The True Crop Factor of Micro Four Thirds

RichardC

Mu-43 Hall of Famer
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Mar 25, 2018
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The Royal Town of Sutton Coldfield, UK.
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Richard
There was this user called "BushmanOrig" whose actual name was Siegfried, and he would start or participate in threads about things like:
  • sensors, photons and ETTR
  • the "conspiracy" against Micro Four Thirds (how people are trying to kill our beloved system by spreading misinformation)
  • his "revolutionary" approaches to achieving the best IQ out of MFT gear (like his "2 step exposure technique", which entailed using wrong settings in step 1, like stopping down the aperture too much and therefore having to raise the ISO unnecessarily, and then in step 2 suddenly realising that you could open up the aperture, decrease the ISO and magically obtain better IQ).
His way of talking about these subjects caused many of these threads to derail and end up in the Back Room subforum. (You can still find those threads, but all of his messages have been removed, so they can be a bit hard to follow.) Many users also opted to put him on the "ignore list", so they wouldn't be distracted by his posts. I am not sure whether he left the site himself, or one of the admins removed him.

I think he got a little bit too cross with the feedback he got here and retreated to his own website.

There was some conflict of interests because a large number of his threads appeared to have been started with the intention of driving traffic to his blog.

When a post starts along the lines of "I have written an interesting article, and you can read it here...." it just gets off to a bad start and the author is just digging a very big hole for himself.

Oh, and branding non-disciples as thick wasn't terribly helpful to his cause.

Clever in many respects though, and it's easy to forget that English is not his first language. I wish him well.
 

JohnJeffrey

Mu-43 Regular
Joined
Sep 17, 2018
Messages
40
We all know the "crop factor" of MFT is 2, right? Wrong!

Just kidding here. For all intents and purposes, using a 2x crop factor works fine, and nothing of what I'm going to write here actually matters.

The thing I wondered was: as the crop factor applies to the diagonal angle of view, what does this mean for the horizontal and vertical angles of view, when you compare 3:2 sensors to 4:3 sensors? In other words, when I take a picture with a 25mm lens on MFT (4:3), how does it compare to 50mm on FF (3:2)? Let's say I'm photographing a building, and the building fills up the entire frame horizontally using 50mm on FF, will it still fit in the frame when standing in the same spot and taking the picture with 25mm on MFT?

So let's do some math. These are the physical dimensions of the imaging areas of the sensors we are discussing:
FF: width=35.6 mm, height=23.8 mm, diagonal=sqrt(35.6²+ 23.8²)=42.82 mm, area=35.6*23.8=847.28 mm²
MFT: width=17.3 mm, height=13 mm, diagonal=sqrt(17.3²+13²)=21.64 mm, area=17.3*13=224.9 mm²

The usual way to calculate the crop factor is to divide the diagonals; in this case: 42.82/21.64 = 1.98 (indeed very close to 2).

What's also interesting to calculate is the ratio between the sensor areas. From a 2x crop factor, you'd expect that an FF sensor is 4 times larger than an MFT one. In fact, the ratio is 847.28/224.9=3.77. (So an MFT sensor is larger than you think.) When you take the square root of that, you get another option for the crop factor: 1.94.

But now the most interesting part: what about the horizontal and vertical angles of view?

The ratio between the horizontal dimensions is 35.6/17.3 = 2.06, so compared to a 50mm lens on FF you'd have a tiny bit smaller angle of view with a 25mm lens on MFT. You would need a 24mm lens to have the same horizontal angle of view. I'd say this is a negligible difference.

The ratio between the vertical dimensions is 23.8/13 = 1.83, so compared to a 50mm lens on FF you would capture more of the scene with a 25mm lens on MFT (similar to what a 46mm lens would capture on FF).

Another way to look at this is that if you applied a "perfect" crop factor of 2 to an FF sensor (thereby leaving just 1/4 of the sensor area, and keeping the aspect ratio to 3:2), you would end up with a sensor with a width of 35.6/2=17.8 mm and a height of 23.8/2=11.9 mm. So compared to that, you "lose" 0.5 mm in the horizontal dimension with an MFT sensor (2,8%), and "gain" 1.1 mm in the vertical dimension (9%).

So my conclusion is: using a crop factor of 2 is pretty accurate, but you will get some pixels for free in the vertical dimension. The building still fits horizontally, but you will include more of it vertically. Awesome, right?

I have seen some people on the internet claim that for instance the Panasonic 15mm lens "is actually closer to a 35mm equivalent than a 30mm one, because of the 4:3 aspect ratio", but I don't believe that's true, now that I've done the calculations. Horizontally, you still get the angle of view of a 30mm on FF, but vertically it's closer to a 28mm.

Of course, different lenses with the same focal length might still produce a different angle of view (even within the same system). For example I read somewhere that the Olympus 25mm f/1.8 is a bit wider than the Panasonic 25mm f/1.4. So you might get a bit different results when you actually do the comparison (between 25mm MFT and 50mm FF) in practice. But in general I think it's safe to assume that your "equivalent" lens will be able to cover at least the same field of view as an FF one, but offers a little bit more in the vertical dimension. :)
All the flak about “crop factors and angles of view” from family members is why I leave my Kodak Instamatic openly on the table to keep the arguments at minimum! Want groans? I use my Autocord! When smartphones come out, all is well! LOL!!
 

Brownie

Thread Killer Extraordinaire
Joined
Sep 3, 2018
Messages
3,752
Location
SE Michigan
Real Name
Tim
I think he got a little bit too cross with the feedback he got here and retreated to his own website.

There was some conflict of interests because a large number of his threads appeared to have been started with the intention of driving traffic to his blog.

When a post starts along the lines of "I have written an interesting article, and you can read it here...." it just gets off to a bad start and the author is just digging a very big hole for himself.

Oh, and branding non-disciples as thick wasn't terribly helpful to his cause.

Clever in many respects though, and it's easy to forget that English is not his first language. I wish him well.
Yes, self styled blogger who thought he was a revolutionary. Most of his posts had a line about checking out his blog for the whole thing, or to offer feedback, etc. Maybe he made money by clicks. Back when he was at his zenith, I checked his profile. The vast majority of his posts were technical, very few images and most of those were to support his theories.
 
Joined
Aug 30, 2015
Messages
245
Real Name
Jeff
I first remember seeing him on DPR, with an article he had written about m4/3 that he said he had spent months researching and writing. Within the first few paragraphs he had gotten something (I can't remember what it was now) so basically fundamental that everyone knows it, wrong, and spent a few pages defending it while he got raked over the coals by anyone who was willing to argue about it (and we know there are many of that type on DPR). He finally either realized he was wrong, or gave up replying to those specific arguments. A lot of his arguments were basically "No, you don't understand" and "You just have to read it some more". The article was also quite lengthy.

Then there was the time here when he claimed to have found a much better way of figuring out or explaining the exposure triangle. It was . . .

(wait for it) . . . . (drumroll) . . . the exposure triangle.
 
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