Using eyepieces/Barlow with 50AZ PowerSeeker

[Roosto]

When I drop an eyepiece into the telescope, fine, everything works, though the image is backwards. When I drop an eyepiece into the Barlow, nothing works. With one eyepiece, things just go dark. From a beach city in Southern California, I am looking at the houses on Catalina Island about 40 miles from here. Visibility is clear. What am I doing wrong when using the Barlow?

[rwilkey]

The Barlow is probably pushing the telescope over its maximum magnification, which for your scope is 100x, though 50x is the optimum. Tell us the focal length of your scope, and what eyepiece and Barlow you were using and we can work out the magnification (focal length of scope divided by focal length of the eyepiece = magnification).

[Roosto]

The Barlow is probably pushing the telescope over its maximum magnification, which for your scope is 100x, though 50x is the optimum. Tell us the focal length of your scope, and what eyepiece and Barlow you were using and we can work out the magnification (focal length of scope divided by focal length of the eyepiece = magnification).

Hi Robin. Thank you for your reply. You are talking over my head, so, I can only tell you what I have with the telescope. There is a 3X and a 1.5X Barlow. There are three eyepieces, marked H12.5 mm, SR4 mm, and H20 mm. For the close Catalina, which eyepiece and which Barlow should I use? Or, can't a Barlow be used when so close as 40 miles, though buildings look tiny with the naked eye? Or, again, is there a technique to focusing that I don't understand when using the Barlow?

[rwilkey]

Hi Roosto, apologies that I did not explain it too well. So, I have checked out your telescope on the internet and it looks like it has a 600mm focal length which gives a focal ratio of 12 (this will not mean much but just establishing a few details for others to comment). The eyepieces are the smaller fitting, ie. 0.965" or 1". So you have three eyepieces plus a 3x Barlow, The 1.5x Barlow is probably what is called an 'erecting' eyepiece which is for terrestrial/land viewing (it places the image the correct way round and the right way up). The mount is a table mount.

With the focal length stated your eyepieces will produce the following magnifications:

20mm (600/20) = 30x or with 3x Barlow (600/20x3) = 90x

12.5mm (600/12.5) = 48x or with 3x Barlow (600/12.5x3) = 144x

4mm (600/4) = 150x or with 3x Barlow (600/4x3) = 450x

Unfortunately, only some of these magnifications are useable with your telescope as it's maximum magnification is 100x. I am not sure why manufacturers include items for use with a telescope where the magnifications are beyond the capability of the scope. The only useful eyepieces are the 20mm which can produce 90x magnification with a Barlow and the 12.5mm, which produces 48x magnification without the Barlow. As you will note, the 4mm is completely unuseable in your scope, and a completely pointless inclusion.

So, if you just use the 20mm and the 12.5mm you should get some results, but the 3x Barlow can only be used with the 20mm.

Using the telescope for land objects will be a bit easier with the 1.5x Barlow as this will not ramp up the magnification so much. You could use it with the 20mm giving 45x and the 12.5mm giving 72x.

I hope this makes some sort of sense to you, magnification is always limited by aperture (the size of the main lens) and by seeing conditions in your area. I think it is very wrong for manufacturers to include accessories that cannot possibly be used with the telescope, but that's what they do to make it look as though the telescope is more powerful than it really is.

Apologies if all this sounds a bit harsh, but just being straight with you and trying to manage your expectations. Good luck with your viewing.