Focal length comparison - portriat - crop

[MOREGONE]

I understand crop so no need to explain that.

So we all know that focal length affects how a portrait and that is why wide angles really aren't used. Lengthens the face and looks odd, in contrast the telephoto is flattering etc.

So what I am looking to confirm is that crop factor does NOT affect a focal length looks?

So a 50mm on a crop is near 75mm, but it will still look like a 50mm, cropped, right? It will not look more like 85mm magically or will it? It will be cropped closer to the 85 but the quality of the image will still be that of a 50mm focal length right?

 

[Braineack]

Depends how you frame the shot when comparing it to a full frame shot...

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[WayneF]

So what I am looking to confirm is that crop factor does NOT affect a focal length looks?

? The crop in a camera with cropped sensor is EXACTLY the same crop as if you cropped the larger full image to the same smaller size in a photo editor later. Crop merely cuts off the outer borders all around, and leaves the central portion. This is exactly true of cropped sensors too (why it is called a cropped sensor).

Now, it is true that when you then enlarge that smaller crop larger, to appear normal size again, same as the big boys, it does make you think a telephoto lens was used. But that is what crop does. Try cropping ANY image in your editor to see this effect. It seems necessary to believe it.

The perspective effect you mentioned (wide angles, etc) is not a crop, exactly. The difference in perspective is only about where the camera stands, and for head and shoulders portraits, you were surely standing too close with a wide angle lens.

Crop and perspective are very different things. But crop is simply crop, in all cases.

 

[MOREGONE]

Depends how you frame the shot when comparing it to a full frame shot...

No, thats not what I am talking about. That's crop and or composition. I am inquiring about the way focal length affects an image.

I am not even sure why I asked the question since I pretty much knew the answer. But in all the talks of crop vs fx, people hardly ever discuss how the appearance of focal length plays a roll. Using a 35mm on a DX to replicate a 50mm is not the same as using a 50 on FX. Sure it may achieve the same composition but the appearance of the image/portrait will be different because of the focal length.

http://www.bubblewrapstudio.net/wp-content/uploads/2013/01/focal-length-portrait.jpg

Assume those are FX pictures. Shooting that same picture at 24mm on a crop will not look the same as the 35, it will look the same as the 24mm, but cropped

 

[Braineack]

35mm on a DX will achieve a very similar result as a 50mm on FX, since the cameras will be in roughly the same physical location. This is crop.

50mm on a DX will achieve a very different result as a 50mm on FX, when trying to achieve the same composition, since the cameras will be in much different physical locations in order to frame the same shot.

If anything the DX user will be less susceptible to the distortion since to frame the image, compared to an FX user with the same lens, they must stand much further back. This will also affect the DOF and the background characteristics.

An FX user using a 85mm 1.8 will have better background magnification and better bokeh, since they will be closer to the subject than the DX user with the same 85mm 1.8, all framing being equal.


I think the question I have is: why are we comparing DX to FX stuff if all you wanted to talk about what how focal length affects an image?

 

[jaomul]

To OP your understanding is correct. Just imagine your cropped sensor photograph. If you stood in same spot with a fullframe you would get more surrounding area but the "look" from the cropped sensor photo would look the same as if you cropped your fullframe photo to that size and area of the photo

 

[robbins.photo]

Depends how you frame the shot when comparing it to a full frame shot...

No, thats not what I am talking about. That's crop and or composition. I am inquiring about the way focal length affects an image.

I am not even sure why I asked the question since I pretty much knew the answer. But in all the talks of crop vs fx, people hardly ever discuss how the appearance of focal length plays a roll. Using a 35mm on a DX to replicate a 50mm is not the same as using a 50 on FX. Sure it may achieve the same composition but the appearance of the image/portrait will be different because of the focal length.

http://www.bubblewrapstudio.net/wp-content/uploads/2013/01/focal-length-portrait.jpg

Assume those are FX pictures. Shooting that same picture at 24mm on a crop will not look the same as the 35, it will look the same as the 24mm, but cropped

I must be reading different threads than you have been because everytime I've seen the topic come up it's followed by 6-10 pages of one person after another trying to one up the last guy in giving an even longer winded and more technical explanation. Lol

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[kundalini]

I did this a couple of years ago, but I doubt much has changed. Relative cheap lenses were used... 50mm f/1.8 and 35mm f/2.

http://www.thephotoforum.com/forum/...rence-between-full-frame-cropped-sensors.html

 

[Braineack]

I was hoping you would post that link, I couldn't find it again.

Depends how you frame the shot when comparing it to a full frame shot...

35mm on a DX will achieve a very similar result as a 50mm on FX, since the cameras will be in roughly the same physical location. This is crop.

....................................DX 35mm.....................................................................FX 50mm...........................

50mm on a DX will achieve a very different result as a 50mm on FX, when trying to achieve the same composition, since the cameras will be in much different physical locations in order to frame the same shot...This will also affect the DOF and the background characteristics.

....................................DX 35mm..................................FX 35mm (recomposed for 16" camera to subject).....

 

[curtyoungblood]

I don't think the 35mm and 50mm focal lengths are the best way to illustrate this particular effect. 35 and 50 are pretty close together and have relatively similar distortion effects on an image. I think it is a lot more pronounced at the extremes of focal lengths (particularly wide). A lot of people put super wide angle lenses, like the 10-22, on a crop camera and those always look weird to me. Seeing a 10mm distortion on a 16mm crop of an image feels like an incomplete image to me.

 

[table1349]

Understanding Camera Lenses

Read the part on perspective control.

 

[MOREGONE]

Thanks for the responses

I was looking for the thread and it may have been on a different forum (sorry I check a few), but the person was "looking for a proper portrait lens" and because they DX, the consencous was 50mm would be good for them because its close to the 85mm equivalent. I was hung up on the fact that FX shooters don't choose the 85 because they like being _X_ feet away from the subject, they use it because of the look of the image. And all I kept thinking was it won't be like a 85mm, it will be like a 50mm... cropped

Thanks

 

[Braineack]

a 85mm looks good on any camera. Such an awesome lens.

 

[DM110]

Hi everyone - first time posting anything on this forum. Haven't been on any forms in a while, but really wanted to chime in on this. Perspective and whether this is consistent between a FX sensor and DX sensor with "equivalent" lens is the question from what I understand.

Perspective is based on FOV and distances from the lens to the subject plane and from the subject plane to everything else not on that exact plane. If the FOV is the same and the scene doesn't change (same distances), the perspectives will be identical (illustrated well by the first set of stuffed monkey images above). A DX sensor with a 50mm lens produces the same FOV as a FX sensor with a 75mm lens, so they will produce the EXACT same perspective if the subject is composed at the same distance.

I've made diagrams to illustrate why this works. First one shows why objects not on the subject plane appear differently within the frame if the FOV is different. We can see that despite the front of the 7' tall subject nearly filling the frame, the back of the subject (still 7' tall) fills different amounts of the frame based on FOV. This is the perspective "distortion" seen by using wide angle lenses. The basic diagram should illustrate why the same FOV and subject plane crop would yield the same perspective and thus perspective based "distortion." The second diagram shows how a DX sensor with a 50mm lens produces the same FOV as a FX sensor with a 75mm lens. The caveat to all of this is that the lenses must not have (or have minimal) 3rd order distortion such as barrel or pincushion which would affect the portrait's perceived perspective. Basically, a 50mm lens on a DX sensor is going to work very similarly to a 75mm lens on a FX sensor since both have minimal distortion. 16mm DX versus 24mm FX is another story due to the inevitable barrel distortion differences.

Sorry this came out so long!