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FORUMS Photography Talk by Genre General Photography Talk 
Thread started 04 Apr 2009 (Saturday) 17:05
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STICKY: Perspective Control in Images - Focal Length or Distance? (a tutorial)

 
SkipD
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May 28, 2012 20:18 |  #166

WaltA wrote in post #14497002 (external link)
Wilt, I know this is an old post and I've read "most" this this thread and I have a question that I hope has not been already asked and answered.

Is the phenomenon that you describe above enhanced even further when the distances between the 4 objects increases?

The reason I ask is that when I lived on the west coast a few years back I noticed a strange thing happening. Lets say that "A" was a pier I'm shooting while standing on the beach in White Rock BC. The "other item" is Orca Island 10 or 15 miles out to sea.

As I moved back off the beach to location B and even further up to 4 miles back (and higher in elevation) I noticed that Orca Island seemed to be getting bigger. As a matter of fact I could see a lot more detail, such as the cell towers and antenna on top of a hill on the island that I could not make out when I was on the beach at sea level.

It seems that moving back (a couple of miles) as well as up ( 500 or 600 feet) seemed to exaggerate amount the background item grew in size.

Your thoughts? (Great thread, by the way)

I wrote the following near the end of the first post in this thread. It should answer your question.

Let's assume that you are taking a photo of some friends in a scene that has mountains in the background. You stand 20 feet from the people and view the scene. A 50mm lens will let you fill the frame with the group of people and some of the background quite nicely, so you take a shot. Then you realize that the mountains are rather small in the background.

Back up to to 40 feet (twice the distance) from the group of people and view the scene, you will see that the mountains are now larger relative to the people - twice the size they were before, in fact. However, the people are smaller in your viewfinder. You now need a 100mm lens to keep the people the same size as in the first image, but the mountains now appear twice the size that they were in the first shot.


Why is this? It's because the additional twenty feet that you put between yourself and the people is insignificant relative to the fifteen miles between your viewing spot and the mountains.


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May 29, 2012 09:34 |  #167

SkipD: So my question was "does that phenomenon continue as you move forther back? 5 miles instead of 20 feet?"

Wilt: I was using the same lens - probably my EF28-105. Shouldn't the change in perspective be apparent after moving away from the subject even with the same FL?


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May 29, 2012 10:33 |  #168

I'm about to attempt to put this to good use. I saw many shots of the "Supermoon" looming large over a monument or historical site. Figured out this is how it was done. So, next weekend when the moon is almost as close as it was on the 5th of May (some 800 miles further away, not significant) I am going to attempt a shot with a 2032mm lens (8" telescope) from some 6 miles away from the local hospital catching the moon rising from behind the hospital in an enormous size differential! I had a tip from someone here to use The Photographers Ephemeris to plan the shot and it's helped enormously! Anyone taking outdoors shots can use TPE to plan the time of day and lighting, with consideration given to the weather and atmospheric conditions of course.

Will post here if I get lucky and it turns out like I've planned...


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Wilt
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May 29, 2012 12:04 |  #169

WaltA wrote in post #14499883 (external link)
SkipD: So my question was "does that phenomenon continue as you move forther back? 5 miles instead of 20 feet?"

To your question to SkipD...
A: The perspective does continue to change, but as my distance to the subject increases, the relative change (vs. the background diminishes)

For example the condition at start: subject at 2', background item at 200'; relative distances 1:100

  • Move to 5' from subject (add 3' from start), subject at 5' and background item at 203', relative distances now 1:41
  • Move to 10' from subject (add 8' from start), subject at 10' and background item at 208', relative distances now 1:21
  • Move to 20' from subject (add 18' from start), subject at 20' and background item at 218', relative distances now 1:11
  • Move to 50' from subject (add 48' from start), subject at 50' and background item at 248', relative distances now 1:5
  • Move to 100' from subject (add 98' from start), subject at 100' and background item at 298', relative distances now 1:3
  • Move to 200' from subject (add 198' from start), subject at 200' and background item at 398', relative distances now 1:2
  • Move to 500' from subject (add 498' from start), subject at 500' and background item at 698', relative distances now 1:1.4
  • Move to 1000' from subject (add 998' from start), subject at 1000' and background item at 1198', relative distances now 1:1.2


As the relative distance ratios get smaller, the relative object size difference which is apparent at that position will diminish in rate of change.
The relative size of the [near object will get smaller and smaller] at a more rapid rate than the relative size of the [far object getting smaller and smaller] with increased distance to both, and the rate of change diminishes.

WaltA wrote in post #14499883 (external link)
Wilt: I was using the same lens - probably my EF28-105. Shouldn't the change in perspective be apparent after moving away from the subject even with the same FL?

To your question to me...
A: Yes, which is why my earlier reply states,

" if I move myself from point A to point B, the background item seems to grow in size relative to the primary subject within the frame. What is happening is that my position relative to my main subject is changing much more radically than my position relative to the background object....

" In the 'compression' of the distance between the two objects, I am seeing actually a difference of perspective, a change in relationship of my subject to the background item."


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WaltA
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May 29, 2012 14:01 |  #170

Thanks, Wilt. I've been meaning to pose that question ever since I observed it first hand that one day at the beach but when I saw your drawing it was obvious you were explaining why it was happening.

Appreciate your response.


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canonbdj
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Jul 07, 2012 08:49 |  #171

What an interesting article. I wish I'd found it sooner. So now when I photograph groups I can avoid large heads and small feet by stepping back a bit. I might need external flash for indoor shots but that I have.

I particularly liked the advice re relative sizes of groups and background mountains.

Perhaps I could I simplify my life by buying a camera with a quality fixed wide-angle lens, adjusting camera-subject distance to get the desired perspective, then cropping the result to achieve the desired framing.

Anyway, something to think about. Many thanks.




  
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budi
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Aug 07, 2012 10:19 |  #172

is this mean crop camera is better because you would need to step further than the full frame? :D




  
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Aug 16, 2012 15:30 |  #173

Very helpful explanation, thanks for sharing it!


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Wilt
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Aug 16, 2012 18:32 |  #174

budi wrote in post #14825694 (external link)
is this mean crop camera is better because you would need to step further than the full frame? :D

Not if you simply use a FL which is appropriate to the format size!

For example, 50mm is 'normal' for FF, 24mm is 'very wide'; with APS-C your 'normal' is about 30mm, your 'very wide' is 15mm. So if you shot with 24mm on FF, you would be able to shoot from the exact same position with both cameras by using 15mm on APS-C.

Some might say APS-C is 'better' because in a scenic shot you want maximized DOF, and DOF is deeper with the smaller format and the same framing.
OTOH, others will say FF is 'better' because a portrait shot has less DOF with the larger format.
Different goals mean different camera formats are 'better' in different circumstances!


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HiRes
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Sep 23, 2012 16:51 as a reply to  @ Wilt's post |  #175

Thanks for the writeup -very useful and enlightening!
It also explains why my 35 f/2 lens isn't suitable for all sorts of indoor portrait/people photography as I first thought!

1) Understanding that focal length does nothing other than frame the subject and that distance does everything in regards to distorting/not distorting the subject my question is: how much distance do I need to the subject in order not to distort it?

2) This brings me on to my next question which concerns which lens(es) to get next. Apart from the 35 f/2 I have a couple of zooms (see signature) which aren't that fast and therefore less suitable indoor without a flash, so I'm looking at faster lenses and primes because of the increased image quality.
So would using say, an 85 f/1.8 strictly for headshots eliminate the problem of distorted subjects simply because I would be forced to keep a specific distance (for framing just the subject's head in camera)? Likewise, using the 35 f/2 strictly for full body portraits would eliminate subject distortions with that particular lens, right?

3) So with a zoom able to do wide angle and tele (such as my 17-70 f/2.8-4.5) and my question #1 above; wouldn't this "freedom" in choice of focal length combined with shifting my distance to the subject make it easy to distort the subject if I didn't know what I was doing? Thus, zoom lenses are harder to use in regards to distortion?


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SkipD
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Sep 23, 2012 17:36 |  #176

HiRes wrote in post #15032541 (external link)
1) Understanding that focal length does nothing other than frame the subject and that distance does everything in regards to distorting/not distorting the subject my question is: how much distance do I need to the subject in order not to distort it?

Typical recommendation is six to ten feet between the camera and a portrait subject for "conventional" portraits.

HiRes wrote in post #15032541 (external link)
2)This brings me on to my next question which concerns which lens(es) to get next. Apart from the 35 f/2 I have a couple of zooms (see signature) which aren't that fast and therefore less suitable indoor without a flash, so I'm looking at faster lenses and primes because of the increased image quality.

So would using say, an 85 f/1.8 strictly for headshots eliminate the problem of distorted subjects simply because I would be forced to keep a specific distance (for framing just the subject's head in camera)? Likewise, using the 35 f/2 strictly for full body portraits would eliminate subject distortions with that particular lens, right?

In the olden days, I often used a 105mm lens with my Nikon F film cameras for head-n-shoulders portraits. Typically, focal lengths of 80mm to 105mm (and sometimes as much as 135mm) are recommended for "full-frame" cameras when doing portraiture.

You will have to determine YOUR style in doing portraits and then determine what focal lengths work for you.

HiRes wrote in post #15032541 (external link)
3) So with a zoom able to do wide angle and tele (such as my 17-70 f/2.8-4.5) and my question #1 above; wouldn't this "freedom" in choice of focal length combined with shifting my distance to the subject make it easy to distort the subject if I didn't know what I was doing? Thus, zoom lenses are harder to use in regards to distortion?

I use nothing but zoom lenses these days and find them no harder to use at all than "prime" lenses. In fact, I find zoom lenses to be easier to use because changing focal lengths is easier to do. For portrait work, I first choose my distance and then choose my focal length for the desired framing.


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Sep 23, 2012 17:44 |  #177

The distance for 'less perspective distortion' is relative! A recent post on POTN by a mother stated that distances of 80-100cm (40") induces noticeable (to her) perspective distortion, and I presume that she was using her 30mm lens on APS-C (achieving same framing as 50mm on FF). That probably illustrates what I try to tell folks...their own lack of everyday familiarity with some of their subjects leads them to not notice and to tolerate the induced perspective distortion, in spite of their close shooting distances that they say they like to use. Since she knows her own child, she'd notice induced perspective distortion even at moderate distances of 80-100 cm!

Most studio portraiture has classically been around 7-10' away, as the 100mm lens on FF which is the classic 'portraiture lens' provides the right framing at those distances.

I have found that if I shoot groups with a lens that sees 84degree diagonal AOV (24mm FF, 15mm APS-C), I can induce perspective distortion in the group which is readily seen as the closest person looming much larger in the photo than others farther away, even at moderate distances when not squared to the group's front.


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Sep 23, 2012 17:53 |  #178

budi wrote in post #14825694 (external link)
is this mean crop camera is better because you would need to step further than the full frame? :D

'different', not 'better'...
you would shoot with about 60mm (APS-C) instead of 100mm (FF) and could shoot with either camera from the same position.

Folks forget that the best use of any format is to "Choose a lens FL which is suited to the size of the format!"

[50mm on 4/3 format] frames the same as [60mm on APS-C] frames the same as [100mm on FF] frames the same as [180mm on 645]

In some ways the smaller format is WORSE for portraiture, when the photographer wants good control in limiting DOF.

I am assuming you were pulling our leg, by the use of the smilie!


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May 16, 2014 10:28 |  #179

On the topic of 'telephoto compression'...

Perspective in action. Just shot this series to illustrate points. (My thanks to my grandson for donating his helmet to this worthy cause.)

IMAGE: http://i69.photobucket.com/albums/i63/wiltonw/POTN%202013%20Post%20Mar1/Perspectivecompare_zps4e587476.jpg

Make these comparisons...


  1. Photo 1 = 260mm vs. Photo 4 = 17mm:
    ...
    to show the concept of 'telephoto compression' vs. wide angle shot,
    both taken with very different camera positions to keep the helmet about the same percentage of the frame height for both shots.
    Note the relative size of the background trees in both shots (top of neighbor's roof included to give a sense of the tree sizes), relative to the helmet. In the tele shot the trees are about 57% of the helmet height; in the WA shot the trees are about 12% of the helmet height...'telephoto compression' illustrated, it would seem
    ...
  2. Photo 1 = 260mm vs. Photo 2 = 17mm:
    ...
    to show what happens to framing when both lenses are used from identical camera position. pay special attention to the relative size of the background trees vs. the helmet....yeah, kinda hard to quantify the tree height in the WA shot, so let me help you...Note the relative size of the background trees in both shots (top of neighbor's roof included to give a sense of the tree sizes), relative to the helmet, the trees are about half the size of the helmet in the shots, right? What?...what happened to 'telephoto compression' in the 260mm shot?!?!?! :confused: ;)

    ...
  3. Photo 1 = 260mm vs. Photo 3 = 17mm
    ...

    photo 3 has been very tightly cropped (actually a cropped virtual copy in LR of Photo 2!). Pay special attention to the relative size of the background trees vs. the helmet


...THE TREES ARE THE SAME SIZE IN BOTH SHOTS, RELATIVE TO THE HELMET...in spite of the fact that the first shot was with 260mm and the second shot was with 17mm! No 'telephoto compression' illustrated with the last comparison, in spite of the 15:1 ratio of FL of the two shots. I changed the FRAMING by cropping tightly the WA shot, I did not alter the relative sizes. No demonstrated 'telephoto compression' in this comparison either...the WA shot is as 'compressed' as the tele shot!

IOW, it is 'perspective' and not the mythical 'telephoto compression' which fools our brains...else I should have seen 'tele compression' in the last two comparisons, right?!

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Feb 22, 2015 12:19 |  #180

just wanted to say that this was one of the first posts i read when becoming a member of POTN. I had just bought my XSi and was getting back into photography after quite a few years off. Years before I had done some "professional" photography to supplement my design work, but my Coolpix 990 had grown old and I basically stopped taking pictures. My formative film days were WAY behind me at that point.

This thread, among many others, was of great help restarting the brain cells that held what i knew to be true from back in my film days. Just wanted to send a thanks out to you Skip for putting it together, and to the others (wilt) for keeping it going and continuing to answer questions about the issue.

cheers to you guys!


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Perspective Control in Images - Focal Length or Distance? (a tutorial)
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