 Maybe I'll just get started because I'll have to be at a clinic right after this, so I don't want to wait too long. I've got a large group so far. So, you're talking about AFocal Systems and Telescopes. Okay, what's going on? So, Optics is obviously one of the books, and there will be four lectures this year talking about Optics. This one would probably normally come second. I'll be doing Prisms and Lenses in November, but that lecture's not quite ready, so I'll do this one again, and then we'll do that. Lenses and Prisms next time. And then Dr. Meyer will talk about Contact Lenses and Refraction. So, today we'll talk about is when and why we use telescopes in clinic, the different types of telescopes. We'll spend a lot of time talking about Keplerian or Astronomical versus Galilean Telescopes, and that's kind of a big difference to know for OCAPs. There's really only a couple formulas that we'll be using, but by the end hopefully you'll be able to use them. I've got some paper and pens up here, so we've got some practice problems at the end that I'll have you work on. A little bit about Fuel of View, Virgin's Amplification that happens when you try to use a telescope to look at an object up close that's not at optical infinity, and then a little bit about Near Telescopes. So, why do we use telescopes? I think typically we think of a telescope being used for stargazing, pirates looking at other ships, they're going to overtake things like that. Clinically, they're used in low vision for a number of reasons. People that we see who have severe macular degeneration or whatever the case may be where their acuity is not very good, can use a telescope to increase the size of the letters that they're trying to look at, whether that's a street sign, a menu, buildings, things like that. They also use them in the classroom, and so I could have a state, we had a low vision clinic, and we fit a lot of telescopes or people that used to sit in class and just appear at the lecture, things like that. So they're also used for intermediate or near distances. One example would just be a slit lamp that we use, and we can just flip that switch, go to between 1 and 1.6x. Some slit lamps go up to 40x, you know, have a lot of magnification. But that's just changing the optics, changing the lenses around and using prisms and things like that to give us magnification to look at close. Sometimes they're used for reading, handheld magnifiers, things like that are used in low vision clinic. The thing with those handheld magnifiers is the patients really have to hold the object that they're looking at, pretty much right up close to their face in order to be able to use them. But they can make a big difference for people, and lots of them have different backlight settings, things like that. So handheld telescopes are usually monoculars. There's also a thing called spectacle-mounted telescopes, so I'll show some pictures of that. I talked about that a little bit last year, nobody had really heard too much about bioptics. Have you heard about them? So in optometry, I think we use them a little bit more. Bioptics are basically their spectacle-mounted telescopes, so they're a little telescope mounted inside a pair of glasses. And it basically allows somebody who doesn't meet the normal vision requirements for driving to still be able to drive, legally. So kind of a little bit scary, but it works. And then once again, we'll talk about the different kinds of telescopes. So would any of you just start right off the bat be able to identify whether or not these telescopes are astronomical versus Galilean? We did this a little bit last year, I'm not sure if any of you are here to remember that. So by the end, you should be able to identify these. These are what we're typically used in low-vision clinic. But based on what we see here, the equations that we use will also help us to figure out what these are. So how do telescopes work? So they're AFocal systems, and what AFocal means is that you have parallel rays coming in and parallel rays coming out. Which means that there's basically a net of zero power in the system, which is kind of cool. But you do get magnification, so while the power may be zero, the magnification is going to be a value. It could be less than one, which would be minification. Which is like if you turn a pair of binoculars backwards and try to look, you see things are tiny in there. Or magnification, where things look bigger. And there's always at least two elements that make up a telescope. The objective lens and the ocular, or the eyepiece. So the objective lens is the lens that's further from the eye, as you can see from this lovely drawing here. And it's always a plus-powered lens or a converging element. And it usually, well, it also has a lower power than the eyepiece lens. So that's one way you can figure out if you're given an equation and they say, you know, you have like a plus-5 lens and a plus-20 lens. You know, the higher number is going to be your eyepiece, the lower power is going to be your objective. So the ocular is the one that's closer to the eye. And this one can be positive or negative, whereas the objective lens is always positive. And depending on which, if it's a plus lens or a minus lens, that'll tell you what kind of telescope it is. It's positioned, this is kind of important, so it's positioned so the image formed by the objective lens is at the primary focal point of the ocular. And depending on which type of lens it is, positive or negative, it'll either be in front of that eyepiece lens or behind the eyepiece lens. And it has a higher power. So an astronomical telescope is going to be two plus lenses. So where the focal points meet is going to be in between the two lenses. And here's just showing the parallel rays coming in, changes the angular magnification. That's why the objects appear bigger looking through the telescope. In this case, so with an astronomical telescope, we're going to be using two plus lenses. Based on the equation that we use for telescopes for magnification, the image is going to be inverted. So if you look through one of these at an object, a tree or whatever, it's going to be upside down. Now these astronomical telescopes are the ones that we typically use. They're typically higher power, so usually we're looking at stars, galaxies far away, so it doesn't matter if it's upside down. We don't care. But if you give one of these to a low vision patient, it does matter if the image is upside down. And so we'll talk about what things they can do to make it so those images are upright. So like I talked about inverted images, so we use prisms or mirrors basically is what we use to fix that image so that it is upright. And you kind of hear Keplerian and astronomical used interchangeably. And kind of the way you tell the difference, any Keplerian with re-inverting optics is a terrestrial because that would be something used more on land, in binoculars or in low vision clinic. Without re-inverting optics is called astronomical because you're typically looking at things very, very far away. And here's just an example of what those re-inverting optics would be. Why it is entering here. It enters a mirrored system, travels through the objective lens, bounces around through a couple more mirrors here, and then through the ocular eyepiece lens so that it would be upright. So these ones, if you think back to that first picture, the way you kind of remember the astronomicals is they're long and strong. So they're longer because with the 2 plus lenses, the focal point is in between the two lenses, so they tend to be longer. But if they're re-inverting, then often they have a mirrored system and so they're usually not straight as well. Another way you can tell them apart is the astronomicals are usually the ones that are greater than 4x. So anything less than 4x is probably going to be a Galilean telescope. Anything greater than that is probably going to be astronomical. And the reason is that it just has to do with the field of view that you're limited by. And the magnification, since it is inverted, is given as a negative number. And we talked a little bit about this. So don't confuse when you're on boards or whatever the case may be. If the magnification is less than 1, that doesn't make it an astronomical. That just means it's minification, or that they've turned their telescope backwards. It's just if it's a negative number, that makes it astronomical. So this is the bioptics that I was talking about. So they're basically mounted on a pair of glasses. This is an astronomical system where the light enters this objective lens and then they would actually be looking through their left eye here. They're pretty pricey, but if it gives them the ability to drive around town, whereas before, without this, they wouldn't be able to drive period because their visual acuity is not high enough. And it's worth it to them to pay the big bucks for those. So this is a different type. This is more like spectacle mounted binoculars. I used to be able to say this looked like my brother Jeff, but now he's got the massive beard, so I don't know if I could quite say that. So now we'll talk about Galilean telescopes. So that was astronomical for the first part. With Galilean, you have a plus objective lens and a minus ocular lens. So since the focal points basically meet up behind the ocular lens, these ones tend to be shorter than the astronomicals. But the way that the parallel rays of light enter and leave the system, with these telescopes, the image is automatically upright, so you don't need inverting lenses inside the system. So this is just like the simplest type of telescope you could make, and you can do this in clinic. You could just get a plus lens and a minus lens. In this case, this is called the Max TV. People use it to watch TV. It's pretty low power, it's just 2x, but it gives them a little bit of magnification to use. And these are some Galilean bioptic telescopes up to 4x. They usually just be one lens on one side. And another area these are used to be in surgical loops, which I guess we're usually just looking through the eyepieces in the surgical clinic, but like a dentist, things like that, they would not use these surgical loops. So those ones, since they don't have re-inverting optics in them, those are going to be Galilean telescopes. And it's just another example. These ones are just tiny 2x to 4x. Okay, so we're back to our little tray of different types of telescopes. So I do have the magnification for all these, so I'll throw those up there right here. Does anybody want to give a guess of what all these are, which kind of telescopes? Let's go for it, Chris. So in front of the 2.5x to the 8x, those all seem like the Galilean. The Galilean? They're for the Galilean. Okay, so these three Galilean? Yeah. These four astronomical? Okay, so good on some of those. So first of all, having the magnification is key, because one of the big keys is like, if it's greater than 4x, you know for sure it's going to be astronomical. So we can kind of eliminate these three as being astronomical. This one we're not too sure of, because it could be either one. It's right at four. Another thing with these ones is you can't really tell from the picture, but the person's actually looking through these optics down here, and then it goes through a mirrored system, and then they're looking out there. But exactly right, these ones are longer, straighter, so these ones look more like astronomical telescopes. Yeah, so astronomical, Galilean, Galilean, astronomical. This one's probably an astronomical, but just because of the tiny objective lens. But, yeah. So just looking at the tray, I think I probably would have done almost as good if you had the magnifications. That makes a big difference, to distinguish what they are. So just remember for OCAPs, if you're just going solely on magnification and they don't give you whether it's a minus or a plus, anything greater than 4 is astronomical. So it's just kind of a summary slide between the two. Galilean has a plus objective, a minus ocular. It's pretty much always a straight housing. And usually 4x or less, because of the poor field of view if you go above a 4x. They're cheaper to make, just because it's just a simple two lens system. Astronomical plus two plus lenses, so they're longer. They can be straight orbit housing, like we saw from that picture. These ones are 4x or above, but they do tend to be more expensive if they have to have to re-inverting optics. So now I'll actually get into the equations that you'll need to use and remember. So this is just talking about the length of a telescope and really if you can figure out the length of a telescope just by having the power of two lenses in a system, you should be able to figure out how long a telescope is. And if you have just the powers and you know the lesser of the two powers, so the smaller power is going to be your objective lens, then you can plug it into this equation which is basically just the inverse of the powers added together and that will give you the length. Or you can also figure out the length just by knowing the length of focus of the two lenses. So this would be the overall length and it's just adding the object length and the ocular length of it. Whereas with this length of a Galilean, we see that it's actually going to be shorter. So let's do an example here. So yeah, there's pens and paper up here if you want to grab some. But we'll just take a couple of minutes on this. So what is the length of a telescope with a 15-diopter objective lens and a negative 37.5 ocular lens? I don't know. Do you get a calculator on the test? You probably don't need it for this one. I don't really know. So length is just the two focal lengths of the lenses. Does anybody have the answer? So length is just 1 over 15 plus 1 over the minus 37.5. Minus is the key. So basically 6 and 2 thirds centimeters minus 2 and 2 thirds come to about 4 centimeters long. So this is a big equation that I do not want you to write down. But at the beginning I talked about how a telescope has basically a net of zero power. There is a change in magnification. But this is the not simplified power equation here where n is the index of refraction and t is the length of the telescope or the length of the system that separates them. But basically if you plug it all in, it turns out that the power actually is zero. So this just proves that with a simple telescope like that example that we just did, there will be a magnification to it with no power. So the second equation, and this one I do want you to write down, is the magnification. So in this case it's basically just the ratio of the focal lengths whereas before it was the sum of the focal lengths for the length. This one is the ratio. And so if you're just dealing with powers, it's the power of the ocular over the power of the objective. If you're using the lengths, then it would just be the inverse of that. But one key with this magnification is that there is a minus built into the equation. And that will help us when we've calculated to determine if it's a capillary or an astronomical or a gallant telescope. So here's just an example. If we are given a plus two lens and a minus 10 lens, we basically just take the inverse. And even though it's a minus 10 lens, just using the equation to come out with a plus five magnification. So another thing with this magnification, sometimes like I have a hard time figuring out, shoot, is it the ocular or the objective lens that goes on top in this equation. Just remember, you're almost always looking for magnification. So if you get them in verse, then you're going to get minification, which should be less than one. If you get them in the correct order, you're going to get a number greater than one for your magnification. So if there's... I mean, you can pretty much just count on it. If there's a number less than one, that's probably not going to be your answer, even though you could actually get that number if you get these numbers mixed up in the equation. So here's an example. Another one I want you to go ahead and do real quick. So what is the angular magnification of a telescope with a plus 15 objective lens and a minus 37.5 ocular lens? Anybody have the answer? There's the inverse ocular over your objective because you have the powers. So yeah, a little bit 2.5x. So really it's just two pretty simple equations is what you need to know for this section. But it is important just to remember the order that they go in. I mean, there's a couple little cheats you can use. You know you're going to get a number greater than one. But you also need to remember that in the magnification equation that there is that minus sign so that you don't mix up whether it's an astronomical or a Galilean telescope. So is this from Galilean or astronomical? Galilean, yeah. Plus, so it used a plus and a minus lens that tells us it's Galilean but the magnification is also possible. So it's going to be an upright image. So there are a few keys. Another one is that it's less than 4x. So that was another one. Okay, so how do we figure out what the visual acuity would be looking through a telescope? So it's actually better than without the telescope by a factor of the magnification which is kind of cool. So if we have a patient with severe macular degeneration, they're 2200 but they still want to read their TV guide. We send them to the low vision clinic which I think we have a smaller one here to get a magnifier and they want to know how strong a magnification do we need in order for them to read what they want to read. So if they're 2200 best corrected and we give them a 4x magnifier or a 4x telescope then we would expect that their acuity would actually be closer to 2050 looking through the telescope. And going back to the bioptics all they have to do is reach that 2040 level through the telescope that's mounted on their bioptics. So they could be 2200 still best corrected and you give them like a 5x telescope mounted on their glasses and if they can look through that in the exam room and get the, you know, better than the 2040 line we would expect them to get a 2025. If they can get that or maybe 2040 but if they can get that 2040 line looking through that then they technically qualify and it's going to be limited it'll probably be more like city driving or something like that but they could still end up getting a driver's license. I have a question about that. Don't they have a certain thing field of vision as well? Exactly. So that's still a limiter if they don't have peripheral vision to meet the requirements then they won't get a driver's license either way but if it's strictly like a macular issue where they still have good peripheral vision because most cars coming at you are not that big I mean the things that I'm worried about are like a kid where it's a little harder to, you know, have that good contrast but they're mostly using the bioptics to like peek down and see a street sign down the road or, you know, look at the traffic light up ahead real quick and they're not driving around looking through that bioptic they're mostly looking through their glasses and then just a quick peek down and so we kind of test them in that, you know, like we'll have them looking just through the glasses and we'll put that 20-40 letter up that's okay, what is it? So they have to peek down real quickly all the tell us and then we switch the letter real quickly all the tell us so we can see if they're like having to hunt around for it or if they can actually get pretty efficient with it They're not legal here in Utah there's only a few states Ohio was one of them we fit a lot of them, you know, Ohio there's a couple out West but Utah does not allow those So virgin samplefication is another really important concept to remember and this is one that Dr. Olson which I think you at least met Dr. Olson before he retired another one that he really wanted to make sure we talked about basically what it means is that if you look through a telescope that's set for viewing something at optical infinity you know, looking far away and you try to look at an object up close your eye has to accommodate a crazy amount in order to see that object clearly to the point with most telescopes that can't do it especially when we're talking about somebody who's presbyopic because they're the ones that normally need these magnifiers or these telescopes and when they don't have any accommodation left anyway but if you try to look at an object up close you're actually having to accommodate by the magnification square times the power of the distance so if you're looking at an object it's just an example if you're looking at an object that's like a half meter away normally using the lens equation you would do 1 over 0.5 which would be two diopters and we'll talk a little bit about them more the lenses and the prisms in the next lecture but normally a person looking at an object a half meter away would just have to accommodate two diopters but if they're looking through a telescope even if it's just a 2x telescope it's that two diopters times the magnification square so it's 2 times 4 they actually have to accommodate eight diopters looking through that telescope which young kids probably know to do that but not certainly not a presbyopic person so here's an example I mean it's just you can just think about it in your head it's the magnification squared multiplied by the diopteric power of the object you're looking at so if an object is 33 centimeters in front of a 2x telescope system does anybody want to try to guess what they would actually have to accommodate in order to see that object clearly looking through there yeah yeah, exactly so it's just 1 over 0.33 is 3 diopters and then it's 2 squared so it's 3 times 4 but you can see how that can add up very quickly to where they're just going to have a blur in front of them so how do we get around that? I mean if most telescopes are set to see something at a distance how do we get around the fact that there's this virgin amplification I guess I have one more example here so a 3x telescope even if the object is one meter away so we're just dealing with one diopter a 3x telescope you're still going to be dealing with 9 diopters of power oh, I guess this is showing it doesn't matter if it's Galilean or Keplerian and since it's squared it doesn't matter which type of telescope you're using it's still going to end up coming out the same in this case if it's a half meter you're already up to 18 diopters of combination so like I said so how do we get around this? basically we can just add a trial lens or add a lens in front of the system that's set for the distance that you need so that works really well if you know you're always going to be looking at something a half meter away you can just add that into the telescope system there are also some of the telescopes I showed you on that tray you can adjust the distance between the lenses and that can change the focus of where you want to be so they're called a reading cap or like I said you can lengthen it for your focus and it's just to note a slit lamp we kind of just move it back and forth to bring that object into focus even though we're moving that telescope but that does have lenses in there for when you're switching between the different magnifications to bring it into focus so if you ended up meaning to figure out what power of lens cap it's basically just the viewing distance is one over the f cap or vice versa if you need to look at 33 centimeters you want a three-diopter it's just the inverse of the distance three-diopter lens cap and this is something that is really important surgical loops in particular so when you're getting fit for surgical loops first you pick the magnification but then you also pick the distance that your hands are going to be working if you're a dentist or whatever so that you can get that into focus but if they didn't have that reading cap on there you'd have to be accommodating you through that which would be really difficult so in this case 2.5x surgical loops 33 centimeters what power of reading cap is required yeah, three-diopter so pretty simple about three-diopter okay so now here's we're just getting kind of towards the end of the lecture so we know those few equations now really the lens cap equation I doubt they're going to ask about that but that's just something to practically know about first whether it's surgical loops or whatever else you need to have a lens in front of it if you're going to look at an object up close but now we'll do some examples that are pretty much straight out of your OCAP book, the BCSC and on what you might need to know for the actual exam so these are some examples for the equations that we gave you so first design two different telescopes with a magnification of 4x at first that seems like kind of a daunting task especially when I don't even give you any lenses or anything but so see if you can design a Galilean telescope and a Keplerian telescope just knowing that the magnification is 4x and then just kind of think about what sort of lens powers you would need to do that and if you need a hint, I can give you one but does anybody have one? for Galilean? sure, yeah exactly, we have whatever is going to give you that 4x so in this case, I think I did a a 3 and a 12 to give you that 4x so for the rest of the equations so yeah, absolutely and you can do anything that's going to give you that ratio that's going to come out to 4 for the rest of the questions I'm going to use this lens system so we'll say they have a plus 3 lens and for the Galilean of course we're going to need that minus 12 lens for the astronomical would be a plus 12 lens I'll give you the 4x in the astronomical if we use the same plus 3 and plus 12 well the same 3 and 12 would be a plus 3 and a plus 12 in this case it would be an inverted okay so here's another example of a question that we'll run through and see if we can answer all four of these questions just based on the information given and technically just with those two equations you should be able to figure it out so we'll just run through all these so see if you can do them all on your own first and then we'll talk about them afterwards but constructive telescope given a plus 10 and a plus 5 and basically if you can answer these four questions just off this information that's literally all you need to know great question so the if you want to magnify it it's going to be yeah so that's the when you're using that equation the magnification equation just remember if you get a number less than 1 you've probably got them in the wrong order test by the magnification or magnification this one obviously said magnification but yeah I think it would have to unless they if they told you that the ocular lens was the plus 5 and the objective was a plus 10 I guess typically that objective lens is a lower power and so you'd have to think in your mind oh the the eyepiece is the lower power in this case they got the telescope flipped around so you're going to get a magnification but I think in general they're going to be looking for what the magnification would be it's pretty rare that you want to magnify something so you got anybody want to answer the first question it's the length any guesses yeah so you add them together so it's actually about 30 centimeters so yeah so 1 over 10 is 10 centimeters 1 over 5 is 20 centimeters so it's about 30 centimeters long so if it will yeah we'll talk about that what is the magnification anybody so is it inverted or upright and how do we know that what do you think Ryan so yes exactly inverted and Galilean or astronomical yes it should be I just realized that was I just had to change this last night because I used different numbers and I totally put that as a plus 2 so I will fix that yeah so it should be a minus based on the equation that's why I was a little bit confused but yeah it would be inverted so it's a minus 2x inverted astronomical number wise I mean it's in this case you would expect the astronomical to be greater than 4 but just for the verses this example it just works out it's a minus 2 and Reese is not even here I was trying to show him that Utah is way better than Alabama but so there's a few more examples in the BCSE books in that section it's worth it to review those I think it's a pretty small section but there's potentially you know like I said there's potentially 4 questions that you could be asked I mean I don't think that asks any more than that it could ask the version of the amplification potentially but so just those 2 basic equations and just kind of remembering like some common sense stuff that you're going to be looking for magnification not and then just knowing the difference which one's inverted which one's upright which one's minus which one's plus and you can figure that out pretty easily clinically you know honestly you're probably not going to be fitting many people with these telescopes you might have somebody in your clinic doing it or whatever the case may be but it is important to know that you know if you have somebody with severely decreased vision they're not totally hopeless or helpless there's options out there for them and it's important to know how to kind of design those so any questions about anything from this section there's nothing too crazy in it like I said I think the one about prisms and lenses is going to be a lot more useful clinically but but these are still things that are important also I mean thank you very much