Category: Ask Tim Grey

Today’s Question: I really enjoyed reading your article on the back button focus technique in the July issue of Pixology and I picked up a couple of neat tips. I’ve been using this technique for some time but have some confusion around using this option along with continuous focus/predictive autofocus. Specifically, how do I ensure that a moving subject will be in focus at the time the shutter releases? A great example of my question comes from viewing your “Parting Shot” at the end of the issue. In this picture you have a crop duster plane coming straight at the camera, at some speed I’m sure. How did you manage to keep the plane in such sharp focus? Were you using back button focus for the shot? If you held down the back focus button while pressing the shutter release, will the camera use predictive autofocus?

Tim’s Quick Answer: Back button focus will trigger predictive autofocus as long as your camera is otherwise configured for that purpose. In the case of the crop duster shot (which you can view here: https://500px.com/photo/112385163/crop-duster-spraying-in-palouse-by-tim-grey), I was indeed using back button focus, and that was triggering predictive autofocus.

More Detail: The key here is to configure your camera for continuous autofocus when you enable back button autofocus. You can then choose whether you want “one shot” versus “continuous” autofocus based on your use of the back button for focusing.

When the back button is pressed and held, the camera will focus based on the current settings. If you have the camera set to a “one shot” autofocus mode, then pressing and holding the back button for autofocus will only enable “one shot” autofocus.

If you have enabled continuous autofocus, pressing and holding the back button focus button will trigger continuous autofocus. And this is where one of the most powerful features of back button focus comes in.

By configuring your camera for continuous autofocus and enabling back button autofocus, you have the best of both worlds. When you want continuous autofocus you press and hold the back button focus button. When you want the equivalent of “one shot” autofocus you press the button until focus is established, then release the button.

It is worth noting that autofocus in general can become even more powerful by selecting a specific focusing point within the viewfinder that corresponds to the position of the key subject within the frame. That is exactly how I captured the crop duster photo referenced above.

If you’d like to get a free copy of the Pixology magazine issue that features the article on back button focus, you can sign up to get that issue for free here:

http://timgrey.me/pixbackfocus

Today’s Question: I am confused by comments from various photographers saying that one RAW processor is better than another. Is it possible to make adjustments so that the results of one RAW processor can be matched to any other RAW processor?

Tim’s Quick Answer: All RAW processing software is not created equal. Some software will indeed produce better results than other software, and it can be very difficult to achieve the exact same appearance when processing the same image with different software tools.

More Detail: Each software tool for processing RAW captures uses its own algorithms for both translating the RAW capture into actual pixel values and applying adjustments to the appearance of those pixels.

For example, you will find differences in the ability of different RAW processing software to extract shadow detail. You will also find significant differences when it comes to minimizing noise in your photos. The specific adjustments that are available will vary, and the range of possible results may vary as well.

To be sure, the overall level of quality that can be achieved by most RAW processing software is very good. In the early days of digital capture you could find dramatic differences in image quality with different software for processing RAW captures. Today I would say there is less variation in terms of quality. However, there is still variation in terms of the specific approach used by different software tools, as well as variation in the specific adjustments available.

However, it is very important to test software yourself rather than relying on reviews from others. I have seen far too many reviews where similar adjustment settings were used between different RAW processing software, with a clear difference in the final result. This seems to indicate that one software tool is better than another for RAW processing, with the result somewhat exaggerated in a way that I would consider unfair.

Instead of relying on reviews from others, I recommend testing out various RAW processing software to see which one works best for you. Try to achieve an ideal adjustment for the same image using different software, and then decide which might be best for you in terms of the quality of the result, the workflow efficiency, the ease of use of the software, and other factors.

Your final decision will depend on your own priorities and preferences, the types of images you tend to capture, and other factors. But the bottom line is that there are differences among RAW processing software, and it isn’t always possible to achieve the exact same result among different software when processing the same image.

Today’s Question: I just purchased a 10-stop neutral density (ND) filter. Could you advise on how to calculate exposure times?

Tim’s Quick Answer: The process of calculating exposures when using a neutral density (ND) filter can actually be very simple. Start with exposure settings that are proper for the scene without the ND filter, using the Manual exposure mode. Then add the ND filter and adjust the shutter speed by the number of stops indicated for the density of your ND filter.

More Detail: In essence, I recommend starting off as though you weren’t using an ND filter at all. Get the camera setup without the ND filter attached to the lens. This makes it much easier, among other things, to compose your photo.

You can use whatever method you want to determine the appropriate exposure settings, but you’ll want to end up in the Manual exposure mode. If you’re not comfortable using Manual mode to establish the initial exposure, you can start with a semi-automatic exposure mode (such as Aperture Priority) to determine appropriate exposure settings. Then switch to Manual exposure mode and dial in the exact same settings.

It is worth noting that under most circumstances I will start off with the ISO at the minimum value and the aperture at the smallest opening (largest f-number) when capturing a long exposure photo that employs an ND filter. However, part of the benefit of using an ND filter is that you can get a relatively long exposure even with an aperture that isn’t stopped down all the way. This enables you to, for example, create a long exposure that also has a narrow depth of field.

Once you have determined your exposure settings and have everything else configured (such as composition and focus), you can add the ND filter. It is worth noting that the Xume Adapters (http://timgrey.me/go-xume) I’ve talked about in the past make this step much easier, since the ND filter can then snap into place using magnets.

With the ND filter attached, the final step is to adjust the shutter speed based on the number of stops of light being blocked by the ND filter. In this case, for example, the question relates to a 10-stop filter.

Generally speaking, your camera will adjust shutter speeds using one of the dials on the camera, in either half-stop or third-stop increments. In other words, you will turn the dial either two or three “clicks” for each stop. Make sure you’re turning in the direction to extend the exposure time, not shorten it. Then turn by 20 “clicks” if your camera is set to half-stop increments and 30 “clicks” for third-stop increments.

I am in the habit of counting out stops of light based on sets of clicks. I generally have my camera set to adjust exposure in half-stop increments, so for each two clicks I will count off a stop. To me this is a little easier than counting out twenty clicks, for example.

Overall the process here is very simple. Setup your camera based on no ND filter being used, then add the filter and adjust the shutter speed by the number of stops needed for that filter.

Today’s Question: How do I capture long exposures at night without blowing out the windows of the buildings?

Tim’s Quick Answer: There are a few options here. The first is to set your exposure to retain detail in the brightest areas (in this case the windows of buildings). The second is to create a high dynamic range (HDR) image. The third is to not worry about the lost detail. And the fourth is to capture your images earlier in the evening before the contrast is so extreme.

More Detail: The problem with creating a night exposure that retains all detail in the bright lights (such as windows of buildings where the lights are on) is that the rest of the image will generally be extremely dark. As a result, if you want to capture only a single image you’ll need to choose between detail for the highlights versus detail for the shadows.

Creating an HDR image is a reasonable option that can greatly improve the overall tonal range represented in the final image. However, with long exposures there are some inherent challenges to HDR. To begin with, it can require considerable time to capture all of the images in the HDR sequence. On a related note, the longer time required to capture all of the images can result in problematic changes within the scene from one capture to the next.

My recommendation is to shift your night photography to earlier in the evening. If you capture your long exposures late enough that the lights of the city are on, but early enough that there is still some degree of illumination left in the sky, you’ll have a narrower range of tonal values to contend with, so you will be better able to capture the full range (or nearly so) with a single exposure.

Note, of course, that you can employ a neutral density filter to extend the exposure longer that would otherwise be possible when photographing in the relatively early evening. But in general, if you photograph as soon as the lights of the city are turned on, you should be able to achieve excellent results with a single frame, likely without the need for a neutral density filter.

Today’s Question: Is there a way to flip a selection in Photoshop?

Tim’s Quick Answer: Yes, of course. You can both invert and flip a selection, using the Inverse command if you want to invert the selection, or the various Transform commands to flip the selection horizontally or vertically.

More Detail: If you want to invert a selection so that the deselected area is selected and vice versa, you can choose Select > Inverse from the menu. This will reverse the selection so that you have the opposite of the original selection.

Before using the general Transform commands to change a selection, first you need to put the selection itself into “transform” mode. To do so, with an active selection choose Select > Transform Selection from the menu. You can then use the various Transform commands on the Edit menu to actually transform the shape of the selection.

If you want to flip a selection horizontally or vertically, you can use the Transform commands. For example, you can choose Edit > Transform from the menu, and then choose Flip Horizontal or Flip Vertical from that submenu based on the direction you want to flip the selection.

There are also a wide variety of other commands available on the Edit > Transform submenu, which can also be used to manipulate the shape of a selection. You can also access the equivalent of the Free Transform command by choosing Select > Transform Selection from the menu.

It is also worth noting that if you have used a selection as the basis of a layer mask, you can also apply the Transform commands (among other commands) to change the shape of the layer mask.

Today’s Question: What’s your opinion on making custom printer profiles for each paper versus using the manufacturer’s profiles? An article that I read on the subject made two primary points. First, manufacturers often make “conservative” profiles that minimize colour issues but may not necessarily maximize the potential of the output device to render their full potential gamut. Secondly, manufacturers’ profiles for glossy and related finishes tend to be very close/indiscernible from custom profiles, but the difference can be significant for matte and related papers. Your thoughts?

Tim’s Quick Answer: The profiles that are included with the driver software for today’s photo printers, as well as those provided with third-party papers, are generally of very good quality. For many photographers and applications, those profiles will be more than adequate. That said, custom printer profiles can help ensure the very best results for very discerning photographers.

More Detail: Back in the early days of photo inkjet printing, the printer profiles included with most printers I had the opportunity to test were of very poor quality. Colors could be very inconsistent relative to the source image, which could prove incredibly frustrating for the photographers.

Fortunately, since that time the profiles included with your printer (often referred to as “canned” profiles) have gotten much better. In addition, third-party companies producing papers for photo inkjet printing are also now providing profiles that have proven to be very accurate in most cases.

It is true that there are some compromises involved when it comes to providing these “generic” printer profiles. A printer profile describes the behavior of a specific printer, ink, and paper combination. While today’s manufacturing tolerances are generally very high, there can still be some variation between individual printers of the same model, individual batches of inks for a given printer, and individual batches of a specific type of photo inkjet paper.

I would also agree that the differences can be more significant with matte papers than for glossy (or semi-gloss) papers. The behavior of matte papers creates great potential loss of tonality and color range, and so with matte papers an accurate profile is even more important than with a glossy paper.

Producing your own custom printer profiles using a package that includes a spectrophotometer (or employing a service provider using such tools) can be very helpful. Admittedly, the differences between many canned profiles and a custom profile will often be somewhat subtle, but those subtle differences can make a big difference in your final print.

One package you might consider if you’d like to build your own custom printer profiles is the X-Rite ColorMunki Photo package, which you can find here:

http://timgrey.me/munkiphoto

Today’s Question: As I understand it, the color temperature for light is rated by the Kelvin scale. The higher the number, the cooler or more blue. The lower the temperature, the warmer or more red. Yet we photographers with Lightroom and Photoshop seem to be using the Kelvin scale in reverse. Lowering the Kelvin temperature makes the image cooler and more blue, whereas increasing the temperature warms the image. What am I not understanding about how the Kelvin scale is applied to color and light temperature?

Tim’s Quick Answer: When it comes to the Temperature slider in most imaging software, the reason the adjustment seems backwards is that you are choosing a color temperature to compensate for, not choosing what color temperature the overall color in the image should look like.

More Detail: First off, your overall understanding of the Kelvin scale is correct. A low Kelvin value (temperature) reflects a warmer color tone (more yellow, for example). A higher value reflects a cooler color tone (more blue, for example). This scale is based on the behavior of a theoretical “black body” that radiates heat in the form of visible light as it is heated up.

Of course, it is worth noting that what is really backwards here is our definition of color values in what I refer to as a “psychological” way. We refer to colors in the red and yellow range as being “warm” colors, and we refer to colors in the blue range as being “cool” colors. But in reality, hotter objects emit what we would refer to as cooler colors. So our psychology of colors could be described as “backwards” to some extent.

When referring to the color temperature of visible light, the Kelvin scale is often used to describe the color of that light. So a warmer (or more yellow) color would have a relatively low Kelvin value, while a cooler (or more blue) color would have a relatively high Kelvin value.

In most imaging software, reducing the color temperature value cools off the image, while increasing that value warms up the image. This certainly seems backwards based on the actual Kelvin scale for color temperature.

However, the color temperature adjustment is actually allowing us to define what color temperature we want to compensate for. So, if the light illuminating a scene was very blue, we would shift the color temperature adjustment toward blue. In essence, we are saying, “The light was very blue, so please shift the image toward yellow to compensate”.

In other words, when you adjust the color temperature Kelvin value up or down, you’re really attempting to define what color the light actually was, so that an appropriate compensation can be applied.

So, if you think of the white balance adjustment as enabling you to define what color temperature the light was in order to produce appropriate neutral values in the image, I think the slider will make more sense.

Today’s Question: I just watched one of your videos from a B&H Photo presentation and thoroughly enjoyed it very much. I focused in on your discussion about the neutral density (ND) filter and I’m convinced that I want to get one. So, what do you recommend? Variable or solid, and what brand?

Tim’s Quick Answer: My personal preference is to use solid neutral density filters, rather than variable. In terms of brands, I’ve been very happy with filters from Singh-Ray and I consider B+W to offer excellent quality at a good price point. However, I’ve also recently discovered Breakthrough Photography filters, and am very impressed with what I’ve seen so far.

More Detail: There is certainly a convenience factor when using a variable ND filter, since you can achieve a range of densities with a single filter. However, it can be challenging to achieve just the right density or exposure. For me those challenges slow down my workflow (and sometimes frustrate me). Therefore, I prefer to use solid ND filters, so that I always know exactly how many stops of light I’m blocking for the exposure.

For a long time I’ve considered Singh-Ray filters (http://www.singh-ray.com) to be among the very best in terms of quality. These filters do tend to be a bit more expensive than those from other companies, but the quality in my experience has been excellent.

I’ve also been a fan of the filters from B+W, such as the 10-stop filter I’ve been using for some time now (http://timgrey.me/bw10stop). I have found the filters from B+W to be of excellent quality, while being offered at a competitive price.

More recently, I’ve been introduced to the filters from Breakthrough Photography, and I am very impressed. A quick test has demonstrated that the ND filters from Breakthrough Photography are very neutral, and the quality is excellent. You can find an example of one of the ND filters from Breakthrough Photography here:

http://timgrey.me/tgtv-bp-nd6

Today’s Question: In all my years of reading your newsletters I’ve never heard you address the question of file degradation due to resizing for printing. If a person has a finished PSD image file and uses that file to print various size prints and at the end chooses to “not save” at any particular image size, will that process after a short number of times begin to degrade or muddy the pixels of that original PSD file?

Tim’s Quick Answer: Not at all. One of the great advantages of digital photography is that an image file will not degrade over time. As long as the actual image file remains intact, you can produce output from the same image file an unlimited number of times without degrading that image.

More Detail: In the days before digital photography, we didn’t have the ability to protect our images over the long term the way we can with digital photos. While many film images (or prints) were rather stable, there was still the risk of slow degradation or damage over time. With a digital file, as long as that file is preserved the contents of the file will not change.

There are other aspects of a photography workflow that can impact an image. For example, if you open a JPEG image, apply changes, and re-save the image file, you are degrading that image to some extent due to the updated processing of the image file for purposes of JPEG compression.

But in the context of a workflow that involves simply opening an existing image, processing that image to produce a print, but then not saving the changes to the original file, the original image file remains in its original state.

Naturally you need to be careful about backing up images, ensuring that the storage media on which your images is stored does not become obsolete, and other considerations. But in terms of the file itself, as long as it is preserved, so to are the contents of that file.

Today’s Question: My understanding has been that prints made on matte surface, inkjet printing papers are generally more archival than glossy surface papers. Do you agree? And how, if at all, does the coating on coated matte papers influence the print’s life expectancy?

Tim’s Quick Answer: There are a variety of factors that impact overall print longevity. However, in general matte papers will provide the greatest longevity. Glossy papers will generally provide the least longevity, and coated matte papers can be expected to provide longevity that falls somewhere in between.

More Detail: Let’s first assume that all other factors are equal in this case. That’s not a small assumption, of course. There are factors related to the composition of the paper substrate, the degree to which a given paper is acid-free, and many others.

However, among the various factors that impact print longevity is how close the inks ultimately sit to the surface of the paper. The closer the inks are to the surface, the more exposed those inks will be to environmental factors.

Glossy papers generally cause inks to stay at the surface rather than being absorbed. As a result, the inks are more exposed to environmental factors that can cause the inks to fade over time. In other words, with a glossy surface there is a greater risk that the print will fade relatively quickly.

Matte papers, on the other hand, absorb the inks so that the inks can be thought of as somewhat “sitting below the surface” of the paper. That helps to protect the inks, so they are not as prone to fading. Of course, that also reduces the overall color saturation and tonal contrast of the print.

A coated matte paper will generally fall somewhere in between. The matte paper itself is more absorbent than a glossy paper would otherwise be. However, the coating causes the paper to behave a little more like a glossy paper than a matte paper. Thus, in general I would expect coated matte papers to have a print longevity that is longer than that of a glossy paper, but shorter than that of an uncoated matte paper.