Streaks on primary mirror

[DAT]

Last night I left my dob out with all the caps on so that when I went out at 4 am it would be ready to go. After a brief session this morning, I have noticed these strange marks that I have never seen before. The scope was probably outside for a total of 8 hours.

The only thing I can think of is it looks like contact I might have made when re spotting the mirror a few months ago which is the only time the primary has been exposed. I can only think that that perhaps I applied too much pressure in parts when I used a re spotting template, hopefully I am wrong.

However, like I said, this was some time ago and I have no idea why this would not have been visible before (could the cold be something to do with it?).

Both last night’s session and this morning were successful with nice clear images, even at high power.

If anyone could tell me what these marks are and wether I need to be concerned and whether/how I need to get rid of them that would be much appreciated.

[DAT]

Update, the streaks are disappearing. I am assuming this could be something to do with moisture? Did dew form as I left the scope out which made wipe marks visible and as it dries they disappear?
Apologies for what may seem like silly questions but in over a year this has never happened to me

[Bignerdguy]

Please tell me you haven't tried to wipe anything on the primary mirror?  That is a really bad idea as the mirror coating is very fragile and should never be hand touched.  When i worked at a telescope shop my boss always told me that the ONLY way to clean these is swishing with ultra pure alcohol and rinsing it with distilled water afterwards.  NEVER touch the primary mirror surface., you could damage the coating.  If you have done so you may need to look into getting it recoated to fix this.

[Alan64]

Isn't that Newtonian on a Dobson base mis-collimated?

[NGC 1502]

In many years of using telescopes I’ve seen all sorts of strange things on optics following time outside.

As already mentioned don’t be tempted to wipe those optical surfaces. Leave the scope to thoroughly dry out, you may well find that everything is fine. Don’t shine a bright light on optical surfaces because most often they can look dreadful, just use natural daylight and if your first glance looks ok……then it’s ok😊

Relax…..and just enjoy the view next time out…..

Cheers from Ed.

[DAT]

Thank you for the reassurance.

the marks did indeed clear up that same morning as soon as things dried up as I always leave all the caps off to let things dry.

It’s obvious where I went wrong but not particularly worried as all looks good and this week I have had my best views of Jupiter yet at x 200, hopefully no need to re coat!

Also, I think it’s nicely collimated, it’s just some picture are taken at an angle 

 

 

 

[Ratlet]

If I is only happening when it is cold it a possibly just a slight variation in the surface of the coating just giving preference to water condensing on it.

Mirror coatings are surprisingly tough from commercial suppliers.  I wouldn't use fine grit sandpaper to clean them but just you won't need to recoat from just touching them.  FLO recommend using tap water and a couple drops of dish soap to clean them with a final rinse with deionised water.  Which works well.  Some (myself included) will use their fingers to wipe as your meat sticks are very sensitive so you can feel for anything solid and not push it across the mirror:

https://www.firstlightoptics.com/blog/cleaning-a-newtonian-mirror.html#:~:text=First run tap water over,gently wipe the mirror clean.

If it has been hand silvered though then maybe but if it's an off the shelf mirror you'll be fine.

[DAT]

I think that explains it as when I had the mirror out what dust could not be blown off with a puffer I tried to gently pick up with a cotton bud. I also must have touched the mirror thorough the re spotting template

I was embarrassed to say as I had repeatedly read that you should never touch the mirror and thought it was fine until it got cold, I just did not understand why it was not visible until it was cold but I think the above explains that.

Learning by mistakes 😬

[Ratlet]

1 hour ago, DAT said:

I think that explains it as when I had the mirror out what dust could not be blown off with a puffer I tried to gently pick up with a cotton bud. I also must have touched the mirror thorough the re spotting template

I was embarrassed to say as I had repeatedly read that you should never touch the mirror and thought it was fine until it got cold, I just did not understand why it was not visible until it was cold but I think the above explains that.

Learning by mistakes 😬

Most likely it will be fine.  There will be a tiny amount of residue from the cotton bud on the mirror.  Literally could be a molecule thick layer.  Imperceptible until you get condensation then the water will bead differently.

I wouldn't worry about it and don't think it'll make any difference.  At some point in the future you'll clean the mirror properly (not required now I think) and it'll go away.

Not sure if you saw them outside or not, but it wouldn't surprise me if they only showed up after the session and the mirror came inside or into a more humid environment and the water only condensed then.

[DAT]

I always check the mirror during and after a session for collimation purposes  but only noticed the marks inside under the light.

Thanks for the advice, silly thing to do but views have been good so I would tend to agree that luckily it has not created major damage