Most kit lenses on entry level cameras aren't fixed aperture though - I am guessing this app targets entry level users.
In any case, the need to have fixed fast aperture lenses is diminishing with IS and high ISO performance. I'd rather carry a fixed F4 than a fixed F2.8 zoom with a 2012 camera. It's going to be a much smaller lens and just as effective for most use cases.
While I agree with the point on quality, constant aperture zoom lenses tend to be MUCH more expensive than variable aperture lenses. Your single lens costs more than twice her entire starting kit :) They also tend to have fairly specialist zoom ranges. I find it hard to imagine somebody with a constant aperture zoom lens would find benefit in this camera simulation. The majority of the kind of people using it will be beginners with kit variable aperture lenses.
The most common advice for them would be to get a prime lens. Especially in this simulation that offers both distance and focal length setting (which are, for this scene and 18-55mm focal length, mostly interchangeable), I'd like to have it. It'd also allow you to go (cheaply) to f/1.8 or f/1.4, which would be much better to illustrate the effect that aperture has on the depth of field. With a common f/3.5:5.6 kit lens and APS-C sensor, you won't get a shallow DOF and nice out-of-focus background easily, and that could be frustrating to a beginner. Especially when you learn to do it in this simulation.
The faster aperture tends to necessitate better glass, but the idea that only fast lenses have good glass would not necessarily be true. There are plenty of "slow" lenses that have very good optical quality.
Are you sure? When a lens claims to be f/2.8 at all zoom levels, it usually means that that the maximum aperture (i.e., minimum f-number) is f/2.8. It can do f/11 etc also.
If it is indeed a lens with just a single aperture setting, can you tell me the model number? I'm quite curious now. Thx.
He means that his 24-70 zoom lens has the maximum aperture of f/2.8 at all focal lengths from 24 to 70. Cheaper lens would get to, say, f/3.5 at 24, but at 70, you wouldn't get more than f/5.6, for example. So you can't set it to 70mm and f/3.5, even though you can set it to 24 and f/3.5, because it can't physically do that. Of course you can set it to f/13 or even more, that's easy to do with an ordinary lens. There are some funnier lenses (mirror lenses, for example) that have fixed apertures. It's f/8 and you can't do anything about it, because there is no mechanism that would allow you to cover more or less of space before the sensor (film).
