Help - is there a bit missing from the mirror ?

[simonrp]

Hi,

With the help of everyone on this forum I bought my wife a Celestron Nexstar 130 Newtonian for Christmas (From FLO).

It is only today we have first set it up and I was about to see if it needed collimating.

Looking into the focuser tube (with no eyepiece) I can see both mirrors and the vanes.

However,  the seconday mirror looks like it has a little piece missing.  It is hard to explain and I wondered if anyone could tell me if this is normal.  Basically, there is a little segment on the edge that isn't reflective.

I have tried to draw this and attached the piccie (the section in red is the section "missing")

Is this normal ?

Many thanks in advance for any help (I am a total beginner to this).

[ronin]

Look at the mirror itself is it complete - as in eliptical and nothing missing.

If so then it may be rotated one way too much - if that is possible.

Is the missing bit missing or is something blocking it off?

What is your actual location?

Astro clubs often have a "help" night for people andf there might be one where you live or in the area.

Or there may be someone from here that can help.

[Coastliner]

Is it possible that the missing bit is actually a reflection of part of the front edge of the tube, as though the secondary is way off?

[simonrp]

Thank you for the responses.  It does appear to be a complete mirror.  I am in Prestatyn, North Wales.

[simonrp]

I have just had another look - I have attached a more accurate piccie - the "missing" bit is at the bottom and is intersected by a vane.

However, the best way of describing it is that the "missing" bit is there but not reflective.  IE:  I can see my skin in the mirror in all parts apart from the section  in red (which, in real life, is smaller than on my piccie).

[Scooot]

Is it the Focuser protruding into the tube? Rack it right out to see if it's still there.

Cancel that just realised its the secondary you're referring too.

[Frenchgow]

Hi there,it sounds like you need to adjust the secondary mirror,Astro baby has a very good collimating tutorial,in it you wiil see how to adjust the secondary and collimate the primary,if you google astrobaby collimating you will find her page,not sure of the link from here,good luck ,regards Gow

[ronin]

Well Prestatyn seems to be in an astronomy desert :eek: 

I can find nothing listed for Prestatyn, Denbighshire or N Wales. :confused:

How did you mange to pick that area?? :grin:

I know there is a club at Chester, bit of a drive. Check their website and see if they have a sort of come along and get help night.

[ghostdance]

Link here:

http://www.astrobaby.com/collimation/astro%20babys%20collimation%20guide.htm

Hope this *great* guide by Astro Baby is helpful - it sure has been to me and many others!

[Peter Drew]

It might just be a small part of the aluminising missing. Secondary mirrors are often aluminised as multiple batches for economy, your's might have been masked by something during the process. If it is, as you say, smaller than your illustration then it should have no effect on the overall image. 

[barkis]

Can't see it being the secondary's coating, more like something is askew in the collimation.

Ron.

[simonrp]

Thanks for all the suggestions folks - much appreciated.  I also  contacted Steve at FLO about this and he said :

"this is normal when you place the eyepiece into the holder you shouldn't see this, if you can see this then please let me know, but if you look at the secondary mirror you will notice it is made on a piece of glass that is slanted your seeing the body part of the mirror at the base, but to be sure just pop in the eyepiece and if you don't see it then it's fine."

So, I then put an eyepiece in and focussed on an outdoor view and the "missing" bit wasn't there anymore so all seems good

[russ.will]

Can't see it being the secondary's coating, more like something is askew in the collimation.

Ron.

As I recall Malc C (I think) had one of the longest running threads concerning what looked like an additional diffraction spike in his images. His secondary had a chord of the silvering, that looks like exactly what's being shown and described here. As I recall, so did his replacement, so it seems a pretty common Synta thing.

If it is this, it'll have no effect of the image as viewed through the EP. The EP probably isn't using the outer part of the mirror anyway.

Russell

[Sirius Starwatcher]

Hello Simon. There is the North Wales Asronomy society near you meeting at llanelian near Conwy. PM me and I will get you the e mail address and website.

Regards Garry

[ddtwelve12]

does your secondary look like the picture ?

[JamesF]

My 250P secondary is missing a small amount of silvering on one edge too.  It's not generally a problem unless you're imaging, when it can cause diffraction spikes.  I've blackened the edges and back of my secondary to reduce the effect.

James