Monthly Archives: January 2007

Technique

Jim’s question about sharpness

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Jim wrote to ask about exposure, color, and sharpness results on photos taken on his Canon 350D/XT. Here is what I wrote in reply to his original email:

First of all, in regards to exposure the histogram display is your friend. I have my XT set to display the very small version of the image after exposure along with the histogram display. The histogram can tell you quite quickly whether your exposure captures the full dynamic range. In fact, I often use the first shot as my light meter – I let the camera make the first exposure in aperture priority mode and then look at the histogram. Then I frequently switch to manual mode and set aperture and shutter speed based on what I saw in the histogram.

If the full dynamic range will not fit into the histogram display – in other words there is a sharp cutoff at the bright and dark ends of the scale and the highlight warning flashes the display – I will give priority to avoiding blowing out the highlights. In other words I close down or increase shutter speed so that I avoid losing detail in the bright areas, even at the expense of seeing the curve shift toward underexposure. When this happens there are still a couple of things you can do to salvage the shadow areas, especially if you shoot RAW mode: you can bring up the dark areas in your software on your computer if they aren’t _way_ too dark, or you can shoot multiple exposures of the scene (obviously on a tripod) with some optimized for highlights and others for shadows and then combine them in Photoshop. (I did that in a major way to create the Pacific Sunset from Windy Hill shots I recently posted.)

Are you shooting in RAW mode or shooting .jpg files? I always shoot in RAW mode because it does not compress the image data at all – it basically dumps the photosite data into a file. (Hence, “raw” I suppose.) RAW files contain greater dynamic range and give you more room to make post-camera corrections in software. In fact, you really _must_ make a number of post-processing adjustments in order to get the most out of RAW files. Plain unprocessed RAW files are not very impressive and, in particular, they are not very sharp looking. (jpg files may appear sharper straight from the camera due to in-camera sharpening and other automatic adjustments, but they cannot be improved much beyond this point.)

In general, when I convert my RAW files (use the Adobe Camera Raw component of Photoshop) I increase the contrast and saturation a bit (the exact amount varies), decrease the exposure (and sometimes compensate by adjusting brightness) so that highlights are not burned out, adjust the shadows setting to the lowest black level, and adjust for chromatic aberration if necessary. Yes, a lot of steps! But that’s not the end.

Once the file comes into Photoshop there is still a lot of work to do. At a minimum (in all but the rarest cases) I adjust levels so that the dynamic range of the image fills out the available dynamic range of my printer. Depending upon the image I may also make adjustments to curves, saturation, and so forth. And then, in classic style, I dodge and burn as necessary. On some images I employ other more exotic techniques (local adjustments to contrast, levels, saturation) to get what I’m looking for.

So a short summary:

No, I don’t use separate light meter, but I do use the camera

as a meter by means of the histogram display.

I try to get the histogram curve to fit into the middle of the

display and avoid blowing out the high end especially. (A good

curve goes _to_ the high end but not beyond.)

If the dynamic range is too great I take multiple frames at

different exposures and combine them later in software, or

if the problem isn’t to severe I can rescue the shadows from

a single exposure in the RAW converter.

I always shoot RAW.

Post-camera adjustments to levels, exposure, saturation,

contrast, and (especially) sharpening are necessary when

you work with RAW files.

—–

Technique

Jim’s question about sharpness

Leave a comment

Jim wrote to ask about exposure, color, and sharpness results on photos taken on his Canon 350D/XT. Here is what I wrote in reply to his original email:

First of all, in regards to exposure the histogram display is your friend. I have my XT set to display the very small version of the image after exposure along with the histogram display. The histogram can tell you quite quickly whether your exposure captures the full dynamic range. In fact, I often use the first shot as my light meter – I let the camera make the first exposure in aperture priority mode and then look at the histogram. Then I frequently switch to manual mode and set aperture and shutter speed based on what I saw in the histogram.

If the full dynamic range will not fit into the histogram display – in other words there is a sharp cutoff at the bright and dark ends of the scale and the highlight warning flashes the display – I will give priority to avoiding blowing out the highlights. In other words I close down or increase shutter speed so that I avoid losing detail in the bright areas, even at the expense of seeing the curve shift toward underexposure. When this happens there are still a couple of things you can do to salvage the shadow areas, especially if you shoot RAW mode: you can bring up the dark areas in your software on your computer if they aren’t _way_ too dark, or you can shoot multiple exposures of the scene (obviously on a tripod) with some optimized for highlights and others for shadows and then combine them in Photoshop. (I did that in a major way to create the Pacific Sunset from Windy Hill shots I recently posted.)

Are you shooting in RAW mode or shooting .jpg files? I always shoot in RAW mode because it does not compress the image data at all – it basically dumps the photosite data into a file. (Hence, “raw” I suppose.) RAW files contain greater dynamic range and give you more room to make post-camera corrections in software. In fact, you really _must_ make a number of post-processing adjustments in order to get the most out of RAW files. Plain unprocessed RAW files are not very impressive and, in particular, they are not very sharp looking. (jpg files may appear sharper straight from the camera due to in-camera sharpening and other automatic adjustments, but they cannot be improved much beyond this point.)

In general, when I convert my RAW files (use the Adobe Camera Raw component of Photoshop) I increase the contrast and saturation a bit (the exact amount varies), decrease the exposure (and sometimes compensate by adjusting brightness) so that highlights are not burned out, adjust the shadows setting to the lowest black level, and adjust for chromatic aberration if necessary. Yes, a lot of steps! But that’s not the end.

Once the file comes into Photoshop there is still a lot of work to do. At a minimum (in all but the rarest cases) I adjust levels so that the dynamic range of the image fills out the available dynamic range of my printer. Depending upon the image I may also make adjustments to curves, saturation, and so forth. And then, in classic style, I dodge and burn as necessary. On some images I employ other more exotic techniques (local adjustments to contrast, levels, saturation) to get what I’m looking for.

So a short summary:

No, I don’t use separate light meter, but I do use the camera

as a meter by means of the histogram display.

I try to get the histogram curve to fit into the middle of the

display and avoid blowing out the high end especially. (A good

curve goes _to_ the high end but not beyond.)

If the dynamic range is too great I take multiple frames at

different exposures and combine them later in software, or

if the problem isn’t to severe I can rescue the shadows from

a single exposure in the RAW converter.

I always shoot RAW.

Post-camera adjustments to levels, exposure, saturation,

contrast, and (especially) sharpening are necessary when

you work with RAW files.

—–

Equipment

What lens for XTi?

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(Note: I have added updates to this older article. Scroll to the bottom to see them.)

Maria wrote:

Hi Dan,

I found your website through a photo discussion thread. First of all, I’d like to say what great photo’s you’ve taken! Very beautiful , and I especially admire the Washington sky & Pacific Sunset piece!

I am an illustrator/designer ready to buy the xti but not sure which lens. Which do you recommend? I’m looking at a Tamron for cost efficiency.

I have an old Canon F1 with many Tokina, canon lenses. I will buy an adapter for them so I was wondering if its worth it to buy a digital lens? Any thoughts would be appreciated.

Thanks for writing, Maria, and thanks for your kind words about my photoraphy and the articles at this web site. Congratulations on the XTi. It sure looks like a great camera for most users – similar in many ways to the XT (which I use) but with some significant upgrades.

I can give some lens advice, but my direct experience is entirely with Canon lenses. (At least recently… in the distant past I also used Pentax and Minolta) I’m afraid I can’t give any personal recommendations regarding the Tamron, etc. third-party lenses.

A few thoughts:

  • If you have really good older lenses there are adapters that will allow you to use them on your Canon EOS camera, but you will not have all of the automation that you would have with newer Canon lenses. For example you may have to focus manually – which is not the easiest task with the APS-C crop sensor cameras and their relatively small viewfinder images. Generally, it may be worthwhile to use an older lens if it is a really great one and you are happy to give up features that would be available with newer lenses. Using the old lens to save money is generally not a very satisfying approach, I’m afraid. (Update: I now understand that many of the older Canon lenses – e.g. FD lenses – won’t really work well on the newer cameras even with adapters. Don’t try to use them on a current Canon DSLR.)
  • The term “digital lens” is confusing. Often the term refers to lenses that project a smaller image circle – large enough to cover the smaller APS-C 1.6x crop sensor of the XTi and similar cameras but not large enough for full-frame sensors or film SLRs. Canon calls them “EF-S” lenses. There are no real optical advantages to these lenses, although they can be made smaller than equivalent full-frame (e.g. – Canon EF) lenses.

I lean towards acquiring Canon EF lenses. While a DSLR body (yes, even the XTi) is likely to have a somewhat short lifespan – as improved bodies come out, you’ll be tempted to replace it sooner than you might imagine – your lenses can be a long term investment. Money spend on good lenses can pay off in better quality photographs.

Keep in mind is that because the XTi is a crop-sensor camera, lenses of a given focal length will seem like longer lenses on your 35mm SLR. For example, a 50mm “normal” lens for a film SLR will act like a slight telephoto, or “portrait” lens on the XTi; it will give you the same field of view that an 80mm lens provided on film. You’ll need to get wider lenses for the XTi to replicate the effect of lenses you would have chosen for a film camera.

If 50mm was a “normal” lens on a film SLR, something in the 28mm-35mm range will provide an equivalent field of view on your XTi. The same holds true with zoom lenses; while a 28mm-70mm lens would have given fairly good coverage for typical use on the film SLR, it would likely seem too long on the XTi and a 17mm-45mm range would be nearly equivalent.

(If there are particular focal lengths you favored on your old SLRs, you can divide their length by 1.6 to identify an equivalent focal length for your XTi. Thus, to exactly replicate the angle of view of your old 50mm lens you would use a 31mm lens on the XTi because 50mm x 1.6 = 31.25mm. Conversely, multiply the focal length of a current lens to see what SLR lens would have been equivalent. Putting a 100mm lens on your XTi is equivalent to putting a 160mm lens on a film SLR since 100mm x 1.6 = 160mm.)

Any recommendation of a specific lens or lenses must be based on knowing something about your photography. For example, I could not answer “What is the best Canon 24mm lens?” without more information. For a landscape photographer the 24mm T/S lens might be best; for a news photographer it might be the 24mm f/1.4; a street photographer might prefer the 24mm f/2.8 with the XT/Xti; a wedding photographer might want the 24-70mm f/2.8 zoom.

Take care,

Dan

Update 3/3/08: For many entry-level photographers getting an XTi or similar Canon body for the first time, the newer image-stabilized version of the Canon EFS 8-55mm “kit lens” is a great choice. Reports are that it is actually quite a good optical performer, and the lens is quite inexpensive. It can be a great starter lens, and after you use it for awhile your additional needs will be clearer to you and you’ll be ready to possibly upgrade to more expensive lenses.

Update 5/8/08: I’ve come to recognize that for some crop sensor camera shooters the EF lenses may not necessarily be the best choice in all cases. (If you plan to move to full frame soon or if you are looking at longer lenses, in general it still makes sense to look to the EF series.) For example, if I were buying a crop sensor Canon DSLR today – either a Rebel or an X0D series body – I would almost certainly consider the EFS 17-55mm f/2.8 IS lens as a first choice for quality work in the “normal” focal length range. There really is no directly comparable EF lens that provides the same feature set on a crop sensor body: f/2.8 maximum aperture, coverage from wide to short telephoto, image stabilization, and excellent optical quality.

(Note: Most of what I’ve written here is applicable to any of the Digital Rebel or Rebel Cameras after the 300D: the XT (350D), XTi (400D), and XSi (450D). As a matter of fact, it isn’t irrelevant to users of the XOD cameras either: 20D, 30D, and 40D.