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What would be better ?


Doc
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If you had a choice between:


 


 


A 16" mirror which was ultra or research grade so 1/10 wave or better from Orion Optics or Oldham Optics.


 


or


 


A 18" mirror similar to the new Skywatcher brand which will be 1/4 wave or maybe a little better at 1/6 wave if you are lucky.


 


 


Is the 2" aperture gain worth it or would you rather have the better optics.


Edited by Doc
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Extra appature for me. I do wonder (for visual purposes only this is) would any body's eyes be able to tell the difference between 1/10 and 1/4 or 1/6, I doubt it, so go bigger.

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Sorry but I would go for the Orion optics -


 

PV Fraction   Decimal Strehl Ratio 

¼                              .82 

1/8                            .95 

1/10                          .97 

  

I'm guessing it 's for a Dob so don't know how important the mirror accuracy is.

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I would have to ask myself though if the seeing conditions we get in the UK would allow the extra quality to be appreciated fully, whereas the extra aperture should still make fainter objects appear brighter. If you were in the Atacama though, well that would be a different matter.


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It also works the other way as well Mike.


 


The larger aperture sucks in a lot more light pollution and makes the view washed out if the aperture is to large.


 


Living in  the Atacama would benefit both ways


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Another point to say is the Skywatcher 18" mirror is a really thin mirror which might lead to problems, the 16" OO is one solid lump of glass 41mm thick.


Edited by Doc
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Guest Tweedledum

Thinness of the mirror should not be an issue if you have a decent mirror cell...


 


I thought you had problems moving large kit Mick. The base of  Pete's 14" dob is a good lift, also the base needs a sizeable  SUV boot to put it in. If you are going to move it around then the logistics of transportation and setup cannot be ignored on an instrument of this size.


 


I'm 6' 3" and barn door so it would be the big un for me :D ...


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Thinness of the mirror should not be an issue if you have a decent mirror cell...

 

I thought you had problems moving large kit Mick. The base of  Pete's 14" dob is a good lift, also the base needs a sizeable  SUV boot to put it in. If you are going to move it around then the logistics of transportation and setup cannot be ignored on an instrument of this size.

 

I'm 6' 3" and barn door so it would be the big un for me :D ...

 

I do have problems in that department, this is why I'm edging towards a 16" at the limit of what I can really lift. I'm considering building this myself so in theory the heaviest part will be the mirror. The rest will be flat pack so not a worry.

 

But saying that I bet the OO mirror weights more then the SW mirror.

Edited by Doc
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Guest Tweedledum

Hats off if you are going to build it yourself :respect: ,worth having a look at pete's orion as I don't think there's an original bit left as  well as modding a means of moving it. And when he has finished drilling the case I can get on with the electronics :D ..


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Hi Mick,

I personally would go for the bigger one since I can lift stuff ok and my main interest is in pulling in faint fuzzies.

You however want the faint fuzzies and pristine views of Cassinis Division and Lunar features etc. so the smaller more accurate mirror might be better and easier to move.

Another option for you to really cure that aperture fever and still move it around, could be to read this book...

http://www.willbell.com/tm/PortableNewtonianTelescopes.htm

The author has some sort of muscle waste disease, so lifting and moving stuff is a problem. In his book he goes into great detail analysing, planning and building a lightweight 22" (I think, on holiday at the mo so dont have the book here) dob that he can transport, erect and use by himself, despite his limitations!

If you would like to borrow the book, I'd be happy to get it to you, or perhaps you are already finalising your own plans.

Good luck.

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I will get the book for xmas, I'll put it on my prezzie list I give to the wife  :lol:


 


My plans are pretty must finalised Pete just waiting on how much money I have to spend once I know where I stand with work.


 


A 16" ultra grade 1/10 wave lightweight dob sounds pretty cool to see those faint rilles on the moon. It will also have a 3" JMI motorised focuser to take adavantage of the 30mm Explorer Scientific 100° Eyepiece.

Edited by Doc
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I know I'm a refractor man but I've messed about with Newts as well and from my experience of Orion UK 1/10th  optics and other newts then my take on this would be:


 


If I were only after photons or bang for buck ( as our cousins over the pond would say) the 18" 1/4 wave would be the favourite.


 


However if I were after finer detail then the 1/10th wave 16" OO for sure. 


 


My experience with an OO mirror set, OK it was only an 8" but it was an excellent performer, (for a newt :) ). I remember 1st light, even with slightly oxidised coatings the detail on Jupiter and lunar was excellent and I knew then it was worth re aluminising and putting some time and effort into doing the scope up. Once resurfaced by OO (Hilux) it was a great performer and getting pretty close to a refractor at times for detail. I also compared it with a standard SW 200p (EMS scope) and the OO views were far superior, it was obvious the OO was more accurately figured with just one look at Jupiter.


 


For refractors and reflectors alike


You cant beat optical quality if you want detail in your views.


Yes agreed on poor nights images from 1/4 or 1/10 optics will suffer but the image you get from the 1/10 will still be that bit better than the 1/4 on that night but you will also have the advantage with 1/10 of having better optics for when conditions improve.

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I actually hold your experience Phil in very high regard, and totally agree in everything you have said.


 


In my experience quality optics do deliver sharper views especially on planets and lunar. But then on DSO's I think aperture rules to the point when light pollution upsets the balance.


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