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5x Barlows?


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Just on my 1st ever few observations, I am immediately impressed with the difference a 2x barlow makes and realise I am, effectively, doubling the size of the scope roughly speaking.

An obvious Q Id have thought and I asked myself within minutes of 1st session, is if this 2x is so effective how would a 4x or even 'as big as I can get' be? (affordably so, I only have a lowly Celestron 130 reflector & not money to throw about, yet). Does the quality drop signignificantly that a 5x is not really a sensible idea? Im impressed with the optics so far. I have a plossl 32mm, the std Celestron 10mm (this one seems a little low-quality but fine for me) and a (celestron) 2x barlow.

thanks, JiLm

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I would not buy a 5x barlow. You will hardly ever be able to use it due to seeing conditions.

I would put money into quality eyepieces.

Once you get in more observing time you will begin to see more and more with the kit you have.

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Hi- Ok

I would not buy a 5x barlow. .

I would put money into quality eyepieces.

Once you get in more observing time you will begin to see more and more with the kit you have.

John- what exactly do you mean by "You will hardly ever be able to use it due to seeing conditions" do you mean general UK weather? but that would apply to any eyepiece be it a 5x, 2x or a wide normal one w'out a barlow at all wluld it not.. ie why moreso a 5x?

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Hi

The 5x Barlow lenses are really tools for planetary imagers not run of the mill visual observing. The problem with these high power Barlows is the amount of available eyepieces that will effectively work with them is drastically cut. You cannot ramp up power indefinitely, the atmosphere and diffraction won't allow it. The max power you can use will be around twice the aperture in millimetres. Bear in mind this is in theory, often in practice you will reach a maximum power point way below this.

Remember a Barlow is only doubling the focal length not the resolution gathering aperture of your scope.

I personally am a fan of Barlows but still wouldn't use any one higher than 3x power for visual use.

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Ok I understand I think now- good advice then/ wont go along the 5x route.

Ok I need to look at a higher power EP than my std 10mm (not vg/ came with).. or a better quality at least. Say a 1/2 decent possl 7.5mm maybe? just so I can get Jupiter a bit bigger at the least.

Btw is there a classifieds section on here? maybe such an EP could be fairly common s/h.

thanks chaps.

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There is a claasified section here but i think you need 50 posts before it become visible/available to you.

I will say that a good quality high powered EP, is a better option than a 3x-5x barlow. Something in the range of 6-9mm will be good for planets.

My personal choice is Vixen NPL's. Many others prefer BST's. Apparently there is little difference between both in quality or cost.

Check them both out.

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There is a claasified section here but i think you need 50 posts before it become visible/available to you.

I will say that a good quality high powered EP, is a better option than a 3x-5x barlow. Something in the range of 6-9mm will be good for planets.

My personal choice is Vixen NPL's. Many others prefer BST's. Apparently there is little difference between both in quality or cost.

Check them both out.

+1 for the BST's, one thing you will find though is that Plossls at a short focal length have almost no eye relief (the distance your eye needs to be away from the group of lenses inside the eyepiece in order to achieve focus), which means you often have to have your eyeballs right up close for a Plossl, not suitable if you need to wear glasses if you suffer from something like astigmatism. The BST's have a much longer eye relief, so are more comfortable and should be suitable for glasses :).

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A 5x Barlow is really for astro-phtography, not visual use. Stick with the 2x, which is perfect for visual use, if you want to push the magnification, get another good quality ep, I suggest an 8mm, the BST Explorer/StarGuiders are very good.

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+1 for the BST's, one thing you will find though is that Plossls at a short focal length have almost no eye relief (the distance your eye needs to be away from the group of lenses inside the eyepiece in order to achieve focus), which means you often have to have your eyeballs right up close for a Plossl, not suitable if you need to wear glasses if you suffer from something like astigmatism. The BST's have a much longer eye relief, so are more comfortable and should be suitable for glasses :).

I wear glasses all day every day but i do not wear them while observing, never have, never will.

So for me eye relief is not an issue, but yes i will admit that the BST's seems to have a longer eye relief then the NPL's so are more suited to people who need to wear glasses while observing.

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I wear glasses all day every day but i do not wear them while observing, never have, never will.

So for me eye relief is not an issue, but yes i will admit that the BST's seems to have a longer eye relief then the NPL's so are more suited to people who need to wear glasses while observing.

I only say so because I've noticed I need to. I am rather unfortunate in having astigmatism in my eyes, and without glasses every eyepiece just looks cheaper than it is!

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There not cheap either, an expensive mistake to make.

Thats a good point! hadnt really considered prices per se, just general basics Im still getting to grips with.

Ive had a peep at Vixen NPL's which seem a little dear.. was hoping £20 maybe rather than £35 for one EP for my humble beginnings.

Why an 8mm (which seems the more common approach) ratherthan a 6mm, or even a 4mm? surely the lwr the mm the bigger the object.. or am I missing a trick/ up the wrong Question-tree (again!). thx

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Thats a good point! hadnt really considered prices per se, just general basics Im still getting to grips with.

Ive had a peep at Vixen NPL's which seem a little dear.. was hoping £20 maybe rather than £35 for one EP for my humble beginnings.

Why an 8mm (which seems the more common approach) ratherthan a 6mm, or even a 4mm? surely the lwr the mm the bigger the object.. or am I missing a trick/ up the wrong Question-tree (again!). thx

8mm can be barlowed with a 2x barlow to produce (effectively) a 4mm, any more and you would be pushing it really.

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Buy the most expensive EP's you can aford, S/H makes sense, but make sure you know what you are buying, you can also look here......http://www.astrobuysell.com.

You will be amazed at the difference quality EP's make, I bought a Meade 5000 25mm and was so impressed with it

I've gone on to aquire 6.7 and 16 UWA's and a 34 SWA all give stunning views.

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8mm can be barlowed with a 2x barlow to produce (effectively) a 4mm, any more and you would be pushing it really.

Yes I was thinking Id use my barlow on the 8mm.. but what exactly do you mean by ..'any more "and you would be pushing it really"'? the 6mm would not be able to focus, or have a too-low light capabilities or s'thing? Im not quite getting the reason for the 'cut off point' of the 8mm as it were you see. Id have thought (naiively obviously but I know not why) a 4mm and a 2x barlow would be twice as good/ Id be getting get right down n groovy to a '2mm' so the object would be even bigger/ best.. no?

sorry for the basic Q: I have read stuff on EP's but this page 1 Q seems to have been glossed over, or Im not getting s'thing. thx

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Yes I was thinking Id use my barlow on the 8mm.. but what exactly do you mean by ..'any more "and you would be pushing it really"'? the 6mm would not be able to focus, or have a too-low light capabilities or s'thing? Im not quite getting the reason for the 'cut off point' of the 8mm as it were you see. Id have thought (naiively obviously but I know not why) a 4mm and a 2x barlow would be twice as good/ Id be getting get right down n groovy to a '2mm' so the object would be even bigger/ best.. no?

sorry for the basic Q: I have read stuff on EP's but this page 1 Q seems to have been glossed over, or Im not getting s'thing. thx

A 4mm would be getting you 162.5x magnification (if your scope is the 650mm Focal Length version), and the maximum useful magnification for that scope is 260x. Beyond that magnification, and the image would have less detail and be much more blurry. At a 2mm eyepiece, you get 325x, which is far too much for practically every object, bar the Moon. Stick to the rule of maximum magnification of 2x your aperture in mm (130 * 2 = 260x) or 50x your aperture in inches (5.1 * 50 = 260).

In addition, in the UK, the conditions of the atmosphere are rarely stable enough to allow you to push beyond 200x and still get good detail.

These links should help generally:

http://stargazerslounge.com/topic/43171-eyepieces-the-very-least-you-need/

http://stargazerslounge.com/topic/25793-primer-understanding-and-choosing-eyepieces/

http://stargazerslounge.com/topic/35441-essential-reading-for-those-who-are-thinking-about-getting-into-astronomy/

http://stargazerslounge.com/topic/98716-abbreviations-acronyms-and-glossary-of-terms/

In addition, look through the articles here:

http://stargazerslounge.com/forum/43-primers-and-tutorials/

HTH.

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Hi Naemeth- really appreciate the links. I have been thru that 1st today in fact/ (7+ pages so quite hefty to sift thru again for the calculation). 2nd and 3rd definitely useful basic astronomy info.

Thanks for explanation re max magnification relating to the scope I have.. thing is I cant remember which/ where exactly I saw the calculation regarding the magnification relation from the scope, and therefore to the eyepice suitable. Its all a bit OTT complicated tbh for sore eyes.. or rather finding an answer w'out being able to ask is hrs of me trawling again like a needle-in-haystack scenario.

Maybe I could simply ask as I dont really understand and all I want to do is just get cracking..

Is 8mm for whatever reason, the lowest mm eyepiece practical/ suitable for my 130EQ scope? it seems so but I still dont know why (IE what exactly is 'usefulness' apart from what I gather bfrom yr reply, that it is atmosphere interferance getting OTT with a lens below 8mm). thanks JiLm

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Q didnt include the 2xbarlow, so should be..

Is 8mm for whatever reason, the lowest mm eyepiece practical/ suitable for my 130EQ scope, using a 2x barlow? it seems so but I still dont know why (IE what exactly is 'usefulness' apart from what I gather bfrom yr reply, that it is atmosphere interferance getting OTT with a lens below 8mm). thanks JiLm

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The point that is being made is that there is a theoretical maximum magnification that can be used with a scope - that is often expressed as 2x the aperture of the scope in mm so for a 130mm scope the figure is 260x. However, that assumes perfect optical quality, perfect viewing conditions and that the optics in the scope are perfectly aligned.

In reality experience tells us that none of the above factors will be true. The biggest factor are the seeing conditions which are just not good enough for 99% of the time to allow a scope to perform to it's maximum capability.

So our experience is that the maximum useful magnification that can be used will be rather less than the theoretical max - perhaps 60-80% of it at best. Useful here means that the views will still be reasonably sharp and will show contrast well. Go beyond this and the object being viewed will appear larger but will loose sharpness and contrast so you will actually see a lesser quality view of it.

This applies to large scopes as well - my 10" newtonian has a maximum theoretical magnification of 500x but the max I've ever usefully used is around 300x and more often 200x-250x gives the best high power views.

Just another point on high magnification viewing, it's most often used for looking at the Moon, the planets and binary stars. Most observing of deep sky objects is done at low or medium magnifications, with a few exceptions now and again.

It's good to have a couple of higher power eyepieces so you can see, by experimenting, what gives the best view of a particular object on a particular night. With a 130mm newtonian I'd suggest that 150x (around a 4mm eyepiece) and 200x (around a 3mm eyepiece) would be good to have. A good quality 2x barlow lens used with 8mm and 6mm eyepieces would be a good way to get there.

Hope that helps a bit.

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John that helps alot- very gateful for your too. The more your knowledge I read, you chaps, the more I get the bug ready set to go.

So which would you go for of these: a 6mm or an 8mm Vixen NPL plossl? I am likely to stick to this and a 32mm plossl (unbranded) and the 2x barlow. The not vg/ came-with 10mm will become redundent I guess.

Id like to use it to get a better view of a planet, primarily Jupiter say: bigger prefarable, with the not VG 10mm + 2x barlow is a bit too small really.

Your advice Is really appreciated. BJiLM

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