Orion Shorty Barlow not too good...

I purchased an Orion Shorty Barlow 2x ($40 US) and must say have not been too pleased with the results. The mag is OK of course, but it seems to have knocked the brightness down more than I expected, especially at higher mags. Any thoughts on this? Should I have gotten an ED Barlow? I use an Orion 120 f/8.4 achro. Maybe what I really need is a better quality diagonal. Thanks for any opinions.

BTW - please no jokes about needing a better quality scope... 8)

Jim,

I'm not to sure I can help but I'll give it a go. One problem is, the more you magnify the dimmer the image becomes, no matter how you achieve it. I suspect the barlow works just as it should. As long as it introduces no false color or other abberations then it is working correctly. This particular barlow is an apocromatic lensed type, one of Orion's better optics. I'm not sure about your scope but most mirrors start to dim quickly above 25X per inch and some need lower numbers than that. You may need a larger primary if the image is to dim with resonable magnification. Exceptional nights only happen every so often in most locations and even a larger scope may not help.

The shorty plus barlow has had good reports. Don't know about the regular shorty.
If your scope came as an SVP package the supplied diagonal should be a good one. At least mine is and I have compared it to a good dielectric I have with very little if any visual difference. The dielectrics withstand cleaning better though, I think.
Harry

>>>I purchased an Orion Shorty Barlow 2x ($40 US) and must say have not been too pleased with the results. The mag is OK of course, but it seems to have knocked the brightness down more than I expected, especially at higher mags. Any thoughts on this? Should I have gotten an ED Barlow? I use an Orion 120 f/8.4 achro. Maybe what I really need is a better quality diagonal. Thanks for any opinions.
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Hi Jim:

I believe the dimming you are seeing is inharent in the fact that you are increasing the magnification by a factor of 2. If you double the magnification, you are spreading the light over twice the diameter and therefore 4 times the area. This means that doubling the magnification will result in an image that is 1/4 are bright. It does not matter how you double the magnification, barlow, shorter focal length eyepiece, this is the result.

As far as the Orion Shorty goes, I have the Celestron Shorty (I think 3 of them) as well as the Celestron Ultima. I believe the Celestron Shorty is identical to the Orion Shorty and I know the Ultima is identical to the Orion Shorty Plus. I also have the long traditional Japanese Meade 2x, 2x-3x and 3x barlows (who said you can't have too many eyepieces :-)

Of these, the standard Celestron Barlow is the one I prefer over all of them. It gives good views that are ghost free. The light loss is neglible. The Ultima is OK but harder to keep clean and is actually something more like a 2.2x or 2.3x barlow in most instances.

As far as the ED barlow vs the standard barlow, Roland Christen, Mr. Optics and the MAN at Astro-Physics says that the concept that some barlows are APO while others are not is quite bogus. Lots of good two element barlows out there.

So, in the end, I think the Orion 2x Shorty Barlow is a decent barlow and that what you are seeing is the result of doubling the magnification and not caused by the barlow itself.

Jon Isaacs

PS: The scope you have is a fine scope, it is a capable of providng some nice widefield views and some nice higher powered views as well. And it will do a great job on double stars. Point it at Izar or delta Cygnus or Epsilon Lyrae (the double-double) and you should have some great views of some pretty close doubles.