Poll! Your favourite focal length, sensor size and aspect ratio ...

[Guest 560a4aedcb80685284629074497fdc75]

Can someone else chime in too? Even if it's just to confirm that I'm wrong?

[dhessel]

Imagine an infinite horizontal square section hallway, you are in the center of it with a camera watching down the hallway. The lines will converge on a point located at the same hight you are observing and located at an infinite point. You can use what ever focal length you want, they will always converge on the same point,and they will always have the same angle. The only thing that changes it the spatial relationship between points with different distances from the observer along the viewing axis.

 

or just watch this image:

Zooming in, or cropping in would have the same effect.

 

From working in computer graphics for the last 14 years I can tell you that this is absolutely correct. With a pinhole camera changing the focal length is identical to cropping in on an image. Changing the focal length doesn't alter perspective only moving the camera can do that. In real life they are not necessarily identical due to different depth of field characteristics and lens distortion, etc... but for all practical purposes zooming and cropping are identical - hence digital zoom.

 

I find this to be a common misconception about speed boosters to, all they do is brighten the image and "un-crop" the image to a larger image but do not alter the perspective or DOF in anyway. Focal length only affects depth of field, the FOV is the result of the relation ship between the focal length and imaging size but the image itself is identical for all sensor sizes the only difference is how much of the image you see. Perspective is purely defined by the physical location of the camera.

[Nikkor]

The compression you are refering to will be the same as if you were cropping. In the image you can see how the perpendicular lines start getting closer and closer, that's the compression you get out of long lenses, but you could to the same cropping (or having a smaller sensor).

[Inazuma]

It's not about shallower dof.

I know this, but could you explain further with your own interpretation?

[dahlfors]

Matt, if you fill the full frame of your sensor to have the object the same size, then YES, different focal lengths give different field of view:

 

 

But, what gives this effect is only the object distance:

 

If you shoot with a 20mm lens on a camera with insane resolution, like a theoretical 500 Megapixel camera, and then crop in and compare it to a photo shot with a 300mm lens - the field of view of the face of you subject will be exactly the same - as long as you and the camera had the same distance to your photo subject (or object distance as in the figure).

 

So, the key to knowing how the field of view will look for a portrait with a certain lens and sensor (without cropping) - is to know what object distance you need to fill the frame.

[noone]

[Nikkor]

I know this, but could you explain further with your own interpretation?

Whoa yea supa dupa dof.

[Guest 560a4aedcb80685284629074497fdc75]

I suppose what I meant to say is that I have a favourite angle of view (the angle of view that a 35mm lens on 35mm film gives or 17mm on m43). After that it's only the DOF that differs; but that's aperture dependent. Would I prefer the same angle of view but on FF for shallower DOF? Yes. Not totally sure if that's relevent to the poll though

 

Apologies for last reply to this ... starting to think I need to understand lens science a bit better  :unsure:

[Guest 560a4aedcb80685284629074497fdc75]

Matt that's not right, there might be some distortion differences between focal lengths, but the perspective/compression only depends on the distance between the observer and the object. That's the way conical projections work. That's not an opinion, it's a fact.

A 25mm on m43 gives the same perspective/compression as a 50mm on FullFrame. The 25mm probably will have more distortions but that's because the m43 and c mount lenses usually have bad designs.

And don't trust nofilmschool, it's a place full of half-knowledge designed for advertising and sponsoring income.

 

But, what gives this effect is only the object distance:

 

If you shoot with a 20mm lens on a camera with insane resolution, like a theoretical 500 Megapixel camera, and then crop in and compare it to a photo shot with a 300mm lens - the field of view of the face of you subject will be exactly the same - as long as you and the camera had the same distance to your photo subject (or object distance as in the figure).

 

So, the key to knowing how the field of view will look for a portrait with a certain lens and sensor (without cropping) - is to know what object distance you need to fill the frame.

 

OK guys thanks for this. I understand now. I feel slightly embarrassed but mostly glad to have learned something new. I clearly need to dedicate more time to aspects of filmmaking other than camera fetishism.  :rolleyes:

 

Apologies to Sebastian. I stand corrected.

[Guest 560a4aedcb80685284629074497fdc75]

So does flange distance affect anything related to focal length and sensor size? Is there any difference putting an MFT 25mm 1.4 lens straight on a GH4 to putting a 25mm 1.4 full frame lens with an adapter? 

 

This may seem like a stupid question ...

[Nikkor]

They will be very similar, but they are different lenses so they won't be the same. The Fullframe lens will be bigger for shure ;)

Flange distance only affects the way the lens has to be built. The 24mm SLR lens will be a retrofocus design, the mft lens might be a simetric design. The problem with non-retrofocus wideangles is that they aren't very telecentric (the rays that hit the sensor in the corners do it with a very small angle -angle between the ray and the sensor plane-) and this gives color shifts because light jumps from one pixel to another, but a 25mm lens on mft is a normal lens so it's ok. 

On the other hand a simetric design is easier to correct (so it's easier to make fast lenses), and in the case of wideangles it's much smaller in size. (leica m and mamiya 7 lenses are extremely good)

[ken]

IMO, if only say focus length without related to sensor's size, there is no meanings.  Like some one measuring distance to compare by using different rulers, one metric system, and other imperial system.   

[Inazuma]

I will give you an explanation which is a little bit funny, so take it easy ;)

 

...

What's your point exactly? You said that it's not about the DOF but then you go on to explain how its all about the DOF :p

[Nikkor]

What's your point exactly? You said that it's not about the DOF but then you go on to explain how its all about the DOF :p

I said its not about shallover dof.

[Inazuma]

But background separation is caused by shallow dof...

[Nikkor]

Shure man.

[Guest Ebrahim Saadawi]

So does flange distance affect anything related to focal length and sensor size? Is there any difference putting an MFT 25mm 1.4 lens straight on a GH4 to putting a 25mm 1.4 full frame lens with an adapter?

This may seem like a stupid question ...

Don't know what you mean by the flange distance point, but each lens projects the image to a specific plane behind the rear element (the sensor), basically the sensor needs to be at a specific distance from the lens, so a lens that projects the image far away (a 25mm EF FF) if mounted on a m43s body will project the image behind the sensor, because it's too close, therefore you need to put the lens farther away from the sensor by using an adapter. In that case the: Distance between the m43s sensor and m43s mount + the adapter length = the distance between the EF sensor and EF mount, so it focuses correctly. This is only about getting correct focus though, if the lens is too far you will focus on closer subjects (macro effect) but lose the ability to focus on farther subjects towards infinity.

About the 25mm ff and m43s, Imagine you have a sqaure drawing on the wall, you have two lights, one small that only covers that square percisely, and one large that covers the square and a large area of the wall outside the square.

When you use either lights the square is covered with the exact same amount of light and is happy, when using the bigger light the bigger light's output outside the sqaure is wasted. But if you use a big sqaure as big as the large light, it will benefit from that larger covering area and will not be filled with the smaller light at all.

Designing a light that covers that larger area requires a bigger construction, more expensive, more complicated, while designing one that covers a small square makes the light smaller and cheaper.

-Now, you can get a piece of glass and put it in front of the large light, this piece of glass gathers the big light circle and concentrates it onto the small sqaure, so non of it is wasted out side. This is the speedbooster.

The small sensor in that case with a SB sees the exact same amount of light/image/information as a larger sensor. And if a manufacturer made that lens they would call it a 12.5mm f1.0 m43s lens, because it only covers m43s now. That's why I don't buy the small size advantage of m43s, it's just they don't make lenses fast as the ff ones. For example a 12-35mm 2.8 equals a 24-70mm 5.6 ff lens, which would be just as small as the m43s 12-35mm 2.8. And if you want the equivalent to a 24-70mm 2.8 in m43s you'd need a 12-35mm 1.4 lens, which again would be just as big as the 24-70m 2.8 ff (proof is that lens does exist when you put a 24-70mm 2.8 + SB).

[Guest Ebrahim Saadawi]

It's no surprise the winners are s35 and fullframe 50/50% and 35mm/50mm 50/50%

What I find interesting is the love for anamorphic aspect ratio.

[andy lee]

40mm lens

s35mm apsc

 

2.40 aspect ratio spherical lenses (non anamorphic)

[Guest 560a4aedcb80685284629074497fdc75]

Don't know what you mean by the flange distance point, but each lens projects the image to a specific plane behind the rear element (the sensor), basically the sensor needs to be at a specific distance from the lens, so a lens that projects the image far away (a 25mm EF FF) if mounted on a m43s body will project the image behind the sensor, because it's too close, therefore you need to put the lens farther away from the sensor by using an adapter. In that case the: Distance between the m43s sensor and m43s mount + the adapter length = the distance between the EF sensor and EF mount, so it focuses correctly. This is only about getting correct focus though, if the lens is too far you will focus on closer subjects (macro effect) but lose the ability to focus on farther subjects towards infinity.

About the 25mm ff and m43s, Imagine you have a sqaure drawing on the wall, you have two lights, one small that only covers that square percisely, and one large that covers the square and a large area of the wall outside the square.

When you use either lights the square is covered with the exact same amount of light and is happy, when using the bigger light the bigger light's output outside the sqaure is wasted. But if you use a big sqaure as big as the large light, it will benefit from that larger covering area and will not be filled with the smaller light at all.

Designing a light that covers that larger area requires a bigger construction, more expensive, more complicated, while designing one that covers a small square makes the light smaller and cheaper.

-Now, you can get a piece of glass and put it in front of the large light, this piece of glass gathers the big light circle and concentrates it onto the small sqaure, so non of it is wasted out side. This is the speedbooster.

The small sensor in that case with a SB sees the exact same amount of light/image/information as a larger sensor. And if a manufacturer made that lens they would call it a 12.5mm f1.0 m43s lens, because it only covers m43s now. That's why I don't buy the small size advantage of m43s, it's just they don't make lenses fast as the ff ones. For example a 12-35mm 2.8 equals a 24-70mm 5.6 ff lens, which would be just as small as the m43s 12-35mm 2.8. And if you want the equivalent to a 24-70mm 2.8 in m43s you'd need a 12-35mm 1.4 lens, which again would be just as big as the 24-70m 2.8 ff (proof is that lens does exist when you put a 24-70mm 2.8 + SB).

 

Good analogies. Thanks. 

 

I'm enjoying using my small Nikkor AI-s primes (all 52mm filter thread) on the GH4 (with the 0.71 speed booster) a lot. They are small and short enough to look and feel 'right' on the GH4, but have the advantage of all having a fast f-stop, particularly with the speed booster. All of my lenses, from 11mm to 105mm are f2 or below with the speed booster. And apart from the Tokina 11-16 none of them are any bigger than the larger MFT lenses.