sulhan said:
Fast short travel focus lens may have tendency for Front/Back focus problems.
Very true, especially for screw driven lenses.
Long travel (high resolution) AF though may thought to be slower (just because they travel longer to get from close focus to infinity), may have less Back Focus/Front Focus problems as slight error movement in the AF will not change focal plane that quickly.
Take for example a macro lens which feel like slow focus.....but due to the large focus distance movement of the focusing (high resolution) that is suitable for pin pointing focus plane in Macro focusing - if a fast short travel is used, then slight shift in AF will cause image to be defocussed easily.
Again very true especially for screw driven lenses.
Thats why in some lens like Macro and Telephotos like the 300mm/400mm/600mm...they are equiped with focus limiters...to avoid AF to rack the whole
distance if you know the subject is at a predetermined distance....
True for all lenses.
It is also true that some AFS/USM lenses are not necessarily faster than screwdriven lenses, but they are the minority rather than the norm.
A screwdriven lens's performance is hugely dependent on the body's inbuilt motor torque and precision. A AFS/SSM/USM/HSM lens has a more consistent performance across bodies.
In general AFS/USM/SSM/HSM] motors are built within the lens and optimized for the lens. They avoid having a transmission train from camera body to the lens and there is no slack/movement/play compared to the normal screwdriven configuration. Given the SAME LENS design, AFS/USM/SSM/HSM lenses are capable of finer focusing adjustments and have faster acceleration/decceleration times for more precise focusing. This is manifested by an almost instantaneous start->stop->settle time compared to screwdriven lense which may have more overshoot/undershoot and experience more microhunting around the focus area.
Not to say that a screw driven lens would suck at focusing, no. I've been shooting alot with screw-driven lenses on my old Minolta 8000i and entry level D70 and getting good results everytime. However, when you try a AFS/USM/SSM/HSM lens of the same class, you will find that your hit ratios increase and minor AF errors are reduced.
When you have experienced using AFS/USM/SSM/HSM lenses for a while, you do wish that all lenses be constructed the same way.
Let's face it, Minolta would not have introduced SSM in their 70-200/300 (and even the unreleased 28-70G)lenses if they did not feel the need.
As for choice of camera. It all depends on a user's needs. If one is a hobbyist and you are unsure how deeply you'll be involved in the hobby, grab a Dynax 5D. It is simply the best bargain and performer at its price point at the moment. Minolta is a brand very suitable for hobbyists and light users because of the relatively cheaper bodies which are always packed with more features than the competition. This has been true for many years.
However, Minolta support in singapore is horribly lacking (I know it, because I've been to all their service centres from Teban gardens to Funan to Haw Par Technocentre.) frontline staff there are BAD in product knowledge compared to Sigma and Nikon service centres and if you require accessories and pro-level equipment you'll have a hard time searching for it even online. Most serious users would already know that by now. However, for hobbyists, this is not an issue and one can always change systems WHEN it becomes an issue.
My advice to a beginner is to never pre-empt or overestimate your needs. Just take what is best for you at your level. Switching equipment isn't so much of a pain that is made out to be, especially if one doesn't even own much in the first place. So if anyone new were to ask me what to buy for his first DSLR, my reply will still be Minolta as the reasons not to choose it are not yet applicable for beginners.
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