Understanding resolution

U
Posted By
usenetzen
Apr 13, 2006
Views
255
Replies
3
Status
Closed
First a little background. I was asked to take a group photo. I have a D70 and a couple of lenses, the one I used was my Nikkor 24-120 VR. In previous years, the photographer (no longer with us) used a medium format (Hasselblad, IIRC) and I knew I couldn’t approach the resolution with my 6Mp.

I set the camera to minimum ISO (200), aperture priority, f/16. VR was off, it was on a tripod. I shot the picture, EXIF tells me the lens was at 34mm, then I asked them to hold still a minute longer. I zoomed in a bit and shot a series of 9 photos — left, middle, right starting at the bottom, then middle of the group, then the top — with a couple of extra shots in there for good luck. The lens was at 70mm for these exposures.

On the pixelboard I converted the RAW images, equalized the exposures as best I could, then set CS2 to work photomerging the shots. In the end, it took me about 6 hours to complete the merge to my satisfaction (if people would only hold still… LOL)

OK, enough background. I compared the original single image to the merged shot. I COULD NOT BELIEVE THE DIFFERENCE. I knew the merged image would be sharper but this was incredible. I don’t understand it, but I would like to, so if anyone has an explanation…

The merged shots were at 2x the focal length which to me would be 4x the resolution. But the image looks MUCH sharper than that.

Here’s a low-res copy of the original single shot
http://faczen.smugmug.com/gallery/452395/2/62072792

Here the same sized merged photo
http://faczen.smugmug.com/gallery/452395/2/62071409

and here’s a detail out of the two pictures for comparison http://faczen.smugmug.com/gallery/452395/2/62072791

Comments?

Glenn
Photo gallery at http://faczen.smugmug.com
Reply via the web portal at www.faczen.com
or email usenet at faczen dot ca
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J
jaSPAMc
Apr 13, 2006
On 13 Apr 2006 06:18:26 -0700, "Guns/Zen4" found these unused words floating about:

First a little background. I was asked to take a group photo. I have a D70 and a couple of lenses, the one I used was my Nikkor 24-120 VR. In previous years, the photographer (no longer with us) used a medium format (Hasselblad, IIRC) and I knew I couldn’t approach the resolution with my 6Mp.

I set the camera to minimum ISO (200), aperture priority, f/16. VR was off, it was on a tripod. I shot the picture, EXIF tells me the lens was at 34mm, then I asked them to hold still a minute longer. I zoomed in a bit and shot a series of 9 photos — left, middle, right starting at the bottom, then middle of the group, then the top — with a couple of extra shots in there for good luck. The lens was at 70mm for these exposures.

On the pixelboard I converted the RAW images, equalized the exposures as best I could, then set CS2 to work photomerging the shots. In the end, it took me about 6 hours to complete the merge to my satisfaction (if people would only hold still… LOL)

OK, enough background. I compared the original single image to the merged shot. I COULD NOT BELIEVE THE DIFFERENCE. I knew the merged image would be sharper but this was incredible. I don’t understand it, but I would like to, so if anyone has an explanation…

The merged shots were at 2x the focal length which to me would be 4x the resolution. But the image looks MUCH sharper than that.
Here’s a low-res copy of the original single shot
http://faczen.smugmug.com/gallery/452395/2/62072792

Here the same sized merged photo
http://faczen.smugmug.com/gallery/452395/2/62071409

and here’s a detail out of the two pictures for comparison http://faczen.smugmug.com/gallery/452395/2/62072791

Comments?

Glenn
Photo gallery at http://faczen.smugmug.com
Reply via the web portal at www.faczen.com
or email usenet at faczen dot ca

You forgot that you have used 3×3 matrix at 4x resolution for a 12x resolution gain.
MR
Mike Russell
Apr 13, 2006
"Guns/Zen4" wrote in message
[re increase in rez of a mosaic vs single zoomed out shot]
and here’s a detail out of the two pictures for comparison http://faczen.smugmug.com/gallery/452395/2/62072791

Yes, this is much more of a difference than I would have expected.

I suggest you recreate the setup in a controlled setting. It may be as simple as the shot at 34mm being out of focus.

Great photo, BTW.
—

Mike Russell
www.curvemeister.com
U
usenetzen
Apr 14, 2006
I don’t think it was out of focus. First of all it was shot at f/16 (EXIF says f/16@ 1/160, on a tripod). I’m actually IN the main picture — self-timer and run — and the AF was on, VR was off.

I’m also in the other photo, through the magic of PhotoShop. While I was setting up and before the others arrived, I tested exposure with some self-timer pictures. When I stripped myself in, I had to do a LOT of PS magic, borrowing cheeks and a beard from other people in the picture to sharpen my image (I’m wearing a hat, second from the right).

Back to the topic… I still don’t think the difference in sharpness makes sense. That is unless I’ve somehow hit the sweet spot on this lens. One or two other shots tell me there is one: look at this tack-sharp picture http://tinyurl.com/jzeds. Mind you that was at 120mm (1//18 under studio strobes in a light tent)

Anyway, I’m going to be using this mosaic technique again. Some nature shots, where you don’t have to tell the trees to "hold still" will be fun!

PS: I made a 16×20" print. It equals some of the 2¼" stuff I did years ago. I’m pretty happy with it although it did take 6 hours to create…

Mike Russell wrote:
Yes, this is much more of a difference than I would have expected. I suggest you recreate the setup in a controlled setting. It may be as simple as the shot at 34mm being out of focus.
Great photo, BTW.

"Guns/Zen4" wrote
[re increase in rez of a mosaic vs single zoomed out shot]
and here’s a detail out of the two pictures for comparison http://faczen.smugmug.com/gallery/452395/2/62072791

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