I need some help with understanding crop factor, focal lengths and buying new lenses

[Ein0r]

I got a camera a while ago, a Fujifilm XT 200. I'm happy with it and I'm reading up on a lot of useful and less useful information. Like this one apparently. But it is such an annoying bugbear that I need to get rid of before I can move on to more interesting and useful stuff again. 

 

Rambling my and my general comprehension:

The XT 200 is an apsc camera with a crop factor of 1,5.

I understand the basics of it. If I use a 50mm lens on an apsc like mine and a 50mm on a full frame(ff) camera, I will get "more image" and a wider angle on the full frame. And I'd have to switch to a 33mm lens on the apsc or respectively a 75mm on the ff to get a near identical image at the same location.

 

I also understand that there are lenses for ff cameras and apsc cameras and that it doesn't matter if I use an ff lens on an apsc camera, but might get a black circle if I use those lenses the other way round because of the sensor size. FF lenses are also more expensive simply because they have to be larger.

 

 

Probably the actual problem

 

Once the man made-distinctions between wide angle-, normal- and tele lenses come into play, it starts to confuse me. Sure, there are no real limitations on  what I can use a normal lens for but it is more beneficial in some situations than a wide angle lens for example.

 

"You should use a normal lens (50mm) for portrait shootings."

Probably because the distance to the model is comfortable, and you don't have to remove too much footage during editing. With a wide angle lense you'd have to get up close to get a decent portrait if you also want good details. And you have a smaller risk when it comes to distorted proportions.

 

Let's say I want to follow that advice, what lens would I have to buy for my apsc camera? Still a 50mm lens that's made for apsc cameras? A general 35mm lens for ff ? Or maybe a 35mm lens for apsc cameras? But isn't a 35mm lens technically considered a wide angle lens? Or do I only have to account for the crop factor if I go out of my way to buy a lens that's actually designed for a full frame camera?

 

And this thought procress feels like a roadblock in other areas as well, like looking at example pictures that also state their settings, as some people here do in the photo sharing thread. Mostly so I can try to understand the basics: "Aha they used a 50mm lens so they got this field of view, and oh, they used an aperture of 1,2 so course the background is more blurry. Would I have to have to use a 35mm lens to recreate this but does it even matter when I don't know what camera they used?

 

 

 

[AbydosOne]

57 minutes ago, Ein0r said:

Let's say I want to follow that advice, what lens would I have to buy for my apsc camera? Still a 50mm lens that's made for apsc cameras? A general 35mm lens for ff ? Or maybe a 35mm lens for apsc cameras? But isn't a 35mm lens technically considered a wide angle lens? Or do I only have to account for the crop factor if I go out of my way to buy a lens that's actually designed for a full frame camera?

All lenses are marketed with their "full frame" focal length, regardless of whether their designed for crop sensors or not. The APS-C field-of-view equivalent of a full-frame 50mm lens would then be (approximately) a 35mm lens. However, if you're in a lens system that has both full-frame and APS-C lenses (like my Sony for example), you can buy an APS-C version, which are almost universally smaller/cheaper/lighter.

 

57 minutes ago, Ein0r said:

"Aha they used a 50mm lens so they got this field of view, and oh, they used an aperture of 1,2 so course the background is more blurry. Would I have to have to use a 35mm lens to recreate this but does it even matter when I don't know what camera they used?

As a bit of a note: crop sensors will increase the depth of focus (i.e. make background less blurry) compared to the equivalent focal length + same aperture on a full-frame camera. Here's a good set of examples that explain it better than I can.

[Ein0r]

29 minutes ago, AbydosOne said:

All lenses are marketed with their "full frame" focal length, regardless of whether their designed for crop sensors or not. The APS-C field-of-view equivalent of a full-frame 50mm lens would then be (approximately) a 35mm lens. However, if you're in a lens system that has both full-frame and APS-C lenses (like my Sony for example), you can buy an APS-C version, which are almost universally smaller/cheaper/lighter.

 

I'm not entirely sure how this translates to Fuji's X-Mount system. From your explanation, I understood that I should check whether the lens was made with an asp-c sensor in mind or not. And if it was, then I get what's written on the lens, and if it wasn't made for an aps-c sensor then I have to keep the crop factor in mind.

 

For example:

I tried to quickly check this and looked up the "XF 8-16 mm F2.8 R LM WR" lens on wikipedia and on a camera review site.

The site wrote: "also the widest-angle autofocus lens you can currently get for cameras with APS-C sized or smaller image sensors."

 

If I were to put this on my asp-c camera, I'd get the 8-16mm focal length.

However if that lens is made for a full frame sensor, I'd need a lens with a 5-10mm focal length if I wanted to achieve that same effect/angle.

 

I've also read that statement that the lenses  are marketed with full frame focal length in mind, but there's just something that doesn't want to click in my brain and I don't know what I'm missing, or what I'm unnecessarily overcomplicating.

 

But why would I even want to achieve that same effect, why would it even matter, as long as it falls into the wide angle category it should be fine.

[AbydosOne]

23 minutes ago, Ein0r said:

If I were to put this on my asp-c camera, I'd get the 8-16mm focal length.

No, like I said, all lenses are marked/marketed with their full-frame focal lengths. An 8-16mm lens on a APS-C body would take a 12-24mm lens on a full-frame camera to match the field-of-view.

 

Lenses specifically for APS-C just don't need to cover as large of a sensor size, so they can be smaller overall. They will vignette extremely badly on full-frame cameras.

[Ein0r]

So, if I buy a 50mm that's designed for apsc- sensors, then I will always have a slight tele effect either way, because 50mm (as it is written on the side of the lens) is considered "normal" for full-frame.

And to get a "normal" look on images, with an aps-c  camera, I would have to buy a lens with 35mm focal length.

But in regards to focal lengh, it doesn't matter for my aps-c camera whether I buy a 35mm lens designed for aps-c cameras or a 35mm lens for full-frame cameras. Except that the full frame lens is more expensive.

 

Which means I'd always have to factor in the crop factor if I want to achieve a certain effect?

The X-T200 came with a 15-45mm kit lens. If I wanted to achieve that "normal focal length look" for whatever reason, I'd have to adjust it to ~35mm?

 

 

 

[mapegl]

2 hours ago, Ein0r said:

So, if I buy a 50mm that's designed for apsc- sensors, then I will always have a slight tele effect either way, because 50mm (as it is written on the side of the lens) is considered "normal" for full-frame.

And to get a "normal" look on images, with an aps-c  camera, I would have to buy a lens with 35mm focal length.

But in regards to focal lengh, it doesn't matter for my aps-c camera whether I buy a 35mm lens designed for aps-c cameras or a 35mm lens for full-frame cameras. Except that the full frame lens is more expensive.

 

Which means I'd always have to factor in the crop factor if I want to achieve a certain effect?

The X-T200 came with a 15-45mm kit lens. If I wanted to achieve that "normal focal length look" for whatever reason, I'd have to adjust it to ~35mm?

 

 

 

Hi.

50mm is always 50mm, but a crop camera only shows a part of what a full frame camera would (specific apsc lenses are optically the same to you unless you put them on a full frame and they would have black corners). 

It is a bit like digital zoom. You don't really zoom, but just take a small part of the picture in the middle. Obviously, this is a very rough explanation, because we are doing the cropping before the image hits the sensor if that makes any sense. 

 

I personally own a Fuji as well and to achieve what people call a 50mm look, you need a 33 or 35, which is equivalent to 50mm.

Now, optically you would still be working with 33 or 35, which means the depth of field is just that and not as shallow as it would be on 50mm. So if you see someone on YouTube or wherever and they show off their 50mm/1.8 on full frame you would need to divide both the focal length and aperture by 1.5 (for Fuji) to know what you need for the exact same look. So basically a 33mm f1.2 would be equivalent in looks. 

Important to point out here is that I am talking about looks! Obviously, the 1.2 aperture would allow you to shoot at fast shutter speeds than 1.8 regardless of which system the lens is for. 

 

It is all a bit confusing at first, but I personally went at it from a physics perspective and that helped when I was facing the same thoughts about what it all means. 

Feel free to hit me up about that stuff if you want. 

[Ein0r]

49 minutes ago, mapegl said:

It is all a bit confusing at first, but I personally went at it from a physics perspective and that helped when I was facing the same thoughts about what it all means. 

Feel free to hit me up about that stuff if you want. 

Thanks, I'll take you up on that

This probably confirms that I just have to factor in the crop factor everytime I want to recreate a certain look. Or when I need it for specific use case.

 

And that I should buy a 35mm lense when a youtuber recommends getting a 50mm prime lens for various reasons. At least if they don't specify that it is for a crop camera.  The fact a single lens could be considered wide angle, normal or maybe even a tele lens, depending on the sensor it gets attached to is confusing af at first.

 

https://imgur.com/a/MKrW6Ne  In theory, the blue 35mm angle should have the same size as the orange 50mm angle, provided the lens is big enough for the sensor.

 

The bright side is that I'm nowhere near of getting a new lens anytime soon. Maybe in half a year or so. My next purchases will be a tripod and some spare batteries. But focal lengths and the looks of the various lense types come up all the time in tutorials and guides. And talking about it helped me a lot with getting all my incoherent thoughts and bits of information on the right track.

[mapegl]

6 hours ago, Ein0r said:

Thanks, I'll take you up on that

This probably confirms that I just have to factor in the crop factor everytime I want to recreate a certain look. Or when I need it for specific use case.

 

And that I should buy a 35mm lense when a youtuber recommends getting a 50mm prime lens for various reasons. At least if they don't specify that it is for a crop camera.  The fact a single lens could be considered wide angle, normal or maybe even a tele lens, depending on the sensor it gets attached to is confusing af at first.

 

https://imgur.com/a/MKrW6Ne  In theory, the blue 35mm angle should have the same size as the orange 50mm angle, provided the lens is big enough for the sensor.

 

The bright side is that I'm nowhere near of getting a new lens anytime soon. Maybe in half a year or so. My next purchases will be a tripod and some spare batteries. But focal lengths and the looks of the various lense types come up all the time in tutorials and guides. And talking about it helped me a lot with getting all my incoherent thoughts and bits of information on the right track.

Love talking cameras, so go ahead. 

 

YouTubers are, depending on their channel focus, not very precise with that stuff. Not their fault, they will just say "get a 50mm" while holding a crop camera with a 35, the next one will say the same but have a crop with an actual 50 (thus 75 equivalent) and the next one will shoot full frame with a 50.... You get the picture.

 

Personally, I love my X100T with the TLC, which makes it a 35mm/2.0. it even says 50mm equivalent on the lens. I would highly recommend either a 23 or 35/2 from Fuji as a first prime. 

A few years ago, I started with a 24/2.8 on a crop canon. Great lens to learn...not that I am great, I just got better.

 

Oh and just buy used. New camera gear is so overpriced and people often just put their stuff on a shelf. I have not once bought a new camera.

[Zodiark1593]

Crop factor is used to simplify what sort of field of view to expect from a given lens relative to a 35mm Full Frame format. The crop factor itself is dependent upon the area of the sensor. In the case of APS-C, the crop factor is ~1.5x, as it is little less than 50% the area of a full frame sensor. 
 

The area impacts how much of a lens’s field of view is captured, an APS-c format on a given lens will appear zoomed in vs Full Frame format, for example. 
 

So following this logic, a 35mm lens on an APS-C camera will result in a similar (close enough) field of view to a 50mm lens on a Full Frame camera. As 35mm x 1.5 crop factor = 52.5mm. 
 

The aperture value is pretty useless for figuring out depth of field, and is best used for exposure. The aperture value itself is a ratio between focal length, and aperture diameter. Longer focal lengths directly reduce incoming light, and so a larger aperture diameter offsets this, giving you the reason for the existence of f-stops. 
 

And finally, depth of field is impacted by focus distance, aperture diameter and pixel pitch. Owing to smaller format cameras using shorter focal lengths to achieve the same field of view, aperture diameter at identical f-stops tends to be smaller, and overall focus distance longer for the same composition. These factors make it more difficult to achieve shallow depth of field on smaller format cameras without resorting to very fast glass. 
 

Though that said, APS-C and M4/3 offer plenty of options nowadays if you like shallow depth of field. You can’t exactly wack a background into oblivion with impunity, but with good composition and background, you can achieve very good results. 

[YellowJersey]

A good way to see the difference is to go to a camera store and look a lens on a full frame and then APS-C sensor. Take, say, a 35mm, look at it on a Canon Rebel and then mount it onto a full frame like a 5DmkIV or 6DmkII. Full frame sensors will show the "true" focal length since there's no crop, so it will show a wider field of view. APS-C sensors will show a "cropped" focal length and therefore a narrower field of view.

A 50mm lens on an APS-C camera will give the same field of view as a 75mm lens on a full frame camera. Just take the focal length and multiply it by 1.5 to get the equivalent field of view.