Dob 10 inch

liljpo (Jessica) · #1 12-10-2009, 06:05 PM

Hello all,

Just wanted a bit of help from you experienced people out there so that i can get the most out of my telescope. I bought a 6.5mm plossl eye piece, but im not completely happy with what i am seeing. I have noticed that people use 2X Premium Barlow lens or a barlow lens of some kind.

If possible could someone shed some light on what this means? What is the difference between Plossl and Barlow? And will the 2X Barlow be a better eye piece for viewing planets and than my plossl 6.5mm???

Thanks in advance for any help given.

PCH (Paul) · #2 12-10-2009, 06:29 PM

Hi Jessica,

it's really quite simple. A plossl is just a type of eyepiece (ep) and refers to the way in which it's constructed. It's basically quite a simple construction, and you can get a few other styles which are much more expensive.

So you can get a range of plossl eps starting at around 6 (or 6.5mm) through to around 40mm. The lower numbers give the most magnification, since the magnification is worked out as "Telescope focal length divided by Ep focal length". In your case this would be approx 1200 div by 6.5 = 185X.

The thing with plossl type eps is that the lower the number, the smaller the hole that you look through. And also, the worse is the eye relief. This refers to the distance between where you place your eyeball, and the actual glass that you're looking through. With a 6.5mm, your eyeball would be almost touching the glass. Not a great idea, and not at all comfortable or easy to look through. You'll find that the larger the number on the ep, the better will become the size of the hole that you look through and the amount of eye relief provided.

So, what some people do, is use the larger number eps in conjunction with a barlow. The barlow lens just multiplies the magnification by 2X (or more depending on the model of barlow that you buy). So, if you found that the 13mm ep in your series had a bigger hole to look through, together with a better and more comfortable eye relief, - you could use the 13mm ep (giving 92X magnification) together with the 2X barlow. This would get the magnification back up to 185X, - the same as your way with the 6.5mm ep, but a much better way of achieving it.

Hope this helps Jessica.

to IIS by the way

PCH (Paul) · #3 12-10-2009, 06:34 PM

PS Jessica,

- imho, the better way to view planets and the moon is by using the barlow/less powerful ep method. I've found this gives a more pleasing and comfortable viewing experience. I don't like the small hole and no eye relief that the 6.5mm plossl gives. But you do however need the magnification

mental4astro (Alexander) · #4 12-10-2009, 07:09 PM

Hi Jessica,

unlike Paul, I don't like using barlows. As I too use a dob (two actually including a 10"er), a barlow adds more weight to the focuser end & can cause the scope to become top heavy & compromise balance. They also put more glass between me & what I'm looking at, reducing the amount of precious light. I, rather, prefer to save my pennies & get better quality EPs. These make viewing at high power much easier with their larger eye lens & longer eye relief & a much larger field of view, making it easier to find objects at high power.

I did have a good quality barlow, a Celestron Ultima 2X job. Never ended up using it!

It also makes for more bits & pieces to get confused with in the dark. Keeps things simple for me.

Just my take on things.

Mental

liljpo (Jessica) · #5 12-10-2009, 07:34 PM

Thanks Paul and Mental for the reply. Mental what ep do you use on your 10inch for best viewing on the planets? Anything you recommend me doing or buying to get the best results out of it?

Thanks to both of you for the post. They wer both very helpful.

Esseth (Alan) · #6 12-10-2009, 07:44 PM

Yeah i agree with that, that was actually some really good tidbits for a nub like myself.

Filed and locked away lol

mental4astro (Alexander) · #7 12-10-2009, 07:54 PM

I recently bought a Meade series 5000 Plossl 5.5mm. Bintel sells it for about $130. Oddly enough, its eye lens isn't the widest, but it outperforms my Vixen LV 5mm at half the price, but a generation younger in technology. In my 10" it gives 230X & my 17.5" 360X. It wowed my eyes out of my head its image of Jupiter.

Andrews sells Williams Optics EPs. The Planetary range is probably better than my Meade at more or less the same price.

Other IIS folk may help out for a better choice.

liljpo (Jessica) · #8 13-10-2009, 03:54 PM

Thanks all, i appreciate the help.

StarGazing (Alex) · #9 14-10-2009, 04:25 AM

Quote:

Originally Posted by mental4astro

Hi Jessica,

unlike Paul, I don't like using barlows. As I too use a dob (two actually including a 10"er), a barlow adds more weight to the focuser end & can cause the scope to become top heavy & compromise balance. They also put more glass between me & what I'm looking at, reducing the amount of precious light. I, rather, prefer to save my pennies & get better quality EPs. These make viewing at high power much easier with their larger eye lens & longer eye relief & a much larger field of view, making it easier to find objects at high power.

I did have a good quality barlow, a Celestron Ultima 2X job. Never ended up using it!

It also makes for more bits & pieces to get confused with in the dark. Keeps things simple for me.

Just my take on things.

Mental

Great point Alex, the less you have to fiddle with the better it is.

Clear skies to all. Alex