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Do I need a new diagonal and Barlow?

meteoriot

By meteoriot
in Discussions - Eyepieces

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meteoriot

meteoriot

Posted
Posted

Hi.

I have a Nexstar 8se with a range of plossl lenses and I am currently considering upgrading my eyepieces. I would really like a Tele Vue but i can get a Baader Hyperion 8mm and a 24mm and a 2x Barlow giving me a wide range for the same price so I am leaning towards that option.

While I would very much welcome as many comments regarding the eyepieces as possible, what I am really asking is will I need to upgrade the diagonal on the telescope as well? Also can you recommend a good Barlow that won't ruin the potential of the eyepieces.

Any suggestions and comments would be very much appreciated.

Regards

Richard

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Stargazer_00

Stargazer_00

Posted
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An 8SE would peforrm very well with hyperions. If you are not planning on moving to a faster scope in the future then the hyperions should serve you well. TeleVue eyepieces are great because, among a host of other things, they are tested to F4. This basically means they will peform well in any scope meaning they will last a lifetime whatever scope you choose to buy. Hyperions soften at the edges at F5 and faster.

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Stargazer_00

Stargazer_00

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Thank you. I'm not sure what you mean by 'faster' but I'm planning on sticking with this scope. I also think I have made my mind up about getting the hyperions. I just need to choose a Barlow. Thanks again. Richard

Just to follow up on this point. By "faster" I mean't the speed of your scope. The speed rating of your SCT is F10 which is the ratio between focal length and aperture. Your scope has a 200mm aperture and a 2000mm focal length so there ratio is 1:10. This is known as F10.

As a scope speed increases the scope becomes more and more prone to revealing optical abberations introduced by the eyepiece optics which are inherent in the way in which the eyepieces are designed (lens spacing, the glass used in the eyepieces, the coatings, the actual light path manipulation by lenses). Typically fast scopes, those with a F rating of F5 or higher (so F4.9, F4.8, F.7 and so on) are usually newtonian based telescopes although some refractors sit in the F5 area.

For example my largest current scope is a 10" newtonian. It has an aperture of 254mm and a focal length of "only" 1200mm. this gives it a ratio of 1:4.7 so it is F4.7. this telescope is very demanding on eyepieces and as such I needed to buy reasonably high end eyepieces to get the best of it.

I have found that increments of as little as 0.1 past F5 make a real noticable difference, similar to those found in full integer jumps from F6 down. So for example a F10 to say F7 jump is about equal increase in demand on the eyepiece to a F5 to F4.7.

What this means, in principle, is that slower scopes can yield fantastic results from cheaper eyepieces when compared to faster scopes. SCTs typically have a focal ratio of F10, Maks have typically slower focal ratios around F11+ and RCTs (Ritchey Chrieten Telescopes) are around F7 or F8. Newtonians then take the baton from usually F6 all the way up to F4 with the overwhelming majority produced at F5 in mainstream visual and as fast as F3 in high end astrophotography. Rerfractors pretty much sit along the whole chain of focal ratios from the fastest the to very slowest.

Speeds of F2 and F1 are the realm of camera lenses and DSLR photography. Also the human eye, when fully dialted is around F2.2 (16mm focal length and pupil of 7mm). F3 would appear glacier slow to a terrestial photographer i'd expect but to us astronomers it scares the bejesus out of us :D

Hope that helps :)

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M4lcs67

M4lcs67

Posted
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I am a huge fan of the Hyperions and have 4 of them. I also have the 2 fine tuning rings which when attached to the eyepiece give you other focal lengths, effectively giving you more possibilities (apart from the 24mm which is fixed). Lovely eyepiece in my opinion and will work great with your scope.

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meteoriot

meteoriot

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I assume you are aware of the versatility of the hyperion eyepieces? with fine tune rings you can make them produce a large number of focal lengths

Sort of!? I'm getting them based on the good reviews and the fact i can get a couple at a reasonable price. I knew they had fine tuning (except the 24mm which I'm getting) but perhaps I wrongly assumed they were just fine tuning rings? My main concern is still wether or not my Barlow will 'downgrade' the optical quality of the view and i need to upgrade or wether my ostara ones wil suffice. Thanks for the help everyone btw. Its appreciated!

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alan potts

alan potts

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Know that people will call for my head on a plate for say this but I would not fancy messing about with fine tuning rings in the dark. My understanding is that to use them they have to be placed within the eyepiece, for me the less we mess with eyepieces the better. I tried a hyperion in my 115mm F 7 APO and against a Telvue there was a visual difference. This was the 24mm.

Alan.

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meteoriot

meteoriot

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I think I'll just stick with the eyepieces as they are. With a 2x Barlow I will have effectively a 4mm, 8mm, 12mm and a 24mm.

I have been offered a very nice 38mm 2" eyepiece and 2" diagonal that comes with a 1.25" adapter. Which I think will complete my setup.

What I would like to know is... Would putting a 2" diagonal on a nexstar8se be a sensible thing to do? That way I can use the hyperions and Barlow with the 1.25" adapter and the 38mm 2" for wide views?

Thanks everyone :)

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John

John

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Posted

The thing to check with the 8SE is, will a 2" diagonal fit beneath the scope when it's pointing towards the zenith or will it contact the mount as it slews ?

If it will fit then it's a sensible upgrade.

There are 2 ways to put a 2" diagonal on an SCT - the SCT fitting diagonal or via a push fit adapter when you can use diagonals with a standard push fitting, as used in refractors etc. The former is a lower profile approach if space between the back of the scope and the mount is tight.

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alan potts

alan potts

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Just to pick up on what John pointed out, I believe there was a thread about two weeks back started by a member that was having a very similar problem. This was with a WO diagonal that was designed for this very job. In the end they had made a small mistake and not fitted it correctly, after doing so it was fine. I am sure a normal diagonal will not slip underneath your scope when vertical, I remember measuring the length of mine in order to help but don't remember the size of it now.

It was on the part of the forum, check back about 2-3 weeks and see if you can locate the thread, it may help.

Alan

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