After reading very many lens reviews on the net and getting thoroughly confused, I decided to post a synopsis of my newfound knowledge for easy access by other newbies like me ..............
A) Lens EF AA-BB L is much better than EF AA-BB no-L
Proof : If you tell someone that you shot a Pic with an L glass, they will all agree with how "Sharp and Contrasty" it is.
However if you show someone a "Sharp and Contrasty" pic, none can say with certainty it was shot with an L glass or not.
B) Canon lens are better than non-Cannon lens, except for a certain Sigma Lens, some Tamrons and maybe some others
C) Lens XX-YY is sharper than AA-BB and also sharper than DD-EE, except that at wide open DD-EE is actually better than XX-YY wide open, also at the Tele end, AA-BB is actually sharper than XX-YY
D) Lens FF-GG was actually the best but is not in production any more
E) The AA-BB is very "sharp and contrasty" but it has some CA when wide open. The other alternative you were thinking about is "less sharp and contrasty" but has less CA. Now you figure it out how to mentally balance and make a logical purchase decision based on above data on sharpness versus CA.
F) Normally Lens AA-BB is sharper than Lens CC-DD, but as you know, Lens being handmade in small Japanese villages, their is a wide range of performance between Lens with the same specifications. I personally have a CC-DD that is actually better than an AA-BB. It also focuses on infinity unlike other regular production CC-DDs
G) It follows automatically from rule F) above that it is useless to believe a Lens review site that lists opinions by one reviewer alone. He might have a "very good example" of a particular lens and that slants his report.
It is better to trust sites where they average the review ratings of many users, except that it is very hard to trust these unqualified unidentified users.
H) An extender is a bad idea. OK, An extender attached to an AA-ZZ makes it equivalent to a higher zoom but smaller apertured AAA-ZZZ. However if you really wanted ZZZ all along, you could have just bought the CCC-ZZZ right away.
Except that the quality of the CCC-ZZZ is worse than the AA-ZZ + Entender Combo. So we dont really know if the extender reduces the quality as per starting premise.
I) Lens with large zoom ratios are a bad idea unless you get US$ or EURO notes with the same denominations
35-350 : Bad idea as there are no 35$ or 350$ bills
50-500 : Excellent idea !!
J) If you do not believe the rules above and can actually prove otherwise with actual photos, it will later on be found that this was due to the back-focus of your 10D.
K) At F/16, all lens are equally "sharp and contrasty"
L) If you think your image was not "sharp and contrasty", you did not USM it enough.
M) Prime Lens are the best as a "walk around lens". However nowadays, nobody likes to walk around anymore. This lead to the creation of the Zoom lens. It main aim is that you can take a photo of any animal in the zoo right from your car parked in the parking Lot.
N) After you have read all the Lens reviews, the only real choice left is --
Should I buy the 70-200 L IS right away
or buy some other glass first and land up buying the 70-200 L IS later on anyway.
O) The best way to afford a more expensive Lens is to buy a cheaper camera body.
P) The L Lens are much better built than other lens. They are designed to last for over 20 years !!
However you can only afford them when you are not so sure you will last for another 20 years.
Q) At very cold places like the North Pole, It is possible to take hand held pictures with exposure up to 5 seconds. There are even reports on this very forum of 1 second Hand held shots right down to the Panhandle and Finland. This is because the extreme cold helps to freeze the shot.
R) If the lens works for you, It is the best lens for you
S) If it is all you can afford, It is the best lens for you
T) Discussing Lens too much distracts you from the main challenge of photography - the Artistry.
U) That which can be measured is not the true measure of a photograph