Do I need a Barlow lens?

[Spdtd]

Hi,

***I am a beginner astronomer with a celestron 90eq. I tried taking a

look at mars (at least what i thought was mars) last night through the

10mm eyepiece I have and it was just a tiny spec. As small as the

point of a sewing pin. What level of magnification would I

need in order to make out the planets in reasonable detail? Be able to

see Saturn's rings, Jupiter's red spot, etc? Is a Barlow absolutely

necessary or can I get by with the 10 and 20mm eyepieces I already

have?

Thanks!

[NGC 1502]

Welcome to SGL.

I've googled your scope, seems to be a 90mm refractor with 1000mm focal length. If that's right then the 20mm & 10mm eyepieces will give 50x & 100x magnification.

It's not easy to quantify what seeing the planets in 'reasonable detail' means, but you should see Saturns rings at 50x, better at 100x, and Titan should easily be visible as a point of light.

Jupiter- the disc of the planet with main cloud bands and four moons easy to see at 50x, better at 100x. To see the 'great red spot' needs good seeing (steady atmosphere) and of course the GRS needs to be on the side facing us, and not too far from the planets centre line, 100x is your best bet to stand a chance.

Mars- much more difficult to see detail on Mars. It's tiny compared to Jupiter, but will appear larger as it reaches opposition in early March 2012. In good conditions (Mars high in the south and steady seeing) you may see the polar caps and the main dark markings. But at 100x it will still be a tiny disc, so if you can get to a higher power (perhaps a 6mm eyepiece for 167x) then that may be better. But don't be surprised if you just see a wobbly pink disc, as I said, Mars is a tough planet to see much detail on.

Personally, I'd avoid a cheap barlow, but get a decent high power eyepiece.

Good luck with your viewing, Ed.

[Spdtd]

Appreciate the quick response. I was concerned if I was actually looking at mars or something else. What I was looking at appeared as a very strong point of light. At 100x I expected to see at least something resembling a planet and not a distant star. I'll have to check out the other planets to at least get some sort of reference at 100x.

Thanks!

[rory]

hi spdtd, ive the exact same scope. the 20mm (x50) will show rings of saturn and jupiter with its moons. more detail will be shown with the 10mm (x100)

a barlow would be no real use with the current e/p's as it will make the x100 a x200 which would push the scope to its practical limit. and the x50 to a x100 ,which you already have.

the two e/p's you have will serve you for a while why you get to know the sky.

my first buy was a wide field (32mm) e/p for nice bright widefield views as well as being usefull for finding objects too, as the plastic finder is pretty awfull.

[barkis]

Mars is about 9 arc seconds in diameter about now, which is rather small to expect any great achievable magnification.

getting the right atmospheric conditions in the UK to be able to ramp up your scopes magnification is not an event likely to occur very often. At present,You might glimpse polar Ice Cap on a good night, but little else I would reckon.

Ron.

[rory]

ive only glimpsed briefly at mars once so far and saw nothing more than an orange star. but that was a month or so ago. im looking foward to seeing more of mars over the coming weeks...clouds permitting !

[LukeSkywatcher]

Mars is well known for being difficult. I also have a 90EQ and Mars is always a let down in it. Jupiter and Saturn on the other hand are mind blowing.

The 90EQ has a LONG focal length of 1000mm and will show great views of the near planets (Jupiter and Saturn). You really do not need a barlow to improve the view.

My favourite eyepice with the 90EQ for planets was/is 9mm. You have a 10mm. Not much difference.

Jupiter with 10mm and your 90mm scope will clearly show banding on the surface. I never saw the GRS but i was looking at all the wrong times. The planet was a very nice size in my 90EQ with 10mm.

Saturn on a good night in the same scope will just blow you away. You will know its Saturn and the ring system is right there before you.

Trust me.

If you get a 2x barlow and use it with this scope and a 10mm EP while observing either planet, its my opinion that you are pushing the scope beyond what it is happy with.

Just use the 10mm and enjoy the view.

[Spdtd]

Appreciate the info everyone. Just looked at Jupiter with what looks to be 3 or 4 of its moons. Great stuff.

Thanks!