Monday, June 21, 2010
Hey guys! Sorry for the late post today. Most of you probably won’t even see this one until tomorrow, so you won’t even realize that this was Monday’s post. (Which means I’m already planning on waiting until Wednesday for the next post – I’ve got to give each post enough time to sink in, right??) Also, I’m sorry that my posts have been rather anemic the last few weeks. Hopefully today’s entry makes up for it, it’s going to be nice and meaty. (And I’m saying that even though I’ve barely even started writing it yet!)
It’s almost the end of June now, which means that the Woodland Park Rose Garden here in Seattle is almost fully in bloom. That meant it was time to bust out some new stuff that I hadn’t yet had a chance to play with, and you can see above one of the results.
A little while back, I found a new (to me) macro lens on Ebay, and I snatched it up. It’s a Kiron 105mm macro. It gets all the way to 1:1 magnification without needing any extension tubes or anything like that. (Which differs a little bit from another old lens that I got that was advertised as 1:1, but that was only when you used the “1:1 attachment”, which was simply an extension tube like any other.) The focus and aperture controls are totally manual, there’s nothing auto on this lens. It’s made for a Minolta mount, which means a few unique challenges when you’re shooting with a camera with a Canon EF-S mount. But it’s totally, amazingly awesome. And I love it. Woooo!
So.. where do I start? I suppose I’ll start with the 1:1 magnification. I’ve talked about this before, so I’ll just give a quick refresher here. The magnification ratio is how large something is in real-life vs how big the projection of it is on your camera sensor. Actually, I flipped that around, it’s how big the projection is vs how big the real thing is. Whoops. Anyway, as an example, let’s say you’re taking a picture of something that’s exactly 35 millimeters across (And, for simplicity’s sake, we’ll say you’re using a 35mm camera, or a digital SLR with a full-frame sensor). You grab your first lens, which has a magnification ratio of 1:4. You zoom in as far as you can and focus as close as you can. You’ll notice that the object (let’s call it a bug) covers one quarter of your sensor. It’ll look pretty big on the screen, or if you print it out, but the actual light from the object will measure 35 divided by 4 millimeters as its shining on your sensor. Now, if you switch lenses, to your 1:2 lens, that same object/bug will take up half your sensor, and if you use a 1:1 lens, that thing will stretch across the entire frame. Meaning, the projection of the bug will be 35mm on your sensor, and if you blow it up to 12×18 or whatever, the image of the bug will be 18 inches long. Make sense? Most lenses that have the word “macro” in the name generally top out at around 1:4. To get any closer than that you need to find a “real” macro lens, which will get you to either 1:2 or 1:1 depending on the lens. (And there’s one that I know of from Canon that actually gets you up to 5:1, but that’s just crazy talk.) So, this lens I got gets me 1:1. Since I shoot with a Canon T1i, which is NOT a full-frame sensor (it’s actually 24mm or something across), that means if I’m shooting something that’s only 24mm across, it’ll fill my frame. Awesome!
Now, here’s what I think is a more interesting topic: mounting old lenses on your new digital camera. The two main concerns (that I care about) are the controls, and the actual attachment to your camera.
By controls, I’m talking about the focus and the aperture. It’s easy to take those for granted with these fancy modern cameras. You hold the shutter button halfway, and the lens magically spins around and focuses for you. Magic! But with a lens with a mismatched mount, the electrical connections are different, so suddenly your lens is dead-weight. And by dead-weight, I mean you’re stuck with manual focus. Aperture is also tricky. The way most cameras work (mine works this way anyway) is that it keeps the aperture wide open while you’re framing the shot. Then, it closes down the aperture to the desired size when you actually press the shutter. This one’s actually even worse than focus; every lens that I’ve ever seen at least has the controls for focusing manually, even if they’re not that handy to use. But most modern lenses don’t have controls for aperture at all! Thus, you’re stuck using the lens wide open! (This is one of the biggest problems with reverse mounting a lens, if you were wondering..)
One way around these is of course to get a mount adapter that hooks up to the electrical connections on both the lens and the camera, and translates the signals as required. I’m assuming things like that exist, although I’ve never actually looked for one, because I’ve never tried to use a lens that was eligible, to use a term that’s not quite applicable. There’s still one huge, glaring caveat that I’ll talk about in a bit, but for the most part you’re good to go at that point. Except, not in this case. I’m using a fairly old lens, which doesn’t do auto focus or auto aperture at all. (Well, to be fair, the term “auto aperture” means the not closing down until you’re snapping the picture, not having the camera set the size, but whatever, I’m going to overload the term, and you’re going to like it.) So, to use this lens, I’ve got to focus it myself (which isn’t really a problem, when I’m shooting macro I always use manual focus anyway, and I do my focusing by swaing back and forth until I’ve got it right), and I’ve got to set the aperture myself. The second one’s actually kind of a pain in the butt. As you all should already realize, shrinking the aperture means letting through a lot less light. But, if you’ve got less light, that means things are, umm, darker! So, when you’re trying to focus using your, you know, eyeball, if you limit the amount of light you’ve got to use, it can get really hard to actually see enough detail to focus. This is just one of those things, I haven’t found a great way around it. I suppose if you’re using a tripod you’re fine, because then you can focus with the aperture wide open, then close the aperture, then take the picture, knowing that your camera isn’t going to move between when you focused and when you shut the aperture. But if you’re going hand-held, that doesn’t work at all. Blah. Whatever, back to the topic at hand.
So, that’s the deal with the controls. But what about the mount itself?
A particular camera mount design has a couple really important characteristics. The first is of course the actual physical connection. You know, square-peg-in-a-round-hole kind of stuff. The hardware has to actually fit. That’s the more obvious one. The more sinister one is the fact that the lens has to be designed to fit on the body in such a way as to have a very precise distance between the optics of the lens and the sensor. Moving the optics back and forth has the effect of changing the focal range you can work with. Meaning, if you’ve got it just right, you’ll be able to focus to exactly what is specified by the lens manufacturer, probably something like from a few feet in front of you at the near end, out to infinity at the far end. If the optics are too close, the closer edge moves further away, so you might not be able to focus on anything closer than, say, 10 feet. (All of these numbers are totally 100% pulled out of my butt, if you were wondering, please don’t take them literally.) If they’re too far away (the interesting case, I’ll tell you why in a bit), the close end moves even closer, but so does the far end. So **you can no longer focus to infinity**. Instead, you’d be able to focus from let’s say one foot away at the near end to about 20 feet away at the far end. It’s worth noting also that the total size of the range shrinks dramatically, from, well, infinity, down to a few feet, or at more extreme ranges, down to a few millimeters.
Sound familiar? Right. That’s exactly what you’re doing with a macro extension tube. You’re moving the optics away from the sensor, which means you gain the ability to focus on things that are really close (and when you move closer to things, they appear bigger, right?), at the expense of not being able to focus on things that are far away, and having a super small depth of field. Wooo!! We just made a connection!
So, if you’re mounting a lens built for a different mount on your camera, two measurements suddenly become critically important: the lens-mount-to-sensor distance that your camera expects, and the optics-to-sensor distance that the lens expects. Fortunately for Canon users, the mounts used on modern Canon SLRs (EF for the full-frame sensor cameras, and EF-S (which can also use EF lenses) for the reduced-size sensors) expect a distance that is smaller than most other mounts. Why is this fortunate for Canon users (and unfortunate for other folks)? Because it means that both the camera and the lens agree that they want to be further apart than they would be if the mounts were compatible. Meaning, you’ve actually got room in there **TO FIT THE ACTUAL MOUNT ADAPTER THAT YOU NEED**. As an example (again, made up numbers), let’s say the lens wants to be 20mm away from the sensor, but the mount on your camera would put the lens 15mm away. That means you can stick a 5mm adapter in between (with appropriate fittings on each end), and bam, the camera is happy (since it’s mounted 15mm away) and your lens is happy too (since the optics are 20mm away from the point where the light is supposed to be focused.) Congratulations, you just made another connection! A physical one this time.
So, that’s all well and good. But what happens if that gap doesn’t exist? Or, in a more extreme example, what happens if the lens wants to be closer than the camera would allow it to be mounted? That means that, in order for the light to correctly focus on the sensor, you would need to mount the lens INSIDE THE CAMERA BODY! Which umm isn’t really possible. So, you’re essentially left with two options. First, you can just deal with the fact that you won’t be able to focus to infinity with that lens/camera combo. You’ll always have essentially a very small macro extension tube on there. Depending on just how big the difference between desired optics-to-sensor distance and the actual distance is, you may still be able to use the lens somewhat normally. But, probably not. The second option is that you can get a mount adapter that actually contains an optical element to correct for it. The problem here just comes back to the old adage that your lens is only as good as the lowest quality optical element in it. So, if you get a super high quality 3rd party lens, and toss a super cheap optical adapter on it, congrats, you’ve now got a low-quality 3rd party lens. If you want to use the lens badly enough, you can try to find a higher quality adapter of course, but it probably won’t come cheap.
Back to the example at hand now. The lens that I got (a Kiron 105mm 1:1 macro, remember) was built for an old Minolta mount. So remember how I said that the Canon EF mount wants a shorter distance than most other mounts? Well, the word “MOST” is the important one in that statement. The Minolta mount of old is one of those mounts that’s actually shorter than the Canon EF. That’s great if you’ve got an old school Minolta camera and want to use a fancy new Canon lens, but not so great the other direction. UNLESS YOU’RE SHOOTING MACRO ANYWAY!!!! WOOOOOO!!!! Or, to put it differently and somewhat less enthusiastically, this isn’t actually a problem if you have no intention of using the lens to shoot things that are far away. There’s no harm in having what essentially amounts to a small extension tube on there if you’re planning on potentially tossing another tube on there anyway. It just means that, while somebody using a Minolta mount camera would get 1:1 magnification with this lens, I’ll actually get a little bit closer than that. To pull another number out of my butt, let’s say I’m getting 1.2:1 magnification or something.
Okay, that’s enough blabbering for one day. But it’s definitely fun stuff. They made some fantastic lenses back in the days before digital, so if you can actually find a use for one, they definitely come cheaper than the modern equivalent, and at the very least it can be a lot of fun to play around with this stuff and figure out what you can get to work. Good times.
Notes: Canon EOS Rebel T1i, Kiron 105mm f/2.8 macro (Minolta mount). 1/320s, ISO 400. Aperture unknown (forgot to write it down).