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Patbloke

Eps and Barlow use...

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I have read the primers on here about eps, and I'm pretty sure I have seen a comment somewhere which answers my question, but I cannot find it... So can someone help?

What is the difference between:

  • Using a 6mm Eps
  • Using a 12mm with a 2x Barlow

Thanks...

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The Barlow solution gives you the same magnification as the 6mm but with the 12mm's Field of View.

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The Barlow solution gives you the same magnification as the 6mm but with the 12mm's Field of View.

That is good news I think... I read once that because I have a 'fast' scope I should get an 8, 18 and 25mm for it... so the fact I have just bought a nice 15 & 32mm and I'm getting a real nice Barlow for my birthday, I should be pretty close to 8 & 18mm when using the Barlow... No need to buy another Eps just yet I feel...

Now back to my filter research?

Thanks for the speedy reply :(

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Just a bit of unrequested advice. :(

Don't look too much into filters, here's why:

1) color ones help to notice details on planets but you get complete false color. I personally don't like it and many shared this opinion on other threads on the subject, 'though not all.

2) The nebula filters (UHC, OIII) will help on nebula only (not on galaxies, clusters or any other thing). The UHC should be ok on your scope, the OIII will be too harsh cutting down too much light. They are expensive so the same money, put into a larger aperture reflector would show you much more on nebulas and also galaxies, clusters and even a bit more on planets (higher resolution).

Bare in mind this is a personal opinion. Others may have a different one so read more about it and ask around before making your mind.

Clear skies!

Edited by pvaz

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Just a bit of unrequested advice. :(

2) The nebula filters (UHC, OIII) will help on nebula only (not on galaxies, clusters or any other thing). The UHC should be ok on your scope, the OIII will be too harsh cutting down too much light.

Clear skies!

Thanks for that advice, much appreciated... I love this site! :)

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The Barlow solution gives you the same magnification as the 6mm but with the 12mm's Field of View.

Not quite sure what you mean. The 12mm will retain it's original apparent field of view, which might or might not be the same as a 6mm. The true field of view will definitely be different.

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Not quite sure what you mean. The 12mm will retain it's original apparent field of view, which might or might not be the same as a 6mm. The true field of view will definitely be different.

One thing that would be retained with the barlow approach is the eye relief of the 12mm eyepiece. This can be an advantage as short focal length plossls (ie: 6mm) have pretty tight eye relief which can make them uncomfortable to use. So the 12mm + 2x barlow would be a bit more comfortable to look through than the 6mm on it's own.

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Thanks for that advice, much appreciated... I love this site! :)

You're welcome. ;)

I just realize I didn't mention light pollution filters. :( Those may actually be handy if you have LP on your observing site(s).

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One thing that would be retained with the barlow approach is the eye relief of the 12mm eyepiece. This can be an advantage as short focal length plossls (ie: 6mm) have pretty tight eye relief which can make them uncomfortable to use. So the 12mm + 2x barlow would be a bit more comfortable to look through than the 6mm on it's own.

That's about it as far as i know and experience. Its all about eye relief. Its more comfortable to look through an 12mm EP then it is to look through a 6mm EP+2x barlow.

Edited by LukeSkywatcher

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Its more comfortable to look through an 12mm EP then it is to look through a 6mm EP+2x barlow.
... but the barlow will degrade the image to some extent, this can be critical when observing low contrast features near the limit of visibility ... in terms of glass, less is better than more, this is why a moderate focal ratio (f/8 to f/10) is preferable as there is then no need to use a barlow - there is adequate eye relief with the 7 to 9 mm eyepiece you need for high power, even if it's a Plossl or Orthoscopic.

If you're going to use a barlow, invest in the best. The cheapest barlow I have found to be even remotely satisfactory is the Celestron Ultima SV.

For imaging, barlow / tele-extender type devices are essential to increase the image scale, but again the cheaper ones are a waste of money.

Edited by brianb

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...

If you're going to use a barlow, invest in the best. The cheapest barlow I have found to be even remotely satisfactory is the Celestron Ultima SV.

QUOTE]

Thanks everyone... Genius, I am so lucky as my girlfriend has bought me the Celestron Ultima Barlow (I think on Johns recommendation?)for my birthday :( So I'm looking forward to trying that out after tonight when she brings it round... John I think it was you that pointed out that a 6mm plossl could be an uncomfortable experience in a past post.

I'm happy now, I might put the 6mm on the 'for sale' page as it's brand new... or I might just keep it just incase I spot something that needs a close up, or ready for my scope upgrade in the future!

So there you go, I'm think I'm sorted and have a strategy for viewing... thanks

P.S I am considering telling the kids that a LP or UHC filter would make a superb birthday gift :)

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