What eyepieces ?

[Dazraz]

Hi

Got a 8" Dob and the EP'S i have at the moment are :

wide angle & a 10mm.

Is there any other EP'S i could do with ?

I also have a 2xbarlow but i put it on with the 10mm EP i goes blurry is this because i have purchased a faulty barlow - it was labelled as a sky watcher 2 x barlow

Regards Daren

[John]

A 32mm plossl would be a good addition for low power. If the barlow was cheap it could be one of the non-achromatic Skywatcher ones which are rather poor I'm afraid.

If you added a 6mm or 7mm plossl to your set that would work well.

John

[Dazraz]

A 32mm plossl would be a good addition for low power. If the barlow was cheap it could be one of the non-achromatic Skywatcher ones which are rather poor I'm afraid.

If you added a 6mm or 7mm plossl to your set that would work well.

John

How much would i be looking to pay for a 32mm plossl ?

[John]

How much would i be looking to pay for a 32mm plossl ?

£29 at First Light:

Skywatcher - Skywatcher SP Plossl eyepieces

Or around £20 if you can find a used one.

John

[John]

Heads up !:

http://www.astrobuysell.com/uk/propview.php?view=27712

John

[Dazraz]

Heads up !:

U.K. Astronomy Buy & Sell

John

Thanks for the link i been looking for that website and could not find it thanks to you i have now

[Dazraz]

Heads up !:

U.K. Astronomy Buy & Sell

John

I have purchased the plossl from the link you sent me to - can you tell me what these lens's will do to my viewing as im very new to all this ?

Many thanks

[Capricorn]

Your scope is 200mm diameter and 1200mm focal length.

It appears to have come witrh an eyepiece of 10mm and 25mm.

Magnification with the 25 is: 1200/25 = 48x

Magnification with the 10 is: 1200/10 = 120x

If you have bought a 32 the magnification is: 1200/32 = 37.5x

For viewing and finding anything it is the Field of View that is relevant. This changes depending on the magnification. More magnification = less field of view.

So FoV = FoV eyepiece/Magnification.

In general most eyepieces will be plossl's and have a FoV of 50-52 degrees. So using the above:

32mm Ep has Fov of: 50/37.5 = 1.33 deg.

25mm Ep has FoV of: 50/48 = ~1 deg.

10mm EP has FoV of 50/120 = ~0.4 deg

The purpose of the 32mm is simply to allow you to see a bigger prooportion of the sky and so locate the object of your desire. You then centre it and start increasing the magnification until it is good size and clarity. Remembering that as the magnification goes up the image will get bigger and dimmer.

Scope details say max magnification = 400x. Only under excellent and exceptional circumstances. So do not expect this to ever occur. It's called marketing.

WH wrote that the smallest EP you should consider is 3/4 of the F Number of the scope. Yours is f6 so that means a 4mm EP, giving a magnification of 300x. Being honest that seems a bit small for your scope, I wouldn't go below 6 or 7mm.