3x or 2x Barlow Lens?

Question

I have the option of getting either a 2x or 3x barlow lens, and I have currently have one 25mm eyepeice, and I am expecting a 9 mm eyepiece later this week. Should I go with the 2x or 3x. I am beginning to think that the three would be too much magnification on my 9mm eyepiece, and too little magnification for my 25 mm eyepiece. Currently with my 25 mm eyepiece I am only getting 22x magnification, so I really need this barlow lens.

And also, is there a difference between using a barlow lens, and using an eyepiece that would get you the same magnification? Which is better. Thanks

Answer 1

3x

Answer 2

I'm into astronomy and I have to disagree with the others about getting a 3x Barlow lens. My short answer is to buy a higher quality 2x barlow lens because it will give you better image quality, it won't overpower your telescope like the 3x barlow could, and it gives you a larger range of usable magnifications.

First, remember that light collection is the most important role of the telescope. Magnifying the image comes second. The more you magnify the image, the less amount of light the telescope will show you in the eyepiece. This means using very high magnifications will reduce image quality.

Now you might say that planets are very bright, and you could afford to lose light in its magnification. However, there is a limit to how much magnification your telescope will handle. To find out this limit, take the aperture of your telescope in inches and multiply it by 50, which gives you the best possible magnification your telescope can reasonably have. This assumes, however, that you have perfect "seeing" or atmospheric conditions. For example, a 4 inch telescope would have about a maximum of 200x while an 8 inch telescope would have a maximum of about 400x. Remember than you CAN magnify the image more, but image quality will NOT get better.

Also, magnification depends on the focal length of your telescope, and is equal to our telescope's focal length divided by the eyepiece's focal length. Your telescopes focal length is essentially doubled by adding a 2x barlow lens.

If you post the information about your telescope, I'd be glad to let you know specifically whether adding a 3x barlow would have too much magnification. The 3x barlow could work, but if you have a small aperture telescope (less than 6 inches) it might be too powerful with the 9mm.

There is another reason why I recommend you should get the 2x, which is because it gives you more options. With the 2x barlow, you "double" your eyepieces in effect, being able to work with 25mm, 12.5mm, 9mm, and 4.5mm. This is a great range of magnifications that you can use with your telescope. But with the 3x barlow, you also "double" your eyepieces but have slightly less variation. You would get a 25mm, 8.3mm, 9mm, and 3mm.

Furthermore, if you use a diagonal (such as on a refractor), you can actually use a 2x barlow as a 3x barlow.

Regular setup for a 2x barlow:

Lens/Telescope --> Diagonal --> 2x Barlow --> Eyepiece

3x setup using a 2x barlow:

Lens/Telescope --> 2x Barlow --> Diagonal --> Eyepiece

In conclusion, if you have done the math and are confident that your telescope can handle the magnification, and you are satisfied with the lesser variation of possible magnifications with the given eyepieces, then go ahead in get the 2x.

But my advice? I suggest you get a 2x barlow lens because of the greater variation in magnification and because it is very unlikely for the barlow to magnify beyond your telescope's abilities. You can use the extra money (as 3x barlows cost more than 2x) to buy a higher quality barlow that would produce sharper images.

EDIT:

So I just realized you indirectly informed us of your telescopes focal length (25mm eyepiece with 22x magnification is 550mm focal length). The maximum magnification you could achieve, assuming perfect atmospheric conditions, is 183x using a 3x barlow and the 9mm eyepiece. If your telescope has an aperture under 3.6 inches or 93mm, this would be too much magnification and the image would degrade.

Answer 3

There isn't any difference between using a barlow and a eyepiece of the same magnification. Barlow's, I find, are good for looking at planets, and planets, bring bright objects, look better under high magnifications. If I were you I'd get the 3x barlow lens.

Wide angle lenses are good for seeing nebulae and other such diffuse objects.

Narrow angle lenses are good for seeing planets and other bright objects.

I currently own and use a 3x barlow and am quite pleased with it.