Confused about crop sensor vs focal length

[ratssass]

Focal Length = 24mm
Maker Note = 33202 Byte
User Comment =
Subsec Time = 0.90"
Flashpix Version = Version 1.0
Color Space = sRGB
Exif Image Width = 2448
Exif Image Height = 3696
Sensing Method = One-chip color area sensor
File Source = DSC
Scene Type = A directly photographed image
Custom Rendered = Normal process
Exposure Mode = Manual exposure
White Balance = Auto white balance
Digital Zoom Ratio = 1x

Focal Length In 35mm Film = 36mm

....ooooooooooooook,so we've learned that my fx lens on a dx bodyshooting at 24mm does not equate to 36mm.Nor is my FoV changed.Can someone,please,just tell me what exactly is meant by the last line??

 

[o hey tyler]

Focal Length = 24mm
Maker Note = 33202 Byte
User Comment =
Subsec Time = 0.90"
Flashpix Version = Version 1.0
Color Space = sRGB
Exif Image Width = 2448
Exif Image Height = 3696
Sensing Method = One-chip color area sensor
File Source = DSC
Scene Type = A directly photographed image
Custom Rendered = Normal process
Exposure Mode = Manual exposure
White Balance = Auto white balance
Digital Zoom Ratio = 1x

Focal Length In 35mm Film = 36mm

....ooooooooooooook,so we've learned that my fx lens on a dx bodyshooting at 24mm does not equate to 36mm.Nor is my FoV changed.Can someone,please,just tell me what exactly is meant by the last line??

It means that to equate to the same field of view on a full frame camera, that you'd need to be at a 36mm focal length.

 

[ratssass]

whew........thank you so much,Tyler............that 1 question has really been bugging me.

 

[o hey tyler]

whew........thank you so much,Tyler............that 1 question has really been bugging me.

Glad you got it sorted.

 

[bratkinson]

In my opinion, all the 'negativity' towards crop sensor cameras leads anyone that owns one to believe their camera is somehow 'handicapped', or that they won't EVER take good pictures with that camera. Throw in all the numerical calculations with 1.5 or 1.6 affecting the 'focal length' of the lens mounted to it and they can quickly become paranoid about their capabilities as well as their camera.

Perhaps it's better that the term 'crop/cropped sensor' were eliminated from our vocabulary. It really serves little purpose other than to 'sell' someone on a more expensive camera.

Consider the film days of the '50s, '60s and '70s. People had cameras that used many different film sizes. Whether it was size 120, 135, 616, 620, 626, or whatever, the cameras used still faithfully recorded what their lenses 'saw'. Even the Kodak Brownie and Instamatic cameras with their tiny film sizes took pictures acceptable to most of their target markets.

So why the digital 'fixation' on the 35mm film size? Probably more to ease the minds of the photographers during the digital revolution years ('85-'99, roughly) to provide means to focal length conversion. But for anyone new to DSLR photography these days, is there really a need to know (initially) that 'this focal length is good for these types of photos, that focal length is good for those types of photos', and by the way, divide/multiply/add/subract/square root/to the power of everything I just told you by 1.6 because you have a crop body Canon! It's simply zoom in/out until you see what you like in the viewfinder, and take the picture! Who needs all the mental gymnastics!

I'll be completely honest...even though I spent roughly 15 years non-35mm and 20 years in 35mm photography before putting the cameras and gear away for about 12 years, after wearing out Canon G-3 and G-5 Point and Shoots, when I moved up to a used 30D and EF-S 18-135 lens, I had never, EVER, heard the phrase 'crop body'. 8 months and perhaps 5-6,000 shots with the 30D later, even after moving to a new 60D, I -STILL- never heard/thought about/considered that I was shooting with a 'handicapped' crop body! I was very happy with the pictures I was taking and the results were very noticably better than what I had been getting with the Point & Shoots.

Call it my lack of doing 'due diligence' on the web and finding websites like this one that explain the differences in field of view (not focal length!) of cameras with a crop body compared to what I had with 35mm film. But did I care? No. Did the lack of such knowledge cause me to make the 'wrong' purchases? Not in my book. Back in the '50s, my parents cars were either Fords or Chevys. Did I have any clue what the ride in a Cadillac was like? or a Rolls Royce? Of course not. The Fords and Chevys got us from here to there without any difficulty, and provided sufficient comfort to make everyone in the family happy. No different than a crop-body camera taking pictures the same way the 'expensive, luxury' cameras take pictures. One pixel at a time.

 

[spd]

I don't know why we can't just say that on a camera with a crop-sensor (canon 7D for instance), a 17-40mm lens effectively becomes as a 27.2-64mm lens...

Just like my 100-400 'effectively becomes' 160-640 on my 7D, and 320-1280 when i put my 2x converter on...

 

[greybeard35 7]

I think a lot of the confusion has to do with trying to understand 2 formats at the same time. If you shoot crop sensor, know that a lens that will give you a "NORMAL" perspective is around 35mm. A good wide angle perspective can be had around 16-18, extreme around 10-12. On the tele end, 50-55 is a nice short tele great for portraits and 200-300 good for sports-nature. So when selecting a zoom, pick one that encompasses a range that you need.

 

[480sparky41 40]

I don't know why we can't just say that on a camera with a crop-sensor (canon 7D for instance), a 17-40mm lens effectively becomes as a 27.2-64mm lens...

Just like my 100-400 'effectively becomes' 160-640 on my 7D, and 320-1280 when i put my 2x converter on...

That's exactly what we all do..... and that's exactly what causes the confusion.

 

[Robin_Usagani]

Sparky did a good job explaining. This is a simple topic but it is so hard to explain. It is also a very popular topic. I think sparky should rewrite a thread with those images and stick the thread on top.

 

[480sparky41 40]

Another way to look at it:

You're in a darkroom ( you know... the old-fashioned kind with a dim red lamp, stinky chemicals.....), and you put a negative into the enlarger. Run the enlarger up so you can make an 8x10 from the negative. Now, without doing anything to the enlarger, remove the 8x10 paper and put a sheet that's 5x7 in it's place.

Compare the 8x10 with the 5x7 after you're developed the prints. The subjects will be exactly the same size. The 8x10 print represents what a full-frame sensor records, and the 5x7 print represents what the crop sensor records.

 

[Robin_Usagani]

Good explaination but most people who ask this question never seen or operate an enlarger.

Another way to look at it:

You're in a darkroom ( you know... the old-fashioned kind with a dim red lamp, stinky chemicals.....), and you put a negative into the enlarger. Run the enlarger up so you can make an 8x10 from the negative. Now, without doing anything to the enlarger, remove the 8x10 paper and put a sheet that's 5x7 in it's place.

Compare the 8x10 with the 5x7 after you're developed the prints. The subjects will be exactly the same size. The 8x10 print represents what a full-frame sensor records, and the 5x7 print represents what the crop sensor records.

 

[480sparky41 40]

Good explaination but most people who ask this question never seen or operate an enlarger.

Another way to look at it:

You're in a darkroom ( you know... the old-fashioned kind with a dim red lamp, stinky chemicals.....), and you put a negative into the enlarger. Run the enlarger up so you can make an 8x10 from the negative. Now, without doing anything to the enlarger, remove the 8x10 paper and put a sheet that's 5x7 in it's place.

Compare the 8x10 with the 5x7 after you're developed the prints. The subjects will be exactly the same size. The 8x10 print represents what a full-frame sensor records, and the 5x7 print represents what the crop sensor records.

OK, slide projectors and screens.

 

[ratssass]

I know I finally got it through my thick skull,but what was really making it hard to understand (for me) was that 1 line in the EXIF.Just couldn't get my mind wrapped around the explanation until Tyler answered that 1 question for me.

You're in a darkroom ( you know... the old-fashioned kind with a dim red lamp, stinky chemicals.....), and you put a negative into the enlarger. Run the enlarger up so you can make an 8x10 from the negative. Now, without doing anything to the enlarger, remove the 8x10 paper and put a sheet that's 5x7 in it's place.

Compare the 8x10 with the 5x7 after you're developed the prints. The subjects will be exactly the same size. The 8x10 print represents what a full-frame sensor records, and the 5x7 print represents what the crop sensor records

^^^^This analogy works well for my simple mind.Thank you,all!

 

[480sparky41 40]

Now, to explain WHY there's a difference:

Simply put, it's because the sensors are different sizes. I put my D600 (FX/Full Frame) body next to my D7000 (DX/Crop Sensor) on a table. I set both of them to Mirror Up For Cleaning, and took this shot.

As you can see, the D7000 on the right has a physically smaller sensor than the D600 on the left.


A lens has no way of knowing what body (full frame or crop) is behind it. It wouldn't care, either. It will still project the subject(s) the same whether there's a FF or crop sensor (or FF in crop mode) in the camera.

So while a FF body will record this:

A DX body will record this:

Note the difference in the size of the two examples. The FF image is larger because the sensor itself is larger. Also note, the size of the subjects are identical. This is because the lens' focal length didn't change. It projects the subjects the exact same size onto both sensors.

However, we, as humans, tend to think of images as generally the same size. We know how big an 8x10 or 4x5 is, and we make our images fit those dimensions.

So we enlarge the crop sensor image so it matches the dimensions of a FF image. And we end up with a comparison like this:

Full frame:

Crop:

 

[o hey tyler]

I don't know why we can't just say that on a camera with a crop-sensor (canon 7D for instance), a 17-40mm lens effectively becomes as a 27.2-64mm lens...

Just like my 100-400 'effectively becomes' 160-640 on my 7D, and 320-1280 when i put my 2x converter on...

No, your 100-400 is a 100-400, and your 17-40 is a 17-40. It doesn't "effectively" become a different lens. Your field of view is just narrower.