britinjapan
New Member
I know the focal length will increase by the crop factor, but what happens to the F stop?
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Tell your friends about us!Does a len`s F stop change with the crop factor?
- Thread starter britinjapan
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streetshooter
New Member
This is a very good question. The crop factor has nothing to do with the fstop but....it does effect the FOV (Field of View), and the DOF (Depth of Field). So, the amount of light theoretically doesn't change with crop factors...what the fstop does besides gathering light does change.
Don
Don
odklizec
PK
No, the F stop does not change with the crop factor. The f1.9 is still f1.9, no matter if the sensor is 1/1.7 or FF. For example, the GRD with its 28mm lens set at 2.8 should give you the same exposure as the GXR A12 28mm set at 2.8. Of course, there could be small differences, because of different programming of GRD/GXR. But basically, the difference should not be significant (let's say more than 1/3 stop).
AlbertTRAL
Member
Just a small clarification, the focal length of a lens NEVER changes. Is a physical parameter and is only one. When shooting with a smaller sensor, the crop factor appears and this generates the "equivalent" focal length in a FF system that will produce the same Field of View.britinjapan":2pe9heni said:
When you use a DOF calculator, the focal length of the lens is the physical, native, focal length. In the case of the GXR A12 modules, it will be 18.3 and 33mm (not 28 and 50).
This takes us to the other common error that smaller sensors generate bigger DOF. NO! is the opposite. Smaller sensor generate smaller DOF because the CoC (circle of confusion) is also smaller. What generates bigger DOF is the "minuscule" focal length of the lens we use in these compact systems to generate similar FOV than in a FF system.
I mean smaller sensor>smaller DOF, smaller focal length>bigger DOF, final effect is that in a compact system we have bigger DOF because the effect of the focal length is stronger than the fact that the sensor is smaller.
Hope I have not confused you more but I think that this concepts must be clear.
AlbertTral's explanation is spot on. This is one of the most tiring subjects that come up in forums, which generates even more tiring and most of the time wrong headed debate.
The sensor size has nothing to do with depth of field.
In case of small sensor cameras the focal length need to be extremely short to generate the field of view of a larger sensor camera, or a 35 mm film.
For example, in grd line, equipped with a 1 1/7" sensor, the focal length to generate the field of view equivalent of a 28 mm lens (on a 35 mm camera) needs to be a mere 6 mm lens.
A 6mm lens, regardless of the sensor behind it, generates a lot of depth of field. The longer the focal length the less the depth of field at a given aperture.
Basically, with a small sensor camera, we all get fish eye lenses, with all its optical characteristics, albeit, cropped in center.
This is also tied to another misunderstood subject, the perspective....
All lenses, regardless of their focal length, will generate exactly the same perspective, which is a function of vantage point, not the focal length. That's why your 6 mm lens on a small sensor will give you exactly the same field of view of the 28 mm on film....but, it will have the physical properties of the 6 mm lens.
The sensor size has nothing to do with depth of field.
In case of small sensor cameras the focal length need to be extremely short to generate the field of view of a larger sensor camera, or a 35 mm film.
For example, in grd line, equipped with a 1 1/7" sensor, the focal length to generate the field of view equivalent of a 28 mm lens (on a 35 mm camera) needs to be a mere 6 mm lens.
A 6mm lens, regardless of the sensor behind it, generates a lot of depth of field. The longer the focal length the less the depth of field at a given aperture.
Basically, with a small sensor camera, we all get fish eye lenses, with all its optical characteristics, albeit, cropped in center.
This is also tied to another misunderstood subject, the perspective....
All lenses, regardless of their focal length, will generate exactly the same perspective, which is a function of vantage point, not the focal length. That's why your 6 mm lens on a small sensor will give you exactly the same field of view of the 28 mm on film....but, it will have the physical properties of the 6 mm lens.
No such thing thing as big sensor f stop, or small sensor f stop....
optics is optics...nothing to do with sensor size.
The source of confusion is somewhat understandable: for equivalent field of view, the focal length increases as the sensor size increases...the depth of field is a function of the focal length, not the sensor size.
The concept needs to be understood correctly.
optics is optics...nothing to do with sensor size.
The source of confusion is somewhat understandable: for equivalent field of view, the focal length increases as the sensor size increases...the depth of field is a function of the focal length, not the sensor size.
The concept needs to be understood correctly.
AlbertTRAL
Member
Well, although I think I understand what you mean, it really does. CoC is reduced by the same amount that the focal length is increased to find the "equivalent" focal length, this is, by the crop factor. This is why smaller sensor implies smaller DOF.rondo":1vo2uw80 said:
Christian, this phrase is not precise. Should say LENSOR and not SENSOR. Tabelle 4 includes both, the brennweite (focal length) and zerstreuungskreis (circle of confusion), so it is an evaluation of how the DOF increases when we go from a complete 50mm/FF to a 9.2mm/Compact system (which varies focal length and CoC) that is what I call "final effect in a compact system" because the focal length DOF increase is stronger than CoC decrease effect of the DOF.olyz":1vo2uw80 said:
Christian you should post all the article of LFI because this "crop" is slightly misleading...
Its too bad that camera companies, like Ricoh, insist on using the "ff equivalent" focal length instead of stating the angular fov for how wide/narrow a lens/sensor combination is. People would get used to it easy enough, but I'm afraid its too late now.
As far as actual "brightness" goes, if I understand correctly, for astrophotography(stars) the actual physical opening of the lens determines the brightness of a point light source. So a 50mm f2 lens will show brighter point sources than a 25mm f2 lens. Back in my film days I used to do a bit of astrophotography, and it takes alot longer exposure and/or faster lens to get bright stars at wide angle than at standard or telephoto.
As far as actual "brightness" goes, if I understand correctly, for astrophotography(stars) the actual physical opening of the lens determines the brightness of a point light source. So a 50mm f2 lens will show brighter point sources than a 25mm f2 lens. Back in my film days I used to do a bit of astrophotography, and it takes alot longer exposure and/or faster lens to get bright stars at wide angle than at standard or telephoto.
streetshooter
New Member
This is all very interesting and the fact is, it has proven that there is a lot of knowledge between us all.
I choose to approach this differently. I approach it as a shooter. So then it does change things on the business end.
Here's how. We now mostly agree that the above charts and concepts written by others are correct and then that means that nothing theoretical changes.
As a shooter, this changes our psychology and approach to using the camera. It make us change our way of thinking. This is the fundmental foundation of creating images, art etc.
I'll use the 28 for example uh...sorry, the 18....hmmmm
Who goes out thinking, I'm using my 18 today? Your are......right?
We think in terms of a 28. Thus it is a 28. The crop factor makes us think that way. We use our 28mm because the crop factor has made us change our way of thinking.
If you don't think the DOF has a change or effect by the crop factor....
Put a lens on the M mode, set the DOF in the lens scale and see if it's correct...
Not on this planet.
So, I'm not arguing anything and I'm not trying to change anything....
What I'm saying is that principals and theories may hold truth on a scientific level but for art purposes..... they are a foundation that is unstable to say the least. We need to think about creating and challenging our thought process if we are to make something that satisfies us in our essence. Buying gear, figuring out what to get is the place for theory. Making images is the place to challenge those theories and many more.
I don't like my 33mm but I sure love my 50....
Peace......
I choose to approach this differently. I approach it as a shooter. So then it does change things on the business end.
Here's how. We now mostly agree that the above charts and concepts written by others are correct and then that means that nothing theoretical changes.
As a shooter, this changes our psychology and approach to using the camera. It make us change our way of thinking. This is the fundmental foundation of creating images, art etc.
I'll use the 28 for example uh...sorry, the 18....hmmmm
Who goes out thinking, I'm using my 18 today? Your are......right?
We think in terms of a 28. Thus it is a 28. The crop factor makes us think that way. We use our 28mm because the crop factor has made us change our way of thinking.
If you don't think the DOF has a change or effect by the crop factor....
Put a lens on the M mode, set the DOF in the lens scale and see if it's correct...
Not on this planet.
So, I'm not arguing anything and I'm not trying to change anything....
What I'm saying is that principals and theories may hold truth on a scientific level but for art purposes..... they are a foundation that is unstable to say the least. We need to think about creating and challenging our thought process if we are to make something that satisfies us in our essence. Buying gear, figuring out what to get is the place for theory. Making images is the place to challenge those theories and many more.
I don't like my 33mm but I sure love my 50....
Peace......
Hallo AlbertTRAL,
here you can see the complete LFI article and 2 photos with different sensor at f 2,8 / distance 1 meter.
Greetings
Christian
here you can see the complete LFI article and 2 photos with different sensor at f 2,8 / distance 1 meter.
Greetings
Christian
Attachments
AlbertTRAL
Member
@Christian: Thanks for posting the complete LFI article. Tabelle 5 clearly shows what I was pointing, they are comparing complete "systems" of sensor+lens with different "native" focal length. Now is more understandable the equivalence you were pointing to rondo.
...and 2 photos with different sensor AND DIFFERENT FOCAL LENGTH at f 2,8 / distance 1 meter...
@Don: Agree completely, although there are some basic concepts that should be clear IMHO (without entering in scientific formulas...obviously):
Although is important to know that compact systems produce bigger DOF for the same FOV as Christian's example,
it is important to know that SMALLER SENSOR implies BY ITSELF (without counting with the focal length) SMALLER DOF.
Why?
A practical example thinking as a shooter and not as a scientific would be:
Using a lens designed for FF system via an adapter in the GXR A12M module...Which will be the equivalent DOF marks in the lens to use for a given aperture in order to do zone focusing?
In this case, focal length remains the same and the only physical change in the chain is the smaller sensor...I have already given the clue...
Is a common error to think...eerrrr...."DOF will be bigger in a smaller sensor".... WRONG!
If you are using a FF lens in an APS-C system, DOF marks to use are those of +1 STOP roughly speaking, and if you are using a 4/3 sensor (not the case of Ricoh) you should use +2 STOPS. I mean, if you are stopping down to 11, you should use the marks of 8 in an APS-C sensor and the marks of 5.6 in a 4/3 sensor.
I really hate to write so much because "blurs" the concepts... but I do not know how to synthesize more... :roll: sorry.
I think that we are the ones to be unstable when we have some "blurred" concepts out of our DOF .
Again your phrase is not really complete and could induce to some misunderstanding, it should say:olyz":2o10cvoj said:
...and 2 photos with different sensor AND DIFFERENT FOCAL LENGTH at f 2,8 / distance 1 meter...
@Don: Agree completely, although there are some basic concepts that should be clear IMHO (without entering in scientific formulas...obviously):
Although is important to know that compact systems produce bigger DOF for the same FOV as Christian's example,
it is important to know that SMALLER SENSOR implies BY ITSELF (without counting with the focal length) SMALLER DOF.
Why?
A practical example thinking as a shooter and not as a scientific would be:
Using a lens designed for FF system via an adapter in the GXR A12M module...Which will be the equivalent DOF marks in the lens to use for a given aperture in order to do zone focusing?
In this case, focal length remains the same and the only physical change in the chain is the smaller sensor...I have already given the clue...
Is a common error to think...eerrrr...."DOF will be bigger in a smaller sensor".... WRONG!
If you are using a FF lens in an APS-C system, DOF marks to use are those of +1 STOP roughly speaking, and if you are using a 4/3 sensor (not the case of Ricoh) you should use +2 STOPS. I mean, if you are stopping down to 11, you should use the marks of 8 in an APS-C sensor and the marks of 5.6 in a 4/3 sensor.
I really hate to write so much because "blurs" the concepts...
but I do not know how to synthesize more... :roll: sorry.I think that we are the ones to be unstable when we have some "blurred" concepts out of our DOF
.Example: you have a 21 mm leica m mount lens.
Mount it on an m9, m8, gxr m, and on a m43 body...
All these cameras have different size sensors, from largest to smallest.
your resulting field of view will differ because of different crop factors. M9 capturing the the widest possible image circle, m43 camera the narrowest...
If you place your camera exactly at the same vantage point, and pick exactly the same focus point for all of your shots, and use the same aperture for all your shots, you will get different crops out of *exactly* the same picture for all your shots, on each and all of the cameras. The optical relationship and characteristic of focused areas to out of focus areas will be exactly the same too...the only thing that will vary is the proportion of the focus area to the entire frame due to crop factor ( magnification factor)
Let me put it this way. In theory, there is absolutely no difference between taking the photograph with the m9 (giving you the widest field of view) and later on cropping it manually or digitally to attain the narrower field of views.
Say, you printed a 8x10 photo of your m9 shot. Blow it up to 200%, and crop the image at center to 8x10...you will get exactly the same image as you would get from the m43 camera...it is as simple as that. There is no difference between optical zoom and digital zoom or plain old xerox blow up. (Of course the image quality will not be the same!, but leave that aside because we are talking optics now)
The optical rendering and focus characteristics of the image will be exactly the same. You will simply be looking at different crops of the same image. If you are looking at the equal size final prints of the same image, you will simply be looking at different magnification of the very same image. You will therefore see less or more things in focus or out of focus, in relation to the cropped frame, but otherwise you are looking exactly at the same image, in different sizes within a given frame size.
Mount it on an m9, m8, gxr m, and on a m43 body...
All these cameras have different size sensors, from largest to smallest.
your resulting field of view will differ because of different crop factors. M9 capturing the the widest possible image circle, m43 camera the narrowest...
If you place your camera exactly at the same vantage point, and pick exactly the same focus point for all of your shots, and use the same aperture for all your shots, you will get different crops out of *exactly* the same picture for all your shots, on each and all of the cameras. The optical relationship and characteristic of focused areas to out of focus areas will be exactly the same too...the only thing that will vary is the proportion of the focus area to the entire frame due to crop factor ( magnification factor)
Let me put it this way. In theory, there is absolutely no difference between taking the photograph with the m9 (giving you the widest field of view) and later on cropping it manually or digitally to attain the narrower field of views.
Say, you printed a 8x10 photo of your m9 shot. Blow it up to 200%, and crop the image at center to 8x10...you will get exactly the same image as you would get from the m43 camera...it is as simple as that. There is no difference between optical zoom and digital zoom or plain old xerox blow up. (Of course the image quality will not be the same!, but leave that aside because we are talking optics now)
The optical rendering and focus characteristics of the image will be exactly the same. You will simply be looking at different crops of the same image. If you are looking at the equal size final prints of the same image, you will simply be looking at different magnification of the very same image. You will therefore see less or more things in focus or out of focus, in relation to the cropped frame, but otherwise you are looking exactly at the same image, in different sizes within a given frame size.
Also to Christian:
The example shots you posted after the article is a perfect example of comparing apples to oranges.
You are looking at two images produced with two cameras, with two different sensors and two different focal length lenses, giving you roughly the same field of view.
If you want to compare how a particular lens will behave in different formats, which happens to be issue raised in this thread, you need to replicate the test by using same vantage point, same focus point, same aperture, on different format cameras.
And when you do that you will get the same image magnified by different crop factors...nothing more, or nothing less...you will have "perceived" difference of depth of field due to magnification factor (relative to the image size) but it will otherwise be the same picture, just a smaller or larger portion of it...
Incidentally, with digital cameras getting better and more pixels every other year, your new generation larger sensor camera can perform as well, if not better than your smaller sensor camera of the yester years...
So digital magnification can be as good as optical magnification, under certain conditions...
The example shots you posted after the article is a perfect example of comparing apples to oranges.
You are looking at two images produced with two cameras, with two different sensors and two different focal length lenses, giving you roughly the same field of view.
If you want to compare how a particular lens will behave in different formats, which happens to be issue raised in this thread, you need to replicate the test by using same vantage point, same focus point, same aperture, on different format cameras.
And when you do that you will get the same image magnified by different crop factors...nothing more, or nothing less...you will have "perceived" difference of depth of field due to magnification factor (relative to the image size) but it will otherwise be the same picture, just a smaller or larger portion of it...
Incidentally, with digital cameras getting better and more pixels every other year, your new generation larger sensor camera can perform as well, if not better than your smaller sensor camera of the yester years...
So digital magnification can be as good as optical magnification, under certain conditions...
streetshooter
New Member
So when I take my GXR out with the A12 18/28 unit....what should I be thinking....?
Should I think I'm using an 18mm or should I think I'm using a 28mm....? Or should I just not think at all and just make photos....
hmmmmmmmm
Should I think I'm using an 18mm or should I think I'm using a 28mm....? Or should I just not think at all and just make photos....
hmmmmmmmm
I don't think it matters that much...
The 35 mm format is indeed the standard, because of the wide spread use and acceptance..but remember different formats existed in film days as well. And a medium format shooter didn't "think" in 35 mm format terms, and the medium format lenses were never labeled or marketed as such...so yes, I think there is a philosophical problem with ricoh labeling his a12 units as 28 and 50, but I don't think it matters...
I would say each format should make you "think" in that format...this is indeed more true when you use the smaller sensors...I know that my grd is not a 28 mm lens. It sure doesn't perform as such!
The 35 mm format is indeed the standard, because of the wide spread use and acceptance..but remember different formats existed in film days as well. And a medium format shooter didn't "think" in 35 mm format terms, and the medium format lenses were never labeled or marketed as such...so yes, I think there is a philosophical problem with ricoh labeling his a12 units as 28 and 50, but I don't think it matters...
I would say each format should make you "think" in that format...this is indeed more true when you use the smaller sensors...I know that my grd is not a 28 mm lens. It sure doesn't perform as such!
streetshooter
New Member
So assuming we have readers from every level, we see that there exist a very well defined theory in the above post. We also see that for practical application, we must change our way of thinking to be able to work that theory in a real world use.
Thanks everyone. The challenge is to always rethink what is real and what we learned to be able to expand our creative minds.
Thanks everyone. The challenge is to always rethink what is real and what we learned to be able to expand our creative minds.
britinjapan
New Member
Many thanks for everyones responses! Can I take it back to basics...my 40mm equates to 60mm on my GXR, if you get what I mean... Does my F1.4 equals 1.4x1.5? Or I guess what I understand is that it`s still 1.4 but the effect in DoF is 1.4x1.5?
Sorry for the layman's questions!
Sorry for the layman's questions!
streetshooter
New Member
Your 40 is a 40 but sees like a 60. So let's think it's a 60 and... your 1.4 fstop stays that always.
The best way to see the DOF is to us a calculator.
The 2 best are DOFmaster and mydof.
Both are available as apps for the iPhone.
Use the ACTUAL focal length.
I'm guessing your using the Nokton. Regardless of crop factor...it's a great lens...!
Don
The best way to see the DOF is to us a calculator.
The 2 best are DOFmaster and mydof.
Both are available as apps for the iPhone.
Use the ACTUAL focal length.
I'm guessing your using the Nokton. Regardless of crop factor...it's a great lens...!
Don