What eyepiece would get the most power out of my telescope?

Hi, Im new to astronomy. I recently bought a skywatcher explorer 130P. It has a 130mm (5.1") parabolic mirror with a focal length of 650mm. I have 2 eyepieces that came with it, a super 10 long eye relief and a less powerful super 25 wide angle long eye relief. I have no idea what those figures mean but I got a great view of jupiter and its 4 main moons the first time I took it out. I feel like it has already paid for itself. I was looking at the moon earlier and I feel like I could get a better magnification than I was getting. I heard that too powerfull of an eyepiece can be bad if the telescope cant handle it. How do I know what my scope is able for? And is a barlow lense a good idea? I would really appreciate any advice. Thanks!

Hi Tianman,

The principal factor that determines the capabilities of your scope is its aperture - 130mm. The larger the aperture, the brighter the image and the smaller the details it can resolve. The magnification is calculated by dividing the focal length of the scope, 650mm, by the focal length of the eyepiece, 10mm or 25mm in your case, giving 65 times or 26 times, respectively. To get a higher magnification you would need a shorter focal length eyepiece. However, increasing the magnification too much is counterproductive, because it does not increase the detail that can be observed, which is limited by the aperture, and because the image becomes darker as the magnification is increased. Your scope would give a magnification of 260 times, if you used an eyepiece of 2.5 mm focal length. In practice, that eyepiece might be quite difficult to use because the beam of light it would give would be very narrow. You could certainly try a 4mm eyepiece, I have one that you are welcome to borrow. Keeping you Newtonian well collimated will also be crucial to getting the best out of it, a poorly collimated scope will give fuzzy images even at low magnification.

Have a look at www.stargazing.net/naa/scopemath.htm to get more details on these topics. Keep enjoying your new scope and let us know how you get on.

Mike

Thank's Mike! That's very helpful. I will invest in a 4mm eyepiece then. Ill have a look on ebay. I will probably get a 2.5mm one also considering I have access to a very good very expensive tripod that im hoping will cancel out some of the wabble you mentioned. Would the addition of a barlow lense be too much along with that much magnification do you think?

I think it would be wise to take up Mike's offer and borrow his eyepiece first, just to save you wasting money if the image is blurred. Stay away from ebay until you are absolutely sure about what you want.

I also think I am right in saying that there is no such thing as a 2.5mm eyepiece (Televue Radian maybe?). I think Mike was only using that as an illustration of the theoretical magnifying power of your scope.

Borrow the 4mm, and if it just gives a blur, invest in a 5mm or 6mm. A 5mm will give you a magnification of 130x, which is very acceptable for planetary viewing. In Ireland, you would be lucky to be able to use over 200x on any given night, with any telescope, just because of the general atmospheric conditions.

I think Stevie's advice is sound. I would check out a 4 mm eyepiece to see if the view is still acceptable (send a PM and I will happily lend you mine). If it is, then a low power Barlow (no more than 2x) in combination with a 5mm or 6mm eyepiece would be worth a try for those occasions when atmospheric conditions allow higher magnification (> 200x).

Mike