Crop Sensor Camera with Full Frame Lens Question

[RScottie]

I am new to "real" Digital Cameras having been out of the hobby for some time.

As such, most of my questions involve gear and all the settings that these wonderful cameras present.

I have a Canon EOS Rebel T7, an APS-C type sensor. Now I understand this to mean that this sensor is smaller than a full frame (35mm) sensor by a factor or 1.6.

And, my understanding is that this 1.6 factor has an effect on lenses that were not designed for APS-C cameras.

As such, per my understanding, if I put an EF lens on my camera body, I am actually getting whatever the focal length is times 1.6, thus a 50mm EF lens would effectively be 80mm?

Is this the correct "direction" of the math for these lenses?

I ask because I want a non-zoom prime lens for general use that is 50mm give or take a few mm, but not give or take 30mm!

I noticed that Canon has another lens that is an 40mm EF but it is slower at F2.8 instead of F1.8.

I would get closer to the field of view I am looking for with that 40mm lens (64mm) than I would with the 50mm (80mm) but I would give up the low light capability that is one of the things I am seeking.

Of course if my math is wrong and I have went in the wrong direction in regards to how the crop sensor camera "sees" these full frame lenses, the whole question is moot.

I may be overthinking this, which I am prone to do, but I appreciate any opinions on the choice of lens as well as whether or not my math is correct in regards to the full frame lens on a crop body.

 

[nerwin]

So regardless of the lens whether or not it's for crop or full frame, it's always going to be what actual focal length of the lens is but crop sensor lenses have smaller image circle so on full frame sensors they will leave a heavy vignette or a circle as they can't cover the entire sensor but the focal length remains the same.

You are right that there is a crop factor, canon crop sensors are a hair smaller than Nikon which is 1.5x while canon is 1.6x.

So yes a 50mm x 1.6 = 80mm so you getting an 80mm full frame equivalent focal length on crop but it's still 50mm just cropped in.

So if you want an equivalent focal length of 50mm on your crop sensor you'll want a 30mm lens, I'm not sure if there is one for that mount otherwise a standard 35mm prime works as well. However those lenses will still bring along the characteristics of a 30mm/35mm lens, it won't match 50mm because what you are getting effectively is an equivalent field of view of a 50mm lens but not actually 50mm.

For an example. If I take my 50mm lens on my full frame camera and crop it in 1.6x to get an equivalent field of view of an 80mm, it would be essentially identical to one taken with a 50mm on an APS-C size sensor camera.

Hopefully this makes sense.

 

[RScottie]

(Snip)

Hopefully this makes sense.

Yes, it does make sense. Thank you as I was doubting if I had it right.

It amazes me all the features on these cameras. I am in no hurry to "upgrade" as I've only had this camera a couple of years and only recently decided I needed to really learn how to use it.

I figure that I will figure out what I like and don't like as I go.

So far I have mainly shot in the "semi auto" modes, mainly Aperture Priority as well as the "full auto/no flash" with the auto focus off. Yeah, I like manually focusing, weird right?

I have decided that the camera in auto, while doing a decent job, sometimes does not quite get it the way I want it.

This was obvious when I looked at my pictures and some of my shots looked "grainy" or not quite right, especially when I zoom in or crop them.

So at this point I am not sure if it is me or the settings I've chosen or even the lens that is the weakest link.

The fun will be in figuring it all out!

Now if it will just stop raining for a day or two when I'm off work....

 

[petrochemist]

Yes, it does make sense. Thank you as I was doubting if I had it right.

It amazes me all the features on these cameras. I am in no hurry to "upgrade" as I've only had this camera a couple of years and only recently decided I needed to really learn how to use it.

I figure that I will figure out what I like and don't like as I go.

So far I have mainly shot in the "semi auto" modes, mainly Aperture Priority as well as the "full auto/no flash" with the auto focus off. Yeah, I like manually focusing, weird right?

I have decided that the camera in auto, while doing a decent job, sometimes does not quite get it the way I want it.

This was obvious when I looked at my pictures and some of my shots looked "grainy" or not quite right, especially when I zoom in or crop them.

So at this point I am not sure if it is me or the settings I've chosen or even the lens that is the weakest link.

The fun will be in figuring it all out!

Now if it will just stop raining for a day or two when I'm off work....

Having an EF camera (which has a short flange distance foe an SLR) and liking manual focusing suggests to me that you would enjoy adapting lenses. With these manual focus is usually required & as you use Aperture priority too setting the aperture on the lens & letting the camera sort out the shutter speed is easy.

Adapted lenses can be very much cheaper than native glass, most of the moderate primes (avoiding ultra wides or ultra telephotos) are quite reasonable, and some can give interesting character... Lenses designed for manual focus actually have much more subtle focus controls than those designed for AF. AF wants a short focus throw so the motor can get there quicker.

You mention some of your results look grainy - this is noise that can be caused by underexposure or too high an ISO setting.

The feeling the weathers only good while at work is a very familiar one! There have been times in the past when I took my camera to work so as to play with it at lunchtime. Finding subjects indoors is another option if you can create enough space to shoot still life or macro...

 

[Dikkie]

So if you want an equivalent focal length of 50mm on your crop sensor you'll want a 30mm lens, I'm not sure if there is one for that mount otherwise a standard 35mm prime works as well.

I have a Nikon crop sensor, with a Sigma 30mm F1.4.
Sigma has this same lens for Canon I think.

Canon has its own 35mm lens.

The sigma gives me nice star effects on street lights during night shots (with longer shutter times at F16):


Place Bara by Bulevardi, on Flickr

 

[Ysarex]

So regardless of the lens whether or not it's for crop or full frame, it's always going to be what actual focal length of the lens is but crop sensor lenses have smaller image circle so on full frame sensors they will leave a heavy vignette or a circle as they can't cover the entire sensor but the focal length remains the same.

You are right that there is a crop factor, canon crop sensors are a hair smaller than Nikon which is 1.5x while canon is 1.6x.

So yes a 50mm x 1.6 = 80mm so you getting an 80mm full frame equivalent focal length on crop but it's still 50mm just cropped in.

So if you want an equivalent focal length of 50mm on your crop sensor you'll want a 30mm lens, I'm not sure if there is one for that mount otherwise a standard 35mm prime works as well. However those lenses will still bring along the characteristics of a 30mm/35mm lens, it won't match 50mm because what you are getting effectively is an equivalent field of view of a 50mm lens but not actually 50mm.

They will match -- they'll match exactly so that you'll be able to take the same photo with either camera. If I mount my 14mm lens on my APC-C camera (1.5 crop) and my 21mm lens on my FF camera, put them both in the same place they'll take matching photos. There's a DOF difference but that can be compensated for.

For an example. If I take my 50mm lens on my full frame camera and crop it in 1.6x to get an equivalent field of view of an 80mm, it would be essentially identical to one taken with a 50mm on an APS-C size sensor camera.

Hopefully this makes sense.

 

[nerwin]

They will match -- they'll match exactly so that you'll be able to take the same photo with either camera. If I mount my 14mm lens on my APC-C camera (1.5 crop) and my 21mm lens on my FF camera, put them both in the same place they'll take matching photos. There's a DOF difference but that can be compensated for.

Field of view wise, yes.

But they are two focal different lengths period. They are not the same, they are completely different measurements.

A 14mm lens will always render like a 14mm lens regardless of its crop factor, the same goes for 21mm lens is what I am trying to say. Just because a 14mm lens mounted on a crop sensor, doesn't magically change its perspective distortion to a 21mm lens. It doesn't work that way.

You're correct that the field of view will be the same but they cannot be exactly the same because the focal length is different and they would have to be exactly the same focal length.

 

[Digger...]

So regardless of the lens whether or not it's for crop or full frame, it's always going to be what actual focal length of the lens is but crop sensor lenses have smaller image circle so on full frame sensors they will leave a heavy vignette or a circle as they can't cover the entire sensor but the focal length remains the same.

You are right that there is a crop factor, canon crop sensors are a hair smaller than Nikon which is 1.5x while canon is 1.6x.

So yes a 50mm x 1.6 = 80mm so you getting an 80mm full frame equivalent focal length on crop but it's still 50mm just cropped in.

So if you want an equivalent focal length of 50mm on your crop sensor you'll want a 30mm lens, I'm not sure if there is one for that mount otherwise a standard 35mm prime works as well. However those lenses will still bring along the characteristics of a 30mm/35mm lens, it won't match 50mm because what you are getting effectively is an equivalent field of view of a 50mm lens but not actually 50mm.

For an example. If I take my 50mm lens on my full frame camera and crop it in 1.6x to get an equivalent field of view of an 80mm, it would be essentially identical to one taken with a 50mm on an APS-C size sensor camera.

Hopefully this makes sense.

All of this is way over my head. As long as the camera takes a picture in the shape of a rectangle im happy...

 

[Ysarex]

Field of view wise, yes.

But they are two focal different lengths period. They are not the same, they are completely different measurements.

A 14mm lens will always render like a 14mm lens regardless of its crop factor, the same goes for 21mm lens is what I am trying to say. Just because a 14mm lens mounted on a crop sensor, doesn't magically change its perspective distortion to a 21mm lens. It doesn't work that way.

It's perspective distortion??? Perspective is a function of camera placement.
If I took the same photo with my14mm lens on my APS-C camera and 21mm lens on my FF camera I would take each photo from the same place and perspective in both photos would be the same.
What do you think would be a visual difference that could identify one photo from the other?

You're correct that the field of view will be the same but they cannot be exactly the same because the focal length is different and they would have to be exactly the same focal length.

 

[nerwin]

It's perspective distortion??? Perspective is a function of camera placement.
If I took the same photo with my14mm lens on my APS-C camera and 21mm lens on my FF camera I would take each photo from the same place and perspective in both photos would be the same.
What do you think would be a visual difference that could identify one photo from the other?

The lens rendering and it's distortion! They are gonna be different because the focal lengths are different. Same field of view but the rendering will be different. I noticed this the most when I had Fujifilm cameras and used a 23mm lens. It was nothing close to a 35mm lens. Sure same field of view but the distortion of the 23mm lens was noticeable and basically looked like I simply cropped in on a 24mm full frame image. It looks different. Maybe some don't notice it. I don't care what anyone says, they are same field of view but not the same focal length. It does matter, you cannot change physics. A 23mm lens will not render the same as a 35mm lens.

 

[Ysarex]

The lens rendering and it's distortion! They are gonna be different because the focal lengths are different.

No, they will not be different because the focal lengths are different. What distortion? You mention a Fuji 23mm lens -- that lens is nearly distortion free and my Fuji 14mm is 100% distortion free. Fujifilm Fujinon XF 23 mm f/2 R WR review - Distortion - LensTip.com

Distortion isn't a function of lens focal length, it's a function of lens design. And with modern digital cameras distortion is pretty well software corrected.

You mentioned perspective; perspective is a function of camera placement and not lens focal length. Took two photos for you. A 25mm lens on a MFT Olympus (crop factor 2) and a 50mm lens on a FF Nikon. If the rendering is different due to focal length then you should be able to tell them apart. There are at best subtle differences and those are due to the software lens corrections. There is nothing in the way of a visible difference in these two photos that is a result of the different focal lengths.

Same field of view but the rendering will be different. I noticed this the most when I had Fujifilm cameras and used a 23mm lens. It was nothing close to a 35mm lens. Sure same field of view but the distortion of the 23mm lens was noticeable and basically looked like I simply cropped in on a 24mm full frame image.

If you take a photo with a 50mm lens and then a 24mm lens from the exact same place and then crop the 24mm photo to have the same field of view as the 50mm photo you will have two photos with identical perspective.

It looks different. Maybe some don't notice it. I don't care what anyone says, they are same field of view but not the same focal length. It does matter, you cannot change physics. A 23mm lens will not render the same as a 35mm lens.

 

[nerwin]

Yes but it's not the same focal length! All lenses have have some kind of lens distortion. Ultra wide angles really expand the scene or I guess make it look as if it's being pushed far away where as more telephoto you go, the more compressed it gets.

So you're telling me if you take a portrait of someone at the exact same position with a 24mm lens and 50mm and you crop that 24mm image to the same field of view of a 50mm lens it's gonna look the exact same? I disagree. The 50mm will compress a person's features where as a 24mm will expand them, "distort" them.

I give up. Then what's the point in any focal lengths anymore. Might as well shoot everything at 10mm and crop in then. Since lens rendering, distortion etc doesn't seem to be applied anymore.

 

[Ysarex]

Yes but it's not the same focal length! All lenses have have some kind of lens distortion.

Not as a function of focal length. A lens can be designed to be distortion free. Your use of the word distortion isn't distortion. Lens distortion is the failure of a lens to render all straight lines in the scene as straight -- barrel versus pincushion distortion. You're talking about perspective "distortion" which is really just perspective and really shouldn't be thought of as distortion -- wide angle versus normal versus telephoto perspective. When referred to as distortion it's common usage causing common confusion. NOTE: the relationship between perspective and wide angle versus normal versus telephoto is only correlative not causal. The causal factor is camera position.

Ultra wide angles really expand the scene or I guess make it look as if it's being pushed far away where as more telephoto you go, the more compressed it gets.

That's not distortion and it's not a function of focal length. There's a focal length correlation. You're talking about perspective and that's a function of camera placement.

So you're telling me if you take a portrait of someone at the exact same position with a 24mm lens and 50mm and you crop that 24mm image to the same field of view of a 50mm lens it's gonna look the exact same?

Absolutely yes -- the camera position determines perspective not the lens focal length. So if I put my MFT Olympus (crop factor 2) at position X and mount my 12mm lens -- click and then place my FF Nikon at the same position X and mount my 24mm lens -- click, I get identical perspective in both photos because of position X. Position X is the perspective determinant.

I disagree. The 50mm will compress a person's features where as a 24mm will expand them, "distort" them.

No, If you move closer with the 24mm lens then being closer expands the person's features, it's not the lens focal length. Back away with the 50mm lens and you compress the person's features by backing away, it's not the lens focal length.

So with different format cameras, to match the field of view and perspective we have to use different focal length lenses from the same camera position. We get the same photo including the same perspective because the camera position is the same.

I give up. Then what's the point in any focal lengths anymore. Might as well shoot everything at 10mm and crop in then.

Because there's some limits to how much cropping you can get away with.

Since lens rendering, distortion etc doesn't seem to be applied anymore.

 

[greybeard]

So, you want a prime lens that will give you on your crop sensor camera, a similar Field Of View (FOV) as a 50mm lens does on a Full Frame Camera? That would be a a 30mm which would give you a the same FOV as a 48mm on full frame. A FF 28mm on your crop would give you something like a 45mm on a FF. Canon makes a 28mm f/1.8 that should do the trick.

https://www.mpb.com/en-us/product/canon-ef-28mm-f-1-8-usm

 

[nerwin]

I give up trying. Good luck. I'm not continuing this conversation anymore.