FULL FRAME SPEAK
Why you always multiply the crop factor *IF* you are going to compare your APS-C gear to full frame.
First off, I have no skin in either game. I'm a long-time Canon 5D original shooter since launch day in 2005 and today I dual-shoot Canon Full Frame and Fujifilm APS-C XT3. Dual. Shooter. Over the years, I've owned multiple copies of most lenses in Canon and Fuji's line up and have done all sorts of tests comparing the two systems. I also have the Youtube sensation Tony and Chelsea Northrup to thank for further clarifying this in a way I never could. You APS-C guys might be thinking... OH WELL... YOU JUST WANT YOUR FULL FRAME TO BE KING. TO BE BOSS. CUZ U OWN IT.
Nope. The same applies to medium format. It trumps full frame in terms of light gathering and overall performance. So you see? I acknowledge off the bat even with owning full frame, I still have an inferior setup. I just bashed my own belongings. It doesn't mean any one setup is bad, it just means relative to others, it's not as good in terms of light gathering and overall performance.
Today, in all camera reviews, on social media, in photography circles and chatter, everyone knows full frame speak, therefore everyone speaks in full frame terms and brags in full frame terms. They hear things like "1.2 glass" and perceive it to be the holy grail. The cool club. The club they want to be in. The pinnacle of photographic equipment. But there are many users, say in Fujifilm circles (including myself) who own Fujifilm's SUPERB f/1.4 or f/2 glass. So they'll loosely (or sometimes not so loosely) proclaim all the benefits of their F1.4 or F2 glass and compare the f-stop #s to full frame lenses with comparable numbers. They'll also compare the focal length.
For example I saw one Youtube reviewer non-chalantly compare a Fujifilm 35mm 1.4 vs a Canon full frame 35mm 1.4/L. I wanted to throw my device out the window as I was watching this. This is wrong on both levels. The Fujifilm 35mm 1.4 would compare to a Canon 50mm 1.8. The Canon 35mm 1.4 is an entirely different lens.
Remember the f-stop is a ratio connected to focal length which is connected to the diameter of the entrance pupil. In laymens terms, a sensor size class and it's associated optics system is simply scaled down (or up) relative to the respective systems larger or smaller than it. Yes on your APS-C setup, in this case Fujifilm, you'd still technically have a 35mm f/1.4 lens. If no other camera system in the world existed and Fujifilm APS-C existed in a vacuum, the #s would be cemented forever in history. The problem is people compare to and TALK OF their APS-C systems in full frame terms since FULL FRAME is the LANGUAGE everyone speaks. So they THINK they have a 1.4 full frame equivalent lens but at the size of a full frame 50mm 1.8 lens. Like some genie came by and suddenly and magically were able to give you all the benefits of a full frame 50mm 1.4 lens but at the size of a 1.8 lens. There's no free rides. If a lens projects a certain amount of light into a sensor for a given angle of view, a lens will always and roughly be the same size, given a particular lens design.
For example here are some popular lenses and their full frame counterparts--what Fujifilm intended to design to compete with in full frame land. I want you to look up the sizes and weighs and you'll notice they're similar.
Fujifilm 35mm 1.4 = Canon 50mm 1.8. Same field of view, similar aperture equivalence, similar light gathering equivalence (the Canon 50mm 1.8 would actually have slightly more light gathering)
Fujifilm 50-140 2.8 = Canon 70-200 F4L USM. Same weight, same FOV. Same size. Check it out. By owning this excellent Fujifilm lens, NO you are NOT in the same league or club as Canon 70-200 F/2.8L owners are. So stop comparing.
Fujifilm 23mm 1.4 = Canon 35mm F2
Fujifilm 90mm F2 = there is no equivalent Canon lens. The closest thing is a Canon 135mm F2 which is a full stop faster when you factor in crop factor multiplication. The Fuji acts as a 135 2.8 would on full frame. Still excellent, but not as excellent as an F2 in terms of speed.
Other examples
Mitakon 35mm f/0.95 = Canon 50mm f/1.4. Nope, you are not a "point nine five" guy. You are an f/1.4 guy. (in FF terms) so stop running around thinking you're gathering more light for a given exposure than the FF guy next to you with his Costco 1.4 lens. You aren't. I've done the testing. I owned both these lenses. In fact, the Canon 50mm 1/4 actually was a tad brighter for a given exposure time vs. the Mitakon. The Mitakon is intended to give you 50mm 1.4 FF results, which it largely does for all intents and purposes.
Kipon Ibelux 40mm f/0.85. This is a doozie. People are really flexing their D****s with this f/0.85 label. They think they descended from heaven and have a photographic edge on the entire planet SIMPLY because they bought into an APS-C system. This lens is FAST for sure, very fast. but equivalent to a 60mm f/1.2 lens on full frame. I suspect the flange distance and sensor size had to do with the selection of this fast aperture which allowed them an optimal price and selling point. Owners of this lens have a fast lens for sure, but in full frame terms, you're like your typical (still exotic) 1.2 lens -- NO FASTER. So stop thinking you're faster. YOU AREN'T.
Out of all my testing, full frame still wins, still has a slight edge in terms of optical performance, light gathering, EVEN WHEN TESTING THEIR APS-C equivalent brothers and sister lenses. I've TESTED ALL COMBOS IN ALL DIRECTIONS OF ALL LENSES. FF has a slight edge no matter what. Purposely designed APS-C lenses such as Fujifilm primes are EXTREMELY excellent and combined with XTRANS technology, those setups give full frame a very good run for the money.
With OPTICS and sensors, SIZE MATTERS. The larger the glass, all things being equal including technology, engineering, design, budgets, the higher the EQ. PERIOD. BIG GLASS EQUALS BIG PERFORMANCE.
How about using full frame glass on crop bodies?
Same rule applies. MULTIPLY MULTIPLY MULTIPLY.
Using a Canon 70-200 F/2.8L on a Fujifilm XT2 gives you a focal length, aperture, AND light gathering of a 105-300 F4 lens.
The light that that lens is projecting out of the rear element of that lens normally falls onto a full frame image sensor but now it's falling on a smaller APS-C sensor, so that light is NOT being used to make an image. You are also MAGNIFYING any lens aberrations and thus REDUCING image quality. Imagine that SAME lens projecting onto a tiny iPhone sensor. That tiny sensor would be reading off a very tiny portion of the glass therefore the sensor would receive a very distorted light signal and thus produce a poor image. That's an exaggeration to make a point. Using full frame glass on a sensor smaller than what it was designed for is NOT optimal and will lead to LESS than optimal results. Note I didn't say BAD results, just not as good results. Cause with some exotic or high end glass, the glass is so good that it can still produce a great image even when it is being projected onto a smaller sensor. In other words, there's a quality buffer built in due to how good the glass is. This is only the case though with EXTREMELY high quality glass. Like the Sigma 40mm 1.4 which has probably the highest quality glass I've ever seen in any consumer camera lens made by man. That lens, within reason, would produce an extremely high quality image no matter what sensor you put it on. Unless the future beings a 300 megapixel M43 sensor. It would present a challenge.
Still not convinced your f/1.8 lens on APS-C is slower than an f/1.8 lens on full frame in terms of light gathering? I present to you the iPhone example.
Think of your iPhone. The iPhone 11 Pro has an F/1.8 lens. Impressive # right? Oh so fast.
Do you think the F/1.8 lens on an iPhone can gather the same light as a full frame f/1.8 lens on a full frame body? Go ahead... I'll wait.
I'm guessing not ;) remember that 1.8# is a function of a ratio for a given lens designed for a particular sensor.
Oh and that full frame 1.8 lens wouldn't hold a candle to the tiny native lens on the iPhone in terms of IQ, if you could theoretically mount it to the tiny sensor on the phone. ;)
So in summary, native rules--get lenses DESIGNED FOR YOUR SENSOR but if you do use a big lens on a smaller sensor, remember to do the math if you want to brag to your full frame buddies.
All in all, it's just camera equipment. Not one system is superior to the other, as long as you stop trying to compare to other systems. Just shoot and have fun and ENJOY what you have for what it is. Speed isn't everything. Embrace it. I do--that's why I shoot both systems!
(I may update this blog with examples later) I have a mountain of testing results. It's not needed anyway, this is quite a simple topic. Nothing comes for free. There are no free rides. There is always a price to pay.
