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Smaller EP Focal Length vs Barlow


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Now that I finally have a telescope, I have already decided I need to see the planets bigger.  So it seems that I could get a 2x barlow and get more magnification, or I can get an eyepiece with a smaller focal length.  Right now I have a 10mm and 25mm plossl. I am looking into getting a 7.5, 6, or maybe even 3.5mm.  Or maybe getting a 2x or 3x barlow.

 

Now for the question.  When it comes to viewing planets (specifically Jupiter and Saturn), would it yield a clearer image using a middle of the road 6mm EP, a 12mm EP with a 2x barlow, or a 18mm EP with a 3x barlow? Or is the answer, assuming a middle of the road barlow, they are all the same?

 

 

Thanks,

Curtis

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HI Curtis,

I know I'll probably be shot down on this, but I'd avoid the Barlow and the 3.5mm ep. Instead, a 5 or 6mm ep (giving X240 or X200 respectively) is probably as much planetary magnification as your scope will allow and still deliver sharp views. Even so, it'll only be sharp on those nights of perfectly transparent 'seeing'. Any more magnification than this will yield a softer, more fuzzy view.

I find that with even rural UK skies, x200 is as much as I can use, with lower magnifications actually giving sharper views.

Kev

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Me too!

In general supplied EPs are not the best. A 25mm EP is probably quite acceptable as size is less demanding, but the 10mm you have is probably pushing it. Barlowing it won't help!

Barlows are essentially an economic alternative to having more EPs. If you want a spread of 8 magnifications, you could either buy 8 EPs or 4 EPs and a Barlow, saving money! But in an ideal situation, specific EPs are the best option.

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A Barlow can be useful, or it can be the weakest-link in your optical pathway. This is why a always suggest that a person get a top-of-the-line Barlow if they decide to get one at all. I have both a 2X and 3X Barlow made by TeleVue. There are comparible ones to the TV ones. A cheap Barlow can impart a dimmer image with fuzziness - regardless of how good the eyepiece you are starting with is. So if you decide to get a Barlow, it's best, imho, to save up for the top-drawer one. Or it will likely serve only to collect dust somewhere.

A PowerMate is another option, but I won't go into these here.

Enjoy,

Dave

 

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I'm not sure what I would do without my Baader VIP barlow-the ultimate astronomers lego set. A good barlow can actually improve an eyepiece's performance, and I agree totally with Dave- it must be of good quality. There may be some VG inexpensive ones, word has it that the Baader Q barlow works well.

I use my barlow for all my planetary/lunar work now if seeing allows med to high mag.

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I use a powermate (2x) which gives the same net result of doubling the image at the eyepiece. This gets some fair useage and it has a valid place in my box.

Recently I have found myself gravitating towards buying eyepieces for gaps that I think I have in my collection even where the PM fits in and in some cases gaps don't even exist. However I have eyepiece buying OCD and this is nothing to do with the powermate.

Back on topic I have had barlows in the past including the Orion Ultrascopic 2x which I found to be a great bit of kit and the views were as good as those through a dedicated eyepiece, at least to my own eyes anyway.

Steve

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Hi again,

On the subject of 'better eyepieces', just remember that they don't have to be hugely expensive to be better than the ones supplied with the scope. Although for general observing I prefer wider fields of view (minimum 68 degrees), for planetary viewing this doesn't really matter, and so 55-65 degrees is probably adequate. So, some decent plossls might be a good place to start (such as Revelation Astros), aren't very expensive. Secondhand is always an option, and there are some good bargains to be had on ebay. My planetary EPs are a BST starguider 5mm (£35), and a William Optics 6mm (about £80).

Kev

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