MFT, APSC, FF lens equivalents

Started Dec 12, 2013 | Discussions
monashee
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MFT, APSC, FF lens equivalents
Dec 12, 2013

Hello, I am considering a MFT camera and have been looking at the lens lineup which seems pretty complete. However, I read something that if true, I need to consider. It is the relationship between FL, Fstop and DOF between the various sensor sizes. I always knew about the FL relationship, i.e. multiply by the crop factor:

FF 36mm = APSC 24mm = MFT 18mm

But then I read that this same factor needs to be applied to the Aperture.

FF 2.8 = APSC 1.8 = MFT 1.4

So for example, if a guy with a FF is shooting his 36mm @ f2.8 @ 1/60 then a guy with a mft would need to shoot his 18mm @ f1.4 @ 1/60 to obtain the same results (angle of view, exposure and DOF). And an APSC guy would need to shoot his 24mm @ f1.8 @ 1/60.

Is this basically correct?

Thanks

Richard Weisgrau
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Re: MFT, APSC, FF lens equivalents
In reply to monashee, Dec 12, 2013

No, it is not correct. Focal lengths are constant regardless of formats that are variable. Aperture is the focal length divided by the a constant (like 8.0, 5.6. 4.0. etc). A 100mm lens at f/4.0 has an aperture diameter of 25mm no matter what sensor format it is directing light to. The so-called crop factor is relative and was intended to give 35mm film users a means of understanding the relationship of digital formats to 35mm film for still cameras.

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Elemental Photography
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Re: MFT, APSC, FF lens equivalents
In reply to monashee, Dec 12, 2013

http://www.sansmirror.com/articles/pick-a-size.html
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A photograph is a creative interpretation of reality.

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MAubrey
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Re: MFT, APSC, FF lens equivalents
In reply to Richard Weisgrau, Dec 12, 2013

Richard Weisgrau wrote:

No, it is not correct. Focal lengths are constant regardless of formats that are variable. Aperture is the focal length divided by the a constant (like 8.0, 5.6. 4.0. etc). A 100mm lens at f/4.0 has an aperture diameter of 25mm no matter what sensor format it is directing light to. The so-called crop factor is relative and was intended to give 35mm film users a means of understanding the relationship of digital formats to 35mm film for still cameras.

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Richard Weisgrau
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Where did the OP say anything otherwise?

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Chatokun
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Re: MFT, APSC, FF lens equivalents
In reply to Richard Weisgrau, Dec 12, 2013

Richard Weisgrau wrote:

No, it is not correct. Focal lengths are constant regardless of formats that are variable. Aperture is the focal length divided by the a constant (like 8.0, 5.6. 4.0. etc). A 100mm lens at f/4.0 has an aperture diameter of 25mm no matter what sensor format it is directing light to. The so-called crop factor is relative and was intended to give 35mm film users a means of understanding the relationship of digital formats to 35mm film for still cameras.

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Richard Weisgrau
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You're attacking an equivalence post by giving a technical answer that hardly helps the person asking. I know people are upset by equivalence, but this isn't a troll, it's someone asking a genuine question. This is just aggressive for no good reason. This is a person considered m43 and asking for help, not a FF troll trying to stir up trouble.

Now, on to the OP:

monashee wrote:

So for example, if a guy with a FF is shooting his 36mm @ f2.8 @ 1/60 then a guy with a mft would need to shoot his 18mm @ f1.4 @ 1/60 to obtain the same results (angle of view, exposure and DOF). And an APSC guy would need to shoot his 24mm @ f1.8 @ 1/60.

Is this basically correct?

Thanks

Somewhat close, but off on some things. First, as regards angle of view and DOF, you are indeed correct, they do correlate that way. Technically speaking, DOF is a function solely of the aperture and the focal length, sensor size only has something to do with it if you're trying to keep the save FOV. Still, from a simply results based perspective, what you said is close enough to correct to not matter.

However, exposure is off. If ISO is kept the same on all 3 (say 200), then the FF will be 2 stops darker than the MFT, and the APS-C the appropriate distance from both (3/4 a stop darker than mFT, 1.25 stops brighter than FF I believe?). So you'd either need to change the ISO or the shutter speed to match. Technically speaking however, this shouldn't be that much of an issue: if the sensors have the same efficiency(ie, same company in same generation), then making the ISO compensate should result in about the same noise. Of course, not all these companies use the same sensor companies or generation of sensors, so there may be differences.

Simply put: angle of view and DOF: close enough to yes, exposure: no, unless you adjust ISO.

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GBC
GBC
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Re: MFT, APSC, FF lens equivalents
In reply to Richard Weisgrau, Dec 12, 2013

It was angle of view, not focal length he asked about.

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monashee
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Re: MFT, APSC, FF lens equivalents
In reply to monashee, Dec 12, 2013

I apologize for my somewhat confusing OP. But I think I have an answer:

To summarize: i don't need to buy faster MFT lenses in order to maintain the same low light capability that I would have with an equivalent focal length FF lens (all else being equal).

Assuming SS, ISO and ambient light level is the same for both pictures, then if a picture taken with a FF 36mm set at f2.8 is properly exposed then a picture taken with a MFT 18mm set at f2.8 will also be properly exposed. However, my DOF will be larger on the MFT.

Did I get it right?

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Anders W
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Re: MFT, APSC, FF lens equivalents
In reply to monashee, Dec 12, 2013

monashee wrote:

Hello, I am considering a MFT camera and have been looking at the lens lineup which seems pretty complete. However, I read something that if true, I need to consider. It is the relationship between FL, Fstop and DOF between the various sensor sizes. I always knew about the FL relationship, i.e. multiply by the crop factor:

FF 36mm = APSC 24mm = MFT 18mm

But then I read that this same factor needs to be applied to the Aperture.

FF 2.8 = APSC 1.8 = MFT 1.4

So for example, if a guy with a FF is shooting his 36mm @ f2.8 @ 1/60 then a guy with a mft would need to shoot his 18mm @ f1.4 @ 1/60 to obtain the same results (angle of view, exposure and DOF). And an APSC guy would need to shoot his 24mm @ f1.8 @ 1/60.

Is this basically correct?

It is partly correct but not entirely. F/2.8 and 1/60 on FF is equivalent to f/1.4 and 1/60 on MFT with regard to DoF, the impact of diffraction, and total light accumulation of the sensor.

But it is not equivalent with regard to exposure. Exposure refers to the amount of light per sensor area unit (e.g., per square mm). In this regard f/2.8 and 1/60 on FF is the same as f/2.8 and 1/60 on MFT. At the same exposure, however, the FF sensor accumulates approximately four times as much light on account of covering about four times as large an area.

If you consider things from a more practical point of view, the MFT camera is likely to do about as well as the FF camera for equivalent photos (photos with the same DoF and same shutter speed, but with the different f-stops and different ISO settings required to make DoF the same). However, if you frequently want to shoot at f-stops wider than about f/2.8 on FF (corresponding to f/1.4 on MFT), then an FF camera is likely to serve you better since there are few lenses for MFT that are faster than f/1.4 and since these lenses are unlikely to perform as well at, say f/1, as an FF lens at f/2.

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exdeejjjaaaa
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Re: MFT, APSC, FF lens equivalents
In reply to monashee, Dec 12, 2013

monashee wrote:

Hello, I am considering a MFT camera and have been looking at the lens lineup which seems pretty complete. However, I read something that if true, I need to consider. It is the relationship between FL, Fstop and DOF between the various sensor sizes. I always knew about the FL relationship, i.e. multiply by the crop factor:

m43 is 3.7 times less than FF (and that is if you really believe that image is off 36mm x 24mm, where actually the image might be from a less area..) so the crop is not 2, but 1.9

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Anders W
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Re: MFT, APSC, FF lens equivalents
In reply to monashee, Dec 12, 2013

monashee wrote:

I apologize for my somewhat confusing OP. But I think I have an answer:

To summarize: i don't need to buy faster MFT lenses in order to maintain the same low light capability that I would have with an equivalent focal length FF lens (all else being equal).

In order to get as noise-free an image, the MFT lens would have to be faster. Otherwise, the FF image would be better with regard to noise while simultaneously having less DoF (possibly less than you would want).

Assuming SS, ISO and ambient light level is the same for both pictures, then if a picture taken with a FF 36mm set at f2.8 is properly exposed then a picture taken with a MFT 18mm set at f2.8 will also be properly exposed. However, my DOF will be larger on the MFT.

Yes, if the FF image is correctly exposed, then the MFT image will be as well. And yes, the DoF of the MFT image will be greater.

Did I get it right?

Again, partly. For me personally, MFT is fine since I rarely want more shallow DoF than I can get with fast MFT primes like the 45/1.8 and the 75/1.8. However, if you frequently want more shallow DoF than you can get with lenses like these, FF might be a better idea.

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monashee
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Re: MFT, APSC, FF lens equivalents
In reply to Anders W, Dec 12, 2013

Thank you Anders.

A larger DOF is actually beneficial to my application so I have no concerns about that.

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exdeejjjaaaa
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Re: MFT, APSC, FF lens equivalents
In reply to monashee, Dec 12, 2013

monashee wrote:

A larger DOF is actually beneficial to my application so I have no concerns about that.

then you might want just go for Sony 1"  P&S w/ 20mp... more DOF, more sensels, still good sensor tech.

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Anders W
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Re: MFT, APSC, FF lens equivalents
In reply to exdeejjjaaaa, Dec 13, 2013

exdeejjjaaaa wrote:

monashee wrote:

A larger DOF is actually beneficial to my application so I have no concerns about that.

then you might want just go for Sony 1" P&S w/ 20mp... more DOF, more sensels, still good sensor tech.

But not an interchangeable-lens camera and restricted to the aperture range from about f/2.5 (short end of zoom range) to about f/7.1 (long end of the zoom range) if we translate to MFT equivalent f-stops.

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ApertureAcolyte
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Re: MFT, APSC, FF lens equivalents
In reply to monashee, Dec 13, 2013

monashee wrote:

Hello, I am considering a MFT camera and have been looking at the lens lineup which seems pretty complete. However, I read something that if true, I need to consider. It is the relationship between FL, Fstop and DOF between the various sensor sizes. I always knew about the FL relationship, i.e. multiply by the crop factor:

FF 36mm = APSC 24mm = MFT 18mm

But then I read that this same factor needs to be applied to the Aperture.

FF 2.8 = APSC 1.8 = MFT 1.4

So for example, if a guy with a FF is shooting his 36mm @ f2.8 @ 1/60 then a guy with a mft would need to shoot his 18mm @ f1.4 @ 1/60 to obtain the same results (angle of view, exposure and DOF). And an APSC guy would need to shoot his 24mm @ f1.8 @ 1/60.

Is this basically correct?

Thanks

Best to think of your lens like this:

DOF = As per focal length.

FOV = About double the rated focal length due to smaller image circle.

Aperture = Is as written or given. Aperture is not halved on m43. This is a myth made by people who do not correctly understand lenses.

Therefore, a 45mm has similar DOF to a standard prime, but the FOV of a 90mm lens. Aperture has nothing to do with it.

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exdeejjjaaaa
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Re: MFT, APSC, FF lens equivalents
In reply to Anders W, Dec 13, 2013

Anders W wrote:

exdeejjjaaaa wrote:

monashee wrote:

A larger DOF is actually beneficial to my application so I have no concerns about that.

then you might want just go for Sony 1" P&S w/ 20mp... more DOF, more sensels, still good sensor tech.

But not an interchangeable-lens camera

not everybody needs interchangeable-lens camera ( w/ hand made UV filters to fix camera-lens mating )

and restricted to the aperture range

good for DOF, who says that m43 is the sweet spot

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Richard Weisgrau
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Re: MFT, APSC, FF lens equivalents
In reply to MAubrey, Dec 13, 2013

MAubrey wrote:

Richard Weisgrau wrote:

No, it is not correct. Focal lengths are constant regardless of formats that are variable. Aperture is the focal length divided by the a constant (like 8.0, 5.6. 4.0. etc). A 100mm lens at f/4.0 has an aperture diameter of 25mm no matter what sensor format it is directing light to. The so-called crop factor is relative and was intended to give 35mm film users a means of understanding the relationship of digital formats to 35mm film for still cameras.

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Richard Weisgrau
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Where did the OP say anything otherwise?

The OP asked: "Is this basically correct?

I answered the question he asked.

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Richard Weisgrau
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Re: MFT, APSC, FF lens equivalents
In reply to Chatokun, Dec 13, 2013

Chatokun wrote:

Richard Weisgrau wrote:

No, it is not correct. Focal lengths are constant regardless of formats that are variable. Aperture is the focal length divided by the a constant (like 8.0, 5.6. 4.0. etc). A 100mm lens at f/4.0 has an aperture diameter of 25mm no matter what sensor format it is directing light to. The so-called crop factor is relative and was intended to give 35mm film users a means of understanding the relationship of digital formats to 35mm film for still cameras.

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Richard Weisgrau
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You're attacking an equivalence post by giving a technical answer that hardly helps the person asking. I know people are upset by equivalence, but this isn't a troll, it's someone asking a genuine question. This is just aggressive for no good reason. This is a person considered m43 and asking for help, not a FF troll trying to stir up trouble.

"Attacking!" Wow. I thought I was answering the question he asked " Is this basically correct?

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Richard Weisgrau
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Re: MFT, APSC, FF lens equivalents
In reply to GBC, Dec 13, 2013

GBC wrote:

It was angle of view, not focal length he asked about.

Angle of view is a result of focal length combined with the size of the focal plane.

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JeanPierre Martel
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Re: MFT, APSC, FF lens equivalents
In reply to monashee, Dec 13, 2013

Angle of view: FF 36mm = APSC 24mm = MFT 18mm

Taken from the same place, if they have the same number of Megapixels, a 36mm lens on a fullframe camera and a 18mm lens on a m4/3 camera will shoot the same image.

Bightness: FF F/2,8 = APSC F/2,8 = m4/3 F/2,8

If the lenses have the same aperture, a picture taken on a fullframe will be as bright (or as dark) as the picture taken by a lens with the same aperture on a m4/3 camera. All of them will send exactly the same number of photons per square mm on their respective sensor.

DOF: FF F/5,6 = m4/3 F/2,8

In order to get the same shallow DOF, the aperture on a m4/3 lens has to be twice as big. But the ISO will be higher on the FF camera precisely because the aperture has to be narrower.

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Anders W
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Re: MFT, APSC, FF lens equivalents
In reply to exdeejjjaaaa, Dec 13, 2013

exdeejjjaaaa wrote:

Anders W wrote:

exdeejjjaaaa wrote:

monashee wrote:

A larger DOF is actually beneficial to my application so I have no concerns about that.

then you might want just go for Sony 1" P&S w/ 20mp... more DOF, more sensels, still good sensor tech.

But not an interchangeable-lens camera

not everybody needs interchangeable-lens camera

Sure. But the OP seemed interested in one.

( w/ hand made UV filters to fix camera-lens mating )

The filter you refer to is surely not "hand-made" but it's a nice thing to have when needed.

and restricted to the aperture range

good for DOF, who says that m43 is the sweet spot

I wasn't saying it is for everyone. For me it is though. For you too, it seems.

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