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iggyiggs

How do I view anything on a telescope? - complete newbie

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I'm sorry if I ask such a basic question but I'm really new to all this and have never used a telescope before.

I need basic instructions.

My boyfriend got me this for my birthday Sky-Watcher Explorer-130 EQ2 Telescope. We just assembled it. I put this Barlow lens on and the the one that says 10mm inside that one. I have the moon right there and I'm trying to look into the eyepiece squinting but no matter how I angle anything I don't see a thing. I don't even know what side of the telescope tube should be pointed at the sky. As you can tell I'm hopeless. If you could help me with this model I'd be grateful. Thanks in advance. 

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Posted (edited)

Welcome to the forum. If you have an eyepiece with 25mm (like the one with 10mm) use that WITHOUT the Barlow. 

 This will give you a lower magnification and make finding and focusing on the moon easy!

10mm plus the Barlow means very high magnification = harder to locate in eyepiece and harder to focus and more critical on other factors like atmosphere and optics.  

The open end (remove the black cover) points towards the moon, the end nearest where you stick the 25mm eyepiece. 

Edited by tooth_dr

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Thanks for the reply.

How do I use that finder scope thing? That's another thing I haven't understood.

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4 minutes ago, iggyiggs said:

Yep, we did that properly. Took a while. 

Now go outside and disassemble it, and then reassemble it. That's what you might be doing every time you use it. You can of course use a torch (red light) to see what you are doing. I wasnt suggesting for you to go out and do it in the dark.lol.

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Hi and welcome. The finder probably isnt aligned to the scope at the moment. You can dial them in in daylight (Do NOT point anywhere near the sun of course) using a distant chimney, pylon etc. I use a widefield eyepiece (25 or 30mm) in the dark, locate a known object in the scope then adjust the finder to match.

its all quite a lot to take in at first tbh but the community here are great and I promise the end result is worth the teething pains!

Clear skies

Simon

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7 minutes ago, LukeSkywatcher said:

Now go outside and disassemble it, and then reassemble it. That's what you might be doing every time you use it. You can of course use a torch (red light) to see what you are doing. I wasnt suggesting for you to go out and do it in the dark.lol.

The telescope is outside at the moment. In the garden. 

Tried to put the 25mm eyepiece in but it's not screwing in place. 

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Posted (edited)

There should be a small silver screw at the side where you put the eyepiece in. Tighten this until it has a good grip. Dont over tighten it. You dont screw in the eyepieces, just place them in the focuser and tighten the screw.

Silver screw is circled in red in the image here.

Untitled.jpg

Edited by LukeSkywatcher

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Or loosen it more to let the 25 slide in fully first lol

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1 minute ago, Simoncwr said:

Or loosen it more to let the 25 slide in fully first lol

Good point. They usually arrive with the screw fully inward.

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You may need to back off the locking-screw(s) to insert an eyepiece, and don't tighten the screws too much after it's inserted.

That's a very nice kit to receive out of the blue; congratulations.  The mount, the EQ-2, is an equatorial, and for tracking objects with the slow-motion controls.  You can track objects automatically with a little 9V motor attached to the RA-axis...

https://www.rothervalleyoptics.co.uk/skywatcher-ra-economy-drive-for-eq2.html

It takes just one wee 9V battery to power it.

With the motor attached, you can keep any object centred in the eyepiece, standing still, and for however long you'd like.

 

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Practice tomorrow in day light, but remember to never point it near the sun 

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This is a good video on how to use your telescope's mount.

 

I really wish you had somehow managed to come to us before buying a telescope. I had the exact telescope you do when I started and it gave me teething problems oh so very similar to what you are experiencing now.

I'm going to talk about some basics of telescope terminology, since you mentioned you need some basic explanations:

1: Focal length (eyepieces and telescope)

On your telescope you will see a sticker under the eyepiece saying something along the lines of "focal length =900" and "diameter = 130". This represents the size of your primary mirror (the big one at the bottom of the tube) and the "focal length" of that mirror.

The focal length is, in sort, the distance away from the mirror at which the rays of light "converge" (i.e. achieve focus). The longer this distance is, the more "zoomed in" the image becomes.

Your eyepiece works in the opposite manner. A 30mm eyepiece provides a rather wide field, in your case 30x magnification, whereas a 5mm eyepiece would give you 180x magnification!

To work out the magnification an eyepiece will give you with your telescope, use this formula:

magnification = focal length of telescope / focal length of eyepiece
i.e. 900 / 25 = 36

Fairly simple, right? In order to account for a barlow lens, simply multiply the magnification your eyepiece provides by the barlow's magnification factor. In the above example with a 2x barlow, you would get 72x magnification.

2: Exit pupil

The exit pupil is the circle of light that you see when taking a step back from the eyepiece, if the eyepiece is pointed towards a bright object. At lower magnifications the exit pupil is larger, while at higher magnifications the exit pupil is smaller.

The formula for calculating it is as follows:

exit pupil size = aperture / magnification

so for a telescope with an aperture of 130mm used at 36x magnification:
130 / 36 = 3.6
The exit pupil of your telescope with the 25mm eyepiece is 3.6mm

The main difference you will experience with changing exit pupil is brightness. Stars do not get dimmer as they are point sources of light - they will only dim at extreme magnifications, but typical objects will change brightness with exit pupil.

The human eye can normally expand to around 7mm for a young person, or 5-5.5mm for a "more mature" person. If the exit pupil is larger than your dilated eyes, you do nothing but waste light. In reflecting telescopes which have a central obstruction (the secondary mirror) exit pupils larger than your eye's pupil will cause a shadow in the center of the image.

0.75mm (the exit pupil produced by your 10mm eyepiece and barlow) is very small. Many objects will be dim at this size. Also, at that exit pupil size specks of dust floating in your eye will be visible. Opticians call them "floaters" and you may have been asked if you see any before taking an eye test. The small exit pupil makes them very obvious and as such many people try to avoid exit pupils below 1mm.

3: Focal ratio

The focal ratio of a telescope is simply:

focal ratio = focal length / aperture

for your telescope:
900/130 = 6.9

If you are a photographer you will recognize it as "f.stop" or "f number". For DSLRs, a lower focal ratio like 2.8 (bigger aperture, shorter focal length) gives a brighter image, while a higher focal ratio (smaller aperture, longer focal length) gives a dimmer one.

For visual purposes, this number means little. Your version of the focal ratio as it is to the camera would be the exit pupil. However it can mean a lot to other factors:

  • Lower focal ratios are less forgiving of mirror mis-alignment - halving the focal ratio in a Newtonian reflector makes it 16x more sensitive to imperfections!
  • Higher focal ratios can be unwieldy - long tubes can be annoying to carry, store, and put more stress on your mount to keep it steady.

Yours at f6.9 is average. It is not "fast" (low f number) or "slow" (high f number).

4: Resolution

Resolution is determined by many things, but if we assume the optics are perfect (and for the most part, Newtonian reflectors are close enough for this to hold true) then your image will get twice as sharp every time your aperture doubles. That is: the resolution of the optics you use increase linearly with the size of the objective.

There is an equation you can use to roughly calculate the smallest distance two objects can be apart by while still being distinguishable individually, and I will include it, but bear in mind that it should be used as a guide only:

resolution = 1.22 x (wavelength / aperture)

1.22 is a constant, wavelength is the wavelength of the colour of light you are observing.

For your telescope, if you were observing a deep red:

1.22 x (0.000656 / 130) = 0.00000615630769231
A very small number! This is because it gives us the result in radians, not degrees.

To convert 0.00000615630769231 to degrees we simply:

0.00000615630769231 * (180/pi) = 0.00035

And to get it in the (generally) universal measure we use around here for resolution scale: the arcsecond:
0.00035 * 3600 = 1.26

The theoretical resolution of your telescope is thus: 1.26 arc seconds
This means that, in theory, two stars could be 1.27 arc seconds apart and you would still be able to tell that it were two stars and not one.

The detail of the image you actually get is also dependent on the quality of your optics, the condition of your sky and your skill as an observer.

 

 

This is probably all a lot to take in, and I may have explained it poorly, I will happily clarify if I've confused you further.

I hope this helps you (in some form) to understand the equipment you are using better.

 

Good luck, and have clear skies :)

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Thanks for the polite replies and the understanding.

It was a birthday present for my upcoming birthday. I'm a girl but I'm into astronomy and space so boyfriend decided to gift me a telescope and this one had good reviews so he went for this one. They said it was good for beginners.

 

I did some reading etc before it was delivered today but, like I said, I haven't been near one before and the set-up seems daunting to me. 

I managed to put the 25mm eyepiece in but I didn't have much luck. I'm sure that finder thing isn't aligned.

I do seem to see shadows when I squint into the eyepiece (which is not exactly easy to do for me) and I think it's my eye. 

 

I'm gonna watch that video that has been recommended and practice in the daylight to align that finder thing. 

I also know not to look at the sun. I know it would fry my retinas 👍

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Posted (edited)

You shouldn't have to squint. Maybe your eye is too close to the eyepiece. The eye relief (how far away you have to hold your eye) might be too short for you. Do you wear glasses. What kind of shadows do you see?. Perhaps the scope is not focused. Try using it in daylight on something far away from you and turn the focusing wheels slowly until you can see the far away object clearly. 

Edited by LukeSkywatcher

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I found it impossible when I was a beginner to see anything through a barlow (presume you are putting the lens on the end of the Barlow as well?)  As stated above use lower magnification until you have had a lot of practice.

The finderscope needs aligning with the main scope, but of course you need to put an eyepiece into the main scope in order to do this.  Do the alignment in the daytime and point at a distant land object and adjust the finderscope triple screws until the finder and main scope are looking at the same thing.  The finder gives you a big field of view (FOV), and makes it easier to find things.

The eyepiece as stated above will be held on by a small screw, this needs to be retracted to get the eye piece in in the first place.

Carole 

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Hello and a warm welcome to the SGL. You have had a lot of advice given already and there is much to take in. For the moment I will only say that every one of us has been through this stage so do not worry you will get there in the end with just a little patience and practice. Let me assure you it will all be worth it in the end as you progress in this fascinating hobby.

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Posted (edited)

I think I managed to focus on some aerial on a roof with the 25mm. No, I don't wear glasses. 

 

Now I need to figure out the finder alignment. The one I have looks like this:

51LpVmyfmWL._SL1152_.jpg

Edited by iggyiggs

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You may still have the eyepiece rubber rolled down. After you remove the eyepiece cap there is a rolled down rubber that needs unfolding, that will increase the distance between your eyeball and the actual glass lens.

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Posted (edited)
On ‎20‎/‎05‎/‎2018 at 09:19, iggyiggs said:

Now I need to figure out the finder alignment. The one I have looks like this

I have one of those, they are great little finders.  The finder button with the white dot on it rotates and turns on a red dot of light - continuing to rotate the control increases the brightness of the red dot (make sure that you have removed any plastic tab that might be covering a battery when it was first delivered (lots of things seem to come with those to stop batteries wearing out).  You can see this red dot if you are bobbed down right behind the finder and are looking through the pink lens in that photo above.  If necessary take it off and bring it inside the house, point it at the wall and dodge about behind it until you see 'see the light'  {Somehow I've got visions of the Blue's Brothers at this point} - you need to be fairly straight behind it. 

Now put it back it back on the telescope and dodge about behind it again until you work out how to see the dot in the centre of the the pink screen whilst it is attached.  Then being sun careful, point the telescope roughly at a distant object (say a mile+ away if you can) - chimney pot, tree, church spire, water tower etc.  Look through the finder (possibly with both eyes open - sometimes that helps) and move the telescope until the red dot is on your object of choice.  Now dump the 25mm lens in the focus unit (loose the barlow for the time being) and all things being equal you should be roughly close to the object you are looking at through the finder - twiddle the focus knobs until said object is nice and clear and then while looking through the EP shift the telescope on its stand until the object of interest is dead centre in the eyepiece view.  Now unless you are very lucky the finder won't be exactly on the object any more.  Being careful not to move the telescope eyepiece view from dead-centre use the other knobs on the finder and these will move it up and down and left and right until the object of interest is back in the centre of the finder with the red light in the centre of the object.  Check that you are still central in the eyepiece view and now you have a finder that is aligned with the telescope (if you move the telescope or dismantle it you will need to check this each time you use it).  If you can't get the finder aligned you may need to lift it with a little sliver of cardboard in the mount, however, yours IS designed for the telescope and should be capable of aligning OK - I adapted mine and I need to shift v. slightly beyond what I can adjust it to so a shim is needed.

To find things in the night sky bob down behind the finder in the same way and put the finder's red dot centrally on the object of choice (at night you might need to turn down the brightness) - moon, star, planet etc.  Since the finder is aligned with the telescope by now (because you've done what is described above) you will now see the object in the telescope (use the 25mm eyepiece again to begin with)  - once you get used to putting the objects in the centre of the Eyepiece you can experiment with gently changing the eyepieces and adding in Barlow to get closer to the objects. 

I hope this helps - I am still a relative newby so I know how you feel at the moment.

Edited by JOC

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To add to the above. The finder should be mounted on the scope with the coloured glass pointing to the sky and the on/off knob with the white dot pointing to the eyepiece in the scope. I'm sure you probably knew this. 

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Thanks again for the explanations. I appreciate! When I look into the finderscope I don't see any dots or light. 

Just got back in. It's cloudy tonight but we managed to see the moon! At last I saw something. I haven't aligned the finderscope yet so it took a while to locate it but we did it in the end. We only used the 25mm eyepiece and it was pretty bright but I saw detail. 

We have trouble keeping the scope still as it seems to move back from where we move it. I'm sure it's because I need to figure out that equatorial mount alignment. 

My next objective is to see a planet. I have to do this from the garden and there are trees and houses blocking the view so it won't be easy. 

I wanted to take a pic with my phone but how do I do that?

I know I only saw the moon but I'm pretty satisfied as I was getting discouraged thinking I'd never be able to figure how to view anything. 

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Welcome from land down under

Everything is upside down where I am

Google astronomy club close to you, and members only to happy to assist with issues you having, and also show you equipment they have

My own club, also has loan scopes for new members

Try before you buy

Members night nights also have presentation

Happy Viewing

John

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Posted (edited)
6 hours ago, iggyiggs said:

Thanks again for the explanations. I appreciate! When I look into the finderscope I don't see any dots or light. 

Just got back in. It's cloudy tonight but we managed to see the moon! At last I saw something. I haven't aligned the finderscope yet so it took a while to locate it but we did it in the end. We only used the 25mm eyepiece and it was pretty bright but I saw detail. 

We have trouble keeping the scope still as it seems to move back from where we move it. I'm sure it's because I need to figure out that equatorial mount alignment. 

My next objective is to see a planet. I have to do this from the garden and there are trees and houses blocking the view so it won't be easy. 

I wanted to take a pic with my phone but how do I do that?

I know I only saw the moon but I'm pretty satisfied as I was getting discouraged thinking I'd never be able to figure how to view anything. 

Glad to hear you saw something. The planets are not well placed in the sky for us at the moment and won't be for some time. They are very low down to the horizon. Not impossible, but difficult. Because they are at a low angle, the light from them has to pass through a thicker layer of atmosphere and pollution, so the views won't be as good as when the planets are higher up. 

Do you mean the scope is moving or what you are looking at goes out of view when you're looking. To align the whole scope and tripod you want to point the polar axis leg of the tripod as close to North. This can be done easily using a compass. It's good enough for observing, but for imaging it has to be perfect. If you can see Polarise from your location, use it to align your scope to North. The polar axis leg on your tripod is the one on the left in this picture. 

 

sky-1_2.jpg.f8d678b58d286a4a9e34219c6a2e7c9b.jpg

Edited by LukeSkywatcher

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