Getting new Eyepieces:

[GRX40]

Well first off, I have a 8" Skywatcher dob (f=1200mm, D= 203mm) I live in a fairly light polluted city, I know going to a much darker site will enable me see alot of subtle details .

Anyway I would like to buy an eyepeice allowing a larger magnification without destroying too much of my field of view. My current eyepieces are 25mm,and 10mm both apparent FOV's = 52degrees.

25mm --> 1200/25 = 48X mag, 65 arcminute FOV.
10mm --> 1200/10 = 120x mag 26 arcminute FOV.

I'd like to purchase

4.7mm --> 1200/4.7 = 255X, 19 arcminute FOV
18mm ---> 1200/18 = 66X, 72 arcminute FOV (more mag than the 25mm, with a larger FOV)



1)Should I invest in larger mags to be able to see further objects (such as M104), or larger FOV's because the arms of galaxies will surpass my FOV.

2)I know a larger FOV will be of aid for M31, but if I use a large FOV, I will end up with 60X mag. Is a 60X mag from a dark site enough to resolve spiral arms on M31 or other DSO's? What is the minimum magnfication to be able to see the spiral lanes?

3) Meade 5000 series 82degree eyepieces are pricey. Very pricey actually. I've noticed a cheaper TeleVue Nagler Eyepieces but am not sure how good the quality might be. Do you guys suggest I go for the cheaper (Nagler) brand?

If I'm interested in DSOs, which 82 degree eyepiece should I buy? Which magnificaton would I need?

[randb]

I'm not a pro at this, but from what I've heard Televue eyepieces are one of the best in the world!!! Naglers >> meade 5000.

[Tog_]

Okay, first to clear up a bit of confusion, the aperture determines resolution, not power. If you are looking at a binary star that has components too close to separate with an 8" scope at 40X, all you will got at 200X is a bigger unseparated pair of stars.

With higher magnification comes reduced image brightness. If you can barely see somethig at 100X, moving to 200X could make it vanish. In this case, stepping DOWN is a better option. With practice, you will be able to more subtle detal even in small images.

Averted vision is awkward at first, but once you get used to it, you can really pick out a lot of details. Averted vision is where you center an object in the field, then look at the edge of the field, letting the light come in from the edge of your pupil, rather than straight in. The way the eye is built, this hit the more sensitive black and white receptors and makes for a bigger, bright image in low light.

High powers are best suited for small, bright objects, like planets and binaries. There are some globular clusters that will be edge to edge at high power. The Great Nebula in Orion is about 60 arcminutes in diameter, and with any object like that, it looks better with a bit of black around it as a border.

Since your scope is a Dob, high powers will mean you will need to be moving the tube almost constantly to keep the object in view; that may be a consideration as well.

My scopes are a 16" Dob, and a Meade LX90 8" SCT. When I bought the SCT, Meade was offering a set of EPs for $99. I picked up the set as well as getting 1 ultrawide angle. I will say that when seeing supports it, that ultawide is nice. The other EPs are good as well. I've never used anything other than Meade. That's not due to brand loyalty or anything, mainly because the cost of the set was too good to pass up. Aside from cost, and in a few cases wieght, I've never heard anything bad about Naglers. In fact, almost everything I've heard has been positive.

Given the set up you have right now, I think I wold go with the 18mm, and make a note to get a good quality apochromatic Barlow in the near future. A 2X barlow will give you:
25mm
18mm wide
12.5mm
10mm
9mm wide
5mm
which is a good spread.

As always, see below for corrections and additions.:)

[Dave Mitsky]

M31 spans over 4 degrees so you won't be able to see it in its entirety no matter what eyepiece you use. (You'll need a rich-field telescope to accomplish that feat.) Since there aren't any northern hemisphere galaxies that are even remotely close to the apparent size of M31 (and only a handful of other deep-sky objects of that size or larger), don't be overly concerned about spiral arms. M104 will fit into the true field of view of your 25mm ocular quite nicely. I do recommend getting a good 32mm Ploessl (or a 30mm or 35mm Celestron Ultima) to produce the maximum true field of view possible with your Dob, however. It will make star-hopping a bit easier. (A 24mm Panoptic would be even better but it carries a high price.)

Which 18mm ocular are you considering?

I can't recommend purchasing a 4.8mm Tele Vue Nagler type 1, despite the relatively low close-out prices that are currently being offered. This eyepiece has very tight eye relief and is not particularly good for planetary work. The type 6 Naglers, which replaced the type 1 line, are clearly superior and are excellent for both deep-sky and planetary observing. A 13mm type 6 would probably be a good choice for DSO work.

You might want to consider a narrowband nebula filter if you don't have one already.

Dave Mitsky

[GRX40]

M104 will fit into the true field of view of your 25mm ocular quite nicely. I do recommend getting a good 32mm Ploessl (or a 30mm or 35mm Celestron Ultima) to produce the maximum true field of view possible with your Dob, however. It will make star-hopping a bit easier. (A 24mm Panoptic would be even better but it carries a high price.)

If I get a 32mm, my mag would drop to about 37x, is that sufficient to see DSO's?

Which 18mm ocular are you considering?

A meade 82degree 18mm or a nagler equivalent (I'm looking for one at least)


So the higher the mag, the larger the picture, the lower the brightness. Correct?

Saturn at 48x appeared quite tiny, but once I used a 120X, it was a little dimer, but much more obvious to the eye. But DSO's are nowhere near as large as planets are. If I did use 37-48X wouldn't I have a tough time spotting them? I understand that they would be much brighter at a low power, but wouldn't they be extremely tiny?

[redshifter]

I'd get a wide feild 30 - 32mm eyepiece (as Dave suggests above) for maximum FOV for DSO's and starhopping as well as max exit pupil size. Personally, I use my 42mm Lanthanum superwide (which really gives too large an exit pupil at over 8mm) and 17mm Lanthanum superwide as my primary eyepieces. I will also use my 9.5mm Orion ED-2 as well, though it gives 125 power in my Orion XT10 (1200mm focal length), it's about as high a mag as I can use most of the time due to seeing. You won't have too much trouble spotting DSO's at 37-48X, my 42mm gives 29X and I have no trouble spotting DSO's, plus the low power wide field makes locating them easier. Many DSO's are actually quite large but dim, a higher power eyepeice isn't necessarily the best one to use for some DSO's.

To find the exit pupil, divide the aperature by the magnification, IOW, for my 42mm, it yields 29X, so divide (in my case with my 10" or 254mm aperature) 254/29 which = 8.75. A better max exit pupil would be no more than 7mm if you're a younger guy, if you're over 30, you'd probably want to get closer to a 6mm exit pupil. At your 200mm aperature, your lowest power eyepiece would be about a 32mm (would give a 5.3 mm exit pupil in your scope and 37.5X). Does your scope have a 2" focuser? If so, a Televue panoptic would be nice but spendy, though not as much as a Nagler. Orion has the Optiluxe series, but I have the 32mm and cannot recommend it. I have the 17mm Vixen superwide which I highly recommend. It gives me 70X and at 68 degree FOV, yeild about 1 degree, which at 70X is pretty good. It's a great DSO eyepeice. http://vixen.telescopes.com/products/Vixen_17mm_Lanthanum_Wide_Eyepiece_-_1.252_Inch_27404.html It also has a nice 20mm eye relief which is important. Makes for much more comfortable observing.

[aurora]

Saturn at 48x appeared quite tiny, but once I used a 120X, it was a little dimer, but much more obvious to the eye. But DSO's are nowhere near as large as planets are. If I did use 37-48X wouldn't I have a tough time spotting them? I understand that they would be much brighter at a low power, but wouldn't they be extremely tiny?

Mostly no. Some deep space objects are tiny (very small planetary nebula's for example, need high magnification to appear as anything other than a point) but most of the brighter galaxies (M81 and M82 for example) and Globulars (M5 and M13 for example) can be viewed with lower powers quite nicely. Not to mention open clusters, which usually need low powers and wide fields. Heck, you can see many of the Messiers with binoculars, which are even lower power than this.

With the Dob, you are going to enjoy having a low power wide field to find and observe many of the DSO's. As was already mentioned, at high powers you need to continually move the scope to keep the object in view, which gets somewhat tiresome although isn't as bad as one might think.

I have found the Televue Panoptic line to be nice in the lower powers, wider field. They are expensive but not as expensive as some of the other eyepieces.

[Dave Mitsky]

If I get a 32mm, my mag would drop to about 37x, is that sufficient to see DSO's?



A meade 82degree 18mm or a nagler equivalent (I'm looking for one at least)


So the higher the mag, the larger the picture, the lower the brightness. Correct?

Saturn at 48x appeared quite tiny, but once I used a 120X, it was a little dimer, but much more obvious to the eye. But DSO's are nowhere near as large as planets are. If I did use 37-48X wouldn't I have a tough time spotting them? I understand that they would be much brighter at a low power, but wouldn't they be extremely tiny?

Higher magnification equals a smaller true field of view and lower image brightness.

Most DSOs are larger than the planets. The largest planet in apparent size is Venus, which is at its maximum now. It spans a little more than one arc minute when at inferior conjunction. (This is about the same size as M57, the Ring Nebula.) It is true that some DSOs will be not be apparent at low power, particularly small planetary nebulae, which will appear stellar unless "blinked" with a narrowband or line nebula filter.

I have heard both good and bad reports on the new Meade series 5000 line but I think that the 1.25" 18mm UWA may be a reasonably good choice for your telescope. Does your scope have a 2" focuser? If not, the 16mm Nagler type 5 is the only option close to a focal length of 18mm.

Dave Mitsky