Help me understand crop sensor?

[pixie08]

So I am going on this Alaskan cruise in 3 months, renting a telephoto L series lens. I have been using an SLR for a while, but this will be the first with such a large lens and I am really an amateur in all manual shooting. In my research I keep seeing people mention they took this pic and that pic at this length, but it had crop sensor etc.

Well I am a little confused, because wouldn't all digital SLR's have crop sensor? Isn't full frame a thing of the 35mm past? I thought crop sensor does NOT affect the lens really, just the crop? I think my Rebel had a 1.6 crop. I really never thought about it before, but I am trying to do some more manual shooting and think about things more in advance.

Is this just something I have to think of in terms of framing or am I totally missing something?Thanks everyone for your help!

 

[PhotographyDR]

Well I can try to explain this but I will have to use a little bit of physics. Promise not too hard. The attached

image might help.

Basically as light travels through a lens it is redirected to a single point. Then the light starts to travel outward

at the same angle it came in at until it hits the sensor. That distance it travels after being focused is called the

focal length. In the film days the angle of view (how much you could see in the frame) was based on a 35mm piece of

film on the back. Today it is based on the size of the sensor. There are cameras today that have a 35mm size and give

the same field of view as the older film cameras. (D800 -Nikon, 5D Mark III are examples). These cameras "see" the

same viewpoint from edge to edge as a 35mm film camera. These cameras also are very expensive.

Most cameras come with a crop sensor. This smaller sensor sits on the same plane as the film but because the sensor is

smaller it can "see" a smaller field of view. Now what does this mean? It means that you basically crop the photo to a

smaller area and you loose the information on the edges. So the lens is still the same focal length but you get a

narrower field of view. In order to help explain this you do some quick math and say that your 50mm lens with a 1.6

crop factor is equivalent to an "80mm lenes field of view". So the lens will still act like a 50mm lens exept you are

loosing the edges on the outside.

Now on your camera the view finder is already adjusted and you are only seeing what the camera sensor sees. So you can

frame the shot in the view finder to the edges and you will get the entire thing into the frame. You don't have to

worry when taking a shot that something won't be in frame. The only time you really need to think about a crop factor

is when you are buying a lens because you will want to realize that your camera won't pick up as much in the frame as a full frame.

 

[YesDear]

Yeah! What he said!

 

[photo_chick]

A real life analogy... you have a dinner plate that's the projected image from the lens (one designed for 35mm or full frame). Set a pop tart in the center and that's the crop sensor. The full frame sensor would be a rectangle whose corners touch the edge of the plate (if you have a 12 inch plate it'd be close to a sheet of paper).

Don't get tripped up in the field of view. Those numbers are great for comparison if you switch between full frame and crop. But if you have only ever shot crop knowing that your 50mm looks like an 80mm on a full frame camera really doesn't mean a whole lot. You know what 50mm on your crop body looks like and that's really all you need to know.

I really don't like the focal length equivalents because it gives the idea that the focal length changes. It can get confusing because people tend to think that lenses designed for crop cameras have the crop factor applied to those focal lengths. They don't. 50mm on my 18-55 EF-S (crop only) lens is the same as 50mm on my EF lens. The scale stays the same. The difference is that the crop lens projects a smaller image. To go back to the plate analogy, it's like putting a pop tart on a saucer.

Full frame is still with us, it's only found on the higher end DSLR's right now.

 

[KAT4DISNEY]

The only time you really need to think about a crop factor

is when you are buying a lens because you will want to realize that your camera won't pick up as much in the frame as a full frame.

Or if you own a full frame then you need to be concerned about not purchasing lenses designed for crop sensors or you will limit your full frame.

As photo-chick stated if you've only shot with a crop sensor body then there isn't much of a concern over the focal length because you will have only been used to that field of view.

 

[pixie08]

Well I can try to explain this but I will have to use a little bit of physics. Promise not too hard. The attached

image might help.

Basically as light travels through a lens it is redirected to a single point. Then the light starts to travel outward

at the same angle it came in at until it hits the sensor. That distance it travels after being focused is called the

focal length. In the film days the angle of view (how much you could see in the frame) was based on a 35mm piece of

film on the back. Today it is based on the size of the sensor. There are cameras today that have a 35mm size and give

the same field of view as the older film cameras. (D800 -Nikon, 5D Mark III are examples). These cameras "see" the

same viewpoint from edge to edge as a 35mm film camera. These cameras also are very expensive.

Most cameras come with a crop sensor. This smaller sensor sits on the same plane as the film but because the sensor is

smaller it can "see" a smaller field of view. Now what does this mean? It means that you basically crop the photo to a

smaller area and you loose the information on the edges. So the lens is still the same focal length but you get a

narrower field of view. In order to help explain this you do some quick math and say that your 50mm lens with a 1.6

crop factor is equivalent to an "80mm lenes field of view". So the lens will still act like a 50mm lens exept you are

loosing the edges on the outside.

Now on your camera the view finder is already adjusted and you are only seeing what the camera sensor sees. So you can

frame the shot in the view finder to the edges and you will get the entire thing into the frame. You don't have to

worry when taking a shot that something won't be in frame. The only time you really need to think about a crop factor

is when you are buying a lens because you will want to realize that your camera won't pick up as much in the frame as a full frame.

Thank you ..amazing explanationI am worrying because I am renting a 100-300 L series and so I am thinking this might change the crop, so I guess I will be able to tell through the view finder though?

 

[pixie08]

Or if you own a full frame then you need to be concerned about not purchasing lenses designed for crop sensors or you will limit your full frame.

As photo-chick stated if you've only shot with a crop sensor body then there isn't much of a concern over the focal length because you will have only been used to that field of view.

I have a Canon rebel, I amm pretty sure that is just a crop sensor. Only the higher end D's are full frame right? Does it work in reverse? I am renting a telephot L series for my Alska trip so i don't want to rent the wrong lens.

Thanks for all your help everyone!

 

[disneyboy2003]

Thank you ..amazing explanationI am worrying because I am renting a 100-300 L series and so I am thinking this might change the crop, so I guess I will be able to tell through the view finder though?

I have a Canon rebel, I amm pretty sure that is just a crop sensor. Only the higher end D's are full frame right? Does it work in reverse? I am renting a telephot L series for my Alska trip so i don't want to rent the wrong lens.

Thanks for all your help everyone!

Yes, your Canon Rebel has a crop sensor. The only Canon cameras that have the full-frame sensor are the Canon 5D (the 5D mark III goes for $3499) and the Canon 1D (the Canon 1D mark IV goes for $4999). If you didn't spend that much on your camera, then you probably have a crop sensor camera.

If you're worried about a lens' view on a crop-sensor camera, the ONLY way you can tell a difference in the view is if you've also got a full-sensor camera right next to you to compare. How else are you going to know that the view from your crop-sensor camera is more "zoomed in" than on full-sensor camera, especially if you've never looked through a full-sensor camera before? (I think that's what the previous posts were trying to tell you)

Crop-sensor cameras like your Canon Rebel can take ANY Canon lens, including all EF-S lenses, all EF lenses, and all L lenses (all L lenses are actually EF lenses).

(It is only the full-sensor camera people who can't use EF-S lenses. EF-S lenses are made specifically for crop-sensor cameras.)

Actually, for Alaska, you have an advantage in using a crop-sensor camera because of the "1.6x crop factor", which makes your view appear more "zoomed in" compared to a full-sensor camera. So the 100-300 mm lens that you'll be renting will appear like 160-480 mm on an equivalent full-sensor camera (ie. If someone else were to bring a Canon 5D camera, they would have to have a lens that reaches from 160-480 mm to get images similar to yours). The reason why your crop-sensor camera is an advantage in Alaska is because all the scenery (such as whales, bald eagles, glaciers, etc.) is so far, far away that you can never have "too much zoom" in Alaska.

 

[pixie08]

Yes, your Canon Rebel has a crop sensor. The only Canon cameras that have the full-frame sensor are the Canon 5D (the 5D mark III goes for $3499) and the Canon 1D (the Canon 1D mark IV goes for $4999). If you didn't spend that much on your camera, then you probably have a crop sensor camera.

If you're worried about a lens' view on a crop-sensor camera, the ONLY way you can tell a difference in the view is if you've also got a full-sensor camera right next to you to compare. How else are you going to know that the view from your crop-sensor camera is more "zoomed in" than on full-sensor camera, especially if you've never looked through a full-sensor camera before? (I think that's what the previous posts were trying to tell you)

Crop-sensor cameras like your Canon Rebel can take ANY Canon lens, including all EF-S lenses, all EF lenses, and all L lenses (all L lenses are actually EF lenses).

(It is only the full-sensor camera people who can't use EF-S lenses. EF-S lenses are made specifically for crop-sensor cameras.)

Actually, for Alaska, you have an advantage in using a crop-sensor camera because of the "1.6x crop factor", which makes your view appear more "zoomed in" compared to a full-sensor camera. So the 100-300 mm lens that you'll be renting will appear like 160-480 mm on an equivalent full-sensor camera (ie. If someone else were to bring a Canon 5D camera, they would have to have a lens that reaches from 160-480 mm to get images similar to yours). The reason why your crop-sensor camera is an advantage in Alaska is because all the scenery (such as whales, bald eagles, glaciers, etc.) is so far, far away that you can never have "too much zoom" in Alaska.

thank you. That's what I was wondering. I want to make sure I get the right lens for the job