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Thread started 22 Apr 2017 (Saturday) 16:34
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What is the focal length of my 300mm f2.8 on my 7D?

 
Dan ­ of ­ Troy
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Apr 22, 2017 16:34 |  #1

First off, I am a newbie so be kind.

Here is exactly what I mean by the above title: I was shooting a high school baseball game yesterday with a Canon EF 300 mm 1:2.8 L IS USM lens on a Canon 7D.

My friend shoots Nikon, and while I do not know the exact model, he had a 300mm 2.8 lens on a Nikon full-frame sensor body.

I complained that from our location I was too tight on focusing on the action at second base, and he said that was because I was using a crop sensor instead of a full frame sensor.

I looked through his viewfinder and he saw much of the area around the second base bag than I did. My viewfinder was noticeably tighter than his. We both had 300mm lenses, but my magnification was greater.

He said that I was shooting closer to 500. I have read threads on other posts that has it estimated at 480mm.

First of all I hope to own a full frame body one day, and that is my goal, but is this accurate?

Does a 7D crop sensor with a 300mm 2.8 have greater focal length than any camera body with a full frame sensor.

Thanks,

Dan of Troy




  
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Wilt
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Post edited over 1 year ago by Wilt. (7 edits in all)
     
Apr 22, 2017 16:40 |  #2

The focal length of the 300mm f/2.8 on your 7D is 300mm.

The Field of View is the only thing that changes (we'll simplify by ignoring the DOF difference seen in an 8x10 from your 7D vs. a 6D). The crop factor multiplier arithmetic only says

"100mm on APS-C is like using 160mm on FF" (100 * 1.6 = 160)

Your 7D (approx) 15mm x 22.5mm sensor is 1/1.6 the size of the 24mm x 36mm sensor of a 6D, and for that reason it only captures 1/1.6 % of the horizontal and the vertical dimensions captured by the larger sensor. This point is illustrated with this

IMAGE: http://i69.photobucket.com/albums/i63/wiltonw/cropvFF_Imagecircle.jpg

in which the whitish rectangle represents the smaller 15 x 22.5mm sensor of the APS-C camera

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Left ­ Handed ­ Brisket
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Apr 22, 2017 16:40 |  #3

The focal length and characteristics associated with that focal length are the same on all cameras.

However, the area that the sensor captures is smaller with crop cameras. Multiply the focal length by 1.6 to get the equivalent angle of view a full frame body would need in mm to see the same cropping in the final image.


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Apr 22, 2017 16:42 |  #4

Argh! Beat by 14 seconds!

;)


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johnf3f
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Post edited over 1 year ago by johnf3f.
     
Apr 22, 2017 16:56 |  #5

It can be a little confusing!

Basically a 300mm lens is a 300mm lens full stop. Changing the size of the sensor (film) will alter the field of view - but not the focal length. Most comparisons are given relative to 135 (35mm film or full frame digital) format these days.

In you case the sensor on the 7D is smaller than your friends Nikon Full Frame camera. Therefore you are only recording part of the image that the lens projects - this is often called the "Crop Factor". In your case this is 1.6, so with a 300mm lens your sensor "sees" the same field/angle of view that a 480mm (300 x 1.6 = 480) lens would do on a full frame camera. This makes you lens appear longer - but it isn't!

To get a rough equivalent of your friend's 300mm on full frame you would need around 200mm to get a similar field of view.

Hope that lot makes some sense!

P.S. there are differences in the Depth of Field too but I didn't know if you wanted to go into that.

PPS! Went to make a cuppa:-P


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Wilt
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Apr 22, 2017 17:10 |  #6

Left Handed Brisket wrote in post #18335149 (external link)
Argh! Beat by 14 seconds!

;)

I can delete that post, and then re-post, if you wannabefirst!


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Apr 22, 2017 17:21 as a reply to  @ Wilt's post |  #7

If you both delete then I can be first:twisted:


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sploo
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Apr 22, 2017 17:50 |  #8

Dan of Troy wrote in post #18335143 (external link)
First off, I am a newbie so be kind.

Here is exactly what I mean by the above title: I was shooting a high school baseball game yesterday with a Canon EF 300 mm 1:2.8 L IS USM lens on a Canon 7D.

My friend shoots Nikon, and while I do not know the exact model, he had a 300mm 2.8 lens on a Nikon full-frame sensor body.

I complained that from our location I was too tight on focusing on the action at second base, and he said that was because I was using a crop sensor instead of a full frame sensor.

I looked through his viewfinder and he saw much of the area around the second base bag than I did. My viewfinder was noticeably tighter than his. We both had 300mm lenses, but my magnification was greater.

He said that I was shooting closer to 500. I have read threads on other posts that has it estimated at 480mm.

First of all I hope to own a full frame body one day, and that is my goal, but is this accurate?

Does a 7D crop sensor with a 300mm 2.8 have greater focal length than any camera body with a full frame sensor.

Thanks,

Dan of Troy

Wilt's post is excellent and right on the money.

One other way to put it - Imagine you put a lens on a tripod (lens attached to the tripod using a tripod ring, so it's fixed in place) and then mounted a Canon APS-C body (like your 7D) and took a shot, and then a full frame body and took a shot (same settings for both cameras).

If you took the full frame photo into an image editing app and cropped a section out of the middle of the photo that was ~1.6x smaller in both width and height... you should have an identical shot to the image taken on the APS-C body (ignoring resolution differences).

This also explains the point of EF-S lenses - they can be physically smaller because they don't need to project an image circle large enough to cover an entire full frame sensor (only the smaller crop sensor). Conversely, using an EF lens on a crop body "wastes" some of that projected image circle, as the sensor never "sees" it.


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Apr 22, 2017 17:55 |  #9

The 300mm lens has a focal length of 300mm even when it is not on a camera.


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Wilt
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Apr 22, 2017 18:20 |  #10

sploo wrote in post #18335219 (external link)
This also explains the point of EF-S lenses - they can be physically smaller because they don't need to project an image circle large enough to cover an entire full frame sensor (only the smaller crop sensor). Conversely, using an EF lens on a crop body "wastes" some of that projected image circle, as the sensor never "sees" it.


...the EF-S lens image circle is depicted via the red circle of my earlier illustration


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lowrider
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Apr 22, 2017 20:58 |  #11

Look here:

https://www.bhphotovid​eo.com …understanding-crop-factor (external link)

Lou




  
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John ­ from ­ PA
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Apr 22, 2017 21:29 |  #12

Go to https://www.learn.usa.​canon.com …tors/fov-comparator.shtml (external link) and "play" with two Canons. To simulate the Nikon, use a 5DIII as it to is full frame.




  
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Dan ­ of ­ Troy
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Apr 23, 2017 09:14 |  #13

Thanks to everyone for your great input. It is very much appreciated.

Dan




  
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MikeWa
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Apr 27, 2017 16:30 |  #14

300 X 1.6 = 480. With a 300mm lens the 7D provides a field of view equivalent to 480mm on a full frame camera. Many, including me, consider this an advantage since it is cheaper to buy a 300mm lens than a 500mm lens.

Mike


Mike...G9; 7D; 7D Mark II; EF-S 10-22mm; EF-S 18-135mm IS STM; EF 28-300mm F3.5-5.6L; EF 70-300mm IS USM; EF 70-200mm F2.8L IS-II; EF 100-400mm f4.5-5.6L IS; EXT 1.4-II & 2.0-III; The more I learn the less I know.

  
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sploo
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Apr 27, 2017 17:51 |  #15

MikeWa wrote in post #18340330 (external link)
300 X 1.6 = 480. With a 300mm lens the 7D provides a field of view equivalent to 480mm on a full frame camera. Many, including me, consider this an advantage since it is cheaper to buy a 300mm lens than a 500mm lens.

Mike

That's true, but the earlier replies in this thread focused (no pun intended) on the fact that it's still a 300mm lens, and still projects the same image.

For example, if you shot a 300mm lens on a 50MP 5DS and then took a 1.6x crop out of the middle of the captured image you'd have a ~19.5MP image with the effective 480mm field of view. It just happens that the pixel density of the 5DS is similar to that of many crop bodies, so a 1.6x crop from a 5DS shot is almost exactly what you'd get from a crop sensor (same sensor area, and about the same number of pixels).

It's still a 300mm lens though ;-)a


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What is the focal length of my 300mm f2.8 on my 7D?
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