Just in case anybody was in anyway offended by my posting above, it wasn't intended as anything other than a posting to prompt discussion about the way we answer questions like these. In this particular case, it was simple and therefore avoided links to sites full of complex maths etc. but for some of the other examples I gave above, it has done in the past.

Glad you're sorted Ali.

Good catch NikoDoby :D I have recently acquired the 70-200 2.8 VR II, in-conjunction with the 1.7 teleconverter, and want to make sure that the combination of the two would not hinter the amount of light coming into the camera, given that I own the D7000 (or for that matter anyone that own's a DX/cop factor camera body, ie. Canon).

Though, my intentions had nothing to do with the DOF discussion that followed, it provided itself for much thought provoking stimulation. I thank all those that left feed back...even those that deviated from the topic.

Well Golf007sd seems happy with the answers he got...

Perhaps the loss of light while using a teleconverter might have something to do with why he was asking?

interesting question though, I would like to know his reasoning behind the question.

I agree the it is a simple answer, however, to agree with Niko, the reason for the question probally makes the answer more complicated, because, the 2.8 will allow the same shutter speed [fx/dx] given that the iso remains the same, however if the reason for asking the question has to do with DOF, then, as stated by sprayandpray thats a horse of a different colour.

nice thread, makes you think.

"-perspective doesn't change with focal length. Duh!"
"but yes- the perspective does change with focal length."

And you accuse others of causing confusion?!?! Not sure what you are carrying on about but the OP's question was directly answered. So what's the problem?

Oh and if you are going to "complain" and quote a thread then you should post in the thread you are actually "complaining" and quoting from. There's less confusion that way.

I listened to a podcast over the weekend in which the question was asked "does perspective change with focal length?" The answer given was very long winded and concluded no it doesn’t. The reasoning given was if you took a picture of something with a 300mm and a 35mm then cropped the picture taken with the 35mm until it showed the same field of view as the 300mm, the perspective would be the same, so no – perspective doesn’t change with focal length. Duh!

That podcast put me in mind of the linked to thread about depth of field and focal length comparisons between FX and DX and made me wonder why people can’t answer questions simply. Written in the thread linked to are such gems as “50mm is 50mm whether used on DX or FX” and “the focal length doesn’t change it is the crop factor of the sensor that changes” also “ the magnification doesn’t change between DX and FX, it is the angle of view” – all being true but not helping the OP. IMHO I think we ought to think about the question AND who is asking it before we go down a path which causes confusion for the OP and not clarification.

Let’s start with the perspective point: Who the heck thinks like that? It’s retarded! Obviously people mean when the subject is similarly framed with say, a 35mm and 300mm lens does the perspective change? Answer? Of course it does. You have to change your shooting position to get the same image size on the sensor (picture), but yes – the perspective does change with focal length.

Now DoF and DX/FX: Does the DoF Change between DX and FX? Yes. Let’s not start by trying to make ourselves look clever by making the explanation as technical as possible, in most cases the OP doesn’t need or want that. Suffice it to say that for a given image size on the sensor (picture), FX has a shallower DoF than DX.

Finally focal length: Does a given focal length on a DX magnify an image more than it would on a FX? Yes it does. Often OP’s just want that and find trying to get to the bottom of technically accurate and complete explanations of the reasons behind the answer given just OTT.

We all should at least start off with the simple answer. Most people who want to know more will either ask the question an a way that makes it obvious that they want/need to know more, or come back after the simple answer and ask why. Much is made of ‘it’s the artist and not the gear’, so why not keep it simple as a lot of artistic types I know are not interested in getting too deep into technicalities?

To this OP's question does the f-stop change between DX & FX, that actually is simple – no it doesn’t.

Thank you for the clarification.

Cheers to all,

Ali

There are several threads explaining FX vs DX. Here is one discussion about depth of field in FX and DX lenses. Make sure you have some aspirin and an abacus handy as you read through it! ;^)

http://nikonrumors.com/forum/topic.php?id=2165

But to answer your specific question, no the aperture does not change between FX and DX.

ggweci said:
The amount of light entering remains the same, but the effective DOF would be increased by 1.5 vs FF.

No, the DoF of a lens does not increase either.

What does change is the lens length one would use for any given framing. Shorter lenses have deeper DoF.

A crop sensor is no different than cutting the edges off a photo. No magic zoom, no magic increase in DoF. What changes is the lenses people use. The lens does not care if you use all of it or half of it.

No, the aperture does not change. In fact the focal length also does not change, but due to the smaller sensor the viewing angle is different. The "change" in focal length is used to give people that are used to the viewing angle of 35 mm film an idea about the viewing angle of that lens on a smaller sensor.

If you use a 200 mm lens on a 1.5 crop factor sensor you get the same field of view as with a full frame (or 35 mm film) sensor using a 300 mm lens. But the 200 mm lens will be a 200 mm lens, no matter what camera you attach it to...

The amount of light entering remains the same, but the effective DOF would be increased by 1.5 vs FF.

Good day ladies and gents, I have a question that I hope some of you may clarify for me, I wanted to know if I buy a 24-70mm 2.8 (or any 2.8 hence 70-200, 14-24mm) and use it on my D7000, does the aperture also change (like the focal length), throughout the range due to the 1.5 crop sensor or not?

Thanks for feedback,

Ali