Is the effect because of collimation req'd or something else?

[upahill]

Hi All,

The closest I can get to focus on any star (or planet for that matter) leaves me with the effect I have tried to illustrate below, is this normal or because I need to do something/get something?

Thanks in advance,

Sam

[John]

I can't read the scope you have Sam - the script is a bit too small !

Knowing the scope and its spec will help the diagnosis.

[upahill]

Have made my signature a bit larger.

I wish I knew what the scope is, its a 8" newt reflector, manual says Helios Explorer, but no branding on box other than "Astronomical Telescope" - Its a chinese unbranded. Tube length 650mm, Stated spec is 203mm f/4

[astronymonkey]

Hi upahill,

Are the stars nearly in focus but just not sharp or are the just huge and now where near sharp.

At f4 this could be coma due to the fast optics ie the mirror is really trying hard to brig the light to a focus over a short distance and this isnt helped by mediocre eyepieces. One tell tale sign is if it gets worse the further from the centre of the field of view the star is as this is where the mirror has to work harder.

With and F4 scope you collimation would need to be spot on and not letting the mirror cool would cause poor images.

Cheers

Astronymonkey

[John]

If this is with quite bright stars then it looks a bit like like diffraction spikes. Normally these are quite thin but if the vanes that support your secondary mirror are thickish they could cause more obvious spikes.

How many secondary mirror support vanes does your scope have ?

[upahill]

4 vanes support the secondary.

Its with pretty much every star, and I do feel a little as though the focuser just isn't quite smooth enough.

I think I am going to buy a laser collimator next pay day and try to set everything up perfectly.

[acey]

If it was diffraction spikes then the pattern would be symmetrical (no matter how many vanes you have).

If it was collimation then you would more likely see stars as elongated ovals.

It could be flaring due to turbulent air in the scope. It could also be due to imperfect optics.

Try leaving the scope outdoors for a longer period before observing, and try observing in steady air if you can. Make sure you aren't observing over a heat source (e.g.someone's roof) and make sure the optics have had time to cool.

Try a different high power eyepiece if you can.

If you still have the problem, check your collimation, and if that doesn't help, make sure that the primary and mirror aren't screwed tightly in their cells - the screws should be just tight enough to hold the mirrors in place, but no more.

Make sure it's not your own eyes - if you normally wear glasses, then wear them while looking through the telescope.

To see if the problem is the eyepiece, leave the eyepiece loose in the focuser and turn it, to see if the spikes turn.

To see if it's an atmospheric effect, rotate the telescope tube in the mount. If the pattern still looks to be in the same direction then it's caused by turbulent air; if the pattern turns with the telescope then it's to do with the optics.

[upahill]

Thanks Acey,

Pretty thorough diagnostic method there! I will give this a go on the next clear night.

At first I thought it was my own eyes, I wear glasses, but find focussing on an object much better without them (just cant get close enough with glasses) but I thought the cold air + light in the eyes were making them water a bit, but wifey confirmed she could see the same effect.

Interesting that you reccomend keeping glasses on, is there a particular reason for this?

[John]

I've sent you a PM (private mail) Sam

[upahill]

Thanks John

Im pretty sure thats the scope, looks like major changes/upgrades are the way forward, or a new OTA

That review was not particular favourable!

Sam

[acey]

Interesting that you reccomend keeping glasses on, is there a particular reason for this?

I only suggested it as a way of checking if it's your own eyes. People have their own preferences but mine is always to remove my specs when observing.

[upahill]

This probably isnt helping...

[Peter Drew]

From the photo it looks like the mirror retaining clips are siliconed to the mirror, if so this could cause distortion and result in the unusual star images. The mirror should be free enough to just move.

[upahill]

Its not siliconed, there just rubber, but were rather tight.

Main problem is the amount of dirty I guess, and dust, and a few little scratches around the edges.

[Planetesimal]

Its not siliconed, there just rubber, but were rather tight.

Main problem is the amount of dirty I guess, and dust, and a few little scratches around the edges.

I wouldn't be worried about the dust and dirt to be honest. It doesn't look much worse than mine - I don't think that would cause the effects you're seeing.

If it really bothers you, you can clean the mirror using de-ionised water. I'm pretty sure there's a guide to the process on Astro Baby's website.

[upahill]

Yeah have done that, wifey wants me to try everything I can to get it working as best as possible before I sell and upgrade.

I just found in the man cave a few square metres of black flocking material so thinking of doing the tube, just because I can and its free

[Astro_Baby]

Hard to say from the pic but the mirror clips do look tight. They should be free enough so that you can slide a thin pece of paper between the clip and the mirror.

Looking at your image at the start of the thread it could be imagined its a tringular star shape which is a sure sign of a too tight mirror.

[upahill]

Ive flocked the inside of the mirror with my freebie material and loosened up that mirror.

Its definately going to need collimating now

Fingers crossed