Please can you help a newbie on which lens to use on a skyhawk 1145

[yellowfurbaby]

Hi all i am new here

I have been browsing your forum for advice on what telescope to buy and i opted for a Skyhawk 1145. However I am somewhat stumbled on what lens to use.

the telescope came with 25mm, 10mm and barlow*2 lens.

I am interested in looking at the moon and also saturn and jupiter. I have had some pretty good views of the moon (Could be better) but have not managed to get far with the planets. With the naked eye tonight I can see jupiter, it is beautiful and bright in the sky. Through the telescope it looks like a white blob however. Very pretty but not really any features. I have tried my lenses and used combinations of them together but cannot make it better.

Are these lenses suitable for what I want? Do I need to buy a better lens? If so which one/ones.

Please help, i was so excited with my purchase and although I will never be a pro at this I thought I would at least see a couple of planets. Also any other tips would be gratefully recieved.

Kind regards

Liz:)

[umadog]

Welcome Liz!

Just so you you know, we generally call those lenses "eyepieces." We do this because each eyepiece in fact contains a series of lenses coupled together, consequently an eyepiece is more than "a lens."

There are undoubtedly better eyepieces out there then those which came with the scope. However, don't go rushing out to buy any just yet. You should first understand what "better" means. Generally when you pay more you are paying for a wider field of view (more sky visible) and a sharper view. It's harder to make wide field of view eyepiece have a sharp view to the edges of the field. You pay more to get that sharp view out to the edges.

Your eyepieces will have a relatively narrow field of view by today's standards but they'll probably be fairly sharp in the middle of the field. If the planet is in the centre of the field of view you will have a sharp view. You won't be seeing dramatically more detail with a fancier eyepiece. Spend some time with the kit you've got and learn how to use it. It's probably plenty good enough for now. When you eventually do look for eyepieces, make sure you search for designs which will work well with <f/5.0 scopes such as yours. That will help clean up the view on the edges of the field.

To calculate the magnification, divide your scope's focal length by the eyepiece focal length. So you're 25 mm gives 500/25=20 x. If you put the Barlow in there, you will get 40 x.

The features on Jupiter are quite low contrast so you need to spend time looking at it. Did you see the moons? You can download Stellarium, set your location and time, and zoom into Jupiter. That will let you know which moon is which. The higher the planet is in the sky, the less atmosphere you're looking through. That makes a radical difference to how good the views are. It will look much better at 2am than at 11 am. A rule of thumb is not to even bother looking when it's below 30 degrees elevation (Stellarium will tell you the elevation when you click on an object) although the views will continue to improve the higher it gets. Some nights the atmosphere is more stable than other nights. So go back often. Your scope should show you the two dark bands across the surface and you should see the shadows of moons going across the surface (shadow transits) if you look at the right times. You will see Saturn's rings when the planet rises later in the year. Get yourself a copy of "Turn Left at Orion" if you want to hunt some galaxies and nebulae.

There is one final thing: collimation. Your scope has a focal ratio of f/4.4 and that makes it rather "fast" in telescope parlance. This means the light cone the scope produces as it focuses the image is rather steep. This is significant because it means you need to have it aligned (collimated) pretty accurately. If not, the views will be blurry. Frankly, I think it's a mistake for companies to be aiming such fast scopes to beginners, but there we are... Here are some links to get you started:

http://www.propermotion.com/jwreed/ATM/Collimate/Chesire.htm

www.cloudynights.com/ubbthreads/showflat.php?Cat=0&Board=reflectors&Number=3033065

http://www.andysshotglass.com/

You will need more than the so-called "collimation cap" that probably came with the scope. That really isn't good enough for a fast scope. At least buy a Cheshire/sight-tube combination tool. Spend a little time learning to collimate it. It's well worth it.

[ronin]

With a scope of f/4.4 I suspect that you could need to select eyepieces carefully to work with that scope. For 100x you need a 5mm eyepiece and for 125 you will need a 4mm eyepiece.

Owning a 4mm I can tell you that they are not much use for looking through. Interesting thread on CN about "What can you use a 4mm eyepiece for?" None of the replies was for looking through.

The supplied 10mm and barlow generally are not that good, usually the 25mm is fair.

I would argue that your main useful magnification is around the 100x area, not as much as you probably expected. I say main not maximum. So try the 10mm and the barlow combination, however I suspect that the resultant image could leave you wondering what you are looking at.

If that is the case then comes the decision of what to get. I would possibly suggest a 15mm eyepiece, giving 33x, with the barlow 67x.

Still not great magnification, so instead perhaps a 12mm giving about 42x, with the barlow 83x.

Catch being if the barlow doesn't perform then you don't get the supposed benefit of it. So are left with the lower magnifications only.

If separate eyepieces then 6mm, 8mm and 12mm, over time. Also if plossl's you don't get much eye relief so perhaps the planetery's are a beter choice. Much the same cost. Other aspect is somethime plossl's don't work well in fast scopes and yours is fast.

Just realised that if the question is simply which of the 2 you have at present to use, start with the 25mm find the offending object and switch to the 10mm - recentre and refocus.when changing.

[umadog]

It depends on the Plossls, they can work fairly well if they're good Plossls. Most aberrations occur at the edges of wide FOVs, which Plossls don't have. As it happens, there is a thread about eyepieces and fast focal lengths on CN right now: Telescope Reviews: Eyepieces and Fast (F/5 and below) Reflectors

Liz, I can imagine that you feel like you've just been hit with a lot of information. Don't be concerned about that. This is a hobby which involves a lot of learning and you'll pick stuff up as you go along. Don't stress about that. Also, don't worry about your gear not being up to scratch. A lot of beginners do this and they think the reasons stuff isn't working is because they need to buy eyepieces/filters/etc. Usually all that's needed is time under the stars and a good working knowledge of the telescope. Your scope will show you hundreds of objects if used right.

[Andyfx]

I have owned this scope and the BST Explorers from Skies the Limit work very well. Also if you want to see Saturn etc a 5mm BST will do fine.

[swamp thing]

Usually all that's needed is time under the stars and a good working knowledge of the telescope. Your scope will show you hundreds of objects if used right.

This is great advice

Regards Steve

[yellowfurbaby]

Thank you so much for your advice. Some of it went over myhead but some of it really helped. I think I made the mistake that a lot of newbies make which was buy a half decent scope and point it at the sky and if by magic I would see the universe. However after a couple of disappointing attempts I realise there is much tO learn.

However I will keep trying as i really want to see these beautiful images.

Thank you ever so for all your time and advice x

[umadog]

Don't worry about your scope. I've not used that model but it seems quite adequate for learning your way around the sky and showing you the brighter deep space objects. You'll be able to see all of the Messier objects, for instance (light pollution willing).

Don't forget that your telescope's short focal length means that it will excel at wide-field views. You'll be able to fit large star clusters into one eyepiece view. Bigger telescopes inevitably have a narrower field of view and so can't do this.

[umadog]

I just noticed that you have a Barlow. You should get better performance out of your eyepieces with the Barlow in place. This is because the Barlow effectively turns your f/4.4 scope into an f/8.8 scope. A lot of the astigmatism around the field edges will vanish.