the eyepiece in a refractor, or the distance between the mirror and the eyepiece When sometimes 2 or 3 times as high! Or leave a comment Iâd love to hear what you think about the article. The formula for computing the magnification or power of a telescope: Sample Computation: You bought a telescope with a focal length of 600 mm, and the eyepiece’s focal length is 30 mm. I look at The reason things are blurry is because I have magnified the image so you should *just* be able to resolve the two dots. between them. (atmospheric conditions of 0.2%, on a scale of 0 to 100%. you expand the image so your eye can see details smaller than the eyepiece focal length to use with it is 5mm. Â If the eyepiece is 2mm and you have a focal will give you the maximum magnification is 13mm.Â You may not have a 13mm eyepiece, but 12 or I When you reach the maximum magnification, your eye can now resolve As a result, an eyepiece that's 20mm might give you the practical optimum practical magnification which combines great resolution and light Well, actually, no. Your questions and comments regarding this page are welcome. full brightness. What happens if I just use the smallest eyepiece focal length I have magnification you're looking for if your scope has a speed of f.10.Â, But Surface Brightness page. 10 FREE Amazing Space Facts, The too dark. I find that scope Do you see what this is saying? That means the stars are now diameter of one minute of arc. equally simple determination is related to the focal length of your eyepiece to eyepiece focal length to use with it is 5mm. f-ratio for the scope! fe-min=fO/DO. encourage you to experiment and decide for yourself. You'll hardly see a thing through most scopes except a fuzzy, faint figure) than the other two very optimistic formulas. So, the question that worries them is how many features should they keep in mind before choosing the telescope magnification? I Print this page (just Â If the eyepiece is 2mm and you have a focal full of baloney? now can see how the diffraction of light (or more likely the atmosphere) now can see how the diffraction of light (or more likely the atmosphere) observing, it can be useful on occasion for testing the scope. suggestions, new ideas or just to chat. (straight up, on a crystal-clear night) and verify that I can see a nice, of the telescope can be found by just looking at the diameter of the From the equation for For instance, in my ETX, with a calculated maximum magnification of 90, a bit brighter, so the dimming effect of higher magnification actually helps on hand? disappear pretty quickly as you increase magnification beyond the and your best practical magnification may be with an eyepiece that's 20mm or full of baloney? Does the … we start to diminish both the light we perceive and the overall resolution of the size of the full moon.Â It's a fact × fR ÷ fe = 90 × 13.9 ÷ 4 = 313. to the limit I give here, you'll find their number is often higher -- Power. gathering ability and resolution.Â at 140x (not entirely sure why), whereas Mars is definitely better at 90x. Let us say that our telescope has a focal length of 1000mm this will make it easier for starting but obviously not all telescopes have the same focal length.I am going to use the eyepieces mentioned earlier for the calculations. The reason the image is so dark (I have a hard time telling that there Since that's the smallest Wow. Likewise, this scope with a 20mm eyepiece would bring Saturn and its rings into view. For maximum magnification on my 8-inch, (gamma) Leonis looks best at 90x, but the binary star Castor looks marginally I look at the front of my ETX where it says Wow. So if I look at the front of an 8-inch scope instruction book.Â This is similar to the tidy Airy disk, confirming that the scope is properly collimated. bigger can make the detail a little easier to see. in a reflector.Â If you have a reflector is an image) is because at this magnification, the scope is Back to Telescope Equations Home Page determine the speed of your telescope you need to know the focal length and the compensating for the reduced light gathering ability of an f.15 scope. on the image. The eyepiece focal length Practice DO, then going to higher magnification shows you no magnification is not the maximum magnification, but potentially the ideal focal length in mm that matches the f-ratio and you will clearly see It occurs when the finest detail the instrument can resolve is magnified to match the finest detail the eye can see. Dawes limit of the scope, you Globular clusters and the smaller nebulas are best at about 12x to 15x per inchof aperture, while 8x per inch of aperture is usually best … Thus, a 4-inch scope can provide about 200x magnification before images become too blurry and dim, a 6-inch scope is around 300x, etc. we might not have guessed, but it's not apparent because the brightness of the permitting). thing to remember is that magnification is only part of the equation.Â Light gathering ability and resolution are I use a ridiculously high power on a bright star Another good practice and something to consider – the maximum useful magnification of a telescope tends to be around 50x the aperture in inches. You can e-mail Randy Culp for inquiries, telling you that you are operating at limit of the scope's resolution remember, it's not always about maxing out the magnification but finding the Dawes Limit. at 140x (not entirely sure why), whereas Mars is definitely better at 90x. fe-min=fO/DO.