Archive for the ‘instruction’ Tag
My blog series on video for still photographers continues. It’s not been too popular, something I figured would happen because of the the nature of blogging. The blogosphere is quite biased toward still photography. Videos are very popular overall, but tend to be concentrated in other places on the web. It’s sad to say but most serious photographers still don’t think video is worth doing, I believe because they think the learning curve is too steep. But when you’re out shooting photos you’re also carrying a very good video camera around with you. So why not add movement and sound, even if the results aren’t likely to measure up to those of a pro videographer?
Last time we looked at landscape videos. Today let’s talk about critters, or animals. Specifically wildlife. Domestic animals have their own challenges. Video of wildlife is not easy. But it’s one of the few subjects that even non-video people think of shooting. The reason is that wildlife often do interesting things that are very hard to capture with still pictures. They also make fascinating sounds.
To view the videos don’t click the play button right away. First click the title at top left, then the play button.
Wild animals are generally shy and not easy to find. In modern times there is a two-edged sword. Plenty of roads and easy access make it a snap to go looking for wildlife. But the same development and population growth that gave us those roads also causes most species to decline in numbers. And the survivors normally become very shy and elusive.
A general truism is that the easiest critters to find also tend to have the fastest and most unpredictable movements. On the flip side, leaving aside rarity, if they’re very difficult to find they tend to be slow and easy to follow. Sloths come to mind. But it’s not always true that the slow ones are hard to find. It could be the animal is simply not afraid and instead looks on you as lunch, like the Komodo dragons below.
Location, Location. There are just a few main strategies that will make it easier to find wildlife. One is heading to protected areas. Parks and preserves concentrate the wildlife that we have chased out of most parts of the world. Some African parks even fence them in, which is actually to prevent them leaving the park where they can be poached. Of course the poachers just go into the park to kill, so the fences are relatively ineffective in that way. The fences do cut down on human-wildlife conflict, as well as reduce road-kill.
The Right Time. Another strategy is to go out looking when animals are most active. And I’m not just talking about dawn and dusk, when most (not all) animals are likely to be moving about. I’m also talking season. Fall is when many animals become active, and spring (or the start of wet season in Africa) is also good because many have their young and are thus forced to go out hunting, foraging or browsing to feed them. Also, the babies are irresistible.
‘Tis the Season. Seasonality also affects the ease with which you’ll be able to spot critters because of vegetation. For example going on safari in Africa during the dry season is popular because the general lack of green leafy growth on shrubs and trees of the savannah makes it easier to spot wildlife.
Some wildlife during a specific season will ignore their natural instinct to avoid humans and come right down into our towns. In late fall, the elk of several western U.S. National Parks (Rocky Mountain and Grand Tetons for e.g.) descend from higher country and congregate in gateway towns like Estes Park, Colorado.
Showing their Moves
Animals move (I know, duh). And they move apparently without warning and in unpredictable ways. But really not so unpredictable once you observe and learn about them.
Ready & Steady. Be ever ready to move the camera instantly. It’s a mindset that is applicable to still photos of critters as well. Your positioning and stance needs to be such that you can swivel or pivot easily. I liken it to when I was a kid being coached on how to take a lead in baseball. You also need a way to smooth out your motions, covered in a previous post: Video on the Move.
Observe. The most important thing in this regard is careful observation. The more you learn about a species, the better you’ll be able to predict its movements. But avoid the trap even experienced people fall into. You can know the species but not the individual. Like us, each one is different and unique, in ways that seem quite subtle to us (but presumably not them). So even if you know the species well, a little pre-shooting observation goes a long way.
If you record the voices of animals (and why wouldn’t you have sound recording turned on?), you can be sure that even the chattiest of them will choose the time after you press the record button to give you the silent treatment.
Observe some More. Same goes for sound as for video: if you have the opportunity, observe the animal for awhile before you press record. You’ll gain a sense of the periodicity or patterns inherent in the animal’s vocalizations. The keys, as it is in general nature observation and photography, is patience and timing.
Examples. At Yellowstone Park I went out in the very early morning to film the buffalo above. On a previous morning I’d seen them crossing the Lamar River and figured they were sleeping on one side and eating breakfast on the other, with a bath in between. Also the early hour meant only one other tourist, and he stayed up by the road. A shotgun mic helped to capture their voices. Below, on the Kafue River in Africa, I couldn’t get close enough to these hippos but their voices carry so well across the water that I didn’t need the shotgun mic.
That’s it for this Friday, thanks for looking. Have an excellent weekend and don’t forget to press that record button!
Addendum: Dry Run
Try is a dry run from time to time. For example you could walk out into a forest in the wee hours to hear the dawn chorus of birdsong. Try leaving your camera in the bag, at least at first. The goal is to find the best locations and to simply listen. Note when certain bird species begin and end (it’s strictly regimented), along with how long the singing lasts. If you go out several times you’ll begin to learn how the weather affects timing along with other features of bird vocalization and behaviour.
Believe it or not I did this for a job one summer. I surveyed forests in the Pacific NW proposed for logging, looking for evidence of use by endangered bird species. Since most of the areas lacked trails, I would go out during the day with some white surveyor’s tape. I’d find a good spot to observe from and then, on the way back to the road, flag a route by every so often tying a piece of surveyor’s tape around a branch.
Then in the morning, at “zero dark thirty” I returned with my flashlights (I recommend two, a headlamp and a strong hand-held) and followed the trail in. White shows up in the dark a lot better than orange. On the hike out after sunrise I’d remove the surveyor’s tape. This is, by the way, also a good way to find and shoot out-of-the-way places at dawn, your “secret” spots that are away from roads and trails.
Let’s start off with a non-macro image: morning sun on the Colorado Rockies.
As promised, here’s a follow-up to my macro series. Rails (or sliders) are devices that allow small movements of your camera without having to move the tripod. The heart of a rail is its gear/screw mechanism, and the quality of the rail is in how finely this part is made.
This post also aims to give a step by step on setting up a macro shot, whether or not you’re using a rail. Of course I don’t always follow this exact procedure. In photography like a lot of things there’s always “more than one way to skin the cat”. Sorry cat lovers!
BUYING A RAIL: As always with photo accessories, you have to be careful buying cheap. Check out rails in the shop if at all possible, using your camera and macro lens to see how they work under load. Or if you can’t do that just go a bit more expensive for something with good reviews online. I bought a medium-quality one. It’s fine but would not be okay if I used it a lot; I use it very infrequently. I spent about $50 on it.
Here are the things to look for in a rail. If when it is mounted with the camera on top the rail wiggles around, even a small amount, it’s obviously no good for macro. And if movement along the screw & gear is not slow and steady enough, that rail is probably not worth buying.
A SMALL CAVEAT: I chose a very simple shot for an example. In other words, it’s not the most spectacular subject, just a little flower in the weeds. Also, the close-ups of my camera make it look like I’ve beaten it to hell. It’s not actually that bad, honest. The crack you see isn’t the LCD screen itself, it’s the protective cover. Okay, I admit it, I’m hard on my gear.
By the way, I made sure to pick a good day for this (photo below). Notice the boring white cloud cover, mid-morning, really perfect for what I call “illustrative” macro. That means no real shadows or directional light.
Each rail works a little differently, but what follows is how mine works. It’s pretty typical.
A typical rail/slider.
- There is an Arca-Swiss plate screwed to the bottom of the rail assembly, so the whole rail mounts right on top of the ball-head (see pictures below). This isn’t the place to discuss tripod heads, but make sure you always get plates that match your head’s clamp. Arca-Swiss is sorta the standard, and is pretty simple to use.
Rail clamped down on ball-head.
- Make sure the rail is set somewhere in the middle of its range (rotate the knob to slide it). If it’s at one end of its range you won’t have flexibility to adjust it in one direction. The picture above shows mine a bit too far forward, so I had to slide it to the middle part of its range.
- Once the rail is mounted securely go ahead and screw your camera right down onto the top plate as shown below. This setup allows the whole rail/camera assembly to rotate around with the ball-head.
Screw the camera down onto the top plate of the rail.
- Now you need to get your tripod in about the right position next to your subject. Decide about how close you want to get to your subject. Your rail will get you a few inches closer or further, so you don’t need to be perfect here. But definitely decide how low your point of view will be and adjust the height of your tripod legs. The rail can’t help you with up and down movements. Just make sure the tripod is very stable (tip: spread the legs wider when the tripod is lower)
Camera on the rail. But I’m a little too high, so…
My tripod allows me to go lower by rotating the center column to horizontal.
- Now it’s time to set up the camera. Go to manual focus and pre-focus so your subject is in approximate focus (see pictures below). Use either the viewfinder or LiveView for this step, whichever is easiest for you. Again, don’t worry if it’s not perfect. If you want to get as close as possible and fill the frame as much as possible, as I’m doing here, pre-set the focus ring to the smallest focal length. But if you do this, re-check your tripod position and make sure it’s positioned so your lens is no closer to the subject than this smallest focal length (about a foot with my macro lens (see pic below).
Use manual focus.
Pre-setting focus at the shortest focal length.
- Now you can slide the camera closer or further along the screws on the rail, turning the knob as shown. Your focus is pre-set. Moving the knob on the rail is the way you are focusing now. I recommend using LiveView and magnifying as necessary to focus on the exact part of the subject you want in perfect focus.
Rotate the knob slowly while at the same time you…
…watch LiveView for the part of the subject you want to come into perfect focus.
Still in LiveView, I magnified on the flower’s yellow center and adjusted the knob on the rail to focus precisely.
- You can also use the rail at this point to fill the frame more or back off and show a little more surroundings. In other words, change the composition. So if while you’re sliding the camera along the rail you get a composition you like but you’re not in focus, go ahead and rotate the camera’s focus ring to get perfect focus. See the Bonus below for more on focus and depth of field.
- While you’re at it and have LiveView up, you should check exposure before taking the picture. On my camera I press the “info” button to pull up the histogram (see below). In this case, with a white flower, I pay attention to the right end. I want to avoid the peak on the right climbing up the right side, causing over-exposure. But I don’t want that peak to move too far toward the center. That would underexpose and make the white petals look gray. When using LiveView to check exposure, make sure your camera’s LiveView setting is on “Exposure Simulation” (check your owner’s manual).
LiveView with histogram. The histogram reads what is inside the white box, and I’m over-exposing the yellow just 1/3 stop. When I moved the box over to the petals, the histogram’s right peak slid over to the right, but not quite all the way to the right edge (which would have meant over-exposure).
- Some rails only have one screw/gear setup to move forward and back. Mine also has a screw and gear at right angles to allow small movements right and left. This can be handy to get slightly different compositions, with your subject off to one side. I can remove that part to go lighter (see images below). With my rail I also get a more stable camera mount (no wiggle) when I get rid of that extra part.
Using the side-to-side adjustment knob to move the flower off-center.
I slid the rail/camera slightly to the left, which put the flower just off to the right. This still needs a little tweaking in the computer, but this isn’t a bad final image.
Rail with side-to-side part removed, leaving only the forward-back adjustment. My hands are starting to look like my mom’s!
BONUS: FOCUS & DEPTH OF FIELD
DEPTH OF FIELD & MACRO: Macro lenses have very little depth of field in front of the focal plane, with much more (but still limited) in back. In other words, you will normally focus on the closest important part of the subject, not trusting anything closer than that to be in focus. Then you’ll play with aperture, experimenting to get the right amount of depth of field.
Remember also that the closer you get to your subject, the narrower your depth of field will be, and the reverse is also true. Get more depth of field by moving back away from your subject.
DEPTH OF FIELD PREVIEW BUTTON: You can either shoot and review to experiment, or use LiveView in combination with the depth of field (DOF) preview button. Not all cameras have a DOF preview button. If yours does, there are times when it comes in very handy. Pressing the DOF preview button closes down the aperture to the one you select (see pic below). Otherwise anything you see through the lens, either using the viewfinder or on LiveView, reflects the lens’s widest aperture (shallowest depth of field).
LiveView without the DOF preview button depressed. Even though my aperture is set to f/11 here, the LiveView shows what it would look like at f/2.8, the largest aperture for this lens.
Here I’m pressing the DOF preview button to see what f/11 actually looks like. The petals in rear are in better focus than in the LiveView image above.
APERTURE: Realize as you close down aperture for more depth of field you are doing two important things to the picture. First, you are slowing down shutter speed. So if your subject is moving, for example in a breeze as mine is doing here, you may end up blurring your subject. Raise ISO to keep your shutter speeds fast enough to freeze that movement and avoid subject blur.
The only way to see how much you need to raise ISO and check for blurring is to shoot and review. It also pays to watch closely for the subject’s least amount of movement and shoot then. If your shutter speed is fast enough (about 1/100 sec. or faster for this lens), you can just press the shutter gently. If speeds are much slower, you need to keep your hands off the camera, using either a remote switch or shutter delay.
At f/11 and ISO 100, shutter speed is 1/25 sec., which will result in a sharp picture if I wait for the breeze to pause and the flower to be mostly still.
But I wanted more depth of field so I went to f/22. I had to raise ISO to keep shutter speed up. If I had more wind (or less patience) I’d need to raise ISO even more.
The second thing you’re doing when adjusting aperture for more depth of field is of course bringing the background into better focus. Use the DOF preview button or shoot/review to get just the right balance between focus in your subject and the amount of detail in the background.
I slid the rail/camera slightly to the left, which put the flower just off to the right. This needs a little tweaking on color and contrast, but it’s not a bad final image.
Phew! That’s enough for now. If all this sounds too complicated to bother with, please don’t despair. It’s actually much simpler than it appears. Try re-reading this. But really, you just have to play around with the rail and see how it works. It also helps to get some practice shooting macro before adding a rail into the mix. As mentioned in the last post, rails come into their own mostly when you are shooting very close with high magnifications. I’d recommend skipping them when you’re doing “less-close” close-up photography.
Blooming lupine is decorated in dewdrops at Mount Rainier National Park, Washington.
A new image: one arm of Utah’s Great Salt Lake in dawn light. Shot at 16 mm.
This is a two-parter, the second coming next Friday. This first part will lay out some basic knowledge, so if you’re beyond a novice photographer you might want to just enjoy the photos and be sure to catch next week’s post. I’ve been traveling through the northern Great Basin, and some of these images are from the last couple days. By clicking on these you’ll go to the main part of my webpage, where the images will be uploaded soon. Please contact me if you are interested in one right now. Other images are older and may have appeared in past posts. These are available right now on the website by clicking on the image.
Mount Hood and its enveloping forest are highlighted in this image shot at 28 mm. Most photographers would zoom in on the mountain to make it bigger, but I wanted equal emphasis on the surrounding forest.
First off, the wide angle lens is undoubtedly a must-have if you want to do landscape photography. I don’t know anybody who is serious about landscapes who doesn’t have one. The good news about that is if you’re starting out and don’t have a DSLR yet, most consumer cameras with a built-in zoom lens go to fairly wide angles.
So let’s back up. What is a wide-angle lens? Since It has to do with focal length, let’s see what that is first. I’m sorry if this is too basic for some of you by the way, but I’m assuming some will benefit from this stuff. Technically, focal length is the distance the light rays travel from the lens to where they’re focused to a point (yielding a sharp image on the sensor/film just beyond that point). By the way, was this not the most fun topic in physics class? Optics rocks!
But for photographers, all you need to know is that the longer the focal length, the more magnified the subjects in your frame will be, and the narrower your field of view. For short focal lengths, you get less magnification and wider angles of view.
Falls Creek Falls in Washington’s Cascades is in flood here, so I got as close as I could to it and shot at 16 mm.
New image from the Alvord Desert of eastern Oregon. I found this group of wind-riders camped at the edge of the playa. They ride lightweight and aerodynamic carts equipped with sails, shooting across the normally windy playa at high speeds. Shot at 24 mm. from a point mere inches from the ground.
So we finally come to the definition of a wide-angle lens, yay! It’s a lens for which the magnification of objects is small and the field of view large or wide.
What are the actual focal length values we work with? It gets a little complicated here because of different sensor (and film) sizes in different cameras. If you have a full-frame DSLR (or an old SLR film camera), you’re in luck. Yours are the standard focal lengths, what we call the 35 mm. efl (equivalent focal length). Think of the largest rectangle that will fit in the circular field your camera sees, and you have a great idea of what a full-frame sensor is.
A pond reflects Mount Rainier in Washington, shot at 24 mm.
If you have a camera with a smaller sensor, what’s called a crop-frame, your focal lengths are correspondingly shorter. The corners of your rectangle are inside the circle that your camera sees. In order for the two groups of folks to speak to each other, we convert everything to full-frame focal length. To convert from cameras with smaller sensors, you multiply your focal length by some factor that depends on your camera brand. This is normally about 1.4 – 2 times, but usually pretty close to 1.5.
This is one of the most important traditional food and medicinal plants for American Indians of the Columbia Basin in the Pacific Northwest, lomatium (or biscuit root). Shot at 16 mm. with the Columbia River beyond.
Please realize that if you’re shooting with a crop-frame camera, you are able to get excellent photos. You just get used to thinking in terms of the (shorter) focal lengths you work with. You certainly don’t go around multiplying every time you take a picture! I nearly always shoot landscapes with a full-frame camera, and encourage anyone serious about landscape photography to save up for one. But I’m certainly no full-frame snob. I have a point and shoot with a tiny sensor plus a crop-frame DSLR with a crop factor of 1.6. I don’t use them as much as I used to, but they definitely have their strengths.
A new image, a small pool on the floor of the Alvord Desert of Eastern Oregon. Shot at 26 mm. with my camera placed a few inches from the water’s surface.
A train runs up the Columbia River Gorge in Oregon. This is not an image with many tradeoffs.
This is the second of two parts. Last time we discussed lens sharpness in general, & learned how to find a lens’s sweet spot. Check out Part I. Did you do your homework? Hint: it was finding the sweet spot for your lenses! Remember all these images are copyrighted and not available for free download without my permission. Just click on them to check out purchase options on the main part of my webpage. If you can’t find something or have any other questions just contact me. Thanks for your interest.
Now we come to the meat of the matter. How much does all this matter? For one thing, you should realize that photography has changed with the advent of digital cameras, specifically the emergence of high-quality digital cameras. Sharpness and clarity are now expected by people. This is not generally a bad thing. But it is narrowing the range of images that people will look at for longer than a nanosecond. And that is a bad thing.
Dawn on the upper Columbia in Washington. Shot at f/22 to maximize depth of field. Sharpness is not at maximum for this lens though.
Notice I said sharpness and clarity, not focus. As an example take my post for Single-image Sunday, the Fog Returns. It’s an image that, while perfectly focused, is not particularly sharp. I’m using the word sharp in its broader sense here. It is encouraging that I a little push-back against this quest for sharpness in all images. But there are currents that are taking us in the other direction as well. For example focus stacking (where several images are captured and combined in Photoshop to have several focus points in the same image) is subtly changing the expectations of image viewers. To think I’m essentially being forced to do composites in Photoshop: ugh!
This image from Olympic N.P. appears in a previous post, but here it is again because it’s one of just three images I have thus far captured & processed by photo stacking.
But let’s leave that aside and focus on sharpness vs. depth of field. You might be aware of all the tradeoffs in photography, and this is certainly one of them. But before we discuss that, here are a few givens:
- Some lenses are sharper than others, but that’s not your concern. Your concern is to get the best pictures possible with the equipment you have.
- Most images that are not as sharp as they could be are down to user error. If you don’t stabilize your camera on a tripod (or shoot at a fast-enough shutter speed if hand-holding), do not expect a sharp image. Use a cable release or timer delay as well. Mirror lockup, if your camera has it, has a lesser effect but is still worth doing.
- Atmospheric conditions, particularly at longer focal lengths, will also affect apparent sharpness.
- Some lenses are capable of being sharper stopped all the way down than other lenses, and can thus give you a greater apparent depth of field.
- The wider your focal length, the greater your depth of field will be. Though it’s a continuous change, think about 21 mm. as the cutoff between very short/wide focal lengths and just wide/longer focal lengths. Telephoto lengths (greater than 70 mm.) will yield much shallower depths of field.
- Despite the above factor, aperture is still the biggest influence on depth of field.
Sandstone formations in Utah. I was very close to the foreground and my focal length was not super wide. While managing to get good sharpness in the foreground, I sacrificed some sharpness in the background. Since I did not want this to be too noticeable, I used a small aperture – f/22.
Shooting “Deep” Scenes: The Trade-off
Now let’s get to that tradeoff between sharpness and depth of field. If you want to maximize depth of field in your image (that is, sharpness from very close to very far away), you will be shooting at small apertures. So unless you are going the focus stacking route as mentioned above, you will be shooting a good ways past your sweet spot. Once you are two stops above the sweet spot (f/16 if your sweet spot is f/8, for example) you’ll notice a small drop in sharpness.
Let’s take an example. Say you are shooting a sunrise over a lake, with interesting rocks close by and beautiful forested mountains in the background. If you get low and close to those rocks, you might choose a very wide angle in order to get everything in. This will also help to maximize depth of field, but to really get there you will also use a small aperture like f/22. In order to show the fascinating detail in those foreground rocks, you will be focusing fairly close, perhaps only a foot or two past the closest rock.
Sunrise at Lost Lake with Mount Hood emerging from the fog. This is the same scene as last Wednesday’s post, the Fog Returns.
This all sounds wonderful doesn’t it? But as with many things in life, there’s a hitch. One of photography’s tradeoffs has raised its ugly head! Depending on your lens the overall sharpness of your image will be just a bit less than what it is at the sweet spot (say that is f/8). This is because of diffraction, as mentioned in Part I.
But that’s not all. With most lenses, that image will also have its background slightly out of focus. If you’re lucky (rich?) enough to have a Nikon 14-24 mm. or other similar lens with a big curved front element, this effect is certainly minimized. But it is still there. You can focus deeper into the image, but then your foreground will be slightly out of focus. Shooting at a very wide angle and with a high-quality lens helps out with this tradeoff, but it will always be a balancing act.
This is hot off the presses, from last night. If you are interested in the high-resolution version, just click on it.
I normally just accept some diffraction-related softness and go with f/22. But this is when I’m using my Tokina 16-28 mm. lens. With my Canon 24-105 f/4, I know it’s softer at f/22 than the Tokina and does not attain quite as large a depth of field. This is only partly because of the longer focal lengths; some has to do with the lens optics. The Canon does more things than the Tokina, so it can’t do the one thing as well. More tradeoffs.
Focal Point & Depth of Field
Let’s dive a bit deeper into the focal point: where to focus? It’s a question many photographers struggle with. For me, it not only depends on my desired focal length, but on the balance between background and foreground in the image. You should ask yourself, which is the dominant feature in my image: is it in the foreground or background? That main subject is what you should try to keep as sharp as possible.
Sometimes I will sacrifice and move back from my foreground, especially if my background subject is a strong one. This will increase apparent depth of field, but it might also force a longer focal length, which in turn decreases depth of field. Again, a balancing act.
Death Valley, California. Good detail in the foreground sand was most important here, and the background dunes were not as big a part of the image. So I shot at f/16 and focused on the sand in front of me.
Blooming beargrass on Silver Star Mountain, WA. At this focal length (165 mm.), no chance for sharpness in both the flowers & Mt. Adams. But I still shot at f/22 so the mountain wasn’t too out of focus.
Focal Point & Subject
Say you have a strong foreground and a less important background. It’s a seascape with a fascinating foreground and no interesting boat or other element in the background. You may just focus on the foreground and not care much about the background, even shooting at f/11 in some cases. This is how I handle those scenes. But I will often bracket my apertures, shooting at f/11 to f/22 (or whatever the minimum aperture is).
Now say you’re shooting a scene where your background subject is most important, yet you still want maximum depth of field. First off, definitely consider putting your foreground a bit further away as mentioned above. But this time, since the background is dominant, focus closer to it; about one third into the scene is the rule of thumb. Since your background is most important, you might increase focal length to make it bigger (longer focal lengths increase magnification). But careful! You could lose too much depth of field, putting your foreground out of focus. This is more likely if you’re tempted to shoot at wider apertures (smaller f/number) to get closer to that sweet spot.
Mount Rainier in the morning. This is a shot where sharpness on the background is important but so is good depth of field.
Recent foggy shot at Lost Lake. While sharpness is somewhat important for the baby tree, great depth of field is not that important.
You can always keep a very wide angle and crop later, thus helping to get better (apparent) depth of field and sharpness both. The tradeoff in that case is a smaller digital file, which is not really good if you’re thinking of printing the image large. If you’re using focal lengths of 50 mm. or greater, focusing one third into the scene should be your default point of focus. Just don’t get too locked into this, and always try to check focus right after the shot by zooming in on your LCD.
Okay, that’s enough for now. I’m willing to answer any questions on this somewhat convoluted topic, so fire away. If you’re not getting a quick answer it means I’m probably out shooting! Have a great weekend everyone.
It’s getting dark earlier! Although some depth of field is important here, I opened aperture up a bit (f/8) to avoid using a high ISO and keep exposure time reasonable (to avoid smearing the clouds and moon out too much).