Rab-Eye Loc: Indiana

I had never heard of this before. If accurate, it means my FX 70-300 f/4.5-5.6 zoom is an f/8.4 at 300mm. This led me to investigate the Nikon DX 70-300, which I have now rejected for several reasons, including but not exclusively because of its plastic mounting ring.

I assume that not only focal length but aperture as well must be multiplied by the crop factor is accurate because Nikon itself is the source of the information. Still, it's odd to me that it is virtually never mentioned; in my own experience it has never been referenced except by this Nikon video. Have I been living under a rock, or is this news to you as well?

chase4 Loc: Punta Corona, California

Take a look at this video, however this guy is somewhat controversial:

http://www.youtube.com/watch?v=YDbUIfB5YUc

chase

delkeener Loc: SW Rhode Island, USA

I have not heard of the crop factor affecting the f stop. Do you have a reference for the Nikon video you mentioned?

MichaelH Loc: NorCal via Lansing, MI

Can you post a link to the video? I am sure others will chime in but doing a quick search yielded a Tony Northrup vid on Petapixel ( https://petapixel.com/2014/03/28/concise-explanation-crop-factor-affects-focal-length-aperture/ ). He is making the case that you loose that sweet bokeh when you go to a smaller sensor. Hence the fake bokeh on the new iPhone. But I think the concept of aperture would have to be redefined for him to have his way on this subject.
I am now going to wait for smarter members to weigh in.

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

An FX 70-300 used at F5.6 at 300mm will not let in less light than a DX version of the same zoom. That is pure nonsense put out by Tony Northrup who has a tenuous relationship with the facts on this.

Where it makes sense to adjust aperture to compensate for crop factor, to a point, is when considering depth of field for the "same" composition. Clearly for the same composition with a 300mm on a full frame camera, you'd have to move back with a crop sensor camera and the same 300mm lens, increasing your depth of field. To get the same depth of field with the 300mm on the full frame camera you'd have to close the lens down a bit. But this has absolutely nothing to do with whether the lens is a DX or FX lens. I suggest you to to a store, put a DX 70-300 on your DX camera, then put an FX 70-300. You'll see that they will pretty much provide the same thing, provided the light transmission (T-Stop) is comparable.

Another validation is to look at any light meter. Does it have a scale or compensation for when you use an FX lens on a DX camera?

Follow your gut and question everything that just doesn't sound right.

In the meantime, can you point me to the page where Nikon says aperture must be multiplied by crop factor?

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

Read this:

http://www.uglyhedgehog.com/t-377405-4.html

I went toe to toe with Mr. Northrup, and basically debunked most of that video, using his own source DXO Labs. He seems quite confused by all of this, and has caused many to be similarly confused. He may be good for other matters, but he gets a zero on this topic.

a6k Loc: Detroit & Sanibel

I never heard of it either.

Focal length is a physical characteristic which is independent of crop factor.
Aperture expressed as an F stop is the ratio of the diameter of the aperture to the focal length.

For example, my bridge camera has a 220 mm max zoom and at that focal length, it's an F 4.0. I am taking Sony's word for this. My other long lens, also Sony, is a "full frame" lens 70 to 200 mm which I have used on both my a6000 (crop factor 1.5) and a rented a7R2 (crop factor 1.0 or "full frame"). The aperture must then be 1/4 of 220 mm or of 200 mm respectively. I have used legacy manual lenses (Nikon) on my Sony a6000 which also work as expected. I also used a 150-600 Tamron (for Nikon) in manual mode on both.

As for "equivalent" focal length, it's a misnomer. It's a popular way of describing a restricted angle of view. For example, my Wife's Nikon P900 has a 357 mm lens, F 6.3 but an equivalent focal length of 2000 mm. The reality is that the center 6.17 mm is filling the sensor. The sensor crop factor is 6.17 / 36. The lens is still a 357 with the same size aperture. Since you are a regular here you likely know all this already.

So if we pretend the focal length of my 200 mm lens on my a6000 is really 300 then the 50 mm aperture is now a 6.0. BUT that does not work when computing exposure and there is a good reason why. Simply put, the same lens is making the same image regardless of the size of the sensor. If the sensor is smaller, we are simply discarding the margins, so to speak. That means that the exposure for a sunny day at 1/100 sec should be F 16 (using the rule as an example) regardless of the crop factor. Any attempt to interpret all this as a different F stop is going to be wrong for purposes of exposure control.

Respectfully, I don't know what you are seeing, but either they are wrong or you are mis-interpreting what you saw. I suspect you are accurately reporting what you saw and I'm amazed that anyone, let alone Nikon, would get this wrong.

Or I'm wrong. Nah, never, right?

chase4 Loc: Punta Corona, California

Thanks Gene51 - I had heard not to believe this guy and his ideas/suggestions are inconsistant with my experience. chase

MichaelH Loc: NorCal via Lansing, MI

In the video I mentioned Mr. Northrup seemed to be saying that with the same lens mounted on decreasing sized sensor bodies you get a "bokeh" effect as if you had decreased the aperture - similar to how people say "my 100mm IS a 150mm on my DX body" rather than "has the field of view of" ....

Here is a DOF by sensor size calculator from Cambridge in Colour ( http://www.cambridgeincolour.com/tutorials/digital-camera-sensor-size.htm ). And it shows why large sensors are still used.

Rab-Eye Loc: Indiana

Well, I have the reference but I was wrong about it being from Nikon. I had watched a Nikon video about using FX lenses on DX bodies and vice versa, and thought that was where multiplying the aperture by the crop factor was mentioned. It was not. It came from the next video I watched, which was this one:
https://www.youtube.com/watch?v=YDbUIfB5YUc

It turns out that this guy is known to some of our members and is not considered reliable. This was the first piece of his I had seen. I guess he is in the Ken Rockwell category. My apologies for wasting everyone's time. My error.

Rab-Eye Loc: Indiana

I posted this already, but let me respond to you directly: I had watched a Nikon video, then as you surmised, I watched one (the first one I had ever seen) by Tony Northrup, and indeed it was he who said you have to multiply the aperture by the crop factor. It was my error saying Nikon was the source, and I apologize for wasting everyone's time. I did not know Mr. Northrup's reputation.

Rab-Eye Loc: Indiana

You are exactly right and I was wrong. I had watched a Nikon video and then watched Northrup's, and I mistakenly attributed what Mr. Northrup said to Nikon. My error, and I apologize for wasting your time. The thread was a great read, though!

TriX Loc: Raleigh, NC

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

There is a lot of word salad in that video.

DoF does change even if you use two lenses that provide the same field of view on both sensors, as I wrote in my first post on this thread. But not the amount of light. However, if you look at any DoF chart, something is at play. The same focal length on both cameras at the same distance will show the crop camera as having LESS depth of field compared to the full frame. The smaller circle of confusion on the smaller sensor camera will reveal out of focus more readily than the full frame, which makes sense, since you have to magnify the image from the crop sensor 50% more to get to the same size print. Depth of field will also change on a given print size as you move further away from the print - giving the impression that there is greater depth of field, regardless of what camera took the picture.

jerryc41 Loc: Catskill Mts of NY

I doubt you'rte living under a rock, but this has been discussed here before.

Yes, there are lots of numbers involved in photography, but I generally ignore them. Focal lengths, aperture, and shutter speed are my main numerical interests when it comes to photography.