Orion XT8 Dobsonian Questions; Seeking Advice

[SHC]

Hello all! I happened upon this forum, and frankly I've noticed that people here seem incredibly polite and helpful, which is new for me where internet forums are concerned. So, for that, I'm grateful already! Restoring faith in mankind and all that jazz... haha....

Anyway, I bought the standard Orion XT8 Dobsonian, my first major telescope purchase a few months ago (I also own a pair of Zhumell astro-binocs, which I've had for a few years). Long story short: I love the telescope. I use it absolutely as much as I can, but East Tennessee weather is very uncooperative. At any rate, I currently only have the default 25mm Sirius Plossl, and a 2X Barlow I got as a gift.

I've seen a nebula (Orion, easy for a beginner like me), Saturn and moons, Jupiter and moons, and, you know, THE MOON, and that's about it other than just sort of scanning to see what I can see. I use the program Stellarium, but either I simply can't find what I'm looking for, or my eyepieces or the "seeing" aren't good enough. I'm guessing it's a mix of all three.

I looked around at some of the photos of Jupiter listed in the astrophoto section, and I was pretty blown away and, admittedly, a little let down! These are startlingly huge, colorful, detailed images of the planets! My 'scope has a theoretical limit of 400X under the best conditions, I've read. With a better eyepiece or two, what sort of increase in size and clarity can I really expect with this 'scope? What eyepieces as far as eye-relief and field of vision would you guys recommend? The prices of the eyepieces I've sort of had my eye on (no pun intended) vary wildly.

I was hoping for a more experienced set of opinions, and I hoped someone could temper my expectations... or reassure me that I'm going to be pretty blown away by new eyepieces. But, that said, I've already gotten a lot of joy out of seeing Jupiter and Saturn (and the Moon) with my 25mm eyepiece in tandem with the 2X Barlow (I believe this puts the magnification around 96X, and Jupiter is detailed -- I can see cloud bands when the seeing allows them to waver into view -- and colorful, but it's around the size of a BB).

Sorry for the long first post; thanks for any advice/words of wisdom you might have.

[erick]

Hi Sean and :welcome: to IIS.

I also started with binoculars then moved to an 8" reflector on dobsonian mount.

Do you have a local star-gazing club? If so, you should join and go along. You will see equipment, be shown how to do things, be able to borrow eyepieces to try out in your scope.

I'm sure you have already worked out that you will never see anything through the eyepiece like the images of Jupiter on this site. To put it simply, the camera collects lots and lots of light and adds it up - minutes worth, even hours worth. With our eye we see what we can see at any instant of time. With experience, the eye and brain can work together to allow us to observe more detail if we look at an object for minutes. Also there is the use of averted vision to see fainter objects. But nothing like the images.

They are also working at magnifications of maybe 2000x or more! Obviously lots of good quality equipment is required to follow the object accurately and transmit the light to camera without distortion.

But, don't despair, visual observing is fantastic, and with everything working well, you can have very exciting nights under the stars.

Presuming your mirrors are working well - and they would be in your scope, unless covered in mud or cobwebs! - then we have to look at:-

1. temperature of primary mirror relative to ambient air in the tube
2. collimation of the optics
3. eyepieces
4. seeing conditions

Let's check these off.

1. a warm primary mirror means a small layer of air above its surface which is disturbed and distorts the light paths leading to blurry image. The usual problem is that the mirror is warmer than surounding air as the evening cools. Try to get the scope out into the air an hour or two before observing. If it is fitted with a fan that blows onto the mirror, use it.

2. collimation is alignment of the mirrors so that the image that you are trying to form in your focusser tube (which you will then magnify with your eyepeice) is forming at the right spot and is made up of all available light that your primary mirror can capture. You need a suitable tool and some instruction (this is where the club members come in). Have a look at the collimation video here - www.andysshotglass.com/collimating.html (http://www.andysshotglass.com/collimating.html)
Try to locate a gloublar cluster in your scope. M4, M22, M13? If you re well collimated, you should be able to see all the pinpricks of light of the multitude of stars and not just a fuzzy "cotton ball". The globular looks "granulated" in the centre.

3. Yes, better eyepieces will "blow you away". You need to think about two at present. An eyepiece around 10mm focal length so that you can have a look at Jupiter, Saturn and the Moon (and other objects) in more detail. A good plossl design should do (unless you have to wear glasses observing, then the eye relief (distance between eye and eyepiece) might be too small) and you should look at the Televue 11mm plossl. Not cheap compared to others, but one of the best of this design. When seeing conditions are really good, you can even try that in your 2x barlow for quite high magnification.

You also need an eyepiece around the 26-30mm focal length, but with a greater apparent field of view (AFOV) than the plossl you have. Its AFOV will be 49 or 50 deg. If you can get an eyepiece with 68deg or maybe 80 deg, you will find that much better for looking at the Orion nebula, for example. You see more in the field of view. Also some more money will mean better glass, better coatings to transmit light and stop reflections, better design to avoid distortion in the field of view. Now such eyepieces can get very expensive (check the Televue Naglers!) but there are good performing and more economical eyepieces - Meade? Here is where going to a star party will help. They will often let you view through different eyepeices, even let you try them in your scope. Also go to a specialist astronomy dealer for advice.

4. Finally everything is perfect with your scope. Now, unfortunately, the air above is the problem. If you observe objects at a low elevation above the horizon, you have to look through lots of air which will distort the view significantly. The best view is of objects higher than, say 60 deg above the horizon. Next problem is transparency - what is in the air. Sometimes it is clouds - therefore zero transparency :sadeyes:. Sometimes it is dust, smoke, water droplets - all reducing the light transmission. The other problem is the stability of the air. Rule of thumb - if the stars are twinkling madly, the air is unstable and you can be confident that your stars will look a bit bloated and resolution on Jupiter, the Moon will be terrible. You will learn from experience what is good. Look for articles on star testing - there should be examples of good and bad seeing. ON a bad seeing night, forget Jupiter, the Moon and splitting double stars - stick with looking at nebulae and galaxies.

You mentioned the problem of finding things. Make certain your finderscope is well aligned and learn how to use it and your eyepiece view to star hop. Have you found the options to invert the view that Stellarium gives on the screen? You can make it the same as you are seeing in your eyepiece. Makes it much easier to compare the computer screen with the eyepiece view.

Let us know how you go with these suggestions.

Cheers
Eric :)