The difference between eyepieces

[Lerxst]

I just got as the signature says, a Meade Series 4000 eyepieces and filter set (£150 - purchased in the US ). Because of this, I suspect, it's naturally cloudy today.

Anyway, there are 6 super plössl eyepieces and what I'm wondering about is, the 9.7mm, 12.4mm and 15mm are fairly close to each other, so is there any benefit at all in using i.e. the 12.4mm over the 15mm or vice versa?

And if there's any difference, what would it be suitable for? Planets? DSO's?

And will there be any difference on my Explorer 150PL as opposed to other scopes with a shorter focal length?

[John]

You have a good set of eyepieces there - they will work very well in your scope.

For higher power viewing (ie: planets, the moon, double stars etc) you would use the eyepieces with the shorter focal length (eg: the 9.7mm gives higher power than the 15mm). You find out how much power by dividing the focal length of you scope in mm

(1200mm in the case of the 150PL) by the focal length of the eyepeice in mm so the 9.7mm eyepiece will show an image magnified 124x approx - this would be considered a medium power for your scope. You can repeat the calculation for all your eyepieces. In a shorter focal length scope the magnification an eyepiece gives would be less of course.

The lower power eyepieces are used for deep sky objects such as star clusters, nebulae, galaxies etc.

These are not hard and fast rules of course - your can look at planets at low power and you can look at DSO's at high power just as you wish.

John

[Lerxst]

Thank you for your reply, but with the case of the 9.7mm and 12.4mm; that makes 124X (as you say) and 96X respectively, but will the difference be that much when viewing i.e. Jupiter or the moon?

Yeah, I've seen that lower power are good for DSO's, but why? In my (limited) view and take on these things, the higher the magnification, the better and more detailed the object will be?

[The Warthog]

I try to space my eps so I have a 50% increase from one to the next. This seems to be a good spacing, as I don't find the difference between 15mm and 12.4mm to be all that significant. A kit is a jumping off point, to build your ep collection on, although you may still use it for many years. After a while, check on which eps you are leaving in the box most of the time, and consider selling them off for eps you will use.

[mike.brightmore]

Problem is that the more we magnify an image the fainter / dimmer it becomes. Most DSOs are very faint to begin with so magnifying the image just makes them disappear. Also some are quite big to start with (the Andromeda Galaxy M31 is about the width of 6 full moons) so a magnified image only gets a very small portion of the object in the field of view. So high magnification is fine for bright objects like the moon and most planets. Its also ok for the brighter DSOs like Globular Clusters and splitting double stars. For faint objects like nebulae and galaxies you're best with lower magnification - unless you have a mega big telescope to collect more light in the first place.

[Lerxst]

Yeah, I know what you mean, Mike. I was just out watching Jupiter (the clouds disbanded!), and with the blue filter and 32mm (through 2 barlows just to see if it would work!) I hit instant paydirt! The planet was clear, I could see both bands very clearly and more - and much better than through the 25mm and 10mm that came with the scope, so I regard those two as just a cheap gimmick.

But 32mm through 4X barlows meant 8mm, so any other eyepiece, i.e. the 15mm which would give me a 3.75mm, gave nothing but an out of focus blur. So I guess the 300X max magnification for my scope is pretty spot on.

Anyways, fantastic!

On the more embarassing side, is there any trick to working the finder scope? I found this link in another thread on this sub forum, and trying to find M31, I was completely unable to locate the 'lower' star in the W on Cassiopeia and navigate from it. First and foremost since the magnification was as far as I could tell, too large to fit Cassiopeia in the finder scope, but also because it's upside down and possibly left/right reverted?

[Lerxst]

I try to space my eps so I have a 50% increase from one to the next. This seems to be a good spacing, as I don't find the difference between 15mm and 12.4mm to be all that significant. A kit is a jumping off point, to build your ep collection on, although you may still use it for many years. After a while, check on which eps you are leaving in the box most of the time, and consider selling them off for eps you will use.

Sounds reasonably, Warthog! I've been thinking along the same lines. I know a lot of people hate these kits and would rather have one save up for some "real" eyepiece, but the thing is, I don't know what to expect with the different eyepieces and as far as I can see, there's no astro club nearby in which I could try other eyepieces and make up my mind, so this is the easiest route for me.

And besides, US $249 is not exactly going to break the bank

[John]

..... So I guess the 300X max magnification for my scope is pretty spot on....

You will find that you can only use that sort of magnification on the very, very best of nights - thats because of our UK viewing conditions, not any problems with your scope !.

Some objects can take magnification better than others. Jupiter I've found best at around 170x - even with my 5" and 12" scopes more magnification than that does not show any more detail. Saturn however seems to take higher magnifications better.

Thats why it's useful to have a range of eyepieces - so that you have something in your "kit bag" to suit a variety or objects and viewing conditions.

John