The Warthog

HI. I just dropped in to this topic as I may need my own advice after nearly 10 years away from the hobby.  My health and energy levels have not been stellar,  especially after the MI in 20112 that left me with a quad bypass and combined with 54 years of T1 diabetes, arthritis an circulatory problems, as well as being old. I'm 71 now and temporarily unable to drive. Bummer! Anyway, I've hunted up my collection of eyepieces and find the ones I have still fit the bill. I tried to  look up Jupiter and Saturn a couple of nights ago, but was successful only with my 32mm ep, and with a focal length of 1000mm didn't give me much of a view. My higher mag eps wouldn't focus, but in the daylight I corrcted a sim[le problem and am ready to try again.  Saturn and Jupiter have not been this close together for about 20 years, so it's a great opportunity, and in summer too, so I don't have to freeze my, er, toes off seeing them.  Clear skies, everyone!

Glad you are back in the saddle warthog. I cannot remember how many people I have recommended your guide to.

That's very generous of you, Damian. We got whacked by snow and cold in late January and February, and went 46 days without going above zero, with temperatures sometimes as low as -25, so what with the constant cloud I've hardly been outside except to take the dog for a pee. However, we are being promised the start of above zero temps, and once the 40cm of snow in my back yard melts, I'll think about putting my scopes on the lawn. After all this time, I have some refurbishing to do. The sky in my location allows only for planets, and things like double stars and brighter clusters, but I will try to get away to some better locations, which we have aplenty in Canada.

Well, no going over the falls in a barrel, but I am thinking about taking up horseback riding, and maybe hitching a ride in a hot air balloon. They are both on my bucket list.

We have had only two significant snowfalls this winter, and at present all the snow has meltted. We are getting temperatures as low at -13, but no significant snow in the forecast.

I've been away for a very long time, and to be honest haven't had my scopes out very often since my second heart attack (and quadruple bypass) three years ago. I hope to do better this spring, as my health has gotten a lot better although I still can't go out on the -10 nights we've been having. I noticed a very nice crescent moon last night, and would have liked to get my refractor out, but it's just too damn cold.

I really appreciate all the kind comments I've seen in response to my post. It seems to have done what I wanted to do, which is to give a reasonable and simple way to create a usable and versatile set of eyepieces that can grow as you save your pounds.

I'll try to hang about here more often. This was my favorite of all the astronomy forums I visited, and the longest lasting by now.

Great post.

I got a second hand WO 102 doublet f7 came with a prism and one eyepiece a 15mm plossl. I'm on a budget and have been searching for info. on what would be the best eyepieces for me too get.

Your post has made things clearer at what ep's I should be looking.

Thank you

Alan

Sent from my LT30p using Tapatalk

Off the top of my head (which is only 70" up) I would say a 5mm, a8 or 9mm, and a 25mm, and keep the 15 as it fills the gap neatly.Get the best quality you can afford, and remember you don't have to buy them all the same day.

Thanks for all the kind comments. I have not been really well the last few months, and seldom have the energy to get out after nightfall these days. I've probably had my scope out no more than three times this year, when I wanted to show my great-niece something special. We even missed our annual perseid safari this year.

great post! im thinking of buying a f/5 scope,would the 3 ep you suggested for f/5 all be plossls?

Not necessarily. That is decided by what you can afford. The advice on the focal length of the ep is the same, whatever the type of ep.

Hi guys and i have spent alot of time reading this post, but i cannot work out the formula above?

I got to the 250mm (size of mirror or aperture) / 5mm (or what exit pupil i require) = 50x (which means an EP which gives this mag will give a exit pupil of 5mm) it is the next bit that throws me, why does it mean a 25mm eyepiece, where is the formula?

I am sure i am missing something, doh!

To work out what an eyepiece can do for my own scope i take the focal length of the scope and divide it with the focal length of the EP = Magnitude, so (1250/25=50x) and from this i can then work out what the exit pupil will be, still assuming we have the 250mm (10") F5 scope, i then use the aperture or mirror size of the scope and divide it with the mag of the EP (250/50=5mm)

In any scope, the exit pupil will be whatever multiple of the f/number is represented by the focal length of the eyepiece. So for an f/5 scope, a 5mm eyepiece will give you an exit pupil of 1mm, and a 25mm eyepiece will give you an exit pupil of (focal ratio/ focal length of ep =) 5mm. This is independent of the magnification calculation.

Perhaps this is the kind of guide you are talking about:

http://stargazerslounge.com/primers-tutorials/63184-primer-understanding-choosing-eyepieces.html

It also goes into the difference between 1.25" and 2" eyepieces.

HTH

Andrew

The difference is in the width of the field of view. For a plossl lens, you get the full FOV at up to a 24mm eyepiece, but above that you need a 2" eyepiece. At 32mm, your FOV is restricted to about 48º, no matter how great the FOV of the eyepiece may be. This makes a great difference in the Widefield eyepieces with FOVs of 60 to 100º.

Am I missing anything by having such a large gap in the range of powers?

Alan

Only if you feel you are missing something. Are there times when 93x isn't quite enough, but 200x is too much? If there are, then you might want to stick something in the 12mm range in there.

I have a gap in my kit at 16mm, but I don't want it, and I get 12mm very occasionally by Barlowing my 24mm, but this is on very rare occasions. I sometimes use my Barlow with the 7.5mm to get 200x on the Moon, but usually I go straight from my 24mm at 31x to the 7.5mm (100x) or the 4.8 (156x).

I do mostly Lunar observing. If my skies were better, I might be interested in filling that 16mm gap.

When you put a Barlow into the mix, you want to consider what focal lenghts it gives you. The 10 mm with your 3x Barlow will give you 3.3mm, which is close enough to the 3.75mm you get using my formula. Try it and see if it works; this article is meant to give you a starting point, not to be the final word. If the quality of the view suffers with the barlow, consider getting a 3 or 4mm ep.

Thanks very much - as a beginner and hopefully soon to buy, it's very informative and hopefully it will help me avoid spending money on things I don't need.

Once I'd worked out that the "100mm scope" you used as an example throughout was actually 1000mm focal length, I could do the maths.

Not exactly. It is a 100mm aperture, and if you follow the formula I give, your ep will give 133x no matter what the focal length is. If you have an f/8 scope and are using a 6mm ep, then 800/6=133. For the f/10 scope, 1000/7.5=133, and for an f/6 scope, 600/4.5=133. This result surprised me a little when I was putting this article together.

Thanks to everyone for your kind comments. Family matters, health and work have kept me away from the ep and from the forums this year, but I am planning a resurgence.

The SW EXP 200p come with 10mm and 25mm eps are they Plossl? and Would the Eyepiece Sets - Celestron Eyeopener Eyepiece and Filter Kit be any good for it. planetary detail and dso's etc....

And again with the SW Skyliner 250xp??

It depends on what you can afford. I started with this kit, and eventually acquired a better set of eyepieces, and then sold all my old eps to pay for the motors on my mount. The case is great; I still use it to hold my present ep collection, and the filters are usefull for planets and the moon. The whole kit costs less than buying the pieces separately. The Barlow makes some ot the eps in the kit redundant, but it's a fairly good Barlow. I never had any complaints about it.

You might want to look further afield for a set of wide angle and/or long eye relief eps. There are some on the market, and they usually come in cases too. As I said, it depends on your budget.

Alternatively, you could buy eps one at a time to fill in the gaps between your present eps and the set you would like to have. The Rigel WA eps are on offer for about £30 each.

If you don't have a Barlow, that would be a good first purchase.

The Rigel WA eps have an AFOV of 65º, which is about the limit of a 25mm 1¼" ep, if you want to build your set around those or similar eps. The 25mm ep will give you an exit pupil of 5mm, which may be all you need. Your scope will not accommodate a 2" ep, and a 32mm ep will be restricted to about 48º AFOV, giving no real advantage over a 25mm one.

I believe the eps that Skywatcher supplies are Plossls, but I am not 100% sure.

I did mention eye relief as a reason to NOT buy a 4mm or 6mm Plossl. Although I wear glasses, I observe without them, and any eyeglass wearer who does not suffer from significant astigmatism should be able to observe without glasses. For people who must wear specs, there are long eye relief eps which start at about twice the price of Plossls. Still, that's not bad.

Brilliant post, thanks!

I have recently purchased SW explorer 150PL so using your guide I should go for 6, 10, 16 and 24mm EP's. The EP's supplied with this scope are 10mm, 25mm and 2x barlow, giving effective range of 5, 10, 12.5 and 25mm which seems like a reasonable match.

Any recommendations on makes/models of reasonably priced quality EPs would be appreciated.

Thanks

My guide is a guide not a precise mathematical rule, so being off by a millimetre or two isn't going to make a whole lot of difference. With your f/8 scope, your 10mm and 25mm eps may produce very good results indeed. I believe SW ships standard quality Plossls with their scopes, which are OK. I agree with John. When you get to the point that you can afford some really good eps, consider getting a bigger scope.

Hi

Been reading up a lot on EP. Seems like I am going to get an 8 inch f/5 reflector. It will come with a 20mm plossl so thats 50x.

I've read that fast telescopes need better EP and more expensive barlow lenses, I was planning on getting the cheapest ones which were the Skywatcher plossls/barlows, do you think they will work well, and if so, what size, if I only buy one I would buy the 7.5mm one and maybe a barlow lens with it

That would be a good choice with that scope, but if you are going to buy only one ep, spend a little more money and get a good one. Apparently the Meade 4000 Superwides are a good choice. You can use the 20mm as a low power ep and add eps as you save for them. It doens't take long to accumulate a good set of eps.

A very imformative post WH must have took some time to type out.

I agree with everything you say and eventually my plan is also to slim my collection down to 4 good eyepieces.

I do not like barlows so my ideal collection to accompany my dob will be.

26T5

17E

13E

8E

Better start playing the lottery

Yeah, my dream kit would look like that, too, but I find my Antares Speers-WALERs good value. This took me about two weeks to write and edit, and there are still a couple of minor things I could change.

Thanks!

I quit. Now I can turn my computer off at night.

When I first got my first decent scope, a 4.5" Meade, I went out and looked at Saturn first, as both Jupiter and Saturn were in the sky. It was so cool I made all my kids come out and look at it in the freezing night air. It is always a wonderful sight! Congratulations.

Mine's been running for over two weeks, and my average is down to about 7, from just over 40 some time ago. Maybe I should take my computer and wind up the springs tighter.

OK, then. It is an astropulse work unit. I allow 70% of my computer time to the projects, and haven't changed anything. Most of the time, Seti has my computer all to itself. I'd better get a huge improvement in my average after this!

I seem to have been handed a very big task. It has been running for four days, and according to the task page, has 312 hours to go, or about two weeks. I've never had a task that took more than a couple of days. I haven't changed any of the parameters of the system, so I don't think I'm being unusually slow. Maybe a bit thick, but not slow...

Has anyone seen a big task like this before?

I have withdrawn from the SETI thingy for now, and my ancient computer works much better without it. I may start up again when I have a 21st century box on my table.

Send me a copy of that PM while you're at it, bud!