My first scope. Looking for answers to a few questions.

[ezydriver]

Hello all.

I decided to buy one of these yesterday. It was only a £60 job from Aldi, but thought as a very first scope it may well serve me OK, for a while.

I've set it up OK, but wanted to ask a few questions. Firstly, it comes with something called an "erecting lense 1.5x". What is this and when and where should I use it?

Also, I have a "Barlow lense 3x", again, what is this, and when and where should I use it?

I have 3 eyepieces which are listed K9, K12 and K20. What are these and how/why/when/where should I know which one to use?

Perhaps the answers to my questions would be obvious should I actually go outside. But it is foggy and I'm keen to know before I do go outside.

Thank you in advance.

[GazOC]

Hi, welcome to SGL,

The erecting lens will show images the 'right way' up for terrestrial use, astro telescopes don't do this as it requires extra glass and isn't really important for that use, you're just viewing an object, the up/ down, left/ right don't matter.

The eyepieces you have will give different magnifications you can calculate the magnification by dividing your telescopes focal length of your telescope, When used inbetween the scope and the eyepiece, the 3x Barlow will increase the power of the eyepiece by a factor of 3.

The "K" eyepeices are called Kellners. The lower numbers (higher mags) should be used for bright objects like planets or the Moon whereas the higher numbers should be used for wider, fainter objects like nebulae and galaxies.

[ezydriver]

Hello, thank you for your reply.

So the lower the K number, the stronger the magnification?

I'm a bit confused as to how to work it out, especially with the barlow lense added to the equation.

Another specification that came with my scope is 35x to 233x. What is this number?

Any chance of an idiot proof explanation?

Thanks.

[John]

Hello, thank you for your reply.

So the lower the K number, the stronger the magnification?

I'm a bit confused as to how to work it out, especially with the barlow lense added to the equation.

Another specification that came with my scope is 35x to 233x. What is this number?

Any chance of an idiot proof explanation?

Thanks.

Your scope is a 76mm reflecting (mirror) type scope with a focal length of 700mm (that's the distance between the big mirror and where the eyepieces will need to be when it's in focus.

"K" means the design of the eyepiece, K =Kellner. The bit that matters is the number next to the K which is the focal length of each eyepiece in mm.

Without using the barlow lens, your 3 eyepieces will give you magnifications (powers) as follows:

K9mm = 77x

K12mm = 58x

K20 = 35x

You use the barlow lens to increase the power of each eypiece by the factor shown on the barlow lens - 3x in your case. I'm sure you can do the maths

You use low power for wider views and high power for closer views of the moon planets etc.

My advice to you is stick to low powers to start with and don't go above 150x (ie: the K12mm plus the barlow lens) as the scope won't provide good views at all.

I think the above probably explains the specfication of 35x - 233x as well - but 233x is a waste of time in a scope with a 76mm mirror to be honest.

Hope that helps a bit

John

[themos]

It's not a "K number". It's a letter K, standing for Kellner, which is the name of the person who invented that particular arrangement of glass that's in there. And there's the "focal length" of the piece in millimetres. It tells you where the focussed light is, how far away from the glass. If you let the sunlight go through it and put a piece of paper on the other side at some distance away, you will see that the piece focusses the sunlight at some particular distance away. That's the focus of the piece.

My guess is that the telescope mirror is a 700mm focal length.

Dividing that 700 by the focal length 20 (the largest of your eyepieces) gives you 35. That's the magnification. Things will appear bigger by that factor when you look through the eyepiece.

700/12 = 58.3 That's the magnification of your K12

700/9 = 77.8 and the K9

Using the 3x Barlow as well would give you 3 times the magnification for each of these: 105, 175, 233

Your scope's mirror is 3 inches in diameter. That means that you don't gain any extra detail beyond 50 times 3 = 150 magnification. That "50" is a magic number, derived from experience and physics calculations. Realistically, that 105 magnification is the highest usable with that scope.

[Tiny]

If you look at the moon you will see lots of detail at well under 100x. Try some star fields too - where there are patches of stars to your eye you will be amazed how many stars are there when you use 35x power.

Just one thing - some people have to learn how to see stars through a scope - which is why it is good to start with the moon which is easy to find and focus on. Once the scope is focused then try some stars to get used to how they look. This might seem silly but I have had to explain to people looking through the eyepiece what is there before they start to see it - once they do we are in business.

[The Warthog]

From my own experience with smaller, cheaper reflectors, I would suggest that 90 - 100 x is the practical limit for observing with this scope. You can see a lot of good stuff at these magnifications and below. Your eyepieces are Kellners, which are generally decent eps, although the field of view is a little smaller than in a Plossl ep. Except for that, there is little to choose between Kellners and Plossls. I used a pair of Kellners for years.

Your best views will be of the Moon and star clusters, particularly open clusters like the Pleiades, Hyades, and the Beehive. The Orion Nebula will impress, too. I have seen these in my 65mm Mak, and they are pretty good. You will be able to see the rings of Saturn and the Moons of Jupiter, but perhaps not detail on the surface of the planets. The Moon is a constant source of wonderful vistas, and you should equip yourself with a decent Moon map.

Best of luck, and come back to discuss what you are seeing.