Author Topic: Dim and unfocused view with Celestron X-Cel LX 5mm on ST80  (Read 237 times)

postbypopect

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Re: Dim and unfocused view with Celestron X-Cel LX 5mm on ST80
« Reply #15 on: January 22, 2018, 10:09:37 PM »
I have a 7mm x-cell lx, and a direct comparison with an ES 6.7 mm showed the Celestron eyepiece to have a "softer" view than the ES. Not startling, but definitely noticeable, and not surprising considering they are in different price classes. I rarely go over 50x with my ST80, and at 80x you are right near where the view really breaks down in that scope. If you really want to push that scope, possibly a higher quality eyepiece might help, IDK. The ST80 is what it is, but it's especially special with a 2" focuser and a 30mm 82 degree eyepiece, lol.

ingeblomes

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Re: Dim and unfocused view with Celestron X-Cel LX 5mm on ST80
« Reply #16 on: January 26, 2018, 01:23:39 AM »
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I recently bought a second handSky-watcher Startravel 80 as my first scope. I´ve bought some eyepieces since, among them theCelestron X-Cel LX 5mm. The look and feel of the eyepiece is great, but the view I get is dim and I can´t get it properly in focus. I suspected the view to be dimmer because there is a lot less light coming in with only 5mm of aperture (is it correct to use that term about the opening where light enters the eyepiece?), but not that the focus was that poor.

Can this perhaps be due to collimation not being a 100%? I haven´t been able to test the collimation since I don´t own a collimator tool yet. With such as small opening in the eyepiece I reckon it´ll be quite sensitive to any collimation problems?

Hi, Gauperaa. That scope has a 400mm focal length, so the 5mm eyepiece should produce 80x. That seems reasonable for that scope, as I own the Orion ST80 (similar refractor) and can achieve sharp enough images at that magnification. I don't think the eyepiece is beyond the theoretical limit of the scope so perhaps you have collimation problems. Although, I ask because of your location, how is your seeing typically? And how long are you allowing the scope to cool down to ambient temperature before viewing at that magnification? Any atmospheric turbulence can cause soft images at that magnification. The dim image is something you can't escape. Optical physics rule here, and you are producing a 1mm exit pupil which spreads the available light thin. You wouldn't refer to the eyepiece as a 5mm aperture, but rather a 5mm focal length. Divide the focal length of your scope by this number to calculate your effective magnification. Also divide this number by the focal ratio of your scope to calculate exit pupil. The larger the exit pupil the brighter the image. 1mm exit pupil is dim, 7mm exit pupil is bright. Hope this helps.
Seeing isn´t that great where I live. During Christmas however I brought the scope to my parent´s house which is in a more rural location with less light pollution. There I was able to try the 5mm on Jupiter during conditions with clear skies, but high winds locally and probably higher in the atmosphere. Anyway, the 5mm which gave me a nice view of it and 3 of its moons. Quite remarkable and almost awe inspiring to realize that you are looking at it with your own eyes. Still dimmer than I expected after reading reviews of the eyepiece, but I understand now that it is to be expected, especially with this scope. I´ll hang on to it though and use it on my next scope .

I think that is a prudent choice. The eyepiece is probably fine. It will only be brighter if the exit pupil is larger, which means using a faster focal ratio telescope. I have a Nagler 3-6 Zoom that I use for this eyepiece range, as others here have already mentioned. It is a fabulous eyepiece, but don't expect the image to be any brighter. I think Dick (havasman) makes a good point, that this really is meant to be a wide field scope, so low power views will allow it to shine. If it were me, I would keep the eyepieces to 10mm and longer for this scope and possible consider buying a 4" maksutov cassegrain as a complimentary scope for high power viewing of planets if that interests you, especially if you still want portability. Just a recommendation.

tanktositsoft

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Re: Dim and unfocused view with Celestron X-Cel LX 5mm on ST80
« Reply #17 on: January 26, 2018, 02:52:15 AM »
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I have a 7mm x-cell lx, and a direct comparison with an ES 6.7 mm showed the Celestron eyepiece to have a "softer" view than the ES. Not startling, but definitely noticeable, and not surprising considering they are in different price classes. I rarely go over 50x with my ST80, and at 80x you are right near where the view really breaks down in that scope. If you really want to push that scope, possibly a higher quality eyepiece might help, IDK. The ST80 is what it is, but it's especially special with a 2" focuser and a 30mm 82 degree eyepiece, lol.

I often consider replacing the stock focuser with a 2". Would make a fun super finder!

boysagiskest

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Re: Dim and unfocused view with Celestron X-Cel LX 5mm on ST80
« Reply #18 on: January 26, 2018, 07:11:28 AM »
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I recently bought a second handSky-watcher Startravel 80 as my first scope. I´ve bought some eyepieces since, among them theCelestron X-Cel LX 5mm. The look and feel of the eyepiece is great, but the view I get is dim and I can´t get it properly in focus. I suspected the view to be dimmer because there is a lot less light coming in with only 5mm of aperture (is it correct to use that term about the opening where light enters the eyepiece?), but not that the focus was that poor.

Can this perhaps be due to collimation not being a 100%? I haven´t been able to test the collimation since I don´t own a collimator tool yet. With such as small opening in the eyepiece I reckon it´ll be quite sensitive to any collimation problems?

Hi, Gauperaa. That scope has a 400mm focal length, so the 5mm eyepiece should produce 80x. That seems reasonable for that scope, as I own the Orion ST80 (similar refractor) and can achieve sharp enough images at that magnification. I don't think the eyepiece is beyond the theoretical limit of the scope so perhaps you have collimation problems. Although, I ask because of your location, how is your seeing typically? And how long are you allowing the scope to cool down to ambient temperature before viewing at that magnification? Any atmospheric turbulence can cause soft images at that magnification. The dim image is something you can't escape. Optical physics rule here, and you are producing a 1mm exit pupil which spreads the available light thin. You wouldn't refer to the eyepiece as a 5mm aperture, but rather a 5mm focal length. Divide the focal length of your scope by this number to calculate your effective magnification. Also divide this number by the focal ratio of your scope to calculate exit pupil. The larger the exit pupil the brighter the image. 1mm exit pupil is dim, 7mm exit pupil is bright. Hope this helps.
Seeing isn´t that great where I live. During Christmas however I brought the scope to my parent´s house which is in a more rural location with less light pollution. There I was able to try the 5mm on Jupiter during conditions with clear skies, but high winds locally and probably higher in the atmosphere. Anyway, the 5mm which gave me a nice view of it and 3 of its moons. Quite remarkable and almost awe inspiring to realize that you are looking at it with your own eyes. Still dimmer than I expected after reading reviews of the eyepiece, but I understand now that it is to be expected, especially with this scope. I´ll hang on to it though and use it on my next scope .[/quote]

I think that is a prudent choice. The eyepiece is probably fine. It will only be brighter if the exit pupil is larger, which means using a faster focal ratio telescope. I have a Nagler 3-6 Zoom that I use for this eyepiece range, as others here have already mentioned. It is a fabulous eyepiece, but don't expect the image to be any brighter. I think Dick (havasman) makes a good point, that this really is meant to be a wide field scope, so low power views will allow it to shine. If it were me, I would keep the eyepieces to 10mm and longer for this scope and possible consider buying a 4" maksutov cassegrain as a complimentary scope for high power viewing of planets if that interests you, especially if you still want portability. Just a recommendation.[/quote]
Funny you should mention that because I ordered a C90 Mak the other day for just that purpose , and to still have portability since the views from my balcony are limited.

David Williams

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Re: Dim and unfocused view with Celestron X-Cel LX 5mm on ST80
« Reply #19 on: January 26, 2018, 07:54:18 AM »
that will be a nice mini pair.

Richard Acosta

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Re: Dim and unfocused view with Celestron X-Cel LX 5mm on ST80
« Reply #20 on: January 31, 2018, 12:04:42 AM »
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I have a 7mm x-cell lx, and a direct comparison with an ES 6.7 mm showed the Celestron eyepiece to have a "softer" view than the ES. Not startling, but definitely noticeable, and not surprising considering they are in different price classes. I rarely go over 50x with my ST80, and at 80x you are right near where the view really breaks down in that scope. If you really want to push that scope, possibly a higher quality eyepiece might help, IDK. The ST80 is what it is, but it's especially special with a 2" focuser and a 30mm 82 degree eyepiece, lol.

I often consider replacing the stock focuser with a 2". Would make a fun super finder!
I´ve already considered it too . Been looking at this:http://agenaastro.co...speed-86mm.html, but don´t know if it´s worth it and if it wouldn´t be better to save up for an APO.

Lamichael Evans

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Re: Dim and unfocused view with Celestron X-Cel LX 5mm on ST80
« Reply #21 on: January 31, 2018, 01:13:51 AM »
I put a 2" focuser on my ST80 Celestron version. It does indeed transform the scope but also more than triples the cost once
you add a 2" diagonal. If I already ownedan ST80 I suppose I would do it all over again but it makes more sense to just to get
a better scope to begin with. Last year I bought an 80mm apo which I love. The ST80 still gets used though because it is a lot
of fun for what it does well.

sennessningwilch

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Re: Dim and unfocused view with Celestron X-Cel LX 5mm on ST80
« Reply #22 on: January 31, 2018, 10:29:22 AM »
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I have a 7mm x-cell lx, and a direct comparison with an ES 6.7 mm showed the Celestron eyepiece to have a "softer" view than the ES. Not startling, but definitely noticeable, and not surprising considering they are in different price classes. I rarely go over 50x with my ST80, and at 80x you are right near where the view really breaks down in that scope. If you really want to push that scope, possibly a higher quality eyepiece might help, IDK. The ST80 is what it is, but it's especially special with a 2" focuser and a 30mm 82 degree eyepiece, lol.

I often consider replacing the stock focuser with a 2". Would make a fun super finder!
While I have considered that as well, I have left it in 1.25" format as a finder. One must remember that it will be a very heavy finder when converted to 2". The largerfocuser will add some weight, as will the 2" diagonal, and then there is the heavy 2" widefield eyepiece. All told it will probably be about 2 pounds heavier than a max-field 1.25" configuration, but of course the available field with 2" would be about 43 to 59% wider depending on the 2" used.

Clint Trotter

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Re: Dim and unfocused view with Celestron X-Cel LX 5mm on ST80
« Reply #23 on: February 09, 2018, 09:03:09 AM »
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It's funny how folks commonly buy SCT's and try to make them widefield scopes and buy richfield scopes and try to make them do planetary.

Or 6" F/8 achros and try to make them do anything!