259 replies to this topic

[edsmx5]

New addition to the family ;( well, new to me, anyway  ). So, basically, this would turn the 28/82 in to a 14; meh, I have a 14/82, I'll put it on that; oh wait, a have an Xcel 7mm , so maybe not. But I can Barlow the 7 ( maybe ) See ? I don't even talk about the 25 and 10 kit plossls any more ,but that would net 12.5 and a 5, ?. Without going over the Noob's head, ( a small leap, I will admit), what are the benefits of a barlow, and more importantly, the drawbacks ( I never liked tele-extenders on my Camera gear either ). Thanks

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[dnayakan]

I think the Barlow is perhaps best used if you use eyepiece lens designs that have decreasing eye relief as their focal length reduces. A good example is a Plossl - very comfortable eye relief at 32, 20 and perhaps even 15mm. At 8 and 4, you're going to be squeezed up next to the glass. So some people prefer using a longer focal length and a Barlow since that preserves the eye relief. 

 

There's also the fact that carefully chosen focal lengths plus a Barlow can halve the needed eyepieces - many Questar owners are very happy with just a couple of eyepieces. 

 

You can, of course, use a Barlow to get to silly levels of magnification if that is your thing. 

 

Cheers, DJ

 

PS: Barlows can actually be decent qualty and better than the questionable experience with tele-extenders in cameras (which I share). The tele-extender is part of an optical system that has to brings rays to a focus at the focal plane. A telescope is afocal - the light rays coming out of the eyepiece are actually parallel rays that are bent to focus by the eye on the retina. 

[edsmx5]

 

Cheers, DJ

 

PS: Barlows can actually be decent qualty and better than the questionable experience with tele-extenders in cameras (which I share). The tele-extender is part of an optical system that has to brings rays to a focus at the focal plane. A telescope is afocal - the light rays coming out of the eyepiece are actually parallel rays that are bent to focus by the eye on the retina. 

 I was told by someone whose opinion I trust that this was a good one to look for, we shall see. I know its a good piece to add to the kit, but I've also been warned of "over barlowing ". Until these three days of clouds pass, doesn't matter much how good it is.

[scottinash]

The Celestron (Japan) Ultima's are good.  I have held on to mine for years but I rarely use it now since I have the specific eyepiece focal lengths to cover the high to low magnifications I like to use the most.

[EsaT]

New addition to the family ;( well, new to me, anyway  ). So, basically, this would turn the 28/82 in to a 14; meh,

2" hand grenade won't fit into 1.25" hole....

[edsmx5]

2" hand grenade won't fit into 1.25" hole....

     Forgot that little detail !!The point is true though, right ? assuming proper barrel size it turns a 28 into a 14, so there would be no point, correct ? Of course, the 2" barrel renders this point moot. 

[therealdmt]

     Forgot that little detail !!The point is true though, right ? assuming proper barrel size it turns a 28 into a 14, so there would be no point, correct ? Of course, the 2" barrel renders this point moot. 

You have the basic idea right — if you have a 20mm eyepiece you like, a 10 mm eyepiece you like and a 5mm eyepiece you like, then a 2x barlow does not help you much. In such case you could use the barlow to get the 5mm to act as a 2.5mm, but that may be more magnification than you can typically use. Otherwise, you can get the 20 mm to act as a 10mm, but you already have an individual 10mm eyepiece. And you could get the 10mm to act as a 5mm, but you already have an individual 5mm eyepiece, so… not much use for a barlow (though if you do not like your shorter focal length eyepiece for some reason, there could in some cases be specific benefits to barlowing the longer eyepiece that make you choose the long eyepiece+barlow combination).

 

However, if you have a 32mm eyepiece, a 20mm eyepiece, an 8 mm eyepiece and a 6mm eyepiece, if you add a 2x barlow you now effectively have:

 

32mm, 20mm, 16mm, 10mm, 8mm. 6mm, 4mm, and potentially even 3mm.

(focal lengths achieved through the barlow shown in italics)

 

Accordingly, if you want to incorporate a 2x barlow, when buying eyepieces, don’t choose eyepieces that are exactly 2x ones you already have 

[edsmx5]

 

 

Accordingly, if you want to incorporate a 2x barlow, when buying eyepieces, don’t choose eyepieces that are exactly 2x ones you already have 

Yeah, the cart was before the horse here . . . 

[therealdmt]

With your current eyepieces (from what I read above, a 2" 28/82° and then 1.25" eyepieces of 25mm plossl (50°), 14/82°, 10mm Plossl (50°), and 7mm X-Cel LX (60°)), the biggest potential benefit from the 1.25" 2x barlow would come with the 10mm Plossl. The barlow adds a bit of eye relief, so the 10mm plossl would become a little more comfortable to use, and it would give you access to 5mm for nights with good seeing when you can use more magnification than the 7mm X-Cell LX gives you.

 

BTW, a 2x barlow can make a good partner for a zoom eyepiece, such as an 8-24 zoom 

[therealdmt]

Yeah, the cart was before the horse here . . . 

It could still come in handy at some point, plus for now you can just experiment with it.

 

And, besides just checking out what the barlow does, you might find that in practice you like the 14/82 barlowed more than you like using the individual 7mm X-Cel LX (although the magnifications would be equal. you’d get a wider field of view). Might. 

Edited by therealdmt, Yesterday, 05:13 PM.