Author Topic: Dim and unfocused view with Celestron X-Cel LX 5mm on ST80  (Read 336 times)

cytiwitqua

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Dim and unfocused view with Celestron X-Cel LX 5mm on ST80
« on: January 03, 2018, 08:25:58 PM »
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?



Isaac Griffin

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Re: Dim and unfocused view with Celestron X-Cel LX 5mm on ST80
« Reply #1 on: January 08, 2018, 07:37:39 PM »
My biggest complaint with high power oculars is the diminishing light they gather. Always seem very dim compared to low power oculars. Guess that is a sacrifice we must make to get in close. Also, with a 5mm you need almost perfect seeing conditions. Period! I rarely use mine for that reason. Mark

headsbigwardsubs

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Re: Dim and unfocused view with Celestron X-Cel LX 5mm on ST80
« Reply #2 on: January 08, 2018, 11:13:18 PM »
That scope is designed for richfield / widefield use. Like any short achromat, it isn't going to perform well with any high power eyepiece.

bermordliro

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Re: Dim and unfocused view with Celestron X-Cel LX 5mm on ST80
« Reply #3 on: January 09, 2018, 04:04:12 PM »
Quote
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.

Jacob Cota

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Re: Dim and unfocused view with Celestron X-Cel LX 5mm on ST80
« Reply #4 on: January 11, 2018, 11:50:57 PM »
I wouldn't go any more than 8mm with that scope on a perfect night.

junktranasop

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Re: Dim and unfocused view with Celestron X-Cel LX 5mm on ST80
« Reply #5 on: January 12, 2018, 02:27:56 AM »
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5mm isn't the size of the opening, it's the focal length of the eyepiece. Smaller focal length eyepieces yield higher power, but at the expense of brightness of the image and apparent fuzziness if you are magnifying near what the scope's objective diameter will provide. You're at 80x magnification with that combination of scope and eyepiece, so I'm not surprised you'd see a bit of dimming /blurring. You should be OK at that magnification, though. Could be that bad seeing (atmospheric conditions), unclean optics, or dew/breath condensation are contributing to the dimness/blurriness... what other eyepieces do you have and how are they? It's to be expected that the higher the magnification, the worse the dimness/blurriness.

I´ve got the standard ones that come with the scope, the 25mm and the 10mm. I´ve also got the celestron kit for the the Astromaster with a 15mm kelner and a 6mm plossl. The other day I got a Celestron Omni 32mm plossl which is my favorite so far - it´s bright and sharp. Thank you for the explanation of eyepiece focal length.

Thomas Homer

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Re: Dim and unfocused view with Celestron X-Cel LX 5mm on ST80
« Reply #6 on: January 12, 2018, 04:19:21 AM »
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That scope is designed for richfield / widefield use. Like any short achromat, it isn't going to perform well with any high power eyepiece.


And in my experience, the 5mm Xcel LX is the weakest offering in the lineup. I had two and both were "muddy". Try a Paradigm 5mm (aka Starguider), it's much better.

David Allen

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Re: Dim and unfocused view with Celestron X-Cel LX 5mm on ST80
« Reply #7 on: January 12, 2018, 07:43:57 AM »
Quote
Quote

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 .

opalytun

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Re: Dim and unfocused view with Celestron X-Cel LX 5mm on ST80
« Reply #8 on: January 12, 2018, 09:59:30 AM »
Quote
Quote

That scope is designed for richfield / widefield use. Like any short achromat, it isn't going to perform well with any high power eyepiece.


And in my experience, the 5mm Xcel LX is the weakest offering in the lineup. I had two and both were "muddy". Try a Paradigm 5mm (aka Starguider), it's much better.
Thank you, I will look into that .

olexecin

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Re: Dim and unfocused view with Celestron X-Cel LX 5mm on ST80
« Reply #9 on: January 12, 2018, 07:07:00 PM »
Your scope looks like what we Americans call the ST80. As others have said, it's not the greatest scope for high powered views.

Also, I have purchased three eyepieces that went straight to the trash can: The X-Cel LX 5mm, the Vixen NP 15mm, and the Agena SWA 10mm. The X-Cel holds a special place in my heart as the first eyepiece I got rid of (I pitched a Barlow well before that) in that manner.

bardersgarli

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Re: Dim and unfocused view with Celestron X-Cel LX 5mm on ST80
« Reply #10 on: January 13, 2018, 11:58:39 AM »
Quote
Your scope looks like what we Americans call the ST80. As others have said, it's not the greatest scope for high powered views.

Also, I have purchased three eyepieces that went straight to the trash can: The X-Cel LX 5mm, the Vixen NP 15mm, and the Agena SWA 10mm. The X-Cel holds a special place in my heart as the first eyepiece I got rid of (I pitched a Barlow well before that) in that manner.

Do you have a recommendation for a 5mm eyepiece? or 6mm? I would love to know about a good barlow too as the one I have from the Celestron starter kit doesn´t seem to be the best.

Bobby Cruz

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Re: Dim and unfocused view with Celestron X-Cel LX 5mm on ST80
« Reply #11 on: January 13, 2018, 02:35:36 PM »
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Quote

Also, I have purchased three eyepieces that went straight to the trash can: The X-Cel LX 5mm, the Vixen NP 15mm, and the Agena SWA 10mm. The X-Cel holds a special place in my heart as the first eyepiece I got rid of (I pitched a Barlow well before that) in that manner.

Do you have a recommendation for a 5mm eyepiece? or 6mm? I would love to know about a good barlow too as the one I have from the Celestron starter kit doesn´t seem to be the best.

You can look at my sig. to see what I use for Barlows and a 5mm eyepiece. The 5mm was a freebie bundled with my 120mm refractor. Flocking the tube helps considerably when looking at the moon. The eyepiece helped "retire" a 5mm Hyperion (which wasn't bad, actually), and eliminate a Barlowed, 10mm ortho and Barlow combination). I also hear good things about the 5mm ED series, like the Paradigm or Starguider ED. I own the 12mm, and it's a keeper.

​My 2x Barlow is no longer being made. For your refractor, I would recommend a 3 element, 2x job, like the Celestron X-Cel Lx 2x. Optically the X-Cel Barlows are much better than the 5mm.

Lamichael Evans

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Re: Dim and unfocused view with Celestron X-Cel LX 5mm on ST80
« Reply #12 on: January 13, 2018, 10:28:55 PM »
I have used my ST80 some at higher power (80x and above using a 5mm Nagler and 3-6mm Planetary Nagler zoom), but it is not really suited to planetary viewing. The problem is that it is a short ratio achromatic refractor operatingat f/5. Chromatic aberration blurs the image as the power increases. I can use it up to 133x or so to resolve some stars in a dozen globular clusters, but the planetary detail is already breaking down at 80 - 100x.

You can examine the diffraction rings of a moderately bright star at 80x (preferably more like 100-150x) to see if there is substantial coma/flaring off in one direction or the other. If you see something like this then there may be some misalignment of the objective cell, the focuser, some play in the focuser, or even a misaligned diagonal. You can rule out the diagonal by doing some checking without it. I have had some horribly misaligned mirror diagonals.

Another problem is often the retaining ring is overtightened on the objective. This produces triangular "pinch." As I recall I had to loosen then lightly retighten the retainer to relieve pinch in my ST80. I did this with the scope pointed up and level so that I could tap the sides of the cell and try to get the objective to settle evenly and centered with one another.

Adam Watkins

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Re: Dim and unfocused view with Celestron X-Cel LX 5mm on ST80
« Reply #13 on: January 16, 2018, 06:24:48 AM »
Another clubmember shared views through his ST80 last week. It worked very well with 31 T5 Nagler and OK with 11mm TV Plossl but below that the views were bested by other scopes on hand.
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.

Micheal Luther

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Re: Dim and unfocused view with Celestron X-Cel LX 5mm on ST80
« Reply #14 on: January 21, 2018, 11:01:24 AM »
I have the 5mm X-cel LX and it is very sharp. Is it possible to get an exchange? I have found the XCel line to be a great value. The other option is the Meade HD60 line of eyepieces