What eye pieces should I be getting

[Jemmo]

Hi guys bit of a noob here. I got a 75/700 newt for Xmas and have since purchased a 10" dob. I didn't get any eye pieces with thedob as it was second hand and he old fella wanted to keep his eye pieces.
I have 3 different eye pieces and 1.5x and 3x lenses to make them better.
The eye pieces came with the Newtonian I got which is not a very flash scope. So I'm guessing he eye pieces aren't the best either. I will use them until I can get something better
My question is if I was to buy 2 decent eye pieces. What sizes should I get and what are some good brands I'm looking to buy second hand so if anyone has some pm me

[dannat]

if i were you id goto the next MPAS [google it] meeting & see what others are using -try some cheap-ish eyepieces & some better ones -see what you like & what you are prepared tobuy

[Jemmo]

Yeah I know the club Dan they are five mins down the road from me. Just trying to get an idea so I know how much money I need to save

[barx1963]

Definitely try to get along to an observing night to see others. One small point, the 1.5x and 3x are barlows (although I think your 1.5x might be an erecting eyepiece) which increase magnification. That does not necessarily make it "better".
You have another post asking a similar question and one thing I would advise against is buying a kit. They are usually overpriced for what you get. The consist of a set of plossls and some filters. Unless you are a very keen planetary observer, the filters will have minimal use and most of the plossls will also stay in the box.

Malcolm

[Renato1]

Well, you can use your eyepieces - the results may be okay in the central part of the image. Don't expect much from using the 1.5X and 3X Barlow though - they may give a decent image, but cheap ones that come with small scopes tend to be pretty hopeless.

I assume that you don't want to spend as much on an eyepiece as you did for the entire telescope, and would want good budget ones. But the budget ones will most likely give you soft edges in the the eyepiece.

Does your telescope have a 2" focuser? If so, you'd want a 2" eyepiece for low power.

The focal ratio of your telescope is it's focal length divided by the diameter of the mirror, and is usually around f5 for your sized dob. Divide the focal length of the eyepiece by the focal ratio to get the exit pupil of your eyepiece. So a 35mm eyepiece divided by f5 gives a 7mm exit pupil - which is the lowest useful power and widest field you'll get in your telescope.

Only problem is that a 7mm exit pupil is only really useful with really dark skies, and makes the image look ugly from light polluted sites like. If you're viewing from a darkish place in Mt Martha, you'd probably like a 5mm (25mm eyepiece) or 6mm exit pupil better. If you are in the built up area, you'll probably like 5mm or 4mm (20mm eyepiece) exit pupils better.

Lots of people like 3mm exit pupils for general viewing at moderate power of open clusters and galaxies. I prefer a 2mm exit pupil for galaxies.

For high power viewing of planets, 0.5mm to 1mm (2.5mm to 5mm eyepieces) exit pupils are best, and you can either buy individual eyepieces or use a Barlow magnifier lens to achieve those focal lengths. Though you would want to buy wide angle eyepieces, rather than Plossls, because you will have to push the dob around a lot and want the wider field.

You can get such eyepieces inexpensively at Andrews Communication in the Guan Sheng (GSO) section or from Bintel, or wait as they often come up for sale here second hand.

If your dob is jerky as you push it around, just apply some car wax to the bearing surfaces and perhaps some axle grease to the main screw, till it goes smoothly.

Regards,
Renato

[Jemmo]

Renato. Super helpful as always thank you very much

[barx1963]

As for a recommendation, I gather you have a 25mm EP already? If so that should be ok for a reasonable low power EP. I did nothing but use a 25mm Plossl for years in my 8" and 12" and was perfectly happy.
An inexpensive mid power EP I have used is the GSO/Bintel 15mm, which is very good for the price. See http://www.bintel.com.au/Eyepieces-and-Barlows/Bintel-/Superview/Bintel-SuperView-15mm/361/productview.aspx both Bintel and Andrews sell these. Nice 68deg AFOV, fair eye relief at 15mm and it works well in my 8" f4. In a 10" f5 it will give 83x.

Malcolm

[Jemmo]

Oh great link they are the sort of price range I'm looking at. Sorry for all the newbie questions but I was reading about wide angle eps. What MM are they or does each ep come in a wide angle as well

[Jemmo]

Also what sizes would get most use and best picture I'm looking to by 3 so maybe 25mm 15 and what's another good size or should I look into a wide one as well

[Allan_L]

I had these recommended by Bintel: 27mm (2") 16mm and 9mm (1.25")
With my DOBs I have found these to be the ones I use time and time again.
Which magnification and field of view depends on the size of the object you are focusing on. Most DSO lists provide size details.

Edit:
They are exit pupils 5.4; 3.2; and 1.8 respectively, if you are into those sort of figures.

[Jemmo]

Thanks for all the info guys.

Renato- here are the pics of the dob of they help

[Jemmo]

And the closer one

[Renato1]

Yes, that's this telescope
http://www.bintel.com.au/Telescopes/Dobsonian/Bintel-BT252-B-10--Dobsonian/30/productview.aspx

which is f5 and which has a 2" focuser to take big eyepieces (you remove the smaller 1.25" adapter from the 2" tube).

And you have a correct image finderscope which excellent for use with maps when you know your position. But it is darn hard to aim it and find your position.

What you now need to make it a cinch to use is a little 1X Red Dot finder. You attach it to the telescope next to the finder using the double sided wall hanging strips that are sold everywhere. Then after aligning everything, you just aim the red dot at something in the sky (a star or group of stars) then look into your finderscope and go hopping to whatever target you are after near to where you aimed.
Cheers,
Renato

[Jemmo]

Is there any difference between the bigger and smaller eps besides the obvious size. Do you get better picture quality etc?
Also with those lasers your talking about can you see the whole beam so you now where your aiming?
I just got home and had a look at my eps they have a H before numbers and mm that's all they have on them no other writting

[Renato1]

H stands for Huygens - which were top of the range back in the early 1900s. The image can be good to excellent, but the field of view is narrow and resembles looking down a well.

The main difference with two inch eyepieces is that with say 32mm and 40mm 1.25" eyepieces you cannot get as big a field of view as with a 2" eyepiece in those same focal lengths. You can only get 52 degrees in the 32mm and 43 degrees in the 40mm 1.25" ones. Whereas in the 2" you can get 60 to 65 degrees in wide angle eyepieces.

I have a 25mm wide angle 1.25" eyepiece which gives the same field of view as the less expensive 25mm Andrews 2" eyepiece. Both are the same in the middle area, but the cheaper Andrews is somewhat better at the edges.

I own a laser collimator, but haven't actually got around to using it, so can't help you there.
Regards.
Renato

[Jemmo]

Awesome thanks for that info. I'll look into buying the same wide view one you have and one other ep

[Wavytone]

1900 ? Even hen they were junk.
The Huygens eyepiece was state of the art in 1703, followed by the Ramsden, in 1783.
It's shocking this rubbish is still being made.

It's high time the world stopped manufacturing cheap junk. Just because it's cheap does not excuse the fact junk will quickly find its place on the rubbish heap, whereas a product actually worth owning should last you many years.

[gaa_ian]

Orthos will give you a sharp image to the edge of field. This is at a much lower cost that the TeleView's Pentax's etc (dont get me wrong, they are superb eyepieces) The only thing you miss against the top end eyepieces is the wider field of view for a given focal length eyepiece. The difference is spending 10's of dollars vs 100's per eyepiece.

[Renato1]

I remember years ago reading a viewing guide to objects in the night sky written in the late 1800s where the author was extolling the virtues of Huygens eyepieces over other types then available.

You have to remember that multicoatings didn't come about till after WW11. Thus all the eyepiece designs prior to then, with more than a few elements, didn't work very well because of internal reflections.

I remember 33 years ago going to AstroOptical and buying a 5mm Orthoscopic eyepiece for $35, expecting to see a much better image of the planets in my 114mm reflector than from my $5 k-mart 6mm Huygens. The ortho was better, but not by that much.
Regards,
Renato

[Wavytone]

Some of you might find this an interesting read. There were quite a few eyepiece designs prior to 1910.

http://www.brayebrookobservatory.org/BrayObsWebSite/BOOKS/EVOLUTIONofEYEPIECES.pdf

The major game changers were antireflection coatings, modern glass types and computers to optimise the designs.

[Renato1]

Good paper, thanks.
Regards,
Renato

[Sylvain]

For the telescope you have, no need to spend hundreds of dollars on eyepieces. Try and get yourself some decent eyepieces like the ones recommended earlier from Bintel, or you could grab yourself some of the ED eyepieces - have a look around eBay.
I would stay under $100 at this stage. They will still be good eyepieces you can keep with you as you progress.

[va1erian]

The "Sample Page 1" available as a PDF file talks about the choice of eyepieces, http://www.springer.com/astronomy/astronomy,+observations+and+techniq ues/book/978-1-4614-7722-8