Telescopes ehhhhhhh?

Question

How come a "barlow lens cannot be used with a diagnal lens"

Just bought a telescope and can not understand the instructions.

Does anyone know any videos online to help with using a refractory telscope.

Answer 1

It's because the barlow lens changes the point where the image comes into focus. you focuser doesn't have enough travel to bring the image into focus with the barlow lens in. A barlow lens works by effectivly increasing the focal length of a telescpoe. One of the effects of this is that it changes the point of focus on your telescope. I suspect that you bought your telescope from some sort of chain store. Most high quality telescopse wont have that issue. Telescopes bought from chain stores are foten of very low quality and can be very frustrating to users. (i know from experience). a great, reliable, quality telescope company, that sells cheap telescopes is Orion. they sell low end refractors for arround 100 dollars that are 10 times beter then anything you will get from costco, walmart or sams club.

I would like to add that when purchasing a telescope, the least important thing to consider is its magnification. Any telescope can be made to go to any magnification with the right eyepiece and/or barlow combination. what's really important is how big the objective lens or mirror is. that determines how much light the telescope gathers and how bright the image is youll be looking at. most telescopic observations are made using 20-30 power per inch of apreture. there are many reasons for this, including the fact that many objects wont fit in the feild of view at high magnifaction. Also there is the fact that it is difficult to track an object at high power by hand. really the list of reasons goes on and on. there is a great guide to buying a telescope on the orion website. if you need to know anything at all about your telescope please feel free to email and I would be happy to answer any additional questions you have about optics or astronomy in general. Please include the manufacturer and model of your telescope if possable along with any other information you have about it.

Answer 2

i use a barlow with a diagonal all the time. good telesscopes have lots of focus travel to allow this.

what aspect of the telesscope are you having trouble with?

Answer 3

It's not so much that it "cannot be used" but that if you tried to use it, the mechanical mounting of the optical elements would not allow the telescope to come to a focus.  Telescopes are not arbitrarily reconfigurable.

Answer 4

You've read the instructions a few times?

Good (even if you don't understand everything).

Take the telescope outside on a nice day. This will help you get used to it (and, as a bonus, if you drop anything, you can find it easier than when it is dark).

Just don't point it at the sun.

Use the most ordinary eyepiece you have (usually, the one with the highest focal length -- it is the one that gives the least magnification).

Pick a distant object (church spire, road sign, whatever -- but not the sun).  Try to avoid pointing it at houses, otherwise people there may report you as a peeping Tom.

Try to find the object in the telescope.  You may need to adjust the focus.  The object will likely appear upside down.  Move the telescope a tiny bit while looking, so that you can get used to see how the image moves.

Once you've had all the fun that you can have doing that,   try the other eyepieces (you may have to readjust the focus).

If you have a diagonal, try with and without (if the object you have picked is low enough, it should be possible to observe it without the diagonal.  This is where you will find out if the focuser has enough "travel" to let you observe without your diagonal.

If it does, you will be able to use your Barlow without the diagonal.

Do try to fit the Barlow with the diagonal in place.  Either it works... or it does not.  You may even try variations like fitting the Barlow first, then put the diagonal after the Barlow, then the eyepiece (normally, this should not work, but why not try it).

Just be careful not to force anything (you do not want anything to break).

And, by the way, you will rarely use the Barlow anyways.  I end up doing most of my observations at the lowest magnification:  the field of view is larger and you still get the same amount of detail (they are just a bit smaller).

Did I mention not to point at the sun?  Well... don't.