Barlow lens help...

[Nastyness]

Hello all,

Hope someone is able to help.

I'm a complete newb who has recently purchased a Crestron AstroMaster 130EQ. Loving the scope and having great fun with it, so no problems there.

We decided to purchase a barlow lens - opted for the Crestron Omni 2x due to decent reviews - but having issues with focus and light, i.e. we can't get a crisp focus and it seems to have dulled the view considerably. Is this normal with a barlow or could it be something to do with set-up?

Look forward to reading your suggestions.

Many thanks.

[oldfruit]

Hi and welcome to the lounge.

As you probably know a barlow such as yours will double the magnification of any eyepiece you use it with. The higher magnification you use, the dimmer the view becomes. Too much magnification is bad especially if the seeing is poor.

What eyepieces are you using and what are you trying to view?

[Rossco72]

Puting the barlow lens in, doubles the focal length of your scope and therefore gives you significantly less light (1/4 for a 2x barlow if memory serves) therefore it will look dimmer.

If the resultant magnification is over 200x then you will fiind seeing becomes an issue and atmosheric condition, collimation and EP quality will all come into play.

[coffee_prince]

I have a low end barlow and its not worth using, it doesn't create a clearer image, at its best it will make an image bigger, but will not show any more detail

[Capricorn]

If the initial image is poor then adding more glass simply makes it poorer. More glass does not add to the quality.

A better eyepiece simply has less aberations then a poor one. When people buy a good eyepiece they are "improving" the quality of what they see by reducing the faults not by having an eyepiece that magically negates problems.

A better eyepiece is simply better because it isn't as bad as the one it is replacing.

When you add in a barlow you are adding the barlow defects to what you see.

[Rossco72]

good quality barlows and powermates are invisible....

[coffee_prince]

as above ^

[Nastyness]

good quality barlows and powermates are invisible....

Could you suggest some then?! I had also considered the Orion Stumpy Plus x2, but couldn't find it in stock anywhere.

[Capricorn]

good quality barlows and powermates are invisible....

They may be invisible to the eye but optically all the glass surfaces add in some aberations. Simply a spherical surface is not the ideal for a lens so having 4, 6 or however many surfaces adds in a small amount of aberations, spherical and chromatic.

None are apochromatic, and even then that is just 3 wavelengths taken care of, just simple achro doublets, if that, so chromatic aberation has to be increased to some extent.

It may be small but is still present, and accumulative.

[Rossco72]

Televue barlows are excellent and really not that expensive (although compared to the cheaper ones maybe they are), I hear good things about the TAL ones but equally some other experienced users have said that the TAL ones whilst good value aren't in the same class as the Televue ones.

The quality control of the manufacturer can minimise any distortions to the point where the human eye wont be able to tell. A machine might be able able to tell but i doubt very much if you will be able to

Cheers

[brantuk]

TV barlows - you can't go wrong as stated above. Tal - great value for money in the budget barlow end of the market. Others - Celestron Ultima 2x are very popular here, as too are the Orion Shorty 2x - great performers in the £50-£100 price bracket.

[Astro_Baby]

Dont you think something like a Televue might be a bit over the top in a Celestron 130 Astromaster ? I'd avoid the Barlow altogether and just get better eyepieces.

Even an eyepioece of modest quality and price will be a big jump over the supplied eyepieces.

For your scope I'd aim for a 5mm, 15mm and 32mm eyepiece which would give you a good spread. They neednt cost a huge amount (TAL Plossls for instance cost about £19) and this would give you a better view.

Most Barlows (unless you really spend) degrade the views to some extent.

Bear in mind the max magnification with your scope is x260 and I'd not push it much beyond about x150.

Dont forget also that the more powerful the magnification the more defects both in the scope and our swirly atmosphere will appear.

[Rossco72]

Dont you think something like a Televue might be a bit over the top in a Celestron 130 Astromaster ? I'd avoid the Barlow altogether and just get better eyepieces.

Even an eyepioece of modest quality and price will be a big jump over the supplied eyepieces.

For your scope I'd aim for a 5mm, 15mm and 32mm eyepiece which would give you a good spread. They neednt cost a huge amount (TAL Plossls for instance cost about £19) and this would give you a better view.

Most Barlows (unless you really spend) degrade the views to some extent.

Bear in mind the max magnification with your scope is x260 and I'd not push it much beyond about x150.

Dont forget also that the more powerful the magnification the more defects both in the scope and our swirly atmosphere will appear.

A good point and worth serious consideration, i suppose the only thing for a TV is that it will be good for any telescope in the future and would retain most of its value.

but if budget is a big thing, you certainly could pick up a couple of decent EP's instead

[johnkirkpatrick]

I had the deluxe barlow used with my old astromaster and hated it completely rubbish, then I got the orion shorty plus barlow and its fantastic really great for the price£51. I found with the astromaster anything above a mag of 150x was a no no. but on a very very good night 180x was just acceptable . so try stay within that mag area.