is 8mm ep as low as i can go?

[lostinspace]

hi guys, i have a skywatcher 6" with an eq3 mount. my question is simply, how small an ep can i use ( for planets and the moon ) with my scope for the best quality? thanks

john

[Capricorn]

An EP giving you 150x magnification is probably the one for magnification and quality.

The scope should go OK to 200x mag but after that I would say that the quality will drop off.

It will also depend on the f number of the scope and if faster then say f/6 you will need a good EP to get quality results.

[SteveP]

Hi John

If it's the 150PL which has a focal length of 1200mm, I'd assume the most realistic highest mag you'll get in the UK is around 200x. So yes, a 6mm ep is probably the maximum you'll need to use. A 5mm would give you 240x and you might just be lucky enough 1 night every year to use it!

Steve

[lostinspace]

yes it is 150p, so no lower than 6mm? what restricts using lower? the scope or location? (hereford England ) thanks for you qick replies guys

john

[SteveP]

In simple terms, it's the seeing conditions in the UK which limit the magnification. Were this question being asked in New Mexico or the Chilean desert, you might well get a different response!

Steve

[lostinspace]

thanks stevep. seeing is good tonight however and just had a lovely look at mars. saturn is rising and here`s praying it stays clear for a few more hours at least. first good night for a while:hello2: thanks again,

john

[SteveP]

Happy viewing!

Back into the cold to see how the camera is doing

[johnkirkpatrick]

I would like to ask the same question, my scope (see sig) 5" 650mm f/5 with 10mm ep. whats the smallest i could use. av also just bought a 2x barlow and waiting delivery to help and with that al get 130x can i increase that by much for my scope??

[SkyExplorer]

Hi John,

The gernal rule is 50x mag per inch of appeture, so for your scope this would be a max of 250x, although as stated before this depends on seeing conditions. This mag may only be usable once or twice a year.

[Astro_Baby]

Magnification is determined by dividing the focal length of the scope by the eyepiece size so for a 650mm scope with a 10mm eyepiece you would get 650/10= x65

Howevere there are two limiting factors. The first is the aperture of the scope. A scopes maximum magnification is 2x for every mm of aperture. So for a 5" scope with an aperture of 130mm you get a theoretical maximum of x260 magnification. Bear in mind image quality drops off as you go towards maximum.

The second limiting factor is the sky. In the UK because of our hazy skies your generally limited to maximum of x200 and quite frequently as low as x130. Remember as the scope magnifies planets it also magnifies heat haze and crud atmophere at the same rate.

There are other considerations too. The big one being the eyepiece. Smal eyepieces give a narrower and narrower view as you push the power up and (generally speaking) Plossls and Orthoscopics give you a smaller and smaller eye relief (distance from your eyeball to the eyepiece) and a smaller and smaller bit of glass to look through. By the time you are at a 2mm eyepiece its like looking through the eye of a needle and some people (me for instance) find them pretty uncomfortable to use and, at the lower end of the market, the view can be quite disappointing. Thats a very general observation.

Another consideration is the scopes mount. As the magnification goes up every movement of the scope is magnified. A small gust of wind will make the scope jitter badly and even the mounts motor vibrations can become a factor if the mount is too lighweight.

You can, under exceptional conditions, buck the rules and get a view. A few weeks ago I was pushing my 4" Maksutove well beyond its theoretical maximum and the view was good BUT that was the coldest its ever been and the scope had cooled for a few hours to ambient temperature. The sky was unnaturally transparent and steady - I'd not expect those conditions to occur more than once every few years.

As a general rule I use a maximum of about x150 mag and thats with an scope thats capable of x400. Its mostly limited by the weather but it also keeps the scopes optics at a point well within its performance.

Its a long post but reasonably concise. Hope thats of help.

Clear skies and peace to you.

[SkyExplorer]

Very true Astro_baby, I'm getting confused again !

focal length \ eyepiece size = mag.

[johnkirkpatrick]

thanks mate thats great advise

[Astro_Baby]

I hope this wont sound patronising in anyway but beginners to this hobby nearly always start aiming to get the maximum magnification. Its naturel enough but more often than not the wrong choice.

Most viewing is at quite low powers and mostly I uses 13-38mm eyepieces. My main interest is deep sky. I do have more powerful EPs but they get a lot less use.

Planets - although they are the 'big event' have limited appeal and they arent often well placed for viewing either.

Personally I never get bored with the moon, Jupiter and Saturn but I wouldnt invest too heavily in gearing up for them. Obviously its a personal choice and some people ONLY do planetary viewing. If thats where you end up going theres nothing wrong with that at all - far from it but as a beginner you need a more rounded experience.

I have seen plenty of beginners (and I include myself in that) rush out and get some massive power eyepiece like a 2mm only to find that its almost unusable apart from the odd night every few years.

On the other hand a good widefield eyepiece will be with you for ages and see a lot more use.

Its kind of counter intuitive in some ways. I'd also reccomend that before you spend a penny on eyepieces you take a look through a few and see what you like rather than buying blind and dont be taken in by how glamorous the EP looks on the outside either.

[John]

I'd just like to echo what Astro_Baby says above. When I started I thought that a telescope was to magnify things - it took me quite a long time (and a lot of frustration) to realise that it's actually primarily a light gathering instrument (which is why the saying "aperture is king" is so true of course).

[johnkirkpatrick]

So which would you advise me to use? (see sig) I havn't seen many planets infact just mars(as a small-ish dot) and the moon is great. but my main focus is DSO's having only seen the great orion neb, small and faint but could see some detail with 10mm. its getting me hungry for a closer look.?? once i have what i need al be really happy to search for dso's for many years to come

[lostinspace]

Its a long post but reasonably concise. Hope thats of help.

Clear skies and peace to you.

thank you for your time and answer AstroBaby, very usefull. keeping in mind what you said about little eye relief with higher mag, what would you (or indeed anyone who reads this post) suggest would be the best all rounder? ie, good mag and reasonable eye relief? i have the ep`s that came with the scope (20mm 10mm barlowx2) i am willing to pay up to £100, i was considering a cheaper range of three ep`s but after reading your advise i think maybie one high quality ep would be a better buy. 8mm is the size i think i will be buying. thanks for all your help people:)

john

[part timer]

Just a little note as you have mentioned Mars.

Mars is in some ways an exception to the magnification rules.

With Mars the best ploy is to gradually employ higher magnifications and spend some time observing at each one (say, at least five minutes) until you find that the last magnification you used gave more detail than the current one.

In general the detail on Mars is vague and a little blurry anyway so the highest magnification you can get away with will help.

[lostinspace]

Just a little note as you have mentioned Mars.

Mars is in some ways an exception to the magnification rules.

With Mars the best ploy is to gradually employ higher magnifications and spend some time observing at each one (say, at least five minutes) until you find that the last magnification you used gave more detail than the current one.

.

should i assume then the bigger i can see mars, does not mean more detail? hi part timer,

john

[pvaz]

should i assume then the bigger i can see mars, does not mean more detail? hi part timer,

john

That's a right assumption. As you use more mag there is a point where you see it bigger but it looses sharpness. This depends mainly on seeing conditions but scope collimation and general quality of the equipment influence it as much. Even your eyes have a role, my left eye shows me much more stable images then the right one. I love every object in the sky and planets are one of the biggest wow factors to me, though I love DSOs as much.

My take on this is you should have at least 2 mags for planets, one around 100x for everyday use and one that doubles it for decent nights. Last night I used 120x, 240x and 300x on Mars. The best view was at 240x as it was big and retained all the sharpness. As I tried 300x it lost a bit of sharpness, it was still decent enough but after a few minutes I went back to 240x and toke my time observing and trying to sketch it. Jupiter doesn't take mag so well, usually after 200x it becomes less sharp. Saturn retains sharpness well even at 300x, provided you have good seeing conditions. I can get up to 480x which is way above my scope limit but the view isn't satisfying, only did that a few times as an experiment and got OK results on the moon but very bad views on everything else.

Bare in mind this is my personal experience observing from Portugal. I'm over 10 degrees south and I'm sure it influences the results.

[Chris H]

I'd like to echo Paulo's comments, this last week I've spent every opportunity viewing Mars and whilst I have had a few short seconds of stable viewing using x300 it is the x200 which has given me the most consistently good views of the planet.

I have read that for scopes up to 5 inches you most often operate between 8 and 40 times magnification per inch. For a 5 inch that's x40 - x200 and for scopes 6 inches and over 6 and 30 times magnification per inch, for an 8 inch dob that's x48 - x240. Using this rule of thumb will give you a good balance between magnification and light gathering ability of the telescope.

[Saturnalia]

I would like to ask the same question, my scope (see sig) 5" 650mm f/5 with 10mm ep. whats the smallest i could use. av also just bought a 2x barlow and waiting delivery to help and with that al get 130x can i increase that by much for my scope??

I would wait and try your 2X Barlow with the 10mm before you jump into buying anything else.

A nice TeleVue 8mm Plossl would give you 81X mag or 162X with your Barlow if you feel financially flushed in the near future.

They are available for around £50 secondhand and are excellent.

[teethgrinder]

hi all, new here, and new to this game - and a lot to learn, me thinks.. I too have just bought a skywatcher 150p - bought just in time for crystal clear skies and some much awaited Mars activity! I have been blown away by the scope so far but much like many other beginners, i guess, disappointed by the detail I have seen on Mars. I have got a 6.3 mm EP which gives about 214x which even with very clear skies 3 nights in a row i only saw a clear bright white disc.

I understand that Pushing the scope to its theoretical Max of 300x is likely to be mostly disappointing but If I were to do so would I see more Mars and general planetary detail? Or am I missing something? Would filters improve matters?

[John]

hi all, new here, and new to this game - and a lot to learn, me thinks.. I too have just bought a skywatcher 150p - bought just in time for crystal clear skies and some much awaited Mars activity! I have been blown away by the scope so far but much like many other beginners, i guess, disappointed by the detail I have seen on Mars. I have got a 6.3 mm EP which gives about 214x which even with very clear skies 3 nights in a row i only saw a clear bright white disc.

I understand that Pushing the scope to its theoretical Max of 300x is likely to be mostly disappointing but If I were to do so would I see more Mars and general planetary detail? Or am I missing something? Would filters improve matters?

I think the only thing you are missing is practice. Filters can help a little but planetary details (Mars especially) are very subtle and certainly don't jump out at you, even in large scopes. You need to keep observing and, in time, you will be able to pick out more detail. 214x is quite enough to see all the details that your scope will show and all that the atmospheric conditions will allow on most nights. You will get momentary glimpses of the details and over time your eye sort of builds up the details.

So just keep at it and the rewards will come - it's not a hobby of "quick wins".

[teethgrinder]

Thanks John, as I thought really - I just wanted to make sure I wasn't missing something obvious.

If I were to risk a purchase on pushing the scope to 300x would a 2.5mm or a 5mm EP with my 2x barlow be a better option. Or would I be better spending my money elsewhere?

thanks

teethgrinding steve..

[John]

Thanks John, as I thought really - I just wanted to make sure I wasn't missing something obvious.

If I were to risk a purchase on pushing the scope to 300x would a 2.5mm or a 5mm EP with my 2x barlow be a better option. Or would I be better spending my money elsewhere?

thanks

teethgrinding steve..

I don't want to hijack this thread so do you mind starting another one Steve ?.

Thanks