tallmanirl
Posts: 272
Location: Ireland
Registered: 5 Jun 2008
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Can Characteristics of Image Taken in One Focal Length Be Changed To Another?
Posted: 16 Aug 2011 at 16:40 GMT
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Hello everyone!
I have the Canon 70-200mm L and 17-40mm L lenses. When it comes to shooting panos, the 17mm is of course very convenient, but it causes serious shrinkage and stretching of say, background mountains and gives a massive foreground.
I've known that for a long time and often use the telephoto at 135mm. That leaves things in their right sizes more or less, but it means a lot more images have to be taken and stitched for a pano.
Is there any way to overcome this stretching and shrinkage of background and the huge foreground while still using the 17mm? Is there a software solution?
CS5 can do so many things and I have tried the Perspective options I could find, but I still couldn't get such images to replicate "reality" like the 135mm.
Any advice?
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Hans Nyberg
Posts: 2791
Location: Denmark
Registered: 28 Aug 2005
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Re: Can Characteristics of Image Taken in One Focal Length Be Changed To Another?
Posted: 16 Aug 2011 at 17:01 GMT
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I am sorry but the lens you use has absolutely nothing to do with any stretching or shrinkage of the background.
If you make a pano with a fisheye lens and one with a 200mm they are identical if you just crop the fisheye to the same area as the 200mm.
What it may have influence on is the sharpness as you will have a much larger depth of field with the fisheye.
Hans
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Gede
Posts: 44
Location: Alkmaar, Netherlands
Registered: 19 Jan 2006
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Re: Can Characteristics of Image Taken in One Focal Length Be Changed To Another?
Posted: 16 Aug 2011 at 17:05 GMT
updated: 16 Aug 2011 at 17:06 GMT
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Hi,
If you would cover (from the same point of view) the same area (field of view) with either 17-40 or with the 135mm, there would be no difference, perspective wise spoken, except for the number of shots you need to take.
You can, to eliminate stuff in the foreground, take a higher point of view.....
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tallmanirl
Posts: 272
Location: Ireland
Registered: 5 Jun 2008
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Re: Can Characteristics of Image Taken in One Focal Length Be Changed To Another?
Posted: 23 Aug 2011 at 15:38 GMT
updated: 23 Aug 2011 at 15:40 GMT
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Eh, the difference between the two is actually very noticable when you take shots of the same area. The best way to see this for oneself is to bring along the laptop, take the shots, in the case of the telephoto, do any stitching necessary and examine which actually looks more like the actual scene you have just photographed.
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Smooth
Posts: 3774
Location: Mount Panorama, Australia
Registered: 21 Jul 2004
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Re: Can Characteristics of Image Taken in One Focal Length Be Changed To Another?
Posted: 23 Aug 2011 at 16:21 GMT
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It can't make any difference. All you have to do is adjust the FOV setting of the viewer to match each other.
The scene is the scene ...
What you are saying is like taking a picture of somebodies head and telling them they have a different head because you used a different focal length lens!
Regards, Smooth 
www.omnipix.com.au
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John Houghton
Posts: 3487
Location: Hitchin, United Kingdom
Registered: 17 Jan 2005
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Re: Can Characteristics of Image Taken in One Focal Length Be Changed To Another?
Posted: 23 Aug 2011 at 16:37 GMT
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tallmanirl said: Eh, the difference between the two is actually very noticable when you take shots of the same area.
I assume you have actually done this yourself - i.e. shot exactly the same scene from the same camera position with two different lenses. Perhaps you can show us sample crops from the images that illustrate the noticeable differences. Obviously they will differ in terms of resolution and possibly depth of field, but the relative sizes of objects at different distances from the camera should remain exactly the same.
John
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DorinDXN
Posts: 2853
Location: Timisoara, Romania
Registered: 14 Nov 2006
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Re: Can Characteristics of Image Taken in One Focal Length Be Changed To Another?
Posted: 23 Aug 2011 at 17:47 GMT
updated: 23 Aug 2011 at 18:07 GMT
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tallmanirl said: Eh, the difference between the two is actually very noticable when you take shots of the same area. The best way to see this for oneself is to bring along the laptop, take the shots, in the case of the telephoto, do any stitching necessary and examine which actually looks more like the actual scene you have just photographed.
The only diffrenece will be the "zoom" needed for the same detail
For example I used two lenses for this pano
livepanoramas.dyndns.org/dorin/dxn_pano/PtaVictor...
one lens was 18mm and the other one was 50mm, they match exactly except resolutions of course
This also is of help, I guess you are aware about some distorsions at the wide extreme which is coorrcted at stitching, but the perspective remain the same, as I said the zoom is diffrent for the same detail
www.usa.canon.com/app/html/EFLenses101/focal_leng....mc_id=C126149
cheers,
Dorin
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DorinDXN
Posts: 2853
Location: Timisoara, Romania
Registered: 14 Nov 2006
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Re: Can Characteristics of Image Taken in One Focal Length Be Changed To Another?
Posted: 23 Aug 2011 at 18:15 GMT
updated: 23 Aug 2011 at 18:33 GMT
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Smooth said: It can't make any difference. All you have to do is adjust the FOV setting of the viewer to match each other.
The scene is the scene ...
What you are saying is like taking a picture of somebodies head and telling them they have a different head because you used a different focal length lens!
Regards, Smooth
www.omnipix.com.au
Smooth, you know the head of somebody is the cause for this missconception among photographers about focal lenght changing the perspective, but not the way head thinks is the cause, instead how the head will look in photo 
I mean in portrait, photographers frame people's head in a nice portrait and then they say:
- what a big nose!
- what a distant background!
- oh! this 80mm is really really nice!
What they forget is they are changing the distance from the subject at different focal lentgh when they take the pictures.
cheers,
Dorin
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tallmanirl
Posts: 272
Location: Ireland
Registered: 5 Jun 2008
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Re: Can Characteristics of Image Taken in One Focal Length Be Changed To Another?
Posted: 29 Aug 2011 at 13:12 GMT
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I have indeed, but it was a few years ago. I'll have to root them out or gladly go back and compare again.
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tallmanirl
Posts: 272
Location: Ireland
Registered: 5 Jun 2008
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Re: Can Characteristics of Image Taken in One Focal Length Be Changed To Another?
Posted: 29 Aug 2011 at 13:21 GMT
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I always reckon that what we are getting in a shot is not an exact copy of the scene, but rather our equipments' interpretation of it and that it's up to us to manipulate that interpretation to get the image we want.
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No One
Posts: 501
Location: Sri Lanka
Registered: 14 May 2004
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Re: Can Characteristics of Image Taken in One Focal Length Be Changed To Another?
Posted: 30 Aug 2011 at 4:03 GMT
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There is NO exact copy of a scene, every photo stitched or not is a compromise of some sort. Photo's, 360's do not in any way present any sort of reality other than 125 fifth or so of a second with all the baggage that the lens, sensors, post (film type), exposure, etc. add.
And the basic answer to your question removed from 360's is no. But if used in a 360 then as others have pointed out, it's irrelevant as the interactive FOV view is the same irregardless of the lens used.
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allSaints
Posts: 4
Location: Stockholm, Sweden
Registered: 30 Aug 2011
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Re: Can Characteristics of Image Taken in One Focal Length Be Changed To Another?
Posted: 30 Aug 2011 at 9:30 GMT
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I happen to have a test page that shows two images taken from exactly the same position. The lenses used are the same as you have, and the images are resized, cropped and overlayed, so you can clearly see that there is no difference in proportions - only in DOF.
You should listen to what Hans says - he's got lots of experience and knowledge.
My test page is here: www.wirestam.com/panos/Sigma/flcompare.html
Regards,
Tommy
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tallmanirl
Posts: 272
Location: Ireland
Registered: 5 Jun 2008
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Re: Can Characteristics of Image Taken in One Focal Length Be Changed To Another?
Posted: 22 Sep 2011 at 11:29 GMT
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That's a close up image. What I'm shooting is miles away. I've tried shooting these using both lenses. For some reason, I'm having difficulty cropping the 17mm image to match the area taken with the 135mm. I set the crop size to the same measurements as the 135mm image size in CS5, but it won't cover the full equivalent area of the 135mm image.
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John Houghton
Posts: 3487
Location: Hitchin, United Kingdom
Registered: 17 Jan 2005
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Re: Can Characteristics of Image Taken in One Focal Length Be Changed To Another?
Posted: 22 Sep 2011 at 13:35 GMT
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Perhaps you will accept this comparison:
tinyurl.com/3zyxm87 (240KB jpeg)
John
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allSaints
Posts: 4
Location: Stockholm, Sweden
Registered: 30 Aug 2011
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Re: Can Characteristics of Image Taken in One Focal Length Be Changed To Another?
Posted: 22 Sep 2011 at 17:27 GMT
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John:
Great example!
tallmanirl:
If there is no difference in a close up shot, why would there be any difference if the objects are far away? Imagine the light rays coming from the objects as straight lines to your lens - they travel the same path and pass the same details in your image, no matter what lens you have mounted. With a longer focal legth, you are just cropping the image.
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