24-70 f4 vs apsc f2.8 lenses?

bclaff said:

beatboxa said:

bclaff said:

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To avoid confusion, I think it's important to separate inputs & outputs and to introduce focal lengths.

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Regarding Angle of View see this ray tracing:


Best viewed "original size"

The dark green line is the chief ray and determines the angle of view.

Note that it points from the object side (left) toward the center of P (entrance pupil).

The angle the chief ray makes with I (image plane) only matches the angle of view in rectilinear lenses and when pupil magnification is 1 (not true above).
--

Bill ( Your trusted source for independent sensor data at PhotonsToPhotos )

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It determines the angle of view of the image circle, though not necessarily the image, as recorded by the sensor.

So I'd say this is only part of the equation.

James Stirling said:

Lance B said:

James Stirling said:

Lance B said:

James Stirling said:

Lance B said:

James Stirling said:

j_photo said:

beatboxa said:

I think the only people who would argue that would be people who don't know how to read.

beatboxa wrote:

A 24-70mm F/4 on a full frame camera is essentially equivalent to a 16-47mm F/2.8 on APS-C in terms of everything. Including DoF, light captured, and shot noise.

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Not everything. The exposure is not the same.

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The misunderstandings of equivalence baffle me read through DPreviews take on it in the link below. Or for a deeper more comprehensive explanation look at the second link

https://www.dpreview.com/articles/2666934640/what-is-equivalence-and-why-should-i-care

http://www.josephjamesphotography.com/equivalence/

Ignoring how folk mislabel exposure that is a whole other kettle of fish . The bottom line from a photographic perspective is. If you take an image on APS with a 16mm lens at F/2.8 and one on FF with a 24mm.

The resulting image { minor modern sensor differences notwithstanding } . You will have two images with the same diagonal AOV, the same DOF and same total light thus same noise { assuming you increase the ISO to match the shutter speed }. So as far as it goes you will indeed have two equivalent images .

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The 16mm on APS-C would need to be f2 to have the same minimum DOF as the 24mm f2.8 goes on FF. Or, if the 16mm APS-C lens is f2.8, then the 24mm FF lens woukd need to be f4.

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We were taking about the 24-70mm F/4 :-) As my concluding point below suggests

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The statement in your original post above was ambiguous and simply stated that "If you take an image on APS with a 16mm lens at F/2.8 and one on FF with a 24mm" it would have the same AOV and DOF. That reads to me that they you are saying both are f2.8.

James Stirling said:

James Stirling said:

James Stirling said:

So it is perfectly reasonably to say that an F/2.8 lens on APS will do the same job as an F/4 lens on FF

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The line at the end of my post which I highlighted for you and is right above this reply . Makes it abundantly clear that I was continuing the discussion about the 24-70mm F/4 . In case this line doesn't make it clear I will reiterate for the sake of pedantry that "it is perfectly reasonably to say that an F/2.8 lens on APS will do the same job as an F/4 lens on FF" You did I presume read the title and content of the OP ? The original title was kept in every post I made and replied to namely "24-70 f4 vs apsc f2.8 lenses"

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If this was your write up in a journal or an exam paper, it would be marked down as being ambiguous. You really needed to add in the same sentence that the 16mm f2.8 on APS C would be the "equivalent" of the 24 f4 on FF for AOV and DOF purposes. I mean, if you accept your last premise of tying it all together "So it is perfectly reasonably to say that an F/2.8 lens on APS will do the same job as an F/4 lens on FF" then why even put aperture in the sentence anyway when you said, "If you take an image on APS with a 16mm lens at F/2.8 and one on FF with a 24mm" It just adds to the confusion of how the DOF will be the "same".

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I was crediting the readers of the post with some common sense. When I read a post in a thread I assume it relates to the topic in hand . Clearly a mistake on my part Your pedantry has reached the level of tedium , thus I will be wasting no more time replying to you

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Pedantry works both ways. All you had to do is say, yes I probably should have added in that sentence that the 24mm on FF needs to be f4 to save any confusion, but you just had to win the argument at any cost.

Much clearer now ! :-D

SpacemanUA said:

beatboxa said:

And here we go with the partial responses again, where people can't read what I wrote in context and respond with only some specs, not understanding that "equivalent" in this context means "the same image output," not "equal numbers" or even "equal lens projection."

A lens projection is not a photograph, and f/2.8 is not a size.

A full-frame 24mm F/2.8 lens actually captures more light than an APS-C 16mm F/2.8 lens because the first one has a larger aperture. They project at the same intensity (light per area), but they also project different enlargements and different areas, since one is 24mm on a full-frame image circle that captures light from an entrance pupil of 57.7mm², while the other is 16mm on an APS-C image circle that captures light from an entrance pupil of 34.8mm².

Comparing aptertures:

• 57.7mm² > 34.8mm²

I literally just walked through an analogy of this, that SpacemanUA obviously didn't understand.

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I see no reason to overquote, like most of forum members do. You literally said: "A 24-70mm F/4 on a full frame camera is essentially equivalent to a 16-47mm F/2.8 on APS-C in terms of everything. Including DoF, light captured, and shot noise". That part in bold is wrong,

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No, it is essentially correct.

If you use a 16-47mm lens on an APS-C body at {1/125, f/4, ISO 100} and the 24-70mm lens on a FF body at {1/125, f/4, ISO 100} they will each produce images of the same lightness but they will not have captured the same amount of light. The FF camera will have captured the same amount of light per unit area over 2.25 times as much area. Thus it will have captured 2.25 times as much light.

Now if you change the aperture on the APS-C lens to f/2.8, it will capture twice as much light as at f/4, or 2/2.25 times as much light as the FF (2/2.25 is close enough to being the same as 1 for beatboxa's statement about light capture to be substantially correct). As for shot noise, it is the square root of the amount of light captured. If the amount of light captured is essentially the same, then the shot noise will be essentially the same.

SpacemanUA said:

and you awkwardly explained later why is it wrong by yourself. All one should care about is f-number. Total light captured irrelevant cause your camera's sensor size is permanent.

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Irrelevant to what?

SpacemanUA said:

So, it's about light per area only.

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What is "it"?

SpacemanUA said:

Who cares about total light of FF lens transmission if it's mounted on APS-C camera?

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Somebody who wants to understand how noisy the image will be.

SpacemanUA said:

Shot noise is determined by sensor model.

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Nope. Shot noise, by definition is the variation present in light even before that light is captured by the sensor. A given amount of light has an amount of shot noise equal to the square root of the amount of light.

SpacemanUA said:

Some 10-years old sensor will have different output than modern one.

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Yes but most of the difference will be in camera-added noise, not shot noise. However, newer sensors can result in a higher SNR for shot noise because they capture more of the incident light - they are more efficient.

SpacemanUA said:

Obvious things.

And there's absolutely no reason to over-complicate this things, what you, apparently, like to do. It's way better to answer "yes" to question "X-t3 with a f2.8 lens with iso 3200 SS 1/60 = Z6 f4, iso 6400 SS 1/80? In terms of noise and exposure?"

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But that would be wrong. An X-T3 with a f/2.8 lens at ISO 3200 1/60 would not produce the same exposure as a Z6 with an f/4 lens at ISO 6400 1/80. The Z6's exposure would be 1.3 stops lower. The noise and image lightness would be similar.

SpacemanUA said:

rather than confusing everyone with few walls of text with unnecessary stuff trying to say the same.

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Indik said:

But they will not be the same images (not equivalent). Noise levels, DR, DoF will be different.

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DoF may be different - but often noise differences will be undetectable in everyday photography - and dynamic range is largely irrelevant to much everyday photography.

The may be for DoF depends in part how much you change the focus distance or crop to compensate for the different angles of view.

Noise difference is there and very visible. Even when we take ASP-C sensor made to of the same sensor used in the FF version, the noise given everything else the same (like ISO, exposure and so on) will be visible.

When we look at different sensors (like fuji vs Nikon FF), it gets even worse.

You statement is correct when you replace everyday photography with "social media usage" or maximum 10x15 prints.

fpessolano said:

Noise difference is there and very visible. Even when we take ASP-C sensor made to of the same sensor used in the FF version, the noise given everything else the same (like ISO, exposure and so on) will be visible.

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This is perhaps a matter of opinion.

As someone who regularly shoots DX alongside FX with the same technology I find it difficult to detect any noise difference without viewing at at least 200% - and sometimes 400%.

I expect lots of problems aside from noise when printing after cropping an A3 to the equivalent of 200%.

Printing at 100% (30 inches long dimension from 45 MP) my experience is any noise difference is close to invisible - even viewing from 12-15 inches.

Individual pixel structure (not noise) can be detected - particularly at 200% and 400% - where DX is hampered by a lower MP starting point.

What type of photography are you referring to(landscape/studio/casual portraiture/macro etc)?

What ISO do you usually shoot at?

I`d say for casual landscape/travel - yes, the difference between FF and cropped cameras shot at the same exposure, FoV and same ISO is unnoticeable (except for low light).

Same goes for studio portraiture and product shots/macro. Everywhere you have lots of light/ability to shoot at long shutter speeds the difference is very small.

But it exists.

For family, kids and events the difference is visible. Higher ISOs involved.

And btw, most people use their phones for photos and see no difference to an ILC. Everything is subjective.

Leonard Shepherd said:

fpessolano said:

Noise difference is there and very visible. Even when we take ASP-C sensor made to of the same sensor used in the FF version, the noise given everything else the same (like ISO, exposure and so on) will be visible.

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This is perhaps a matter of opinion.

As someone who regularly shoots DX alongside FX with the same technology I find it difficult to detect any noise difference without viewing at at least 200% - and sometimes 400%.

I expect lots of problems aside from noise when printing after cropping an A3 to the equivalent of 200%.

Printing at 100% (30 inches long dimension from 45 MP) my experience is any noise difference is close to invisible - even viewing from 12-15 inches.

Individual pixel structure (not noise) can be detected - particularly at 200% and 400% - where DX is hampered by a lower MP starting point.

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I also shoot DX and FX at the same time and from multiple brands.

and I do notice noise as soon as they pass their first ISO invariant level. And even worse when I compare my Fuji with anything Nikon (DX or FF)

Leonard Shepherd said:

Indik said:

But they will not be the same images (not equivalent). Noise levels, DR, DoF will be different.

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DoF may be different - but often noise differences will be undetectable in everyday photography - and dynamic range is largely irrelevant to much everyday photography.

The may be for DoF depends in part how much you change the focus distance or crop to compensate for the different angles of view.

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Why are you mixing & matching variables and reintroducing new ones, instead of following the scope of the conversation? Your post is an example of why things get confusing.

The scope of this conversation is defined upstream from your post, the latest scope being here:

• https://www.dpreview.com/forums/post/63645642

• 16mm F/2.8 APS-C lens
• vs
• 24mm F/4 FF lens

And you are saying those will have different angles of view now and potentially different DoF due to the different angles of view?

Or did you suddenly decide to switch variables and change lenses?

Why make this conversation loopy? Stick to the scope, and don't arbitrarily turn previously defined constants into variables. Another example of a "partial response."

j_photo said:

James Stirling said:

I will leave you with these two examples . Both images are shot with a similar framing . Both are shot at the same nominal aperture, both are shot at the same shutter speed of the same subject in the same light at the same ISO . Going by your suggestion tell me do you think they are "exposed" the same ?

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I don't know what "nominal" aperture means.

If the two images were shot at the same aperture (f-stop), shutter speed (and iso depending on what you mean by exposure), then yes, they were exposed the same. Are we arguing over the definition of exposure?

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The same "f-stop", and I'll agree with you.

The same "aperture", and I won't.

Aperture & f-stop are different things, so I don't agree with putting f-stop in parenthesis after aperture. If you said "aperture setting," then I'd give you a pass, because the aperture setting is usually denoted by f-stop. But that doesn't mean the apertures are the same.

Because the aperture is an absolute concept, while f-stop is relative. What is written above is similar to saying that a total quantity of money is the same as a currency conversion rate.