Crop Sensor Camera with Full Frame Lens Question

[smoke665]

Adding to the explanations put forth by @Ysarex if you shoot from the same position with a 35mm and 50mm lenses, then taking the 35mm lens and cropping it to the same angle of view of the 50mm lens will give you pretty much the same image, other than any differences in optical quality between the two lenses and the resolution lost to cropping. It should also be noted that If you shoot from the same distance and use the same aperture the 35mm will have a greater DOF initially, but by cropping the image from the wider angle lens you increase the magnification factor of the cropped image to view both images at the same display size, which will result in a decrease of DOF, and the same corresponding DOF.

 

[petrochemist]

Adding to the explanations put forth by @Ysarex if you shoot from the same position with a 35mm and 50mm lenses, then taking the 35mm lens and cropping it to the same angle of view of the 50mm lens will give you pretty much the same image, other than any differences in optical quality between the two lenses and the resolution lost to cropping. It should also be noted that If you shoot from the same distance and use the same aperture the 35mm will have a greater DOF initially, but by cropping the image from the wider angle lens you increase the magnification factor of the cropped image to view both images at the same display size, which will result in a decrease of DOF, and the same corresponding DOF.

It's true that the off quoted myth off focal length changing perspective is actually down to viewing position. However there are factors that do depend on the lenses actual focal length such as behavior with given extension (usually macro). So I believe it is important to know the actual focal length & not get too carried away with equivalence.

The crop factor gives the equivalent focal length which gives field of view. Sometimes this can be useful for comparing between systems but most of the time it's better just to know what a given lens does on YOUR camera. Even for those of us who use multiple cameras of different crops it's usually enough to think things like 'the mild telephoto should do for this' - I've used interchangeable lens cameras with 8 different sensor sizes in the last 2 years & equivalence only really comes into my photography when trying odd lens/camera combinations or when getting a new lens.

 

[nerwin]

Adding to the explanations put forth by @Ysarex if you shoot from the same position with a 35mm and 50mm lenses, then taking the 35mm lens and cropping it to the same angle of view of the 50mm lens will give you pretty much the same image, other than any differences in optical quality between the two lenses and the resolution lost to cropping. It should also be noted that If you shoot from the same distance and use the same aperture the 35mm will have a greater DOF initially, but by cropping the image from the wider angle lens you increase the magnification factor of the cropped image to view both images at the same display size, which will result in a decrease of DOF, and the same corresponding DOF.

Right. But what I am trying express is that an ultra wide angle lens cannot look the same as a 50mm lens. Will the field of view be similar? Yes but it doesn't change the lens characteristics such as barrel and pin cushion distortion..wide angles will always push scene away where as a 50mm will have more compression. While the field of view would look the same it's not going to look exactly the same because the focal lengths are different. That's what I'm trying to explain but apparently I'm wrong.

When I had an X100 which has a 23mm lens, an equivalent of a full frame 35mm lens and also shot photos with a 35mm lens on a full frame camera, they simply looked different to me. The 23mm lens while the field of view was similar to the 35mm full frame image, the 23mm lens is still fundamentally a 23mm wide angle lens just cropped in to get the same field of view as a 35mm full frame lens which still will brings along the typical wide angle characteristics of that focal length.

I don't know. That's how I always understood it. Focal length is a physical construct of the lens and it cannot be magically changed by cropping.

All lenses have some sort of distortion, more noticeable on ultra wide angles. You can't make a 24mm full frame lens look like a 50mm lens. You can match field of view, but not the focal length.

Maybe I'm just dumb.

 

[smoke665]

don't know. That's how I always understood it. Focal length is a physical construct of the lens and it cannot be magically changed by cropping.

All lenses have some sort of distortion, more noticeable on ultra wide angles. You can't make a 24mm full frame lens look like a 50mm lens. You can match field of view, but not the focal length.

By cropping you aren't changing "focal length", you're magnifying the center of the image by cropping thereby changing the "field of view". It's still an image shot with a 24mm lens, but you're only using a piece of the total image.

Yes but it doesn't change the lens characteristics such as barrel and pin cushion distortion..wide angles will always push scene away where as a 50mm will have more compression.

Most nomal lenses don't have a fish-eye effect. Ultra wide or fish eyes are a completely different kind of lens. While not always perfect, normal lenses attempt to be rectilinear to minimize barrel and pin cushion distortion, differences in design and quality may come into play because it's harder to build a a wide angle lens, but by and large if there is distortion, it's more prominent at the outer edges. By cropping, you're effectively eliminating it.

 

[nerwin]

I guess you're right. I was wrong. I always thought focal length mattered.

 

[pietdupreez]

I got lost in the discussions and my have missed someone else suggesting it; Canon has an excellent 24mm EF S lens made for you camera. That is 39mm equivalent, and quite affordable. If you have the EF 50 1.8 too, you can use either the one or the other depending on the subject and the space to maneuver. Both are excellent from about f 2.8

 

[Ysarex]

Right. But what I am trying express is that an ultra wide angle lens cannot look the same as a 50mm lens. Will the field of view be similar? Yes but it doesn't change the lens characteristics such as barrel and pin cushion distortion..wide angles will always push scene away where as a 50mm will have more compression. While the field of view would look the same it's not going to look exactly the same because the focal lengths are different. That's what I'm trying to explain but apparently I'm wrong.

When I had an X100 which has a 23mm lens, an equivalent of a full frame 35mm lens and also shot photos with a 35mm lens on a full frame camera, they simply looked different to me. The 23mm lens while the field of view was similar to the 35mm full frame image, the 23mm lens is still fundamentally a 23mm wide angle lens just cropped in to get the same field of view as a 35mm full frame lens which still will brings along the typical wide angle characteristics of that focal length.

I don't know. That's how I always understood it. Focal length is a physical construct of the lens and it cannot be magically changed by cropping.

All lenses have some sort of distortion, more noticeable on ultra wide angles.

Not all. My Fuji 14mm f/2.8 is completely distortion free. And then there's my 35mm f/2 Zeiss Biogon, pretty much the same. I use Fuji cameras because of that 14mm lens. My teacher taught me rule #1 a long time ago. Back then it went like this: Lenses take pictures and cameras hold film, keep your priorities straight. When I was shopping around back in 2012 for a new camera I did what I had learned to do and started looking at lenses. When I found the Fuji 14mm the decision was made.

You can't make a 24mm full frame lens look like a 50mm lens. You can match field of view, but not the focal length.

Maybe I'm just dumb.

No, you just picked up a faulty understanding which is really easy to do in photography -- the discipline is overrun with them. You're trying to ascribe a function to focal length that it doesn't really possess. Once in the age of the internet and Youtube videos more and more of the college photo classes I taught had to have more and more time devoted to debunking this kind of stuff. My students would come to class having seen the newest Youtube nonsense about exposure or depth of field and yes, perspective and lens focal lengths.

Back in the film era one of my main cameras was an Arca which was multi-format. I could put a 4x5 sheet back on it or a 120 roll film back on it or even my Nikon camera body on it. A favorite lens of mine was a Schneider 75mm Super Angulon. So assume I have that lens on the front of the camera and I mount the 4x5 sheet film back. That 75mm is then an ultra-wide angle lens (like a 24mm on 35mm). Take off the 4x5 back and mount a 120 6X6 roll back on the camera and the 75mm lens is now a normal lens (like a 50mm on 35mm). And finally attach my Nikon camera body to the Arca and the 75mm lens is a short telephoto portrait-length lens. If I don't move the camera while switching those backs and I take those three photos, all three photos will render the same perspective with different fields of view.

 

[Ysarex]

I guess you're right. I was wrong. I always thought focal length mattered.

Focal length does matter. For my cameras I need a 74 degree angle of view and I often like to have an 80 to 84 degree angle of view. I need focal length lenses that will deliver that and with little to no distortion. I also often want 55 and 40 degree angles of view and need focal length lenses to deliver that. I can't use the 74 degree angle of view lens if for a particular photo I need 40 degrees. I know photographers who need 7 and even 5 degree angles of view which it takes a big heavy expensive lens to deliver.

 

[petrochemist]

Focal length does matter. For my cameras I need a 74 degree angle of view and I often like to have an 80 to 84 degree angle of view. I need focal length lenses that will deliver that and with little to no distortion. I also often want 55 and 40 degree angles of view and need focal length lenses to deliver that. I can't use the 74 degree angle of view lens if for a particular photo I need 40 degrees. I know photographers who need 7 and even 5 degree angles of view which it takes a big heavy expensive lens to deliver.

In desperation you can crop a 74 degree lens to give 40 degrees, not too bad with today's cameras, but you can;t crop a 40 degree lens to give 74 degrees (you might be able to use panoramic stitching to get the reguired FOV however)

5 degrees has been far too wide for some scenes I've encountered!
This one would be at roughly 3 degrees horizontally
Wind power - old & new by Mike Kanssen, on Flickr
Thats about 450mm on APSC.

Atmospheric effects often limit such long shots, so I don't often try my 1000mm lenses. Both of which were under £150, but they're fully manual & definitely on the slow side...

 

[Ysarex]

In desperation you can crop a 74 degree lens to give 40 degrees, not too bad with today's cameras, but you can;t crop a 40 degree lens to give 74 degrees (you might be able to use panoramic stitching to get the reguired FOV however)

5 degrees has been far too wide for some scenes I've encountered!
This one would be at roughly 3 degrees horizontally

It's a good thing we're all different. Doing this for half a century now I know I see "normal" lens to very wide angle and I'm happy there. I have a 180mm ED IF Nikon that sits in a drawer. I think I might have used it three years ago. It was a gift since I would never purchase something like that. Last year when I decided to start using an MFT sensor camera I got a used Olympus with a standard zoom. The next lens I bought was a 10mm.

 

[Rickbb]

I shot a FF lens on a crop sensor for years. What I saw in the viewfinder was all I cared about. All this conversion, same as, etc. is just noise to me.

If the image in the viewfinder is what I want and the final image matches, (or close), I'm good.

Keep all that math and stuff in the lab please.

 

[VidThreeNorth]

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.

What they are telling you is correct. Rather than arguing, grab the lenses and go and test it for yourself. The main problem is that you do not have "infinite resolution" in your lenses or film or sensor. That and controlling your aperture which results in your depth of field and bokke (it's a Japanese word -- not european).

 

[MontanaDave]

I have a full-frame Canon R5 and a Crop sensor Canon R7.
The R5 is 45mp full frame while the R7 is 32.5 mp full frame.

The crop factor of the R7 is 1.6, so with a 600mm lens the effective zoom is 600 X 1.6 or 960mm. The advantage of the R7 is that with the effective zoom of 960mm, there are 32.5 mp in the photo. With the R5 shooting in crop of 1.6 or cropping in post to that field of view, there are only 18mp in the photo.

So the cropped sensor R7 has a "better reach" compared to the full frame R5.

But the full frame sensor can handle low light/high ISO much better than the cropped sensor R7.

 

[smoke665]

So the cropped sensor R7 has a "better reach" compared to the full frame R5.

A 600mm on a R5 is still a 600mm on a R7. Crop factor on the R7 refers to "Field Of View" and is a magnification of a portion of the same image as the R5. While you're correct that cropping a full frame post reduces the MPs substantially, you're comparing apples to oranges on sensors with different MPs. The way around the reduction is to "upcale & enhance" post, an easy quick procedure that will give you the same or more resolution as the crop sensor.

 

[petrochemist]

A 600mm on a R5 is still a 600mm on a R7. Crop factor on the R7 refers to "Field Of View" and is a magnification of a portion of the same image as the R5. While you're correct that cropping a full frame post reduces the MPs substantially, you're comparing apples to oranges on sensors with different MPs. The way around the reduction is to "upcale & enhance" post, an easy quick procedure that will give you the same or more resolution as the crop sensor.

This post is not up to your usual high standards.
@MontanaDave was careful to twice refer to effective zoom indicating he's quite aware of the crop giving field of view & the actual focal length has not changed.

It's not a case of apples & oranges at all to calculate the pixels in use'

Upscaling does not add any real detail it just estimates what might be there.

In any event if this procedure gave meaningful data it could be applied to the crop image just as the FF one, so the crop version still has the advantage from the point of view of detail.