Barlow or eye piece

[AplexInb4]

Hey as you know I was thinking to buy a Barlow Len x2 but after some reading I thought of buying an eye piece because if a get a Barlow the light will go lower I think this is no good.
But if I get like a 6mm eye piece wont it serve well or a 4mm?
And if I could buy an eye piece could you suggest me a good one that dose not cost that much.



Aplexinb4

[WWPierre]

I suggest a barlow. You probably couldn't see the difference between a 5mm EP and a barlowed 10mm.

[AplexInb4]

Hmm so as smaller is the EP dose the same thing happens with the light?
But why is it better with a Barlow if it's not hard for you to explain to me...I would appreciate it.


Aplexinb4

[jrkirkham]

I'm with Pierre, I would get the barlow.

1) There is a drop in light, but when I compare the drop in light with the drop of light from changing lens anyway, it is not that much more IMHO

2) I like the eye relief and larger exit opening in my barlow. I usually opt for it as a first choice, even when I have a lens in my bag that yields about the same magnification.

3) If you are considering another lens now, you will probably make the leap and get one or more someday in the future. With a barlow, eveytime you buy one, you have two.

[AplexInb4]

Now I get it, yeah you guys are right about the light.
I am ordering on Monday a 6mm EP and an x2 Barlow, so I could se by my self the differences. But I don’t think it's a big problem do you guys think I should not get the 6mm EP because it's a waste of money?

Aplexinb4

[jb32828]

What kind of scope do you have?

Depending on you scope, a 6mm lens may be a waste of money. With my scope it would be, anything more powerful than a 9mm lens is too much magnification and really My goto lenses in an 80mm refractor 900mm FL scope are the 32mm and 15mm, those give me the best detail of the planets.

If anything, you may need a LESS powerful lens. A 2x barlow really isnt magnifying the image by 2x, it is increasing the focal length by 2x.

[deeby]

A 2x barlow really isnt magnifying the image by 2x, it is increasing the focal length by 2x.

Could you explain that a bit please? Usually people say that a 2x barlow is like halving the focal lenght of the eyepeice.

thanks
scott

[Carlos_dfc]

Could you explain that a bit please? Usually people say that a 2x barlow is like halving the focal lenght of the eyepeice.

thanks
scott

As far as working out the magnification goes - either way gives the right answer - so it doesn't really matter which way you think of it.
I suppose it's easier to do the maths by dividing smaller numbers, which is possibly why it's so common to say it halves the eyepiece (or doubles the magnification), rather than doubling the scope's focal length.

A barlow works by narrowing the angle of the light coming through the objective, which has the effect of pushing the 'apparant' focal length of the scope further out in front of the 'actual' objective.

I made a graphic to show the effect on the light rays a little while ago - gimme a few mins to find the thread where I posted it.........


edit
Found it.
The image I knocked-up was in fact an explanation of why a Mak is so much shorter than it's focal length... BUT...
If you imagine a barlow instead of the Mak's secondary mirror, with the angled light rays coming froom a primary lens in front of it (instead of a mirror behind it), a barlow narrows the light rays in pretty-much the same way, and extends the focal length out the front of the scope, to the point where the width of the light-cone matches the aperture of the primary lens
Lowest Magnification for my Mak

[jrkirkham]

I don't know what scope you have or what lens you are now using, so take my comments loosely.

I mostly observe with my 10" dob. I have a 6.3 mm EP, but I seldom use it except on perfect nights, and then only on planets most of the time. When the night does allow me to use it, I am really glad I have it.

I also have a 10mm EP. It yields 120X with my scope, or 240X with my barlow. This is my planetary lens. It is also the lens I use when I want to crank up the power on a star cluster, such as M13. Frankly most of the DSOs are so large that high power doesn't give as good of results as lower power.

I have a 25mm EP. This gives 48X or 96X with/without the barlow. This is my normal viewing lens. It seems to me, that most DSO's yield pleasing resuls around 100X and most planets look good about 200X.

Then I have my 35mm 2" lens. This is my star hopping EP. When looking for faint objects I almost always start with this EP and work my way up in power until I get the best view.

If you have EP's somewhere in the middle, I would buy a low power wide angle EP before I would buy a high power one. I just use the lower power more.

[AplexInb4]

Well my scope is a Omegon 130/920 And i have 2 EP 25mm and 10mm , so it's just best to get the barlow?