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Eyepiece advice


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So I have a Celestron Nexstar 6se telescope and it just has the eyepiece it came with on it. I figured I needed a much better eyepiece if I wanted to be able to see more objects in the sky and was just wondering what the best one to buy is. Looking online I've seen a few from what's called the OMNI series. This link: http://www.telescopesdirect.com.au/Accessories-TD/Telescope-Eyepiece shows the eyepieces they have and I was wondering if the bigger the eyepiece the better it is to see distant objects with. Also I wanted to get the Celestron universal t - adapter with integral Barlow lens 1.25 in and a T ring to take photos with. On the same site as the link above they have both the T - Adapter and a T ring but I am not sure if their T ring will fit my camera. I have a Canon EOS 1100D, and on the front of the camera on the edge of the lens it says 58mm but the T - ring in stock is says it only fits EOS cameras that are 35mm. I was wondering where I might be able to get a T ring that suits a 58mm camera that will ship to Australia and If the T - Adapter I mentioned above is a good accessory to invest in. I'm very new to all of this and don't know much about it so some helpful advice would be greatly appreciated :)

thanks

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Your telescope has come with a standard equipment eyepiece of 25mm focal length which in the 6se will result in a magnification of 60x (telescope focal length divided by eyepiece focal length which is 1500/25). As such you can see that the shorter the focal length of the EP, the higher the magnification. So for example a 10mm EP will yield a magnifcation of 150x in your scope. You will also find that the higher the magnifcation the smaller the field of view. I suspect that the standard EP that came with the 6se is plossl design with an apparent field of view (AFOV) of 50 degrees. To calculate the field of view in your scope, you simply divide the AFOV by the magnifcation achieved with the EP in your scope. So in your case, 50 divided by 60 equals 0.83 degrees. To put that in context, the full moon is about half a degree across, so you can comfortably fit the entire disc of the moon in the EP.

Now there is a limit to the magnifcation you can achieve with any optical system before the quality of the image really starts to break down. The typica rule of thumb is 50-60x per inch of aperture (2-2.5x per mm of aperture) which in your scope would be 300-350x. HOWEVER, rarely will atmospheric conditions allow you to ever use a magnifcation that high. Typically for the UK, 200-250x really is the upper limit, and I personally find I rarely go even as high as 200x. So when considering a short focal length EP, take into consideration that particularly short ones may not get much use. I find I can enjoy exceptional views of the planets at around 150-180x.

I cannot speak to the quality of the EPs you have highlighted, but I would suggest that you purchase from a UK based retailer rather than US (as per your link) as you will be liable for import duty and VAT upon arrival which when combined with shipping costs can rapidly erode any price advantage plus you loose the convenience of a nearby dealer should anything go wrong.

I am afraid I know very little about the camera and t-adaptors you mention so will leave other SGL members to share their knowledge on that subject. But just a few words of caution about photography with the 6se. As the scope is mounted in Alt Az (i.e. not polar aligned), the scope will track an object using 2 axis of motion rather than one, which will result in a phenomena known as field rotation. This will cause the entire field to rotate around a central point, which would over time blur out the detail you are trying to capture. This would not be an issue for lunar or plantary imaging where short exposures are required, but if you are thinking about deep sky objects, you will find the process very challenging. My second concern would be hanging a heavy DSLR body on the back of the scope which might unbalance the scope and strain the motors. Also you may find the altitude you can point to quite limited as the camera body may hit the mount. If lunar and planetary imaging is a goal, you would be better served by a webcam or purchasing a dedicated planetary imager. They are small and far more effective than a DSLR for that task.

If deep sky is a goal, may I suggest you purchase the book "Making Every Photon Count" (written by an SGL member) as it will highlight all the challenges you will face, and save you from purchasing equipment which may not be fit for purpose. http://www.firstligh...e-richards.html

Clear skies,

Edited by DirkSteele
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Your telescope has come with a standard equipment eyepiece of 25mm focal length which in the 6se will result in a magnification of 60x (telescope focal length divided by eyepiece focal length which is 1500/25). As such you can see that the shorter the focal length of the EP, the higher the magnification. So for example a 10mm EP will yield a magnifcation of 150x in your scope. You will also find that the higher the magnifcation the smaller the field of view. I suspect that the standard EP that came with the 6se is plossl design with an apparent field of view (AFOV) of 50 degrees. To calculate the field of view in your scope, you simply divide the AFOV by the magnifcation achieved with the EP in your scope. So in your case, 50 divided by 60 equals 0.83 degrees. To put that in context, the full moon is about half a degree across, so you can comfortably fit the entire disc of the moon in the EP.

Now there is a limit to the magnifcation you can achieve with any optical system before the quality of the image really starts to break down. The typica rule of thumb is 50-60x per inch of aperture (2-2.5x per mm of aperture) which in your scope would be 300-350x. HOWEVER, rarely will atmospheric conditions allow you to ever use a magnifcation that high. Typically for the UK, 200-250x really is the upper limit, and I personally find I rarely go even as high as 200x. So when considering a short focal length EP, take into consideration that particularly short ones may not get much use. I find I can enjoy exceptional views of the planets at around 150-180x.

I cannot speak to the quality of the EPs you have highlighted, but I would suggest that you purchase from a UK based retailer rather than US (as per your link) as you will be liable for import duty and VAT upon arrival which when combined with shipping costs can rapidly erode any price advantage plus you loose the convenience of a nearby dealer should anything go wrong.

I am afraid I know very little about the camera and t-adaptors you mention so will leave other SGL members to share their knowledge on that subject. But just a few words of caution about photography with the 6se. As the scope is mounted in Alt Az (i.e. not polar aligned), the scope will track an object using 2 axis of motion rather than one, which will result in a phenomena known as field rotation. This will cause the entire field to rotate around a central point, which would over time blur out the detail you are trying to capture. This would not be an issue for lunar or plantary imaging where short exposures are required, but if you are thinking about deep sky objects, you will find the process very challenging. My second concern would be hanging a heavy DSLR body on the back of the scope which might unbalance the scope and strain the motors. Also you may find the altitude you can point to quite limited as the camera body may hit the mount. If lunar and planetary imaging is a goal, you would be better served by a webcam or purchasing a dedicated planetary imager. They are small and far more effective than a DSLR for that task.

If deep sky is a goal, may I suggest you purchase the book "Making Every Photon Count" (written by an SGL member) as it will highlight all the challenges you will face, and save you from purchasing equipment which may not be fit for purpose. http://www.firstligh...e-richards.html

Clear skies,

Everything he says Edited by rowan46
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