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Physics/Barlow lens


Dear Dr.Stephen,
I've a simple made home refractor telescope with the details below:
1- The large lens is of 10 cm dia. and 35 cm focal length.
2- The smal lens is of 1 cm dia. and 1 cm focal length.

I'd like to increase the amplification power of the telescope using a biconcave lens(as a barlow lens) which got it from taking apart a compound lens , the diameter of this biconcave lens is 3 cm.
Please advice me if this lens is suitable to be used as a barlow lens?, and also, advice me to the suitable distance for this lens to be mounted from the large lens(objective)?..
waiting for kind help.. Best regards

I don't know the focal length of the Barlow lens, but they're typically placed right before the objective.  1 cm is a very short focal length for the objective, so it shouldn't have any trouble overcoming the defocusing of the divergent Barlow lens.  Since the focal points of the main and objective lenses overlap, you will have to adjust the eyepiece's distance to account for the new focal point using the standard lens equation.


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Dr. Stephen O. Nelson


I can answer most basic physics questions, physics questions about science fiction and everyday observations of physics, etc. I'm also usually good for science fair advice (I'm the regional science fair director). I do not answer homework problems. I will occasionally point out where a homework solution went wrong, though. I'm usually good at explaining odd observations that seem counterintuitive, energy science, nuclear physics, nuclear astrophysics, and alternative theories of physics are my specialties.


I was a physics professor at the University of Texas of the Permian Basin, research in nuclear technology and nuclear astrophysics. My travelling science show saw over 20,000 students of all ages. I taught physics, nuclear chemistry, radiation safety, vacuum technology, and answer tons of questions as I tour schools encouraging students to consider careers in science. I moved on to a non-academic job with more research just recently.

Ph. D. from Duke University in physics, research in nuclear astrophysics reactions, gamma-ray astronomy technology, and advanced nuclear reactors.

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