Using a Barlow

[StarryEyes]

I'm still learning quite a lot as I'm going along with this and not sure of all the ins and outs of different bit of equipment.

So am I right in thinking that a barlow increases magnification?

If so is it possible to image with a barlow? and will they fit to any scope?

Thanks

[Merlin66]

When used for imaging the barlow increases the focal length and hence makes the object appear larger in your camera frame.

You use any barlow on any telescope. Just needs the right fittings ie 1.25" to 1.25" etc.

[StarryEyes]

Cool, thats what I was hoping, I just want sure if you could image through one. So if I were to go for this Skywatcher - Skywatcher Deluxe 2x Barlow which is a 2x barlow, effectivley what focal length would I then have if I fitted it to my 600mm scope? Is it your focal length x2?!

[JamesF]

I feel sure some people might argue that a barlow does not magnify the image, but it doesn't seem to do too much harm to think of it that way in the simple case.

In theory a 2x barlow increases the focal length by a factor of 2, but that does seem to be fairly approximate. Depending on the make the factor may be greater from what I've read. You can also increase its effect by placing it before the diagonal rather than after, or using an extension after it.

I found the barlow shipped with some Skywatcher scopes to be rubbish. I believe the lens is plastic. I removed the lens from mine and use it as an extension tube now. As far as I can tell, opinion seems to be that TeleVue barlows and powermates are the dog's danglies, but if you can't afford a re-mortgage then the Celestron Ultima is one of the best 2x barlows for the money. ISTR that the Tal 3x barlow is also well-regarded. I have no specific experience of the Skywatcher Deluxe one, but if you're putting more glass in the light path, it probably pays to get the most decent quality one you can afford.

James

[StarryEyes]

Thanks for the advice James, I'll take a look at the ones you have suggested.

[brantuk]

The Tal barlow is great vfm - Celestron Ultima (or Orion Shorty) are identical and best ones in the cheaper end (about £80'ish). Beyond that the TV Powermates are the best available

[StarryEyes]

I've noticed that the skywatcher barlow that I refered to is threaded to take a t mount. The others don't seem to be. Will I still be able to attach my camera to them?

[Merlin66]

See post #2 above.

You'll need a 1.25" to T thread nosepiece.

[StarryEyes]

Ah right sorry I misread that previously.

So at the moment I have what I am imagining is called a nose piece (its threaded on one end and tapered backwards on the other and just basically like a ring) that my t mount treads onto, without looking at it I'm guessing it's 2".

So would I need a smaller size one of those?

I think I've just completely confused myself now and made no sense!

[Merlin66]

Adaptors

At the bottom of the page the 1.25" nosepiece is shown.

[StarryEyes]

I think this may be the bit which I already have that I was describing.

I'll measure it to see what size it is and see if I can upload a picture of it later. Thanks or your help.

[Shibby]

Gemma, do you use a webcam for planetary imaging or are you talking about DSO / DSLR imaging? I ask because (and I don't think anyone has mentioned this yet) using a 2x barlow will half the speed of your optics (as the focal length has doubled). This means that for DSOs you will need twice the exposure length. Therefore I'd avoid using a barlow for DSO imaging. Apologies if all this is irrelevant and you're actually talking about planetary imaging - in which case a barlow is a good idea!

The magnification is affected by the distance between your sensor and the barlow. So the greater the distance, the greater the magnification/increase in focal length.

[Uranium235]

Just to add to what Shibby said in regard to barlows and DSOs:

Using a 2x Barlow quadruples your exposure time and you will experience very bad star shapes away from the centre of the frame (looks a bit like coma). A big no no no no no no for barlows, always stick to prime focus (unless doing planetary).

This query pops up so often Im going to get a T-shirt printed stating "No barlows please, were British"

[brantuk]

I like to think that a 2x barlow halves the size of an eyepiece. Not strictly technically true but very useful for quick calculations in your head. So a 10mm ep with 2x barlow makes it a 5mm ep.

So a 1500mm focal length scope with 10mm ep gives 1500/10 = 150x and if you 2x barlow it you'll get 1500/5 = 300x magnification. Simples! Squeak!

[banner001]

I like to think that a 2x barlow halves the size of an eyepiece. Not strictly technically true but very useful for quick calculations in your head. So a 10mm ep with 2x barlow makes it a 5mm ep.

So a 1500mm focal length scope with 10mm ep gives 1500/10 = 150x and if you 2x barlow it you'll get 1500/5 = 300x magnification. Simples! Squeak!

the way ive always interpreted it is as follows (both lead to the same answer):-

So a 1500mm focal length scope with 10mm ep gives 1500/10 = 150x and if you 2x barlow it you'll get 3000/10 = 300x magnification.

[Shibby]

Just to add to what Shibby said in regard to barlows and DSOs:

Using a 2x Barlow quadruples your exposure time and you will experience very bad star shapes away from the centre of the frame (looks a bit like coma). A big no no no no no no for barlows, always stick to prime focus (unless doing planetary).

This query pops up so often Im going to get a T-shirt printed stating "No barlows please, were British"

Oh yes, you're quite right - quadrupled!

This query does pop up a lot, but often it's because a lot of Skywatcher Newtonians can't achieve focus on a DSLR without one!

[StarryEyes]

Hi Lewis, I'm using a DSLR and was hoping to use a Barlow for planetary imaging.

[RikM]

Don't bother with the SW deluxe 2x Barlow. This is the same one supplied with a lot of their scopes and it is not very good. You would be better looking at the Tal barlows or one of the more expensive ones. Don't let the t-thread on the SkyWatcher fool you either. Planetary imaging with a DSLR is possible, but not recommended. Get a cheap webcam and a 1.25" nose piece and a Tal 3x Barlow and you will have a far easier time planetary and lunar imaging.