Shorter eyepice FL versus 2X barlow

[slothead]

Generally speaking is there any advantage in using a 10mm focal length eyepiece over using a 2X barlow with a 20mm EP?  I'd like a wide angle EP, but will the barlow destroy that WA view (or even create the WA view for a narrow angle EP)?

[Ravenspurn]

Hi slothead.

You're going to see about half of what the 20mm ep displays, because what you are observing will be twice as large.

However, your Apparent Field of View (x°) will remain the same. So in essence, you have the magnification of the 10mm, but it won't feel like you're looking down the middle of a pipe.

Hope this helps.

Cheers

Leon

[ronin]

You will in general need to get a good barlow, those extra bits of glass add some aberrations, it all depends on how much they add. Some barlows can be bad others you see no difference.

One way of looking at it is that no barlow was ever actually designed specifically for your scope and eyepiece combination. Another is that a reflector treats all wavelengths the same so no chromatic aberration, introduce a 2x barlow and as that is a lens you have introduced some, even if minimal and you cannot detect it.

Since I do not mind collecting eyepieces I tend to just use an eyepiece and not bother with a barlow.

[mikeDnight]

Many modern top end, short focal length eyepieces use an integral Barlow in their design with absolutely no ill effects. Modern barlows are usually very good and introduce no detrimental effects to the overall quality of the image. Barlows of yesteryear were not so good, as a consequence the Barlow lens has an undeserved bad reputation. Using the Barlow will maintain a decent eye relief and therefore add to the comfort of your observing. In turn you could well see more as you're not straining to look through a tiny eye lens with minimal eye relief.

Mike

[astrofox]

Whilst its true some modern lens (e:g Baader Hyperion) use a barlow element in their design it should be remembered that it is designed specifially to work with the prime elements of that lens. Adding one manufacturers lens to an adhoc designed barlow cant be an optimal solution.

In photography barlows or focal extenders have been arround for many years. Conventional wisdom was they would never equal a prime lens for sharpnes aberation and chromatic control.

IMHO barlows have their place but only after prime lens eyepieces configurations have been exhausted.

[slothead]

Excellent responses all!  Thanks guys.  While I'll acquire a barlow, I may only use it as a last resort (after experimentation).

[bmtta2003]

I'm so glad this question was asked. I'm new to astronomy and just got a good beginner scope. It's an Orion 130st. The scope comes with 10 mm and 25 mm lenses. The maximum useful magnification of this telescope is 260x.  For planetary observation I would like to use a higher magnification than I currently have. I have been thinking of purchasing a 2 and 3x barlow lens, but I could also buy a 3mm and 5mm lens. Which will give me the best results?  The scope has a 650mm focal length so the 3 mm would approach the max useful magnification, but still leave me  a little buffer room. So to condense this question; with this scope will I notice any difference between using a Barlow lens or a new lens giving the same magnification? 

[astrofox]

Whilst the theoretical max magnification is x260 you would be pushed to realise this due to seeing conditions in the atmosphere. I would suggest that on most nights x180 would be a more realistic goal. However if you're in a clear desert area of the States you should do better.

To answer your question as to  "would you see  a differance ?" The answer is perhaps, it depends on the quality of the barlow and the prime lens. Sorry this seems like a fudge answer but there are too many factors in play here.

However the use of the barlow combination would help on eye relief as short focal length lens <5mm have very liitle. You have almost to glue your eyeball to the objective  . If your happy with the 10mm I would take a chance and buy a barlow.

In spite of my reticence over barlows I do possess one for use with my planetary DMK camera. Its a Meade 3 element APO and serves me well. And yes I do use it occasionally for visual work

[bmtta2003]

Thank you for your reply. Unfortunately I do not live in a desert area and am approximately 15 mi from a large city. I will try a Barlow first and hopefully have good results. My 10mm works great, and I can see Jupiter very clearly albeit at this magnification its not very detailed. I would like to get a good view of one of its moons in transit while it is this close to earth. 

[Piero]

Among the advantages of having a 10mm instead of a 20mm+barlow2x are:

- less weight (think about an 31Nagler + 2"Barlow 2x).. 

- less height (similar)

- if the barlow is not very good, you can introduce aberrations

- if you use a refractor, you might need a decent strong diagonal, particularly if you are using a 2" barlow and decide to put it between the eyepiece and the diagonal. 

- it is more practical. 

Rather than a barlow, I suggest you a telextender or a powermate. You just put it and don't realise there is something in between your eyepiece and your scope.

Just a thought

Piero

[astrofox]

I would echo Piero's comments on the powermate. Expensive but a big step up over the conventional barlow. Now if only I could afford one   Hummmmm!

[John]

It's worth remembering that Jupiter does not really respond well to ultra high magnification, even with large aperture scopes. With my 12" dobsonian I find 150x - 200x often gets the most detail out of the cloudbelts of the giant planet. With your 130mm scope I would expect 120x - 140x to be more effective than higher magnifications. You can view the planet at much higher power of course but the surface features get washed out and you see less of them than you do at lower powers despite the planetary disk looking larger in the eyepiece.

Fortunately moon shadow transits are relatively common events on Jupiter so sooner or later you will see one in progress. Jupiter's orbit means that its distance from Earth varies between 588 million km and 968 million km. It's never exactly close !

[bmtta2003]

My 10 mm lens gives me X65 magnification. A 2x barlow lens will put me right in the range you recommend. I dont know what a powermate is, so off to Google I go  thanks for all your replies

[John]

My 10 mm lens gives me X65 magnification. A 2x barlow lens will put me right in the range you recommend. I dont know what a powermate is, so off to Google I go  thanks for all your replies

A Powermate has a similar effect to a barlow lens but does not change the focal position or the eye relief of the eyepiece that it is being used with. They are superb optical devices with a price tag to match - around £150 and upwards.

[bmtta2003]

Okay I just learned what a powermate is and their advantages over a Barlow lens. I found a retailer that has 2.5x and 5x televue powermates. They both sell for $205.00 USD.  I probably wouldn't notice any difference with my current telescope Orion 130st between the barlow and the powermate. However, I assume if I should move to a more advanced telescope I would be better off with higher quality lenses. 

I keep reading that beginners often get caught up in the magnification of an object and actually get worse results. Like most beginners I immediately want the 5x powermate because it's the same price. If i get the 5x and use it with my 25mm that would give an effective x125 lens. If used with the 10mm lens this puts me well passed the theoretical maximum magnification of this telescope. So it would seem in my circumstance I would be better off with the 2.5x powermate assuming that in the future I would want a higher quality lens  for a higher quality telescope.

[John]

If you want something with similar qualities to the Powermate at less cost, have a look at the Explore Scientific Focal Extenders. I've tried the 2x in this range and found it very nice

A 5x amplifier of aby brand / type is going to be of limited use for visual observing I think. They are mainly used by planetary imagers who need to get a large image scale.

[bomberbaz]

I recently bought and have tried out an orthoscopic 2x barlow as in my sig and early results are very good indeed. The views do not appear to suffer when using the barlow although I have not yet compared under dark skies with a decent ep that is equivalent to a barlowed version.

Got it at a very good price and it seems better that the Celestron version I also have. If you search on here it has some very good reviews also.

steve

[Piero]

If you want something with similar qualities to the Powermate at less cost, have a look at the Explore Scientific Focal Extenders. I've tried the 2x in this range and found it very nice

A 5x amplifier of aby brand / type is going to be of limited use for visual observing I think. They are mainly used by planetary imagers who need to get a large image scale.

The ES Focal extenders seems very similar to my Bresser 2x, just a bit larger and less taller.. 

I don't know whether the design is the same, but if so, I agree that it is really a nice piece of optics.

You just put it and forget about it!