Crop Later or When Shooting Actual Photo?

I crop in post, often leaving a little around the edges for that purpose. If I decide to use only one person, a 1:1 ratio will do. If not 4x3 or 8x10 crop is good. But it varies from shot to shot.

Yes-ish.....

If you crop with your zoom versus zooming in via a crop in post, this is likely true, though never tried it my self.

But if you have a fix length lens and crop it 50% in post, versus cropping with your feet until your have cropped out the image to the same coverage ares, you don't have the same DoF.

If you have a full frame camera with an 85 f1.8 on it shooting wide open, and the distance from subject is 20 feet, your DoF will be 1.78 ft

Then you crop with your feet walking up to 10 feet away from the subject, you DoF will be .44 ft.

Just wanted to clear the up. How you "crop" in the field makes a huge difference to DoF.

Using the Flexible DOF calculator which is online on Cambridge Color web site, and assuming 20/20 vision acuity (not looser 'Manufacturer Standard' of typical DOF tables)

1. FF body, 75mm f/4 at 50' (600") focus, 20/20 vision: DOF zone = 139.72", (front = 538.16" to rear = 677.9", or from 61.84" in front of subject to 77.9" behind subject)
   
2. FF body,150mm f/4 at 50' focus (600"), 20/20 vision: DOF zone = 34.33", (front = 583.32" to rear = 617.66", or from 16.68" in front of subject to 17.66" behind subject)
   
3. FF body, 75mm f/4 at 25' focus (300"), 20/20 vision: DOF zone = 34.31". (front = 283.78" to rear = 318.19", or from 16.22" in front of subject to 18.19" behind subject)
   

As far as shooting then I try to remember to frame loose enough that I can chose to print from 3:2 to 4:5 ratio prints with relative ease. Often though I am focal length limited, and as a consequence I have to use a significant level of crop. Even if the "subject" is framed losser to allow for the different aspect ratios it is important that you are paying attention to those areas of the frame. They will still have to be included in the final output when you need the wider aspect ratios. So I'm still looking for a composition that works without cropping too.

As to DoF, for any set of fixed viewing conditions there are only two things that affect the perceived doF. The first as Wilt says is the reproduction ratio of the focus plane, since we will assume that the subject and the focus plane coincide. This is an inverse relationship, as you make the reproduction ratio larger the DoF will get smaller.The other factor, also an inverse relationship is the absolute size of the lens aperture. Make the aperture diameter larger and again DoF reduces. In its most basic form for prescribed viewing conditions the perceived DoF = K / (r × D) Where K is a constant of proportionality, r is the reproduction ratio, and D is the diameter of the aperture. All of the other variables that we see in useable DoF formulas are there to calculate either K, r, or D. In many cases a one of the replacement terms may be being used to find more than one of the three basic terms.

Alan

Just to summarize Wilts table..... because i had to reread it a couple of time...... if your crop by zooming to produce the same "cropped" in the final print.... (150 mm at 50 feet or75 mm at 25 feet) you end up with the same DoF look. But it you use a prime - 75mm at 50 feet and crop it, or cropping by coming closer to your subject - a 75mm at 25 feet , there is a large difference in the DoF zone - nearly 4x the depth. That all makes complete sense.

So my question next on this is one of the things people love about the images from my 400 2.8 is how much it flattens the image - pulls he background in. Is there a good calculator for that? I general hand out near the end zone with three bodies - one with a 400 2.8, another with a 300 2.8, and the lat is a 70-200 2.8. I've never done the math on if I shoot a player 40 years out, how much each pulls the stands in the back in/flattens the image. The difference is very visible. Do I create more space with the background using the 300, or flatten the image with the 400 and bring the stands behind in tighter - but more blured.

Croasdail wrote in post #18679992
So my question next on this is one of the things people love about the images from my 400 2.8 is how much it flattens the image - pulls he background in. Is there a good calculator for that? I general hand out near the end zone with three bodies - one with a 400 2.8, another with a 300 2.8, and the lat is a 70-200 2.8. I've never done the math on if I shoot a player 40 years out, how much each pulls the stands in the back in/flattens the image. The difference is very visible. Do I create more space with the background using the 300, or flatten the image with the 400 and bring the stands behind in tighter - but more blured.

'Flatten the image' is the 'space compression' effect of enlarging far away items to be larger in the background, usually attributed to the use of a long focal length like 400mm, but actually due simply to CAMERA POSITION relative to subject!!! Long ago documented and proven, preserved as a Sticky thread. Here are direct links to the posts with 'meat' for this current discussion topic.

https://photography-on-the.net …/showthread.php​?p=7667310

https://photography-on-the.net …/showthread.php​?p=7667313

https://photography-on-the.net …/showthread.php​?p=7847411 and then https://photography-on-the.net …/showthread.php​?p=7849299

https://photography-on-the.net …showthread.php?​p=16908589

https://photography-on-the.net …showthread.php?​p=17967126

I think we're getting back to folks debating apples and oranges. I do see quite a few photography sources going on about lens compression, and others stating lens compression is a myth. Well they're both right! Ultimately, yes, distance to subject is controlling perspective. But the point of using a long telephoto is to reduce your field of view and frame all of your subject in the frame at a long distance (and optimize all of your camera's resolution). I'm starting to now get back into studio head shots....unfortunately the space I'm in is very confining for letting me get the subject to go far enough from my backdrop to be out of focus, and me be far enough to frame them well enough for head and torso (which personally, when I frame completely in FF, I prefer 100+mm). If I go for a wider angle, I'm in a confined enough space that it shows perspective distortion from my position, my DOF is not as shallow, and my light setup may not be able to be as narrow.

Croasdail wrote in post #18679691
Yes-ish.....

If you crop with your zoom versus zooming in via a crop in post, this is likely true, though never tried it my self.

But if you have a fix length lens and crop it 50% in post, versus cropping with your feet until your have cropped out the image to the same coverage ares, you don't have the same DoF.

If you have a full frame camera with an 85 f1.8 on it shooting wide open, and the distance from subject is 20 feet, your DoF will be 1.78 ft

Then you crop with your feet walking up to 10 feet away from the subject, you DoF will be .44 ft.

Just wanted to clear the up. How you "crop" in the field makes a huge difference to DoF.

This thread has gone far and above what I envisioned. People are now debating things I never knew existed. However, your post brought a question to mind. On my Canon 70-300mm Nano lens the digital depth of field indicator changes as I zoom in. So the DOF isn't just dictated by my feet, it seems there's variables on zoom lenses as well.

The zoom lens is simply bound by the exact same principles which pertain to Post 13's DOF results. The zoom merely has intermediate FL settings which permit more flexibility of camera position. But when the subject size is IDENTICAL percentage of the frame in all the shots, the DOF zone depth is also virtually IDENTICAL -- for ALL the shots taken with the zoom at other FL settings. I could achieve the same

As pointed out in the Sticky on FL vs. position controlling 'perspective', the zoom permits different perspective (since the camera position can vary so much with the same subject size in the frame), even though the DOF itself is 'the same'.