EF vs EF-S lens focal length conversion

I currently own both APS-C and micro 4/3 cameras. For my purposes, my Panasonic GH1 has a "crop factor" of 1.25

Whilst fully understanding SkipD and richardfox at posts 29 and 30 above, perhaps the answer as to "why", might be found in what might be called the 50mm 'syndrome'.

Half the serious photography world seems to insist that everyone must have a 50mm prime lens (and learn to use it by zooming with their feet).

Well, what many non-full frame owners are thinking is "what you see ("field of view") through your 50mm prime lens on a full frame 35mm equivalent camera is absolutely NOT going to be what I see through my cropped sensor camera" so they start thinking about conversion factors - the first step on the slippery slope....

Just a thought.

phreeky wrote in post #10857967
If you only shoot in one format then you have absolutely no reason to bother trying to figure out what "crop factor" is. Just ignore it, otherwise all you'll do is confuse yourself.

Both my wife and I only shoot with crop bodies.

Rightly or wrongly I used the "crop factor" calculation in buying a new macro lens for my wife, she had read that a focal length of 100mm was a sweet spot, I applied the calc and bought her the Canon 60mm to get 96mm.

When I read about how pictures shown here have been taken if the member is using a FF body and a prime I mentally convert it to "my length", ie what lens would that be on a crop body.

I have frequently found the "crop factor" calculation to be useful & informative despite only using one format

lets try pictures instead of words

any lens is going to create the same image on the sensor area of the camera, the 'crop' factor comes from how much area you have to sample that image.

FSM wrote in post #10853952
Is the listed focal length for an EF lens assuming it is on a full frame camera? And therefore an EF-S and EF lens of the same listed focal length would have differing fields of view on a crop sensor camera?

In a simple answer, no.

50mm is 50mm regardless of whether it's EF-S or EF.

EF-S Lenses are unable to fill a Full Frame sensor with Light from Edge-to-Edge. The reason EF lenses look different on Full Frame cameras vs APS-C is because the size of the sensor is actually smaller... so you get a Cropped image when compared to a Full Frame. It tricks you into thinking you are zoomed in farther but in reality your image is just cropped... you will notice the subject is no bigger on the APS-C, instead the area around him/it is just Cropped more tightly.

Let me get this straight... if I put my EF 75-300 zoom lens on a Canon 300D (22 mm sensor) and max out the zoom at f/300 to fill the frame with a deer, and then... if I still had my Rebel 35mm film camera and used the same lens with the zoom maxed out,... would I see the same deer but surrounded by 1.6 more area around it?

Echeban wrote in post #18904517
Let me get this straight... if I put my EF 75-300 zoom lens on a Canon 300D (22 mm sensor) and max out the zoom at f/300 to fill the frame with a deer, and then... if I still had my Rebel 35mm film camera and used the same lens with the zoom maxed out,... would I see the same deer but surrounded by 1.6 more area around it?

Yup.
If you framed a deer which measured on the sensor of the FF camera and it was 8mm tall (filling 1/3 of the FF frame 24mm height), it would also be 8mm tall on the APS-C 'crop' sensor but fill just over 1/2 of the 15mm tall APS-C frame height.

Echeban wrote in post #18904517
Let me get this straight... if I put my EF 75-300 zoom lens on a Canon 300D (22 mm sensor) and max out the zoom at f/300 to fill the frame with a deer, and then... if I still had my Rebel 35mm film camera and used the same lens with the zoom maxed out,... would I see the same deer but surrounded by 1.6 more area around it?

Oh, the confusion! I shoot 1", apsc, full frame (35mm film), 645, and 6x6. Want some REAL confusion? I am looking at some 4x5 cameras. Astoundingly, they shoot bigger film than 6x6. Whhhhaaaaaaaattt?

The easiest way to remember focal length conversions is to forget about them. My 645 A macro lens is 120mm on my Pentax 645N. I do not care what that is equivalent to in any other format. I know how it behaves on the camera I use it on. What else matters?

Echeban wrote in post #18904517
Let me get this straight... if I put my EF 75-300 zoom lens on a Canon 300D (22 mm sensor) and max out the zoom at f/300 to fill the frame with a deer, and then... if I still had my Rebel 35mm film camera and used the same lens with the zoom maxed out,... would I see the same deer but surrounded by 1.6 more area around it?

Yes. . Of course.

The lens projects an image ..... the camera it is mounted to has no way to change that image; it merely determines how much of that image is captured on media.

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This 'crop-factor' irritation is probably the most confusing issue for DSLR beginners - at least it was for me (and I still have to concentrate not to confuse field of view and focal length). Especially, because buying lenses is the most important gear decision you make....

drmaxx wrote in post #18904783
This 'crop-factor' irritation is probably the most confusing issue for DSLR beginners - at least it was for me (and I still have to concentrate not to confuse field of view and focal length). Especially, because buying lenses is the most important gear decision you make....

It has been stated many times previously...

If you do NOT have extensive experience in shooting the 135 format camera or digital FF with zoom lenses or Fixed Focal Length lens (point of clarification: BOTH of the previous lenses are 'primes' (vs 'supplementary' or 'convertor' lens add-on)
one DOES NOT need to understand the term 'crop factor'.
P&S shooters have unconsciously actually been dealing with the 'crop factor' without even knowing it, when their tiny sensor P&S lens says 'equivalent to 28mm - 105mm' it means that it has a crop factor whic 'gives an equivalent FOV to that FL on 135/FF body'.

The media coined the term when digital sensors could not be built larger than 15mm x 22mm yet you could mount lenses from the FF film SLR. But if you have no frame of reference with no usage of the FF film SLR/digital, it is useless (and confusing) unnecessary jargon.
And 'crop arithmetic' is a useless computational skill to have, if you have no prior experience with any FF camera with interchangeable lenses.

Wilt wrote in post #18905192
It has been stated many times previously...

If you do NOT have extensive experience in shooting the 135 format camera or digital FF with zoom lenses or Fixed Focal Length lens one DOES NOT need to understand the term 'crop factor'.
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There are exceptions to your statement, Wilt.

There are actually many times when someone will talk to another photographer about what lenses are needed to shoot a given scene from a given point; situations when the photographer is not able to change his/her distance to the subject. . Real-life, frequently encountered examples of this would be shooting wildlife from an established permanent blind, or shooting a canyon from a designated overlook with a fence that keeps anyone from getting closer, or photographing the set of a play from the back of the theatre.

Often times, a noobie will see a photo online, want to go to that spot to shoot the same thing and frame it the same way, and contact the photographer who took the shot, and ask, "what lens do I need to take a picture like yours?"

This stuff happens all the time, where noobies ask seasoned photographers about what focal length they need to take a very specific shot from a given location. . When the seasoned photographer replies, saying, "I took that image at 40mm, on a full frame", it will really behoove the noobie to understand what effect sensor size (a.k.a. "crop factor") has on framing. . If the noobie doesn't understand crop factor, then how will he know that he will need to shoot at 25mm when he is using his Canon Rebel to shoot that same scene from the same location? . He won't .... and he could screw up and not be able to frame it the right way because he didn't buy the right lens because he didn't understand crop factor.

Such situations are common and happen with great frequency. . Because so many photographers ask other photographers what focal length is needed to frame something a certain way, it really does behoove people to understand the effect that sensor size will have on the framing of the scene - whether they ever shot film or not.


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Tom Reichner wrote in post #18905208
There are exceptions to your statement, Wilt.

There are actually many times when someone will talk to another photographer about what lenses are needed to shoot a given scene from a given point; situations when the photographer is not able to change his/her distance to the subject. . Real-life, frequently encountered examples of this would be shooting wildlife from an established permanent blind, or shooting a canyon from a designated overlook with a fence that keeps anyone from getting closer, or photographing the set of a play from the back of the theatre.

Often times, a noobie will see a photo online, want to go to that spot to shoot the same thing and frame it the same way, and contact the photographer who took the shot, and ask, "what lens do I need to take a picture like yours?"

This stuff happens all the time, where noobies ask seasoned photographers about what focal length they need to take a very specific shot from a given location. . When the seasoned photographer replies, saying, "I took that image at 40mm, on a full frame", it will really behoove the noobie to understand what effect sensor size (a.k.a. "crop factor") has on framing. . If the noobie doesn't understand crop factor, then how will he know that he will need to shoot at 25mm when he is using his Canon Rebel to shoot that same scene from the same location? . He won't .... and he could screw up and not be able to frame it the right way because he didn't buy the right lens because he didn't understand crop factor.

Such situations are common and happen with great frequency. . Because so many photographers ask other photographers what focal length is needed to frame something a certain way, it really does behoove people to understand the effect that sensor size will have on the framing of the scene - whether they ever shot film or not.

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Except, Tom, when the other photographer says, "(such and such) shot works great with 100mm"...is he referring to the 160mm apparent FL FOV of APS-C, or the use of 100mm on his (unknown to you if it APS-C vs. FF vs. 4/3 format!), or with reference to 100mm on FF without regard to what his camera format is --- in which case, if he thinks an actual engraved FL and not the 'crop equivalent', you still don't have a frame of reference with certainty without a whole lot more conversation for clarification of just what he/she means.

Wilt wrote in post #18905241
Except, Tom, when the other photographer says, "(such and such) shot works great with 100mm"...is he referring to the 160mm apparent FL FOV of APS-C, or the use of 100mm on his (unknown to you if it APS-C vs. FF vs. 4/3 format!), or with reference to 100mm on FF without regard to what his camera format is --- in which case, if he thinks an actual engraved FL and not the 'crop equivalent', you still don't have a frame of reference with certainty without a whole lot more conversation for clarification of just what he/she means.

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You are making my point for me.

This is exactly why noobies need to understand the effect that different sensor sizes have on field of view. . If the noobie has this understanding, then he will know that when the other photographer says, "(such and such) shot works great with 100mm", he will then have to ask, "100mm - with what crop factor?"

Unless, of course, the noobie already knows what body the other photographer shoots with (which he probably does, because photographers always know what bodies their photography buddies are using) ..... in which case he would just do the math to figure out what lens to use on his own body to achieve the same framing.

If someone doesn't understand crop factor and the effects thereof, they will not know to ask this question, and asking the question is imperative in many situations. . Or, they will not know what math to do to figure out the focal length for their body. . In either case, photographers need to understand crop factors in order to properly interpret what other photographers say.

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I feel that if a new shooter asks me what I used to frame a shot, it is upon me to ask what they are shooting with and do the conversion for them, I would say what I am using followed with what they should use to get the equivalent view.

If they ask me why, I would use the simplest explanation I can think of and that would be "Your camera has something like a built in Photoshop crop tool, so we have to use different focal length to get the same view and work around that crop tool."