the rubber springs for metal springs within the primary mirror cell, but other than that it's a great value.  It would need a collimation-cap, too.

I've always held sway that all of the outlay available at one time should go towards the telescope only, and thereby in getting the best one possible.  Extra eyepieces, a motor-drive, a 2x or 3x barlow, can all be had later, over the weeks, or months even.

The final choice among all of those, of course, is yours.

 

Edited by Alan64

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Again thanks for all the info and in such a concise 'layman' fashion Alan. The mirror shape is a definite consideration then. Likewise the vanes. The way that the EQ mount is described on some sites it seemed akin to working out the number of particles of sand on a beach.

Is it always going to be a problem with something secondhand with delicate parts? Even the returned one that you linked too would have a caveat? I don't suppose they like too many knocks and bashes? There are quite a few cheaper second hand Explorers floating around the web. :icon_biggrin: Is it a waste of effort trying to snag a cheaper 2nd hand one because of the conditions of the insides. I saw another thread here advising to check pitting and damage to the mirror. I suppose new is new and that is how it arrives.

Arrrgh, forecast looks like cloudy with the chance of cloud. Ho-hum!

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On 4/19/2017 at 09:25, JOC said:

In it's collapsed form mine stands around 105cm high from base to top.  FWIW this is mine when it is pulled out (I've taken off my home-made shroud - which isn't necessary - so you can see the struts) and ready for use.

And if anyone can shift the image to vertical then please feel free to do so :-D

 

open.jpg

Here you go :)

 

IMG_2897.JPG

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On 4/21/2017 at 09:31, torchlight said:

Again thanks for all the info and in such a concise 'layman' fashion Alan. The mirror shape is a definite consideration then. Likewise the vanes. The way that the EQ mount is described on some sites it seemed akin to working out the number of particles of sand on a beach.

Is it always going to be a problem with something secondhand with delicate parts? Even the returned one that you linked too would have a caveat? I don't suppose they like too many knocks and bashes? There are quite a few cheaper second hand Explorers floating around the web. :icon_biggrin: Is it a waste of effort trying to snag a cheaper 2nd hand one because of the conditions of the insides. I saw another thread here advising to check pitting and damage to the mirror. I suppose new is new and that is how it arrives.

Arrrgh, forecast looks like cloudy with the chance of cloud. Ho-hum!

You should get a guarantee with the 2nd-kit purchased from FLO; simply inquire as to its exact condition beforehand.  Anything purchased from a "civilian", however, should be inspected carefully by you before handing over your wherewithal.  Check its innards, the focusser, make sure all the parts are there, etc.

Yes, there's nothing like that new telescope "smell".  And yes, it's decidedly best go with a parabolic mirror.

The moment-arm effect that would present itself with the 130mm f/7 on the EQ-2 would be considerable.  The moment-arm effect is demonstrated when you lock the telescope in place, grab one end of the tube and pull slightly, then let go and watch it shake and shimmy.

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