Building upon last week's Basic Printing with Lightroom video tutorial, this advanced printing tutorial will teach you to print contact sheets, print multiple images at a time, use Lightroom's present...
"From Light to Ink" featured the work of Canon Inspirers and contest winners, all printed using Canon's imagePROGRAF printers. The gallery show revolved around the discussion of printing photographs...
Getting photographs right in the camera is a combination of using your imagination, creativity, art, and technique. In Part 3 of this three part series, we focus on shooting strategy and the role of...
The new Sigma 18-250mm F3.5-6.3 DC Macro OS HSM differs from Sigma’s earlier 18-250mm F3.5-6.3 DC OS HSM lens in that it’s physically smaller and lighter, it has better macro capability and it uses sigma’s TSC (thermally stable composite) material which minimizes the effect of temperature on the lens and allows smaller and lighter construction.
The previous 18-250mm F3.5-6.3 weighed 22.2oz and measured 3.1″ × 4″, while the new Sigma 18-250mm F3.5-6.3 DC Macro OS HSM weighs 16.6oz and is only 2.9″ × 3.5″.
Optically the Sigma 18-250mm F3.5-6.3 DC Macro OS HSM uses three aspheric elements and one SLD (special low dispersion) element to minimize aberrations, plus an optical stabilization system to minimize image blur due to camera motion. Super multilayer coating is used to minimize flare and ghosting, a rounded 7-blade iris is used to smooth out of focus blur and an ultrasonic HSM focus motor is used to maximize focus speed and minimize motor noise.
Sigma 18-250mm F3.5-6.3 DC OS MACROHSM Specifications
16 Elements in 13 Groups
Angle of View (diagonal)
76.5 – 6.5 degrees
Number of Diaphragm Blades
f3.5 (18mm) – f6.3 (250mm)
35cm / 13.8in
Filter Size (mm)
(Diameter x Length)
73.5mmx88.6 mm/2.9inx3.5 in
470g / 16.6oz.
Canon, Nikon, Pentax, Sigma, Sony (not OS)
The Sigma 18-250mm F3.5-6.3 DC Macro OS HSM is quite small and light for a lens with such and extended zoom range (2.9″×3.5″, 16.6oz). The finish is the typical semi-matte black plastic that’s found on most of Sigma’s lenses. Marking for focal length, magnification, switches etc. are printed in white on the plastic rather than being engraved. The lens mount is metal.
Sigma 18-250/3.5-6.3 DC Macro OS HSM
Focal length settings of 18, 28, 35, 50, 80, 135 and 250mm are marked and there is a macro scale which shows the magnification obtained at the closest focus distance (0.35m) at these focal length settings. Maximum magnification is 1:2.9 at 250mm. There is a focus scale marked at 0.35, 1, 2, 4 m and infinity (with corresponding distances in ft.). The zoom scale (at least on the Canon EOS mount verson) has 18mm at the left and 250mm on the right and the distance scale has close focusing on the left and infinity on the right. This means that both the zoom and focus rings move in the same direction as those found on all Canon EF and EF-S lenses.
Minimum aperture at all focal length settings is f22. The maximum aperture varies with focal length setting as follows:
18mm – f3.5
28mm – f4.0
35mm – f4.5
50mm – f5.0
80mm – ff5.6
135mm – f6.3
250mm – f6.3
According to the lens EXIF data, the lens’ maximum aperture is f6.3 from 128mm though 250mm.
The Sigma 18-250mm F3.5-6.3 DC Macro OS HSM extends in length as the focal length increases. Total extension (via two sliding barrels) is 2.8" at 250mm, making a total length of 6.25". Focusing is internal, so the length of the lens barrel does not vary during focusing and the filter threads do not rotate.
There are three slide switches on the lens. One is a lock which can be engaged at the 18mm focal length setting and prevents the lens barrel from extending accidentally. A second switch enables AF or MF operation. Manual focus is not available when in AF mode (i.e. the lens does not have full time manual focus). The third switch turns the OS (optical stabilization) on and off. OS should normally be turned off when the lens is used on a tripod, particularly if long exposures are being used.
A “petal style” bayonet mounting lens hood is supplied. As with all hoods which have to cover a wide zoom range, the hood is much more effective at wideangle settings than telephoto settings.
Sharpness was judged from images obtained using and EOS 7D with mirror lockup and a remote release to minimize any camera vibration.
The sharpness of the Sigma 18-250mm F3.5-6.3 DC Macro OS HSM in the center of the frame was generally quite good. However with the first sample of the lens I tested, sharpness in the corners was more difficult to define since the four corners were not the same. The top right corner consistently showed the highest sharpness, while the bottom left corner showed the least sharpness over a number of different tests.
Given these observations I concluded that there was some element misalignment present in the sample of the lens I had and so I requested a second sample. The second sample proved to be much more uniform across the frame and I’ll discuss the results from that sample below.
Concentrating first on the center, sharpness was good, even wide open and slightly better with the lens stopped down. This pattern was maintained across the whole focal length range. Center sharpness did drop a little at the telephoto end of the range, but I’d still rate it as fairly good, especially if the lens is stopped down from f6.3 (wide open) to f8. The image on the right compares the center of the frame at 85mm and f5.6 taken with the Sigma 18-250mm F3.5-6.3 DC Macro OS HSM with a similar image taken using a Canon 85/1.8 at f5.6. While the Sigma lens can’t quite match the Canon, remember that the Canon image is from a stopped down prime lens, while the Sigma image is from a wide open super-zoom. Taking that into account I think the Sigma does a very respectable job.
Center sharpness was also high at wideangle settings, but softened a little towards the telephoto end of the range. In general center sharpness seems to peak about a stop down from wide open, which is about f5.6 at the wide angle end of the range and f8 at the telephoto end.
Corner sharpness on the second sample of the lens was roughly the same in all four corners of the image, which indicates the elements are in correct alignment.
At 18mm the corners were quite soft with the lens wide open, but improved as the aperture was closed down, peaking in sharpness in the f11-f16 range. However sharpness was compromised to some extent by quite noticeable chromatic aberration. When the CA was corrected, things looked a little better. The image on the right shows 100% crops from the center and corners of the image as shot and the corner corrected for chromatic aberration using RawTherapee.
At 250mm the story was similar, with chromatic aberration significant enough to affect sharpness. Again correction in RawTherapee resulted in an improvement, though corner sharpness never reaches the level of center sharpness.
At 85mm corner sharpness was slightly better since 85mm is the “sweet spot” for chromatic aberration supression and very little is visible even in the corners of the image.
The overall conclusion is that you can fairly safely shoot this Sigma 18-250mm F3.5-6.3 DC Macro OS HSM wide open if your main subject is near the center of the frame, though a stop down is generally a touch sharper. However if you are interested in maximizing overall sharpness out to the edges and corners of the frame you may need to stop down to f11 or even f16, for best corner sharpness.
Chromatic aberration is strongest at the extremes of the zoom range, 18mm and 250mm. It’s at its minimum near 80mm, where it’s hardly detectable. The extent of the CA at 18mm and 250mm is shown in the images above, which are 100% crops from the corners of the image where CA is at its peak.
Distortion is evident across the whole focal length range. At 18mm it’s around 3% barrel distortion. It rapidly flips from barrel to pincushion with slight zooming. At 22mm distortion is at a minimum and from that point on there is pincushion distortion measuring around 3.1% at 35mm and around 2% from 80mm through 250mm..
These are relatively high levels of distortion by the standards of prime lenses and narrower range zooms, but are not particularly unusual for a zoom with the 13.9x range of the Sigma 18-250mm F3.5-6.3 DC Macro OS HSM. At most focal lengths however (expect for around 22mm), you will probably notice the distortion, especially on any image with straight lines near the edges.
Digital distortion correction is possible in many image editors, though for the best correction you’d need an editor which has the distortion parameters of this particular lens in its profiles. At times there’s a hint of complex distortion which the simple distortion correction algorithms cannot completely correct for.
Vignetting (corner darkening) is pretty well controlled, especially at mid focal lengths. It’s strongest at 18mm and 250mm where the corners are around a stop darker than the center with the lens wide open. Stopping down a stop reduces vignetting to under 1/2 stop, even at the focal length extremes.
Although the Sigma 18-250mm F3.5-6.3 DC Macro OS HSM has “Macro” in its name, it doesn’t mean quite the same thing as “Macro” does when applied to a dedicated single focal length macro lens. A true “Macro” lens is specially designed to have a flat field and give outstanding sharpness and low levels of aberration when used at macro magnifications. The Sigma 18-250mm F3.5-6.3 DC Macro OS HSM might better be called a “close focus” lens. It can indeed focus very close, as close as 3.5" (9cm) from the front element of the lens, at which distance with the lens zoomed all the way out to the 250mm position the magnification is close to 1/3 life size. The image of the watch on the right was shot at close to 1/3 life size with the lens set to the 250mm focal length setting and the aperture set to f22. It’s a reasonably good image, certainly good enough for product shots for example.
However, when closely examined, the clarity of the “macro” images don’t really compare with those from a true macro lens at the same magnification. It’s a bit soft wide open and even stopped down to f11 or f16 it still doesn’t become critically sharp. That’s not to say it’s not useful, or that it can’t take closeups (because it can), just that it’s not a substitute for a true “Macro” lens in terms of image quality or magnification.
The images on the right compare 100% crops from the center and edge for the Sigma 18-250 with those from a Tamron 90mm macro lens at the same magnification. The sigma lens was stopped down to f11 to give maximum sharpness, while the Tamron was shot at f6.3 (equal to the Sigma wide open). Of course this is a very unfair comparison. You would not expect a wide range close focusing zoom to come close to the image quality of a prime macro lens, but it gives you some idea of what the difference is.
Incidentally, the Sigma specification cite a 35cm working distance. I don’t really know what that refers to. “Working distance” is normally defined as the distance between the subject and the front element of the lens. That distance for the Sigma 18-250mm F3.5-6.3 DC Macro OS HSM is a little under 9cm at maximum magnification. Even the minimum focus distance (the distance from the subject to the sensor) is less than 35cm.
The Sigma 18-250/3.5-6.3 uses Sigma’s OS (Optical Stabilization) system which moves around a group of elements to compensate for lens movement and keep the image on the sensor as stable as possible. It’s effective and gives around 3 stops of additional stabilization both at 18mm and 250mm. With reasonably steady hands most users should have a 50/50 chance of sharp images at shutter speeds as slow as 1/4s at 18mm and 1/20s at 250mm. Of course image stabilization only improves the odds of a sharp image, it doesn’t guarantee it, so it’s always best to take 2 or 3 shots if you’re working close to the limits.
One point to note is that the OS elements tend to settle when the lens is powered down and then center themselves when the lens is powered up. This means that you may see the image “jump” in the viewfinder as the OS mechanism centers the OS optical group. Not a problem, just something that might take some users by surprise.
Like most telephoto zooms, the angle of view of the Sigma 18-250mm F3.5-6.3 DC Macro OS HSM at 250mm decreases as focus distance decreases. You can look at this as a reduction in effective focal length (and an increase in angle of view) with decreasing focus distance. At infinity I measured a focal length of around 240mm, which is within the usual 5% tolerance on focal length that seems to be the industry standard. At 4m it had dropped to around 190mm and at 2m it had dropped to around 150mm. What this means is that at closer distances you get slightly lower magnification than you might expect from a true 250mm lens. As I mentioned, this is typical behavior for a lens of this type. At very close (macro) distances there’s a drastic change in focal length, but that only affects the working distance. What the user is really interested in in that situation is what the magnification is and it’s 0.31x at the 250mm settings, whatever the true effective focal length of the lens is.
The Sigma 18-250mm f3.5-6.3 DC MACRO OS HSM for Canon, (compare prices) (review) would be a good fit someone who wants to travel with a minimum of equipment. The zoom range from 18-250mm (equivalent to 29-400mm on a full frame DSLR) covers just about all the range that most photographers will need (see images on right). In addition the close focus ability give reasonable macro capability with a magnification of 0.34x (about 1/3 life size). The lens is also small, light and reasonably priced and has an effective optical stabilization system which makes handholding the lens, even at full zoom, a reasonable proposition. If you’re traveling light, leaving the tripod at home is certainly a plus.
Of course there are trade-offs to be made between absolute image quality on the one hand and size, weight, cost, speed and zoom range on the other. The Sigma 18-250mm F3.5-6.3 DC Macro OS HSM is rather slow at the telephoto end of the range. From around 128mm through 250mm it’s only f6.3. Image quality is reasonable, though the corners are a little soft, especially at wider apertures. Distortion is rather noticeable at most focal lengths, though that can be digitally corrected (or at least minimized) via post-exposure processing. While the Sigma 18-250mm F3.5-6.3 DC Macro OS HSM might not be the first lens I’d chose if I wanted to make large display prints with corner to corner sharpness, it’s fine for small to medium sized prints, images for the web and digital photo albums.
So the Sigma 18-250mm F3.5-6.3 DC Macro OS HSM isn’t the fastest or sharpest lens in the world, but it never claims to be. It’s value lies in its small size, light weight and it’s ability to cover a wide number of situations (from wideangle to telephoto to macro) in a single lens.