Barlow?

[gobes]

Hi. I'm completely new to astronomy... so still find my feet a little.

A few people now have recommended getting a 'Barlow'. Can anybody give me a quick, easy explanation of what the Barlow does - and how it will enhance my viewing?

Also - what do I need to take into account when purchasing a barlow?

Many thanks for any advice.

[ukbigd]

This an easy and cost effective way to increase the use and enjoyment of your eyepieces. The Barlow lens effectively doubles the magnification of the eyepiece that you are using, e.g. your 25mm eyepiece works like a 12.5mm, or your 15mm eyepiece will work like a 7.5mm one etc.

[Merlin66]

The "Barlow" is a negative lens mounted in a 1.25" tube into which you set your eyepiece. The combination is then put into the focuser like the original eyepiece.

The effect of the barlow lens is to increase the effective focal length of the telescope by the magnification factor ie x2, x2.5 etc.

This means that the magnification from each of your eyepieces is increased by the same factor ie if a 25mm gives 100 magnification; with a Barlow the eyepiece with act like a (25 x -0.5 = 12.5mm) 12.5mm eyepiece and give a magnification of (100 x 2 =200) x200

Handy to have and give you more magnifications with the eyepieces you have.

Hope this helps.

[gobes]

Many thanks. Much appreciated.

Any recommendations? What brand is regarded as the leader when it comes to these?

[John]

Many thanks. Much appreciated.

Any recommendations? What brand is regarded as the leader when it comes to these?

In my opinion the Tele Vue Powermates are the some of the best barlow-type lenses around but they are very expensive - they start at £130 or so new. Tele Vue also do 2x and 3x conventional barlow lenses which can be picked up for around £50 used.

At the other end of the price scale but good nonetheless are the TAL barlows - a 2x TAL costs £30 new from First Light Optics.

John

[gobes]

Can I assume that there is a reduction in brightness - the more powerful the barlow?

Tal appear to do both a 2x and a 3x version... so should I resist temptation to go with the 3x?

Thanks again.

[John]

There can be some reduction in contrast and brightness because the barlow lenses introduce extra lenses into the light path - this effect is minimal though and is not an issue with the better quality barlow lenses.

The aperture of your scope will determine how much magnification you can practically use - if you double the aperture of your scope in mm then you have the maximum power for the scope - and that will be on exceptional nights - mostly a lower figure will give optimum results.

From this you can work out whether a 2x or 3x barlow is best for you and your scope.

John

[Merlin66]

The image will be fainter due to the increased magnification and lower surface brightness.

I'd start with a x2 Barlow.

I use an old Celestron x2 ("silver top") which does very well;

For fast Newtonians (<f5) University Optics have a KLEE Barlow ( comes in x2.2 and x2.8 - I use both) which corrects for coma.

The AE range seem to be OK, again I have the x4 unit.

Add this to the TV x2, x2.5 and x5 Barlows, you can see it's very easy to get carried away!!!

[Doc]

I would suggest if money is a bit tight go for the x2 TAL I used to have one until I lost it. For the money you won't be disappointed.

[TheThing]

Tal x2 Barlow is excellent. Really cannot be beaten for the price.

I also have a Meade (series 4000 I believe) x3 Barlow which is also very good.

Neither of these would break the bank.

[gobes]

Thanks very much for the advice all.