Beginner questions, but mostly about crosshairs.

[Kaibis]

Hi all.

We recently purchased a 10" Dobsonian (Skywatcher from Aus. Geographcic) as a starter telescope. We have taken it out twice. The first time we left the main cover on the scope (only took off the smaller cover), however we were still very impressed looking at the moon.

This morning (4am) we took it out for a second outing to look at some of the planets. The location (front yard) is not ideal as the street lights are annoying, but we are still working out the mechanics of the scope, so that isn't too much of a concern.

However, this time we took off the main cover, it was impressive just how much more we could see... BUT, the cross-hairs (are they called restraints? The bars that hold one of the mirrors near the top of the scope) and the mirror obstructed the view.

What we did see was just white light. Nothing discernible, other than the circular shape of what we were pointing at (in our case we looked at both Venus and Jupiter).

We were definitely pointed at them, as moving away removed the white circle from view. However the circle was ill-defined and nothing on the surface was distinguishable, and as mentioned it was partially obstructed by the restraints and the mirror.

I don't know what to do next. Any help will be much appreciated.

[omegacrux]

Sounds like it wasn't in focus
With Jupiter you should see a disc with the band's running through and the main moons
Is there an extension tube in the focuser , if so remove it and try again

David

[Allan_L]

It definitely sounds like a focus problem as David suggested.

A common problem people have with the Skywatcher Dobsonians is that they have both the 1.25 eyepiece holder and the 2" eyepiece holder in together.

These are alternatives.

Assuming you have standard 1.25" (barrell) eyepieces, remove the 2" adapter from the focuser.

I have a Skywatcher DOB and would be happy to help you with any further issues.

The secondary obstruction you mentioned will not be apparent when the object is in focus.

PS: This is a great scope - good choice.!

Oh, and Welcome to IceInSpace :welcome:

[wayne anderson]

Hi Cassie, as david said it seems that it was not in focus, a good way to start to get focus right is to place a lower magnification eyepiece in the scope if you have more than one (these are the ones with a higher number on the eyepiece) as you turn the focuser while looking at a bright star you will see the large white circle of light in the eyepiece get smaller untill the star is a bright small pinpoint dot (focused stars should always be just a bright pinpoint dot) now if you point the scope at a planet you will just need a small adjustment to see the planet as a small round ball. To magnify the planet you will need to place a higher magnifing eyepiece in the scope ( these are ones with a lower number on the eyepiece) or place the 2x 3x 5x magnifing barlow lense if you have one, a small adjustment of the focus will make the planet a little larger in the eyepiece.

Hope this helps a little, Wayne.

[glend]

It sounds like the 'cross-hairs' your seeing maybe the spider vanes that hold the secondary mirror in place. Normally you should not really see them other than their diffraction spikes (sorry for the technical term). It does sound like your out of focus, and assuming the scope is properly assembled it should be able to reach focus. As suggested try a wide field of view eyepiece and don't use any extension tubes, and report back. Allan_l is a good teacher on those scopes, I'd follow his advice too.

[Kaibis]

Thank you both.

I think I understand what you are saying.

The first image is what my setup was (sans eyepiece which is packed away), and if I understand correctly, the second image is what it should be next time?


I have always been a bit confused by the 1.25" and 2" thing. I think I have 1.25" lenses, if so what is that piece that I removed for?

[Allan_L]

Yes, Cassie.
This is what I was referring to.
You are now setup for some good viewing.
The other piece (that you removed) is the 2" adapter, and is for when you get (more expensive and bigger) eyepieces which have a 2" barrel.

If you can come along to a viewing night or camp we can let you borrow some to see what sort of difference it makes in your scope.
For now, 1.25" eyepieces are perfectly fine for your viewing pleasure.
The supplied skywatcher eyepieces are pretty good quality for starters.

[Kaibis]

A second question. I know that it is not okay to stick a telescope out the window, however, given that one of the planets is nicely visible outside of one of my windows, and also given the constraints of a fly-in-fly-out husband, my dislike of being outside alone at 4am by myself, and the early evening hours being occupied by kids bed and bathtime.

Would it be acceptable to setup the telescope out the window while I am figuring all of this stuff out? Really at the moment I am just trying to work out how to use the telescope, and not really caring about image quality.

[Allan_L]

Out the window is not ideal, but as you say, if you dont have a flyscreen, and can open the window, go for it.
Issues such as thermal currents may degrade the view a little, and with a dob, you may have some problems pointing, but when you are learning to use it, any practice is good practice. And your safety is paramount.
Enjoy.

[Kaibis]

Thank you for your help. I will have another go tonight and let you know how I go.

@Alan, I just saw that you are from the Central Coast, does that mean you are part of the Newcastle Astronomy Group? I found them on facebook, and am hoping to get along to a few events next year.

[Matthew Lovell]

10" Dobs are generally Rich Field Telescopes. Rich Field Telescope are generally an F/4 Focal Ratio or less. They have a very wide field of View, and provide bright images. If the magnification of the eyepiece is too low, part of the Secondary Mirror will be seen as a dark spot through the eyepiece.

Low magnification of the Planets, especially bright Jupiter, will show no detail. You need to have a minimum of around 150x to spread out the light a bit, and show details. Otherwise the planet is just too bright, using your size of telescope.

Although the hole in your Dust Cap is quite small, observing Jupiter using just this small hole will cut down the light considerably. It will also change the focal ratio of the telescope to a longer one (better for planets). It's important to align the hole where the Spider (cross hairs) isn't. Using this method, the Spider and Secondary Mirror are no longer an obstruction to the Main Mirror, since the Main Mirror only sees the light coming through the small Dust Cover hole. The small hole means the Resolution of Telescope is reduced. This reduces the quality of the clarity of the image. So it's a case of getting the right size hole to suit your type of Telescope. Use a piece of cardboard, instead of the Dust Cap, with a larger circle cut out of it. The circle can be oval shaped, to be larger, and better fit the gap between the Spider Vanes, as long as the shape is curved, it won't bother the optics. You can cut more than one circle, to fit between the Spider Vanes. If you cut 2 circles, opposite each other - hey, you've made a Hartmann Mask! Used for getting perfect focus. Just adjust the Focuser until the 2 images of Jupiter become one.

[Matthew Lovell]

Oh, using a telescope through a flyscreen is fine. The flyscreen is so far out of focus it won't bother the image. The flyscreen will drop the brightness of the image by the amount the flyscreen blocks out the light from the Main Mirror. Windows are not optically flat, so they distort the image.

Oh! Cross Hairs are the hairs that cross in your finder scope, since they were originally, and still are sometimes made from hair.

[Allan_L]

No. I am part of an informal group on the Central Coast.
(No memberships, no fees, no politics.)
You are welcome to join us for observation sessions etc.
But there are a few from IIS who are Newcastle Astronomy Group members.
H0ughy may be able to fill you in better, I believe he is or was involved with them.
http://www.iceinspace.com.au/forum/member.php?u=221

[Allan_L]

Hi Mat
The "crosshairs" Cassie was referring to are more likely the spider veins holding the secondary mirror, as Glen has already said.

But the trick about using the end cover with the smaller cover removed is also good for moon viewing, as you say, to cut down the brightness.

[omegacrux]

Yup what the others said , I have been out for the day
Excellent scope the ten , I recon most of us started with a dob

David

[Kaibis]

Thank you all for your help. I poked it out the window today and had a look at the moon (7ish at night, so still very bright). However the problem is nicely sorted, I will set my alarm for the early hours of the morning and head outside for a better look.

Thank you all.

(The photo is taken using my iPhone, the sun was still up, and the telescope was pointed through a window, and the kids kept shaking the floor.... Ideal conditions!! :rofl:)

[Allan_L]

You gotta be happy with that shot.
A good bit of detail is clear, especially along the terminator (that line on the moon where light meets dark)

[Kaibis]

Very happy with it. Thank you again for your help.

I took another look (same window) at about 11pm last night. I saw my first galaxy which was pretty exciting. I tried to figure out which one it was but I couldn't figure out how to use my planisphere or the book that came with it, and the app (starwalk2) shows confusing amounts of detail.

It looked like a wolf (I thought) with a cluster of 4 stars in one eye (at first I thought I had the telescope badly out of focus).

I plan to have another look tonight and see if I can figure out what I was looking at. It was pretty exciting to stumble across.

I also happened to wake about 2am (and Jupiter was conveniently out the same window) so I took another look. I am certain I was looking at Jupiter (it was extremely bright and the shape was well defined), however I didn't see anything more than a bright white circle. There were smaller circles near it, but they were far enough away that I think they were just other stars.

All in all I am very happy with it set up out the loungeroom window (I mean, for a week or so while I get the hang of it). It is getting used, I have stuff spread out all over the coffee table, and a comfy seat while I try to figure the planisphere out, and best - if a child wakes (which one did), it was nothing to walk to the next room and settle her before returning to the telescope (if it was outside I would have abandoned the exercise and brought it all in).

I mean, I do realise the image quality is not great, and obviously I have a limited angle of view... but as an initial setup for a week while I am learning how to use the tools... I would highly recommend it.

[Kaibis]

Also, can someone explain regarding using the planisphere and looking through the scope... is it all upside down?

[ZeroID]

The Great Nebula in Orion, M42 is what you are looking at there. Have alook in Images, DSO section to find an astrophoto that shows you more details.
Yep upside down and back to front, it's the result of simplified optics. The less glass ( lenses) and mirrors you have in an optics train the less chance of distortion or light loss and simpler to collimate. You get used to it after a while.

[ZeroID]

I'd suggest you get Stellarium ( www.stellarium.org (http://www.stellarium.org) ) loaded onto your PC. It's free and can be setup to show the current sky view from your location. From that you can learn the sky ( when clouds are in the way ) and locate objects to try to find ion your scope.

[Kaibis]

Thank you so much. I have spent the morning reading about how to use the planisphere (surprisingly easier to do during the day then by a red torch at night!).

I think the stars in the upper right of the picture are part of Canis Major (but really I have no idea what any of that means, other than they kind of look like and are in roughly the right position as what I am seeing on the planisphere - which I don't really know how to use :D ).

Thank you, I am downloading stellarium now...and about to go look at better images of the Nebula.

[Kaibis]

Wow, Stellarium is a whole new thing to learn.

One question that my brain is struggling to answer. Are the images on Stellarium rotated the same way as what I see in the telescope?

I am struggling with that at the moment. I am trying to find the nebula that I took a photo of, but the orientation combined with the amount of stars in the program is difficult.

Is there a way to reduce what I am seeing in Stellarium so that what I see is similiar to what I saw in the scope?

[Allan_L]

Hi Cassie.
Well done.
Which direction does this window face?

Re the planisphere,
Assuming it is a Southern Hemisphere one
(it should say it is aligned for Sydney probably like 33 South; 151 East or thereabouts)
You align your local time (but not daylight saving)
with the Month and Date,
by rotating the disk.

Then hold it above you eyes with South (on the planisphere) pointing towards South,
or North pointing toward North. (depending on which way you are looking)
And then the positions on the planisphere should line up with what you are seeing in the sky.

[Allan_L]

at 2 am, it could have been Jupiter, but it also could have been Venus.
Your description sounds like Venus, very bright but with no discernible features.
Depending on how low it was in the sky. Venus was low in the East, while Jupiter was higher and a little more to the north.

Just checked Stellarium and Jupiter at 2am was in almost the same position as Orion at 11pm, so seems it was Jupiter.
The four moons also adds to this conclusion.

There was a bit of high cloud and humidity last night so perhaps you were just not able to get a good focus on it.
This is common, especially with higher powered eyepieces.
Start of with the 25mm eyepiece, and take your time.

But most importantly ... Keep Looking Up !

[Kaibis]

Thanks Allan,

My window faces ENE towards the next door house, and the planisphere is for the southern hemisphere, it came in a book from Aus. Geo. when I bought the telescope... conveniently came with a red light too!

I have been using an app (Starwalk 2) to work out when the planets are due to 'rise', it also helps me find them in the sky. It could also possibly have been lack of night vision (I had gotten up for a drink of water from the fridge).

It is all very exciting. I have been looking at the Great Nebula, the pictures look nothing like what I saw, but I did find some lower quality images that did! So I know that the four stars I was seeing (at 11pm) were the 'trapezium' at the heart of the nebula.
http://www.laughton.com/paul/rfo/trap/trap.html
http://kellyricks.blogspot.com.au/2015/04/drawing-great-nebula.html

Tonight I am going to pull out my journal and have a go at sketching what I see.

Another question... do the planets 'rise' in the same way that the moon/sun does. ie begin low on the horizon and pass over... or is it more like the ISS, where it can be higher on the horizon but disappear because the earth obstructs the light from the sun??

[CJ]

Hi Cassie,
There are all sorts of view controls in Stellarium. Look in the Sky and Viewing Options Window (F4) for the basic ones. There are more in the config section.
Some of the neb's etc are photo's so you wont get to see them through an eyepiece like they are shown in Stellarium. And with your type of scope they will be flipped.

I think the oculars plugin if configured correctly will orientate them as you would see them through your scope, but it is a little tricky. Have a meddle.
Cheers

[Allan_L]

Yes, Cassie,
Planets rise and traverse in the same way that the sun and moon do.
They are far enough away that they are not effected by the shadow of the earth (like the moon and satellites).

There is a line called the ecliptic that the planets follow in their path from rise - transit - set. The ecliptic moves a little further north in Winter, south in summer. Thats why the sun is often shaded for houses by their eaves in summer, but can be lower in the sky and miss the eaves, in winter.

[ZeroID]

Well, you have probably figured out that the answer is no by now. Stellarium shows it as you would with the naked eyeball, the scope will invert and rotate depending on which optical setup you are using at the time. eg a 45* diagonal will flip the image but not invert it and are normally used for terrestial viewing.
Well done on your rapid progress, keep asking questions, we're happy to help. :thumbsup:

[Kaibis]

Well I suppose the latest question is .... what do you do when it rains? :sadeyes:

After all that excitement yesterday it started to rain yesterday afternoon and is forecast for the entire week.

I need a good astronomy book to flick through! :D

Can I ask a question about where telescopes can be stored? Currently ours is in my sewing room, which is a really inconvenient place. It takes up valuable indoor space, and it is a very long way for me to wrangle it outside. I am tempted to put it in an outdoor carport that we have behind our house. The carport is hidden from the front yard, it is enclosed by the shed on two sides, so I am not worried about theft because it is too big to move easily, and we are insured. It won't get wet, but it might attract spiders (but they can't get past the caps, so a brush will get rid of them).

I am thinking that it would make it very easy to setup (just need to move it a few metres) which would mean that it would get a good deal of use.

[ZeroID]

I preferred mine inside before I built the Observatory just for my own peace of mind but an advantage of outside is it is temp stable when you come to use it.
Capped and all I would suggest getting a reasonably waterproof bag to slide over the whole scope if outside. Even just a big plastic rubbish bag can help keep it clean and dry. Maybe make a wee stand up off the ground so you can tie the bag down around the bottom to keep the creepy crawlies out. You'd be amazed how they can get into things.

[Kaibis]

Okay, I think I actually understand what you are saying. I will try putting it back on next time I see it, and making a mask as you have suggested. :thanx:

[Allan_L]

In our moist environment, I would be unwilling to leave mine out in the weather.
I don't even leave it in the garage (after a previous scope started showing signs of corrosion).

Inside where the air is controlled to some extent is best for me.

[Kaibis]

I never thought of moisture. I might just invest in a trolley instead!