Fullframe lenses - softer on crop sensor bodies

[Tim Tucker]

Besides if you use dof equivalence as a guide for f-stop then it follows that you must then use sensor size as part of your exposure calculation when the determination for exposure is light per sq mm.

I actually like his formula. It lets someone know when shooting a pea-shooter 1" sensor, that even at f/2.8, they're going to end up with a background blur more in line with a full-frame at ~f/8.

It's a pretty good rule of thumb that actually does work.

I don't doubt that it works, but then there are a lot of very symmetrical relationships in the whole system. I just don't see how ff suddenly became the benchmark, the constant used to be f-stop and now it's ff to which things are equivalent. What if you don't have a ff camera and have no experience with one how does the comparison help there?

Ignoring the enlargement factor you could say that all 50mm lenses at f2.8 have the same dof characteristics regardless of format. There's a constant right there that doesn't distort the f-stop, and also makes the dof indicator scales on my MF Nikkors quite handy.

 

[Braineack]

oh yeah, Tony completely ignore everything else, there's no doubt about that.

in the video in post #1, he ignores that the simple fact that a smaller sensor simply cannot resolve the same level of "P-sharpness" than a larger one and doesn't factor that in.

Notice is his first example, the soft 24-70 he uses resolves at 14/22MP on FF, and only 7/18MP on a crop. So right off the back there's a loss of 37% sharpness on a FF sensor, but there's a loss of 62% potential sharpness on the 7D. a 25% difference in sharpness just between the two image sensors.

With that said, yeah, there may be some crop lenses that may be sharper than some full-frame lenses on a crop body, but it's not because you're "focusing all that light onto the sensor itself" verses "digitally zooming light".

His friend sent the lens into Canon, because it's a crap soft lens that will be soft on any camera.

 

[astroNikon]

I don't doubt that it works, but then there are a lot of very symmetrical relationships in the whole system. I just don't see how ff suddenly became the benchmark, the constant used to be f-stop and now it's ff to which things are equivalent. What if you don't have a ff camera and have no experience with one how does the comparison help there?

Ignoring the enlargement factor you could say that all 50mm lenses at f2.8 have the same dof characteristics regardless of format. There's a constant right there that doesn't distort the f-stop, and also makes the dof indicator scales on my MF Nikkors quite handy.

I never really understood the crop factor thing with lenses UNTIL I bought a FF camera.
THEN it all made sense.
So using a FF sensor which creates a 1:1 mathematical model with the lens designed for a FF (35 mm film) makes sense to use it as the benchmark.

 

[Overread]

Fullframe/35mm film is only the common benchmark because in the pre-digital era it was the most common film size. Most disposable cameras and many SLRs and other formats were 35mm. Thus the average Joe likely had experience of the 35mm format to the point where when digital first came out it got the name "crop" because its sensor size was smaller than the more common 35mm; even though during the film era there were a huge number of different format sizes.

The only reason the whole conversion thing even exists is mostly because of those who have 35mm film experience coming into the digital world. Today its a null point; most new to photography are entering with digital and this might never touch a 35mm sensor; meanwhile those who do want to shoot with a fullframe camera have affordable new and secondhand options on the market to pick from so they don't have to worry about using a crop camera.


Furthermore then and now the medium and large formats are rather luxury and whilst film medium and large format gear can be gotten cheaper than before its still nowhere near mainstream.

 

[astroNikon]

plus the camera manufacturers have been using that as a standard for marking the lenses for at least FF down smaller. I saw one instance a few years ago with one of the Nikon J or V cameras where the lens was marked with the focal length zoom AND the equivalent focal length.

 

[Overread]

Aye heck most point and shoots mark equivalents in 35mm focal length on their lenses

 

[Derrel]

dPreview's September 2012 article, "Background blur and its relationship to sensor size"
Background blur and its relationship to sensor size
does a pretty systematic comparison of the common digital sensor sizes.

Focal length used and the resulting angular field of view, format size, aperture value, all these things, and more, affect both depth of field AND the degree of background blurring.

This article uses the terms of no blur, very limited blur, limited blur, reasonable blur, strong blur, and very strong blur. These numbers are for a Portrait Image, with an image height of 0.6 meters--so, comparing the degree of background blurring on an image of the SAME height, despite different sensor sizes and different lens lengths and maximum aperture values.

Check it out!

 

[gckless]

I didn't read many responses, but watched about 2 minutes of the video (what I could stomach), and I had to stop. I hate that he's perpetuating that larger photo size (higher MP count) equates to better photos. Also, I see that the aperture piece has been addressed once or twice...lol.

 

[unpopular]

Yes, depth of field changes with capture size..

DOF stays the same also. Working distance changes and this affects focus distance, which gives the impression that DOF changes.

Cropping the image circle doesn't change the lens, only how the lens is used.

 

[Braineack]

Yes, depth of field changes with capture size..

DOF stays the same also. Working distance changes and this affects focus distance, which gives the impression that DOF changes.

Cropping the image circle doesn't change the lens, only how the lens is used.

No. You're wrong. This is why people don't like you.

using tapatalk.

 

[Ysarex]

Yes, depth of field changes with capture size..

DOF stays the same also. Working distance changes and this affects focus distance, which gives the impression that DOF changes.

Cropping the image circle doesn't change the lens, only how the lens is used.

DOF does change with capture size. The size of the film or sensor is one of the determinant factors for DOF. You can't calculate DOF without a value for the circle of confusion. The circle of confusion is calculated based on the size of the recording medium. Therefore the size of the recording medium (film/sensor) is a DOF determinant factor.

This is a hard one to clear up. This misconception is very widespread and deeply rooted.

Joe

 

[unpopular]

So if I took a lens, projected the image on the wall and then drew a rectangle out on the wall and labeled it "image area" the depth of field would change within the rectangle?

 

[Ysarex]

So if I took a lens, projected the image on the wall and then drew a rectangle out on the wall and labeled it "image area" the depth of field would change within the rectangle?

Not a correct usage of DOF. DOF and how it is calculated is well defined by the industry. I.e. DOF is not calculated at the film plane.

Calculations for DOF require a value for the circle of confusion: Circle of confusion - Wikipedia, the free encyclopedia

As I said, the CoC is calculated based on the size of the film or sensor. Show us the math that says otherwise, otherwise here is a simple proof:

Where H = hyper focal distance, f = focal length, N = f stop, and c = circle of confusion. The formula requires a value for c.

Reference: Hyperfocal distance - Wikipedia, the free encyclopedia

Joe

 

[astroNikon]

To my understanding, as mentioned, DOF is based on sensor size.

This is totally obvious when you get to smaller sensors.
My 1/1.7" Nikon P7800 at 50mm has a gigantic DOF at f/2.8 versus the same on a FF. This is totally obvious. On a APS-C this may not be totally obvious depending upon the experience of the viewer.

This is also one of the reasons the f/1.8 DX lenses are out there, to provide a similar DOF as the equivalent f/2.8 FF lens for APS-C sensors.

 

[unpopular]

f the SAME height, despite different sensor sizes and different lens lengths and maximum aperture values.

So if I took a lens, projected the image on the wall and then drew a rectangle out on the wall and labeled it "image area" the depth of field would change within the rectangle?

Not a correct usage of DOF. DOF and how it is calculated is well defined by the industry. I.e. DOF is not calculated at the film plane.

Calculations for DOF require a value for the circle of confusion: Circle of confusion - Wikipedia, the free encyclopedia

As I said, the CoC is calculated based on the size of the film or sensor. Show us the math that says otherwise, otherwise here is a simple proof:

View attachment 117769

Where H = hyper focal distance, f = focal length, N = f stop, and c = circle of confusion. The formula requires a value for c.

Reference: Hyperfocal distance - Wikipedia, the free encyclopedia

Joe

You're absolutely right. And come to think of it, it makes sense.

However, my math is still suggesting that magnification is a significantly greater factor until you get into higher magnifications.