Tuesday, September 7, 2010

Week 2 - Correcting Lens Distortion In PS

Firstly, thank you for taking the time to visit this blog to learn more about photography! We encourage you to subscribe to this blog's RSS feeds - this will help to keep you informed of relevant changes and updates. Moving along...

The purpose of this blog is to:
  • Discuss and evaluate individual photos taken by Gerald Catalano, co-owner of Catalavro Concepts, Inc.
  • Offer one another critical information on techniques, camera settings, lens settings, lighting settings and whatever pertinent information went into getting the shot.
  • Learn from each other to improve our beloved craft.
  • Replies with photos and technical details are welcomed and in many cases, preferred. 
Week 2: Correcting Lens Distortion in PS
Sept. 5th 2010 - Sept. 12th, 2010
Legends of St. Johns Luxury Condominiums - St. Augustine, FL 

Last week we explored the use of an ultrawide lens to photograph a landscape scene. In that shot, the horizon line appeared straight when shot at approximately the same distance and exact same focal length as the image above - but with significantly different results. Distortions may not be as apparent in the example shot of the sunrise from last week because there isn't anything in the foreground to accurately offer us a sense of depth (no foreground objects or vertical lines), but when ultrawides are used on subjects that contain prominent vertical lines either in the subject or foreground such as walls on a building, the distortions become significantly more obvious. Today we are going to analyze an image that I shot using the Tamron 10-24mm 1:3.5-4.5 ultrawide lens - the same lens I used to photograph the sunrise shot from last week.

What is lens distortion? A simple and crude explanation of lens distortion is that it is the skewing or "distorting" of lines in an image caused by the curvature of the glass on the lens. This is primarily caused by the building and camera lens being on two different angles. Basically, the wider the focal length, the more "bowed" or "skewed" the outer edges of the subject become. While I can get uber-scientific with you as to why it occurs, my goal today is to teach how to correct it in photo editing software, specifically in PS (and PSE). My experience with ultrawide lenses has taught me some neat tips and tricks to minimize these effects, but there are times, such as in the example image above (or shooting architecture in general), when there is no getting around this!

If you take another quick look at the image above, it is a building shot from approximately 12ft. at a 10mm focal length. While the exposure is ideal and the colors are rendered well, the image still doesn't quite look right, does it? Do you notice that the walls are tilting inward at the top? This type of distortion is known as a keystone distortion and makes the building appear as if it is leaning backwards. While ultrawide lenses allow us to photograph subjects at very wide angles - there is a price to pay for such an allowance in the form of lens distortion, of which there are many forms and degrees. Today we will be dealing only with keystone distortion. While I have found many artistic uses for an effect such as this, shooting architecture for a keepsake print or for a client who wants an accurate representation of the subject would definitely make this image highly unacceptable and would need to be corrected. Luckily there is such a solution in photo editing software.

I use PS (Adobe Photoshop) CS4 and LR3 (Adobe Lightroom) primarily for these edits but there are many other programs to perform these tasks that work equally well. Today, we will only be learning the method as it appears in PS CS4. Let's go...

 Figure 1
The Lens Correction filter (choose Filter > Distort > Lens Correction) lets you address barrel and pincushion distortion, chromatic aberration, vignetting, and perspective errors. This opens up a screen that allows you to make adjustments.

 Figure 2
By using the slide adjustments found on the right side (specifically the Remove Distortion slider), you can make the necessary enhancements to your images to correct keystone distortion. Since each camera lens presents its own levels of distortion, there is no single setting that will correct keystoning, however, there are charts available online for a variety of lenses that will offer you a "starting point" for commonly used settings on commonly affected subjects. By sliding the remove distortion slider over +4.00,  I was able to remove the distortion from the photo. I used the grid lines available to me in PS to ensure that I was correctly aligning the vertical references.

 Figure 3

This correction does have a drawback, however, in that you lose a part of your image. To correct this, you must enlarge the photo OR crop that part of the image away. I tend to save my images as RAW files for future edits, prints or web applications, however, if you prefer to save them as jpegs, I suggest doing so at a common size used for printing, such as 5x7 or 8x10. This will allow you to print your images later without having to reopen and resize the images over and over. Since cameras do not natively shoot or save to these sizes, we must do so manually.

 Figure 4
Open a new file (choose File > New or Ctrl-N on Windows or Cmd-N on Mac) and set the size and resolution of the image to the preferred size in which the file will be saved.

Figure 5

A new dialogue box will appear with several options for size, resolution, and color mode. While I am not going to go into too much detail about all of these options, I can tell you that these settings will highly depend upon the final use of the image. Since images for non-professional printing are generally referred to in inches, make sure the unit of measurement is in inches and not in pica or pixels. You may change these using the drop down selection boxes. Pica and pixels are used for professional printing and web applications, respectively and will cause you to be quite disappointed when your 8x10 image created in pixels is the size of a flea.

If the final images is for print enlargement, the resolution should be set to 300dpi. If it is for a website application or to upload to a share/social networking site for viewing, then 72dpi is acceptable and in most cases perferable since this will dictate the overall size of the file. A dpi setting means "Dot Per Inch" and directly affects the overall quality of the image (more is better in most cases for print). In general, high quality prints requires larger file sizes and web applications require less. Besides, uploading huge files to Fb, Flicker etc.can be a long process...

The color mode is important also: if you are printing this image on your home printer or local drug store lab printer, select RGB (in most cases - although many larger format home printers are now CMYK also - so if you have more than 4 cartridges of ink in your printer, select CMYK), however, if the image is being printed at an offset printer (for brochures or business cards) select CMYK. Check with your local printer first to see what they suggest as the results can be quite different.

The highlighted part of Figure 4 is for a file name. I tend to rename my files when I save them for easier reference later on (I generally use the original file name with an  _REDO at the end [ e.g: DSC1??_REDO]) but you can place whatever you want there, so long as it's something you can remember later or better yet, organize within your computer!

Figure 6

Now that my 8x10 file is open, I am ready to resize my picture.

Figure 7
The way I do it is to go back to the original file that we corrected and Ctrl-A to select the entire image, type Ctrl-C to copy that image and then go back to the new 8x10 file we just created and hit Ctrl-V to paste that image into the new file. It will always paste it dead center, which is great as we'll see later. Also, if you notice, the image does not take up the whole frame; why? Because we resized that image to be 8x10 even though it isn't...yet

Figure 8

Click Ctrl-T to transform the image (so you can control the image and affect its size). You will notice a box surrounding your image which has little points at each corner and in the center on each vertical and horizontal line. These are used to  "handle" the image. If you grab one of these points and drag your mouse in any one direction, you will be able to move that reference point without affecting the others. This is NOT ideal for image resizing, as it will create a skewed image. Try it...just hit Ctrl-Z afterward to undo it.

The best way to resize the image evenly is to hold the Shift button while you grab the points at the corners. Hit Ctrl-T again (if its not already) and go to the lower right hand corner (if you cannot see that corner, hold the ALT button while using the mouse scroll wheel and you can zoom in and out accordingly). Typically, I drag the lower right down to the lower right and the upper left up towards the upper left while maintaining the image in the center. I will stretch the image until I can no longer see any of the parts that were cut away during the lens correction steps. If you need to re-frame the image after stretching it, just simply grab the center of the image and move it until you are happy with the results. For even better results, go to (choose View > Rulers) and use the center of the image as a guide to properly place your images.
Note: Holding the Shift button is NOT required in PS Elements!

That's it...let's see what we have as a final image.

  • What tips or tricks for correcting keystoning have you used before?
  • Do you have any preferences for resizing that were not covered here?
While shooting with ultra-wide lenses, be aware that barrel distortion and keystoning are more than likely to occur at the widest focal lengths. As well, vignetting is quite possible also...especially with the use of a circular polarizer!

  • Try to keep ultra-wide lenses on a horizontal plain with the subject- refrain from pitching up or down to get a shot if possible.
  • When shooting straight vertical lines (e.g: architecture), always shoot a lot closer to the subject than you may have intended. Wide lenses are not really meant to be used to squish everything into a frame, but more so to capture entire foregrounds while also capturing the background settings. So move CLOSE!
  • Try to shoot low for low subjects and higher up for elevated subjects.
  • Don't shoot people with ultra-wides - unless you are looking for that distorted effect.
Next Week:  Review of the EyeFi Pro SD card -a wireless card that allows you to wirelessly move images directly from the card in the camera to your computer over a wireless network, ad-hoc connection or ATT wireless hotspot as well as Geotag your images using non-GPS triangulation.

As always, I welcome constructive feedback and great suggestions for improving these techniques...happy shooting!

    Sunday, August 29, 2010

    Week 1 - Photographing Sunrises and Sunsets

    Firstly, thank you for taking the time to visit this blog to learn more about photography! We encourage you to subscribe to this blog's RSS feeds - this will help to keep you informed of relevant changes and updates. Moving along...

    The purpose of this blog is to:
    • Discuss and evaluate individual photos taken by Gerald Catalano, co-owner of Catalavro Concepts, Inc.
    • Offer one another critical information on techniques, camera settings, lens settings, lighting settings and whatever pertinent information went into getting the shot.
    • Learn from each other to improve our beloved craft.
    • Replies with photos and technical details are welcomed and in many cases, preferred.

    Week 1: Sunrises and Sunsets
    August 29, 2010 - Sept. 5th 2010
    Hammock Beach - Palm Coast, FL
     Shot Using the following settings
    D300s - RAW
    White Balance - Auto
    Lens - Tamaron 10-24mm f/3.5
    ISO - 800
    EV Compensation - -1.7
    Aperture - F/22
    Shutter Speed - 1/250 second
    Tripod and Shutter Release

    The main consideration I have with shooting sunrises and sunsets has to do with the lack of lighting related to this subject matter and how to correctly meter my camera to get the very best shot possible that would show detail throughout the whole composition while also maintaining detail in the sun without blowing out the highlights. This can be tricky... There is quite a lot of "trial and error" that goes into a shot like this initially and a fairly decent understanding of one's camera equipment is needed- as well as a bit of luck! One thing is for certain -  if I am not out there shooting, luck won't play a role at all and I won't have a photo or blog - or business for that matter!

    For this shot, I left the house at 5:25am for a 6:15 sunrise. I know, that's fairly EARLY - but a shot like this is only possible in the early morning, right? Since I had been to the location one other time for a sunset shot, I was somewhat familiar with the fact that the view was facing East - perfect for sunrises! I locked that tidbit into my mind and made it a point to go back out and shoot a sunrise photograph. And no, an Eastward sunset shot in FL is not ideal and didn't pan out...

    When I arrived to the location, it was mildly raining and very humid. This combination can be a deal breaker for some who don't want to endure the elements to get a shot. Determined, I didn't mind the rain that much so long as there wasn't too much lightning - but the humidity was a serious problem for my equipment. All of my lenses were fogging and rendered useless until I cleaned (and re-cleaned over and over again) them every 5th shot or so. This was a huge inconvenience but I marched on!

    Once I got the lenses into a usable state, I decided that I wanted to shoot very wide to capture the amazing details in the sky and foreground sand. I pulled out my trusty Tamron 10-25mm lens for the job and as always, it pulled through better than my Nikon ultra-wide lens. Although the Tamron lens isn't particularly fast (it's a f/3.5-5.6 lens) for low light conditions where fast shutter speeds are required, it is more than capable for shooting on a tripod with a cable release using longer exposure times. The slower shutter speeds assist the lens to capture as much light as needed while also making moving water appear silky smooth. The only catch is that hand holding in low light conditions is practically impossible, therefore, a tripod and cable release are a must! In this case, I was able to freeze the foreground water by only slowing the shutter speed to 1/250sec. instead of my original setting of 2+ seconds. I made the change after the sun had risen / in lighter conditions because I saw what the water was doing on the shore and wanted to capture it. Shooting at f/22 ensured that the whole image was evenly focused and the Manfrotto tripod/head kept my gear steady to capture a tack sharp photo.

    At first, I found that my camera settings weren't quite right for what I wanted. The images were too flat and lifeless and my composition was, well, BORING and very wide! I decided to set the picture controls to Vivid mode and boost the saturation a bit to get more color. I moved my spot closer to the edge of the water line and lowered the tripod down to the ground to get less than 1 ft. from the sand. At this point, I started my WB and metering configurations while the sun had just started to peak through the clouds on the horizon line signaling the start of a new day.

    The trick I use to WB is to place my camera in Live View and review each setting independently to see which looks best. This trick was actually something I stumbled upon when I started shooting with the Nikon D300s.
    It works! Try it!

    The trick that I used to meter the sun is to place the camera in Aperture priority mode and take a reading just above the sun (but so that sun is nowhere in the frame). While holding my shutter release halfway down to maintain the reading, I notated what the metering value was and changed modes to Manual. I entered those values into my camera and recomposed the shot to include the sun.  From there, I continued to adjust the settings until I found a result I was happy with. I would never try to meter the sun directly and I don't ever suggest doing so - as the result is typically blown out highlights and VERY underexposed images.

    The auto metering settings I got back from the camera in Aperture priority mode weren't quiet perfect for the final shot but were a great start! My initial shots were coming out okay except that the sun continued to be blown out ever so slightly. By looking at the image and then the histogram, I was able to recognize this and make corrections. There is no substitute for the technical data on the camera! For sunrises, I prefer a crisp image with details throughout so I made the necessary subtle changes, most notably to the EV compensation. It was set to (-1.7 ) to get the highlights under control and voila' - the result was a picture that told a story rather than just a wide shot of a sunrise! Who wants that?

    Once I had the colors and highlights controlled the way I wanted, it was time to recompose the shot using the rule of thirds! Like all good photographers, I didn't want the horizon line dead center. I was told that shooting dead center is "deadly" and that has always stuck with me but there are times where exceptions have to be made, right?

    As I started shooting, I quickly realized that I also wanted to capture some of the tide (with the sun's reflection) that had started to rise and wash ashore more closely to where I positioned my tripod. The result was what would become, the final shot. Problem was, to frame this shot, it would have to be cropped dead center! Yuck...so I thought.

    I generally shoot images for large format prints which means I need every bit of data I can muster (especailly on a cropped sensor camera with 12.3MP)! I shoot in RAW with a JPEG backup on a Nikon D300s (which has 2 slots - one for SD cards and another for CF cards). This combination allows me to remain flexible enough to quickly download and  preview images on my computer (downloading and viewing JPEGs first) while also having all of that image data on a RAW file for post production tweaks in PS or LR on photos that I like without any loss of data as a result of any compression found on JPEGS. I highly suggest shooting in RAW when you have to have that perfect shot really come out perfect!

    The final image was shot in RAW also and taken into PS for minor changes to the vibrance and saturation settings in the midtones and shadows. In the end, the composition (length of the subject) forced me into a crop that placed the horizon line dead center. Because there was so much detail in the sky, I didn't want to lose any of it by cropping it out moving the horizon line upwards and vice-versa, so much detail in the foreground (with those waves overlapping) that I couldn't crop down either. After a little debate with myself and the echoes of the person who told me dead center is deadly, a concession was made. Generally, I do not recommend placing shots dead center except in portraits (and even then, there are far better and more contemporary alternatives)!

    • What tips or tricks can be employed to control the effects of humidity on glass?
    • Are there additional tricks that can be used to meter more accurately?

    Metering for sunrises and sunsets can be a little tricky at times. There are 2 completely different light sources that need to be considered and factored by the camera. While our eyes may do a great job doing this, the camera is much more limited!

    While nothing can be done about a seriously underexposed or overexposed shot with great results, minor imperfections can be corrected in photo editing software so long as the image is properly focused. Metering the correct light source is key, however.
    • Meter directly above the sun without the sun being in the frame before you recompose your shot to include the sun. This generally affords the camera an opportunity to do so with more precision.
    • If you can only get part of the shot correctly, try to get the sky, the sun is hard to look at with the human eye, therefore references to it are limited, however, people do know what a sky should look like - so it should be as tack sharp as possible! :)

    As always, I welcome constructive feedback and great suggestions for improving these techniques...happy shooting!