I am curious what lens you use for wildlife shots.
  I am looking for a telephoto lens for my XTI that will work for these type shots.

I intend to upgrade to a 40D in the future so what I get I want to use with that body as well.

Is the canon 100-400 really worth the price since I can get a canon 70-300 IS for half of the price of the 100-400. ?

 I now have the 18-55 MM IS and the 28-135 MM IS. :)

I have never used the 70-300, but have used the 100-400 and its a great lens, but it is expensive. It does have its limitations though, 1) you can not add a TC onto it and still Auto focus 2) its a slow lens so its not the best performer in low light and will require the ISO to be bumped up or tripod shooting for still life.

I will be picking up a 300mm f4L and the 1.4 TC for my wildlife shots in a couple weeks giving me 420@F5.6, just at slow as the 100-400 so during low light situations ISO will have to be bumped up. A friend let me borrow it and I was very impressed, again though it is L glass and L glass isnt cheap but IMO is worht every penny.

you can not add a TC onto it and still Auto focus

Canon 1 Series allow auto focus up to f8 :-)

its a slow lens so its not the best performer in low light

f5.6 at 400 end, need good light otherwise will be struggling...I sold mine!!

Nameless_Wildness what do you use for your bird and wildlife captures.   They are very nice. :)

iloco: I use two Canon bodies: 1DMkii / 5D and two Canon primes: EF500 / EF300.

Thanks you. That is some impressive equitment you are using and I can see where it pays off in your work. :)
 The old saying you get what you pay for still holds true today. :)

For the money the 100-400 lens is hard to beat

danob I keep going back and reading reviews on the 100-400
  I am not a professional and need something for taking wildlife pics.  I am holding off until I can find a camera shop that has one so I can have a look first hand at it. :)

As long as you have good light it should be fine really - the only time i have used the 100-400 was at dusk in the under the canopy in a cloud forest and i missed a great shot because it hunted, so my opinion on the lens is skewed as i had just swapped with another photographer my 70-200 F2.8 which wouldnt have hunted in the same situation. Although i might have had to crop the shot a bit to get what i wanted as i was at the 300-400 end of the other lens trying to get it to focus.

So if you want to go for the 70-300 IS then you should be able to get some decent shots - although a word of warning - the IS is only really useful with still subjects, it is all very well being able to use a slower shutterspeed on a lens in low light, but if the subject moves you have no way of stopping it blurring.  And what danny said is right - there isnt much to beat the 100-400 in terms of picture quality in zoom lenses - it is L glass after all...

www.fredmiranda.com - have you checked out the extensive range of user reviews on lenses there btw?

If budget wasnt a problem we would all have fast primes, but if you arent going professional with your photography it is rarely worth it imo.  And sometimes even going for high quality zooms is only really a self satisfaction clause in your purchasing habits... something which i am falling prey to these days, i have yet to purchase L-glass, but am nearing the threshold of "oh i really must have that lens quality" ;)

Rich said:  the IS is only really useful with still subjects

Really?
Why would one ONLY use IS on still subjects and not on moving ones ?
Please explain!

If budget wasnt a problem we would all have fast primes, but if you arent going professional with your photography it is rarely worth it imo.

So basicaly, you are saying only Pros use Primes but to non pros, not worth it...c'mon Rich!! Not really good advice here!
Sorry...but I cannot agree!

Actually i didnt say that one would "ONLY use IS on still subjects" - i said it is only really useful with still subjects.  You can use IS on a moving subject by all means, but i'm sure you know that a moving subject will blur a shot forced down in shutterspeed by IS... it's a false friend with low light and moving subjects.  IS isnt "oo i can shoot in low light now"... it is "oo i can shoot in low light (but probably get blurred shots if the subject is moving as the IS only minimises the effects of camera shake)."

As for telephoto L-Glass primes... i cannot really see any justification for spending £4k on a lens if you arent doing photography at a professional level, the costs completely outweigh the benefits - i'm sure you are aware of the concept of diminishing returns.  So yes this is good advice, I'm not picking you out here because you didnt say "go prime" but merely pointing out my beliefs as you seem to disagree with what i said and have recently participated in a thread on another forum similar to this.  I am tired of people doing the "go prime" when it comes to telephoto lenses because for the everyday consumer/hobbyist that advice is just wrong imo.  The right lens for the hobbyist is the lens they can comfortably afford which yields the best quality available at that price; spending a good part of a year's salary on one lens for a hobby is not really good economics, spending the same but in terms of revenue in a photography business is good economics and is an investment into the business...

I said it in another similar thread on this subject and i'll say it here... if quality is the only answer to a "recommend me a lens" thread, we might as well tell the guy to ditch the slr and tell him to get a hasselblad!

Didnt mean for this to get into a who is right or wrong thread.
   I dont agree that only professionals need a L telephoto lens.     If someone has the money and that is what makes them happy why shouldnt  they have it. 

 I have 2 motorcycles and don't need either because all they good for is enjoyment.  Thats how I see getting a good lens to use for a hobbly.  I dont need but would like to make some nice photos as others do with a nice L lens. :)

Same can be said about cameras.  Are dslr's for only for professionals and P&S for hobbiest.  All either can do is take a picture. :)

I'm not saying that you shouldnt get one (and i am refering specifically to the prime telephoto lens route) - if it is in your budget by all means do so, but dont think that your shots wont be good if you dont have the lens.  I'm looking at it from the perspective of offering advice, and from that side of the coin i dont think it is good to foment an attitude that only the best will do.  Besides, which would you rather?: have a zoom which gives you flexibility or the option of 1) buy loads of prime lenses, carry them around with you and change when necessary or 2) buy a good prime lens and miss out on shots you could have got with a zoom because you were too close to the subject (thinking of trips to the zoo or chance encounters in the wild) or because you couldnt reach the subject and your 300mm doesnt reach to 400mm like the zoom does...

Compromise is for hobbyists, uncompromising quality is the realm of the professional who needs the quality for large prints and to stand out amoung the competition...

QUOTE:
Is the canon 100-400 really worth the price since I can get a canon 70-300 IS for half of the price of the 100-400. ?

That was my question.  Not who should have one.    Is the 100-400 worth the extra price.?   Not about who should buy and own the lens. :)

Yes i know sorry the thread seemed to get sidetracked there on prime lens routes. 

That is for you to decide really - and the best way is to go into a shop with both lenses, take your camera and take some pictures, ask if you can step outside the shop for a bit for outdoor shots and then take the camera home, open up the shots with the different lenses and then decide if the double price is worth the extra quality.  The quality of the 100-400 is superior to the 70-300 there is no doubt about it - that is why one has the L tag on it and not the other, but whether you are willing to pay the extra is something you have to decide.  "Worth" is relative, and that is why i am of the opinion that telephoto primes are the realm of professionals...

what i will say is that from experience, you will want to get the best you can afford, if you can get the 100-400 then by all means do, because you will not be disappointed.

Did you check out the fredmiranda reviews btw?

http://www.fredmiranda.com/reviews/showproduct.php?product=294&sort=7&cat=27&page=2
http://www.fredmiranda.com/reviews/showproduct.php?product=19&sort=7&cat=27&page=1

and for a spanner in the works you might want to consider a "middle ground" with the 70-200 range... this is the non-IS 70-200 f/2.8 which you could get a 1.4x or 2x converter for if you wanted the extra reach - although the 100-400 might be the better option if you really wanted the 400mm end as teleconverters tend to degrade image quality when compared with the equivalent dedicated focal range lens:

http://www.fredmiranda.com/reviews/showproduct.php?product=13&sort=7&cat=27&page=2

That is the only advice i can give you really

Thanks for getting back on track.
  I am leaning toward the 100-400 since I am not a pro I can have really a couple lens in one compared to the having 2-3 primes with same focal lengths.

 A good example of buying what one enjoys is this.  About 10 yrs back I had to retire dure to heart problems and lot surgery.    I bought over 40,000.00 dollars worth of woodworking equitment and made a lot of wood things before I went on disibility and a fixed low income.    I never sold any of the items I made but gave over 90% of it away.  Clocks, Wooden Bowls and about anything that can be made in a wood shop.
  Now if I could find a buyer for all my equitment at half price I could really buy what I want in photo equitment.  I'd do it the same as I did with woodworking.   Enjoy life because its a one time trip here on this planet.
   lol..........

Yeah - that is a fair way of looking at it...

Personally i think you are sold already on the 100-400, but do consider that if it is wildlife you are after then 400mm is a lot and you will need about 1/640th or faster to get a sharp image/best out of the lens quality if handheld at the 400mm end... and that is a lot of light/high ISO - otherwise it is mopopod/tripod territory. That is the benefit of the IS - so you can take shots of stationary animals at a distance without resorting to monopods or high ISO...  Good weather photography sound like something you can handle?

Another consideration has nothing to do with the pricetag or optical quality - the 100-400 is fairly large and i dont think the 70-300 is, meaning if you have problems lugging kit around the lighter lens might be better for you anyway... as i said - go in and try out the lenses in the shop to see what you think.  I bought my 30D on the basis that the 350D was too small for my hands and i was getting RSI using a similar sized SLR at work, the extra quality was a bonus, and i havent regretted spending the extra cash to this day...

Little update on whats been happening with me and lens and equitment.
 I ordered a canon 100-400 telephoto lens and used it everyday for 2 weeks.  I had more bad pictures than good ones because of blurring.  The IS was not fast and to many pics were lost waiting for it to quit stablizing. Not sure if it was bad or not.  AF was not as good as manual focus. The lens was very soft at 400MM.   I tested the lens for front and back focus problems and it was dead center so that was not an issue.
 I sent the lens back to b&h for a refund and ordered the 400F/5.6 which will be here tomorrow.
B&H has got the best customer service and support I have ever dealt with on the internet and over the phone. :)

 I got a manafrotto tripod with a good ball head and a monopod with a swivel head.  I have been using both everyday depending on what I am doing.  I get a lot of shots out my back window of many different type of birds and when out walking around the monopd is very handy I have found.

Also ordered the 430 canon flash which I find will help with indoor photos.  Might use outdoors if subject not to far away. :)