When barlow lenses are useful/useless, beginner question

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When barlow lenses are useful/useless, beginner question

Postby Marius » Wed Jul 12, 2017 4:44 pm

Hello everyone!

I am completely new to astronomy so this question will probably be both easy and a bit dumb. I recently received a Celestron travel scope 70, a fairly weak telescope for a good price in my opinion. I am happy with what it does so far, but I have the possibility of getting a barlow lens (x3) to use with it.
Now my question is wether this lens is even usefull in the first place. I heard that trying to squeeze too much power out of fairly weak telescopes just leads to problems. The travel scope 70 has a 70mm aperature and a focal lenght of 400mm. I have 4 eyepieces. A 4mm one, a 10mm one, and a 20mm one.
I don't know if these specifications are of any help, but here they are anyway.
Thank you for your time!
Marius
 
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Re: When barlow lenses are useful/useless, beginner question

Postby Gfamily2 » Wed Jul 12, 2017 10:04 pm

Marius wrote:Hello everyone!

I am completely new to astronomy so this question will probably be both easy and a bit dumb. I recently received a Celestron travel scope 70, a fairly weak telescope for a good price in my opinion. I am happy with what it does so far, but I have the possibility of getting a barlow lens (x3) to use with it.
Now my question is wether this lens is even usefull in the first place. I heard that trying to squeeze too much power out of fairly weak telescopes just leads to problems. The travel scope 70 has a 70mm aperature and a focal lenght of 400mm. I have 4 eyepieces. A 4mm one, a 10mm one, and a 20mm one.
I don't know if these specifications are of any help, but here they are anyway.
Thank you for your time!


Hi Marius - welcome. You're right that you can overstretch a telescope by using too powerful an eyepiece with it, but in your case the Barlow could be of use.
I don't know exactly which eyepieces you have; but as you may well have noticed, for normal priced eyepieces, the eye lens of a lower power eyepiece is bigger, which makes it easier to use. So, my suggestion would be to try out the Barlow with the 20mm eyepiece - as this will give you a magnification nearly as much as that that given by the 4mm eyepiece, but it should be much easier to get your eye in the right place.

Personally, I have only used 2x Barlows, but I know people that use 3x ones.

As for your scope, I bought one as a gift for a family member so I had to try it out before wrapping it (as you do), and I thought it gave quite good results given the size and price. It will benefit from a better tripod if you have one, but it's a nice scope and very portable.

If you're planning on developing astronomy as a hobby, you may find the scope a bit limiting, but the eyepieces and Barlow will be usable in any scope that has takes 1.25" eyepiece, and the 70mm Travelscope will always be a quick and easy to take a scope out into the field.
Scopes: Meade 8" SCT, Skywatcher 127mm Mak
For imaging: Pentax K5, Asda webcam, Star Adventurer (new toy)
For companionship: Mid Cheshire Astronomical Group.
Gfamily2
 
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Re: When barlow lenses are useful/useless, beginner question

Postby The Man with the Corrugated Iron Roof » Mon Jul 31, 2017 7:31 pm

For your telescope, I would use the 3X Barlow lens with the 10mm eyepiece to achieve a magnification of 120x. With the 4mm eyepiece, it gives magnification of 300x, rather too much. As a comparison, I once used 600x magnification on a slightly smaller telescope and Venus appeared as a comet, it was so bad.

There are some "rules" about maximum magnification and telescopes but there are some exceptions. For a full explanation, you can read the following book:

http://www.philippughastronomer.com/The ... copes.html

I would not try this on your telescope but I have used 2X and 3X Barlow lenses together to image the Moon and Jupiter with my telescope and DSLR.
How can I be one with the universe when we don't know what 96% of it is.

My website: http://www.philippughastronomer.com/

My blog: http://sungazer127mak.blogspot.co.uk/2015/11/november-2015.html
The Man with the Corrugated Iron Roof
 
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Location: Wiltshire but can be just about anywhere up to 41 000 feet


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