Help me understand a few things?

[maclean]

Hi Everybody,

I'm new to astronomy, however since seeing saturn through a telescope in egypt i've been dead set on getting one of my own!

I done a bit of reading and ended up getting the skyliner 200p, seems what alot of people point to for beginners, and I will be messing around tonight hopefully (skys look clear right now where i am, hopefully will be tonight!)

Anyway, I just wanted to hopefully get some clarification in a few things.

My telescope is an 8" in aperature and I'm trying to understand how eye pieces and barlows change things!

Could I say as an analogy: that my telescope takes an 8inch resolution bite out of the sky - and thats all it will ever be able to take.. There is a limit to the amount of detail it will ever be able to display. Using different eye pieces etc can magnify and make that bite bigger but it will get to a point where it will get blury if you magnify it too much and the only way to get that magnified image sharper is to have a bigger telescope?

If my way of thinking is correct then what is the difference between these barlow lenses and eyepices? I understand they are both used to magnify your telescopes 'bite' out of the sky but whats the difference?

I have watched a few youtube videos of some guys talking about it but to be honest didn't make much sense to me!

Hopefully my weird way of wording things makes sense?

Cheers all!

[umadog]

You're new to astronomy.

A barlow isn't an eyepiece. A barlow is adevice which doubles the focal length of a telescope. Magnification is telescope focal length divided by eyepiece focal length.

[maclean]

Hahaha I really don't know why I wrote astrology. In some part of my brain those two words must have merged as I wrote that, please ignore that, not the best opening sentence!! Edited it now :-)

However your response is already too complicated for me to understand.

Okay so a barlow does what you have written however simply put could I say it makes the image bigger? But then I also understand an eyepiece can make the image bigger? What is the difference between how they make the image bigger and why is it not more straight forward to just use one or the other?

Saying it does this or that to the focal length - I dont really understand this? I only really understand the end result which is what it does to the image you can see with your eye?

[Rustmonkey]

A Barlow is like a x2 converter you can use on a camera zoom. It doubles your eyepiece so a 10 mm will become a 5 mm when used with a X2 Barlow. This effectively doubles your eyepiece collection. I have a 30mm, a 25 and a 10........when Barlowed they also become a 15, 12.5 and a 5. The smaller the number the greater your magnification but be aware that how far you can push magnification will depend on your scope.

There are people on here who have far better knowledge than me but this is my laymens terms take on it. 30mm will give a wider field of view which can be used for finding an object then once centred you can use smaller eyepieces to focus on your subject. Obviously some subjects will prefer a wider FoV. I.e Andromeda galaxy will better in a 30 mm because you will see more of it whereas with a 5mm you will be focussing only on a small section of it.

[acey]

Let's say you've got an eyepiece that gives magnification x100. And you've got an eyepiece that gives x50, plus a x2 barlow, resulting in magnification x100. Are both options equivalent? No, because not all eyepieces are the same (some are better quality than others), same goes for barlows, and in the case of the x50 plus barlow you're looking through more glass (hence more possibility of image degradation).

[maclean]

Okay I think i see now... Essentially its opening up your eyepice collection and giving you more options to mix and match and will allow you to experiment with the magnification more and ultimitley settle on the combination that is just right for the specific object you happen to be observing.

Great this makes much more sense to me! Thanks alot guys!

I will have only two eyepices that come with the telescope I have bought and I know i will be wanting more sooner or later... I just didn't quite have that simple concept in my head!

Many Thanks!

[JamesM]

First off, you were correct in your assumption about the amount of light an 8" scope can capture. Light can be seen as storing information and the more you have, the more detail you will be able to see or as we say, resolve. It's one of the reasons why we all suffer from aperture fever, the bigger the scope the more detail can be seen.

Maginification works by stretching available light that was captured by the size of scope. This explains why, when the aperture and the length of the scope (focal length) are fixed, the resulting effect of stretching the light will be seen as a darkening of the view along with some degradation (fuzziness) of the image. So going back umadogs reply above, we can calculate how much magnification we can generate by comparing the focal length of the scope (fixed) with the focal length of a given eyepiece, which will vary depending on which size of eyepiece you use. Eyepieces come in a variety of sizes from where an 8mm will magnify twice that of a 16mm one. Eyepieces will have different magnified effects on different 'lengths' of scopes and people will often calculate which ones they will need that will best suit their own scope, given that the maximum magnification on a typical night will be around x180-x200.

Now a barlow is an addition piece of kit that we can use to change the relative magnification of our eyepieces. As umadog has already mentioned, it attempts to change the original magnification effect of a chosen eyepiece by effectively 'optically' changing the the length of the of your scope. So by using a 10mm eyepiece in a scope whose focal length is 1000mm, we can calculate that (1000 divided by 10) this eyepiece will produce x100 magnification. Now if we use a barlow lense (e.g x2 barlow) the effect would be (10 divided by 2 = 5mm) and so (1000 divided by 5) will produce a revised magnification of x200. The barlow eyepiece which can come in various types x2, x3 etc can be a useful way of doubling your eyepiece collection so that having a x2 barlow can transform your original collection of eyepieces say a 7mm, 12mm and 20mm into a collection that is actually now 3.5mm, 6mm, 7mm, 10mm, 12mm and 20mm!

To answer the last part of your question as to why do people bother using them. Well some people don't. Some observers feel that introducing more glass via using a barlow lens into the optical path will help diminish the final image and would much prefer to have the actual eyepieces they require in their pocket than to 'extend' the original eyepieces via 'more glass'. Another possible disadvantage is the effect a barlow has on an eyepiece's 'exit pupil'. This is the distance between the the last glass element of an eyepiece and the actual point of focus that your eye can detect. When using a barlow, this exit pupil length will increase and is more noticeable on longer eyepieces (20mm rather than a 5mm) which can make finding the sweet spot when viewing an object a little tricky. Of course it does depend on what you buy, as Televue make a variation of the barlow lens (which has a positive lens element rather than a negative one) ensuring that exit pupil length is the same as he original eyepiece and that its coatings also allow around a 98% light put through, thus solving the ''more glass' problem. There are some imagers who will use a barlow and its effect on increasing the 'length' of a scope to help bring images to focus as they captured the necessary data.

Barlows come in at different levels of magnification and at different levels of performance. You get what you pay for although the x2Tal (around £35) is a good consistent performer. So there many problem the barlows help solve but some can trade away their advantage against other disadvantages, of which some may or may not be desirable.

James

[maclean]

Many thanks for that detailed answer James, I feel I am comfortable.to make some decisions on kit to buy in future based on what ive read here so thanks a lot!

Another question I have is about eyepieces. Is The mm the thickness of the glass lenses in the eyepiece? And thinner lenses = more or less magnification? Probably sounds daft but I honestly don't know lol!

[acey]

Is The mm the thickness of the glass lenses in the eyepiece? And thinner lenses = more or less magnification?

mm is the "focal length" of the eyepiece. Divide the focal length of the telescope by the focal length of the eyepiece and you get the magnification. It has nothing to do with the thickness of the lens. The smaller the eyepiece focal length, the higher the magnification.

[JamesM]

No worries but remember that there is no such thing as a daft question (answers maybe) but if you want to improve your understanding you should always feel free to ask your question on the forum. Regarding eyepieces in general, you might want to ready this 'sticky' from the beginners section. Sometimes people are a bit put off by any of the math involved in calculating what eyepiece might best suit a given scope but most of it is very straight forward calculations and it also helps you understand how these components all fit together.

Keep the questions coming!

James

[maclean]

Went out last night for the first time with my new scope. Perfect night for it although I live in a relativley light poluted area so probabbly not as ideal as being in the country side however will take mine out into the middle of nowhere one day!!

Had Saturn lined up first brilliant!, followed by Mars, with the scope and eyepieces couldn't see amazing detail tbh although perhaps getting some more bits and pieces will improve this (and going to a less light poluted area). Antares is another star I found particularly interesting considering I know it is a massive one. Couldn't see the moon from my location so ended up randomly jumping around...

I shot the scope straight up and noticed what looked like a blury star! After playing with the focus, all the other stars came in nice and sharp but this one blob wasn't! Threw on the 10mm more powerful eyepiece and it revealed a lovely detailed star cluster which after consulting Stellarium appeared to be M92... Really awsome moment when I realised this smudge was a detailed cluster. Although I lost it and couldn't find it again after coming back out from the computer... I was out in the back till 3am!

Seen a beautiful shooting star, done my best to track some satalites, but failed lol. Scoped in on a plane flying miles above! Really great night of observing for me as a beginner!!

On one occassion I was looking through the scope then all of a sudden noticed a solid fast moving light, it was quite faint whilst looking through the scope. I tracked it for a second but then lost it and couldn't find it again. Would this likely have been a satalite or space junk or what?

I seemed to struggle to find any nebulae etc (however finding m92 I feel has given me a huge burst of excitement and enthusiasim to find more!) do I probabbly just need some more time and practice?

[Capricorn]

The streak will have been one of the several thousand satelites that are up there. If you ever decide to spend time looking for them specifically then start with a pair of eye's and a set of binoculars.

You see more by eye and binoculars will be most useful.

Have a look at the site heavens-above, put you lat and long in and where in the world you are (UK) and see if there are any iridium flares due. Basically at the time given and in the direction stated there should be a bright 4-8 second flash cause by one of the iridium satelites.

To find more smudges you need a couple of things. Most of the smudges are Messier objects so get a list - try the wikipedia list, easist way to get to it is enter "Messier list" into a search engine. You can save the list and reorder it if you like. Reorder as in group all Galaxies or Nebula together.

Best for what I am going to suggest is to reorder to group them by the constellation they are in. Then get a book and locate where they are in the constellation. Then go search through the constellation with your scope.

There are many suitable book around, for what I have described I find that the Monthly Sky Guide by Ridpath is about the best. Easier to read a book ourtside then going in and out all night.

[onesmallstep]

Hi and welcome to the Lounge.

The only daft question is the one you don't ask so ask away. Everyone on SGL would have asked the same questions and made the same mistakes while learning their craft.

Hopefully you have the eyepiece / barlow lens query sorted now. In terms of finding targets I'd like to recommend the following books, as well as being popular with SGL members they are the ones I use (see sig).

Turn Left At Orion (4th ed). This is the latest reprint and is spiral bound.

http://www.amazon.co.uk/s/ref=nb_sb_ss_i_1_18/280-4150489-6326141?url=search-alias%3Dstripbooks&field-keywords=turn+left+at+orion+4th+edition&sprefix=turn+left+at+orion%2Cstripbooks%2C444

Sky & Telescope Pocket Sky Atlas. A5 star atlas that I keep in my EP case for reference in the field.

http://www.amazon.co.uk/s/ref=nb_sb_ss_i_0_5?url=search-alias%3Dstripbooks&field-keywords=sky+%26+telescope%27s+pocket+sky+atlas&sprefix=sky+%26%2Cstripbooks%2C928

HTH!

[rwilkey]

You'll struggle to hunt out nebula at the moment, seeing conditions are not very good in the summer, atmoshpere too fuzzy, I think.

[umadog]

Those are nice books, John!

[stevetynant]

It wont get really dark now until the

End of july, that will make out a lot easier to spot the faint grey smudges we hunt for.if you can safely get out of town to a darker location it will be better again so even though your off to a great start the best is yet to come:D:D

Sent from my GT-I9000 using Tapatalk 2

[Ags]

Don't worry about Mars being a bit small, this is not due toy your scope's optical or your accessories, it is simply because the planets is now far away and very small - you will have to wait two years until it gets close again unfortunately.