Basic Knowledge: Eyepieces

Amateur Astronomy for Beginners: Eyepieces

Category:

Science & Technology

Tags:

• amateur
• astronomy
• beginner
• telescope
• eyepieces

[posterpopman]

HI there, about the 2x barlow, you say that the barlow doubles the magnification of the eyepiece. Ive heard from another video on youtube that the barlow is actually doubling the focal length of the Telescope and not the eyepiece. So now this is confusing to a beginner like myself. Can you clarify please. Excellent videos. Thanks for sharing.

[truemartian]

@posterpopman That is precisely how the barlow works to increase magnification. Increasing the focal length of the telescope has the effect of increasing the magnification. You can see this by playing around with the numbers a little bit in the magnification formula: telescope focal length / eyepiece focal length = magnification.

[posterpopman]

@truemartian So the eyepiece is not magnified, the 15mm stays at 15mm and so on, and it is only the Telescope focal length that is magnified. Is this correct?

Thanks for replying so quickly.

[truemartian]

@posterpopman The magnification that the eyepiece provides is doubled by a 2X barlow and tripled by a 3X barlow. For example, say you have a 15mm eyepiece on a 1200mm telescope. This provides you with 80X magnification. Applying the 2X barlow will double the 80X magnification to 160X. How the barlow does this is another story. The barlow does this by either lengthening the focal length of the telescope OR (and this is more typical) it shortens the focal length of the eyepiece.

[Universound57]

@posterpopman hey just a quick word of advice, i would avoid barlow lenses whenever possible. i say this because adding the barlow will decrease the full image quality. what im saying is that, say you have a 10mm eyepiece and a 2x barlow = 5mm , now lets say you have a 5mm eyepiece, image quality will be greater in the 5mm eyepiece then the 10mm barlowed. it wont be significant in most cases but the truth is as soon as light passes through your barlow lense, you lose some image quality

[truemartian]

@Universound57 I would have to agree with you there. I've never really found a barlow I liked. This is why I always recommend three eyepieces with low, medium, and high magnification.

[AroundSun]

@NintendoWiigangster sounds like you haven't found the focus knob? maybe too much light pollution? bad weather?

look for a focusing knob when you have that bright blurry object in your eyepiece. keep turning it until the picture comes in crisp. it may turn out to be a planet, may turn out looking the same way it did with the naked eye because its too damn far away. when i started twisting that knob on a random star, i was amazed to find it was jupiter and its moons

[AroundSun]

@NintendoWiigangster what kind do you have

[AroundSun]

3048mm / 4mm eyepiece in Vermont during the winter nights up in the mountains. new moon, clear weather

[truemartian]

@NintendoWiigangster Ahhhh Somehow I missed your initial posts. I see you already gave details on your scope. Let me take a look here.