Tal Barlow query

[euphony]

Hi all,

I purchased a Tal x2 barlow a few months ago as everyone recommends them highly. After a couple of months use I have noticed a pattern when using it. It seems that most the time when I use the barlow, no matter what eyepiece I use it with, the image becomes less clear and seems to come slightly in and out of focus constantly. I have adjusted the focus manuallyof course, but that only seems to make a difference for a couple of seconds. I put it down to perhaps warm air currents, but then I figured that I would get the same effect when using my 7mm eyepiece for instance, which I don't.

Anyone have any idea why it is doing this?

Chris

[knobby]

It could be that the higher may is showing up the poor seeing ... occasionally it will be really good and it will look great, then fuzzy again!

What EP are you using in the Barlow?

Sent from my HD2Droid

[euphony]

I've used all of them, mostly my Celestron X CEL and Baader Hyperion eyepieces. Like you say, the barlow could just be enhancing the sky conditions as often it appears clear, but you can struggle to see a great deal.

[rory]

i bought a tal barlow a while back ( my first and only barlow) and quickly sold it again. i found i just couldnt get along with it at all.particulaly the eye placement.

i think its like eyepieces ,a personal thing. but my initial barlow experience wasnt good.

[brantuk]

The Tal barlows are great value for money but you have to remember they are still at the lower end of the vast range of available barlows. The CPC1100 is a high quality insturment with a focal length of 2800mm. The 7mm eyepiece will give you 400x magnification. The highest useful magnification is 661x so adding a barlow takes you way beyond that to 800x.

Although higher magnifications are possible on very rare occasions of crystal clear "seeing" and excellent transparency, mostly the UK will only allow you around 200x - 250x tops. Otherwise you will just be magnifying atmospheric imperfections which (as you rightly observe) just make the image go dim and fuzzy. Hope that helps

I'd recommend a Powermate 2x or Antares 1.6x and don't go over 250x mag.

[John]

I'd second brantuk's advice.

Barlow lenses do affect the eye / eyepiece placement distance - they usually lengthen it which can be an advantage, or a pain, depending on how you adjust to the change.

The Powermates mentioned above do not affect the eye placement and are superb optically, just seeming to add the magnification but nothing else to the image being viewed. This sort of performance comes at a cost of course !

With an F/10 11" scope I can't really see the need for a barlow lens / Powermate at all for visual use - even the 7mm eyepiece on it's own will be more power than can be usefully used on many nights.

[euphony]

Brilliant, thanks for the helpful replies guys, that clears up a lot