On-location Demo Focusing Demo for ALP + SharpStar 2
Okay, so in this section, we're going to talk about focusing at night. And focusing is probably one of the most difficult parts of working in these really dark environments. So people tend to struggle with focusing just because autofocus doesn't work, and the autofocus lenses that most of us are using does not have a hard stop at infinity. What that means is the lens is engineered for autofocus, and it's required to not put so much stress on the autofocus motor, that it has to go a little bit beyond infinity. In the old days with manual focus film camera lenses, you could just turn the lens until it stopped moving, and you were guaranteed to have infinity in focus. Infinity, of course, is really important in astro-landscape photography, because we wanna have those stars be nice, sharp, and crisp. So there are a couple of different techniques that we will use, and the simplest, most basic technique of all would be to just go ahead and use infinity autofocus in the daytime, before it get...
s dark. Point your camera at infinity, let it autofocus, switch to manual focus, and then just take a little piece of gaffer's tape, and stick it on the lens barrel. So I can just put it right on there, and that will keep the lens from moving when you put it in your camera bag, or when you pick it up and maybe zoom the lens, or what have you. If you've got it locked in position, you're good to go. Now, the limitation of focusing with this technique is that if you have anything in the foreground, you're kind of out of luck. Because remember with astro-landscape photography, we're shooting really wide apertures, which are gonna give you a limited depth of field. So, you can infinity focus in the daytime on autofocus. The next thing is say you forgot to do that before you went out and before it got dark. You can infinity focus on a distant light source. So if the moon is up in the sky, you could use autofocus to infinity to focus on the moon, or if you're camera's autofocus isn't that sensitive, you can go ahead and use infinity focus through the viewfinder, or a better technique would be to use magnified live view to focus on an infinity light source. And that could be the moon, it could be a bright star or a planet, or it could be if you're in a situation where there's some artificial light, it could be just a streetlight in the distance. Now, if you're shooting with a wide angle lens, infinity's really not going to be that far away. So if you have something that's 50 feet or 100 feet away, it doesn't matter, once you focus at that distance, that's infinity. So, it doesn't have to be light years away. All right so, the next technique would be, let's say you don't have any infinity light sources to focus on. You can just use a flashlight-assisted magnified live view technique to focus on infinity. So we've got this scenario here. We have the lighting for the cameras here, so it's a little bit brighter than it would normally be. But we have a scenario here where there's some rocks to the foreground, there's some rocks in the middle ground, and then there's these majestic white mountains in the background. So, we're gonna start off with infinity focus using magnified live view and the assistance of a flashlight. So, the middle ground rocks, they're probably 70 feet away, something like that. So I'm gonna take a flashlight, and I'm gonna go into the scene. I'm gonna put the light down on a rock, turn it on, and then I'm gonna come back to the camera, and focus on that light where I've shown my, the raw flash on my flashlight. All right, so give me one second, I'm gonna go out there, put my light in the scene, and come back and focus. If you're not familiar with using live view, different cameras have different live view settings, but one thing that's kind of universal is when you activate live view, whatever your camera is, you'll have a little box that you can move around in the scene. And on my Nikon D750 here, that's a little red box. So I'm gonna take this toggle wheel, and I'm just gonna move the red box to the point where I want to focus. And then I'm gonna zoom in all the way onto that illuminated section. Now, it's important to pick your spot with the box first before you magnify, because once you zoom in and magnify, then you have to hunt around all over the image trying to find your focus spot. So, turn on live view, move the box over to your focus point, then zoom in. And then at that point, we're gonna be doing our manual focusing. So I'm gonna make sure that my camera is set to manual focus, and I'm just gonna manually focus the lens. And because I wanna make sure that it's really gonna focus, put my glasses on. And there, that looks pretty sharp. So that should be good. And there's our scene. And you know what, I kind of like the way it looks with the lighting for the film set and the lighting on my flashlight, and the little bit of light in the sky, it's kind of cool. So I'm gonna go ahead and shoot that, and take our shot, and let's see what that looks like. So, I think that's an eight second exposure. And I'm gonna zoom in all the way and just confirm that infinity is indeed sharp. And it is. But now I'm gonna come down to the foreground and, you know, but the closest part of the frame that's in my shot is probably seven or eight feet away. And because I focused at infinity, my foreground isn't sharp, right? So I've gotta come up with another way to get the whole scene into focus. All right, let me go back and retrieve my flashlight. I'll be right back. So that worked out just fine. We got infinity in focus, but we don't have the near foreground in focus. So what could we do to make sure we've got everything in focus? Well, of course we could stop down to a smaller aperture like f11 or f16, but that's gonna have its limitations as well because it means that we have to either go for a longer shutter speed, which we don't wanna do because then the stars will start to trail, and we're trying to do star points. Or, we can raise up the ISO. However, we've already got the ISO cranked up to 6400, and we can't really afford to stop down the aperture much more than f4 or so. So, we're gonna use hyperfocal focusing as a way to maximize our depth of field. Hyperfocal focusing is a technique that has been around for a long, long time, and it's especially useful when you need to get every little bit of depth of field out of your aperture. So, hyperfocal focusing is defined as the nearest point you can focus, and still maintain infinity in sharp focus. The nearest point you can focus, and still maintain infinity in sharp focus. So, how do we determine hyperfocal distance? First, it is dependent on focal length, aperture, and camera format. And there is a fixed number, a fixed hyperfocal distance for every combination of focal length, aperture, and camera format. In this case, we've got a full frame DSLR, and we have a 20 millimeter lens. So, now we need to figure out what is our total need for depth of field, and what aperture are we gonna be able to use to get that in there? So, we're gonna say our near foreground is about, I'm gonna say it's eight feet away, so we basically need to get from eight feet to infinity in focus. So you can have a chart, you can have a chart or write down your hyperfocal distances for your common lenses and apertures, or you can just pull out your phone, and there are about, oh, a hundred different apps you can use for finding your hyperfocal distance. Some of the more complex photography planning apps like PhotoPills or Photographer's Ephemeris, have that option but there are also standalone options for flat calculating depth of field and hyperfocal distance. The one that I'm using is called Field Tools, and unfortunately I believe it's only available for iOS. But like I said, there's lots of them to choose from, they all have basically the same functionality. So what I'm gonna do here is I'm gonna set my focal length for 20 millimeters, 'cause that's what I'm shooting with. Get right on there, there we go. Okay, and I'm gonna check, I'm gonna start off with, I think I'm probably gonna need to use, well, let's see. Let's try 3.5 and see if we can get it there. So I'm gonna start off with f3. and see if we can get enough depth of field with that. So I'm gonna click on hyperfocal distance, and that tells me, 20 millimeter lens on a full frame camera f3.5, the hyperfocal distance is 3.8 meters. Okay, well I figure this near distance in feet, let's say it's three meters. Yeah, eight to 10 feet, let's say it's 3 meters. So if our hyperfocal distance is 3.8 meters, I can click right here and see what our near and far focus would be if I focus at the hyperfocal distance. And it tells me I've basically got from half of the hyperfocal distance to infinity. Hyperfocal is 3.8 meters. That gives me a depth of field of 2.4 to infinity. So again, I will focus at hyper, and my depth of field will be 2.4 to infinity. Okay, so the next question is how do you actually find your hyperfocal distance out in the field, right? So the first, kind of the old fashioned way is to walk it off. And basically an average person's large stride or large step is roughly three feet or a meter. So, we need to focus at 3.8, let's call it four meters to be safe. And this is a good time to mention that depth of field gives you the zone of relative sharp focus, which is different from your point of focus. So when you focus on a specific point, that's your area of specific or your point of focus, and your depth of field extends in front of and beyond that point of focus. And as you move away, further and further away from the point of focus, your critical focus starts to fall off a little bit. So when you get out near the edges of your depth of field, it's relatively sharp, but it's not as sharp as your point of focus. Okay, so because we have a sky full of stars here, we want those stars to be absolutely sharp, and we wanna make sure that our depth of field, or our zone of relative sharp focus, really covers the stars. We want infinity to definitely be sharp. So for that reason, it's a good idea to be a little bit conservative with your hyperfocal distance. There are a couple of ways to go about doing that. We established that for this shot, the hyperfocal distance is 3.8 meters. So the first thing we could do is focus a little bit beyond that, say four meters or a little bit more than four meters. And that way, we're going to sacrifice a little bit of depth of field in the foreground, but we're going to absolutely assure that we have infinity in tack-sharp focus. So that's one way, is to focus a little bit beyond your hyperfocal distance. Number two is you can stop down a third or a half of a stop more than what you've calculated hyperfocal for. So in this case, we calculated hyperfocal for f3.5. So I could stop down to f4, and then I would have, again, I'd be assuring that we would get infinity in tack-sharp. And that way, I'm not gonna be sacrificing part of depth of field in the foreground, but what I'll be sacrificing is a little bit of either ISO or shutter speed because I'm stopping down another third of a stop. That means I have to raise my ISO a third of a stop, or increase my shutter speed by a third of a stop. Neither one I really wanna do. So there is one other and probably my preferred method of assuring that hyperfocal is giving you the depth of field that you need, is almost every one of these apps in the settings menu allows you to change the circle of confusion size. So my preferred way of assuring that your hyperfocal distance is going to give you the depth of field that you need is by adjusting the circle of confusion size in the settings on your app. So in this app, I go into the settings, and by default for this particular camera, it's giving me a circle of confusion size of 0.03 microns. So I'm gonna customize that, and go down into the custom settings, and I'm gonna change that to 26. So I'm gonna go into the settings, and I'm gonna reduce the circle of confusion size from the default setting of 0.03, and I'm gonna make it 0.026, there we go. So by making the circle of confusion size smaller, what that does is it's going to move the hyperfocal distance back a little bit. And that, again, will assure me that I've got the most accurate depth of field, and I will certainly have the stars in relative, in sharp focus, not relative sharp focus but true focus. Okay, so we're done. Now I have to go in here, and I've gotta find my hyperfocal distance. And the easiest way to do that, or the old fashioned way to do that, although it's easier and slightly less accurate is just walk it off. We determined it's gonna be 3.8 meters, which is roughly 11 or 12 feet. So I'm gonna start at the camera position, and I'm gonna take four big steps into the scene. And then, I'm going to again put my flashlight on the ground and focus on the flashlight. So I stand off even with the camera sensor, and take one, two, three, four big steps. Flashlight on the ground. And I'll come back. Activate live view, and I'll move that little red box over the flashlight. I will magnify my image, make a little adjustment, I'm now gonna go back in here and focus. The light's so bright it's a little bit difficult to focus on the light itself, but there we go. All right, and good. So at this point, I focused on my hyperfocal distance. I'll go in and retrieve my flashlight. Okay, now I'll take the shot, and eight seconds again. It's gotten darker, so it's gonna be underexposed in the background, but it'll work for the purposes of what we're doing here. And now I can zoom in to maximum magnification, and look at the foreground and see, yep, I've got everything in the nearest point of the frame is in focus. So now I'm gonna confirm that infinity is in focus, and I'll zoom in 'til I can find a nice, bright star and take a look, and yep, so we've got foreground to infinity in focus by using f3.5 and the hyperfocal distance. Okay, so there's some situations when you can't necessarily walk out to your hyperfocal distance. Say it's over a body of water, or over the edge of a cliff or something like that. There's just for one reason or another, you can't get out your hyperfocal distance. Or you're not really confident in walking off those steps. Maybe it's uneven terrain, you're going up and down, and it's not necessarily a straight line. So what you can do is use a handy dandy laser measuring device. Very cool tool. So what I'm gonna do with this device, they're relatively inexpensive. These are used by contractors and builders in the construction industry for measuring distances, maybe also by surveyors. It's very simple to use. Push a button to turn it on. And I'm now gonna point it at my scene, and there's a little red dot. And I'm gonna move that around until I find, what are we looking for, 3.8, yeah. 3.37. Just one more spot. There we go, so now I've got 3.8 meters. So now I know exactly where it is based on this laser measuring device. I'll turn that off, and because I have an excellent memory, I know exactly where that little red dot was, and I'm now gonna place my flashlight in that scene. But actually, you know what? 3.8 meters is pretty close here. So here's another focusing technique. You don't necessarily have to put that light out in the scene, but it's close enough that I can activate live view, and look at that. I can shine the light from the camera position on my hyperfocal distance and I'll zoom in on there. And look at that, it's a little too bright. So I'm just gonna move this off to the side, and that's where I'm gonna be right there. And there we go. So that's potentially a more accurate way to measure your hyperfocal distance, and just make sure that you're getting every little bit, every little inch, or every last centimeter of your depth of field out of whatever aperture you happen to be working with. So perhaps it would be a little more accurate if you've got somebody to help you to maybe stand in the position and hold the light at the spot, rather than just try to guess and remember where the dot was, like I just did. But I think you get the idea, and that's really the most accurate way to focus and get the maximum depth of field for astro-landscape photography, or for that matter, any kind of night photography when you have to focus manually and you're limited in what aperture you can use. So those are the main focusing techniques that we've got, except for in the next section, we've got our guest, Ian Norman, who's gonna talk about a focusing aid that he's developed called the SharpStar2. So I'd like to introduce you to our special guest. This is Ian Norman from Lonely Speck. Hi there, Ian.
Hi Lance, how's it--
And Ian has developed a focusing aid called the SharpStar2. It's a really cool device that makes it much, much easier to focus on stars, and I'll let you describe what it's all about and how to use it?
All right, so the SharpStar2, I've got one in my pocket right now. It's a small optical plastic filter, and it fits into a standard filter holder. It comes in several different sizes to fit a 57 millimeter, 85 millimeter, 100 millimeter, and now a 75 millimeter standard filter holder. These are filter holders made by Cokin or LEE, or Formatt-Hitech. And the way that the SharpStar works and what it's used for, is for focusing at night. I think you would probably agree with me that even with all of our knowledge about exposure and composition, one of the challenges at night is always focusing. And especially having confidence in your focus. It's always kind of a drag to go out and shoot photos at night, only to come back and review them on the computer just to find out that you were just slightly out of focus. And so the SharpStar is, the design of the SharpStar is derived from an open source design called a Bahtinov mask. And the Bahtinov mask was developed by an amateur astronomer named Pavel Bahtinov on an internet forum. And it's essentially a black piece of plastic with some slits cut in it. And this is something that was made for telescopes. And I saw the design for the Bahtinov mask, and I really wanted to make one for my DSLR so I could use it on just a regular camera lens, like a 50 millimeter or 35 millimeter. And one of the problems that I encountered is that the Bahtinov mask just doesn't work all that great on a really small lens. It works really great on telescopes, but it just kind of fails to have the same effect. So, I developed a version of the Bahtinov mask that I call the SharpStar that works on standard camera lenses. So, let's take a look at how it works, I guess.
All right well, let's say why is it useful? Why do we need this?
So one of the things that I always struggle with in terms of night photography and focusing is really having a lot of confidence in my focus. And when you're focusing and you're getting close to your focus point, there's always that last little bit of focus where you think you're in focus, the stars seem relatively sharp, but you don't really have a positive indicator. You think you're at infinity, the stars seem like a pinpoint, but what the SharpStar2 gives you is a really distinct visual aid that indicates when you have perfect focus.
Right, and we used to be able to just turn the lens until it stopped, and we were focused at infinity. But now with the autofocus lenses, they go beyond infinity. So you know, having that confirmation, that visual confirmation is really useful, and that's what I like about your tool.
Yeah, I agree, I think that the first time that I made a prototype for the SharpStar, and I put it on my lens and I used it, it was just so quick. It was really, really quick to acquire focus, and after taking a test shot you can review it under magnification on the back of the LCD, and really boost your confidence that you're gonna be in focus.
All right, well, show us how it works!
Okay, so like I said, the SharpStar fits into a standard filter holder. And what we wanna do is we wanna take the SharpStar, and we wanna center it in the filter holder so that the center of the pattern on the SharpStar is right in line with the lens. As long as you put it flush with your filter holder so that it's centered, you should be good. And we use, much like with standard live view focusing, we wanna use the brightest star in the sky, or some other distant light source that's really, really bright. So let's go ahead and point this at, I think that's Mars over there. And we've got some lights shining right now for this video. Normally you'd be doing this in some darker conditions. So we have a little bit of glare, but we can still have enough to demonstrate what the SharpStar is doing. So we're gonna center a really bright star in the very center of our frame, and when we zoom in on it using live view magnification, we can see that the star has some distinct spikes radiating out from the center of it. So when we shift our focus, those spikes move in position. We have a set of spikes that form a shallow X, and then we have a central spike that shifts in the opposite direction as that little shallow X. And all we need to do is focus so that central spike sits directly in between the X.
Right, and it's really clear, too. It's quite obvious when you get it to that spot.
So I mean, that's basically it. You put it on, you zoom in using live view, and you adjust your focus. And once you have those lined up then you know you have perfect focus. As long as you're not touching the focusing ring, you're good to keep on shooting. And then we can go ahead and just remove the SharpStar, careful not to touch the focusing ring, and continue with our shooting for the night. And we'll go ahead and take a test shot here. And I'm just taking a test shot of about six seconds with my lens wide open. That way I can see any small discrepancies in focus. And with the test shot, if we zoom in on that, we can see that we have really sharp focus on the stars.
Yep, perfect. And you can also take a picture through the SharpStar too, and get confirmation of that alignment of that center spike.
Right, yeah, so depending on different types of camera equipment, some slower lenses, for example, might be a little bit difficult to see the diffraction pattern while you're viewing in live view. And different cameras have different levels of low light capability.
Right, the noisier live view image is kind of harder to tell, a little bit?
Right, yeah, I know. Like, the difference between a Nikon and a Canon, for example, is actually pretty tangible in which one has a good low light live view feed. And I'm using a Sony a7S, which happens to be a very good low light camera. So it was easy to see the diffraction pattern in live view.
Even with these!
Yeah, sometimes you need to just take a quick test shot. And a test shot doesn't have to be the full length of your exposure if you're wanting to do star trails or something like that, and you're doing a full minute your test shot with the SharpStar only actually needs to be about one second to about five seconds long.
I guess depending on the brightness of the star that you're focusing on.
Yeah. So we can go ahead and take a test shot with a SharpStar installed. I'm gonna double-check my focus here and just make sure that those spikes are aligned, it looks like they're still good. If we zoom in on it, actually we can still the star. And we can see that the central spike, it's pretty good, it actually looks like it's maybe slightly off to the right. So now that we're seeing that, maybe we can make a small adjustment to try and get that spike to sit slightly over to the left. So if I go back to my live view and I adjust my focus just slightly, I really try and get that central spike in between the two outer spikes. And then take my next test shot. Then we can go ahead and review our image here. I think that looks a little bit better.
Yeah, I think so too, and this is really useful for people with, let's say, diminished eyesight. You know, youngsters like yourself, you can see just about anything, but I could really use that added little punch that you get from this.
Yeah, a lot of the feedback that we've gotten from our customers has been that maybe their vision isn't the best at night, and that it's really given them a positive way to feel confident in their focusing. And I definitely think that's one of the benefits of the SharpStar.
Yeah. Well, thanks very much for bringing it in and showing us how to use it.
Yeah, thank you, Lance.
And thanks for making this contribution to the night photography community, because it really is a valuable tool for a lot of people to use. `
Absolutely. So if you wanna buy the SharpStar, we have it available in all of the common square filter sizes. From 67 millimeters, which is like a Cokin A-style filter, all the way up through 75 millimeters for the LEE Seven5 system, 85 millimeters for Cokin P and Formatt-Hitech. And then 100 millimeter, which is our best-selling size, which is for the LEE 100 system, as well as the Cokin Z and the Formatt-Hitech 100 millimeter system. And you can find those on LonelySpeck.com/SharpStar.
All right, well, thanks very much.
Appreciate you coming out to do this.