Cropping and perspective -once again (split thread)

[jaapv]

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[ckern]

On 6/30/2025 at 8:21 AM, LocalHero1953 said:

I've never understood the meaning of 'render' in photographic terms.

The term typically is used to describe the process of "demosaicing" the red-green-blue matrix captured by a camera's light sensor—i.e., the method in which all the other colors are interpolated—either by in-camera firmware or external post-processing software.  A JPEG is a rendered image, for example.

Fine points (albeit omitting some nuances):

The "raw" data from the camera sensor are said to be scene-referred: they represent the light that passed through the lens to reach the sensor.  Typically a rendered image is output-referred: the sensor data have been converted to specific colors and tones that are intended to be pleasing to the human eye and brain.

Some post-processing software such as Adobe Lightroom is designed to perform image manipulation on the raw camera sensor data by storing a list of proposed edits and delaying the rendering process until the user is ready to export an edited version of the image.  This approach offers the user extensive control over color, tonal, and some other adjustments.

Lightroom and some other post-processing applications under some circumstances will convert raw sensor data into a "linear DNG," a intermediate rendered image that is still scene-referred and therefore retains essentially all the potential for adjustments that was available in the raw data.  The conversion to output-referred colors and tones from this format is treated similarly to the raw data—i.e., it is delayed until the time of export.

[S Maclean]

On 6/29/2025 at 6:23 AM, Oxfordian said:

I like my Q3, I could have bought the Q343 but decided that having a moderate wide angle lens was more useful for day to day photography, if I need to go wider than 28 then I can use my SL2 with the wide end of my Sigma 24-70 or the Sigma 20mm prime, if I need a quality image beyond 50mm on the Q3 I can use the SL2 with longer lenses. A lot of my photography is taken using the full width of the Q3's sensor or using the 35 and 50 frame lines I rarely use the 75 or 90 frame lines with the Q3.

Even in post I crop hard into the image hardly at all, unless it was a once in a lifetime shot, I decided that the Q343 was too limiting for general out and about photography, now I do appreciate that I am only looking at this from my own needs but that is the only way that you can decide.

Would I like a Q343 - Maybe. But, what I would really be interested in is Leica bringing out a Q4 with a fixed optical 28/35/50 lens rather than a digital crop, if they could make it a fast f2 or f2.8 aperture that would be brilliant - Over to you Mr Leica.

Like a d lux on steroids? 

[S Maclean]

All science aside, there is merit in having different lenses instead of cropping. otherwise we would all only have a 35 on the m11 or sl3 and crop from there.

lenses have different character.  Lenses do distort differently, and focusing on, lets say, the left eye with a nice fall out in focus is not as easy with a 28 cropped into a 75 as it is with a 75.

and if you do get close enough that the 1.7 aperture of the 28 can have the effect it will probably come along with some distortion. 
 

perspective and general DOF is one thing, subtle nuances brought by being able to use a good Focal length for the purpose is other.

and I get that the ethos of the Q may be to crop on a 60 mp sensor, but the same sensor and the same cropping is possible with the M and the SL and we all have several lenses. 
 

 

[lencap]

After enjoying photography as a hobby for 60+ years I continue to have difficulty clearly explaining the differences between cropping and using different focal length lenses when the images are initially created.  I asked an AI to provide a clear comparison.  Here's the reply:

This chart and explanation should help a photographer understand why cropping a 28mm image doesn’t replicate the exact look of a 50mm lens, particularly in terms of depth of field, while clarifying that perspective remains unchanged when cropping.

Depth of Field vs. Perspective in Photography

Aspect	Perspective	Depth of Field (DoF)
Definition	How objects appear relative to each other in size and position, based on camera position.	The range of distances in the image that appear sharp and in focus.
Controlled By	Camera-to-subject distance. Focal length affects framing but not perspective if distance is adjusted.	Focal length, aperture, and camera-to-subject distance.
Effect of Focal Length	Wide-angle (e.g., 28mm): Exaggerates distance, foreground larger, background smaller. Longer focal length (e.g., 50mm): Compresses scene, objects appear closer together.	Longer focal length (e.g., 50mm): Shallower DoF, more background blur. Shorter focal length (e.g., 28mm): Deeper DoF, more in focus.
Cropping 28mm to 50mm (Leica Q3)	Perspective stays the same as 28mm (wide-angle look), as camera position doesn’t change.	DoF remains the same as the original 28mm f/1.7 image (deeper than a 50mm lens), as cropping doesn’t change lens properties.
Using True 50mm Lens at f/1.7	Perspective is more compressed (objects closer together) due to farther camera distance to achieve same framing.	Shallower DoF than 28mm f/1.7, with more pronounced background blur, due to longer focal length.
Visual Impact	Affects the “look” of spatial relationships (e.g., dramatic wide-angle vs. natural standard lens).	Affects how much of the scene is sharp vs. blurred (e.g., isolated subject vs. everything in focus).
Example (Leica Q3)	28mm: Subject’s face looks slightly larger relative to background. Cropped to 50mm: Same perspective, just magnified. True 50mm: Face and background more proportional.	28mm f/1.7: More of the scene in focus. Cropped to 50mm: Same DoF as 28mm. True 50mm f/1.7: Background more blurred, subject stands out more.

Key Takeaway:

• Cropping a 28mm image to match a 50mm field of view keeps the wide-angle perspective and deeper DoF of the 28mm lens.
• A true 50mm lens (at the same f/1.7) requires stepping back, which slightly compresses perspective and creates a shallower DoF, making the background blurrier.
• To change perspective, move closer or farther from the subject. To change DoF, adjust aperture or use a different focal length lens.

Key Differences Summarized

For a photographer, the critical takeaway is:

• Perspective is about how objects relate spatially in the image, controlled by where you stand (camera position). Cropping a 28mm image to 50mm doesn’t change perspective.
• Depth of Field is about how much of the image is in focus, affected by focal length, aperture, and distance. A true 50mm lens at f/1.7 will have a shallower DoF than a 28mm lens at f/1.7, even if the subject is framed the same way, because of the longer focal length and increased camera-to-subject distance.

Edited July 3 by lencap

[ianforber]

Everything has already been said, but not yet by everybody. 

I bought my Q2 specifically to replace my other digital cameras because it allows me to crop very heavily to get the image I want. Most of my images are landscape or street so the difference in DoF is irrelevant. I always crop in post, often very heavily and I’m fine with that  I didn’t buy it to use all the pixels, I bought it so that I could throw a lot of them away.

I do use the in camera crop modes but purely to bring up the viewfinder guides so that, in the rare occasions when I’m taking a portrait, I can remind myself to stand back and not fill the frame with the person’s face thereby distorting their face. 

[jaapv]

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Typical self-contradictory AI . A million words to say two things, laced with nonsense  and irrelevancies  which, in the end, it seems to have found out  I call AI: IS  Idiot Savant  

If you don’t change position the perspective won’t change. If you change focal length the DOF will change. That is all that needs to be said. 

[IkarusJohn]

On 7/4/2025 at 8:45 AM, jaapv said:

Typical self-contradictory AI . A million words to say two things, laced with nonsense  and irrelevancies  which, in the end, it seems to have found out  I call AI: IS  Idiot Savant  

If you don’t change position the perspective won’t change. If you change focal length the DOF will change. That is all that needs to be said. 

Simple, clear, incontrovertible

[jaapv]

4 hours ago, IkarusJohn said:

Simple, clear, incontrovertible

Actually, to muddy the waters, the DOF does not change either, because it does not exist.🤩😜
 An image is sharp in the plane of focus only and nowhere else. However, if the static resolution of our eyes is unable to detect the unsharpness of parts of the image, we perceive that as DOF or area of acceptable unsharpness. Obviously this is determined by magnification throughout the system until the image is formed on the retina. 
If you change focal length you change the angle of view of the lens and thus the magnification and thus the DOF-illusion. 
 

[ckern]

2 hours ago, jaapv said:

Actually, to muddy the waters, the DOF does not change either, because it does not exist.
 

True enough, but aren't you concerned that pointing out technical details like this may only serve to add to the circle of confusion in this forum?

[jaapv]

Not if they believe me😇

[adan]

On 7/3/2025 at 2:45 PM, jaapv said:

If you change focal length the DOF will change. That is all that needs to be said. 

Well, almost.....

"If you change focal length the DOF and field of view will change. That is all that needs to be said."

The FoV of course can then also be changed, by cropping - digital crop from the sensor (Q series); a "permanently cropped" sensor (M8, CL/TL); in page-layout software (InDesign, Pagemaker, Quark XPress); with the easel blades in a chemical darkroom; with scissors or a paper cutter for completed prints.

But still will have no effect on "perspective."

[SrMi]

6 hours ago, jaapv said:

Actually, to muddy the waters, the DOF does not change either, because it does not exist.🤩😜
 An image is sharp in the plane of focus only and nowhere else. 
 

The definition of DOF is the distance between two points that are in acceptable sharp focus.

[Pyrogallol]

Cropping after you have taken the picture is either a way of correcting inaccurate framing in the viewfinder or a lazy way of composing the picture.

HCB rarely cropped a negative when printing ( or having printed for him).

Compose your picture in the viewfinder and make best use of the available film/pixels.

[jaapv]

10 minutes ago, Pyrogallol said:

Cropping after you have taken the picture is either a way of correcting inaccurate framing in the viewfinder or a lazy way of composing the picture.

HCB rarely cropped a negative when printing ( or having printed for him).

Compose your picture in the viewfinder and make best use of the available film/pixels.

HCB did not have a Q nor 60 MP

[jaapv]

3 hours ago, SrMi said:

The definition of DOF is the distance between two points that are in acceptable sharp focus.

Strange, leaving out the part of the quote where I said exactly that. It suggests selective reading. 

[jaapv]

4 hours ago, adan said:

Well, almost.....

"If you change focal length the DOF and field of view will change. That is all that needs to be said."

The FoV of course can then also be changed, by cropping - digital crop from the sensor (Q series); a "permanently cropped" sensor (M8, CL/TL); in page-layout software (InDesign, Pagemaker, Quark XPress); with the easel blades in a chemical darkroom; with scissors or a paper cutter for completed prints.

But still will have no effect on "perspective."

Yes Post # 49. 

 

9 hours ago, jaapv said:

Actually, to muddy the waters, the DOF does not change either, because it does not exist.🤩😜
 An image is sharp in the plane of focus only and nowhere else. However, if the static resolution of our eyes is unable to detect the unsharpness of parts of the image, we perceive that as DOF or area of acceptable unsharpness. Obviously this is determined by magnification throughout the system until the image is formed on the retina. 
If you change focal length you change the angle of view of the lens and thus the magnification and thus the DOF-illusion. 
 

 

[jaapv]

4 hours ago, adan said:

Well, almost.....

"If you change focal length the DOF and field of view will change. That is all that needs to be said."

The FoV of course can then also be changed, by cropping - digital crop from the sensor (Q series); a "permanently cropped" sensor (M8, CL/TL); in page-layout software (InDesign, Pagemaker, Quark XPress); with the easel blades in a chemical darkroom; with scissors or a paper cutter for completed prints.

But still will have no effect on "perspective."

 Not the field of view but the angle of view. The field of view is defined at a given distance , focal length controls the angle of view. 
As DOF occurs at various distances around the focal plane it cannot be interpreted by the field of view without defining the position of the focal plane. 
Hence the shift in DOF from 1:3 close up to 1:1 near infinity. 
Also , as we all know empirically, DOF is at its most shallow with macro and long focal lengths. That , again, is due to magnification. 

[IkarusJohn]

10 hours ago, jaapv said:

Actually, to muddy the waters, the DOF does not change either, because it does not exist.🤩😜
 An image is sharp in the plane of focus only and nowhere else. However, if the static resolution of our eyes is unable to detect the unsharpness of parts of the image, we perceive that as DOF or area of acceptable unsharpness. Obviously this is determined by magnification throughout the system until the image is formed on the retina. 
If you change focal length you change the angle of view of the lens and thus the magnification and thus the DOF-illusion. 
 

And you were doing so well!🙄

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[jaapv]

I love to present Andreas with large numbers of posts. Sowing confusion with basic facts is a good technique. 🤪