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How Well Does a Sketch Represent the Eyepiece View

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#1 Jeremy Perez

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Posted 22 January 2008 - 01:11 AM

One of the great values I attach to astronomical sketches is that they can help convey what an object looks like visually much better than a photograph can. However, there are some caveats I've been wanting to discuss. What you see in a well-executed sketch is not necessarily what the object will look like when you first peer into the eyepiece. Of course, there are a number of variables that can affect what you see, including equipment used, atmospheric conditions, light pollution, and level of experience. But even if all of these variables are equalized, the view of an object through the eyepiece will not always be as detailed and robust as it appears in another observer's sketch.

I think it is important to distinguish between what an object looks like as a whole, or at-a-glance, compared to what it looks like when your compile a half hour or more of accumulated observations across the entire object. This is especially true of subtle, extended objects like nebulae, galaxies, comets, solar phenomena, and planetary albedo features. This composite view is what many observers try to accomplish with their sketches. By spending ample time, gradually pulling numerous details from the object, an observer is able to slowly build up a picture that contains much more structure than a normal gaze will allow.

To demonstrate, here are some progressive images of a sketch I made of M17 a couple summers ago. To better convey the subtle impression of structures seen in the eyepiece, I've kept contrast low--so it will be helpful to view the images with as little glare on your screen as possible.

This first image shows how the nebula may appear at first glance:

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#2 Jeremy Perez

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Posted 22 January 2008 - 01:11 AM

The next image shows what you may begin to see under good conditions as your eyes grow accustomed to the view. The "swan" shape becomes more apparent, and a soft glow may begin to appear above the swan's back, and to the northeast of its body.

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#3 Jeremy Perez

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Posted 22 January 2008 - 01:12 AM

If I were to finish the sketch there, it might very well represent the basic appearance of the nebula through the eyepiece. But there is still more detail to be observed. The following animated image shows the individual details I noticed while using averted vision to pry into the mottled glow. The animation lasts about ten seconds before starting over again.

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#4 Jeremy Perez

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Posted 22 January 2008 - 01:12 AM

As you can see, much of the finer detail is not observed all at once, but is picked up in pieces. By gradually adding these pieces together I am able to build up a composite sketch that describes all of the details I was able to observe.

In addition to including all of these separate details I also tend to increase the contrast of the finished sketch for a couple reasons. First, I apply a bit more contrast to the pencil drawing itself so that real details stand out above any unintentional irregularities caused by the paper or shading process. I also increase the contrast of the scanned image, since I know that people will be viewing the images using a wide range of monitors with glare and conditions that are often less-than-ideal.

This last image shows how I chose to present this sketch:

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#5 Jeremy Perez

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Posted 22 January 2008 - 01:13 AM

So, although the sketch may appear more obvious than the object looks all-at-once through the eyepiece, it does achieve my goal of presenting all the details I observed during the two hours I spent observing the nebula.

Given more time, I would love to produce both an at-a-glance version and a detailed version of every sketch to convey what an object looks like at first, and what can be discerned with more time and effort. For now I'll be sticking with the detailed versions :)

#6 Acheron

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Posted 22 January 2008 - 04:06 AM

Impressive tutorial Jeremy. Your second step sketch looks exactly as I see in the EP of 8" scope under mag 5.5 skies.

Clear skies

#7 THEPLOUGH

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Posted 22 January 2008 - 05:33 AM

Amazing. Truly. Amazing.... I have looked at this site often and wondered how you managed to get such wonderful images. Thank you for that very informative explanation.

-------------
Geoff.... :thanx:

#8 Rich (RLTYS)

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Posted 22 January 2008 - 06:21 AM

Jeremy

Your tutorial is excellant and is so true. Part of the challenge in observing is "learning how to see" which only comes with lots of practice.

Clear Skies.
Rich (RLTYS)

#9 pike_fly

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Posted 22 January 2008 - 09:32 AM

A nice pictoral to show many beginners or people who don't understand sketching why we spend so much time on one object. Detail doesn't become apparent without a lot of time with your eye in the eyepiece. Well done.

#10 Special Ed

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Posted 22 January 2008 - 12:19 PM

Jeremy,

Nice demonstration of how the eye/brain combination can "stack" images of the target object when the observer takes time in a session. :cool:

It is very true that it is hard to get the contrast to reflect the actual view in the eyepiece--it may not even be desirable in some cases. Many sketchers enhance the contrast in order to draw attention to certain areas or to emphsize how two areas may differ. Much subtle shading can be lost in the scanning process or, as you point out, just because of irregularities in the paper.

#11 CarlosEH

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Posted 22 January 2008 - 01:44 PM

Jeremy,

Thank you for your very instructive and revealing tutorial on the appearance and recording of deep sky objects (applies to the Moon and planets as well). As you point out, many factors affect the visibility of objects in the eyepiece. The multitude of factors, as you also point out, do not explain the differences in observer's sketches. This may be accounted by differences in artistic styles, media used, degree of image manipulation, among other factors. Your sequential series is excellent in showing what the observer may expect as the seeing conditions improve (as well as the observer's eye becoming more sensitive to faint detail over time). Obtaining the correct contrast of an object is not an easy task but with practice one may achieve an acceptable result.

I look forward to your future observations.

Carlos

#12 FJA

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Posted 22 January 2008 - 02:35 PM

That is why I believe that people who don't sketch, or describe, what they see do miss a lot. Before I sketched or took notes - this was when I first got into deep sky observing - I just glanced at the object: 'That's nice' and moved on. I missed tons and when I revisited these objects to sketch them I saw what I'd missed.

#13 cildarith

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Posted 22 January 2008 - 02:48 PM

Jeremy, thanks for this excellent demonstration! There's not much I would add to what has already been said, except... that averted vision animation is very cool! :bow:

#14 Erix

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Posted 22 January 2008 - 03:18 PM

This is a great demonstration, Jeremy. It'll be good to use this when discussing the observing/sketching sessions with others that are thinking about trying their hand at sketching their observations, or giving detailed descriptions as well.

Thanks for doing this!

#15 rodelaet

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Posted 22 January 2008 - 03:52 PM

Great demonstration, Jeremy!!!

I believe that there are a few mechanisms in our brain which handle the 'image processing'. My experience has thought me that patience is important while observing. I've learned to count not to much on 'first impressions' when it comes to observing. It looks like the brain works with a stacking mechanism in order to enhance the image. The human retina has a specific but varied structure. While looking through the eyepiece in different directions, the observed object is projected onto different area's of the retina. Some area's are very sensitive to low light while other area's provide sharper vision. The combined impressions gathered by these area's of the retina are processed by the brain into an enhanced image. Which make me think : What was the first impression, was it when I looked left, or was it when I looked up in the eyepiece? I don't know the answer. I've learned that the retina is very sensitive for 'objects in motion'. I find that the wiggling of the scope provides very usefull 'vision'. Which will not show on a first impression. The procedure of making a sketch also adds to the whole observing experience. While looking for anchor stars, the brain sub-consciously starts accumulating visual information about the eyepiece view. During this phase of the sketch, I use a lot of 'flashlight' to see my sketchpad. This large amount of light prevents my eyes to 'dark adapt'. Therefor only the brighter aspects of the desired object show up. While the sketch continues, I use lesser and lesser light. My eyes can see better now, and the object grows in my eyepiece. When it comes to the moment where no new visual information shows up, I start wiggling the scope. My retina is then stimulated by the movement and new information can be accumulated by the brain. The whole sketching process can take 20 minutes to one hour. So how valuable is the very first impression?

The visual information is then represented in a sketch. It is up to the sketchers taste to put emphasis or not to certain features of the observed object. My approach (and I don't say that this approach is the only way to go!!) is to try to represent the eyepiece view with all its subtle details. Here is where digital sketching comes in handy. I first draw features too bright on purpose on separate layers. Then I dimm the layers to the desired level. There is the risk that the occasional observer (this time the person that sees the sketch) misses the subtle details of the sketch. It happens that I turn out the lights in the room, sit back and relax in front of the monitor to evaluate and correct my new made sketch.

Just my two cents :)

#16 Sol Robbins

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Posted 22 January 2008 - 04:38 PM

Jeremy,

Thanks for taking the time to make one of the better explanations in communicating by illustrating, (without words, physiogomy and optical theory), what happens when observing. The animation works very well to this end. This goes for observing any kind of object.

This thread should get a "sticky" attached to it so it doesn't get lost when new threads are added as time goes on.

Well done!

#17 Dan Chalmers

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Posted 22 January 2008 - 05:27 PM

Thank you for the great demonstration of how the view develops. I've noticed this too - but would never have tried to capture the different levels of view in multiple sketches - that you've done really nicely.

In a similar vein, something I'd like to try is making sketches of the same object on different nights and/or with different eyepieces and then combining them once indoors. If only I could get some clear skies I might even get to try this!

#18 Jeremy Perez

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Posted 22 January 2008 - 05:54 PM

Thanks for the encouraging comments everyone :D

The idea to put together that article arose from comments I notice from time to time in the observing forums. Although people often note that the sketches they see come very close to the eyepiece view, there are still times when an observer describes the opposite. Occasionally someone will mention that what they saw in the eyepiece was nowhere near as detailed as a sketch they looked at. This can lead to the implication that either the sketcher is super-human or is embellishing what they already know is there, or that the other observer's equipment or sky conditions are much worse than they thought.

In particular, a question was raised last month in the Planetary Observing forum that noted the detailed sketches of Mars albedo features looking nothing like the washed-out, colorless, extremely low-contrast view they saw through their eyepiece. (That thread eventually evolved into a highly detailed discussion of optical theory that I fear turned me a little cross-eyed.) While the original observer's equipment and sky quality may have played a part in the disappointing view they got, I have to sympathize that I've never had a view of Mars that came within a mile of looking like a picture-postcard myself. Any Martian details I've managed to accrue have always been painstakingly won piece by piece (and I'm sure that's true of the rest of you who are much better planetary observers than I am :) ).

If I can shoehorn a block of time in, I'd like to try doing the same demo with a Mars sketch at some point!

Rony, I really enjoy the subtle way you present the softest details in your sketches. I should note as you did, that the way I present my sketches (with the tendency toward more contrast), is simply a personal preference.

Dan, welcome to the sketching forum! The multiple-sketches idea sounds like a great project. Let us know how it goes once the weather has some mercy on you!

#19 Erix

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Posted 22 January 2008 - 09:56 PM


This thread should get a "sticky" attached to it so it doesn't get lost when new threads are added as time goes on.


I did indeed sticky it right after seeing this thread earlier today. ;)

Tips sticky thread at top of sketching forum

#20 frank5817

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Posted 22 January 2008 - 11:52 PM

Jeremy,

Very innovative sequence and use of animation as an instructional tool for pulling out detail and showing how your eye perceives it. Very interesting. Do you find you can pull out all the elements of fine detail in the final sketch faster after full dark adaption? What I'm getting at is if you begin observing fully dark adapted and having struggled intensely in the past with M-17 to see and record all you can see, do you get there quicker the next time? Sorry for the run-on sentence.

Frank :)

#21 xfile101

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Posted 23 January 2008 - 10:57 AM

I really enjoyed that tutorial (read it at least 3X) and glad it was made a sticky, I will come back to it alot. :bow:

#22 Jeremy Perez

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Posted 23 January 2008 - 02:50 PM

Hi Frank (frank5817 =),

It sounds like there may be two parts to your question. 1) Does starting off the observation fully dark adapted coalesce the image better right off the bat, and 2) Does coming into that observation after having observed/sketched it on another occasion help obtain more details in the next sketch.

Let me know if I missed what you were looking for!

For the first part, I never feel like I'm fully dark adapted when I first stick my eye into the eyepiece. Even with all lights out, the brightness of the sky--especially if the Milky Way is overhead--requires that I keep myself pressed into the eyepiece for a while before the fainter things start to emerge. With low power views like the M17 example, I'm not going to reach my best dark adaptation (such as with my ideal 120X view), but it's still a lot better than the overall ambient sky glow.

Before I start the sketch, I'll glue myself to the eyepiece for several minutes, let my eyes gradually adapt, and just see what I can see. I'll make a mental note of the subtlest details I begin to see so that I can be sure to concentrate on those areas after I've started sketching. Once the sketch light turns on, I'm in a constantly recycling state of recovery from the light...but as long as I keep the light low, it doesn't take horribly long to recover each time I return to the eyepiece.

For the second part of that question, I'd say I definitely notice more on subsequent observations. After putting a lot of effort into seeing those details the first time around, they just seem to come easier the next time. So that can provide an opportunity to dig deeper into other areas of the object I'm studying.

Does that apply to what you were asking?

And Frank (xfile101), I'm really glad the article was helpful!

#23 frank5817

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Posted 23 January 2008 - 08:56 PM

Jeremy,

Yes you have answered my combo questions. It is so infrequent I observe in truly dark sky anymore, I have forgotten how long you need to peer into the eyepiece to pick out very faint details when you are "sort of" dark adapted (an hour or 2). In my question I was not even thinking of the task at hand namely sketching. Turning on a faint light, even if it is red, will take you above the adaptation point and its minutes before you are back.
Thank you Jeremy. Great post.

Frank 5817 :)






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