How low can you get?

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How low can you get?

Postby Aratus » Mon Feb 08, 2016 5:15 pm

Time for me to ask a question!

Has anyone used a low magnification eyepiece for an 8" SCT? (higher than 25mm) How low can you get without vignetting or the secondary mirror appearing? What were the specifications of the eyepiece?
I use an 11" Celestron SCT (CPC 1100) on an equatorial wedge, housed in a 2.2m Pulsar observatory. I use a ZWO ASI1600MC and Canon 500D for imaging.
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Re: How low can you get?

Postby dave.b » Tue Feb 09, 2016 10:12 pm

I have and use a Baader 36mm Aspeheric Hyperion EP. Fantastic for low power wide angle views with a 2m f/l telescope. Its also useful when you are playing hunt the calibration star during the mount's setup!

I haven't noticed any vignetting with it. Next time the moon is full-ish I 'll try and remember to have a closer look.

Dave B.
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Re: How low can you get?

Postby Aratus » Wed Feb 10, 2016 7:39 pm

Great.

I have a Celestron X-cel 25m which is fine but I have wondered about getting a 31 or 36mm. It is certainly a lot less frustrating to use a wide angle eyepiece when aligning. I usually get it within the view of a 25mm, but something wider wouldn't hurt.
I use an 11" Celestron SCT (CPC 1100) on an equatorial wedge, housed in a 2.2m Pulsar observatory. I use a ZWO ASI1600MC and Canon 500D for imaging.
Aratus
 
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Location: East Lincolnshire

Re: How low can you get?

Postby dave.b » Thu Feb 11, 2016 1:01 am

I should have said that the 36mm EP is 2" diameter one at the nose piece.
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Re: How low can you get?

Postby Aratus » Sun Feb 14, 2016 7:04 pm

I did wonder about that. How does that work in practical terms? Would I need another, larger, star diagonal, or what?
I use an 11" Celestron SCT (CPC 1100) on an equatorial wedge, housed in a 2.2m Pulsar observatory. I use a ZWO ASI1600MC and Canon 500D for imaging.
Aratus
 
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Joined: Tue Jan 12, 2016 2:17 pm
Location: East Lincolnshire

Re: How low can you get?

Postby dave.b » Sun Feb 14, 2016 11:07 pm

Yes, you'll need a 2" star diagonal. Get a dielectric one.

Dave B.
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Re: How low can you get?

Postby Aratus » Tue Feb 16, 2016 7:05 pm

You just know what I'm going ask you now, don't you ? :D

What is an dielectric eyepiece? I'd always assumed they were rather passive devices! :?
I use an 11" Celestron SCT (CPC 1100) on an equatorial wedge, housed in a 2.2m Pulsar observatory. I use a ZWO ASI1600MC and Canon 500D for imaging.
Aratus
 
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Joined: Tue Jan 12, 2016 2:17 pm
Location: East Lincolnshire

Re: How low can you get?

Postby Gfamily2 » Tue Feb 16, 2016 7:25 pm

Aratus wrote:You just know what I'm going ask you now, don't you ? :D

What is an dielectric eyepiece? I'd always assumed they were rather passive devices! :?


It's the mirror in the diagonal that's dielectric - basically it's a multi layered mirror surface that gives up to 99% reflectivity.

Details from the WIki

I accidentally bought myself a 2" eyepiece - Explore Scientific were selling them in the US for $20, so I bought it, not realising the larger size. I managed to get a normal glass 2" mirror diagonal on ebay for about £27. It's good enough to be worth buying for a single eyepiece.
Scopes: Meade 8" SCT, Skywatcher 127mm Mak, Raffle winner of SW ST80
For imaging: Pentax K5, Asda webcam, Star Adventurer (new toy)
For companionship: Mid Cheshire Astronomical Group.
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Re: How low can you get?

Postby Aratus » Tue Feb 16, 2016 11:12 pm

Ahh - its the way it is manufactured! There was me thinking that it ran off a battery! :oops: Every photon counts I suppose.

I'll have a look around after I've seen the contents of my piggy bank! :)
I use an 11" Celestron SCT (CPC 1100) on an equatorial wedge, housed in a 2.2m Pulsar observatory. I use a ZWO ASI1600MC and Canon 500D for imaging.
Aratus
 
Posts: 809
Joined: Tue Jan 12, 2016 2:17 pm
Location: East Lincolnshire

Re: How low can you get?

Postby Gfamily2 » Tue Feb 16, 2016 11:32 pm

Aratus wrote:Ahh - its the way it is manufactured! There was me thinking that it ran off a battery! :oops: Every photon counts I suppose.

I'll have a look around after I've seen the contents of my piggy bank! :)


I thought about the difference between a 92% reflective standard diagonal and a 99% reflective dielectric diagonal, and the difference between £27 cost and a £135 cost.

A $20 bargain isn't a bargain if it costs £135 to use it :)
Scopes: Meade 8" SCT, Skywatcher 127mm Mak, Raffle winner of SW ST80
For imaging: Pentax K5, Asda webcam, Star Adventurer (new toy)
For companionship: Mid Cheshire Astronomical Group.
(Not a moderator)
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