Depth of Field and Focal Length


Today’s Question: I am hoping to get some insight on how Depth of Field is influenced by the variables of Aperture, Subject Distance and Lens Focal Length.

I have recently come across websites that indicate that the common assumption that Depth of Field is influenced by Aperture, Subject Distance and Lens Focal Length is in fact, erroneous.  Specifically, the first 2 variables, Aperture & Subject Distance do affect Depth of Field (DOF), while Focal Length has no effect on DOF.

To further confuse matters, a number of reputable web sites provide online DOF calculators (and also downloadable Apps). Why is focal length included as a factor to be added to the calculation for DOF?

Hoping you can provide ‘clarity’ on seemingly contradictory situation.

Tim’s Quick Answer: I would argue that lens focal length does indeed impact depth of field. A longer focal length will result in less depth of field. That said, I would also argue that distance to subject and lens aperture to be the more important variables to consider.

More Detail: Those who argue otherwise generally stipulate that if you frame the subject the same way, suddenly focal length is not a factor. But in order to accomplish that change in framing you must also change the distance to the subject. In other words, you would be changing one variable (distance to subject) in order to pretend that another variable (lens focal length) was not a factor.

In other words, I could also argue that distance to subject has absolutely no bearing on depth of field, but that instead it is a change in focal length that alters depth of field. If you change your adjust your focal length you obviously must change your distance to the subject to maintain the same framing, so I could argue that it is the focal length (and not the change in distance) that caused the change. But that is obviously (I hope) not a reasonable argument.

In reality, all three factors (distance to subject, lens aperture, and lens focal length) impact the final depth of field you will achieve. And in fact there are additional factors, such as the overall image sensor layout (the size of each “pixel” on the sensor, for example) that also have an impact on depth of field.

To be sure, the calculations involved in determining depth of field for a given photographic situation can be a bit complicated. But as far as I’m concerned there is no question that distance to subject, lens aperture, and lens focal length play the primary (though not exclusive) role in determining final depth of field.

Proper Exposure


Today’s Question: You said something in a recent post on exposure for RAW captures (November 16th) that goes contrary to what I have always been lead to believe. You said that you feel it is better to (if necessary) OVER expose an image without blowing out highlights to preserve detail. I was always thought that it is better to UNDER expose (if necessary) the image to preserve detail.

Tim’s Quick Answer: For a digital capture, it is indeed best to capture an exposure that is as bright as possible without blowing out highlight detail. That differs from exposure for slide film, for example, where it was generally better to err on the side of an under-exposure in part to preserve saturation and detail in the image.

More Detail: Part of the issue here relates to how the information contained within a photo is being captured. In a very basic way, you can think of more information as being “good”, at least up to a point. In other words, you want as much information (light) to be recorded as possible, without capturing so much light that you’ve blown out all of the detail in a photo.

In the context of slide film, a slightly dark exposure provides greater density, which in turn can provide greater color saturation and possibly more detail. Thus, the general rule of thumb with slide film is to slightly under-expose the image. You don’t want to go too far, but when in doubt it is generally better to expose slide film slightly too dark rather than slightly too bright.

With digital cameras, a dark exposure is generally not going to produce the best results. By capturing as much light as possible without actually clipping highlight detail, you’re capturing as much detail as possible. An image that is captured with an exposure that is too dark contains less information, and will exhibit more noise when you need to brighten up the image to produce a better final result.

So, with digital photography the best exposure in terms of maximum detail and minimum noise is an exposure that is as bright as possible without clipping highlight detail. This may, of course, require a bit of darkening of the image in post-processing, but in my mind that is a small price to pay in order to ensure the maximum possible detail and the minimum possible noise, all other things being equal.

Exposure by Channel


Today’s Question: Is there a way to prevent exposure clipping of a specific color channel? I noticed that I was getting clipping of the blue channel on the left side of its histogram (no other color channels were clipped) and the combined RGB histogram and luminosity histograms showed no clipping on the back of the camera.

Tim’s Quick Answer: Preventing the clipping of a single channel requires that the overall exposure is adjusted, which in turn can require a review of the individual histogram channels for the image you’ve captured. And, of course, in some cases a single channel can be enough to require multiple exposures to create a high dynamic range (HDR) image.

More Detail: When a single channel is clipped, it means you have lost detail for that channel. In other words, you’ve captured an exposure that is less than optimal. In many cases you can compensate for this type of issue when processing your RAW capture on the computer, but I always recommend getting an optimal exposure in the camera.

It is important to review all three color channels (red, green, and blue) rather than just the overall luminosity histogram for a capture. Even when the luminosity histogram indicates there is no clipping of highlight or shadow detail for a photo, there may still be a loss of detail on an individual channel.

To be fair, in some cases it is not critical to retain detail for all three color channels in a photo. However, it is always better to have detail you don’t need than to lose detail you later wish you had.

When it comes to the original capture, the best approach to evaluating your exposure settings is to configure your camera to display individual histogram displays for each color channel. Most cameras include this option, or the option to overlay the histogram for all three color channels into a composite display. If a single color channel indicates it is clipped on the histogram, it is probably worthwhile to adjust your exposure settings and capture another image.

It is worth noting that the color space setting on your camera has an impact on the histogram being displayed. As a general rule I recommend using the Adobe RGB color space option in your camera in order to provide a more accurate histogram display. The sRGB color space option will generally provide a more pleasing image preview on your LCD, but a histogram that isn’t quite as accurate compared to the final result you can expect.

Synchronizing Changes


Today’s Question: On my primary computer in my home office I have a primary backup and a secondary backup that sync via Carbon Copy Cloner. I have a tertiary backup as well but I keep that at my other office in another town. I can see a problem when I want to bring all of the copies of my images together to create a unified synchronization. Is there a way to sync the files that have been changed on all three drives so ALL of the changes, regardless of on which drive it took place on will happen?

Tim’s Quick Answer: Put simply, this type of workflow is very difficult to maintain. Unless you’re using a software tool that specifically enables synchronization across multiple storage locations, it is very difficult to update images in multiple storage locations and have your changes reflected across all copies of your photos.

More Detail: Lightroom provides a good example in this case. While you can work with Lightroom across a variety of computers and mobile devices, this type of workflow requires that you synchronize specific images within your Lightroom catalog. You can’t achieve the same benefits by working with your photos directly on various hard drives, as opposed to images managed by a single Lightroom catalog.

In general, if you want to maintain synchronized information about your photos, you need to make sure that you are making use of a centralized source of information about your photos. In other words, you can’t work with backup copies of your photos to update metadata about your images, and expect to have that information updated for the “master” copy of your photos.

While Lightroom is somewhat limited when it comes to synchronizing adjustments across multiple computers and devices, I highly recommend limiting yourself to this type of workflow when you want to update photos in multiple locations. In other words, you can’t simply update a backup copy of your photos and expect that the “master” copy will be updated as well.

In theory it would be possible to update multiple copies of your images and synchronize those updates across multiple devices. But in reality that is a challenge that can lead to updates that don’t get updated properly. Thus, I highly recommend working with a single “master” copy of your photos, along with a catalog if you are using software such as Lightroom. That translates into a scenario where you only update one copy of your photos, and synchronize those updates to your multiple backup copies.

Sequential Renaming


Today’s Question: I shoot for local running races and send files to the organizers. I import from several different cards. When exporting the photos, the number sequence is not sequential. This makes it difficult for the organizer of the race to tell me which images they want. Is there a way to have the images export in a number sequential order? Is there a way when importing from several different cards to change the “File renaming” so when I export the files would be numbered sequentially?

Tim’s Quick Answer: In this type of situation, I generally recommend renaming your photos after importing them into Lightroom. This will ensure that you can rename the photos based on the actual capture sequence, so that even if you are using more than one camera to capture images during an event, the filename sequence will reflect the order that the images were captured.

More Detail: If you are renaming photos during the process of importing the photos into your Lightroom catalog, there is a risk that the sequence number used for that renaming won’t reflect the actual capture order of the photos. For example, if you import images from two different cameras, you would likely use a sequence number where the images from the first camera would always represent a lower sequence number than those from the second camera.

Due to the potential for this type of confusion, it can often be helpful to rename photos after they have been imported into your Lightroom catalog. Once all images have been imported (and any outtakes have been deleted), you can rename all existing photos so the filename sequence will match the capture sequence.

To accomplish this, all you really need to do is make sure that the photos are sorted by capture time before you rename the images. So, for example, you could switch to the “grid” view in Lightroom by pressing “G” on the keyboard, and then change the Sort option on the toolbar below the grid view display to the “Capture Time” option. You can then select all images and choose Library > Rename Photos from the menu. At that point you can use a file renaming template based on your specific needs, but that includes a “Sequence Number” option so that the photos will be renamed with a structure that includes a sequence number based on the capture order of the photos.

Exposure for RAW


Today’s Question: With today’s advanced software for processing RAW captures, how important is it really to achieve perfect exposure in the camera?

Tim’s Quick Answer: While software for processing RAW captures is certainly very advanced and capable of compensating for a less-than-ideal exposure, there can still be significant benefits to an optimal exposure in terms of maximizing detail and minimizing noise.

More Detail: Exposure latitude in post-processing is often presented as one of the key reasons to capture in the RAW capture mode rather than JPEG capture. While there is certainly the potential to recover highlight or shadow detail (or both) that could have been lost with a JPEG capture, image quality will likely suffer if you need to apply a strong exposure correction in RAW processing.

Put simply, there is no replacement for recording the light present in the scene with an optimal exposure. You can certainly apply significant adjustments in post-processing, including refining the overall exposure when processing the original RAW capture. But the result in terms of quality won’t be as good as you would have achieved with a proper exposure.

In the context of a digital capture, I would say that an optimal exposure is different from what a photographer would normally think of as a “proper” exposure. That’s because there is an advantage in terms of maximizing detail and minimizing noise by exposing the scene as brightly as possible without blowing out highlight detail.

As a general rule, I highly recommend using the “expose to the right” approach to exposure, capturing an image that is as bright as possible without sacrificing highlight detail. Alternatively, an exposure that is as close to the intended final result will also produce very good results.

There is certainly a good amount of latitude in terms of exposure adjustment when processing the RAW capture. But I highly recommend treating this as a last resort for situations where you inadvertently created a less-than-ideal exposure. In other words, the better the initial exposure in the camera, the better quality you can expect in the final image, regardless of the potential “magic” of today’s advanced image processing software.

Panning Thoroughly in Photoshop


Today’s Question: I would like to scan around an image in Photoshop to check for things that might need to be changed or removed. Is there a technique for quickly moving from one section of the image to another (other than just dragging and guessing) so that I am certain to hit every section of the image?

Tim’s Quick Answer: You can indeed move around a zoomed-in view of the image in an organized way in order to be sure to evaluate every area of a photo. This involves using keyboard shortcuts that enable you to use the Page Up and Page Down features to jump through sections of an image, including the ability to modify the Page Up and Page Down commands to enable left-to-right movement within the image.

More Detail: The Page Up and Page Down commands cause Photoshop to “pan” across an image in single “page” increments. Let’s assume you’re viewing the top-left corner of the image. The Page Down command would cause the last visible row of pixels to move up just above the visible area, with the first hidden row of pixels becoming the top row you are able to see. The Page Down command obviously moves downward in a similar fashion.

You can also modify the Page Up and Page Down commands to move one “page” of pixels left or right. In this way you can use the Page Up and Page Down commands, along with the left and right variations on these commands, to move around your image in organized blocks. The result is that you’re able to review the entire image up close in a very organized way.

On the Windows platform these commands make use of the Page Up and Page Down keys on the keyboard. Simply press Page Up on the keyboard to move up one page in the image, and the Page Down key on the keyboard to move down one page. You can move left and right by adding the Ctrl key to the keyboard shortcut. So Ctrl+Page Up will pan one page to the left, and Ctrl+Page Down will pan one page to the left.

On Macintosh there aren’t actual Page Up and Page Down keys, but you can still access these features through keyboard shortcuts. The equivalent of Page Up on Macintosh is to hold the “fn” key on the keyboard and use the up arrow for the Page Up command and the down arrow for the Page Down command. You can add the Command key to this combination to pan left or right. So fn+Command+up arrow will cause Photoshop to pan left, and fn+Command+down arrow will pan right.

I do recommend starting at a corner of the image to ensure a through review. The keyboard shortcuts for panning can admittedly be a little bit awkward to use, especially in terms of panning left and right. But when you get used to using these keyboard shortcuts, they can be tremendously helpful for closely (and thoroughly) evaluating all areas of a photo.

Export for Print


Today’s Question: I want to export a file using the profile from the print section of Lightroom and have a 12”x18” print made.  When I do this I run into problems because I am unable to get a border-to-border print.  Lightroom wants to include borders or only print a 7”x8”, or so, image in the center of the 12”x18” paper. How do I set up Lightroom to allow me to export a full-resolution JPEG image that will allow me to make a 12”x18” inch border-to-border print, using the Costco Fuji Printer profile?

Tim’s Quick Answer: There are two options here. You could define a custom paper size for the print, and then save the final print layout as a JPEG image using the “Print to File” option. Or you could use the Export feature in the Library module to export an image at the desired output size with the appropriate printer profile embedded in the exported image.

More Detail: To enable custom print sizes in the Print module (and thus custom-sized JPEG images for printing) you’ll need to define a custom paper size. This can be managed with the Page Setup dialog. The process is slightly different on Macintosh versus Windows, and on Windows there are variations in the Printer Properties dialog based on the model printer you’re using. But you can create a new custom paper size at the desired output dimensions, and with the margins set to zero on all four sides.

Once you have this custom paper size defined, you can use that custom size as the basis for configuring the print in the Print module. You can then use the “JPEG File” option for the “Print to” setting, so that you can then click the “Print to File” button at the bottom of the right panel in the Print module to create the image that is ready to be printed, with the selected printer profile embedded.

If you want to use the Export dialog to create the image file for printing, the only additional step required is to crop the image to the applicable aspect ratio so you can create a file at the exact print size. You may want to create a virtual copy for this purpose, which can then be cropped to the applicable aspect ratio (12×18 in this case) for the intended print.

When exporting the image you can then specify the exact dimensions (in inches, for example) as well as choosing the applicable printer profile for the exported file. The profile can be established using the Color Space popup in the File Settings section of the Export dialog, after you’ve selected “JPEG” from the Image Format popup. If the desired printer profile is not already available on the Color Space popup, you can add it to that popup. Start by choosing the “Other” option from the Color Space popup, and then turn on the checkbox for the desired printer profiles in the Choose Profiles dialog. Click OK, and the profiles you enabled will then appear on the Color Space popup.

With either of these approaches you can create an image ready for printing at a specific size, and with the appropriate printer profile embedded in the final image.

Destructive Camera Raw


Today’s Question: One thought relative to a recent Camera RAW question [related to the use of Camera Raw as a filter in Photoshop]. Shouldn’t your answer include a warning or caveat about adjustments made in Camera RAW being “destructive,” or non-reversible? Or am I wrong about that?

Tim’s Quick Answer: The Camera Raw filter in Photoshop can indeed be destructive to pixel values, although it doesn’t necessarily need to be. By contrast, using Adobe Camera Raw to process an original RAW capture is never destructive, by virtue of producing a derivative image based on the original RAW capture rather than altering that RAW capture.

More Detail: When opening a RAW capture in Photoshop, you’ll need to perform the intermediate step of processing that RAW capture using Adobe Camera Raw. When you complete that processing, the result is a new image based on the RAW capture, and the original RAW capture file remains untouched. In other words, Adobe Camera Raw provides a non-destructive workflow for RAW captures.

The Camera Raw filter within Photoshop provides the convenience of access to the various adjustments available within Adobe Camera Raw, but as a filter within Photoshop. However, this filter can indeed be destructive, meaning it can cause a change in pixel values within your image.

There are two ways you can work in a more non-destructive way with the Camera Raw filter within Photoshop.

The first is to simply create a copy of the Background image layer, and to apply adjustments to the resulting “Background Copy” image layer rather than the Background layer. This enables you to return to the Background layer if you decide you’re not happy with some of the adjustments you’ve applied to the Background Copy layer.

The other option is to work with the Camera Raw filter as a Smart Filter. This involves either converting the Background image layer to a Smart Object, or creating a Background Copy layer and converting that to a Smart Object. If you want to use the Background layer for this purpose, you’ll need to first double-click on the thumbnail for the Background layer on the Layers panel and click OK in the New Layer dialog, to convert the Background layer to a normal layer. Or simply create a Background Copy layer as noted above.

You can then convert the image layer to a Smart Object by choosing Filter > Convert for Smart Filters from the menu. You can then choose Filter > Camera Raw Filter from the menu to apply the Camera Raw filter as a Smart Filter. You can think of this as essentially providing the behavior of an adjustment layer in the context of the Camera Raw filter.

When you’re finished applying any desired adjustments with the Camera Raw filter, you can apply those changes by clicking the OK button in the Camera Raw dialog. If you later want to make changes to the adjustment settings, you can simply double-click on the thumbnail for your Smart Object layer to bring up the Camera Raw dialog again, where you can refine the settings for the adjustments you’ve applied.

However, applying a filter such as the Camera Raw filter as a Smart Filter can lead to some problems with a layer-based workflow. For example, if you have applied image cleanup work on a separate layer, and then make changes to the underlying image using the Smart Filter, the cleanup work you performed will no longer match the underlying image.

The bottom line is that there are some relatively non-destructive ways to work with the Camera Raw filter in Photoshop, but it is also possible to directly alter pixel values in a photo with this filter (or other filters).

Of course, if the original capture was indeed a RAW capture, and you’re using the Camera Raw filter to apply adjustments to the image derived from the RAW capture, it is worth noting that you could always return to that original RAW capture to start over with processing the image if that becomes necessary or desirable for any reason.

DNG as RAW Workaround


Today’s Question: I’m toying with the idea of getting Canon’s 5D Mk IV. This will create a “problem” though, as I don’t like the idea of Creative Cloud and am still working with Photoshop CS5. I’m pretty sure I can use a DNG converter to open the RAW files. But I gather there might be some inherent disadvantages to this. Wondering what you might suggest as the best way to approach the situation?

Tim’s Quick Answer: Actually, from an image quality and processing standpoint I would say that there is no inherent problem with converting your RAW captures to the Adobe DNG format in order to enable you to process those captures with an older version of Photoshop.

More Detail: The Adobe DNG converter enables you to convert most proprietary RAW capture formats to the Adobe DNG (digital negative) format. You can then process those DNG files using older software that doesn’t support the latest proprietary RAW capture formats.

In other words, if you are missing out on support for the latest RAW capture formats because you are using an older version of Photoshop, the Adobe DNG format provides a workaround.

Even better, the Adobe DNG Converter is free. So, you could convert captures from the Canon 5D Mark IV to the Adobe DNG format, and then open those DNG files using an older version of Photoshop that hasn’t been updated to supported the newer RAW capture formats.

With this approach you are naturally missing out on the newer features available in the latest updates to Photoshop. When it comes to Photoshop CC, for example, there have been a variety of updates and new features that I do find compelling.

That said, if you’re perfectly happy with your existing version of Photoshop, and don’t want to subscribe to the Adobe Creative Cloud, you can most certainly employ the free Adobe DNG Converter in your workflow, with no significant impact other than missing out on the latest new features in Photoshop CC.

You can learn more about the Adobe Digital Negative (DNG) file format, and find links to the free Adobe DNG Converter (with separate versions for Macintosh and Windows) by following this link: