Equivalent focal length for MFT lenses

[rrr_hhh]

KenBalbari wrote:

JeanPierre Martel wrote:

KenBalbari wrote:

Yes, that's what I said in the first place

Bravo. We are all saying the same thing. So sorry if I misunderstood your message.

If you change the focal length, you change the f-number. Unless you fix the f-number instead, which means you are changing the aperture (which also changes the depth of field in the image).

Say that otherwise. I have no clue about what that means.

If you mean that 300mm m4/3 lens at F/2,8 = 600mm FF lens at F/5,6, that's true for the depth-of-field and for the angle-of-view only. But that's not the case for the brightness of the picture (the ISO being the same of course).

I mean that f-number equals f/D. So if you change f, you change the f-number. Unless you choose to change D (the aperture diameter) instead. But as I explained it above in my first post, if you keep D the same and change the f-number, then you have also changed the exposure, and have to increase ISO as well to compensate.

This is where you are in error : you can change the focal length of the lens without changing the F number which is a standardized ratio. Things are simple : set the ISO, set the shutterspeed and the F number you need to expose your scene correctly : whether you are using a 28mm wide angle, or a 90mm tele you will have to use the same aperture on both lenses, although you have changed the focal length. Now take two cameras with a different sensor : use the same ISO and same shutterspeed, you will need a 50mm on FF or a 25mm on MFT in order to keep the same angle of view, but in order to get the same brightness, you will have to use the same aperture, aka the same F number on both (Well there will be some difference in reality, because each camera manufacturer design their jpegs engine differently, but that won't be linked fdirectly to the size of the sensor).

In fact, you don't even need a lens to measure the light and the aperture you need : you can find it using a separated lightmeter; it will be valid for all lenses on all formats.

You have three parameters to consider in the equivalence :

• the exposure producing a certain level of brightness : F5.6 will remain F5.6 whatever the format is;
• the DOF : F5.6 on FF correspond to F4 on APSC and to F2.8 on MFT
• the different kinds of noise produced during the process of capturing the light; the MFT sensor being four times smaller will produce more noise than a similar sensor on full frame; in theory this could correspond to two stops difference in matters of ISO, but in practice it is much more complicated (the smaller sensors are usually packing more pixels than the larger sensor and their efficiency are usually different too). This is better determined by experience and by reading results of tests like those of DXO.

--
rrr_hhh

 

[rrr_hhh]

s_grins wrote:

draleks wrote:

There is a lot of talk about comparing lenses for MFT with APS or full format lenses. So I want to check if the following comparison is correct. If I have an MFT 300 mm f/6.7 lens, and a full format 600mm f/6.7 lens that is of a worse manufacturing quality and just happens to be twice as soft as the MFT lens. Then, on equal ISO values, those two lenses will be an exact match. Right?

Firstly, let me remove all the BS:

You have MFT 6.7/300 attached to MFT camera, and you have FF 6.7/600 attached to FF camera. Now, you're taking shot from the same spot with both cameras.

1. you will get the same FOV

2. If you set the same F stop and shutter speed, you will get the same IOS.

what do you mean by IOS ? Illumination of the scene ?

3. If F stops are the same, DOF will be 4 times deeper on M43

No it will only be twice deeper check at DOFmaster.com if you are in doubts.

 

[s_grins]

rrr_hhh wrote:

s_grins wrote:

draleks wrote:

There is a lot of talk about comparing lenses for MFT with APS or full format lenses. So I want to check if the following comparison is correct. If I have an MFT 300 mm f/6.7 lens, and a full format 600mm f/6.7 lens that is of a worse manufacturing quality and just happens to be twice as soft as the MFT lens. Then, on equal ISO values, those two lenses will be an exact match. Right?

Firstly, let me remove all the BS:

You have MFT 6.7/300 attached to MFT camera, and you have FF 6.7/600 attached to FF camera. Now, you're taking shot from the same spot with both cameras.

1. you will get the same FOV

2. If you set the same F stop and shutter speed, you will get the same IOS.

what do you mean by IOS ? Illumination of the scene ?

Under IOS I mean ISO, or something like that . It use to called "film sensitivity". I suspect ISO stands for International Standards Organization that maybe a branch of UN

3. If F stops are the same, DOF will be 4 times deeper on M43

No it will only be twice deeper check at DOFmaster.com if you are in doubts.

Maybe you're right. I do not use calculators, so I can forget some math. Anyway, M43 has deeper DOF, and it makes me proud

 

[draleks]

Detail Man wrote:

draleks wrote:

Detail Man wrote:

draleks wrote:

There is a lot of talk about comparing lenses for MFT with APS or full format lenses. So I want to check if the following comparison is correct. If I have an MFT 300 mm f/6.7 lens, and a full format 600mm f/6.7 lens that is of a worse manufacturing quality and just happens to be twice as soft as the MFT lens.

You've scaled the Focal Length by the ratio of the Crop Factors (for FOV), but haven't scaled the F-Number by the ratio of the Crop Factors (for DOF). "Twice as soft" is a vague phrase. The spatial frequency response of subject-matter across the image-frame is different than Depth of Field.

I don't think this is how it works.

That is exactly how it works to achieve equal DOF and Total Light delivered to any two formats.

If you maintain equivalent total light delivered, then you will have to have four times higher ISO sensitivity on the FF than on on MFT. The FF looses at least some of its advantage.

An MFT f/6.7 will illuminate the sensor with the same amount of light per unit area as an FF f/6.7. The difference is of course that the FF area is four times as large, so an FF sensor should be able to take equally "good" picture with four times less light per unit area. So my idea is that:

If

1) The lens on the FF system is of worse quality then the MFT lens, so that the softness (and possibly other optical imperfections) are vaguely twice as large as the MFT lens.

and apparently also,

2) The sensor on the FF system is of worse quality (for example older), and has the same ISO capability as the MFT sensor,

then the IQ of those two system should be a very close match.

Nonetheless, the FF system will offer a more shallow depth of field.

That sounds like a lot of "ifs and buts", there. Yes, the FF DOF will be shallower (if the MFT F-Number is the same). My point was that if the MFT F-Number equals one-half of the FF F-Number (divided by the ratio of the Crop Factors), then the DOF will be the same (because the diameter of the Entrance Pupil, and thus the Total Light delivered, will be the same).

Depending on the shot DOF may or may not be an issue. The total light delivered is of course always important.

Then, on equal ISO values, those two lenses will be an exact match. Right?

Shutter Speed is what you want equal. Exposure/Total Light are not functions of ISO Sensitivity.

 

[Detail Man]

draleks wrote:

Detail Man wrote:

draleks wrote:

Detail Man wrote:

draleks wrote:

There is a lot of talk about comparing lenses for MFT with APS or full format lenses. So I want to check if the following comparison is correct. If I have an MFT 300 mm f/6.7 lens, and a full format 600mm f/6.7 lens that is of a worse manufacturing quality and just happens to be twice as soft as the MFT lens.

You've scaled the Focal Length by the ratio of the Crop Factors (for FOV), but haven't scaled the F-Number by the ratio of the Crop Factors (for DOF). "Twice as soft" is a vague phrase. The spatial frequency response of subject-matter across the image-frame is different than Depth of Field.

I don't think this is how it works.

That is exactly how it works to achieve equal DOF and Total Light delivered to any two formats.

If you maintain equivalent total light delivered, then you will have to have four times higher ISO sensitivity on the FF than on on MFT. The FF looses at least some of its advantage.

Your statement (directly below) is correct. In equal DOF conditions, the Photon Shot Noise will differ by the square-root of the ratio of Quantum Sensitivities, and the Read Noise will depend upon the particular image-sensor design. Past that, your other "assumptions" seem tenuous.

FF area is four times as large, so an FF sensor should be able to take equally "good" picture with four times less light per unit area.

An MFT f/6.7 will illuminate the sensor with the same amount of light per unit area as an FF f/6.7. The difference is of course that the FF area is four times as large, so an FF sensor should be able to take equally "good" picture with four times less light per unit area. So my idea is that:

If

1) The lens on the FF system is of worse quality then the MFT lens, so that the softness (and possibly other optical imperfections) are vaguely twice as large as the MFT lens.

and apparently also,

2) The sensor on the FF system is of worse quality (for example older), and has the same ISO capability as the MFT sensor,

then the IQ of those two system should be a very close match.

Nonetheless, the FF system will offer a more shallow depth of field.

That sounds like a lot of "ifs and buts", there. Yes, the FF DOF will be shallower (if the MFT F-Number is the same). My point was that if the MFT F-Number equals one-half of the FF F-Number (divided by the ratio of the Crop Factors), then the DOF will be the same (because the diameter of the Entrance Pupil, and thus the Total Light delivered, will be the same).

Depending on the shot DOF may or may not be an issue. The total light delivered is of course always important.

Not sure what it is that you are trying to say. Is there some doctrine that you are espousing ?

Then, on equal ISO values, those two lenses will be an exact match. Right?

Shutter Speed is what you want equal. Exposure/Total Light are not functions of ISO Sensitivity.

 

[KenBalbari]

rrr_hhh wrote:

This is where you are in error : you can change the focal length of the lens without changing the F number which is a standardized ratio. Things are simple : set the ISO, set the shutterspeed and the F number you need to expose your scene correctly : whether you are using a 28mm wide angle, or a 90mm tele you will have to use the same aperture on both lenses, although you have changed the focal length.

No, this is where you are in error. Yes, it's a ratio, but the focal length is the numerator of that ratio. So if you change the focal length, you also change the ratio, unless you also change somthing else.

And if as you say, you use the same aperture on both lenses, that leaves nothing else in that ratio that you can change. The ratio is focal length to aperture diameter.

Now take two cameras with a different sensor : use the same ISO and same shutterspeed, you will need a 50mm on FF or a 25mm on MFT in order to keep the same angle of view, but in order to get the same brightness, you will have to use the same aperture, aka the same F number on both (Well there will be some difference in reality, because each camera manufacturer design their jpegs engine differently, but that won't be linked fdirectly to the size of the sensor).

The confusion seems to come from you believing that F-number is the same thing as aperture. Clearly it isn't. Did you read the wikipedia article you linked? The F-number is the ratio of the focal length to aperture diameter. When I say aperture here, I am always refering to the actual aperture diameter.

In fact, you don't even need a lens to measure the light and the aperture you need : you can find it using a separated lightmeter; it will be valid for all lenses on all formats.

You have three parameters to consider in the equivalence :

Here's the thing. If all you care about is equivalent angle of view, then you only have to consider one parameter, focal length. Go with that if you want to keep it simple and avoid confusing anyone.

• the exposure producing a certain level of brightness : F5.6 will remain F5.6 whatever the format is;
• the DOF : F5.6 on FF correspond to F4 on APSC and to F2.8 on MFT
• the different kinds of noise produced during the process of capturing the light; the MFT sensor being four times smaller will produce more noise than a similar sensor on full frame; in theory this could correspond to two stops difference in matters of ISO, but in practice it is much more complicated (the smaller sensors are usually packing more pixels than the larger sensor and their efficiency are usually different too). This is better determined by experience and by reading results of tests like those of DXO.

--
rrr_hhh

Once you bring these other parameters into it though, then what on mFT is most equivalent to 100mm f5.6 at ISO 800 on a 135 film sized sensor? I think there is no denying that 50mm f2.8 at ISO 200 will be more equivalent than 50mm f5.6 at ISO 800. In the later case you only have equivalent field of view and image brightness. In the former, you have equivalent field of view, equivalent image brightness, equivalent depth of field, and roughly equivalent noise and dynamic range characteristics.

I'm not saying there is only one way to do equivalence. By all means if you like keep it simple and limit it to angle of view, as DP Review generally does when discussing it.

But, much as I hate to argue semantics, when I think you do understand the priciple, in this case I think it's important. Because once people bring f-stop into it insisting that f5.6 is always f5.6 and doesn't change, and then on top of that use the word aperture to refer to the f-stop, that's bound to cause in some readers the kind of misunderstanding that leads some to make posts like this:

"If I have an MFT 300 mm f/6.7 lens, and a full format 600mm f/6.7 lens that is of a worse manufacturing quality and just happens to be twice as soft as the MFT lens. Then, on equal ISO values, those two lenses will be an exact match. Right?"

Now maybe I would also have been clearer if I said "aperture diameter" rather than "aperture", but I thought that much would be understood. In any case, to be clear, all I have been saying all along is that f/6.7 means that the aperture diameter is equal to the focal length divided by 6.7 and as a consequence, the f-stop (6.7) is equal to the focal length divided by the diameter. So you can't change the focal length without also changing either the aperture diameter or the f-stop, it has to be one or the other.

So if you are going to fix the f-stop, I think you should be clear that this means you are changing the aperture (and thus depth of field).

 

[KenBalbari]

draleks wrote:

1) The lens on the FF system is of worse quality then the MFT lens, so that the softness (and possibly other optical imperfections) are vaguely twice as large as the MFT lens.

This is still not quite right, as I think you would want the lenses to be of equal quality. The FF system won't have a chance using an older sensor with no resolution advantage unless it is also using good quality lenses. Image sharpness doesn't generally change as you reduce the focal length.

Think of it as though the longer focal length lens is just spreading the same image out more to cover a larger area. Spreading the light out more doesn't change the image sharpness or otherwise improve image quality.

Nonetheless, the FF system will offer a more shallow depth of field. If this holds, then a high quality 300 mm MFT lens on a high quality MFT body produces as good photos as an older FF system with a 600 mm lens, despite the latter being much more bulky and probably also more expensive.

Yes. I've been arguing that for more complete equivalence, you might use the higher f-stop and ISO on FF, and so have no advantage in noise or dynamic range, either. In which case the only advantage is if the sensor can produce a higher resolution, which a sensor from a couple of years ago can't.

However, to be fair, FF users aren't often shooting at f/13 and high ISO. In many cases, they would either open the aperture or lower the ISO, as needed, whether to increase the shutter speed, or reduce depth of field, or lower the noise levels. But if none of these is needed or desired, there is really no image quality advantage at all on a sensor with no more resolution.

But even on a current generation sensor, which can achieve more resolution, I think you may need to use a pretty good lens and get most other things right, maybe use a tripod for example, to really see the resolution difference in a real world photo, if you are comparing to an OM-D and a good lens.

 

[RichRMA]

Lamp black used inside 50 year old lenses was far better at killing reflections than the paint they use today.

 

[RichRMA]

Are there any lenses today that can produce decent edge definition (stopped down, even) on a modern sensor with 16-36mp?

 

[RichRMA]

David Kieltyka wrote:

draleks wrote:

There is a lot of talk about comparing lenses for MFT with APS or full format lenses. So I want to check if the following comparison is correct. If I have an MFT 300 mm f/6.7 lens, and a full format 600mm f/6.7 lens that is of a worse manufacturing quality and just happens to be twice as soft as the MFT lens. Then, on equal ISO values, those two lenses will be an exact match. Right?

The poorer quality of the 35mm-format lens will reveal itself quite clearly compared to the M43 lens. I've checked this stuff out under real-world conditions.

Now--if you mount the theoretical 600mm lens on the M43 camera via adapter, and the lens just happens to perform great in the center but totally stink towards the corners--you might end up with a useful ultra-long lens for M43 cameras. I own some lenses that perform okay on 35mm but noticeably improve on M43 due to their good center performance.

If what you're getting at is DOF stuff...that's a different subject altogether, and your notion about poor lens quality being an important factor is wrong.

-Dave-

I'd have guessed the lens could have looked worse, given the higher pixel density on the m4/3 than the FF, but lenses tend to fall apart more readily on the edges which would look worse, even if the center wasn't as good as on the FF.

 

[cheeky chooky]

draleks wrote:

There is a lot of talk about comparing lenses for MFT with APS or full format lenses. So I want to check if the following comparison is correct. If I have an MFT 300 mm f/6.7 lens, and a full format 600mm f/6.7 lens that is of a worse manufacturing quality and just happens to be twice as soft as the MFT lens. Then, on equal ISO values, those two lenses will be an exact match. Right?

No. They are different lenses.

 

[rrr_hhh]

KenBalbari wrote:

rrr_hhh wrote:

This is where you are in error : you can change the focal length of the lens without changing the F number which is a standardized ratio. Things are simple : set the ISO, set the shutterspeed and the F number you need to expose your scene correctly : whether you are using a 28mm wide angle, or a 90mm tele you will have to use the same aperture on both lenses, although you have changed the focal length.

No, this is where you are in error. Yes, it's a ratio, but the focal length is the numerator of that ratio. So if you change the focal length, you also change the ratio, unless you also change somthing else.

Ooops, yes, I goofed confusing numerator and denominator, but the resulting ratio remains the same. And what I said still hold. I used the term aperture the way most photographers use it : aka to indicate what is on the lens aperture ring, or what appears on the LCD when you adjust aperture. By the way : how many of us know the actual aperture of the lenses they are using (aka the diameter of the entrance pupil of the lenses in mm ) ?

As for the rest, I hate these equivalence debates and won't go further. You have been caught of guard stating that the F stands for focal length while it isn't and you are now trying to rationalize this, using the term aperture in a way most photographers won't use it, unless they are into optics and lens design. Just admit you have goofed with that minor thing, like I admitted myself above.

All I need to know is that

• for brightness F5.6 will aways be F5.6
• for DOF F5.6 will be like F11 on FF
• and for noise : the total amount of light reaching the sensor will be 1/4th of what reach a FF sensor which has some consequence with noise. Anyone knows that smaller sensor have a disadvantage there. Theoretically, all other things equal this could lead you to two EV loss in matters of ISO with respect to FF (aka ISO 800 instead of ISO 200) but this is practically of few usability since all sensors are different and it is better to look a tests comparing the noise of the cameras you are considering rather than draw arbitrary conclusions based on the unprobable hypothese that everything else is equal on the sensor.

I don't think it as simplistic as you want to make it, it is just very operational and all what people on these forums will ever need to know.

With this I'm done with this argument which I find extremely boring.

--

rrr_hhh

 

[Pedagydusz]

You are correct, of course, I don't know what went through my mind! :-(

 

[KenBalbari]

rrr_hhh wrote:

As for the rest, I hate these equivalence debates and won't go further. You have been caught of guard stating that the F stands for focal length while it isn't and you are now trying to rationalize this, using the term aperture in a way most photographers won't use it, unless they are into optics and lens design. Just admit you have goofed with that minor thing, like I admitted myself above.

But all I was saying is that the f in f/6.7 stands for focal length. That is correct.

You are right though that I should take some of the responsibility if I am being misunderstood. And especially that photographers generally think of the f-number as indicating the aperture, so I should have been clearer what I meant there. For myself though, I think things become clearer when I stop thinking along those lines and remember that the aperture adjusts with the focal length in order to keep the f-stop the same.

For example, there was a recent thread where a less experienced user seemed to be confused about whether getting closer to a subject would change the exposure, with the idea that the inverse square law should apply to the reflected light the same way it does to the lighting source. Now everyone could tell him that this was wrong, and that changing the distance of the camera doesn't change the exposure. But some of the explanations of why this is so were quite confusing. I read through a couple and was still baffled as to why.

But the simple explanation that clicked for me was that if you move the camera position and keep the focal length the same, the size of the area captured changes so that the total light captured is the same, and if you change the focal length to capture the same scene, the aperture diameter changes to keep the total light (and the exposure) the same. But if you change the distance of your strobe light from the scene, nothing automatically adjusts in the camera, so you have to change your exposure to account for the difference in total light being captured.

So I think understanding what f/6.7 really means can be helpful in answering many questions photographers sometimes have, from why the F-number gets larger when the aperture gets smaller, to why moving closer to the subject and using a wider angle doesn't change the exposure, to why you need to adjust the F-number when you change focal lengths if you want to maintain the same depth of field.

But there's also a good reason we often take the shortcut of simply associating the F-number with the aperture. It's because thinking in terms of relative aperture rather than absolute aperture makes the rules of exposure simpler, and makes picture taking easier. This is why the F-number system emerged and became standard in the fist place. In the past, other systems for designating aperture were used which led to even more confusion.

So in the future I'll try to use "aperture diameter" when that is what I mean, so as to avoid confusion. I wasn't really wanting to get into one of those convuluted equivalence debates either, if anything I think I was maybe too brief in my initial explanation because I was trying to keep things simple.

 

[s_grins]

KenBalbari wrote:

rrr_hhh wrote:

As for the rest, I hate these equivalence debates and won't go further. You have been caught of guard stating that the F stands for focal length while it isn't and you are now trying to rationalize this, using the term aperture in a way most photographers won't use it, unless they are into optics and lens design. Just admit you have goofed with that minor thing, like I admitted myself above.

But all I was saying is that the f in f/6.7 stands for focal length. That is correct.

Ken, please stop it.You're doing a great disservice to those whom you wnt to support.

F/5.7 is not a focal lens, it is aperture.

Nobody here thinks that aperture is a diameter of the opening in iris (please wikipedia this word for yourself- iris).

Stop Ballsh^tting and begin to learn things you do not know.

Again - aperture is F-stop, not a diameter. This hole will be 2 times less in diameter on M43 lens, than on FF lens to keep F-stop aka aperture the same

 

[Detail Man]

s_grins wrote:

KenBalbari wrote:

rrr_hhh wrote:

As for the rest, I hate these equivalence debates and won't go further. You have been caught of guard stating that the F stands for focal length while it isn't and you are now trying to rationalize this, using the term aperture in a way most photographers won't use it, unless they are into optics and lens design. Just admit you have goofed with that minor thing, like I admitted myself above.

But all I was saying is that the f in f/6.7 stands for focal length. That is correct.

Ken, please stop it.You're doing a great disservice to those whom you wnt to support.

F/5.7 is not a focal lens, it is aperture.

Nobody here thinks that aperture is a diameter of the opening in iris (please wikipedia this word for yourself- iris).

Stop Ballsh^tting and begin to learn things you do not know.

The f-number N is given by:

N = f / D

where f is the focal length, and D is the diameter of the entrance pupil (often called the aperture). It is customary to write f-numbers preceded by f/, which forms a mathematical expression of the entrance pupil diameter in terms of f (a symbol denoting the focal length), and the f-number. For example, if a lens's focal length is 10 mm and its entrance pupil diameter is 5 mm, the f-number is 2 and the aperture size would be expressed as f/2.

Source: http://en.wikipedia.org/wiki/F-number

I am surprised by just how much Wikipedia does not appear to contribute to the forum ...

 

[s_grins]

Thank you for the snip

Now, open this link and read this:

"The confusion seems to come from you believing that F-number is the same thing as aperture. Clearly it isn't. Did you read the wikipedia article you linked? The F-number is the ratio of the focal length to aperture diameter. When I say aperture here, I am always refering to the actual aperture diameter."

 

[Art_P]

Are we assuming the same pixel count in both sensors or a higher pixel count in the FF sensor?

Are we assuming the same ISO capability or noise level at a given ISO?

Is what you're getting at that the 4/3 lens must resolve twice the lines per inch to achieve the same level of detail as the FF lens? (assuming same pixel count and noise level)



Here's a wrinkle for you: Some FF lenses can give better edge to edge sharpness on 4/3 than on their native mount because the softer edges are cropped out by the smaller sensor, which only sees the best part of the image.

 

[Detail Man]

Detail Man wrote:

s_grins wrote:

KenBalbari wrote:

rrr_hhh wrote:

As for the rest, I hate these equivalence debates and won't go further. You have been caught of guard stating that the F stands for focal length while it isn't and you are now trying to rationalize this, using the term aperture in a way most photographers won't use it, unless they are into optics and lens design. Just admit you have goofed with that minor thing, like I admitted myself above.

But all I was saying is that the f in f/6.7 stands for focal length. That is correct.

Ken, please stop it.You're doing a great disservice to those whom you wnt to support.

F/5.7 is not a focal lens, it is aperture.

Nobody here thinks that aperture is a diameter of the opening in iris (please wikipedia this word for yourself- iris).

Stop Ballsh^tting and begin to learn things you do not know.

The f-number N is given by:

N = f / D

where f is the focal length, and D is the diameter of the entrance pupil (often called the aperture). It is customary to write f-numbers preceded by f/, which forms a mathematical expression of the entrance pupil diameter in terms of f (a symbol denoting the focal length), and the f-number. For example, if a lens's focal length is 10 mm and its entrance pupil diameter is 5 mm, the f-number is 2 and the aperture size would be expressed as f/2.

Source: http://en.wikipedia.org/wiki/F-number

I am surprised by just how much Wikipedia does not appear to contribute to the forum ...

.

s_grins wrote:

Thank you for the snip

I thought it appropriate to point out that what Ken stated (regarding the symbolism of the letter "f" in the expression "f/") is correct. You are most welcome for the Wikipedia reference, my friend.

Now, open this link and read this:

"The confusion seems to come from you believing that F-number is the same thing as aperture. Clearly it isn't. Did you read the wikipedia article you linked? The F-number is the ratio of the focal length to aperture diameter. When I say aperture here, I am always refering to the actual aperture diameter."

There is absolutely nothing incorrect in Ken's statement quoted above. It is refreshing to see people use the term "aperture" to refer (only) to the (effective) diameter of a pupil (the lens-system entrance pupil to be exact), as opposed to the all too common vague and misleading use of the term "aperture" to refer to F-Number (F-Ratio, F-Stop), which we all seem to agree (?) equals the Focal Length divided by the Virtual Aperture Diameter (Entrance Pupil Diameter).

If there is a problem with the accuracy of anything that Ken stated, I do not see one. Please advise.

DM ...

 

[CharlesTokyo]

draleks wrote:

There is a lot of talk about comparing lenses for MFT with APS or full format lenses. So I want to check if the following comparison is correct. If I have an MFT 300 mm f/6.7 lens, and a full format 600mm f/6.7 lens that is of a worse manufacturing quality and just happens to be twice as soft as the MFT lens. Then, on equal ISO values, those two lenses will be an exact match. Right?

Not exact, but similar.

Think of it this way, a 300mm f6.7 on m43s is like putting a 300mm on your FF camera, but cropping the final image so that the view is the same as it would have been with a 600mm lens. Exposure values are the same f6.7. The difference is in the focal length of the lenses. A short focal length lens gives a bigger depth of field than the a longer focal length. Shooting with a 300mm lens gives more depth of a field than a 600mm lens regardless of the format you are using.

So, no they aren't an exact match. Framing, exposure should be the same. (Well similar at the transmission values of the lenses maybe slightly different as well as camera metering). The difference is that the 300mm on m43s will have the depth of field of a 300mm lens at f6.7 and the 600mm on full frame will have the depth of field of a 600mm lens at f6.7.