Star diagonals

[Jimtheslim]

Hello again, I have another probably stupid question, however I have looked everywhere for an answer and it's doing my head in! I received a Skywatcher 90mm refractor for my birthday last month and going forward I understand that upgrading eyepieces from the standard ones supplied is a good way to improve your views and I am currently in the process of procuring Plossls by keeping an eye out for them second hand.

My question is this: My scope takes 1.25" eyepieces and the star diagonal is the same. I have read a lot about the benefits of a 2" star diagonal of better quality. Along with eyepieces I know it's something I could take to an upgraded scope in time. Can I use a 2" with my scope and if so how do you convert it? What else would I need to buy? Is it worth it or would there be any value in buying an upgraded 1.25 diagonal such as an Orion or Revelation?

Thanks

[ronin]

A 2" will not make a great deal of difference, unless the one you have is too small for the optics.

However I will say that a 1.25" diagonal looks small and as if it is not up to the task - well mine does and maybe you have the same experience.

You can fit a 2" diagonal, then you would need an adaptor to fit the 1.25" into it, and then the focus is likely to be anywhere but where it started and could be a problem. 2" eyepieces and 1.25" eyepieces seem to have their object planes at different locations relative to the eyepiece.

I am thinking that buying a 2" diagonal and adaptors then finding that they just will not work with a 1.25" eyepiece would be annoying and an expenditure you don't want. It is a good case for borrowing one and finding out before commiting money yourself.

Could look into the WO diagonals and others, I get the idea they are "bigger" as in the actual mirror used is bigger.

The main advantage is in the quality of the mirror itself, a good one would be flatter and have a finer surface finish, and I have read of people upgrading from a stock item to a higher grade one and notiing a substantial improvement in what is seen. So upgrading is a reasonable idea. But not sure a 2" would reasistically do much - unless of course you wanted to use 2" eyepieces.

[Cornelius Varley]

The Skywatcher Evostar 90 (your telescope ?) has a 1.25" focuser, so you would probably need to replace the stock focuser with a replacement 2" focuser, if one were available for your telescope.

[Peter Drew]

I would save that decision until you upgrade the telescope. 

[Jimtheslim]

Thanks, yes I was wondering how a 2" would fit the end of the scope without an adapter (I'm very new to this). I will consider a 1.25" upgrade if one comes up for sale at the right price and in the mean time see how I get on with better eyepieces. I just couldn't find any kind of step-by-step info on what would be needed to go from a 1.25" to 2".

[damnut]

Hi There,

I think Cornelius has the answer above. The focusser tube on the evo 90 has a 1.25" apperture, so the upgrade path would be replacing everything that goes into the end of the tube, that would cost £120 ( http://www.rothervalleyoptics.co.uk/skywatcher-dual-speed-2-crayford-focuser-for-refractors.html ) whilst this is a lovely focusser and a dual speed one it exceeds the cost of your 'scope. So whilst it is beneficial to upgrade your eypieces as you can keep them if you decide to change your scope, it is not worthwhile to change the focusser so that  you can fit a 2" diagonal onto it.

[Moonshane]

Balancing the scope is another challenge with a small aperture and 2" accessories. Stock to 1.25" for that scope I would say. A 32mm plossl will serve you well.

[Gazabone]

Personally I would advocate using your money to buy quality ep; what I've been collecting (?) in recent months is Baadar Hyperion - they have the advantage that with the bottom piece unscrewed and removed, it becomes a 2" ep. I'm sure some other ep are equally convertible but I've become a bit of a Hyperion fan.

[damnut]

Hi Gazabone,

Thats true but in unscrewing the field lens you alter the focal length of the ep. If you can get the Hyperions used they are a great alternative, but the BST's and Excels also provide excellent value at half the Hyperion price, granted they are true 1.25" only ep's.

[Rainmaker]

Lots of good advice above !!!!  Usually fellow astronomers are more than happy to help you spend more on this pursuit.  I would very much echo the thoughts of others here that the difference in diagonals would be unlikely to be noticeable at all.  'First' scopes are usually just that, first in the line of many to come.  Spend your money wisely by buying quality eyepieces that you will want to keep for your next and next after that, scopes.  Plössls are great eyepieces, although a little narrow in their field of view, they are excellent for lunar/planetary viewing where your actual target is a small object in the centre of view.

With regard to eyepieces, you really only need 4 to be able to cover the usual needs.  I like to have magnifications of about 35x, 70x, 120x & 200x which seem to work with most of my observing with my 1000mm focal length refractor. Whilst the scope can handle more, the moments of great seeing here are few and far between.

All my eyepieces are 1.25" and used with a small (34mm) prism diagonal. 

[John]

Personally I would advocate using your money to buy quality ep; what I've been collecting (?) in recent months is Baadar Hyperion - they have the advantage that with the bottom piece unscrewed and removed, it becomes a 2" ep. I'm sure some other ep are equally convertible but I've become a bit of a Hyperion fan.

If you remove the 1.25" barrel of the Hyperions you remove the lower lens set and the eyepiece becomes a mediocre one and rather poorly corrected. They are not well corrected in scopes faster than F/7 even with the lower lens set in place. Nice eyepieces in slower scopes such as the F/10 90mm refractor that jimtheslim has but at the end of the day they are 1.25" ones.

[Jimtheslim]

Thanks, I'm in the process of upgrading the stock eyepieces so will look out for a used 32mm as well.

[Lowjiber]

The Skywatcher Evostar 90 (your telescope ?) has a 1.25" focuser, so you would probably need to replace the stock focuser with a replacement 2" focuser, if one were available for your telescope.

I agree.

GSO makes a 2" focuser that will bolt right up to your scope.  Then, you can install a 2" diagonal.