Seeing secondary mirror in lense?

[Tyman17]

Hello all, I am a beginner to astronomy who has spent a very long time attempting to figure out the components of telescopes before making my purchase. I ended up buying a Celestron 127eq, and I really love it. The problem is that whenever I attempt to focus on stars, or even planets, I seem to see the shadow of the spider veins and the secondary mirror. I'm not sure why this is happening, is it a problem with my collimating or is it just that my focus is wrong? Thanks!

[brantuk]

Hi Tyman and welcome to SGL.

The problem as you describe it sounds like a focusing issue. Use your highest mm eyepiece (lowest power) and go slowly from one end of the focus range to the other - somewhere in the middle the spider/mirror shadow will disappear and whatever you're focusing on will come into view. Try it on a star and ensure there is only the eyepiece in the focus tube. It takes a little practise but you will find it eventually.

Once you have the star nice and tight and at it's smallest - move to another object like a cluster - I'd suggest M45 the Plieades and they should look like diamonds glittering on a black cloth. Move to M42 (Orion Nebula) and you should see sharp swirling clouds of gas and dust.

The images will appear small in your 5" scope but you'll definitely see it as described. You may have to adjust focus slightly (one way or other) each time you change object. Hope that helps and good luck.

[Tyman17]

Thank you for your help! I will try that out on a clear night in the near future and report back. Also, could the eyepiece contribute to the issues focusing? I have the standard 20mm, a 4mm, and a 3x Barlow that all came with the scope. Would you suggest upgrading lenses to enhance quality?

[brantuk]

The Celestron 127's that I'm aware of are Sct's with a focal ratio of 9.84 giving a focal length of 1250mm. If you divide the focal length by the eyepiece size you get magnifications of :

20mm = 1250 / 20 = 62.5x

4mm = 1250 / 4 = 312.5x

With a 3x barlow you get 187.5x and 937.2x. I would suggest the barlow and 4mm eye piece will be far too high, and without the barlow is ambitious but doable on a very clear transparent night. So start with just the 20mm and no barlow to get good focus at a low magnification.

Once you've mastered the focal point with it - train the scope on a planet like Jupiter or Saturn and pop the 3x barlow in with it. You should be able to get a great view at 187.5x - if your observing site is well dark and the sky very clear it's worth trying 312.5x but expect the view to be "grainy" cos it'll magnify the atmosphere as well.

The Sct's are mainly good planetary scopes - but you can see other stuff too - it'll just be small so you have to study the object for 5 mins or so to tease out the detail and get the best out of it.  A 10mm eyepiece would be a good addition, and probably a 6mm as well. I'll follow this thread so do let me know how you get on.

[brantuk]

Also - as you approach the focal point - you'll see a set of white "airy" rings getting gradually smaller. You are getting very close by then as you hone in on a clear view. If you continue past the focal point the rings get larger again and you'll be going away from the best image. The Sct has a long focus throw - so it may be worth marking with a felt pen on the focus tube so you have an approximate starting point each session.

[Stu]

Kim, I think the OP has the 127EQ which is a Newtonian, f7.87 1000mm focal length. This would explain him seeing the spider veins which obviously wouldn't be there on an SCT.

It changes the calculations a little but basically everything said remains valid I'm sure, the mags just change to x50 for the 20mm and x250 for the 4mm.

Tyman, as Brantuk says, use the low power eyepiece and slowly work through the focus range until the stars reach the smallest/tightest image. Note that you will still see a 'cross' of light on the brighter stars which are diffraction spikes caused by the secondary vanes. This is not a fault, just a characteristic of Newtonian scopes.

Have fun with it [emoji3]

[brantuk]

Ah yes - thanks Stu - if it's the Newtonian version it does change the magnifications I worked out. And it does make sense there's no spider on an Sct so it's gotta be  the Newtonian. Thanks for confirming that.

(My 127 is the SW one which is a Mak)

[Peter Drew]

If all else fails with careful focusing it's possible that a short extension piece may be needed.   

[rockystar]

One of my first mistakes was that mine came with a 2" extension and a 2" to 1.25" extension and they where already stacked together, this gave me far too much outward focus, so when I worked this out and remove the 2" extension (I only have 1.25 eye pieces) it all came into focus. Not sure if you have the same extensions, but if so, it might be something to check and consider.

[John]

Try using the lowest magnfication eyepiece (20mm on it's own) while you get used to getting the scope into proper focus.

What will happen is the image of whatever you are looking at (eg: star, planet or the moon) will get smaller and smaller as you get closer to sharp focus and the shadow of the secondary mirror will dissapear. When the image is at it's smallest it will be at sharp focus. If the image is getting larger and the secondary shadow appears, you are going the wrong way !

The 4mm eyepiece gives 250x with your scope even without using the barlow lens, which is probably going to be too much power most of the time. The 20mm with the 3x barlow will give a more useful high power of 150x. At some point you might find it useful to get an eyepiece to give you a medium magnfication - something like a 12mm would be useful.

[Tyman17]

Thank you all for the replies. Was able to go outside early this morning and was able to focus in on the moon with no shadow, will try on a star on a clear night. Thanks for helping an amateur!

[brantuk]

Great stuff - glad you're sorted now Tyman - have fun