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Pistnbroke · September 2020

In the post on reviews today we got the old " a 50mm becomes a 75mm on DX" along with a f1 lens is 1.4 on DX.
Not wanting interrupt the high level discussion on sensor dyes etc I just want to say I dont get it.
A 50mm lens is a 50 mm lens just putting its image on a sensor of whatever size and this f1 going to 1.4 seems the ultimate stupidity. Its just passing light through to a sensor.
Perhaps the brains of this outfit can explain without telling me that a 75 on FX has the same angle of view as a 50 on DX

WestEndFoto · September 2020

Read this. It is the best written piece on equivalence that I have ever seen.

https://www.sansmirror.com/articles/equivalence-in-a-nutshell.html#:~:text=Equivalence in this context means,the same angle of view.

Pistnbroke · September 2020

yes I read that before . The way these ideas are used is just sloppy science combined with sloppy english. A lens is a lens.

WestEndFoto · September 2020

Uh huh.

mhedges · September 2020

The way I see it is -

Field of view - this seems pretty straightforward to me - a 50 mm lens on DX will give approximatly the same field of view as a 75mm lens on FX.

Noise performance - this is directly related to the total amount of light gathered - so since a DX sensor is about half the size of an FX sensor you need to be one stop faster on DX to get the same amount of light.

DoF - kind of a hybrid between the field of view and the noise performance. Basically, continuing with the 50mm example on DX you get the field of view of a 75mm lens but keeping the DOF of a 50mm lens.

It kills me to recommend them because of all their other BS but the Northrups did have a good video on this, if you care to look:

spraynpray · September 2020

I think that Vid shows it well enough - @Pistnbroke ?

Pistnbroke · September 2020

To say a DX required more light to get noise levels the same as FX is fine but to say a f1 lens becomes f1.4 on DX is total rubbish

WestEndFoto · September 2020

Yet it is true. Just remember to also add 50% to the focal length.

WestEndFoto · September 2020

mhedges said:
The way I see it is -

Field of view - this seems pretty straightforward to me - a 50 mm lens on DX will give approximatly the same field of view as a 75mm lens on FX.

Noise performance - this is directly related to the total amount of light gathered - so since a DX sensor is about half the size of an FX sensor you need to be one stop faster on DX to get the same amount of light.

DoF - kind of a hybrid between the field of view and the noise performance. Basically, continuing with the 50mm example on DX you get the field of view of a 75mm lens but keeping the DOF of a 50mm lens.

It kills me to recommend them because of all their other BS but the Northrups did have a good video on this, if you care to look:

Nicely done Mhedges.

tc88 · September 2020

Pistnbroke said:
but to say a f1 lens becomes f1.4 on DX is total rubbish

@Pistnbroke, ok, I wouldn't phrase that way. Here is what I will phrase it.

Shooting 50mm f/1 on DX is equivalent to shooting 75mm f/1.4 on FX when comparing the two final pictures for both noise level, field of view, and DOF.

WestEndFoto · July 2021

Another interesting perspective on this issue.

I have always maintained that one of the main reasons that I have chosen full frame is that it inherently has higher resolution than APS-C. I was perusing Photography Life lens reviews the other day and started comparing the Nikon 1.8 primes against "equivalent" Fuji lenses. I think Fuji is a good example because Fuji is committed to making APS-C as best as it can be.

So let's consider two equivalent lenses as an example.

Here is the review for the Fuji 56mm f/1.2 R:

https://photographylife.com/reviews/fuji-xf-56mm-f-1-2-r/2

And here is the review for the Nikon 85mm f/1.8S:

https://photographylife.com/reviews/nikon-z-85mm-f1-8-s

Now to compare apples to apples, we need to adjust aperture. For example, the Nikon at 1.8 and 50% farther from the subject than the Nikon will have the same depth of field and field of view as the Fuji at 1.2.

So how does the sharpness compare using Imatest:

Nikon @ 1.8 vs Fuji @ 1.2:
Centre 2,683 vs 1,966
Mid 2,630 vs 1,375
Corner 1,880 vs 1,221

Nikon @ 2.8 vs Fuji @ 2.0:
Centre 3,776 vs 2,615
Mid 2,902 vs 1,744
Corner 2,051 vs 1,488

Most of the comparisons between equivalent lenses follow this pattern.

So remember, when some lens manufacturer claims that their f/1.0 APS-C lens is somehow better than the competition (usually implying so regardless of the format size) - multiply the focal length by 1.5 and Nikon and Canon will likely have been producing an equivalent full frame 1.4 lens for forty years.

bald_eagle · July 2021

Pistnbroke said:
to say a f1 lens becomes f1.4 on DX is total rubbish

I used to have a really hard time understanding this.. Of course a f1.0 Lens on doesn't become a f1.4 on DX BUT...

We accept that depth of field is a product of aperture, focal length and distance from the subject.
With an APS-C camera the field of view with a 50mm lens is around the same as taking the same photo on a full frame camera with a 75mm lens (at the same distance from the subject).

Or.. we can use the same 50mm lens and move further away to get the same image field of view with the DX camera.

Obviously, this has to affect the DoF - giving the "equivalency".

Don't believe me? Try it.. take a photo with the same lens and same aperture on both APS-C and FF at the same distance and at 1.5x the distance again with the APS-C (to attempt to get the same image as the FF). (I had to do precisely that to eventually understand it).

You will see that the APS-C image at the same distance has the same field of view as cropping to the APS-C sensor region of the FF image.

The APS-C image at 1.5x the distance to subject is essentially the same field of view as the FF Image.

However, in both cases the DoF on the FF Image is shallower!

The 1.5x distance shot is clear - the camera is 1.5x further away - ergo, with the same aperture, the DoF will be different.

The same distance shot is a bit more difficult to explain.. in order to get the field of view and DoF of the APS-C on the FF camera, we would need to move 1/3 the distance nearer to the subject and increase the aperture to account for the decreased distance to maintain the DoF - thus giving rise to this "equivalency"

Hopefully this helps explain this "equivalency" and doesn't confuse anyone further

Cheers,
Baldy!

WestEndFoto · July 2021

It is quite a bit to wrap your head around. I think that for most photographers, they need to be alive to it to make their gear purchase decisions. Don't let the APS-C marketers get away with implying that their 1.4 lens is the same as Nikon or Canon's.

My favorite example is the Sigma 18-35 1.8 which is really an "FX Equivalent" 27-52 2.5. Not bad, but nothing to write home about.

Pistnbroke · July 2021

Quote "Hopefully this helps explain this "equivalency" and doesn't confuse anyone further "

There is no confusion a 400mm lens is a 400mm lens. Whatever sensor you put it in front of its still 400mm so stop wasting your life writing and thinking about the consequences,

Ton14 · July 2021

The difference for me in practice is, if I put for example the Nikon Z6 with the 85mm lens on DX, I get 10mp photos and a smaller image area. If I put the same lens on the Nikon Z50, I get 20mp photos and the same frame size as the DX mode on the Nikon Z6. Yes it is still the 85mm lens.

Pistnbroke · July 2021

True Tony and the images are the same physical size on the sensor its just the POI that is different due to the differing pixel density on the two different sensors.

WestEndFoto · July 2021

Pistnbroke said:
Quote "Hopefully this helps explain this "equivalency" and doesn't confuse anyone further "

There is no confusion a 400mm lens is a 400mm lens. Whatever sensor you put it in front of its still 400mm so stop wasting your life writing and thinking about the consequences,

I will decline your order about what to do with my time and I recommend that Bald Eagle do the same.

Capt_Spaulding · July 2021

For me, it's simple. I have two camera bodies - both are 25 MP. One is APS-C the other is FF. If I want to cram a smaller portion of a scene onto 25MP (or extend the "reach/effective focal length" of the lens or whatever) I use the APS-C. If I want to maximize the IQ of the image, or shoot in low to no light, I use the FF. The f ratio stuff I see as mumbo jumbo. I "think" f 1.4 is f 1.4 regardless of format. The depth of field behavior will change but not the light gathering of the lens. If all of that is true - I'm probably good to go. If it's not, I guess I'll put my fingers in my ears and hum loudly.

WestEndFoto · July 2021

:-). Probably the only truly sane approach!

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