How Come My Camera Keeps Doing This?

Yep, it's a conspiracy.

Fast, long and cheap lenses really exist. NASA shot the whole moon landing in a studio at Grumman. Global warming is a myth.

JeffreyG wrote in post #4292416
It's not just cost, it's size. Johnny's lens would need to be a lot bigger to be f/2.8 at the long end.

The aperture of a lens is expressed as a ratio of the lens pupil to the focal length. So long lenses that are fast also need to be big.

So Johnny.....are those white telescopes you used to rant about starting to make more sense now?

Yep...didn't think about that aspect of it....if you're looking for a smaller and lighter lens...a variable aperture lens would be the way to go.

JohnnyGalaga wrote in post #4292367
But why would tnhey make it like that? Wouldn't it be a lot better if you could just keep it at 2.8 no matter what?

You can get constant f/2.8. There are quite a few of them. But as was pointed out in several posts, to make a lens like this costs $$$. For those who don't want or cant afford that type of lens, Canon offers other lenses which are less expensive.

It sounds to me like Canon is trying to cover all bases instead of only catering to the wealthy.

If you are refering to your point and shoot in your sig, It would cost ALOT more to make it f2.8 the whole zoom range. Not only that it would be HUGE too.

Johnny,

There's a lot that goes into lens design, and a lot of factors in lens cost. There are a lot of variable aperture lenses out there, especially at the consumer level. Every lens manufacturer makes them, and it's not because they're stupid.

It's because they're smart enough to realize that some people are willing to save some money and some weight by sacrificing the constant aperture.

Even some expensive and very high quality lenses, like the EF 100-400, are not constant aperture.

yeah exactly the 100-400 is ~1200 bucks just for the lens but I knew before I bought it that it was F4-5.6 it it was a constant F2.8 it would be easily 3x the costs and about the size of a rocket launcher

didn't you read up on all of this before you bought it? sorry but I don't see how this is canons fault here its a simple design and quite common

well yes and no if it did cleary state at certian focal lenght that would be at the widest point.

true if it did stay at the widest apature in full focal zoom. would it not creat a shallow depth of feild when zoomed in.

Then again it all depends on the type of photography you want to achive.

Of course it would make the picture slightly darker but then you can compseate it by decreasing the shutter speed time or increase the ISO.

Just a thought to help out to make it easire.

You wish. Do you know what a Nikon 200-400 f/4 costs? And you want 100mm more on the short end and another stop for a mere $4200? I don't think so.

Welcome to the world of DSLRs Johnny! When you dive into this hobby, you got to be prepared of how much you are going to love it(maybe). I love it bcoz I know what these expensive lenses can do in the right hands. That doesn't mean you have to shell out the big bucks for quality glass but, you can do so with these variable lenses. Yes, some of us are crazy for spending lots of money on these lenses but, I don't regret spending it if you LOVE this hobby. Know what I mean?

Well now I see what kind of camera you have I guess there is a limation to what can be done if you do have manual seeting maybe you can experment with it.

other than that I don't think there much more we can do to recify the problem.

JohnnyGalaga wrote in post #4292553
But that makes the picture blurrier and with more grainy sand in it, so there's no way to win.

Photography is all about compromise. I used my 18-55 (variable aperture) kit lens for a year and a half before I could afford to upgrade. In the mean time, the limitations of that lens helped me learn to think like a photographer. I even used it on some paid gigs and made some money with it.

Those who shoot wildlife and sports with really long lenses learn to live with smaller apertures (a 600mm f/2.8 would be so heavy you'd need a forklift to haul it around). And shutter speed is even more critical with long focal lengths.

Every shot is a compromise. The challenge is to find the best compromise.

I just traded my 28-135mm f/3.5-5.6 for the Sigma 24-70 f/2.8 (thanks snsgraphics). I found out this past week that I am going to miss the extra reach, but will love the fixed f/2.8. I wouldn't put the Sigma 24-70 up against the Canon 24-70L in a head to head competition. This comes down to build quality and glass quality. Sigma offers a lower priced, quality lens.

Can you please tell us exactly what kind of camera you are using.
Then we can help you recify the problem.
If You are using a Point & Shoot they are not inter changable lens.

JohnnyGalaga wrote in post #4292423
Now I see what they're doing. They intentionally design the camera to increase the "F" number like that on you to try to get you spend more money for simply keeping the "F" number the same.

Why do you want to shoot at just 2.8? If it "gets darker" thats because the lens is stopping down - so you'll need a slower shutter speed. There's nothing wrong with your lens. Many of the world's greatest photos have been taken with variable fstops. Maybe a good idea to take a basic photography class.

There are certain logical expectations of gear at defined quality/price levels. Your expectations just happen to be out of phase with your budget.