Photography: Focal distance and perspective...

[Danoz]

Lately in my photography endeavor I've decided I want a very strong understanding of the technical side, which has resulting in a lot of reading/sketching diagrams and brushing up on my physics. I've recently been doing a lot of side-by-sides to see how things look at different apertures and shutter speeds. This morning, I went for comparing perspectives.

I shot at a fixed aperture of f/5.6 (in aperture priority) altering shutter speed and ISO as needed; I used three different lenses from focal lengths along 18mm to 300mm. Interesting to see how the telephoto zoom at 300mm increases the size of the bokeh/blur exponentially (as I read it would) and the appearance of the object in the background (which appears to change size but does not change location). The only thing changing is where I'm standing and the focal length-- trying to keep the target object in the same frame and at the same straight-on angle. Interesting also that depth of field is technically unchanged (despite that illusion from the telephoto magnification). Pretty interesting.

At 18mm - corrected for barrel distortion (f/5.6 - 18-105mm VR). I'm very close to the object, and it's not very sharp. Not the best lens for shooting at 18mm (and I am lacking in a better wide-angle at the moment).

At 35mm - (f/5.6 - 18-105mm VR)

At 50mm - (f/5.6 ----- 50mm 1.8 lens). Probably the most pleasing shot and closest to the human eye (and my favorite lens).

70mm (f/5.6 ---- 70-300mm VR).

135mm (f/5.6 ---- 70-300mm VR).

200mm (f/5.6 ---- 70-300mm VR).

300mm (f/5.6 ---- 70-300mm VR). You really can't see anything but the sushi-cat. Standing rather far back at full zoom.

Hope you enjoy! What's your take on this stuff? Still trying to get a grasp at how different lenses render bokeh in different ways...

 

[backstept]

well . . . with zoom lenses you're narrowing the field of view to nearly parallel, thus the background objects appear closer and larger

 

[Danoz]

well . . . with zoom lenses you're narrowing the field of view to nearly parallel, thus the background objects appear closer and larger

No that much I understand, of course, but it appears that the size of the bokeh circles seem to increase as well. I'm still not entirely clear on how the lens renders the bokeh or "circle of confusion."

I rather enjoyed this site's comparison... http://www.rickdenney.com/bokeh_test.htm

 

[Arrqh]

The perspective with a 50mm lens is only equivalent to the human eye if you're using a full frame/35mm equivalent camera. On a APS-C crop frame, 50mm is a mild telephoto and you need to go down to the 28-35mm range for a "normal" lens. I have a cheap nifty 50, but I personally prefer my 30mm as it fees much more natural to me on my crop camera.

Circles of confusion aren't really describing the bokeh, they're describing what areas of the image are acceptably in focus. Technically speaking, everything except for an infinitely thin slice of the subject is out of focus and will be blurred to the shape of a circle (assuming a perfectly circular aperture), but anything smaller then the circle of confusion will appear to be acceptably in focus. And this will vary as well based on what medium and resolution the resulting photo will be viewed in.

With a telephoto lens, bokeh is more pronounced for the same reason that background objects appear larger... just as you've perceptually enlarged the background, you've enlarged the out of focus circles that it generates on your sensor. I wouldn't really describe the lens as "rendering" bokeh... since the lens is circular, all the light passing through it will be projected as circular discs on the camera sensor. If the light rays are coming in completely parallel, which would mean they were completely out of focus, the only shape they could take would be that of the circle created by the lens. The more in focus the rays are the more they converge, but they're still being shaped by the lens they are passing through.

Some good diagrams on the subject here: http://www.cambridgeincolour.com/tutorials/depth-of-field.htm

 

[Danoz]

The perspective with a 50mm lens is only equivalent to the human eye if you're using a full frame/35mm equivalent camera. On a APS-C crop frame, 50mm is a mild telephoto and you need to go down to the 28-35mm range for a "normal" lens. I have a cheap nifty 50, but I personally prefer my 30mm as it fees much more natural to me on my crop camera.

Circles of confusion aren't really describing the bokeh, they're describing what areas of the image are acceptably in focus. Technically speaking, everything except for an infinitely thin slice of the subject is out of focus and will be blurred to the shape of a circle (assuming a perfectly circular aperture), but anything smaller then the circle of confusion will appear to be acceptably in focus. And this will vary as well based on what medium and resolution the resulting photo will be viewed in.

With a telephoto lens, bokeh is more pronounced for the same reason that background objects appear larger... just as you've perceptually enlarged the background, you've enlarged the out of focus circles that it generates on your sensor. I wouldn't really describe the lens as "rendering" bokeh... since the lens is circular, all the light passing through it will be projected as circular discs on the camera sensor. If the light rays are coming in completely parallel, which would mean they were completely out of focus, the only shape they could take would be that of the circle created by the lens. The more in focus the rays are the more they converge, but they're still being shaped by the lens they are passing through.

Some good diagrams on the subject here: http://www.cambridgeincolour.com/tutorials/depth-of-field.htm

Very clear explanation, and interesting... thanks! I enjoyed testing the different images (and it's kind of neat that it seems like the car is actually moving down the street).

 

[Mr Awe]

Well, there's a reason that they call them the "nifty fifty"! I'm surprised that your 50mm prime lens is out classed by 18-105mm zoom @ 35mm. And, it's about on par with your 70-300mm @ 70 mm. So, you don't have the best 50mm lens by a long shot assuming that the pictures in the sequence accurately the typical results.

The 50mm lens in general is probably the most perfected lens, you should be able to pick up one with stellar quality for relatively little money.

For example, I'm a Canon guy who has a bunch of pro L lens but I have a relatively inexpense Canon 50mm that I got for a couple of hundred dollars. This 50mm prime is superior to the zoom L lenses (that are 5 times more expensive) at 50mm.

Just pointing this out because you mentioned it was your favorite lens. If you like it now, you might be heaven with a little shopping around!

Mr Awe

 

[Danoz]

Well, there's a reason that they call them the "nifty fifty"! I'm surprised that your 50mm prime lens is out classed by 18-105mm zoom @ 35mm. And, it's about on par with your 70-300mm @ 70 mm. So, you don't have the best 50mm lens by a long shot assuming that the pictures in the sequence accurately the typical results.

The 50mm lens in general is probably the most perfected lens, you should be able to pick up one with stellar quality for relatively little money.

For example, I'm a Canon guy who has a bunch of pro L lens but I have a relatively inexpense Canon 50mm that I got for a couple of hundred dollars. This 50mm prime is superior to the zoom L lenses (that are 5 times more expensive) at 50mm.

Just pointing this out because you mentioned it was your favorite lens. If you like it now, you might be heaven with a little shopping around!

Mr Awe

I am currently using the 50mm 1.8 Nikkor-- which reviews fairly well for the price. I've been using it mostly indoors-- here is the result (low light-- 3200 ISO). A better option might be the 50mm 1.4, but it's four times the price and I'm told the mechanics aren't that different... thoughts?

 

[Mr Awe]

Well, there's a reason that they call them the "nifty fifty"! I'm surprised that your 50mm prime lens is out classed by 18-105mm zoom @ 35mm. And, it's about on par with your 70-300mm @ 70 mm. So, you don't have the best 50mm lens by a long shot assuming that the pictures in the sequence accurately the typical results.

The 50mm lens in general is probably the most perfected lens, you should be able to pick up one with stellar quality for relatively little money.

For example, I'm a Canon guy who has a bunch of pro L lens but I have a relatively inexpense Canon 50mm that I got for a couple of hundred dollars. This 50mm prime is superior to the zoom L lenses (that are 5 times more expensive) at 50mm.

Just pointing this out because you mentioned it was your favorite lens. If you like it now, you might be heaven with a little shopping around!

Mr Awe

I am currently using the 50mm 1.8 Nikkor-- which reviews fairly well for the price. I've been using it mostly indoors-- here is the result (low light-- 3200 ISO). A better option might be the 50mm 1.4, but it's four times the price and I'm told the mechanics aren't that different... thoughts?

I don't know Nikon lenses that well. I just know that with my non-pro 50mm prime that the results are startlingly clear when I see them even when compared to my pro quality L class zoom lenses that cost much more. Just by judging from from the initial sequence of pictures that you posted in this thread, I don't see that startling difference between your prime lens and the 2 zoom lenses. I suspect that there is room for improved there for image quality.

But, not knowing Nikon lenses, I don't have a recommendation other than that usually if you pay 4 times the price for a similar lens (two 50 mm primes in this case) you should get notably better image quality. But, obviously money is a factor and we can't have everything! For instance, I'm drooling over a couple of Canon 100mm macro lenses (the non-L and the L versions) but even the cheaper of the 2 is over $500. Hard to justify for something that I wouldn't use too often.

Does Nikkor publish something like the MTF charts that Canon does? That would give you a good objective comparison between the 2 lenses.

Nice picture! It's probably hard to judge by image quality though because the ISO is understandably cranked up pretty high. When you crank up the ISO, you get more noise which the camera combats with noise reduction algorithms. These algorithms eat into the image details; basically, smoothing out the noise means smoothing out some of the detail. So, not a good picture in the sense of comparing sharpness. But, the large aperature was undoubtedly a big asset here.

Mr Awe

 

[Bears Discover Fire]

Well, there's a reason that they call them the "nifty fifty"! I'm surprised that your 50mm prime lens is out classed by 18-105mm zoom @ 35mm. And, it's about on par with your 70-300mm @ 70 mm. So, you don't have the best 50mm lens by a long shot assuming that the pictures in the sequence accurately the typical results.

The 50mm lens in general is probably the most perfected lens, you should be able to pick up one with stellar quality for relatively little money.

For example, I'm a Canon guy who has a bunch of pro L lens but I have a relatively inexpense Canon 50mm that I got for a couple of hundred dollars. This 50mm prime is superior to the zoom L lenses (that are 5 times more expensive) at 50mm.

Just pointing this out because you mentioned it was your favorite lens. If you like it now, you might be heaven with a little shopping around!

Mr Awe

I am currently using the 50mm 1.8 Nikkor-- which reviews fairly well for the price. I've been using it mostly indoors-- here is the result (low light-- 3200 ISO). A better option might be the 50mm 1.4, but it's four times the price and I'm told the mechanics aren't that different... thoughts?

First off, great pic.

Second, an amateur photographer probably doesn't need the extra stop of a 1.4 lens, unless they feel inclined to spend the money. Whether gaining a stop in aperture is worth gaining a quadrupled price tag depends on what kind of shooting you're doing.

To a pro photographer, an extra stop can make or break a shot. Sports photographers who are already maxed in ISO but need to increase shutter speed without resorting to pushing in post (and dealing with degredation on that level), wedding/event photographers who work in low and unpredictable lighting, fine art photographers who need extremely shallow DoF - to most of them, paying the premium and gaining an extra stop can make or break their assignments and pay itself off quickly. I reckon most of them would consider faster glass worth its price many times over.

Long story short, while the quality of a 1.4 is not appreciably different than a 1.8, the utility of a 1/4 is greater.

 

[Tiberius]

No that much I understand, of course, but it appears that the size of the bokeh circles seem to increase as well. I'm still not entirely clear on how the lens renders the bokeh or "circle of confusion."

You gotta think of cones of light.

Let's say you are shooting in a dark environment and there is a single point of light, like a star. No matter how much you zoom in, it's always gonna be a single point of light.

Now, assuming that you have focused properly, the light from that star is going to enter the lens and be bent by that lens so all the light that entered the lens from that star will be focussed on one point on the sensor.

So it creates a cone of light, with the wide base at the lens (well, the aperture iris inside the lens technically) and the point on the sensor.

if the image is not focussed propoerly, then the point of light will be behind the sensor, or in front of it (once the light reaches the point of the cone, it starts spreading out again).

That means that the sensor is not sitting at the point at the end of the cone, but is, in effect, taking a slice through the cone. And of course, a slice through a cone is a circle.

That's why a point of light, out of focus, is a circle.

Now, the aperture can control this. if you set a higher aperture number (such as f16), then the iris will close, and the cone will become narrower. So when it's out of focus and the sensor is slicing through the cone, the cone won't be as wide. So the circle is smaller. It's still a circle, yes, but it's a smaller circle, which reduces the fuzziness of being out of focus.

That's how pinhole cameras get around the need for a focussing lens. They create light cones that are so narrow that the sides of the cone are almost parrallel.

 

[Danoz]

No that much I understand, of course, but it appears that the size of the bokeh circles seem to increase as well. I'm still not entirely clear on how the lens renders the bokeh or "circle of confusion."

You gotta think of cones of light.

Let's say you are shooting in a dark environment and there is a single point of light, like a star. No matter how much you zoom in, it's always gonna be a single point of light.

Now, assuming that you have focused properly, the light from that star is going to enter the lens and be bent by that lens so all the light that entered the lens from that star will be focussed on one point on the sensor.

So it creates a cone of light, with the wide base at the lens (well, the aperture iris inside the lens technically) and the point on the sensor.

if the image is not focussed propoerly, then the point of light will be behind the sensor, or in front of it (once the light reaches the point of the cone, it starts spreading out again).

That means that the sensor is not sitting at the point at the end of the cone, but is, in effect, taking a slice through the cone. And of course, a slice through a cone is a circle.

That's why a point of light, out of focus, is a circle.

Now, the aperture can control this. if you set a higher aperture number (such as f16), then the iris will close, and the cone will become narrower. So when it's out of focus and the sensor is slicing through the cone, the cone won't be as wide. So the circle is smaller. It's still a circle, yes, but it's a smaller circle, which reduces the fuzziness of being out of focus.

That's how pinhole cameras get around the need for a focussing lens. They create light cones that are so narrow that the sides of the cone are almost parrallel.

Awesome, very visual and now that I think in "cones" as I change the aperture I can really envision the flying toward the sensor. Fascinating! ---thanks

 

[Small White Car]

I really need to get a long lens. The problem is that my dad keeps letting me borrow this one:

So my motivation to pay for one is low! But man, I wish I had it with me all the time. They really make my personal photos feel...well...personal!

They're great for putting focus on the subject and the subject only.

 

[Danoz]

Wow those are beautiful, thank you for sharing them!

Apparently we have a lot of shutterbugs here .

 

[Mr Awe]

Second, an amateur photographer probably doesn't need the extra stop of a 1.4 lens, unless they feel inclined to spend the money. Whether gaining a stop in aperture is worth gaining a quadrupled price tag depends on what kind of shooting you're doing.

Long story short, while the quality of a 1.4 is not appreciably different than a 1.8, the utility of a 1/4 is greater.

Well, it depends. Is the extra stop the only difference? I doubt it. You may be getting more image quality, sharpness, contrast in the deal. Need to look at an MTF chart if Nikkor does those.

But, it's true, for an amateur photographer nothing beyond the basics is really required. It's all what you want to spend your hard earned money on.

Mr Awe

 

[Bears Discover Fire]

Second, an amateur photographer probably doesn't need the extra stop of a 1.4 lens, unless they feel inclined to spend the money. Whether gaining a stop in aperture is worth gaining a quadrupled price tag depends on what kind of shooting you're doing.

Long story short, while the quality of a 1.4 is not appreciably different than a 1.8, the utility of a 1/4 is greater.

Well, it depends. Is the extra stop the only difference? I doubt it. You may be getting more image quality, sharpness, contrast in the deal. Need to look at an MTF chart if Nikkor does those.

But, it's true, for an amateur photographer nothing beyond the basics is really required. It's all what you want to spend your hard earned money on.

Mr Awe

Could be, but I don't assume that without looking at the charts. Between photography school and talking to dealers at trade shows, I've learned you're paying for more stops, full stop, and I've shot both lenses and have not seen a noticable difference in quality between the two. So I picked the premise that all over variables are equal and went from there.

 

[Mr Awe]

^^ I certainly would not assume either. It's usually the case with reputable brands though that you are getting some better image quality. But, charts are the way to go and then your own personal priorities. But, heck, if you've used both then there's the answer.

I use Canon and I've got this sweet Canon 50mm lens that is so sharp that it's instantly recognizeable. I don't see that quality in the the examples in this thread. Definitely not knocking the photographer at all, just musing about the lens.

Mr Awe

 

[Mr Awe]

I really need to get a long lens. The problem is that my dad keeps letting me borrow this one:

That looks like a Canon 20-700 f4 L? If so, I've got one myself and LOVE it! I use it quite a bit. Tough choice deciding between it and the f2.8 version. But, I usually use it in decent light and figured that the weight savings, which are significant, would be worth it. Looking back, I'm happy with that decision.

Mr Awe