Help with Barlow

[NosyTrader]

Hi all,

I've recently purchased a Celestron Nextar Evo 8 and a 3x Barlow. I've been informed that for viewing Jupiter with the 3x barlow and 13mm eye piece, isn't such a great idea as the magnification will be too high (I always get a blurry image).

Does anyone know if the 3x barlow will be effectively useless for me and I should potentially get rid and get a 2x? Or perhaps there are other objects out there that the 3x barlow would be useful for with this scope.

Thanks,

Firoze

[Piero]

Welcome to SGL,

Your telescope has a very long focal length already (2000mm). Therefore it does not make much sense to use a Barlow for visual at all, to me.

On your telescope, a 13mm gives you ~150x in magnification. Adding a Barlow 3x you get 450x which is far too much. Adding a Barlow 2x gives you 300x which is still too much due too the seeing. If I were you and want to buy a high power ep I would consider a 10mm, 200x.

Barlow lens make more sense on medium short telescopes where you need short focal length eyepieces for high power but you don't want to sacrifice in eyepiece eye relief, particularly in optical schemes such as plossl or orthoscopic.

[Stu]

Hi,

Your scope already has a long focal length at 2032mm. The x3 barlow triples this to 6096mm which is huge, and gives x468 magnification.

This is very high and unlikely to be useable on anything other than double stars or perhaps the moon.

I normally consider that x3 and above barlows are useful only for planetary or lunar imagers who use long focal lengths to get the fine detail by stacking multiple short exposures to capture the moments of good seeing.

I would lose the Barlow completely and get a couple more dedicated eyepieces. Your scope is considered slow at f10 so will not need expensive eyepieces to show you good results.

The 13mm will give you x156 which is a good mid high power for planets and globs etc.

I would perhaps look at a 10mm or 11mm to give you a high power for planets on good nights.

Something around 20mm will give you a 2mm exit pupil at x100 ish for great DSO observing, whilst perhaps a 32mm plossl or even a 28mm UWAN (if you have a 2" diagonal) would be a reasonable 'finder' eyepiece giving just over 1.1 degree fov.

So, 4 eyepieces would cover the bases to start with.

[NosyTrader]

Thanks for the feedback guys. Much appreciated for the advice and for you taking time to reply comprehensively! As you can probably tell I'm new to all this, but learning as I go!

[PeterCPC]

The Barlow could be used with a DSLR to take planetary AVIs.

Peter

[NosyTrader]

Thanks Peter, I will give this a go.

[Piero]

Thanks for the feedback guys. Much appreciated for the advice and for you taking time to reply comprehensively! As you can probably tell I'm new to all this, but learning as I go!

We are all here to learn and to share, so no worries about your experience level! 

In his comment, Stu (BigSumorian) also made an important comment about the type of eyepieces. As your telescope is slow (it is an F10), you don't need to buy expensive eyepieces because optical aberrations introduced by the eyepieces are usually detectable on fast telescopes (<= F5). 

[NosyTrader]

Thanks Piero. I'm going to take yours and Stu's advice and get a 10/11mm eye piece. Will ebay the barlow at some point! Used twice

Unfortunately the skies have been really dusty these past few days in Abu Dhabi. Hoping they clear up for the weekend!

[Piero]

If you were glasses, get something with eye relief >15mm . If you don't, I would still buy something above 10mm for now. 

You might feel comfortable with something below 10mm but a lot of people don't. 

[NosyTrader]

Thanks Piero, appreciated