Barlow lens

[Ryaen]

Hi, I am pretty much new in Astronomy. Recently I have bought Meade Polaris 127mm telescope. The Barlow(2x) which Meade has provided is pretty basic. It gives pretty blurry view.

I have read few blogs and get to know that for 127mm, 2x-3x magnification is more than enough. Now I’m confused in its specs(element in it).

Wondering which one I choose, 2.5x Barlow 3 element or 2x Barlow with 2 element to get clear and crisp viewing.

Ryaen

[andrew s]

What  type and focal length eyepieces are you using the the Barlow? 

Regards Andrew 

[RT65CB-SWL]

Hi @Ryaen and welcome to SGL. 

+1 above, as per @andrew s.

To add to the confusion of which Barlow lens... 
I have a Klee 2.8x Barlow and a 1.6x Astro-Engineering 'MagniMax' that screws into the filter thread of the eyepiece.

[vlaiv]

Meade Polaris 127mm seems to be Bird-Jones design and has focal length of 1000mm.

Using barlow with this scope is going to bring in very high magnifications - more than atmosphere and scope can support. Things are going to be blurry.

For the time being, just avoid using barlow lens until you get some experience of how different sky conditions impact quality of the image. Once you learn to distinguish between different conditions (good or bad atmosphere) - then you can start using barlow lens and you'll be able to tell if it is atmosphere that is causing the most damage to the view or is it barlow lens.

[Ryaen]

52 minutes ago, Philip R said:

Hi @Ryaen and welcome to SGL. 

+1 above, as per @andrew s.

To add to the confusion of which Barlow lens... 
I have a Klee 2.8x Barlow and a 1.6x Astro-Engineering 'MagniMax' that screws into the filter thread of the eyepiece.

It’s Meade Polaris 127mm aperture, 1000mm focal length of the objective, f ratio 7.9.

I have got 15mm, 20mm GSO super view, Plössl eyepieces. To avoid, buying higher magnification(6 to 10mm), I thought to go for a good Barlow lens.

The Barlow provided by Meade is basic, gives quite dark and blurry viewing even in clear calm Night sky and thus looking to upgrade it.

I even put my telescope out for acclimatisation for about 40mins to an hour.

[vlaiv]

1 minute ago, Ryaen said:

It’s Meade Polaris 127mm aperture, 1000mm focal length of the objective, f ratio 7.9.

I have got 15mm, 20mm GSO super view, Plössl eyepieces. To avoid, buying higher magnification(6 to 10mm), I thought to go for a good Barlow lens.

The Barlow provided by Meade is basic, gives quite dark and blurry viewing even in clear calm Night sky and thus looking to upgrade it.

I even put my telescope out for acclimatisation for about 40mins to an hour.

In theory, you should be fine with that scope with magnifications of about x120-x150 range. That should give you good sharp image even in average seeing conditions.

With x2 barlow, you'll get x100 and x133 magnification. With x2.5 barlow you'll get x125 and x166 magnification.

This really gives you idea of what barlow you want - one that is x2.5 (but in reality is closer to x2.2), is triplet lens and is sensibly priced - look no further than:

https://www.365astronomy.com/GSO-2.5x-Achromatic-3-Element-Barlow-31.7mm-1.25.html

Given that you already have 15mm and 20mm eyepieces, x2.5 GSO barlow should not be too hard to purchase locally?

[Ryaen]

3 minutes ago, vlaiv said:

In theory, you should be fine with that scope with magnifications of about x120-x150 range. That should give you good sharp image even in average seeing conditions.

With x2 barlow, you'll get x100 and x133 magnification. With x2.5 barlow you'll get x125 and x166 magnification.

This really gives you idea of what barlow you want - one that is x2.5 (but in reality is closer to x2.2), is triplet lens and is sensibly priced - look no further than:

https://www.365astronomy.com/GSO-2.5x-Achromatic-3-Element-Barlow-31.7mm-1.25.html

Given that you already have 15mm and 20mm eyepieces, x2.5 GSO barlow should not be too hard to purchase locally?

Much appreciated. Thanks mate.

However, my confusion is all about element present in a Barlow. 2 element or 3 element ? Does it really make a big difference in quality of viewing like getting sharp images with a decent field of view.

 

 

 

 

[vlaiv]

2 minutes ago, Ryaen said:

2 element or 3 element ?

That topic is rather complicated. You don't need 3 elements, 2 is enough to get a "perfect" barlow.

Barlow is really simple optical design so you can't go wrong much in design itself - but you can in manufacturing. Much more important than number of elements is how good the product is in use.

That x2.5 GSO barlow is very good barlow and certainly very good value for the money. Much better than stock / plastic items that usually come with the scope.

There certainly are better barlows out there like Baader VIP barlow that you can "tune" to required magnification by using extensions but it costs like x3-x4 more than GSO one and difference will be minimal.

In fact - I'm more concerned with fact that you are using Bird-Jones type scope than anything else. Again similar thing with that - in itself Bird-Jones design is not a bad design - only problem is that it is often poorly executed design and advice that you'll find most often on such scope is to stay clear of them.

Not saying that your particular model is poor - I've neither seen Meade model nor read review of it so far. It could be rather decent, but there is a chance that scope simply provides blurred image at higher magnifications (having cheap plastic stock barlow won't help either).

Knowing this, I don't think you should go overboard with expensive barlows - as it might not result in improvements that you are after.

[Louis D]

Don't most people report the GSO 2.5x to be closer to 2.2x?

[vlaiv]

1 hour ago, Louis D said:

Don't most people report the GSO 2.5x to be closer to 2.2x?

So I've heard:

3 hours ago, vlaiv said:

This really gives you idea of what barlow you want - one that is x2.5 (but in reality is closer to x2.2), is triplet lens and is sensibly priced - look no further than:

https://www.365astronomy.com/GSO-2.5x-Achromatic-3-Element-Barlow-31.7mm-1.25.html

Mind you, I've have had that barlow and did not do measurements of how much magnification it gave. Also - my sample was not as good . Cemented pair was not properly cemented together - there was something like 1/4 of mm of decenter and that produced chromatic dispersion at very high power.

I used it as ADC one time because it countered atmospheric dispersion perfectly

 

[Ryaen]

3 hours ago, vlaiv said:

That topic is rather complicated. You don't need 3 elements, 2 is enough to get a "perfect" barlow.

Barlow is really simple optical design so you can't go wrong much in design itself - but you can in manufacturing. Much more important than number of elements is how good the product is in use.

That x2.5 GSO barlow is very good barlow and certainly very good value for the money. Much better than stock / plastic items that usually come with the scope.

There certainly are better barlows out there like Baader VIP barlow that you can "tune" to required magnification by using extensions but it costs like x3-x4 more than GSO one and difference will be minimal.

In fact - I'm more concerned with fact that you are using Bird-Jones type scope than anything else. Again similar thing with that - in itself Bird-Jones design is not a bad design - only problem is that it is often poorly executed design and advice that you'll find most often on such scope is to stay clear of them.

Not saying that your particular model is poor - I've neither seen Meade model nor read review of it so far. It could be rather decent, but there is a chance that scope simply provides blurred image at higher magnifications (having cheap plastic stock barlow won't help either).

Knowing this, I don't think you should go overboard with expensive barlows - as it might not result in improvements that you are after.

Hey that’s a quite an information for me being a noob. Thanks a lot.

I will stick to GSO 2.5x Barlow lens as of now.

 

 

[Louis D]

2 hours ago, vlaiv said:

So I've heard:

6 hours ago, vlaiv said:

This really gives you idea of what barlow you want - one that is x2.5 (but in reality is closer to x2.2)

Totally missed that. 🤣  It's just one of those days.

[Don Pensack]

To yield a short barlow means the curves on the lenses must be deep.

This makes the barlow harder to make (read: more expensive to manufacture).

If a 3rd lens is added, the barlow can be shortened without the deep curves on the lenses that would be required of a 2-element barlow.

That is the reason why some short focal length barlows have 3 lenses.  A 2 element can be free of false color, so 3 elements are not necessary for that.

4 element barlows are typically telecentric, and have a positive lens following the negative lens.  This is done to allow the barlow to have the same magnification

at various distances from the lens, whereas a regular barlow's magnification increases with distance from the lens.

I haven't really figured out the why of a 5 element barlow (there are some), but perhaps the configuration merely added a positive lens to a 3-element barlow to make it telecentric.