Archive for the 'photography' Category

24
Oct
09

Straws in a lake

A fairly new one shot with my Pentax K-7 and the DA70mm Ltd.

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04
Sep
09

An image from the archive

Just a shot I rediscovered while cleaning up the archive.

12
Aug
09

Fire in the sky

Just an image to prove that I’m still here.

29
Jul
09

Maybe LightRoom wasn't that slow

A while back I wrote about how slow LR was when using gradients and brush tools. Even on my 8-core MacPro, the beach ball kept on spinning forever. Today, as I was watching the L-L video “Where are my #$$$”% images”, I realized that I had turned on the “Automatically write changes into XMP” option. This makes LR write every single movement on my sliders into the XMP sidecar file (or the DNG file) as I do the movement, and the slowdown is caused by the disk bandwidth. When I turned off this option, LR in snappy, and I am happy.

So, go into the catalog settings and uncheck the “Automatically write changes into XMP” option inside the “Metadata” tab. You should also go into the “View Options” under the “View” menu, and tick off the “Unsaved Metadata” checkbox. That way you will get a small arrow on each photo that contains unsaved metadata. Every once in a while, and at least every time you quit the session, select those photos and hit Cmd-S. You will not lose work even if you don’t save, but then the metadata is only stored in the LR database file, and not as part of the image file. If the metadata is stored in the image files, you will get back everything if you reimport them into a new catalog, which is good if the lightroom catalog gets corrupted.

22
Jul
09

Auto focus is confusing?

I while back, I looked through the archives at Cambrigde In Colour, and found this article about auto focus technologies. The author tried to describe how the autofocus of dSLR’s are working, when in fact he was describing the contrast based autofocus most commonly used in compact cameras. Later I found Tim Jacksons D70 site, where he also describes a focus system that I don’t really think exists in any camera on the market. After looking around on the net, it occurred to me that there are many attempts to explain autofocus out there that are just plain wrong. It seems like the phase dection autofocus system used by all SLR cameras, both digital and film, is a bit hard to grasp, so most authors explains the conseptually more easy contrast based autofocus instead. Or maybe they just fail to see that there is a difference.

Contrast based auto focus

To start with contrast based auto focus. This type of system is most commonly used in compact cameras, and on some dSLR’s when the Live View function is used. It uses the actual imaging sensor to determine focus, and here is how it works:

  1. It shoots a series of images at different focus settings.
  2. For each of these images, it will determine how  much contrast there is in the designated focus areas.
  3. It selects the image with the most contrast, and reset the focus to the value it used to capture this image.

This process is relatively slow since the camera must take a large number of shots and process them before finding the focus. On many cameras you can observe this if you look at the lens while trying to focus. It will cycle focus from one endpoint to the other before it snaps back to somewhere in between which hopefully is the right focus setting.

A major drawback with this kind of focus is that the camera has no way of predicting if the focus is in front of, or back of the current setting. It must just try in one direction and hope that it is right, and if not, it must go the other way.

Phase detection auto focus

This type of auto focus works kind of like the good old split prism in the days of manual focus. The focus system will take a part of the light coming from one side of lens and project it on one sensor, and a part of the light coming from the opposite side of the lens and project it on another sensor. These sensors are dedicated AF sensors, and are usually formed as narrow strips. When the image is in focus, the two images are perfectly aligned, but they will get more and more misaligned as the system gets more and more out of focus. Just like the split prism, all the AF system has to do is to rotate the focus until the two images are aligned.

A major benefit with this type of AF is that it can predict which way the focus shall be turned. Not only that, but it can even predict how far it shall be turned. This is accomplished by detecting to which side the misalignment is, and how much the images are off.

Here is a short drill down how it works:

  1. The AF sensor detects the direction and amount of misalignment.
  2. Based on the information about the lens, if predicts how far the focus must be turned.
  3. The focus is then adjusted accordingly (focus is not measured when this happens since the focus changes too fast).
  4. When the focus motor stops, a new measurement is performed. If the focus is not perfect the drill (1 through 3) is performed over again, but now the adjustments are much smaller, and therefor more precise.
  5. This goes on until the focus is good, or the system times out because it is unable to find focus.

The big misconception is that this system optimizes contrast, when in fact it correlates two one-dimensional images. When the contrast based system relies on a sharp edge to focus, this system only need some sort of recognizable pattern. In theory, it should be able to focus on a smooth gradient that goes along the focus sensor.

Here is an illustration by Canon (go to the bottom of the page).

And here is the Wikipedia article.

So, this is an overview of my understanding of these systems. If anyone more knowledgeable than me finds this to be wrong, please write me a comment.

16
Mar
09

Participating on photo sites

I just found a site called Onexposure, and at first glance it seemed quite interesting. It’s a photo sharing site where you upload pictures, but unlike most others, the contributions are screened before they are allowed to get published. I was a bit bored last night, so I signed up and submitted my alotted 3 pictures for review. To my surprise, they were reviewed this morning, and not that surprising, they were all rejected. I’m not really dissapointed since I didn’t plan to submit more pictures. It was just an experiment to see if I would have a chance, and to test the response time of the screening.

Some time ago I decided not to participate on any such sites for a couple of reasons. First of all, the feedback you get is rarely of any value. The people writing comments are mostly there to draw attention to themselves, and the only motivation for writing is to make someone else post a comment to your own photos. Then there is the urge to comply with the accepted style for the site. If you submit to a site like this, you’d be fooling yourself if you say you don’t care about comments. You want appraisal of your peers, and inevitabely you will change your photography style to match.

All said, I think the quality to the photos on Onexposure was higher than usual, which I guess is due to the screening. I will probably spend some time browsing through the pictures, and maybe find some inspiration. Since many of the photos on the site is post processed quite heavy handed, I will probably find some Photoshop inspiration there.

Its been a quiet month now. I’m in a serious dry rut right now, and it is one that I really don’t feel like fighting. I just use to wind down for the big happening that is due any time between now and mid April. I may post some more before that, but I make no promises. Oh, and I got a package from Australia this morning. It’s waiting at the post office, and I’ll pick it up tomorrow. Maybe it’s a print from Robert 🙂

25
Feb
09

Everybody and his brother is talking about it

Resistance seems to be the topic around my usual blogosphere hangout these days. I thought I should stay off the topic, but hey, why should I be the one sticking out.

I think, but I may be wrong, that it started over at Gordons blog in this post about Resistance. I have seen other posts on Paul Lesters blog, Doonster, Paul Butzi and uuuuhm, a lot more. I think you should be able to find most of them from the links I’ve provided.

Well, to the point. I too, like most people I suppose, also suffer from this. The natural instinct to avoid doing something that seems hard, or that I am not confident in doing. The thing is, when I’m out walking, or doing some other form of physical activity, everything seems to be possible. Even so when I’m out photographing. If I have a slow day, and I can’t really find anything good, I can just speed up my pace, and let the world fly by faster. That usually helps. I guess I look like those Canon tv adds, you know those where some people where dropping out of the sky with an EOS 400D or something and immediately started to litterarily run around taking pictures. I’ll admit that it is not the best way to cover the subjects. After all, it’s hard to be very observant when the pulse is punping hard, but it gets the creativity juices flowing, so why not.

I guess I should have a threadmill in front of my desk at work as well 😉

The good feeling fades fairly quickly when I get back home an sit down, but some of the ideas and inspiration remains for a while.

So if you have problems with “Resistance”, try physical exersize. And even if it doesn’t work, the side effect isn’t that bad either




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