Piotr Maciak
Posts: 64
Location: United States
Registered: 6 Mar 2009
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Edge sharpness and fisheye focusing
Posted: 7 Dec 2009 at 7:37 GMT
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I noticed that my nadir shots are much sharper than the edges of all around frames which leads to ugly transitions between sharp and not so sharp regions in the final panorama. Initially, I attributed this problem to the fact that typically the center of a lens is sharper than the edges but after reading michel.thoby.free.fr/Fisheyes_Focus/Focus_mapping... and some discussion on panoguide I concluded that maybe my focusing was not optimal. I carried out some tests yesterday and I found out that indeed the problem was indeed intensified by improper focusing. Out of 5 focusing distances 2.5m , 2m, 1.5m, 1m, 0.5m, the distance of 1m gave the best results. However, these results are not fully satisfactory. The problem is not as severe but I can still notice some difference in quality. My question is whether it can be eliminated completely. Should I continue to search for a better focusing distance, say make test shots focused at 70cm, 80 cm, ..., 130cm? I shoot 6+1+1 with Nikkor 10.5mm on a DX sensor.
Piotr
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John Houghton
Posts: 2839
Location: Hitchin, United Kingdom
Registered: 17 Jan 2005
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Re: Edge sharpness and fisheye focusing
Posted: 7 Dec 2009 at 10:56 GMT
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The simplest solution is to degrade the quality of the nadir by blurring so that it better matches the horizontal shots. Otherwise, you can use more of the nadir image and less of the bottoms of the horizontal shots and/or tilt the horizontal shots down a little.
John
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Mark Schuster
Posts: 1071
Location: Welwyn Garden City, United Kingdom
Registered: 25 Jan 2006
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Re: Edge sharpness and fisheye focusing
Posted: 7 Dec 2009 at 11:08 GMT
updated: 7 Dec 2009 at 11:15 GMT
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Piotr,
For an 8mm fisheye like the Sigma f/3.5 focus is best set at about 90 cm. The exteme depth of focus of the fisheye takes care of the rest, from even closer right up to infinity. A compromise, but what's the alternative? Many tape the focus ring so it isn't accidently moved. Please remember to set the mechanical selector to manual if you have an autofocus system like Canon/Sigma so as not to strain the motor.
Mark
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jimmyd
Posts: 149
Location: United States
Registered: 6 Nov 2004
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Re: Edge sharpness and fisheye focusing
Posted: 7 Dec 2009 at 14:18 GMT
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With the Sigma I usually set the focus between .5 and 1m. As Mark suggests you get pretty good sharpness throughout the scene. However, With fisheye lenses it is usually good practice to implement a sharpening regiment to your workflow post stitch to combat some of the inherent softness associated with DSLR cameras combined with such a broad area covering lens.
I think 90cm as Mark uses is spot on and i only deviate toward .5 when I am focused to shoot with objects very close to the lens. (Think of a dining room with only a small area next to a chair that is the most room you may get in a less than ideal tight shooting scenario.)
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Doug Aurand
Posts: 1797
Location: Albuquerque, NM, United States
Registered: 2 Jan 2008
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Re: Edge sharpness and fisheye focusing
Posted: 7 Dec 2009 at 15:05 GMT
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Assuming you're creating an Equirectangular Projection saved as a .tif from PTGui or similar software, just open the stitched image in Photoshop and apply an Unsharp Mask from Filters
Doug Aurand
Albuquerque, NM
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Ken Warner
Posts: 643
Location: Mammoth Lakes, United States
Registered: 14 Aug 2004
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Re: Edge sharpness and fisheye focusing
Posted: 7 Dec 2009 at 19:49 GMT
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John Houghton said: The simplest solution is to degrade the quality of the nadir by blurring so that it better matches the horizontal shots. Otherwise, you can use more of the nadir image and less of the bottoms of the horizontal shots and/or tilt the horizontal shots down a little.
John
Depending on what I'm shooting, I might take two or three shots straight down at the pano head and then one offset to get the very center of the nadir. Then mask the tripod out and blend and you get a perfectly sharp nadir.
But all that for the nadir is more work than the whole rest of the pano so I usually just clone 
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erik leeman
Posts: 65
Location: Netherlands
Registered: 24 Aug 2007
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Re: Edge sharpness and fisheye focusing
Posted: 7 Dec 2009 at 20:48 GMT
updated: 7 Dec 2009 at 21:02 GMT
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Sorry, but I somehow get the feeling some of you guys didn't fully understand (or read) the OP's question:
I noticed that my nadir shots are much sharper than the edges of all around frames
I think Piotr should do what John suggested: use more of the nadir image, and less of the bottom edges of the horizontal series. Perhaps setting a different aperture could improve image quality at the edges of each image too.
Most lenses perform best at around f/8.
I usually have to reduce contrast of my nadir and zenith images a bit and make them a bit darker to make them blend in with the horizontal series, but differences in sharpness shouldn't be a problem if you focus at about 1 meter away from you.
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DennisS
Posts: 355
Location: Los Anglels, United States
Registered: 1 Sep 2007
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Re: Edge sharpness and fisheye focusing
Posted: 7 Dec 2009 at 23:01 GMT
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Piotr Maciak said: I noticed that my nadir shots are much sharper than the edges of all around frames which leads to ugly transitions between sharp and not so sharp regions in the final panorama.
Piotr,
Whenever I use my Sigma 8mm lens, I see the exact same effect. My fix is to use Photoshop and blur the Nadar shot prior to stitching. Seems counter productive to blur a perfectly good picture. Once you get the blur level correct (and it won't take much), the boundry will dissapear. The final panorama will look fine. You will be reducing the quality for publishing on the internet anyway. Nobody will notice the slight intentional blur.
Another fix is to focus to .5mm for the Nadar shot. You just need to remember to set the focus back to 1 for your next panorama.
Dennis
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Piotr Maciak
Posts: 64
Location: United States
Registered: 6 Mar 2009
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Re: Edge sharpness and fisheye focusing
Posted: 8 Dec 2009 at 5:51 GMT
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Sorry, but I somehow get the feeling some of you guys didn't fully understand (or read) the OP's question
Erik,
Thank you for pointing this out.
I shoot at f/8 and I already do what John and Dennis suggested but I am not very happy with such a solution. I simply wondered whether more experienced panographers knew a better solution.
John, Dennis,
About the blurring, what kind of blurring do you use? The Gaussian blur does not match really well out of focus areas. I thought that maybe the lens blur filter would give better results but I never had enough patience to test it.
John, Erik,
About using more of the nadir image, what is the best strategy to achieve that? My ideas are:
1. Blend nadir manually with the rest of panorama.
2. Use a higher value of blend priority in PTGui.
3. Create a photoshop action that will create alpha channels for all horizontal shots. The alpha channels will prevent a blender from using the edges of horizontal images.
What do you do/recommend?
Thank you for your answers.
Piotr
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John Houghton
Posts: 2839
Location: Hitchin, United Kingdom
Registered: 17 Jan 2005
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Re: Edge sharpness and fisheye focusing
Posted: 8 Dec 2009 at 7:37 GMT
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Generally, I find the best results are obtained by merging the (vp corrected) nadir in manually, using extracted rectilinear views. The blurring at the bottom of the horizontal images is nasty because it is directional due to the stretching effects. Using a mask to select precisely where the image transitions occur helps to avoid the worst problems and hide the seams effectively. A bit of selective sharpening and blurring where appropriate usually produces an acceptable result.
John
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erik leeman
Posts: 65
Location: Netherlands
Registered: 24 Aug 2007
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Re: Edge sharpness and fisheye focusing
Posted: 8 Dec 2009 at 9:01 GMT
updated: 8 Dec 2009 at 9:16 GMT
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I use roughly the same method John uses.
For complicated/high quality work:
After finishing the initial stitch from the horizontal series only, using PTGui and Photoshop, I'll make two copies of the equirect. Again in PTGui I'll pitch one copy +90 degrees, the other -90 degrees.
These are then used as background images for aligning and warping the individual nadir and zenith shots in PTGui.
I will not let PTGui merge them with those background images, instead I export them all as individual layers and do it myself in Photoshop using masks etc. like John described.
The two patched but still pitched equirects are then rotated back to their original orientation in PTGui, and subsequently carefully merged with the original equirect in Photoshop.
For simple and/or quick'n dirty work I'll just edit the top and bottom cubefaces in Photoshop, rotating, warping, adjusting and masking the zenith and nadir shots by hand.
Generally you'll get best results if you do all work on the full-sized images. Also make the largest possible cube faces first, edit them if necessary, and then scale them down in Photoshop to the size you need them to be for making the Flash or QuickTime VR versions. Sharpen only as a last step. So only (moderately) sharpen the final cube faces!
Erik
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DennisS
Posts: 355
Location: Los Anglels, United States
Registered: 1 Sep 2007
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Re: Edge sharpness and fisheye focusing
Posted: 8 Dec 2009 at 15:03 GMT
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Piotr Maciak[b said: John, Dennis,About the blurring, what kind of blurring do you use?
Piotr,
I use lens blur. I have the nadar shot open in Photoshop and the the panorama open in PTGui. I apply blur, save, then do a preview stitch. It usually takes about 2 or 3 tries to get a match. PTGui's auto load function is wonderful.
Dennis
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