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F number on lenses





Tony The Tiger
I was talking with a friend about various lenses. He was telling me to try to look for lenses with 1s or 2s for their F numbers. I did not understand this. I was asking him about various wide angle zoom lenses. I need a lens with a wide angle for some very tall buildings that I have not been able to shoot correctly in the past. I am considering a lens that is in the 4s and 5s range for its f numbers (http://www.sigmaphoto.com/shop/8-16mm-f45-56-dc-hsm-sigma). It is one of the widest angle lenses on the market. However, its 4.5-5.6 f-numbers are quite lackluster. My friend says that you can tell the quality of a lens by its F number. For a given focal length or range of focal lengths, lower f-numbers mean that the lens is higher quality according to my friend. As I looked around I find prices to be consistent with this belief. Looking at the two 10-20mm lenses at http://www.sigmaphoto.com/shop/wide-angle-zoom-lenses, I see clear evidence of this. Is my friend correct?
Ankhanu
Lens quality isn't determined by the widest aperture (lowest f-stop), it's determined by the quality of the glass elements; the lenses.
That said, a low f-stop allows more light in, meaning you can use faster shutter speeds in less light. This is where the term "fast lens" comes from. Using a low f-stop produces a shallow depth of focus as well... Occasionally, but not always a desired effect.

It's hard to get zoom lenses that go much below f4 at their widest zoom; if you want wide apertures, you'll need to go with a prime lens... That or she'll out thousands of dollars Razz. Wide apertures (low f-stops) are hard to design without causing distortion in the image, this is why they're expensive, and their flexibility makes them desirable; there useable under a wider range of light conditions. Low fs don't necessarily translate to quality, but, it can correlate; manufacturers don't normally go through the trouble, just to fit plastic lenses and the like Wink
william
f numbers refer to the aperture, which is honestly something I would suggest mastering control of before you spend hundreds of dollars on a wide angle lens. In a nutshell, aperture is a small hole in your lens that allows light in. It works pretty much just like the pupil of an eye. The smaller the f number, the larger the aperture, and the more light that is allowed in. A larger aperture allows you to use slower shutter speeds and lower ISOs (which reduces noise). It also allows you to reduce your depth of field and blur the background. With the exception of prime lenses, the majority of lenses that go below f/2.8 are very expensive and often quite large. But you have to understand the purpose of these lenses and what a high aperture can do for you. A portrait lens, for example, usually has a high aperture (and a ~100mm focal length) so you can easily blur the background and keep the focus on the model.

Can you tell the quality of a lens by the maximum aperture? No, not really. I mean sure, the higher aperture lenses tend to be quick, but there are plenty of crummy lenses out there that have low f numbers. Often, lenses are softest when they are wide open (maximum aperture), so even if you have a high maximum aperture, you won't necessarily be using it all the time. There's much more to look into when trying to determine the quality of a lens, and most of what you need to know will not be found in spec sheets. You either have to read reviews or test it yourself.

That Sigma lens you posted, for example, doesn't go up to f/2.8 or anything like that, but I fear that if it did, you would see severe drops in quality. If I recall correctly, that lens isn't very sharp to begin with, and serves a very special purpose by going down to 8mm.

Also, I would like to say, be careful before buying a wide-angle lens. Not only are they far more expensive than your consumer orientated kit lens and telephoto lens, they are probably the most difficult lens to use properly. There's an assumption among newbies that a wider lens lets you get the whole scene in. That's simply not necessarily true, and most photos taken with that mindset end up boring and uninspired. Remember that your own vision is equivalent to about 35mm, give or take. 8mm is VERY wide, and will without a doubt lead to distortion on the edges. The proportions will not be right and you have to put a lot of thought into your composition. If you want 8mm, by all means go for it, but understand what it is you're getting yourself into. Master the basics first.

And for what it's worth, if you know what you're doing and find yourself actually needing a wide angle lens, you can likely get a higher aperture 10mm lens for less money.

Edit: Beaten by seconds. Razz
Ankhanu
william wrote:
Edit: Beaten by seconds. Razz

But much better written and more informative than my 3am ramble Wink
Tony The Tiger
william wrote:
f numbers refer to the aperture, which is honestly something I would suggest mastering control of before you spend hundreds of dollars on a wide angle lens. In a nutshell, aperture is a small hole in your lens that allows light in. It works pretty much just like the pupil of an eye. The smaller the f number, the larger the aperture, and the more light that is allowed in. A larger aperture allows you to use slower shutter speeds and lower ISOs (which reduces noise). It also allows you to reduce your depth of field and blur the background. With the exception of prime lenses, the majority of lenses that go below f/2.8 are very expensive and often quite large. But you have to understand the purpose of these lenses and what a high aperture can do for you. A portrait lens, for example, usually has a high aperture (and a ~100mm focal length) so you can easily blur the background and keep the focus on the model.

Can you tell the quality of a lens by the maximum aperture? No, not really. I mean sure, the higher aperture lenses tend to be quick, but there are plenty of crummy lenses out there that have low f numbers. Often, lenses are softest when they are wide open (maximum aperture), so even if you have a high maximum aperture, you won't necessarily be using it all the time. There's much more to look into when trying to determine the quality of a lens, and most of what you need to know will not be found in spec sheets. You either have to read reviews or test it yourself.

That Sigma lens you posted, for example, doesn't go up to f/2.8 or anything like that, but I fear that if it did, you would see severe drops in quality. If I recall correctly, that lens isn't very sharp to begin with, and serves a very special purpose by going down to 8mm.

Also, I would like to say, be careful before buying a wide-angle lens. Not only are they far more expensive than your consumer orientated kit lens and telephoto lens, they are probably the most difficult lens to use properly. There's an assumption among newbies that a wider lens lets you get the whole scene in. That's simply not necessarily true, and most photos taken with that mindset end up boring and uninspired. Remember that your own vision is equivalent to about 35mm, give or take. 8mm is VERY wide, and will without a doubt lead to distortion on the edges. The proportions will not be right and you have to put a lot of thought into your composition. If you want 8mm, by all means go for it, but understand what it is you're getting yourself into. Master the basics first.

And for what it's worth, if you know what you're doing and find yourself actually needing a wide angle lens, you can likely get a higher aperture 10mm lens for less money.

Edit: Beaten by seconds. Razz


Yes, there are slightly cheaper 10mm wide angles. I have a couple of objectives. I take a lot of architectural photos in Chicago. Downtown is quite dense and sometimes you have to use very odd angles to capture a whole building unless you have a wide angle. Most notably a lot of buildings in the LaSalle Street Canyon are very difficult to shoot without a wide angle. I also have a few other needs for a wide angle. I think I definitely need the lens. I just can't afford to pay for a 2.8 F telephoto lens.
william
Alright then, try this. Take your 18-55mm lens and take a picture of a building, first at 18mm and then at 35mm (step back a bit for the latter to counter the extra zooming). Now compare the two photos paying attention to the lines and the tilts of the buildings. Which one looks more realistic?

My point is, wide angle lenses aren't just a sure-fire way to get everything in cleanly. Generally when used in architecture, the buildings will look like they're leaning backwards and the perspective will be distorted. Now, of course, this can be used as an artistic effect and I've seen some beautiful photos taken this way (some actually prefer this distorted reality). But you have to know how to use the lens properly to create this artistic effect.

There are, however, a few ways to take a more "realistic" photo. In the old days they used to use a medium format, or some cases a large format, camera. You can still go that route, but it will be very expensive (I'm talking five figures). Another option is to use the perspective correction tool in photo editing software. This works...kind of. It's not bad, and if you're on a low budget it's probably your best choice, but if you ask me, it still doesn't look right. So therefore, the best option (and the one most professional architectural photographers seem to use today) is using a full-frame DSLR with a tilt-shift or perspective control lens. This type of lens will allow you to shift the frame of the camera and control the perspective, fixing up all the problems brought up by a wide angle lens. More importantly, tilt shift lenses are actually even better than regular wide angles at creating an artistic effect since you have so much more control.

There are one or two issues, though. A tilt-shift lens is a fair bit more expensive than your usual wide angle. And they're really best used on a full-frame camera since the same focal length on one of those is much wider than it would be on a cropped sensor camera like your T3i. But with that said, I strongly suggest that if you really want to do architectural photography, even as a hobby, and are willing to learn the basics of photography that you consider a tilt-shift lens. Pair one of those with a sturdy tripod and some creativity, and you'll be taking excellent photos. Also, let's face it, even though a wide angle is cheaper, what good is it to spend four figures on a lens that might yield poor photos?

Just trying to help you not waste your money. If, despite the perspective issues and distortion, you still feel you need a lens that wide be sure wherever you buy it from has a good return policy like Amazon, Adorama, or B&H. They are tricky lenses to use properly.

And if you're considering it, here is an example of a tilt-shift lens.
Tony The Tiger
william wrote:
Alright then, try this. Take your 18-55mm lens and take a picture of a building, first at 18mm and then at 35mm (step back a bit for the latter to counter the extra zooming). Now compare the two photos paying attention to the lines and the tilts of the buildings. Which one looks more realistic?


I am unsure what you mean by 35mm in my Canon APS-C world (Canon Rebel T3i). The only other camera I have is my BlackBerry Torch 9810. I'll show you some buildings I would like to retake. Look on wikipedia for One North LaSalle, Roanoke Building, Franklin Center (Chicago) for starters. They all have images from me (two of the three have my image as the main image).

william wrote:
My point is, wide angle lenses aren't just a sure-fire way to get everything in cleanly. Generally when used in architecture, the buildings will look like they're leaning backwards and the perspective will be distorted. Now, of course, this can be used as an artistic effect and I've seen some beautiful photos taken this way (some actually prefer this distorted reality). But you have to know how to use the lens properly to create this artistic effect.


I am not entering a photo contest. I am just challenging myself to take better pictures.

william wrote:
There are, however, a few ways to take a more "realistic" photo. In the old days they used to use a medium format, or some cases a large format, camera. You can still go that route, but it will be very expensive (I'm talking five figures). Another option is to use the perspective correction tool in photo editing software. This works...kind of. It's not bad, and if you're on a low budget it's probably your best choice, but if you ask me, it still doesn't look right. So therefore, the best option (and the one most professional architectural photographers seem to use today) is using a full-frame DSLR with a tilt-shift or perspective control lens. This type of lens will allow you to shift the frame of the camera and control the perspective, fixing up all the problems brought up by a wide angle lens. More importantly, tilt shift lenses are actually even better than regular wide angles at creating an artistic effect since you have so much more control.

There are one or two issues, though. A tilt-shift lens is a fair bit more expensive than your usual wide angle. And they're really best used on a full-frame camera since the same focal length on one of those is much wider than it would be on a cropped sensor camera like your T3i. But with that said, I strongly suggest that if you really want to do architectural photography, even as a hobby, and are willing to learn the basics of photography that you consider a tilt-shift lens. Pair one of those with a sturdy tripod and some creativity, and you'll be taking excellent photos. Also, let's face it, even though a wide angle is cheaper, what good is it to spend four figures on a lens that might yield poor photos?

Just trying to help you not waste your money. If, despite the perspective issues and distortion, you still feel you need a lens that wide be sure wherever you buy it from has a good return policy like Amazon, Adorama, or B&H. They are tricky lenses to use properly.

And if you're considering it, here is an example of a tilt-shift lens.


You are going way beyond my level of photo skills. I have just moved up from point and shoot ccds of 1/1.8" and 1/2.5" (my prior three digital cameras were the Nikon Coolpix 4500, Canon Powershot A620 and Canon Powershot TX1) to Canon APS-C (Canon EOS Rebel T3i). I.e., my ccd from my TX1 to my T3i has jumped from 5.76mm x 4.29mm to 22.2mm x 14.8mm. It will be a long time before I jump to full frame, medium format or large format. I got my T3i body for $511 plus tax from Canon in a buyer loyalty program when my TX1 went on the fritz. I am not looking to spend 4 or 5 figures on a body any time soon.

Also, tilt shift lens? That is a bit beyond my basic needs. I am going for the kit lens, one wide angle zoom and one telephoto zoom. I am done for a few years, except for possible a single cheap 1.4 or 1.8 F lens.
Ankhanu
Tony The Tiger wrote:
william wrote:
Alright then, try this. Take your 18-55mm lens and take a picture of a building, first at 18mm and then at 35mm (step back a bit for the latter to counter the extra zooming). Now compare the two photos paying attention to the lines and the tilts of the buildings. Which one looks more realistic?


I am unsure what you mean by 35mm in my Canon APS-C world (Canon Rebel T3i). The only other camera I have is my BlackBerry Torch 9810. I'll show you some buildings I would like to retake. Look on wikipedia for One North LaSalle, Roanoke Building, Franklin Center (Chicago) for starters. They all have images from me (two of the three have my image as the main image).

If your kit lens has a zoom range of 18-55mm, 35mm will be near the middle of your zoom range.

Tony The Tiger wrote:
william wrote:
My point is, wide angle lenses aren't just a sure-fire way to get everything in cleanly. Generally when used in architecture, the buildings will look like they're leaning backwards and the perspective will be distorted. Now, of course, this can be used as an artistic effect and I've seen some beautiful photos taken this way (some actually prefer this distorted reality). But you have to know how to use the lens properly to create this artistic effect.


I am not entering a photo contest. I am just challenging myself to take better pictures.

Does "better" include lens distortions? Figure out what you mean by "better" and you can better determine what will work for your needs. Personally, I enjoy the bulge created by a wide angle, and, with practice, it can be used to great effect... but if you're hoping to just pop one on and off you go, it's not gonna happen.

William is giving you suggestions for how to make a conventionally "better" photo, one that includes the capability of capturing straight lines.

Tony The Tiger wrote:
You are going way beyond my level of photo skills.

That's kind of the point. He's offering you insight that you have not considered, because you don't know to consider them. Also, it's always good to challenge your current skill level.

Tony The Tiger wrote:
I have just moved up from point and shoot ccds of 1/1.8" and 1/2.5" (my prior three digital cameras were the Nikon Coolpix 4500, Canon Powershot A620 and Canon Powershot TX1) to Canon APS-C (Canon EOS Rebel T3i). I.e., my ccd from my TX1 to my T3i has jumped from 5.76mm x 4.29mm to 22.2mm x 14.8mm. It will be a long time before I jump to full frame, medium format or large format. I got my T3i body for $511 plus tax from Canon in a buyer loyalty program when my TX1 went on the fritz. I am not looking to spend 4 or 5 figures on a body any time soon.

Most photographers never do move to Full-Frame, Medium or Large format; they're specialty cameras. Professionals included. Don't worry about it Smile

Tony The Tiger wrote:
Also, tilt shift lens? That is a bit beyond my basic needs. I am going for the kit lens, one wide angle zoom and one telephoto zoom. I am done for a few years, except for possible a single cheap 1.4 or 1.8 F lens.

Cheap f1.4 doesn't really happen, but the 50mm 1.8 is decent, and super cheap... at least for Nikon; I'm not as impressed with the Canon version.
The tilt-shift suggestion is a good one, and it's a direction I've wanted to take my own shooting, but I'm also pretty hampered by cash flow. But, look into it. It may not be beyond your needs, it really depends on what you want to produce in your photographs. It may be beyond your techniques currently, but, if that's what will deliver the images you actually want to produce, it's not beyond your needs. Your needs and your skill level are different concepts Wink

Moral of the story that william and I are getting at: Really take the time to analyze what you want to shoot (not what you can currently shoot), research similar photos, the equipment used, and techniques used. From that starting point, you'll be able to then figure out what kit you should be pursuing... it might not be the stuff you currently think.
Tony The Tiger
Ankhanu wrote:
Tony The Tiger wrote:
william wrote:
Alright then, try this. Take your 18-55mm lens and take a picture of a building, first at 18mm and then at 35mm (step back a bit for the latter to counter the extra zooming). Now compare the two photos paying attention to the lines and the tilts of the buildings. Which one looks more realistic?


I am unsure what you mean by 35mm in my Canon APS-C world (Canon Rebel T3i). The only other camera I have is my BlackBerry Torch 9810. I'll show you some buildings I would like to retake. Look on wikipedia for One North LaSalle, Roanoke Building, Franklin Center (Chicago) for starters. They all have images from me (two of the three have my image as the main image).

If your kit lens has a zoom range of 18-55mm, 35mm will be near the middle of your zoom range.


I thought he was suggesting shooting 18mm with my camera and then shoot with a 35 mm camera.

Ankhanu wrote:
Tony The Tiger wrote:
william wrote:
My point is, wide angle lenses aren't just a sure-fire way to get everything in cleanly. Generally when used in architecture, the buildings will look like they're leaning backwards and the perspective will be distorted. Now, of course, this can be used as an artistic effect and I've seen some beautiful photos taken this way (some actually prefer this distorted reality). But you have to know how to use the lens properly to create this artistic effect.


I am not entering a photo contest. I am just challenging myself to take better pictures.

Does "better" include lens distortions? Figure out what you mean by "better" and you can better determine what will work for your needs. Personally, I enjoy the bulge created by a wide angle, and, with practice, it can be used to great effect... but if you're hoping to just pop one on and off you go, it's not gonna happen.

William is giving you suggestions for how to make a conventionally "better" photo, one that includes the capability of capturing straight lines.


O.K., but I do not believe I am buying a fisheye wide angle.

Ankhanu wrote:
Tony The Tiger wrote:
Also, tilt shift lens? That is a bit beyond my basic needs. I am going for the kit lens, one wide angle zoom and one telephoto zoom. I am done for a few years, except for possible a single cheap 1.4 or 1.8 F lens.

Cheap f1.4 doesn't really happen, but the 50mm 1.8 is decent, and super cheap... at least for Nikon; I'm not as impressed with the Canon version.

I think I can get the 50mm 1.8 for under $100. That is probably something I will pick up since I have nothing else under f4.0.

Ankhanu wrote:
The tilt-shift suggestion is a good one, and it's a direction I've wanted to take my own shooting, but I'm also pretty hampered by cash flow. But, look into it. It may not be beyond your needs, it really depends on what you want to produce in your photographs. It may be beyond your techniques currently, but, if that's what will deliver the images you actually want to produce, it's not beyond your needs. Your needs and your skill level are different concepts Wink

Moral of the story that william and I are getting at: Really take the time to analyze what you want to shoot (not what you can currently shoot), research similar photos, the equipment used, and techniques used. From that starting point, you'll be able to then figure out what kit you should be pursuing... it might not be the stuff you currently think.


Thanks for the advice.
Ankhanu
Tony The Tiger wrote:
I thought he was suggesting shooting 18mm with my camera and then shoot with a 35 mm camera.

Nope. Use the same lens; that's part of the point. You'll see how focal length can cause distortions, using the same lens, the same framing, etc.

Tony The Tiger wrote:
O.K., but I do not believe I am buying a fisheye wide angle.

This is a feature of ALL wide angle lenses, including fish-eyes, but not limited to them. It's part of the nature of light passing through convex lenses; the greater the convexity, the wider the angle, the greater the distortion... but it is present in all wide angles.

I suggest reading into some basic refraction physics to understand angle of view, focal length and lens shapes, and what they do to light. It will really help you improve your photography as you understand the science that supports it.
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