Am I asking too much from a 130mm mirror & 5mm EP?

[the lemming]

Yesterday I received my 5mm eye piece in the post from Sky's the Limit. And very nice looking it is too. I was not able to play with my birthday present yesterday however tonight is as clear as a bell with nothing to spoil the view.

Being a novice and new to telescopes, I can only base my findings on the two kit eye pieces that came with my 130p telescope. My observations are that the 5mm eye piece is exceptionally hard to focus with using the rudimentary focusing mechanism of my Heritage 130p Telescope. I am not blaming the eye piece because a bad workman does not blame his tools. I simply have to work with what I have got.

Aiming my telescope with the 5mm for the first time was a shock. I wasn't expecting the moon to be so bright but once I got over that shock I was able to focus and get good detail. I'd be a bit of an idiot not to get good results aiming at the brightest and biggest thing in the sky.

My attention then moved to Jupiter where I became disillusioned by what I was looking at. Using the 5mm eye piece took ages to learn to focus properly. I'm not too sure if it was atmospheric conditions, with being such a cold night and high thin crystal cloud cover, or if the simple focusing mechanism was making life hard but I could never quite get Jupiter in focus. And yes my telescope is collimated as accurately as I can achieve with a Cheshire Collimator.

Using my new 5mm eye piece and a 2x Barlow was a complete let down. Before I put my eye to the telescope I was expecting to see a bigger image of Jupiter with several red lines across it. Sadly all I could see was a dark grey disc with no definition at all and three bright dots beside it, representing the moons.

Going off tonight's atmospheric conditions and the modest technical abilities of my budget telescope was I expecting too much when trying to use a eye piece + Barlow at the edge of its magnification limits?

I then had a play with my kit 10mm lens + Barlow and strangely it provided better definition of Jupiter, provided the subject was placed dead centre to be observed, otherwise it went out of focus on the edges of the eye piece. This fuzziness never happened with the 5mm eye piece. And to confuse matters, for me, the 25mm kit eye piece + Barlow was even better at showing Jupiter. Yes, the image was smaller however it was brighter and sharper.

So, to cut a boring and long story short, am I asking too much from a 130mm mirror and 5mm eye piece when viewing a subject such as Jupiter?

if the answer is yes, and I should rein in the magnification level, then what should I realistically aim for so that I don't own an eye piece that will only ever gather dust until I fork out on a bigger telescope?

Personally I do not believe that the 5mm eye piece is a dudd as I could spot the clangers prancing around on the moon, that is when I fine-tuned the focusing mechanism on my telescope. You do get what you pay for. :-)

Sorry to post such a long OP for such a short question.

[Moonshane]

Hi there

with your scope you should get good sharp images if Jupiter, assuming it is collimated (you seem sure it is) and cooled - about 30 minutes minimum before high power use.

the focal length is 650mm so the 5mm will give 130x and your scope should be capable of that. you may have been seeing the effects of the atmosphere which may have been poor for high power observing. sometimes Jupiter only allows 100x or so due to either local or high up poor seeing. sometimes I manage 200-240x with my 6" scope.

my method for finding focus on Jupiter is look and wait. does the image get sharp (like pinging into clarity for a split second every few seconds). if not tweak the focus again and wait. follow this until you get brief periods (longer and more of them on good nights) of clarity. this is normal and to be expected - welcome to planetary observing!

I find with Jupiter a light pollution filter helps increase contrast - I use a Baader Neodymium.

[Capricorn]

No idea where you re but the skies here all day have been nothing but cloud, I wonder if you have some cloud just high up

The 5mm and the barlow are too much.

The 5mm is I suspect as much as makes normal sense to use, you might get away with a 4mm.

Think you have just found out that a small sharp image can be better then a large one.

Think the 5mm would have been better then you describe, althiough I often read that the better the eyepiece the more there is a narrow band where the focus is sharp. So it could be the focuser is the problem. You often get people recommendignthe DS focuser as that has the finer 10:1 ratio as well.

I'd be a bit of an idiot not to get good results aiming at the brightest and biggest thing in the sky.

There are many who have failed.

Recall reading one person who asked where the moon was?

I am guessing the thin cloud, lower brightness of Jupiter, the slightly coarse focuser and a narrower depth of focus are the problem.

The moon being very bright will get through the thin cloud, Jupiter will not. That could be 4 things that have ganged up on you all at the same time. When written like that it could be amazing you saw anything. :eek:

[Naemeth]

The 5mm and barlow is too much for a lot of the time. When I've viewed Jupiter with a 2.5mm eyepiece (260x), the seeing has only been good for about 2-3 seconds out of a minute, after the scope has been thoroughly cooled. Jupiter is fairly big and crisp for about 1 second of those 2-3 seconds, you really don't get much time! Jupiter looks like it goes in and out of focus, just use the moons of Jupiter, when they are sharp then Jupiter should be, if it's not then the seeing wont allow the magnification. I had this when Jupiter was a featureless sphere and the moons were sharp.

Move the focusser slowly, not quickly, a little oil helps if it's stiff.

HTH

[the lemming]

As I'm at the limit of my theoretical max magnification, and more importantly on the wrong side of it, what magnification should I drop down to if at all when I get good results with my kit 10mm+Barlow?

Would I be better ditching the idea of a 5mm lens now that I have learnt how it operates in the real world as opposed to on paper?

[Moonshane]

The theoretical limit of your scope is about 2x aperture in mm so 260x. this will rarely be achieved unfortunately in the UK. I would think your 5mm will regularly be OK for short periods of good seeing. it's not that usual to see a rock solid image of Jupiter at say 100x or more, it will pop in and out of sharpness with the atmosphere.

if you want another suggestion then a 15mm Plossl would give you 43x and 86x with the barlow and this would almost always be sharp; small but sharp. I feel though that you should persevere with the 5mm

[jonathan]

You could try taking your telescope to a dark place out in the countryside, away from town or village lights and traffic. You may well find the view much better through the 5mm, but if it's thin cloud or atmosphere that's the problem then the view may still be a bit muddy.

[Capricorn]

I would ignore the term theoretical maximum, it means very little and is as it says theoretical. Not many years back the maximum was 1.5xaperture, and I have seen 2.5x and 3x creeping in, think I read 4x once.

If the theoretical occurred all the time why have cheap achros and expensive apo's, they would all deliver the same and we know they don't. Does a spherical mirror deliver the same as a parabolic ? If it did why are we/you paying for the parabolic. So the simple answer is they don't and 2x is pretty useless.

After the eyepiece focal length being equal to the f number I have the view, right or wrong, that you are losing definition at the expense of magnification, sometimes it is worth it sometimes it is not.

I would have expected the 5mm to be better then described, really suggest waiting for a clear night - no cloud at all - and having another shot. However be aware that a clear sky is one thing, the atmosphere may still not be stable, up there are several bands of air often moving very fast.

[billybob]

I've got a 5mm and a130p heritage only used it once due to clouds but when I did inad good sharp views of Jupiter bands clearly visible I've got fairly dark skies even though iwas only in our garden and views are better up the road, I've used some plumbers tape on the focuser which has helped a great deal when focusing