[MMVIII]

Let's stop this equivalence stuff it gives me a headache. If you want to think about it read this recent thread of many: Do we calculate Aperture to when using FF lenses on Crop Bodies? - PentaxForums.com

Equivalence does not have to be confusing.
The focal length of the lens is an intrinsic measure. The aperture opening is an intrinsic measure. Both don't change wherever you mount your camera on. The only thing that changes is the field of view. It is the same as cutting of the edges of an image. The unsharp area does not change. What changes is the magnification we will use to have the crop image at the same viewing/printing size. The DOF is dependent on the acceptable circle of confusion, which, due to the different necessary magnification is defined different for each format. Thus from the same image the lens collects, the DOF is considered differently on different formats.

[normhead]

Me too. I kind a started it...but seems to be over by now.

If I never heard the term again, I'd be really happy. It's so imprecise in it's meaning it's a misunderstanding waiting to happen.

For exposure ƒ2.8 APS-c is equivalent to ƒ2.8 FF
For DoF ƒ2 APS-c is equivalent to ƒ2.8 FF
For reach 200mm APS-c is equivalent to 300mm FF.

They are three different things, people never seem to tell you which one they are talking about. Equivalence says different things for different topics and if accurate for one, is not accurate for the other two, even though the same word is used. How could there be a word more open to misinterpretation and less likely to be understood in context?

[MMVIII]

I guess you missed the part where I'm done. I've adequately explained my point. Your question is answered above.

All right, I was not alone with the irritation you stirred. Nevermind

[normhead]

All right, I was not alone with the irritation you stirred. Nevermind

You mean with my assertion that the lens was designed solely for FF? Oh wait, that wasn't me.

You mean the assertion that sharp corners have no value for APS-c shooters? (This lens has much sharper corners on APS_c than any other lens besides the 50 and possibly 70-200. If you shoot APS_C and you want sharp corners at wide apertures these lenses are your only choices.) Oh wait, that wasn't me either.

You mean the assertion that APS-c shooters don't need lower CA and distortion values. (Actually CA values are more important on sensors with smaller pixels so I could actually argue that the CA control was designed to look good on the 24 MP APS-c sensors, not the bigger FF sensor sites), no, that wasn't me either.

In fact I see absolutely no value to such assertions. Sorry if that's irritating to you.
People get irritated with me because I challenge their assumptions. I expect it.

They make up these scenarios where their camera is important, someone else's isn't for no apparent reason. seriously, what difference does it make? There are important features to this lens for both APS-c and FF shooters, and with the CA control, more for APS-c shooters. Would I ever write some thing like "APS_c shooters will benefit more from this lens because of the control of CA, it was designed strictly for APS-c and FF users won't benefit as much from that feature because their pixels are larger?" Why someone would claim it was created for just for a specific camera is beyond me. Some features benefit FF users more. Some features benefit APS-c shooters more.

But since you find me irritating, maybe you can explain it.

---

Last edited by normhead; 05-31-2020 at 08:56 AM.

[MMVIII]

You mean with my assertion that the lens was designed solely for FF? Oh wait, that wasn't me.

You mean the assertion that sharp corners have no value for APS-c shooters? Oh wait, that wasn't me either.

You mean the assertion that APS-c shooters don't need lower CA and distortion values. (Actually CA values are more important on sensors with smaller pixels so I could actually argue that the CA control was designed to look good on the 24 MP APS-c sensors, not the bigger FF sensor sites), no, that wasn't me either.

In fact I see absolutely no value to such assertions. Sorry if that's irritating to you.

I see strawmen. Done, thanks

[Wheatfield]

Let's stop this equivalence stuff it gives me a headache. If you want to think about it read this recent thread of many: Do we calculate Aperture to when using FF lenses on Crop Bodies? - PentaxForums.com

Better still, move it to DPR.

---------- Post added May 31st, 2020 at 09:52 AM ----------

Equivalence does not have to be confusing.
The focal length of the lens is an intrinsic measure. The aperture opening is an intrinsic measure. Both don't change wherever you mount your camera on. The only thing that changes is the field of view. It is the same as cutting of the edges of an image. The unsharp area does not change. What changes is the magnification we will use to have the crop image at the same viewing/printing size. The DOF is dependent on the acceptable circle of confusion, which, due to the different necessary magnification is defined different for each format. Thus from the same image the lens collects, the DOF is considered differently on different formats.

Please just stop.

[normhead]

I see strawmen. Done, thanks

Ya, I thought so.

[bxf]

They aren't different, that's what I meant. See why I talked about the brick wall?

Sorry, that was stupid of me. In my brain, when reading your response, my own question was "would the readings be the same", rather than "different", so your answer made no sense. Back yo sleep...

[Class A]

If you set FF and a crop bodies on the same scene, with the same lens, and the same f-stop and ISO, will the two bodies show different shutter speeds?

No, they show the same shutter speed (provided the focal lengths are different so as to account for the different AOV (so technically, I'm not happy with your "same lens" assumption, but I don't think you meant to make it yourself )).

Note that I wrote that the lens is a "f/1.4 lens" on APS-C.
Nothing wrong about that.

The only wrong claim to make is that "f/1.4 on APS-C is equivalent to f/1.4 on FF".

For DoF ƒ2 APS-c is equivalent to ƒ2.8 FF

Yes.

For reach 200mm APS-c is equivalent to 300mm FF.

Yes.

For exposure ƒ2.8 APS-c is equivalent to ƒ2.8 FF

Technically "yes", but only in the sense the technical term "exposure" is independent of the format.

Most people associate the term "exposure" with a measure of "brightness of the result" and when using a standardised output size, the brightness (and hence noise levels) will differ between formats when the same shooting parameters (e.g., "f/2.8") are used.

I won't elaborate because this thread is not about equivalent lens parameters. I only responded to @bxf because they asked a question, and I only commented on the statements by @normhead because the confusion starts when

• partially correct information is mixed with incorrect statements,
• unfounded ideas are presented as "known facts", and
• proper information is denigrated as being "nonsense" just because it doesn't align with someone's (incorrect) world view.

[BarryE]

Maybe it's me, but I've consciously never bothered thinking precisely about DOF and therefore whether I'm using cropped or FF I don't get stressed about it. I know that a wide aperture gives me a narrow dof and visa versa. I know that dof calculations are only trying to give a numeric value to a subjective range of planes that are in-focus to being considered out of focus. I know this dof varies with the distant of the focal point and the FL of the lens. It matters to me not a jot whether I'm using cropped or FF. What matters is the appearance/feel/emotion of the shot. If I'm not sure whether I'm getting it "right" for that composition, I bracket. Why bother with the numbers when photography is an art and therefore the final image is subjective?

The 85mm on cropped or ff will work just fine. Differently, creatively and optically, but fine, although perhaps an overkill on cropped. I'll stick with my 77, for now ...

PS: my career was numeric, from physics, electrical engineering to software. Maybe I've just had it with numbers and formulae etc ;-)

[Kunzite]

No, they show the same shutter speed (provided the focal lengths are different so as to account for the different AOV (so technically, I'm not happy with your "same lens" assumption, but I don't think you meant to make it yourself )).

The f-stop-based exposure system was invented so it would work regardless of the focal length and format.

[Wheatfield]

I only mentioned it in passing.

I wish I hadn't

You could do us all a favour and put an end to it......

[monochrome]

‘If I buy this lens I’m sure the images will be stunning (subject to operator limitations) on K-1, KP and K-new. Any other discussion or consideration is somewhere between marginal and meaningless to this thread.

[Serkevan]

‘If I buy this lens I’m sure the images will be stunning (subjec to operator limitations) on K-1, KP and K-new. Any other discussion or consideration is somewhere between marginal and meaningless to this thread.

What, we cannot complain about those three purple pixels up there in that corner somewhere where no rational person would ever focus their eyes?
You have committed the ultimate DPR-heresy!

I took a couple glances at the comments over there and my gosh those people haven't bothered to make an actual photograph of an actual subject in their lives.

[monochrome]

What, we cannot complain about those three purple pixels up there in that corner somewhere where no rational person would ever focus their eyes?
You have committed the ultimate DPR-heresy!

I took a couple glances at the comments over there and my gosh those people haven't bothered to make an actual photograph of an actual subject in their lives.

Have you washed you hands?