Barlow with Diagonal ?????

[tasco578]

How come I can't use Barlow lens with a Diagonal lens. It would make it a lot easier to see with a diagonal attached to the telescope. Even the manual says that "Never use the diagonal and Barlow at the same time".

 

[MeteorWayne]

It could be because of weight. I imagine the combination would be quite heavy. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[tasco578]

Ok. Here's the specs on my telescope; Magnification: 578x <br />Telescope Type: Refractor <br />Mount: Alt-azimuth 1/STAB <br />Eye Piece: (1.25") H25mm (28x), H12.5mm (556x), SR4mm (175x) <br />Finderscope: 6x24mm <br />Finish: Metallic Champagne <br />Tripod: Adjustable Aluminum <br />Objective Lens Diameter: 60mm <br />Focal Ratio: F/12 <br />Barlow: 2x/3.3x

 

[tasco578]

I don't think that would be the case. I think it's pretty sturdy.

 

[heyscottie]

I'd like to point out a few things about your telescope specs.<br /><br />Aperture is listed at 60mm<br />Focal Ratio is listed at F/12.<br />This means the focal length is 720 mm. I'll assume they fudged this slightly based on the listed eyepiece magnifications, and that the true focal length is 700 mm.<br /><br />The magnification of any eyepiece is the focal length of the telescope divided by the focal length of the eyepiece.<br /><br />So your magnifications are:<br />H25 = 700/25 = 28X<br />H12.5 = 700/12.5 = 56X<br />SR4 = 700/4 = 175X<br /><br />A rule of thumb for the maximum useful magnification of a telescope is 50X per inch of aperture. You have 60mm = 2.36" of aperture, so your maximum magnification is 118X. If your optics are excellent and you have excellent conditions, you can push your telescope up to 118X. Anything higher than that, and your image quality starts to suffer greatly due to diffraction and loss of contrast.<br /><br />So notice that your SR4 is already beyond the limits of what the telescope can do. <br /><br />Adding in all possible eyepiece combinations:<br />H25 = 28X<br />H12.5 = 56 X<br />H25 2X = 56X *** Same as H12.5 ***<br />H25 3.3X = 92.4X<br />H12.5 2X = 112X<br />SR4 = 175X *** Not usable ***<br />H12.5 3.3X = 184.8X *** Not usable ***<br />SR4 2X = 350X *** Not usable ***<br />SR4 3.3X = 577.5X *** Not usable ***<br /><br />So the only useful barlow combinations for you are the H12.5 2X and the H25 3.3X.<br /><br />Tasco always sells scopes with eyepieces that are too powerful for them, and sell their telescopes based on magnification. This is a fabrication. Remember, the telescope can't REALLY usefully magnify any greater than ~118X. Phsyics comes and bites you.<br /><br />Now having said all of this, I should mention that I very rarely use higher than 150X or so anyway. In fact, most interesting things out there are better viewed at lower magnifications. The moon, planets, and double stars are some of the only things you want high magnific

 

[MeteorWayne]

heyscottie!!<br />Excellent summary. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[tasco578]

Thanks for giving me all possible combinations. It all make sense to me now. (Saw planet Saturn the other day. It was about 0.6 mm in size. It was pretty cool and the profile was well defined.) I guess it's true "bigger is better" when it comes to telescopes. Thanks again.