Pushing beyond the 'useful' magnification limit

[Overtime]

Hi all,

I bought my first telescope, the NexStar 4SE, over the summer

and I am really pleased with it. It came with a 25mm plossl eyepiece.

Towards the end of last year, I bought a 2x barlow lens in order to get a better view of Jupiter and now I'm thinking of investing in another eyepiece.

The maximum useful magnification for the 4SE is stated as

x240. The focal length is 1325mm which gives me

magnifications of x50, x100.

My question is what focal length eyepiece should I go for next:

I want to get the 9mm but that results in a magnification x147,

x294. Is the maximum magnification a hard limit in your experience? Would I be better off with a 12mm eyepiece which

gives me x110, x220 mag. Note the x110 magnification is largely redundant given that I have x100 with my 25mm + x2 barlow.

Also, I'm thinking of buying the X-Cel LX series. In your experience, is it a good model?

Thanks for your help.

Cheers

Cheers

Jas

[RikM]

My experience has been that the maximum potential magnification is usually a bit optimistic. I can very rarely use any more than 170x magnification. Since I live on the edge of a housing estate, my local seeing is not great but about average. On the moon and double stars I can use higher magnification sometimes.

I find it best to stick to a maximum magnification equal to the aperture in mm of the scope. E.g. 150x in my 150P, or 240x in my 250PX.

[Squagnut]

In my experience, "maximum useful magnification" is a matter of opinion. You can push it all the way with a 6mm EP, but while that will show e.g. Jupiter nice and large, you'll have poor definition - i.e. little surface detail. This has more to do with the aperture of your telescope than the EP you're using.

I'd get a 10-12mm EP anyway, rather than rely on a 25mm + 2x Barlow, simply on the principle that the less glass the light goes through, the better.

[kenmyers]

You should get something mid way like a 18mm plossl or similar as you can always use your barlow on it and will give you excellent views.

With the barlow you will see Jupiter very well but it will be blurred because of the magnification but not too blurry to make it bad. It will still show detail in the cloud bands. Max magnification is a limit beyond which your views start getting dimmer and blurryer. At 9mm it is your limit, but it will work. You always get a fantastic view at 18mm of jupiter, this will show the clouds too.

[WayBig]

I think it depends on the target.

Agreed re Jupiter, too much magnification gives a large but poorly defined view.

I like going way beyond the 'useful' magnification on the moon and watching it drift past. The view might not be pin sharp, and looks like it's water, but it's great fun

[kenmyers]

In my experience, "maximum useful magnification" is a matter of opinion. You can push it all the way with a 6mm EP, but while that will show e.g. Jupiter nice and large, you'll have poor definition - i.e. little surface detail. This has more to do with the aperture of your telescope than the EP you're using.

I'd get a 10-12mm EP anyway, rather than rely on a 25mm + 2x Barlow, simply on the principle that the less glass the light goes through, the better.

Also agree with this. I have a 4mm eyepiece which, with the barlow still shows the orion nebula and detail (although at low res) This is using effectively a 2mm eyepiece which sounds rediculous, and is rediculous, but it does work.

Get a 18mm and go for a 10mm or 12mm as well. A good selection for different targets is a real upgrade that can save buying a new scope.

[umadog]

The maximum potential useful magnification assumes excellent optics. In practice, all of these maxima are restricted by the atmosphere. However, with a smaller scope the image is also getting very dim at higher powers.

[Overtime]

Thanks for all the advice guys.

I ended up going for a X-cel LX 9mm eyepiece.

I really wanted to push the magnification factor out,

even if it was to a semi-ridiculous level.

I think I'll wait 6months and buy an 18mm eyepiece

next. I really want to get into astrophotography

too but I'm a bit concerned with the cost.

In a few months I'll probably be back asking more questions!

[kenmyers]

nice choice. For your next eyepiece you should get (depending on your success with the 9mm) a 14mm-16mm as this will give you more magnification options with your barlow (getting an 18mm would make your 9mm an extra that you wont need as the 18mm with the x2barlow = 9mm)

14mm = 7mm with x2barlow

16mm = 8mm with x2barlow

[Catweazel]

Hi, what would be the real difference between an 8mm and a 10mm eyepiece. For example, in my scope (f8) with 120mm apperture, I can see Jupiters bands (although they drift in and out), with a 10mm eyepiece, and it looks obviously bigger than in the 25mm eyepiece. Would there be much difference though between 10 & 8 mm? I Have a barlow on the way to me, but I think that barlowing the 10mm, which will push mag up tp 200x, might be a bit of a stretch, so thought 8mm might be better?

[Carbon Brush]

Following on from Catweazel's question.

I have found that the atmosphere, rather than the optics is usually the limit.

When pushing around the limit, a small increase in mag makes a significant degradation in image. For example 8mm vs 10mm EP. That is keeping all else equal. Same time, same scope and EPs from the same family.

David.

[John]

Some objects respond to higher magnification better than others. Jupiter almost always looks crisper and more contrasty with my scopes at 150x - 180x wheras Saturn and Mars seem to stand up well at over 200x, seeing conditions allowing.

Binary stars are one subject where I do push the magnification up beyond "sensible" levels on occasions.

While the seeing conditions are a major factor, I think optical quality of the objective lens or mirror plays a part too. Top drawer optics and spot on collimation do seem to allow higher magnifications to be used more often and more usefully.

[kenmyers]

@catweazel The real difference will be the size of the viewed object and the brightness and the clarity. By gaining viewable size you are decreasing clarity and brightness by a factor. This matters more for larger, faster scopes.

Although this will not really make that much difference with your scope but the size will be a BIG improvement (pun intended).

I have loads of eyepiece options and even more including the barlow on to each. I love to play around and find my limits night by night. Many times I have used my 4mm on jupiter and I can see cloud bands and the GRS, also it really shows off how far away those four moons really are from the planet itself. The cloud bands are blurred at this FL but you can pick them out (clearly around 6 of them) and gain as much detail as you can put in time-wise. The colour of the planet also really stands out at higher mag.

Since you have a barlow on the way just try to barlow your new 9mm and see what happens and report your findings here

[umadog]

"By gaining viewable size you are decreasing clarity and brightness by a factor. This matters more for larger, faster scopes."

Why does this matter more for faster scopes?

[kenmyers]

@all

"By gaining viewable size you are decreasing clarity and brightness by a factor. This matters more for larger, faster scopes."

I do believe that I am wrong about this in this situation, I think it relates more to imaging as you will notice the loss in brightness more. I heard about this when asking about imaging the veil nebula on cloudynights.com. Disregard that part.

[Catweazel]

Since you have a barlow on the way just try to barlow your new 9mm and see what happens and report your findings here

Thanks Ken, advice is much appreciated

The lens is 10mm, but I will certainly barlow it (when barlow arrives) and let you know what Jupiter looks like at 5mm in my scope! The barlow is a great idea, as my 10, 25 & 32mm can all be halved, thus giving me quite a nice broad range of eyepieces

Cheers

CW

[twotter]

It only happens occasionally but those nights when I can go to the highest mag my setup allows are very special. January 2010 and viewing Mars is an astro memory I'll never forget

[umadog]

Oh I see. Yes, for imaging the angle subtended by the primary is the equivalent of the exit pupil and is what regulates image brightness.

[Overtime]

Hi all,

So the 9mm X-Cel LX eyepiece arrived a few days ago and

I had a go with it tonight.

It's a really nice eyepiece. Much better than I expect (but then

again the only other one I have is the default 25mm Plossl

which came with my NexStar 4SE)

The crescent moon was available to see so I decided to take a

video... with my iphone. It's a little shaky because I was holding my phone.

Here are the results:

I also took a video of Jupiter but the focus was all wrong.

It was quite hard to align it too:

Cheers

p.s my first videos using a telescope!