Help, am I being stupid

I have a 400D with a Sigma 18-200mm F3.5-F6.3 zoom lens on it and I am considering going for the Canon 70-200L F4 IS lens. My question is do you think I'm being mad going for this considering I'm on a crop camera?
The reason I'm interested is that I've tested the 70-200L F4 IS lens at the weekend and can see noticable IQ increase ... and I have found a few times that during duller days I've been struggling to get 1/200th second or faster with my Sigma lens as it's a "slow" lens.
Therefore I'm thinking the 70-200L F4 IS will be good as it's a faster lens, has great IS and also the IQ is better. However ... I'm not sure that I'll be able to afford the 24-70L lens for quite some time.
Do you think I'm being mad? Or is this still a good move.
p.s. not sure I'll ever go to a full frame camera to be honest.

Many thanks

Golfboy

UPDATE: In relation to some questions in the responses, I will be keeping my Sigma 18-200 and 50mm f1.8 and Tamron 10-24mm to cover the rest of the range below 70mm ... and hopefully eventually get a nicer quality lens to replace the 18-70 range of the Sigma.

Nope, nothing mad in that decision, you'll love the gain in IQ that you get over the sigma lens.

If you can't afford the Canon 24-70L there are other options you can consider - look at offerings from Tamron & Sigma in the 17-50 range or Canon's EF-s range within those sort of focal lengths.

Is the Sigma your only lens? The 70-200 f/4L IS is a great lens, if you shoot tele pretty regularly. Pairing it with the cheap but good IS kit lens would cover your bases for a lot of situations.

No, you're not being stupid. You are doing just the opposite: making a very intelligent move. The Sigma 18-200, any "super-zoom" is not going to give you quality IQ. It can't. It sacrifices IQ for convenience.

With the 70-200 F/4 you will see a dramatic increase in IQ. What difference does it make if it is on a cropper or not? IQ is IQ.

Down the road consider the Tamron 28-75 as an alternative to the 24-70L. It has very comparable IQ to the Canon at about 1/3 the cost.

thanks for the alternative lens suggestions everyone, that's certainly food for thought. My reason for thinking I'm being mad is a few friends have said I'd be buying quite a limited lens if I'm sticking it on the front of a 400D .(effective 112mm to 320mm) .. i.e. they're saying it's full-frame camera lens really.

WhyFi, regarding your question, no, I also have the Tamron 10-24mm and the Canon 50mm f1.8 II.

Many thanks

Nope, it is not a limited lens in the slightest. I have used my Canon 70-200 2.8 L IS for a few years on my cropped cameras and it is superb. I would ignore your friends on this matter!

"they're saying it's full-frame camera lens really"

Your friends are totally wrong when they state that the 70-200mm f/4L IS lens is a, "full-frame camera lens really"

I use my 70-200mm f/4L IS lens with my 1.6x cameras much of the time with totally great results..

However, I know where your friends are coming from... The 70-200mm focal length has some wonderful capabilities but, really needs to be matched with a mid-range zoom of some type.

I shoot my 70-200mm f/4L IS along with my 17-55mm f/2.8 IS lens on a pair of older 1.6x cameras. This is a heavier and slightly more expensive solution to the slower aperture, slower auto-focus and lower image quality of an extended range zoom like you are presently using. However, I am quite content with using a pair of older 1.6x bodies (30D and 40D) which allows me to afford the better glass.

I traveled to China for two weeks carrying my two cameras and two lenses and I shot next to an equally accomplished photographer who was using a Nikon with an extended range zoom. There were times (like climbing the Great Wall) that I envied his lighter outfit but, I was able to shoot in lower light levels and my system was a lot more versatile that my that of my fellow photographer.

On the down side... I could not have accomplished my China coverage ( see my China galleries at: http://rpcrowe.smugmug​.com/ ) shooting solely with the 70-200mm lens. I shot about 1/3 of my images with that lens and the remaining 2/3 with the 17-55mm f/2.8 IS lens.

As an alternate to my quite expensive system, I might suggest the 17-50mm f/2.8 Tamron along with the Canon 70-300mm f/4-5.6 IS lens. This system would be about 1/2 the cost of my two lenses and would gie you great versatility and very good to excellent IQ.

70-200 works great on a crop as a telephoto. Pair it with something like a Sigma 17-70 and you've got just 2 lenses that cover 98% of the average photographer's needs.

Golfboy1971 wrote in post #11245849
I have a 400D with a Sigma 18-200mm F3.5-F6.3 zoom lens on it and I am considering going for the Canon 70-200L F4 IS lens. My question is do you think I'm being mad going for this considering I'm on a crop camera?
The reason I'm interested is that I've tested the 70-200L F4 IS lens at the weekend and can see noticable IQ increase ... and I have found a few times that during duller days I've been struggling to get 1/200th second or faster with my Sigma lens as it's a "slow" lens.
Therefore I'm thinking the 70-200L F4 IS will be good as it's a faster lens, has great IS and also the IQ is better. However ... I'm not sure that I'll be able to afford the 24-70L lens for quite some time.
Do you think I'm being mad? Or is this still a good move.
p.s. not sure I'll ever go to a full frame camera to be honest.

Many thanks

Golfboy

The 70-200 is quite long on a crop. That said there's plenty of users who shoot at 70-200 as their primary focal length. I would look at what you shoot at and go from there. For me personally, I could never shoot with only a 70-200... it's just too long. But others seems to enjoy it, it's really just a matter of personal choice.

Golfboy1971 wrote in post #11245849
I am considering going for the Canon 70-200L F4 IS lens. My question is do you think I'm being mad going for this considering I'm on a crop camera?

Why would you be mad? Plenty of folks (like me!) use this lens on crop bodies? Why do you think it would be a problem?

I love the 70-200mm focal length on crop, just make sure you have a wide-standard zoom to cover that focal length range. Even the 18-55mm IS will likely be better than the Sigma "all-in-one."

Just beware that not many would find the focal length 70-200 usable. The focal length is great for sports and fast action shots. Nature photography. Distance portraits (mostly outside or larger indoor area). You will lose the wider end over the Sigma.

Are we talking about the 70-200 as being your ONLY lens? Yes, that is quite limiting ("stupid" is too subjective )
Now if you also have a Canon 18-55 IS to use as well, than go ahead and get the L!

I was a little unclear from the original post.

Sounds fine to me...

Thanks everyone so much for your advice ... It's certainly helped me and thanks to all for the advice on other lenses. I think I may go and click the "checkout" button on the basket

Thanks
Golfboy