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Help with basics of deep sky observing with 8" SCT


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Hi all,

I bought my first telescope (Celestron Nexstar 8 GPS - the older twin-fork arm one) last summer, but as I suffer quite badly from the coldness of the winter evenings, I have just started getting into regular use of it at last!

I am wondering how to best use my scope to get optimum results of deep-sky observing.

I have talked to loads of different people in different shops, etc about this and I have had all sorts of different responses, a lot of which contract other opinions or say that some other advice is either incorrect or unnecessary.

I am taking my scope out tonight (hopefully) and was hoping that you clever chaps wouldn't mind offering me some of your knowledge on what eye-pieces to use and why, whether I would benefit from a focal reducer as some people have suggested, and what I can expect to see through the scope...

Any help is very much appreciated...

Many thanks!

Simon

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start with low power eye pieces to give you a lower magnification and a wider field view to find and centre your DSO's, i find this helps especially as the higher power you go the darker your view gets i.e. things will be clearer in say a 25mm EP than a 10mm

hope this helps

rich

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Evening Simon,

I'm sure that you will get some 'technical' replies soon. I'm gonna go down the more basic route : )

Your scope is an 8inch Schmidt right? with thatI should see you having no problems in seeing:

Jupiter and the Galilean Moons (or Medici's) namely Io, Europe, Ganymede and Callisto.

Saturn and the rings

M81 & M82 (feat. NCG3077)

Some of the shizzle in Leo and Virgo

M51

M101

Other things later in the night such as M13 & M92 in Hercules, these are great star clusters to look at

Also M27 & M57 are good nebulae too look at.

I assume you have an eyepiece with your scope? Most scopes come with a 25mm eyepiece (EP), this gives a good combination of zoom and field, higher magnification EP's such as a 10mm give more magnification but sacrifice widefield views. I would stick with the 25mm for now, its a good choice for observing.

You mentioned a focal reducer....i wouldn't bother getting one unless your going to be using it for astrophotography as they can be quite expensive. I believe focal reducers also widen the field of view, this may be a benefit when looking at open clusters such as the Pleiades (M45) or the Beehive Cluster (M44).

Does your scope have a wedge facility built into the mount? i.e. can you adjust the angle to the bas of the scope to allow it to track the night sky in alignment with the apparent movement of the stars.

If you do then this will greatly improve your deepsky observing as you will only have to move the scope in one axis. Here's what I mean by a wedge:

http://dvaa.org/images/C8Big.jpg

If your scope is a goto scope then you should learn to use the star-alignment features, this allows the scope to track the night sky and also locate objects for you to observe..once it has found them you should be able to see the object through the EP and it will continue tracking them for the following few minutes very accurately.

Maybe invest in a laser pointer, these things are great for shining through the viewfinder scope to check that your scope is aiming in the right place before you get into an awkward position under your scope, risking broken bones and fractured hips etc : p

Also make sure you have a red torch and a star chart at hand, aswell as warm clothes.

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I owned an 8" SCT a while back (a Celestron C8) and I found the F/6.3 focal reducer an essential accessory for viewing deep sky objects. For me it proved a better alternative to a 2" diagonal and 2" eyepiece as the extra weight of the latter caused some balance problems with the fork mounted scope, not to mention being a little more expensive.

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Hi Simon, i have an 8" LX-10 and unlike John, i rarely use the f/6.3 F/R (focal reducer). Someone advised me to get one a long time ago so i did, but the only thing i ever used it for was when taking prime focus (35mm film) lunar images.

The only time i use the F/R now is to get a wider view of large DSOs but TBH when i use it visually i get an eyestrain headache and it gets me nauseous, isn't that odd? The F/R is also called a 'field flattener' and i'm wondering if it does something weird to my eye muscles that i'm not used to.

Other than that, the 8" SCT is great for most targets. In fact, that's why i got one as my first "big :D girl" scope. As a newbie i didn't know if i'd be more interested in deep sky or solar system targets, and info i'd read about the SCT said that it was a good all-around scope... i've found that to be true. It's shown me all of the Messiers, most of the two Herschel 400 lists, and fantastic lunar views.

Faint targets seem to be brighter when the field of view is wider, so my favorite eyepiece for detecting them is the 32mm Plossl. The magnification i then toss at the target depends on it's size, surface brightness, sky conditions, etc.

My eyepiece of choice for the Moon is a 9mm orthoscopic. My scope is wedged and has tracking, so the ep's narrow fov isn't an issue. I just love the contrast the orthos give.. excellent for lunar work.

Admittedly i'm not much of a planet observer and generally can't squeeze too much detail out.. the 10mm Plossl is usually ok but the magnification needs to be adjusted to go along with conditions.

Best of luck and enjoy your scope! :p

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Hi Simon,

I totally agree with all the above. I have an 8"SCT, and it's a great all-round 'scope.

For seeing the fainter nebula I've purchased an O111 filter, which is essential in our polluted skies. Light pollution is a real limiting factor with any 'scope. I agree with Talitha when she says 'Faint targets seem to be brighter when the field of view is wider, so my favorite eyepiece for detecting them is the 32mm Plossl. The magnification i then toss at the target depends on it's size, surface brightness, sky conditions, etc'. Low power eyepieces give not only the most dramatic views, but you get a real sense of scale. If your lucky enough to live in an area of low pollution then the 8inchSCT will give you fantastic views of the cosmos. Enjoy!

Edited by MickyWay
spelling!
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I am wondering how to best use my scope to get optimum results of deep-sky observing.

1. Find the darkest sky you can get to. Your scope is highly transportable and if you can see the Milky Way with the naked eye you'll see lots of detail in DSOs, if you know what to look for.

2. Concentrate on acquiring experience rather than gear. In a year you'll be an expert, if you work at it.

3. Get warm clothing: the long nights of winter are the best time for deep-sky viewing. At my latitude (northern England) it's pretty much impossible from mid-May to mid-August, as the sky never gets dark enough.

4. Let your eyes get properly dark adapted. Use a hood to screen unwanted light if necessary. For note-taking, map reading etc, use the faintest red light you can see with.

5. Start with low power and work up. You'll see something different with every magnification - add those details up in your head (or in a sketch) and you'll get a rounded view of the object. If your sky is dark enough you'll find it's possible to go pretty high before the object disappears - so you'll see more detail.

6. Read some books on deep-sky viewing. O'Meara's on the Messier Objects is an excellent start. You're looking for very subtle features at the limits of perception, and this requires a different kind of looking from what we're used to - far more active and requiring lots of patience.

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i have an 8" LX-10 and unlike John, i rarely use the f/6.3 F/R (focal reducer). Someone advised me to get one a long time ago so i did, but the only thing i ever used it for was when taking prime focus (35mm film) lunar images.

Same here except that I had a 8" LX90 & upgraded to CPC1100.

The focal reducer is probably a good idea for imaging DSOs (with a small chip camera, the 0.33x will be better than the 0.67x) but visually I do not find it helpful at all - just more glass to reduce the contrast.

I do have a 2" diagonal &, with the LX90, I really liked the Antares W70 34mm. With the CPC1100 this is a bit too much power & I now use the Meade series 5000 Super Plossl 40mm as my "low power" going straight up to 26mm for the next power. The 40mm is unusable in bright twilight or when the moon is full - the sky background is too bright ...

In addition to the other good advice above, don't forget that some of the brighter Messier objects (M45, M31, M42) are really too big to show up well in an 8" scope. By means of a balance, you have access to lots of smaller, fainter objects that people with 4" can't see at all.

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I have talked to loads of different people in different shops, etc about this and I have had all sorts of different responses, a lot of which contradict other opinions or say that some other advice is either incorrect or unnecessary.

Many sales people will say whatever they think you want to hear in order to sell you a scope or even a single EP. That is the price we pay for not knowing our stuff when buying. We usually walk out of the shop with something that really isnt gonna do what we want it to. We have all done it at one stage or another.

The best way to narrow down the list of scopes you are interested in is RESEARCH,RESEARCH,RESEARCH.

The best way to research scopes that you are interested in is to come to an astronomy forum like this and ask questions. There is bound to be people who either own or have used the scope you are interested in.

You can read "user reviews" of scopes til the cows come home but they dont contain the wealth of knowledge that is held within astronomy forums such as this place.

What was the question again?

Oh yeah..................DSO observing!!!!!!

As has been said....................start of with your lowest magnification power EP (25mm-32mm is good...............but whatever you have will suffice). When you have your target in view increase your magnification and refocus your scope. But dont go too high on the magnification (I mean there is NO point in observing the Orion nebula with a 5mm EP because you will be so close to it that you wont see it for what it is).

Edited by LukeSkywatcher
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A C8 is a really powerful scope. It's surprsing what you can see, even under light polluted skies with a bit of effort. Had mine since 1994. Still going strong. Few tips;

1. Worthwile collimating the scope - once set they hold quite well. Plenty of instructions on the web and in your CPC manual.

2. Give the scope a good hour to cool down - it makes a big difference, especially on planetary viewing.

3. I've got a focal reducer - never use it apart from astro-photography.

4. My low power eyepiece is a 22mm Lanth wide angle. Tremendous eyepiece, but any good plossl works well with SCTs. An OIII filter or a UHC one is handy - the latter would proably be a better all rounder.

5. Draw up a quick lst of what you want to look at before observing. Wth the universe to choose from, it's good to have a bit of structure. Don't omit galaxies - you can see plenty of 'em, even from the suburbs.

6. Best of luck.

Richard

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Fingerless gloves, balaclava, woolly hat with drop down ears, lots of layers, and a big thick coat. Two pairs of trousers (I wear track suit bottoms under mine), and possibly tights for extreme cold, and some of those hand warmer pouches that you boil to reset (in camping shops). Have lots of warm drinks available too (flask or camping stove).

Oh and I agree with all the astronomy advice above too - all good stuff :D

Edited by brantuk
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