How “cloudy” should a new telescope mirror be?

[sockatume]

This is probably a common new telescope owner question but I’d been having some trouble finding an answer by searching. Basically, my secondary mirror seems to be quite hazy in bright light.

My second or third night out, I thought I might have got some dust on my improvised telescope shroud (Heritage 130p) and hence on to the secondary. After I packed everything up I pointed a torch at the secondary to check and gave it a few puffs with a rocket blower, one of the ones that’s not got any bristles. (I’m sticking with the general rule of not ever touching any of the surfaces until the day comes that they’re completely filthy.)

I noticed that the mirror looks irregularly hazy when lit this brightly. An image is below, along with the dust that’s too small or too sticky to blow off. (My main observing site is next to a tree that has now gone in to bloom, I figure some of this is pollen.)

Is the haze just the inevitable light scattering you get with the surface coating? It’s not really hazy looking in daylight, just under a lot of contrast like the LED below. I figure any light actually hitting the mirror is both fainter and moving through the coating at a steeper angle than this, so it’ll scatter far less. Looking through the ‘scope seems fine but I thought I’d ask anyway.

Thanks in advance!

[Ally8446]

You have absolutely nothing to worry about. That's pretty clean in comparison to some mirrors I've seen. They have to get really rather dirty before it will degrade your view. 

Al

[sockatume]

Thanks, that’s what I’d been hoping to hear!

[sockatume]

8 hours ago, Ally8446 said:

You have absolutely nothing to worry about. That's pretty clean in comparison to some mirrors I've seen. They have to get really rather dirty before it will degrade your view. 

Al

Sorry, just to confirm, you think the haze is normal? It's not dust or anything that's landed on the surface as far as I can tell. The telescope's only been used a couple of times so far.

[Geoff Barnes]

I'd say it probably is pollen from the trees and a bit of dust, but nothing at all to be concerned about.

[Carbon Brush]

New new(ish) mirror will not have any hint of haze. Unless of course you are looking at condensation.
A quick blow from a hair dryer will exclude this possibility.

As for bits of dust and the like that are in your photo - don't worry. These have no effect.

It is difficult to comment further on the photo. Depending on how photos are taken, mirrors can look awful or superb.
A bit of playing with lighting and exposure can make specks of dust look like rocks, or make a dirty mirror look clean.

If the scope is giving good views, don't worry.
When you have viewing issues, or can make a side by side comparison with another scope and see a difference, that is the time to look further.

In the meantime. Enjoy the sky.

David.

[kirkster501]

Shining a flashlight onto a mirror is always a terrifying experience  Oftentimes when mirrors have been cleaned they can have that haze. It can be a microscopic level of cleaning residue or impurity left behind that is too risky to rub off and nor is there any need to, it makes absolutely no difference whatsoever.

Now, quit worrying and enjoy your scope!

[Zakalwe]

Is your scope capable of giving better views than the one at Kielder observatory? I ask, because this is a picture that was taken of their mirror a few years back

 

 

Learn to forget about obsessing about the cleanliness of mirrors. Telescopes are for looking through, not for looking at.

[Zakalwe]

Well worth a read if you want to see the amount of muck and physical damage needed to affect an image

 

http://kurtmunger.com/dirty_lens_articleid35.html

[Saganite]

55 minutes ago, Zakalwe said:

Well worth a read if you want to see the amount of muck and physical damage needed to affect an image

 

http://kurtmunger.com/dirty_lens_articleid35.html

Very interesting to read, and it confirms my own experiences. I have a Nagler eyepiece with a scratch on the eye lens, which makes no difference that I can see. I also have an ED100 with the internal lens of the doublet shattered in many places, which I obtained for nothing, and which performs perfectly well.

[Gfamily]

The rule is "only shine a torch down someone else's scope, never your own".

 

?

[F15Rules]

On 01/04/2019 at 21:37, sockatume said:

This is probably a common new telescope owner question but I’d been having some trouble finding an answer by searching. Basically, my secondary mirror seems to be quite hazy in bright light.

My second or third night out, I thought I might have got some dust on my improvised telescope shroud (Heritage 130p) and hence on to the secondary. After I packed everything up I pointed a torch at the secondary to check and gave it a few puffs with a rocket blower, one of the ones that’s not got any bristles. (I’m sticking with the general rule of not ever touching any of the surfaces until the day comes that they’re completely filthy.)

I noticed that the mirror looks irregularly hazy when lit this brightly. An image is below, along with the dust that’s too small or too sticky to blow off. (My main observing site is next to a tree that has now gone in to bloom, I figure some of this is pollen.)

Is the haze just the inevitable light scattering you get with the surface coating? It’s not really hazy looking in daylight, just under a lot of contrast like the LED below. I figure any light actually hitting the mirror is both fainter and moving through the coating at a steeper angle than this, so it’ll scatter far less. Looking through the ‘scope seems fine but I thought I’d ask anyway.

Thanks in advance!

That looks like a great image of the Milky Way!

So perhaps there is a great deal of dust there...

Dave

(Only joking - nothing at all to worry about!)

[mert]

On 02/04/2019 at 08:42, kirkster501 said:

Shining a flashlight onto a mirror is always a terrifying experience  Oftentimes when mirrors have been cleaned they can have that haze. It can be a microscopic level of cleaning residue or impurity left behind that is too risky to rub off and nor is there any need to, it makes absolutely no difference whatsoever.

Now, quit worrying and enjoy your scope!

Absolutely, shine a torch onto a brand new mirror and you will always see something. ?

 

[Prolifics]

Nothing I would be worried about.

[sockatume]

Thanks everyone, I really appreciate you taking the time to set my mind at ease! I tend to get anxious about big purchases (which this was for me). Understanding how much dust it can really deal with has, I think, helped me stop babying the telescope and encouraged me to drag it out and just use the darn thing. It's a tool after all!

[Space Hopper]

If you can source one, use a dew shield on your Newtonian.

It keeps the dew at bay, and just gives your mirrors that extra barrier pf protection.

[sockatume]

Now that you mention it...

[niallk]

On 04/04/2019 at 18:56, sockatume said:

Thanks everyone, I really appreciate you taking the time to set my mind at ease! I tend to get anxious about big purchases (which this was for me). Understanding how much dust it can really deal with has, I think, helped me stop babying the telescope and encouraged me to drag it out and just use the darn thing. It's a tool after all!

Congrats on the scope + enjoy!  Nice job on the shroud/dew shield.  I just bought a 130p too as a travel scope when with the family - need to craft something neat like you've done.

I did an experiment before where I stuck my hand in front of the aperture of my 15" while viewing Jupiter: it was remarkable how little impact it had!  Probably better to do this little test with a stick or something to avoid heat plumes

That being said, I do give the exposed mirrors in my 15" truss dob a wash every two years or so. I think I went 8 years before washing my solid tube 10" dob mirror!  That was mostly because a fat fly was decomposing on the surface.

I too have learned the hard way that it is best NOT to shine a torch on mirrors 

[veedub1955]

Phew I was stressing too on my primary mirror, excuse the head haha