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Old 05-10-2019, 11:15 AM
Lioness (Lina)
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Question Refracter Equivalent to a 11 inch Reflector ?

Hello! I have a Celestron edgeHD 11inch Reflector and I'm keen on selling it to get a Refractor, but what would be the equivalent in terms of magnification?

Updated edit: I'm interesting in targeting the following objects; planets, moons, comets, eclipses and ISS.

Last edited by Lioness; 05-10-2019 at 02:30 PM.
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Old 05-10-2019, 11:42 AM
casstony
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Hi Lina, it would be easier to answer your question if you let us know what objects you wish to observe - planets, faint nebulae, double stars?
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Old 05-10-2019, 12:51 PM
gaseous (Patrick)
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Originally Posted by Lioness View Post
Hello! I have a Celestron edgeHD 11inch Reflector and I'm keen on selling it to get a Refractor, but what would be the equivalent in terms of magnification?

Hi Lina, and welcome.


Your EdgeHD 11 inch is a Schmidt-Cassegrain telescope, so it's a combination of lens (refractor) and mirror (reflector) components. With your scope having a focal length of 2800mm, which determines your magnification, you're unlikely to find a straight refractor to achieve the same focal length. Most readily available refractors these days have a maximum focal length of 1500mm or so, meaning you would only get around 50-55% of the magnification with the same eyepiece. A 1500mm refractor is starting to get on the large side of things too, and would have an aperture of 6" or less, meaning you're getting less light/resolving power than the 11". As Casstony said, your scope choice would depend on your preferred target objects.
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Old 05-10-2019, 01:49 PM
Wavytone
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Well, a 280mm refractor objective is available for 100k euros, with exchange shipping and duties etc close to $200k. A mount for such a beast is another $150k. Neither are portable - you’d need an observatory and a block of land to put it on so not much change out of half a million...

You might need to win lotto.
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Old 05-10-2019, 02:17 PM
Lioness (Lina)
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Originally Posted by casstony View Post
Hi Lina, it would be easier to answer your question if you let us know what objects you wish to observe - planets, faint nebulae, double stars?
Oops sorry, I didn't mean to leave that part out!
Planetery objects and moons, eclipses, comets and hopefully the ISS.
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Old 05-10-2019, 02:20 PM
Lioness (Lina)
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Originally Posted by Wavytone View Post
Well, a 280mm refractor objective is available for 100k euros, with exchange shipping and duties etc close to $200k. A mount for such a beast is another $150k. Neither are portable - you’d need an observatory and a block of land to put it on so not much change out of half a million...

You might need to win lotto.

You mean a 2800mm refractor?
And yes an observatory is the first thing on the list if I win the lotto lol
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Old 05-10-2019, 02:27 PM
Lioness (Lina)
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Originally Posted by gaseous View Post
Hi Lina, and welcome.


Your EdgeHD 11 inch is a Schmidt-Cassegrain telescope, so it's a combination of lens (refractor) and mirror (reflector) components. With your scope having a focal length of 2800mm, which determines your magnification, you're unlikely to find a straight refractor to achieve the same focal length. Most readily available refractors these days have a maximum focal length of 1500mm or so, meaning you would only get around 50-55% of the magnification with the same eyepiece. A 1500mm refractor is starting to get on the large side of things too, and would have an aperture of 6" or less, meaning you're getting less light/resolving power than the 11". As Casstony said, your scope choice would depend on your preferred target objects.
Geez that's some great information there, thank you for simplifying it! Yes, as I answered Casstony, my preferred targets are planetary objects, moons, eclipses, comets and the ISS.

Thank you for your welcome
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Old 05-10-2019, 02:28 PM
casstony
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The C11 Edge will work well for your observing targets provided it is collimated and cooled to ambient temperature.

A 5" refractor would also work well for your targets and needs less works to make it perform well - you just need to wait for 30 minutes or so for the lens to cool and it will give sharp images. It's also more portable than the C11.

A 6" refractor would be even better but can be quite long and heavy and need a tall, solid mount.
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Old 05-10-2019, 02:37 PM
Lioness (Lina)
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Originally Posted by casstony View Post
The C11 Edge will work well for your observing targets provided it is collimated and cooled to ambient temperature.

A 5" refractor would also work well for your targets and needs less works to make it perform well - you just need to wait for 30 minutes or so for the lens to cool and it will give sharp images. It's also more portable than the C11.

A 6" refractor would be even better but can be quite long and heavy and need a tall, solid mount.
Thank you! Do refractors give a sharper or clearer image of planets than a reflector? Or is that just a myth.
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Old 05-10-2019, 02:44 PM
casstony
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If you're inexperienced at collimating or the Schmidt cassegrain isn't cooled it won't give sharp images at medium to high power.

The refractor will always give sharp images after half an hour or so, up to whatever magnification the atmosphere allows on a given night. Refractors generally stay in collimation unless they get a sharp bump (during shipping or by being dropped for example).
I have a feeling that you would be happier with a refractor.
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Old 05-10-2019, 03:26 PM
Wavytone
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You mean a 2800mm refractor?
Nope ... http://apm-telescopes-englisch.shopgate.com/item/363134

Cost of refractors goes up astronomically past 130mm aperture... 510mm fir 495,000 euros...

A C11 is a bargain in comparison.

Last edited by Wavytone; 05-10-2019 at 03:49 PM.
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Old 05-10-2019, 03:43 PM
Lioness (Lina)
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Originally Posted by Wavytone View Post
Nope ... http://apm-telescopes-englisch.shopgate.com/item/363134

Cost of refractors goes up astronomical past 130mm aperture... 510mm fir 495,000 eyrie...

A C11 is a bargain in comparison.
Oh wow! ..
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Old 05-10-2019, 03:49 PM
Lioness (Lina)
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Originally Posted by casstony View Post
If you're inexperienced at collimating or the Schmidt cassegrain isn't cooled it won't give sharp images at medium to high power.

The refractor will always give sharp images after half an hour or so, up to whatever magnification the atmosphere allows on a given night. Refractors generally stay in collimation unless they get a sharp bump (during shipping or by being dropped for example).
I have a feeling that you would be happier with a refractor.
Yeh I was contemplating on selling my c11 edge hd and cgx mount for a refractor hoping I could find one that would give me the same magnification power, considering I also use a 9mm televue eyepiece.
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Old 05-10-2019, 04:09 PM
Wavytone
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Well, 9mm gives 300X or so and for a refractor...

You could buy a cheap 6” achromatic but that won’t be much good past 100X, you do need premium glass such as an ED doublet something like this...
http://apm-telescopes-englisch.shopg...m/333631363633

But bear in mind this no lightweight and will need a mount - at the minimum an AZEQ6 or G-11. The downside is it’s not much good for DSOs as the aperture is small. The fun begins at 200mm (eg a C8).

Alternative along focal length Newtonian(dobsonian), or a schiefspiegler (you will have to build that)... or a 9” maksutov like my MK91 and these are very rare.
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Old 05-10-2019, 04:10 PM
croweater (Richard)
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Hi Lina, Just in case you don't know divide your eyepiece focal length into your telescope focal length to work out the magnification. In your 2800mm fl edge your 9mm eyepiece will give you 311x. This is pretty high and is only useful/achievable on nights with good seeing. Cheers, Richard.
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Old 05-10-2019, 04:22 PM
casstony
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If your CGX mount is permanently situated or on wheels and portability isn't an issue, it would be a good mount for a 6" refractor such as the ED150 in the classifieds (which happens to be in Adelaide).

If you want to move to a more portable mount you might need to consider something like a Skywatcher HEQ5 with a Skywatcher ED120 refractor. There's a massive difference in portability between those two setups but the ED120 will still give nice planetary views without breaking the bank.
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Old 05-10-2019, 05:04 PM
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cometcatcher (Kevin)
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Keep the SCT. No affordable refractor will come close to it.
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Old 05-10-2019, 07:01 PM
Lioness (Lina)
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Keep the SCT. No affordable refractor will come close to it.
Thanks for the advice
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Old 05-10-2019, 07:02 PM
Lioness (Lina)
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Hi Lina, Just in case you don't know divide your eyepiece focal length into your telescope focal length to work out the magnification. In your 2800mm fl edge your 9mm eyepiece will give you 311x. This is pretty high and is only useful/achievable on nights with good seeing. Cheers, Richard.
Oooh thank you, I never knew how to do that before!
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Old 05-10-2019, 07:06 PM
Lioness (Lina)
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If your CGX mount is permanently situated or on wheels and portability isn't an issue, it would be a good mount for a 6" refractor such as the ED150 in the classifieds (which happens to be in Adelaide).

If you want to move to a more portable mount you might need to consider something like a Skywatcher HEQ5 with a Skywatcher ED120 refractor. There's a massive difference in portability between those two setups but the ED120 will still give nice planetary views without breaking the bank.
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