Using a full frame lens on APS-C body - what crop factors apply?

Started Jun 4, 2016 | Discussions
Brajesh Forum Member • Posts: 67
Using a full frame lens on APS-C body - what crop factors apply?

Hi guys,

Since the e-mount is physically the same on the A6xxx and the A7, I was wondering if the crop factors still apply if I use an e-mount full frame lens on my A6000 APS-C body.

FOR EXAMPLE:

If I were to take the sony full frame e-mount 50mm f1.8 lens and put it on my A6000 body, would it become

A 75mm f2.7 ?

Or a 75mm f1.8?

Or stay as a 50mm f1.8?

Or something else?

Sony a6000 Sony a7 Sony FE 50mm F1.8
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RealCereal Contributing Member • Posts: 538
Re: Using a full frame lens on APS-C body - what crop factors apply?
1

Brajesh wrote:

Hi guys,

Since the e-mount is physically the same on the A6xxx and the A7, I was wondering if the crop factors still apply if I use an e-mount full frame lens on my A6000 APS-C body.

FOR EXAMPLE:

If I were to take the sony full frame e-mount 50mm f1.8 lens and put it on my A6000 body, would it become

A 75mm f2.7 ?

no

Or a 75mm f1.8?

yes

Or stay as a 50mm f1.8?

no

Or something else?

Focal length will change because the smaller sensor, but will yield slightly better IQ depending on the lens. hope this helps

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Pixel Pooper Veteran Member • Posts: 3,978
Re: Using a full frame lens on APS-C body - what crop factors apply?
3

The lens will still be a 50mm f/1.8 on APS-C, which is equivalent to a 75mm f/2.8 on full frame. The mount, and the fact that it's a full frame lens have no bearing on this. The aperture and focal length are the same as a 50mm f/1.8 APS-C lens.

talkinghorse
talkinghorse Contributing Member • Posts: 604
Re: Using a full frame lens on APS-C body - what crop factors apply?
9

focal length is a function of the lens - it has nothing to do with what camera the lens was made for or the size of the sensor.

ALL 50mm lenses on an APSc camera will have the field of view that a 75mm lens would have on a full frame 35mm camera

this is not because of the lens, it is because the smaller sensor cant see the larger area that a 35mm sensor would see

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Mr. Ed

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Sympa Senior Member • Posts: 2,600
Re: Using a full frame lens on APS-C body - what crop factors apply?
9

Please, this is confusing.

Lenses do not 'become' different lenses.

A 50 mm FE lens will give the same results as a 50 MM E lens on the A6000. Because the focal length is and stays 50 mm.

And while a 50 mm lens on an A7 is a 'normal' focal length, on a crop sensor it is used more as a portrait lens and is too narrow for most general use.

How you should use the 'crop factor' is like this: "hmm, I always use an 19 mm focal length for this on my A6000. When I want to do the same with the A7, I'll get a 19 mm * 1.5 = 27 mm lens".

Or the other way around: "I used to enjoy the 28 - 80 kit zoom on my film SLR. Now I am getting an A6000. Let's see... 28 / 1.5 = 19 mm, and 80 / 1.5 = 53 mm. So, a 19 - 53 mm zoom is what I need to replace it on the A6000."

The focal length on the lens stays the same; it is a physical property of the lens. In combination with the sensor size of the camera it determines how wide the field of view of the lens + camera is.

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Sympa Senior Member • Posts: 2,600
Re: Using a full frame lens on APS-C body - what crop factors apply?

I saw you also had a question about aperture. The aperture is again a physical property of the lens. A 50 mm f/2 lens has an "entrance pupil" (the size of the lens actually doing the work) of 50 / 2 = 25 mm diameter. Of course, that stays the same no matter what camera you put the lens on.

People generally agree that a bigger sensor means less depth of field and better low light results for the same aperture lens. Which is true.

One can also do a calculation and come to on an 'equivalent' aperture.

But if you have experience with for example the A6000, and for example you like a 23 mm focal length @ f/4, you can get any 23 mm focal length that can be set to f/4. No matter it was meant for APS-C or for full frame.

Only if you are comparing systems (lens plus camera) it makes sense to do the calculations:

"How would the Sigma 18-35 mm f/1.8 on an APS-C camera compare to a full frame setup?" and the answer is then "It is like a 27-53 mm f/2.7 on full frame, for focal length, sensitivity, depth of field and image noise". Which means really identical in these aspects for the same year of sensor crop.

But I just have an A6000. And I think about 16 mm as a nice focal length for the zoom to start. And never apply a crop factor when thinking about it. Not for native lenses and neither for adapted lenses.

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Vermont3133
Vermont3133 Senior Member • Posts: 1,082
Re: Using a full frame lens on APS-C body - what crop factors apply?

This 'crop factor' thing is the first thing a new APS-C user stumbles on.....and then get progressively more confused after that.

It's something you just don't need to know!!.....unless someone is moving to full frame after a stint with APS-C bodies....or vice versa...in which case most experienced people would be able to do the conversion in their head without even thinking about it.

If a new APS-C user puts on a 50mm lens and looks through the viewfinder they know instantly what a 50mm lens does.......and also have a fair idea what a 24mm or a 100mm lens will do also.

The only other thing to remember is that 50mm means 50mm....regardless of the body.

Endless talk of 'crop factor' wont help one iota.

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fip Regular Member • Posts: 244
Re: Using a full frame lens on APS-C body - what crop factors apply?
2

The smaller size of the APS-C-sensor covers a smaller area of the whole picture a lens actually provides  than the full-format-sensor.

In this sketch you can take the red part of the picture as a full-frame-sensor ("Sensor A) which shows 13 sections of the black/yellow line.

The APS-C-sensor only sees the blue part with 5 sections of the black/yellow line ("Sensor B") of the same picture provided by the same lens with the same distance to the object because it is smaller.

"Sensor C" is representing the larger medium-format-camera we can ignore here.

So it's all about the mapping on the sensors area.

cplunk Senior Member • Posts: 1,834
Re: Using a full frame lens on APS-C body - what crop factors apply?

Brajesh wrote:

Hi guys,

Since the e-mount is physically the same on the A6xxx and the A7, I was wondering if the crop factors still apply if I use an e-mount full frame lens on my A6000 APS-C body.

FOR EXAMPLE:

If I were to take the sony full frame e-mount 50mm f1.8 lens and put it on my A6000 body, would it become

A 75mm f2.7 ?

Or a 75mm f1.8?

Or stay as a 50mm f1.8?

Or something else?

The crop factor is based on the size of the sensor in the camera body, and is the ratio of the sensor size vs. a the size of a 35mm film frame. A7 has a "full frame" sensor, same size as 35mm film. A6xxx (and A5xxx and all the NEX) have a small sensor, crop factor is 1.5.

This does not change the measurement of the lens focal length. So the FE 50mm f1.8 lens is the same focal length and aperture as the older APS-C 50mm f1.8, and would have the same view and aperture on the A6xxx. On the A7, the APS-C lens would likely vignette on the areas of the sensor that are larger than the APS-C sensor the lens was designed for. But, they are the same focal length. (and the APS-C lens has OSS, I think, unlike the new FE lens?)

The smaller sensor effects the width of the view, amount of light collected and depth of field. And these are changed the same amount regardless of the APS-C design or FE full frame design of the lens.  This is due to the different sensor size. So these changes will be the same between the FE 50 mm f1.8 and the APS-C 50 mm f1.8.

The view that you would be framing, standing in the same place, looking at the same subject, an Axxx with a 50mm lens (ANY 50mm lens) would be about the same as being in the same place looking at the same thing with an A7 using a 75mm lens.  This is what the "crop factor" tells you. Some people get awful hung up on this, but with so many people coming into photography these days that have never used film or a full frame camera, APS-C is more of "the standard", and telling them what focal length would be comparable for full frame, I don't see the point....

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Tannguyen
Tannguyen Regular Member • Posts: 135
Re: Using a full frame lens on APS-C body - what crop factors apply?

cplunk wrote:

The view that you would be framing, standing in the same place, looking at the same subject, an Axxx with a 50mm lens (ANY 50mm lens) would be about the same as being in the same place looking at the same thing with an A7 using a 75mm lens. This is what the "crop factor" tells you. Some people get awful hung up on this, but with so many people coming into photography these days that have never used film or a full frame camera, APS-C is more of "the standard", and telling them what focal length would be comparable for full frame, I don't see the point....

in this example, regarded to DOF, the 50f/1.8 on a6000 will give the same DOF as 75f/2.7 on a7?

if so, with CZ35f/1.4 on A7, in the very same condition, if you want to have the exact same frame and DOF with A6000, you will need an 24f/1.0?

thank you.

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OP Brajesh Forum Member • Posts: 67
Re: Using a full frame lens on APS-C body - what crop factors apply?

Hi everyone,

I received a lot of very detailed replies but I'm still confused reading through them.  I'm grateful for everyone trying to explain things to me, but would anyone just be able to tell me very simply what equivalent lens would the FE 50/1.8 become on the A6000?

thank you

talkinghorse
talkinghorse Contributing Member • Posts: 604
Re: Using a full frame lens on APS-C body - what crop factors apply?
1

Brajesh wrote:

Hi everyone,

I received a lot of very detailed replies but I'm still confused reading through them. I'm grateful for everyone trying to explain things to me, but would anyone just be able to tell me very simply what equivalent lens would the FE 50/1.8 become on the A6000?

thank you

its simple - the field of view (the magnification so to speak) of a 50mm lens on your a6000 will be equal to a 75mm lens on a standard 35mm camera

with any lens you use on your A6000 if you want to know how it would compare to what you used back in the day on 35mm you simply multiply by 1.5

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Mr. Ed

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Vermont3133
Vermont3133 Senior Member • Posts: 1,082
Re: Using a full frame lens on APS-C body - what crop factors apply?

Brajesh wrote:

Hi everyone,

I received a lot of very detailed replies but I'm still confused reading through them. I'm grateful for everyone trying to explain things to me, but would anyone just be able to tell me very simply what equivalent lens would the FE 50/1.8 become on the A6000?

thank you

I'm just curious [and with reference to my above post].....why  is it important to you?

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cplunk Senior Member • Posts: 1,834
Re: Using a full frame lens on APS-C body - what crop factors apply?

Brajesh wrote:

Hi everyone,

I received a lot of very detailed replies but I'm still confused reading through them. I'm grateful for everyone trying to explain things to me, but would anyone just be able to tell me very simply what equivalent lens would the FE 50/1.8 become on the A6000?

thank you

Equivalent to what?

Typically, with various size sensors in digital camera's they express an equivalence to the "view" of a certain focal length on a 35mm film size sensor, helping people understand if it's wide angle or telephoto, and to what degree.   And usually give a drop factor for you to do the math yourself.  A6000 has a 1.5x crop factor, so a 50mm lens would have the 35mm "equivalence" of a 75mm lens.  A short telephoto.

If you want to compare with other APS-C E mount lenses, 50mm f1.8 is 50mm f1.8, same 50mm and same f1.8 as the Sony lens that has been available in E mount for years. Nothing about the mount (which is actually the same) or the designed image circle size changes the method of measuring the focal length, they both have a 75mm "35mm equivalance".

I'm sure there is some math to help you determine the difference in aperture to give similar DOF, and am sure it's more complicated than multiplying the crop factor.

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blue_skies
blue_skies Forum Pro • Posts: 12,208
Re: Using a full frame lens on APS-C body - what crop factors apply?

Brajesh wrote:

Hi guys,

Since the e-mount is physically the same on the A6xxx and the A7, I was wondering if the crop factors still apply if I use an e-mount full frame lens on my A6000 APS-C body.

FOR EXAMPLE:

If I were to take the sony full frame e-mount 50mm f1.8 lens and put it on my A6000 body, would it become

A 75mm f2.7 ?

Or a 75mm f1.8?

Or stay as a 50mm f1.8?

Or something else?

Crop factor relects the sensor crop ratio wrt/ Full Frame sensors, e.g. 1.5x for APS-C, 2.0 for MFT, and so on.

Lenses do not change focal length. The only thing that the crop factor highlights is the change in FOV (or crop).

So, an 50mm lens on APS-C yields the same FOV as a 75mm on FF.

As to exposure, then you have to take the relative sensor size into account, look for equivalence. Read e.g. http://www.dpreview.com/articles/2666934640/what-is-equivalence-and-why-should-i-care

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Cheers,
Henry

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S. Miller Senior Member • Posts: 1,088
Re: Using a full frame lens on APS-C body - what crop factors apply?
3

Brajesh wrote:

Hi everyone,

I received a lot of very detailed replies but I'm still confused reading through them. I'm grateful for everyone trying to explain things to me, but would anyone just be able to tell me very simply what equivalent lens would the FE 50/1.8 become on the A6000?

thank you

I've read the replies and understand why you might be confused. Here's the simplest way I can explain it. When you use the FE 50/1.8 lens on the A6000:

  • The field of view will appear to you as being equivalent to a 75 mm lens on a FF body...i.e. it increased by a factor of 1.5x
  • The aperture doesn't change and it will still allow you to shoot at f/1.8 (good for low light situations)
  • The DOF will be the equivalent depth of field that you would see if you had an f/2.7 aperture 75mm lens on a FF body...i.e. it increased by a factor of 1.5x

In summary, you'll feel like you have a 50% longer lens that let's in the same amount of light (not technically, but for your purposes, yes), and greater depth of field.

Steve

P.S. You have unknowingly asked the most hotly debated question on DPR forums...equivalence.

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SeanTXK Regular Member • Posts: 338
Re: Using a full frame lens on APS-C body - what crop factors apply?

Brajesh wrote:

Hi everyone,

I received a lot of very detailed replies but I'm still confused reading through them. I'm grateful for everyone trying to explain things to me, but would anyone just be able to tell me very simply what equivalent lens would the FE 50/1.8 become on the A6000?

thank you

If you put an FE 50mm f/1.8 lens on an A6000, it will act just like an E-mount 50mm f/1.8 lens would. Nothing changes. If you already have an A6000 and an E-mount "SEL50f18" and let's say that taking a picture of a nearby lamp:

A. Gives you an image with the entire lamp from base to shade in the frame.

B. The lamp is in focus while the bookcase behind it is out of focus by "X" amount.

... And you borrow your friends FE-mount 50mm f/1.8 lens and take the same picture...

It will look the same.

Same magnification, same depth of field. Same amount of out of focus background.

The complication is when people want to jump between sensor size formats, (like going from 35mm film or digital full-frame to crop-sensor or vice versa). AND they want to re-use their old lenses. What happens then is that the images produced are different from what they expected.

A 50mm f/1.8 lens (regardless of FE or E installed on an A6000 will produce an image that...

...(when compared to full frame) appears to be cropped by 1.5x or put another way, looks like it was taken with a 75mm lens on full-frame. This is where equivalency is used.

Equivalency is also used with some classic rule-of-thumb equations for photography, like "handheld shutter speeds should not drop below focal length" or "star trails will be visible if your shutter speed multiplied by focal length equals a number above 500" and so on.

In other words, unless you want to reuse lenses between cameras of different sensor sizes or want to use older rule of thumb equations, this is all a non-issue.

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virgil1612 Regular Member • Posts: 485
Re: Using a full frame lens on APS-C body - what crop factors apply?
2

Brajesh wrote:

Hi everyone,

I received a lot of very detailed replies but I'm still confused reading through them. I'm grateful for everyone trying to explain things to me, but would anyone just be able to tell me very simply what equivalent lens would the FE 50/1.8 become on the A6000?

thank you

1. The field of view (what you actually see looking through the eyepiece) will be equivalent to 75mm FF.

2. The light gathering power (determining exposure) will be the same, f/1.8

3. The depth of field will be equivalent to approx. f/2.8 FF.

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Ionlab Regular Member • Posts: 111
Re: Using a full frame lens on APS-C body - what crop factors apply?

This was my exact first or second post.

A lens does not "become" anything by moving it around ff or apsc.

this means that a ff 50mm/f2 lens is still a 50mm/2 lens either on apsc or FF.

So you can select any lens vintage, canon, nikon and use it on your camera and compare the mm and aperture with other lenses.

The only thing that you have to remember is that the FOV changes when mounting the same lens on a apsc or ff. This means that "in order to get the same FOV" = make a specific building fit in your frame from the same spot then you need to mount a lens that is 1,5 times longer on the Ff camera. So if you use an apsc camera and a friend of yours with a ff camera sits in the same place in order to get the same things in the frame you use a 50mm lens and your friend uses a 75mm lens.

Then there is a thing called dof which is determined by the aperture. As before in order to get the same dof with your friend that sits in the same spot and uses the ff camera you When you take a picture say you use 50mm/2. You friend has to use a 75mm lens and set his aperture at 3. Now from the same spot you and your friend would have taken the same picture (ss same).

Buuuut still there is iso equivalence to be accounted for. This is iso * crop factor ^2

so finally we have our maths correct and can now say that from the same spot a picture taken with a 50mm f4 iso 200 m43 camera (crop factor 2) will be equivalent to a

100mm f8 iso 800 ff camera using the same ss.

So equivalence is only useful when switching cameras. For all other purposes a 50mm/2 lens is a 50mm/2 lens....ie better in low light than a 50mm/4 lens.....narrower than a 35mm/2 lens etc....regardless of whether you can mount them on a ff or apsc only camera.

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dawson31 Regular Member • Posts: 149
Re: Using a full frame lens on APS-C body - what crop factors apply?

blue_skies wrote:

Brajesh wrote:

Hi guys,

Since the e-mount is physically the same on the A6xxx and the A7, I was wondering if the crop factors still apply if I use an e-mount full frame lens on my A6000 APS-C body.

FOR EXAMPLE:

If I were to take the sony full frame e-mount 50mm f1.8 lens and put it on my A6000 body, would it become

A 75mm f2.7 ?

Or a 75mm f1.8?

Or stay as a 50mm f1.8?

Or something else?

Crop factor relects the sensor crop ratio wrt/ Full Frame sensors, e.g. 1.5x for APS-C, 2.0 for MFT, and so on.

Lenses do not change focal length. The only thing that the crop factor highlights is the change in FOV (or crop).

So, an 50mm lens on APS-C yields the same FOV as a 75mm on FF.

As to exposure, then you have to take the relative sensor size into account, look for equivalence. Read e.g. http://www.dpreview.com/articles/2666934640/what-is-equivalence-and-why-should-i-care

Oh man it's so confusing,

so why don't they name it FE7518 and sel5018 instead? Since we are compare equivalent to FF.

i mi understand for wide angle.. Ifs have a 16mm lens . It will be 16mm on a FF and 24mm on a apsc. So definitely not the same..oh man.

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