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Old 05-10-2018, 05:13 PM
Filippo
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How do you look through a telescope?

Yes, that’s right, I’m seriously asking this question.

I’ve just set up my Celestron 4SE. I found a distant object, in daylight, and used it to align my finderscope. Job done.

However...

While I was doing it I really struggled to get a consistent image from the eyepiece of the scope. I’d be looking through it, seeing my target, then all of a sudden it would all go black like I’m looking at the inside of the eyepiece, rather than through it. Clearly, I must be moving...or blinking...but it seems a hell of a lot harder than I imagined.

Is this normal? Am I a complete cretin? Is there a particular technique to this that I’m not aware of?

Thanks in advance.
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Old 05-10-2018, 05:22 PM
brian nordstrom (As avatar)
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Google ' Kidney beaning ' in a telescope eyepiece .

That is what you are seeing , it is always worse during the day as you have distractions from keeping your head still , it still happens at night but you are focused on whats in the eyepiece so you are seeing only that .

Brian.
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Old 05-10-2018, 05:25 PM
Wavytone
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Quote:
Originally Posted by Filippo View Post
... then all of a sudden it would all go black...
OK... this is a "known issue".

Practice makes perfect.

The telescope has what is known as an "exit pupil". You must align the pupil (iris) of your eye and hold it there to allow all the light from the telescope to enter your eye. See
https://www.google.com/imgres?imgurl...9QEwAHoECAQQBg

There are two snags.

Telescopes with have a secondary mirror (like your 4SE) are very prone to this at low power, because the black spot is actually the image of the secondary mirror as seen by the eyepiece. The problem is significantly worse in daytime because the iris of your eye will have closed to 1-2mm aperture - which makes accurate eye placement absolutely critical, whereas at night your iris may open up to 5...7mm, making it a lot easier. Alternatively - in daytime - use a higher power eyepiece (shorter focal length).

If your eye is off to one side of the exit pupil, the black-out can occur, very suddenly. Secondly this is also dependent on the specific eyepiece - some are worse, some are very tolerant of poor eye placement. The black-out effect is also known as "kidney bean" (it may resemble a big black kidney-bean in the field) and is caused by spherical aberration in the eyepiece. Some have it, many do not. A couple of Televue Naglers were notorious for this.

Last edited by Wavytone; 05-10-2018 at 07:57 PM.
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Old 05-10-2018, 07:43 PM
RyanJones
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Hi Phil,

If you are using the standard Plossl that comes with the 4SE then as has been stated by others, yes it's really common. I can add this eye piece to the others that have been talked about. I personally got used to it quite quickly but if I went to show anyone else what I was looking at they couldn't see anything. Hence why I started Astrophotography so I could show other people. Looking back now at what I got myself into, just a better eye piece would have been a way easier option lol.
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Old 05-10-2018, 08:16 PM
Filippo
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Thankyou all for the replies!

After looking at the diagrams in that google link, I can see what I was doing wrong. A bit of practice and it’s all getting a lot easier. Basically, look straight down the barrel and you’ll be right.

Now onto my next drama. I can’t get this damn thing to do it’s SkyAlign. After about 10 attempts I’ve given up and tried the two-star alignment. Unfortunately this requires me to know the names of the stars I’m looking at. Is there any way for me to work this out? I’ve got the sky safari app but I still can’t tell which star is which. Im quickly realising that I’ve got a lot to learn!
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Old 05-10-2018, 08:51 PM
RyanJones
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Hi Phil,

Sky safari or google sky, even stallerium. They're all going to teach you what you're looking for/at. First you'll need to familiarise yourself with the brightest stars. These have the lowest magnitude. 10 is feint, 1 is bright. Only concentrate on he brightest for now. Early in the night, just after dark you'll be able to see the southern cross and next to it 2 bright stars. Alpha centuri is the brightest. To your south east, again early in the night, formhault and a Achernar. Slightly dimmer and slightly west of directly overhead will be a row of 3 stars. The middle reddish orange one is Anteres. These are good alignment stars and probably the first you should learn for alignment. Watch the stars and see what hey do throughout the night. They rotate around a point 37 degrees above the horizon to the south. This is called the south celestial pole (SCP). This is all a lot to take in but it will give you an idea of where to start.

Re: Alignment. The 2 star is a good place to start. I never used sky align. If you want to take photos you'll need to use the wedge and that's a totally different kettle of fish. Start where you're starting and keep trying and learning and welcome to the fun
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Old 05-10-2018, 08:52 PM
Wavytone
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Ok ... take a deep breath and prepare to dive in.

Old-school way - buy a star atlas (map) - the best for beginners is “Norton’s Star Atlas” available from Amazon and others, now in its umpteenth edition. There are others but nowhere near as useful.

If you are a millennial, get a copy of Sky Safari on an iPhone/iPad or Android. Use this to show the night sky above you; selecting a bright star will show its name.

The stars have common names, as well as Latin names and IAU designations, Sky Safari supports all of these.

Sky Safari is a full-feature planetarium as well, you have much to learn from it.

The other aid you will need is a compass so you can find north/south/east/west. Either a real one or a smartphone app, your pick. Once you are confident with the southern cross and pointers you won’t need a compass.

The starting point is to learn the southern cross and pointers, then several bright stars such as Canopus, Antares, Fomalhaut, Achernar, Sirius, Canopus, Vega, Rigel, Betelgeuse and so-on. After these, finding your way through the constellations along the zodiac is a good start.

Another thing to learn quickly is which ones are planets (not stars). October 2018 is a rare month indeed because in the evenings in the middle of this month it is possible to spot 8 planets, all 9 if you count Pluto, and the one you’re standing on.

Last edited by Wavytone; 05-10-2018 at 09:09 PM.
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Old 05-10-2018, 09:10 PM
Filippo
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Thanks Nick. I’m 33 mate but firmly in the phone app camp. I’ll give that a go, thankyou.

Thanks Ryan, I’ll go have a look and use your notes for reference.

I’m from the UK so even the Southern Cross is new to me. Lots to learn, indeed.
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Old 05-10-2018, 09:22 PM
RyanJones
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Quote:
Originally Posted by Filippo View Post
Thanks Nick. I’m 33 mate but firmly in the phone app camp. I’ll give that a go, thankyou.

Thanks Ryan, I’ll go have a look and use your notes for reference.

I’m from the UK so even the Southern Cross is new to me. Lots to learn, indeed.
I don't know if anyone else picked it up but you said " cretin " in your first post so I knew you were from the UK lol. I am too.
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Old 05-10-2018, 09:38 PM
Wavytone
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Well, we may not have Polaris but the Cross and Pointers are circumpolar, ie never set. Plus the Magellanic Clouds.

Eta Carina, Omega Centauri, 47 Tuc, NGC5128 and the Jewel Box are things you could start with. If you have a dark sky the Magellanic Clouds are rewarding too, many nebulae and clusters there..
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Old 06-10-2018, 07:22 AM
AndrewF (Andrew)
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Sky Safari is excellent but I reckon a planisphere is a must when first starting out.
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Old 10-10-2018, 09:41 AM
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Quote:
Originally Posted by AndrewF View Post
Sky Safari is excellent but I reckon a planisphere is a must when first starting out.
For apps, I'd suggest having both Stellarium and Sky Safari.
Stellarium is good because you can easily set it to emulate the Bortle scale of light pollution, so you can more easily see what stars are actually visible to you, and see those at their approximate brightness after light pollution has been factored in.
Sky Safari, is more like an electronic planisphere in that it shows everything, without any light pollution.
However, in terms of being able to identify what I'm actually looking at, by the relative positions of stars within groups of stars visible in my eyepieces, Sky Safari seems to do a better job of showing where the stars are, relative to each other, than Stellarium.
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Old 16-10-2018, 05:10 AM
AEAJR (Ed)
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Cool

Quote:
Originally Posted by Filippo View Post
Yes, that’s right, I’m seriously asking this question.

I’ve just set up my Celestron 4SE. I found a distant object, in daylight, and used it to align my finderscope. Job done.

However...

While I was doing it I really struggled to get a consistent image from the eyepiece of the scope. I’d be looking through it, seeing my target, then all of a sudden it would all go black like I’m looking at the inside of the eyepiece, rather than through it. Clearly, I must be moving...or blinking...but it seems a hell of a lot harder than I imagined.

Is this normal? Am I a complete cretin? Is there a particular technique to this that I’m not aware of?

Thanks in advance.
Each eyepiece has a different amount of eye relief, or distance your eye should be from the lens in order to see the full image. With low power eyepieces, which normally have long eye relief, you can get too close and will have part or all of the image black out on you.

It is a matter of practice to get your eye in the proper position as it is different for each eyepiece. Sitting down makes is to much easier and more comfortable to observe, including having your eye at the right position.

Observation Chair- Denver Chair – Works Great!
I built this one . It took about 2 hours. Can be built from scrap but if
you went all new, about $30.
http://valleystargazers.com/Chair.pdf
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