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Smifwiz

Celstron Firstscope unable to focus

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Hi all, I'm new to astronomy as a hobby. I got my first telescope, the celstron Firstscope, for Christmas and I have been getting less than satisfactory results.

I've tried looking at random stars, Mars and the moon.

The stars and Mars look like little triangles when using both the included 20mm and 10mm eyepieces. The moon has given me the best results, but even that barely focuses.

I've looked at some people's advice on leaving the scope out for it to adjust to the temperatures but that hasn't worked for me.

Is there anything I can do? Thanks.

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Welcome

When you are looking at the Moon with the 20mm if you start with the focuser all the way in and slowly wind it back out do you see it focus then move out past focus?

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9 minutes ago, happy-kat said:

Welcome

When you are looking at the Moon with the 20mm if you start with the focuser all the way in and slowly wind it back out do you see it focus then move out past focus?

Yes when I do that it comes in and out of focus.

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One thing you could do is to try it during daylight on distant objects.   You could also line up any finder the scope has.

Start with the lowest power eyepiece, that’s the one with the largest number.   Point at a distant object, building or whatever, then focus.   Keeping that object in view in the eyepiece, adjust the finder so it’s pointing to the same object visible in the eyepiece.   Without the finder being aligned, it’s a tough job pointing the scope exactly where you want to, especially at night.

Focus carefully, try any other eyepieces you may have that give a higher magnification ( lower number on the eyepiece ).

Having hopefully been successful with all this, you should be on your way to the wonderful hobby of astronomy.

Good luck, Ed.

 

 

 

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4 minutes ago, NGC 1502 said:

 

One thing you could do is to try it during daylight on distant objects.   You could also line up any finder the scope has.

Start with the lowest power eyepiece, that’s the one with the largest number.   Point at a distant object, building or whatever, then focus.   Keeping that object in view in the eyepiece, adjust the finder so it’s pointing to the same object visible in the eyepiece.   Without the finder being aligned, it’s a tough job pointing the scope exactly where you want to, especially at night.

Focus carefully, try any other eyepieces you may have that give a higher magnification ( lower number on the eyepiece ).

Having hopefully been successful with all this, you should be on your way to the wonderful hobby of astronomy.

Good luck, Ed.

 

 

 

I have gone and lined up my finder to my telescope, so that shouldn't be the problem. As I try to focus in and out, the stars and smaller objects in the sky will not focus into a single, clearly defined point. The best I can focus it makes the star into a hollow triangle.

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Triangular stars are usually an indication of 'pinched optics', possibly due to over tightened primary mirror clamps.  See this link.  But it may be just that your scope needs collimating.  If you don't know how to do that, these articles might help:

Gary Seronik

Sky and Telescope

AstroBaby

Best of luck,

Peter

Edited by petevasey
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In general a triangle might suggest the main mirror  is pinched, the fixers holding it in the mirror cell are too tight and cause the mirror to not lay relaxed.

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18 minutes ago, petevasey said:

Triangular stars are usually an indication of 'pinched optics', possibly due to over tightened primary mirror clamps.  See this link.  But it may be just that your scope needs collimating.  If you don't know how to do that, these articles might help:

Gary Seronik

Sky and Telescope

AstroBaby

Best of luck,

Peter

Thank you, I will see what I can do about it.

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On 12/01/2019 at 03:47, Smifwiz said:

Hi all, I'm new to astronomy as a hobby. I got my first telescope, the celstron Firstscope, for Christmas and I have been getting less than satisfactory results.

I've tried looking at random stars, Mars and the moon.

The stars and Mars look like little triangles when using both the included 20mm and 10mm eyepieces. The moon has given me the best results, but even that barely focuses.

I've looked at some people's advice on leaving the scope out for it to adjust to the temperatures but that hasn't worked for me.

Is there anything I can do? Thanks.

Hello, and welcome...

Your telescope is a 76mm f/4 Newtonian, and designed primarily, if not exclusively, for low-power wide-field views.  There is reason to expect to reach a power of 125x, or 150x, with the telescope, but the higher in power you go, the more critical, the more accurate the collimation, the alignment of the two mirrors with the focusser/eyepiece, must be.  I have the next size up from yours, a 100mm f/4 Newtonian...

kit2a.jpg.ecd626ec07a928bf0f5db0eeba583501.jpg

I got mine for one purpose, primarily: to observe the galaxy in Andromeda, as its huge, and requires very low power and a very wide filed-of-view to even hope to see it in its entirety.  I resigned myself to that whatever else might be seen with it would be icing on the cake, particularly at the higher powers; miraculous even.

The primary-mirror of my own was glued in place at the factory overseas; no clips, no adjustments, but no matter really...

618948646_primarymirror.jpg.07b6a341b116e5f39796db1a8e469b0b.jpg

However, I couldn't use my collimation-cap.  Through the cap, I saw only this...

1812083294_orig.collimation2.jpg.2c17870487475bb99b8835aa8015b4f1.jpg

...along with those dreadful spider-vanes.  So, I set to center-spotting the primary-mirror...

https://garyseronik.com/centre-dotting-your-scopes-primary-mirror/

I used a polyvinyl(plastic), not paper, reinforcement...

3d.jpg.e67ffb404aef370c8c426e8596597b08.jpg

Now I can use the collimation-cap, or a Cheshire, and to its fullest potential...

011417d.jpg.b573a8b8ffa54423baf050e2fcbc3f31.jpg

As you can see, it was practically bang-on from the factory.  Yours may be, too, but you won't know it until you add a spot to your mirror.  The more precisely the spot is placed, the more accurate the collimation will be.  Incidentally, I suspect that the primary-mirror of your telescope is also glued into its cell, and therefore may not be pinched.  If so, the astigmatism that you're seeing lies either with the eyepieces that came with your kit, or with your own eyes.  I do hope the former.

Now, I'm not seeing any ready-made caps being offered over there in Australia.  If the focusser of your telescope, the drawtube specifically, came with a dust-cap, you can make a collimation-cap out of it...

1911581764_collimationcap.jpg.8542285955a3dd29cba2c81b922dcbe1.jpg

You would need to drill a very small hole, as shown, precisely in the center of the cap, then line the underside, as shown, with either the dull or shiny side of a circular piece of aluminum foil.  Try it with both sides, and see which is best.  The telescope must be illuminated at the front opening.  I place a white cloth over the opening, and then a lamp in front of that.  You may also find that by using a small camera that you can zoom in on the scene and for a closer look, and just as I did within those images.  

If you did not receive a dust-cap, others have used the old-style 35mm plastic film canisters.  I would cut the canister down to half, and line the underside of the snap-on cap with the foil.

The secondary-mirror of your telescopes appears to be adjustable from what I've seen online, but the primary most likely is not, not in a conventional sense.  If you ever do need to adjust the tilt of the primary-mirror, you can slot out the round mounting-holes on the tube for the mirror's cell...

slot.jpg.511745dfed13ee67d70757b55ca51437.jpg

That would allow for enough movement to accurately tilt and adjust the primary, then to batten down the screws.  That modification will be possible only if the mounting holes are not threaded for the screws.

All of that, therefore, is if you desire to get the most out of the telescope.  In addition, you can get improved eyepieces, not only for that telescope, but for others that you may acquire in future.  The minimum in performance eyepieces are Plossls.  Plossls tend to play well with the f/4 parabolas of Newtonians.  A 32mm Plossl would serve as your lowest power, 9x, a binocular-like power, and would aid the finder in the finding of objects to observe.  It would also enable you to see the largest part of the sky, for cruising the star-studded fields of the Milky Way for example.  A 15mm Plossl would give you a power of 20x.  A 12mm Plossl...25x.  Those are all rather low powers.  The 10mm included with your kit...30x; a bit higher, but still a low power.  The planets come into their own at about 150x.  Let's see what that would take.  Your telescope has a focal-length of 300mm, and quite short...

300mm ÷ 150x = a 2 mm eyepiece

That short of an eyepiece is quite difficult to come by.  Let's try 125x instead...

300mm ÷ 125x = a 2.4mm eyepiece

300mm÷ 100x = a 3mm eyepiece

100x seems to be the most practical, in so far as eyepieces combined with barlows.  You can get an 9mm eyepiece and a 3x barlow, and for a simulated 3mm(100x).  You can get a 6mm eyepiece and a 3x barlow, and for a simulated 2mm(150x).  You would probably want to get wide-angle eyepieces for those higher powers, as the sky grows smaller as you go up in magnification.  Plossls, shorter than 9mm or so, have rather small eye-lenses and short eye-relief; uncomfortable to use.

Eyepieces range, in general, from 4mm to 40mm.  That range is pretty inflexible, static, unchanging.  But telescopes come in many different focal-lengths, and all must conform to that unyielding range of eyepieces.  For example, an ideal focal-length for matching with said range of eyepieces would be about 900mm to 1000mm, like that of this 114mm f/8 Newtonian...

kit4c.jpg.5d06b4971069e82ea21b48584aafa164.jpg

Although, even a 650mm(130mm f/5) or 750mm(150mm f/5) focal-length would do, and with the aid of 2x and 3x barlows.

Edited by Alan64

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