[Giklab]

That is not a very good comparison, You are comparing a pro zoom to a (quite good) kit lens. The D7100 will produce much sharper images, also due to the lack of an AA filter.

[DavidSKAF3]

Equivalence makes it easy to compare two camera systems and determine which is going to give you the capability you need.

For instance, you'd have approximately the same image noise level with a Nikon D7100 + 17-55 f/2.8 (or whatever that Nikon lens is) and a Nikon D600 + 24-85 f/3.5-4.5.

It's not a perfect comparison of course as the larger format will generally give you better colors and in practice will always give you sharper images.

All Pentax DSLR's have the same sensor size so it's not really a big concern in the Pentax world.

What exactly are you trying to take pictures of... where is your current camera 'failing' right now?

Thanks for taking an interest and for your comment!


I just bought the very last brand new K-5 recently, and I am trying to pick a few used lenses to go with it. Hopefully I can give myself some choices that will make it more interesting to use. And I guess I am trying to familiarize myself with the Pentax line. And I guess I am trying to pick people's brains who already know stuff I don't!


Anyway, I saw a chart recently that seemed to say f/2.8 on the Panasonic FZ200 is really f/15.5, because of the sensor size or something, and that by comparison the f/5.6 on the Canon 18-135 lens is really much brighter than f/5.6, and that it's not really a 18-135 zoom but actually reaches much longer, because of its sensor size or mount whatever. And so I felt confused.


And I wanted to know what the lens numbers mean to my K-5, like if a 50mm reach is actually 75 or something on the K-5, or the F/2.8 is actually bigger or smaller. Confused? I know I am!


The link to the chart is in one of the posts above.


Thanks!

[ElJamoquio]

Anyway, I saw a chart recently that seemed to say f/2.8 on the Panasonic FZ200 is really f/15.5, because of the sensor size or something, and that by comparison the f/5.6 on the Canon 18-135 lens is really much brighter than f/5.6, and that it's not really a 18-135 zoom but actually reaches much longer, because of its sensor size or mount whatever. And so I felt confused.


And I wanted to know what the lens numbers mean to my K-5, like if a 50mm reach is actually 75 or something on the K-5, or the F/2.8 is actually bigger or smaller.

There's a few things to consider.

When you're trying to compare cameras with different sensor sizes, specifically...

1) Field of View (FOV - what's in the picture)
2) Signal to noise ratio (SNR - how noisy the picture is... and usually fidelity of colors scale with this as well)
3) Depth of field (DOF - how far in front and behind the focal point is actually 'in focus')

Those ^ things scale with equivalent f-stop, equivalent focal length, and equivalent ISO.



When you're trying to figure out the actual ISO, you can either convert from 'equivalent ISO' (in practice no one does this) or you can use the

A) actual f-stop
B) actual shutter speed
C) actual ISO.


You've already chosen a sensor (in your K-5) with a crop factor of about 1.53. So, let's say you wanted to take an 'average' picture - in 35mm/full-frame terms, that's generally defined as 50mm. Let's say you were used to a 50mm F/1.8 lens... thirty years ago this would've been a standard lens that most consumers would own.

If you wanted to replicate this lens on your camera, you would take

1) Equivalent focal length = 50mm/1.53... approximately 35mm
2) Equivalent aperture: = 1.8/1.53... approximately F/1.2.


A 18-135mm, on an 'average' DSLR (crop factor of 1.53) would have a much, much larger equivalent aperture than any point-and-shoot camera, where the crop factors are generally in the 4x to 7x variety, which is what your author was actually speaking to.

In practice, if you don't already have a baseline of what a '35mm' or P&S camera does with aperture/dof/noise, you're probably better off delaying learning about equivalence unless/until you think about switching to a camera with a different sized sensor.

[ElJamoquio]

That is not a very good comparison, You are comparing a pro zoom to a (quite good) kit lens. The D7100 will produce much sharper images, also due to the lack of an AA filter.

I should've compared the D7000 or the D800e, then, and it would still hold.

I haven't seen any scientific analysis of the increase in resolving power allowed in moderate lenses/20ish MP sensors by removing the AA filter.

The increase in resolving power from the D7000 to a D800 is ~1.5 with any level lens.

I don't think this is particularly relevant in this thread though, if you'd like me to comment further please start a new thread.

[stevebrot]

Lots of members here like the rubber hood because it has adjustable depth.

Some have adjustable depth, some don't. Mine doesn't. The main advantage is that it collapses down for easy stowage.


Steve

[stevebrot]

For instance, you'd have approximately the same image noise level with a Nikon D7100 + 17-55 f/2.8 (or whatever that Nikon lens is) and a Nikon D600 + 24-85 f/3.5-4.5.

Huh? What does noise have to do with focal length equivalence (crop factor)?

Or does this have something to do with the current trend of expressing everything from shake reduction to noise in terms of "stops"?


Steve

[ElJamoquio]

Huh? What does noise have to do with focal length equivalence (crop factor)?

Or does this have something to do with the current trend of expressing everything from shake reduction to noise in terms of "stops"?


Steve

http://4.bp.blogspot.com/-eAu2f_kDB1U/UXgs0gqlHeI/AAAAAAAAABw/HczXkU0KNaQ/s1...Hyperfocal.tif

Anyway, probably not relevant to the thread.