What is the reason behind the "50mm prime" theory?

adamandbean

Senior Member
Hello, I need some help.
I have a D7000 and want to buy a fast prime. I realise the crop fator of the D7000.
However, why does everyone say" bla bla is equal to a 50mm"?
My question is: why is this 50mm thing so important? Is 50mm better than 75mm for prime lenses? What is wrong with having a prime that with a crop factor is not a true 50mm?

Any help would be appreciated

Adam in Japan
 

480sparky

Senior Member
A 50mm lens is a 50mm lens is a 50mm lens is a 50mm lens.... regardless of the camera it's mounted on. The difference will be the smaller field of view a crop sensor body records. An ASPC body will have the same FOV with a 50mm as a full-frame body does with a 75mm.

50mm primes are, as a general rule, the sharpest lens you can buy. And they don't cost $1000+. Many can be had for the price of a good dinner.
 
50mm Originally when used with a 35mm film camera would give you about the same view or magnification as your eyes do. With the APS-C sensors like you D7000 that 50mm acts more like a 75mm.

Is it important? I personally think to much is made over the issue. Decide what effect you want and what kind of photography you want to do and decide which lens works best for you.
 

480sparky

Senior Member
50mm Originally when used with a 35mm film camera would give you about the same view or magnification as your eyes do. With the APS-C sensors like you D7000 that 50mm acts more like a 75mm.

Is it important? I personally think to much is made over the issue. Decide what effect you want and what kind of photography you want to do and decide which lens works best for you.

And a 50mm on a crop sensor will be the exact same magnification. You only have a narrower field of view. (Imagine looking through the cardboard core of a paper towel roll.... things aren't magnified any, the roll just gives you 'tunnel vision')
 

Michael J.

Senior Member
If you want a view similar to the 50mm on a FX Body go for a 35mm.

BTW. nothing is wrong with any lens you like or want until you think it is wrong for your needs. After the lens is not wrong your choice was wrong. A Review is just a guide to help you to decide. At the end everyone chooses by themselves.
 

JDFlood

Senior Member
Personally, I much prefer a 35mm lens on a full frame. I hear that pro-journalists do also. The extra depth of field... All I know is, I am never going back. For general photography, the equivalent is around 24mm. It makes you get a little closer sometimes, but the result is sharper, more dramatic photos. The 50mm thing was for "Kodak", family oriented pictures. Three heads of relatives or stand back and get five folks in the photo. Not so much for dedicated amatures and pros. Give it a try, 24mm before you commit, sure wished I changed years before I did. JD
 

Rick M

Senior Member
Personally, I much prefer a 35mm lens on a full frame. I hear that pro-journalists do also. The extra depth of field... All I know is, I am never going back. For general photography, the equivalent is around 24mm. It makes you get a little closer sometimes, but the result is sharper, more dramatic photos. The 50mm thing was for "Kodak", family oriented pictures. Three heads of relatives or stand back and get five folks in the photo. Not so much for dedicated amatures and pros. Give it a try, 24mm before you commit, sure wished I changed years before I did. JD

​Which 35 are you using?
 

Sandpatch

Senior Member
And a 50mm on a crop sensor will be the exact same magnification. You only have a narrower field of view. (Imagine looking through the cardboard core of a paper towel roll.... things aren't magnified any, the roll just gives you 'tunnel vision')

Perfectly written -- thank you. After shooting 35mm for 30+ years, it took me a long time to wrap my brain around this concept with my D5100. As you wrote, my smaller D5100 sensor didn't turn my old 50mm into a 75mm telephoto.
 
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adamandbean

Senior Member
That is exactly what I meant! Why do most people say" you should get a 50mm equalivant" I always wondered what the big attraction with the 50mm film thing was.
So many expert users out there so prefer the 35mm...
 

riverside

Senior Member
Hello, I need some help.
I have a D7000 and want to buy a fast prime. I realise the crop fator of the D7000.
However, why does everyone say" bla bla is equal to a 50mm"?
My question is: why is this 50mm thing so important? Is 50mm better than 75mm for prime lenses? What is wrong with having a prime that with a crop factor is not a true 50mm?

Any help would be appreciated

Adam in Japan

Photography vernacular. During the 35mm film era regardless of camera body a 50mm lens was always identified as the "what you see is what you get" lens. And they were (are?) the sharpest piece of glass one could get without selling a child into slavery. I personally enjoy the 35mm 1.8g on my D7000 for indoor low light work but that's just me and my laziness.
 

Rick M

Senior Member
I think if I where shooting Dx, the 28mm 1.8g would be my main prime, or a 24mm as suggested. On Fx, I have rarely used my 50mm and plan to get a 35mm (sigma 1.4). Perhaps I just like the wider perspective a bit more.
 

Horoscope Fish

Senior Member
To my understanding the "normal" focal lengths are so called because they produce natural-looking perspective at moderate shooting distances. What’s normal? By convention, a focal length a bit longer than the diagonal measurement of the film frame or digital sensor. A full-frame (FX) sensor has a diagonal measure of about 43mm, so lenses around 50mm are "normal". For DX sensor cameras, which have a diagonal of about 28mm, a focal length of 35mm is considered "normal".

......
 

480sparky

Senior Member
To my understanding the "normal" focal lengths are so called because they produce natural-looking perspective at moderate shooting distances. What’s normal? By convention, a focal length a bit longer than the diagonal measurement of the film frame or digital sensor. A full-frame (FX) sensor has a diagonal measure of about 43mm, so lenses around 50mm are "normal". For DX sensor cameras, which have a diagonal of about 28mm, a focal length of 35mm is considered "normal".

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The 'perspective' seen by a 50mm on an FX is exactly the same as the 'perspective' seen by a 50mm on a DX.

What is different between a 50 on DX and FX is the field of view.
 

Horoscope Fish

Senior Member
The 'perspective' seen by a 50mm on an FX is exactly the same as the 'perspective' seen by a 50mm on a DX.

What is different between a 50 on DX and FX is the field of view.
Yes. They both give the same natural looking perspective. Field of view is different, perspective is the same.

I don't see what in my previous post contradicts that concept.

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480sparky

Senior Member
Yes. They both give the same natural looking perspective. Field of view is different, perspective is the same.

I don't see what in my previous post contradicts that concept.

......

This:

..........For DX sensor cameras, which have a diagonal of about 28mm, a focal length of 35mm is considered "normal".

......


The perspective of a 35mm on a DX is NOT the same as a 50mm on an FX.
 

Horoscope Fish

Senior Member
The perspective of a 35mm on a DX is NOT the same as a 50mm on an FX.
Depends on how you define 'perspective'. 'Linear perspective' is the size relationship of objects to each other, and so assuming both cameras are at the same position, the linear perspective has not changed. But a different use of the same term 'perspective' is the perception that you and I have as viewers of a photo, and because the smaller format crops off the outer areas of the image, the 'perspective' has changed in this connotation although not in the context of 'linear perspective'.

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Rick M

Senior Member
Wow, nothing like the dissection of a simple discussion. Everyone please make sure you have full grasp of these concepts before stepping in! :)
 
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