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Intermediate Deep Sky advice?

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#1 Almagne

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Posted 20 May 2013 - 11:27 PM

Is it possible to get some good advice as to "how to best observe" certain classes of objects? Perhaps something more than just the standard advice of taking a well collimated dob to a dark site during a new moon. The idea is the get some advice on how to best use the equipment one has, rather than recommend some specific eyepeice, etc.

Lets assume an intermediate sized, well figured dob (12 to 18 inches). It is well collimated with a decent selection of quality eyepieces ( let's not get bogged down into the merits of one eyepiece over another.) Given that what are your techniques?

1. How best it observe galaxies? Its been said that 150 to 225 power is best; others say 2- 3mm exit pupil. What is your rule of thumb on this? Any other advice as to how to maximize the quality of the view (other than getting a better eyepiece.)

2. Any techniques on getting the views for nebulas? Emission, reflection, dark, and planetary - these are all very different objects. Do you do anything different for each class of these objects?

3. Globs? Any special techniques?

4. Finally open clusters. Maybe these would not all be considered deep sky objects, but any techniques?

#2 Tony Flanders

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Posted 21 May 2013 - 04:37 AM

Is it possible to get some good advice as to "how to best observe" certain classes of objects? Perhaps something more than just the standard advice of taking a well collimated dob to a dark site during a new moon. The idea is the get some advice on how to best use the equipment one has, rather than recommend some specific eyepeice, etc.


The first five pieces of advice are:

Use averted vision.
Experiment with different magnifications.
Use averted vision.
Practice, practice, practice.
Use averted vision.

That kind of sums up deep-sky observing. It's also extremely helpful to compare your observing against what other people see (numerous examples in print and online) and against photographs.

How best it observe galaxies? Its been said that 150 to 225 power is best; others say 2- 3mm exit pupil. What is your rule of thumb on this?


Personally, I find that a 1.5-mm exit pupil is usually best overall. But you should definitely try different magnifications for yourself. Often different magnifications show different aspects of an object.

The other big piece of advice is: when looking for spiral arms, concentrate first on the dark areas between them. In time, the spiral arms will swim into view.

Any techniques on getting the views for nebulas?


Always experiment with different filters; you never know what you'll find until you try. Don't be afraid to use high magnifications, especially for planetary nebulae.

Globs? Any special techniques?


Averted vision and plenty of magnification. It's hard to go too high.

Finally open clusters.


To my mind, this is the most challenging class of objects because open clusters are extremely varied. And when looking through an eyepiece, it's impossible to tell for sure which stars are true cluster members, or even if the thing you're looking at is a true cluster. Truth be told, the pros with all their photographs and spectroscopes often don't know either.

Here, there's no substitute for observing many different clusters to get a sense of their diversity. And experimenting with different magnifications can be particularly helpful.

#3 galaxyman

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Posted 21 May 2013 - 09:26 AM

Tony certainly nailed it, and I'll add patience.

Meaning waiting for moments of good seeing or sky conditions to optimize.

He also mentions trying different magnifications, which is correct since many of these objects are best seen with a particular telescope using or trying varied magnifications. This is because of the variance of magnitude, surface brightness, shape, size of the object, and the particular sky conditions that night. Galaxies for instance can be extremely variable, plus even large galaxies the use of very high power can bring out small details within the galaxy.

Planetary nebula can also be terrific using very high magnifications, bringing out photographic detail.


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#4 Astrojensen

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Posted 21 May 2013 - 10:08 AM

Planetary nebula can also be terrific using very high magnifications, bringing out photographic detail.


I'll second (or third) this. I have used extremely high magnifications on planetaries, around 200x per inch, and seen amazing detail. You can only do this with the brightest ones, those with very high surface brightness. Don't try it on the Ring, M57, or M27, they'll just disappear. DO try it on NGC 6210, NGC 6543, NGC 7662, IC 2149, NGC 2392, J900, PK64+5.1, NGC 6826...

It does require an extremely stable mount. An EQ-6 is barely adequate, even for a very small instrument. You really need a rock-solid mount. Also, wide-field eyepieces with good eye ergonomics and good eye relief, such as Radians, Naglers or ES82s are a godsend. You'll also need a very strong barlow, 3x - 5x, depending on your scope and eyepiece collection.

You will also want very good seeing...

What you DON'T need is a large scope. A high-quality 4" refractor or maksutov on a stable mount is more than enough to begin to show some truly fascinating details in the bright planetaries listed above, using magnifications in the 600x - 800x range. A 6" can be taken to well over 1000x, provided it has a stable enough mount. My 63mm Zeiss Telemator shows detail in some planetaries, using 381x (I don't have a strong enough eyepiece/barlow combination for this scope to take it any higher), details usually though to require a substantially bigger telescope.

But all things equal, a bigger scope will of course be better, just remember, it needs to track and be stable at those ultra-high magnifications. These are no easy requirements to fulfill for a large scope.


Clear skies!
Thomas, Denmark

#5 BillFerris

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Posted 21 May 2013 - 11:59 AM

I'll offer a couple of observing strategies. One, is to focus your observing on objects near the celestial meridian. This is when objects are highest above the horizon and, as a general rule, best placed for observing. Two, observe the most challenging objects after midnight. This is the time of night when the contribution to local light pollution from nearby communities is at its lowest. Depending on where you live, you may pick up a few tenths of a magnitude in sky darkness, which could mean the difference between a positive or negative detection.

As for good general observing techniques, I'll echo the recommendations to use high (~2mm exit pupil) magnification. Studying an object at high power for at least 5-10 minutes will darken the surrounding sky enough to allow your eye to further dark adapt. The more complete your dark adaptation, the more sensitive you will be to faint light sources. High magnification will also make fine details large enough to be discernible as having dimension. Personally, I like to spend a minimum of 15 minutes on each object and have often devoted 30 minutes to an hour to studying complex, detailed or otherwise interesting objects. The more time you invest, the more you will be able to see.

Averted vision is a valuable technique. You can also maximize your ability to detect a faint, extended object by gently tapping the eyepiece or watching as the object drifts through the field of view. When fully dark adapted, an object in motion is easier to detect than a stationary one. These techniques introduce motion and can aid in your detection of objects at the threshold of visibility.

Above all, remember that deep-sky observing is primarily an exercise in contrast detection. Anything you can do to improve object contrast vs the surrounding sky will allow you to see fainter objects and details. When all else fails, find the largest aperture on the field and ask the owner if they wouldn't mind taking a brief look at your object. The reduced threshold contrast of the larger aperture may allow you to make the observation. Armed with that beta, return to your scope and have another go.

Bill in Flag

#6 Tyranthrax

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Posted 21 May 2013 - 12:56 PM

My biggest advice I've gotten off of here is patience and persistance. One day you see the objects that take your breath away and marvel at the complexity the next you are scratching your head wondering if the tracking is off, then realise its just not a good night to see it. The rest of thier advice here is pretty sound.

#7 Sasa

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Posted 21 May 2013 - 03:00 PM

Tony, I would also add to your excellent suggestions:

Try to sketch what you see.

This goes with your recommendation of comparing the observations with others. Sketching forces me to really think about what I see. I need to answer questions like, is this tiny brightening real or just my imagination? Next time my brain has have more intuition what is real and it will react more quickly. This helped me a lot on my way to becoming more experienced observer.

#8 Nick Anderson

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Posted 21 May 2013 - 09:42 PM

My biggest advice I've gotten off of here is patience and persistance.


I was going to say exactly that: "patience and persistence". I've had numerous people say "that object is impossible for an 8-inch scope!" and later on I prove them wrong. It's all about putting your time in.

-Nick Anderson

#9 kfiscus

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Posted 21 May 2013 - 11:56 PM

Great advice above. I'd add the use of a hood to block extraneous light.

#10 galaxyman

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Posted 22 May 2013 - 10:10 AM

Great advice above. I'd add the use of a hood to block extraneous light.


Yes, I mention much of these in the video series, particularly the GL an Intro video.

DSO observing is a skill as many above have suggested, and getting to or observing under the darkest sky you can get to, will make a HUGE difference.


Karl
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#11 Kraus

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Posted 22 May 2013 - 01:01 PM

Don't expect to see images resemble magazine photographs in the eyepiece. I think that's why many little scopes are on e-Bay.

Patience cannot be over-emphasized.

I do like Herr Ferris. The air is thinest overhead. No need to look low to the east. The object will rise overhead, eventually.

Oh and did I say patience cannot be over-emphasized?

#12 Sarkikos

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Posted 24 May 2013 - 11:20 AM

All the advice given so far is very good. I'll try to think of some tips that have not been given already.

1. How best it observe galaxies? Its been said that 150 to 225 power is best; others say 2- 3mm exit pupil. What is your rule of thumb on this? Any other advice as to how to maximize the quality of the view (other than getting a better eyepiece.)


There is no rule of thumb, since galaxies can vary so much in apparent size, angle to the observer (face-on, edgewise or something in between), and surface brightness. Try different magnifications for each galaxy. One of the best ways to accomplish this is to use a good zoom eyepiece. My Baader Hyperion Zoom 8-24mm is in the focuser about 80% of the time when I'm at a dark site. A zoom can dial in the optimum image scale and perceived contrast for each object.

I know the OP requested no specific recommendations on eyepieces, but a zoom is such an underutilized and unappreciated accessory for deep sky, I felt compelled to mention it. I really do not understand why more DSO observers don't use them. If you want more power, put the zoom in a Barlow. If you want better outer-field correction, but the zoom in a Paracorr. eh... :shrug:

2. Any techniques on getting the views for nebulas? Emission, reflection, dark, and planetary - these are all very different objects. Do you do anything different for each class of these objects?


Try DSO filters for emission and planetary nebulae. If a dark nebula is in front of an emission nebula, DSO filters can help (for instance, an H-Beta for the Horsehead - B33). They are not so helpful for reflection nebulae. Better to keep the view natural and as bright as possible for them. Consult David Knisely's excellent summation of best DSO filters for different objects.

FILTER PERFORMANCE COMPARISONS FOR SOME COMMON NEBULAE by David Knisely

3. Globs? Any special techniques?
4. Finally open clusters. Maybe these would not all be considered deep sky objects, but any techniques?


Again, use a good zoom eyepiece. It is very instructive and entertaining to see how radically the appearance of a star cluster can change as you increase the magnification. The lower power setting will give you a wider context to help determine exactly which stars contitute the specific open cluster you want to locate and observe. DSO filters will not help much for these, except maybe open clusters that are associated with a bright nebula.

Of course, for really big DSO, you need to put in a low-power wide-field eyepiece. And for very faint fuzzies, an eyepiece with high light-transmission is nice.

Mike

#13 Sarkikos

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Posted 24 May 2013 - 11:37 AM

Another tip:

Avoid all white light at the dark site! This will degrade your deep dark adaptation for an hour or more after each exposure. In fact, avoid any light except for dim red light. If you use red light for your tablet, notebook, or flashlight, dim them as much as you can and still retain ability to see. Use Velcro to attach red filters over any lights inside your vehicle.

If you are serious about observing DSO at a dark site, don't view bright planets except for when you first arrive and immediately before you leave. A look at Jupiter will degrade your dark adaption.

But here's something that many observers don't seem to understand: It's also important not to mix observation of the faintest galaxies and other dim objects with any brighter objects, not just planets. After locating and viewing faint galaxies for a couple hours, I've noticed serious damage to my level of dark adaptation after a quick look at a bright globular or even a moderately bright star.

Mike

#14 David Knisely

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Posted 24 May 2013 - 01:02 PM

Sarkikos wrote:

Try DSO filters for emission and planetary nebulae. If a dark nebula is in front of an emission nebula, DSO filters can help (for instance, an OIII for the Horsehead - B33).


No, the OIII should *never* be used on the Horsehead. That nebula emits mainly light in the hydrogen lines, so an OIII filter completely kills it. The H-Beta filter is best for the Horsehead, although a narrow-band nebula filter like the DGM NPB or Lumicon UHC will help it as well, since those filters generally pass the H-Beta line. Clear skies to you.

#15 Sarkikos

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Posted 24 May 2013 - 01:26 PM

You are correct, David. That was a mistype. :o I should have put in "H-Beta," not "O-III." In fact, a couple months ago I saw the Horsehead for the first time. I had a Lumicon H-Beta in my 10" Dob, NOT an O-III. I'm glad you caught this so I could change my original post while it can still be edited. (But I wish I'd seen the mistake and changed it before you alerted me. You do teach, correct?)

:grin:
Mike

#16 Dhellis59

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Posted 10 October 2013 - 08:15 AM

This has been an extremely helpful post. Thanks to all the contributors and the OP.

Clearr skies.

#17 aatt

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Posted 11 October 2013 - 08:22 PM

All of the above sounds great. I would also recommend extended/prolonged viewing of each object.Don't jump around quickly. A long hard look at an object will bring out details.

#18 ADW

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Posted 12 October 2013 - 07:09 AM

Another tip:

Avoid all white light at the dark site! This will degrade your deep dark adaptation for an hour or more after each exposure. In fact, avoid any light except for dim red light. If you use red light for your tablet, notebook, or flashlight, dim them as much as you can and still retain ability to see. Use Velcro to attach red filters over any lights inside your vehicle.

If you are serious about observing DSO at a dark site, don't view bright planets except for when you first arrive and immediately before you leave. A look at Jupiter will degrade your dark adaption.

But here's something that many observers don't seem to understand: It's also important not to mix observation of the faintest galaxies and other dim objects with any brighter objects, not just planets. After locating and viewing faint galaxies for a couple hours, I've noticed serious damage to my level of dark adaptation after a quick look at a bright globular or even a moderately bright star.

Mike


That is excellent advice.

When you first wake up you are very well dark-adapted. When I have plans to attempt a challenge object I will avoid using any light at all between the time that I wake up and my eye goes to the eyepiece (I figure that since the blind can operate without lights, so can I). Before I go to bed, I open up the observatory, uncover my telescope, and lay out my clothes in the order that they will be put on. That means that I don't degrade the excellent dark adaption that one has when they awake (I almost always sleep for several hours before deep-sky observing).

Almost all red flashlights that you see at star parties are FAR too bright -- mine only allows me to see a small circle on the chart from a few inches away. Any brighter red light is only for working around the scope or double star and planetary observing, not for serious deep-sky observing.

Best,

Alan Whitman

#19 mwedel

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Posted 16 October 2013 - 11:29 PM

Almost all red flashlights that you see at star parties are FAR too bright -- mine only allows me to see a small circle on the chart from a few inches away. Any brighter red light is only for working around the scope or double star and planetary observing, not for serious deep-sky observing.


Strongly agreed. I taped a coin over the business end of my red flashlight so only a dim glow leaks around the edges. Someone more technically inclined would go in and yank all but one of the LEDs, but hey, my solution only cost me $0.10, and that only temporarily. :)

Here's something I haven't seen mentioned: breathe deep, all the time, and for the very hairiest detections, try hyperventilating for a few seconds. I got this from one of Jay Reynolds Freeman's essays, and at first it sounded like, um, hooey. But I have tried it and gotten good results.

I should say that this only works on top of (a) fanatical dark-adaptation, (b) fanatical use of averted vision, and © fanatical patience.

Why all the fanaticism? Because when that edge-of-what's-possible object finally swims into view, it will be so worth it.

#20 aatt

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Posted 17 October 2013 - 08:24 PM

Continual deep breathing? Well that one is new to me. Thanks for the tip!

#21 kfiscus

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Posted 17 October 2013 - 10:42 PM

Inhale as deeply as you want- but don't exhale near your eyepieces! This advice may not apply to those with warm weather, but up here in Minnesota, the temps are dropping.

#22 JakeSaloranta

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Posted 17 October 2013 - 11:41 PM

Avoid all white light at the dark site! This will degrade your deep dark adaptation for an hour or more after each exposure. In fact, avoid any light except for dim red light.


It is also important to remember that red light degrades the night vision as well but just not as much as say, a white light. If I'm trying for something very very faint, I try not to use a light at all.

/Jake

#23 Astrodj

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Posted 18 October 2013 - 01:24 AM

All of the above sounds great. I would also recommend extended/prolonged viewing of each object.Don't jump around quickly. A long hard look at an object will bring out details.


I would place this high on my list of techniques for discerning maximum detail of most DSO's, or indeed any object. So many people observe an object for 5 minutes and assume they have seen what there is to see. What's the rush? Are you late for something? Spend at least 20 or 30 minutes on a target and you will accomplish two things: you will see more detail, and you will learn to appreciate the value of patience.

Concerning more detail with a prolonged view:

My experience is that long observation of a target enables the brain to "stack images" during moments of good seeing when observing planetary or double star detail, and for DSO's the brain can compile a kind of "time exposure" akin to old fashion film photography. You will never experience this phenomenon with a "check this off my list" mentality.

#24 kfiscus

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Posted 18 October 2013 - 11:14 PM

Yabbut, for someone like me (a total list freak), if I spent 20-30 minutes on each object, I'd see VERY few of the thousands of objects I hope to find and see. I only get to stargaze about 12 hours a month. If I did spend 30 minutes per object, I'd see 24 objects per month. No thank you.

Some objects like the Veil, M-42, or a great comet can make me slow down, especially to sketch.

#25 azure1961p

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Posted 19 October 2013 - 08:53 AM

Here's some tips Ive read about from accomplished authors as well as accomplished observers here - all are quite meaningful....

1. Five or ten minutes on a galaxy is hardly conclusive. If there's one paramount but of advice Ive gleaned from CN its PATIENCE . Let the mental "stacking" of your deepsky eye/brain have time to really saturate itself with the subject.

2. This is extremely important: the most sensitive part of your averted vision at night is between the bridge of your nose and straight ahead. With your left eye try not to have the object on your left.

3. Everything they've told in this thread about planetaries benefitting from absurdly high magnifications is true - provided however its of good surface brightness. Abell39 for example wouldn't be fit from 1000x through a 6" scope. Its also too big. Understand that on the smaller bright planetaries a night if good seeing AND transparency AND high magnification is the golden ticket. Unlike large diffuse galaxies that can look wonderful at just 140x where the disturbences of atmospheric refraction a d such are held at bay (unresolved), these super high magnifications will show the ugly truth. Even a little less transparency ( not too much) is ok if you can just have a tack sharp focus at 1000x. These little objects are conditional in ways many galaxies simply aren't - but that's the fun of it too. Those little depot store scopes advertising 400x alas weren't completely wrong - they just never supplied the hardware to facilitate the claims.

4. Never get serious with less than a full hours dark adaption that doesn't involve lighting a cig, sitting in the car fiddling with the radio, opening the trunk of your car or taking a phone call.

5. A hood provided good ventilation is had is the best way to go. The night sky in the country is bright once you try go skotopic.

6. This is EXTREMELY important: the day or two before you have a deepsky night planned make sure wether its the beach, a ski trip or wherever you wear nice dark sunglasses. You can't blast your eyes by day with excessive sunlight and have your best night vision. Even ultra-dark sunglasses might be a nice thing. Too if you work directly under a bright fluorescent or incandescent light try reducing but in some way if possible the day or two before.

7. Expectations are a true player here. The novice that misses a lot often doesn't yet have the grasp that experience teaches in what to expect in terms of the challenge.

8. When the aperture isn't wildly divergent - the expert with a smaller aperture sees more than the novice with larger. Observing is a refined skill in both planetary and deepsky. Its not unlike a golf-swing, a fly cast or playing violin. There's this deliberate presence of senses you gather together and again through it all - patience.

9. BREATHE. This is in the EXTREMELY important realm too. With the brightest targets at comfortable magnifications it can be a little negligible. At your visions threshold though where most anything will happen that's unforgettable, even momentarily holding your breath will have stars a d such grain away into invisibility and so much retinal noise. It'll happen without your thinking about it - you'll steady yourself at the eyepiece waiting very carefully and not realizing for a few seconds you held your breath - and away goes your threshold. Good breathing restores quickly with short time.

10. My deepsky observer acuity theory: books are rife with testaments of lunar and planetary observers "learning to see" and how unlike deepsky where your limit never grows - lunar and planetary contrast detection markedly grows. I used to believe this . I now think its wrong...

Part of this "learning to see" in lunar and planetary observing us the *quickening* involved of the brain learning to accommodate for the exceedingly fast moments that detail is presented. It does the same thing when a person learns to speed-read. The brain is trained to process visual stimuli at a faster and faster rate.

So too I now believe with deepsky.

Details that due loom into view on a galaxy for example are minute fractions of a second. The simple confusion of a mottled surface brightness for one observer can be seen as discrete structural detail for the experienced observer simply because that observers brain has been *quickened* through repeated training. The sensory threshold of dim light has not increased. To this end the adage about "learning to see" not applying to deepsky could be seen to be true in that this is relatively fixed. But that's not what's at work here - the fast shutter effect of fleeting deepsky detail does finally *slow* some when the observer whose taken the time to train his brain to process visual stimuli at faster and faster intervals in dim light has taken place.

I can't PROVE this but its my distinct belief. I will say "learning to see" on Jupiter does nothing for learning to see on M51. It has to be dim light training.


Hope this helps.


Pete






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