Weird stuff they don’t tell you at the camera shop.
Plastic lens mounts exist only on the cheapest Sony/Nikon/Canon lenses. These lenses are generally of low quality and may also use plastic or composite elements rather than ground glass. This is a lens where compromises have been made to lower the price. You don’t want a lens sporting such a mount unless you’re never planning to get serious about photography.
Pentax do not make any lenses with plastic lens mounts, and are in fact the only brand whose kit level lenses have good sharpness and performance.
Cross point AF sensors
Canon cross point AF sensors work as cross point only to f2.8. Horizontal points are sensitive to f5.6. Some models have a double cross points in the center offset by 45 degrees.
Nikon/Pentax/Sony cross point AF sensors work as cross point to f5.6. Horizontal points are sensitive to f8.
Above f8, no autofocus works. Note this is the max aperture, not the aperture set in the camera. Most general use lenses are f4.5 or faster. But remember, an f2.8 lens + a 2x teleconverter becomes an f5.6 lens!
This seems to put Canon at a disadvantage, since you only get cross points on f2.8 or faster lenses and you can’t use an extender. The reason for their choice is that f2.8 cross points can be more accurate than f5.6 cross points. However they are less sensitive in low light situations.
You can expect this to mean that even consumer level gear will grab focus more readily on a Nikon/Pentax/Sony even in the dark.
Nikon uses full-color three-dimensional 1,005 pixel light meter AF system. Distance info from the lens as well as the color of the object will help the AF system obtain and track focus. If you use auto AF point selection, facial recognition is used to choose focus.
Canon used to use a black and white AF system, which does a tremendous job given that it only sees in shades of grey. With the 7D, Canon has switched to a 2 color system which has improved low light performance. However auto AF point selection still merely tracks the closest object.
This is why Nikon has always had much better low light AF performance than other brands in the market. Note that beginner DSLR models of all brands have cut down versions of the AF systems with slower and less accurate response no matter how much you spent on the lens.
Full frame vs crop
Some people insist the 35mm sensor format is the end-all of all photography, and all serious DSLR users should assume that they will one day buy a full frame DSLR.
Ignoring the fact that other formats such as medium format and large formal DSLRs exist, there is also the issue of AF. I consider AF the most important part of a camera, because without the ability to quickly focus on a subject in any situation, you will have no photo to speak of at all.
While crop DSLRs have AF points covering the whole sensor area, full frame DSLRs only have points covering the center portion of the frame. Although there are no Canon crop DSLRs with as many AF points as their full frame counterpart, the top end Nikon crop DSLRs use obstensibly the same AF matrix as their full frame counterpart.
This means on a crop, you will be able to track a running soccer player right to the edge of the frame. Or for portrait shots, you can have your model’s head closer to the edge of the frame and track their eyes using an edge AF point without needing to recompose.
Nikon uses the F mount, introduced in 1959. Every modern body can use the oldest lenses. If a DX lens is mounted on an FX body, the sensor and viewfinder will automatically be masked to APS-C. This can be overridden, since many DX lenses are quite usable on an FX sensor with minimal falloff.
Pentax uses the K mount, introduced in 1975. Every modern body can use the oldest lenses. Pentax currently has no 35mm DSLR. There are adapters to use K mount lenses on Pentax’s 645 medium format body.
Canon EOS bodies use the EF mount, introduced in 1987. It is incompatible with old lenses. It removes the AF screw from the body, which is why Canon DSLRs are slightly lighter than other brands. In 2003 Canon introduced the EF-S mount for 1.6x crop DSLRs. EF-S lenses are not compatible with EF mount bodies due to an extra mechanical tab, which has led to a situation where crop users will overbuy full frame lenses to futureproof their investment. One would assume that 1.6x crop lenses would otherwise work quite well on at least 1.3x crop bodies.
There is a belief amongst some groups that film lenses are of ultimate quality and a lost art never to be found again in the present day. While there are certain film lenses that are better than certain digital lenses, there are also plenty of digital lenses that are superior to certain film lenses.
For one thing film lenses do not have anti-reflective coatings on the rear element. Film didn’t reflect light back onto the rear of the lens, but digital sensors do and this may cause ghosting issues.
Also, if there was such a magic film lens of ultimate quality, surely a for-profit company would rebadge and sell the lens with a few new coatings rather than spend money to design a new-but-inferior lens? I would argue that all the great classics have been and continue to be improved in new designs.
Canon 3 digit models (eg 550D) have built in circuitry to reject teleconverters. The camera will refuse to use the lens. However there is no technical reason it should not work. You can mod the TC to make it all work, so it seems it’s just Canon’s way to say you should upgrade your body.
Currently Canon EF-S lenses appear to be the only class of lenses that do not come with lens hoods (and pouches for that matter) out of the box. This is presumably to lower costs for crop users who are seen to be more sensitive to price than image quality.
Official lens hoods can be purchased from $50 up, 3rd party for $5, and paper ones can be made for free, but most people end up going without to the detriment to their images. Official lens hoods have a velvet inner lining which is more costly to produce than the 3rd party ones which don’t.
All other brands of lenses come with lens hoods, including Nikon, Pentax, Sigma, Sony, Tamron, and Tokina. Some really really old lenses do not have a lens hood mount.
Pentax DSLRs and higher level Nikon DSLRs have connections at their base for battery grips. This consists of a rubber seal over some contacts. The seal fits in a groove in the battery grip, and the grip screws into the tripod thread at the bottom.
Canon and Sony DSLRs, and lower level Nikon DSLRs have connections inside the battery slot. This means grips require you to first remove the battery cover completely, then insert the grip into place.
Apart from the obvious annoyance having to remove the battery cover, which you don’t want to accidentally snap, this also means you cannot attach or take off the grip in the middle of shooting, as the battery must be removed from the camera.
Note that absolute beginner models of DSLRs do not have official battery grips for sale at all, but usually you can still find some 3rd party solution.
Macro lens maximum aperture
Macro lenses generally come with a maximum aperture setting of f2.8. With macro shoots and close focusing distances, the effective (real) aperture changes as the internal glass elements move around. This means your maximum aperture while focused on a certain object may be f4 at 1:2 magnification and f5.6 at 1:1 magnification.
Nikon DSLRs will automatically compute and display the real aperture in the LCD as you focus to different distances. Canon will display the set aperture and not the true aperture.
Since the aperture affects the exposure of an image, this means the exposure of some macro shots will be slightly off, or inconsistent in a set depending on focusing distance.
If you always shoot your macro at f8 or above you may not notice this issue.