12" Dobsonian ... its a Revelation !

[Stu1smartcookie]

Mirror delivered safely to Galvoptics … really friendly service and some good news as I was told my mirror is in fact in really good condition ( ie no scratches or gouges ) now just a wait for a week or so ! #impatient 

[Piero]

Regarding the central spot, I use the Catseye 1/4” white triangle on my 12" and 16" reflectors. The mirror is rotated as Craig said in a previous post.

[Piero]

On 09/08/2021 at 08:46, Stu1smartcookie said:

 It had stood in storage for many years and the primary needed some TLC . Took the mirror off and cleaned it as best as i could , but unfortunately the mirror will need a re-coat . This was not a surprise and was understood at the point of purchase . So after cleaning the mirror as best i could i used the scope for the first time last night . I have to say , i had no right to expect the view that i had ... just viewing bright stars , such as Arcturus and Vega as well as the lovely Albireo and its blue companion . The stars were all bright and if anything , although i think the mirror degradation has meant a little lack of contrast they seemed to show colour very well . The scope is well out of collimation ( i thought i had done a reasonable job after putting the primary back but a star test soon told me otherwise) . But as i didn't have a collimating device it was a shot to nothing and something that will be addressed this evening . I was shocked how a mirror, when in poor condition , can "work" so well . Now i realise that mirrors should only be cleaned when absolutely necessary !

 

I'm glad that you bought a new telescope, but I'm a bit confused when reading your first post.

- First of all, I don't understand why you thought that the mirror needed to be recoated. Was this suggested by the previous owner?

- if the telescope is not collimated, it isn't possible to assess how it performs.

- if the coatings are damaged, the effect is more light scattering and a dimmer field of view, due to the reduction in reflectivity.

- whether the coatings are damaged (erosion, many many scratches) or the surface is significantly dirty / dusty, the effect on the views is pretty much the same. Therefore, I don't understand your statement when you said that a mirror should be cleaned only when absolutely necessary..

- finally, don't you think that if your mirror hadn't been left covered with dust and particles, fungi etc, maybe, this recoat would not have been necessary?

 

There is nothing wrong with cleaning optics, it's just maintenance really.  Recoatings is also maintenance although a bit more invasive.

If done properly, there is no harm.

Edited August 14, 2021 by Piero

[John]

3 hours ago, Piero said:

 

I'm glad that you bought a new telescope, but I'm a bit confused when reading your first post.

- First of all, I don't understand why you thought that the mirror needed to be recoated. Was this suggested by the previous owner?

- if the telescope is not collimated, it isn't possible to assess how it performs.

- if the coatings are damaged, the effect is more light scattering and a dimmer field of view, due to the reduction in reflectivity.

- whether the coatings are damaged (erosion, many many scratches) or the surface is significantly dirty / dusty, the effect on the views is pretty much the same. Therefore, I don't understand your statement when you said that a mirror should be cleaned only when absolutely necessary..

- finally, don't you think that if your mirror hadn't been left covered with dust and particles, fungi etc, maybe, this recoat would not have been necessary?

 

There is nothing wrong with cleaning optics, it's just maintenance really.  Recoatings is also maintenance although a bit more invasive.

If done properly, there is no harm.

The mirrors of these 1st generation Revelation branded dobsonians do seem to need re-coating quite early in the mirrors lives. At the time they were sold, it was quite widely rumoured that the over-coatings (usually quartz or similar) that protect the reflective coatings from degrading early were either quite poor or even not present on this line.

Over the years, I have seen quite a few of that vintage where the mirror coatings were notably degrading after quite a short time. The 8 inch version that I had (bought a couple of years old) included.

Once properly re-aluminised and then over-coated, the mirrors perform quite well though and the new coatings should last what would be considered a more normal span of time before requiring more attention.

As long as the buyer is aware of this then good bargains can be had, provided that the cost of re-coating is taken into account

 

 

Edited August 14, 2021 by John

[Stu1smartcookie]

22 hours ago, Piero said:

 

I'm glad that you bought a new telescope, but I'm a bit confused when reading your first post.

- First of all, I don't understand why you thought that the mirror needed to be recoated. Was this suggested by the previous owner?

- if the telescope is not collimated, it isn't possible to assess how it performs.

- if the coatings are damaged, the effect is more light scattering and a dimmer field of view, due to the reduction in reflectivity.

- whether the coatings are damaged (erosion, many many scratches) or the surface is significantly dirty / dusty, the effect on the views is pretty much the same. Therefore, I don't understand your statement when you said that a mirror should be cleaned only when absolutely necessary..

- finally, don't you think that if your mirror hadn't been left covered with dust and particles, fungi etc, maybe, this recoat would not have been necessary?

 

There is nothing wrong with cleaning optics, it's just maintenance really.  Recoatings is also maintenance although a bit more invasive.

If done properly, there is no harm.

Ok , so the primary mirror had sat in the scope for 15 years ... as the previous owner said , he had used the scope only approx 5 times .. the mirro was completely covered in dust . Of course i set about cleaning it but on cleaning the mirror had some blemishes that could not be removed . The rest of the scope is in fantastic condition . I want to use the scope to its fullest capacity . The mirror needed a recoat , i'm getting it done.. its a simple solution ad hopefully one which will bear fruit . Not sure why you are questioning me , or indeed the previous owner regarding the validity of a recoat ?... i refer to your "finally " quote . The owner sold the scope to me in good faith ... i knew the primary would need attention , i'm happy as i have a fantastic scope which will hopefully have a spotless mirror in a couple of weeks . Happy days all round , in my book . By the way , the reason it wasn't collimated because i used the scope after cleaning the primary and at that point i didn't have a collimation device , but did a star test that showed it was out of collimation . Many people say not to clean the mirrors on a scope unless absolutely necessary . Thats a great scope you have by the way. 

Stu

Edited August 15, 2021 by Stu1smartcookie

[Stu1smartcookie]

UPDATE .... 

So , primary mirror has been recoated and collected from Galvoptics , Basildon ... i fitted it yesterday . The mirror is pristine compared to the original coating. I have hopefully left enough of a gap when tightening the clips on the mirror . Collimation was performed using a cheshire .  I prefer using a laser to a cheshire ( awaits howls of derision from purists ). I did re-spot the mirror using the catseye template. ... and after all that , clouds appeared and have pretty much stayed ever since .... zzzzzz . 

[NGC 1502]

I’m sure you’ll be keeping an eye on forecasts. Hoping first light will be great and you can post a report 👍