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Do the math - focal length and Format demystified

Shashin

Well-known member
This all has been discussed in length - e.g. here:

Full Sized vs. Cropped Sensors

Oh, an article on LuLa. Well, I don't have time to debunk this either...
.....
1. The sensor size alone determines the maximum useful f-number (N); and, in fact, the maximum f-number for high-resolution photography is given by 0.5 times (sensor diagonal in mm).
Now, why you are bring diffraction and diffraction limit into this?


2. We can take an essentially identical photograph with any sensor size by scaling the focal length, the f-number, and the ISO sensitivity.
Well, not quite. You also need to have the same pixel resolution, which means that the smaller sensor also has smaller pixels and so each pixel is collecting less light. But if the sensors have the same pixel pitch, then each pixel has the same number of photons and then you don't scale the ISO. But you see the trick here, while you are matching those three attributes, you are not matching shutter speed and so the image will not be identical.

But so what? Photographers don't go shooting identical pictures of some abstract ideal. All of these things are variables--there are no correct value for any of these, there is no correct product. What you need to learn is the significance of these variables. Just because the function of multiple variable can intersect, does not mean the intersect is a new law in photography--correlation does not equal causation.


3. The smallest sensor we considered (denoted 1/2.5”) achieves maximum useful DoF at an f-number of N=3.5 while the full frame 35 mm sensor requires N=21 for a factor of 36 difference in transmitted light. If the full frame sensor gives the same signal/noise ratio (S/N) at ISO sensitivity 1600 as the small sensor does at ISO 80, the small sensor can still use a higher shutter speed. A PS sensor that could give low noise at ISO 800 or 1600 would appear to have a real advantage over FF sensors.
Sensor size is irrelevant in regards to total light intercepted. It is pixel size that determines light gathered. You cannot determine S/N by sensor size alone.


4. If maximizing the DoF is not the aim, larger sensors clearly win because of their ISO sensitivity advantage. A fast lens (N=1.4) with a full frame detector is impossible to match with the small sensor. Probably N=1 is the maximum aperture we can expect with a small sensor, and no company at present even offers N=2. The take home lesson is that small sensors should be coupled with large aperture lenses, i.e. small N values. Also, small sensors that support large ISO sensitivities should be sought. The vendors are showing some interest in higher sensitivities, but larger lenses are in conflict with their drive to smaller cameras. Unfortunately, none of the available PS cameras offer very high quality lenses......
You are simply cheery picking your variables to chose a winner. No one is disputing different optical qualities or performance. I am simply saying the presenter's equivalency scheme is just a whitewash of "factoids" to try to win an argument. The problem is that is it rubbish.
______________________________________________________

It is clear that a small sensor is not having the same signal to noise ratio like a larger one, both with the same resolution. the conclusions in the video are exactly stating that.
I did not see the presenter state anything about an equal pixel resolution. He certainly does not discuss equal pixel pitch. Obviously, he is either ignorant or being purposefully deceptive. He certain does not understand ISO nor f-numbers.

there is another very good article
Do Sensors ?Outresolve? Lenses?

see

Figure 2. Graphic representation of the MTFs of two hypothetical lenses and a sensor of 100 lp/mm (5 microns). Wavelength of the light is 0,000555mm.

and:
"...The signal-to-noise ratio, however, imposes an inflexible limit to the effective resolution of the whole system, mostly due to photon shot noise.
."

Regards
Stefan
It might be clear to you, but the argument presented in the video is factually incorrect. No one is saying different systems don't give different results. But what the presenter is stating is simply wrong.

BTW, aren't you the guy that was bashing MFD digital because that smaller sensor D800 was "better"? So, I guess you don't believe the presenter either because 35mm does not gather more light than MFD, or so he claims...
 
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picman

Member
A guy who does not know that P divided by squareroot of P simply equals squareroot of P is telling us how to do the math with measurements :ROTFL:
 

Stefan Steib

Active member
I have never stated something like the D800 being better than MFD globally.
Show this to me and tell me when I have written ANYTHING like this.

I keep saying on and on that MF needs to innovate and I was demanding a MF CMOS for years now. It happened.

I further demand that the industry needs to adapt to the changed market by pricing - this is also happening - see Pentax 645Z.

And as nice as MFT is and the cameras do deliver an amazing quality, for a higher resolution than maybe 25-30 Mpix they have hit a wall.
And I am definitely not the only one who says this:

Pros and Cons of Four Thirds & Micro Four Thirds Cameras

Regards
Stefan
 

ohnri

New member
Or are you saying cropping an image makes it noisier?
Cropping it does not make it noisier but it may be noisier than if I shot it with the more telephoto lens to start with.

Example: I shoot a scene on my D800 with my 50mm lens at 1/100 sec, f/2 and ISO 800. Then I crop it to a FOV equal to a 100 mm lens.

The next day I return to the scene and shoot it with my 100mm lens at 1/100 sec, f/2 and ISO 800. I carefully focus on the same point. My 50mm and 100mm lenses are of very similar quality.

The light is identical both days and I use my best tripod.

I make a 24" x 36" inch print from each day. I use the identical settings in my software.

What difference is there between these prints?

The print from the second day has much less DOF.

The print from the second day also has less noise.

If I wanted my print from the second day to look nearly identical to my print from the first day I would have to shoot my 100mm lens, 1/100 sec at f/4 and ISO 3200.

Then the equally sized prints would have similar DOF and noise.

So, does cropping make my prints have more noise?

I'll just say that shooting tighter with a longer, equally fast lens will make my prints have less noise.

-Bill
 

ohnri

New member
Cropping it does not make it noisier but it may be noisier than if I shot it with the more telephoto lens to start with.

-Bill
To continue -

Cropping an image does not make it have more noise.

Cropping an image and printing it to the same size as a print from the uncropped image does make the print from the cropped image have more noise.

Basically, printing bigger makes prints noisier.

Also, bigger sensors, all else being equal, make prints with less noise at the same exposure and print size than smaller sensors.

I found about a 2 stop difference in noise between my Nikon D4 and Olympus OMD EM5. That is pretty much what you would expect based on sensor size.

That does not mean that smaller sensors are lousy or always have inferior IQ because, in real life, there are many determinants of image quality besides noise.

But it does mean that saying a 20mm f/2 lens on a 1" sensor is equivalent to a 54mm f/2 lens on a FF sensor is not telling the whole story.

I'm also not sure it matters.

-Bill
 

Godfrey

Well-known member
I got in three minutes. It's the same tired hogwash that I've read on DPI a thousand times, and 99% bullpucky.

Shashin has it just right:

There are only a few things the presenter does not understand:

Focal Length
ISO
Aperture
Depth of Field
Bokeh

It is amazing that one person can put so much nonsense in one video about photography.
G
 

Ben Rubinstein

Active member
I think it boils down to the following, for a focal length you will get more DOF on crop and for a given ISO you will have more noise. If the sensors are of the same efficiency and generation. None of that is in any way news or controversial. Whether it is at all a problem has always been an argument, it's hugely subjective and far less likely to be an issue today than say in 2007...
 

Annna T

Active member
(...)

And as nice as MFT is and the cameras do deliver an amazing quality, for a higher resolution than maybe 25-30 Mpix they have hit a wall.
The real question is : who need more than 16Mpix ? And also, every camera system (body, lenses etc.) is the result of a compromise. The real question is whether the compromises made for a given system are meaningful or not. Personnally I think that MFT is a great place to be. It allows much smaller bodies and lenses than FF or even APSC, while the compromises on IQ aren't that big. Plus the technology has advanced a lot, the new EVFs have more advantages than disadvantages IMO (this is true for Sony too).


And I am definitely not the only one who says this:

Pros and Cons of Four Thirds & Micro Four Thirds Cameras
I followed that link in order to learn more about the resolution wall. But found nothing about that at that link, just a dated analyse, written in 2011 while we are now in 2014. Even for 2011 the authors got many things wrong. Because the analyse has a pro and a cons column doesn't make it impartial. It seems to contain all the prejudices of traditional DSLRs shooters.

It doesn't even name the numerous advantage of an EVF. Even more ridiculous it staates that there is no true wide angle lens for mirrorless system ?? the 7-14mm F4 Panasonic is a very well regarded zoom, extremely sharp and is available since 2009 or 2010. There is a 12mm F2 Olympus, a 14mm F2.5 Panasonic pancakes and a 9-18mm Olympus zoom. Are those not truee wideangle ? Nowadays there are more than 30 native lenses available for MFT.. so the least one could say is that this page is not particularly well informed.

I wonder why you even quoted it (may be you goofed with the link ?). It doesn't even speak a lot about the Mpix wall you are talking off in your post (I went there to read more about it, but there is nothing more).

There is a place for each camera, a task for each camera. What is clear for me is that apart of focus tracking and billboard printing, the small MFT bodies are able to achieve as much as DSLRs were not so long ago.
 

Stefan Steib

Active member
This is starting to get tiring. I don´t want to attack anybody´s camera system. If you are happy with it - so may it be. But facts are facts.

And of course some people will never believe it but well, here is another link from DigLloyd. Loyd says exactly the same. Now I can already hear: "oh he doesn´t have a clue....." ???? Really ? Come on....It´s becoming boring.

"....The smaller lenses with Micro Four Thirds are smaller mainly because they cheat by being one or two or even three f-stops slower than the format equivalence...."

Micro Four Thirds vs APS-C: Lens Size

Greetings from Germany
Stefan
 

Godfrey

Well-known member
My Micro-FourThirds lenses have f/2.8, f/1.4, f/2.8, f/1.8 maximum aperture. I've measured: they're all exactly what they're labeled to be.

So what point ARE you trying to make, Stephan? Neither Panasonic nor Olympus are lying about the size of the lens opening. Only people who don't understand anything and want to equivalence this to that and that to this and the other thing to whatever they prefer make a big deal of this.

I've been impressed that the Olympus E-M1 16Mpixel sensor responds virtually the same, with the same noise appearance, as the Sony A7 24 Mpixel sensor right up to the ISO 6400 setting. The A7's sensor can hold the same dynamic range and noise another stop or so. Not bad for a sensor with 1/4 the area and 1.5x the photosite density. Both formats produce the photos I want to make very nicely and print beautifully (if I've done the right things) up to gigunda sizes.

The only mystery I get out of this whole kerfuffle is how some no-little yutz on YouTube is getting sensible folks like you to post and promote his regurgitated pap.

G
 

Guy Mancuso

Administrator, Instructor
Okay folks everyone calm down please. Thanks Im trying to setup my new A6000 and your all noisy. LOL

Seriously this can all be looked at in several ways. One thing I did see was on some buying websites they do give you the equivalent FF focal lengths and they also do give you the effective aperture as well. Just depends where you are shopping
 

tsjanik

Well-known member
................"....The smaller lenses with Micro Four Thirds are smaller mainly because they cheat by being one or two or even three f-stops slower than the format equivalence...."

Greetings from Germany
Stefan
Stefan,

At the risk of piling on and :deadhorse:, Lloyd is referring to depth of field equivalence with the same angle of view; e.g., from his table: a 14mm f/1.4 on m43 has the same AOV and DOF as a 28mm f/2.8 on FF.
A given f stop is transmitting the same amount of light regardless of the size of the image circle and format. Ask yourself the following question: When you use an external light meter and it indicates an exposure of f/8, do you need to adjust for format size?
 

Stefan Steib

Active member
Guy - this will be my last post in this thread.

To the naysayers: Why do you think Metabones has made the speedbooster ? Do you also think this is nonsense ?

I understand that this is a discussion with some people who insist the world is flat and it is only 6000 years old.

It is impossible to speak on such a base, especially when some start doing comments like the Gentleman from India.

I wish you all fun and good photography.

Good evening.
Stefan
 
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