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04-20-2019, 12:25 PM - 2 Likes   #31
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I managed to get through a whole year of photo arts without ever hearing the word "equivalence".
We did notice that a 250mm lens does something different on 4x5 film than it does on 35mm.

The image above that everyone loves is nonsense, and only true if you are shooting both 51MP FF and 24 MP APS-c so the pixel pitch is the same.

The notion you can blow up the FF image bigger is also only true with the same dimensions. With a 24 MP FF and 24 MP APS-c you can blow them both up to the same size. With a 12 MP FF and a 24 MP APS_c you can blow the APS-c image up bigger. In the Pentax world the whole notion is nonsense because the pixel pitch is different. In the Pentax world the FF will give you a wider field of view. The APS-c will give you a bigger more detailed subject as it squeezes 24 MP and 2700 lw/ph (24 MP) into the same area the K-1 puts just 2000 lw/ph (15 MP)
Until you reach the maximum aperture of the lens (or the diffraction limit) the smaller format will give you more depth of field than the larger format at the same ƒ-stop.
My advice, quit trying to understand this stuff. It's worthless. Look through your camera viewfinder, see what you have. Take the picture. Time working out equivalents for DoF or anything is time wasted. If your 100 is too short try a 200, then a 300. All your problems can be solved by using what you have in your camera bag. Or better yet buy a zoom and check what each focal length does in post processing.

You need to know one thing. What is a "normal"field of view for the sensor size you use. Everything you need to know can be derived from there.
Equivalence is a rookie thing of use only to people who haven't learned how to use their gear. Once you understand your gear, it has no use.

In 60 years I have never once used equivalence in the field, it's really only useful for spawning internet arguments.


Last edited by normhead; 04-20-2019 at 01:28 PM.
04-20-2019, 01:34 PM   #32
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Of course, equivalence is only a useful guide when comparing one format to another. It does in fact have practical meaning. We buy lenses based on what the images will be like when used on a camera we own. This is really not complicated.

Sure a 300mm lens focal length is always a 300mm focal length. So what? Will it produce the same image on APS-C as on a 35mm camera or a FF DSLR? No. If we want the image to be the same, we look at equivalence to find out in practical terms what we can expect. We outfit ourselves with lenses categorized in terms of wide angle, normal, and telephoto. The focal lengths for each category will be different depending on the format used, therefore the equivalency factor. A 50mm lens will be near ideal for portrait use on APS-C, but not as ideal when used on a FF body, even if the lens circle was cut for use on a FF body. The equivalency factor is not a gimmick or abstraction, it is to identify use in practical terms.

Last edited by mikesbike; 04-20-2019 at 01:41 PM.
04-20-2019, 02:12 PM   #33
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QuoteOriginally posted by mikesbike Quote
Of course, equivalence is only a useful guide when comparing one format to another. .
So comparing apsc to a 1/1.2 sensor needs to be compared to fullframe? A 1.5x-2x telephoto is a good portrait lens on all sensors. Why figure a 75-100 on full frame is good then find the equivalent on my camera sensor? After all I should know already that the 75-100 is good because it's a short telephoto on fullframe, not the other way around.

If I had a 18" monitor and switched to a 32" monitor what is the distance away from the monitor i need to be for equivalence of 10' away from a 60" monitor? It's silly here but the same thing.

Last edited by swanlefitte; 04-20-2019 at 02:19 PM.
04-20-2019, 02:23 PM   #34
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This is my take on trying to explain, using a modified cmohr's picture:

A DA labelled lens is not designed to cover more than the corners of an APS-C sized sensor. That way it can be made with smaller lens elements and be lighter and cheaper. If used on a FF sensor camera like the K-1, it will deliver pictures with black corners.

Name:  modified lens projection.jpg
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Some of the DA labelled lenses, like the DA* 300mm nevertheless cover the entire FF sensor area, which means that it does more than it promises.

But 300mm is always 300mm, no matter on what camera it is used.

Kjell

04-20-2019, 03:05 PM   #35
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QuoteOriginally posted by Kunzite Quote
That's fine, but I'm right.
Confusion? It's what "equivalence" does. It doesn't have any purpose, other than to confuse people into one company or another's marketing ploy
Enjoy your dogma.
04-20-2019, 03:31 PM - 1 Like   #36
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QuoteOriginally posted by UncleVanya Quote
Enjoy your dogma.
"Dogma"... don't you think that describes "equivalence" perfectly?

---------- Post added 21-04-19 at 01:53 AM ----------

Oh, and let's go back to the first post of this thread because it's priceless:
QuoteOriginally posted by oh_9000 Quote
just got bit confused here about DA* 300mm. What focal distance will this lens give on APSC camera? DA* would suggest it is made for APSC and it would be 300mm on K3 as such, however the description in the lens review on the forum states it is designated for 35mm/full frame. Then the note below on the same tab mentions it works ok for full frame...
and to this:
QuoteOriginally posted by oh_9000 Quote
I also understand that if I take for instance DFA 100mm macro lens and mount it on my K3, the pictures it takes would be same as with using a 150mm apsc designated lens.
cheers Ondrej
The OP is blameless, of course - he was just fed dogma (UncleVanya won't get upset if I use his term, right? ) instead of information.
He's misled to assume that a label on a lens somehow has an influence on its focal length. He's actually trying to make sense of the nonsense. He's trusting the supposedly more experienced people who aren't there to help, but to mislead.

Ondrej, if it isn't clear at this point: 100mm is 100mm period. Any 100mm will behave exactly* the same** as any other 100mm you can put on the same camera.
On a K-1, using APS-C designated lenses might give you vignetting, but otherwise you will get the same result as with a FF designated lens of the same focal length.
On a K-3, using FF designated lenses will give you the same result as with an APS-C designated lens.

* allowing for some variation due to different optical construction, focal length marking not being extremely precise, focus breathing etc.
** in terms of field of view

How come "equivalence" threads (including those hijacked) include both clear example of the confusion it creates, and people claiming that no, it's not confusing but "useful"?

Last edited by Kunzite; 04-20-2019 at 03:55 PM.
04-20-2019, 03:58 PM   #37
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I just confirmed tv viewing distance is based on screen size x1-2. It's not based on the equivalent distance of 50-100 of a 50 tv. But now I have done the math and know that for a 32unit tv the full50 frame viewing distance of 50-100 equivalence is 32-64 units.
Seriously what's the real difference that makes this silly and the other not?
04-20-2019, 04:06 PM   #38
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Well, in one case you look at the TV and place it so you'll be at about 1-2 times its screen size. You can eyeball it easily, you don't even need a ruler.
In the other, you'd think about a TV you don't have, compute its imaginary position at 1-2 times its screen size, compute the ratio between the TV you do have and the one you don't and finally, apply this "crop factor" to the previously computed imaginary position.

04-20-2019, 04:12 PM   #39
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My point exactly.
04-20-2019, 06:32 PM   #40
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In this thread I did the real math (equivalence + fsrop equivalence) and showed that this is the equivalence. Then it comes down to if you can do it. Meaning it was all pointless unless you know your personal media.
How can a 1
I also was confused by this because of the terminology as shown in this thread.
04-23-2019, 05:20 AM - 1 Like   #41
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The only.. Repeat only. Equivalence referred to by the OP. Was about what he would see, in the viewfinder. There is no, repeat, no argument, that changes, the absolute fact, that, in the viewfinder, a 200mm lens on a APS-C camera, undisputedly, gives you basically, the same field of view as what you will see, in the viewfinder of a FF camera fitted with a 300mm lens in terms of Field of View, this is fact, take all your depth of field arguments and put them in your pocket, it was not asked, and, why, I was very particular to always talk in terms of Field of View. The only equivalence ever decided on, by the manufacturer was, field of view, this is why Pentax made, the 16-50, and the 50-135 zooms, when others didn't, to make lenses with the most popular fields of view, solely for APS-C format. Too many people get fooled into the depth of field arguments, that have nothing to do with the particular question that the OP asked and are completely irrelevant to the particular question the OP asked, and understood, some 2 pages ago.
04-23-2019, 08:23 AM   #42
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Cmohr,
It was answered on the first couple of pages. So why answer it again?
Fleshing out the whole understanding is what's left. I read footnotes and addendums, is that bad? Some don't read them. A post on a forum takes a life of it's own. The answers are not just for op's answer but it for others as well. Have you never read a thread started by someone else to get your answer? I would hope people do a thread search before asking a question to avoid redundancy. Their question may not be equivalent to the initial question and the extra information might be just what is needed.
04-23-2019, 04:17 PM   #43
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Cheers guys, this is all very helpful. Appreciate all the background insight as well!
Bottom line for me, will try and go for DA*200mm rather than 300mm if there is a good one to be found.

Ondrej
04-23-2019, 04:18 PM   #44
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QuoteOriginally posted by cmohr Quote
The only.. Repeat only. Equivalence referred to by the OP. Was about what he would see, in the viewfinder. There is no, repeat, no argument, that changes, the absolute fact, that, in the viewfinder, a 200mm lens on a APS-C camera, undisputedly, gives you basically, the same field of view as what you will see, in the viewfinder of a FF camera fitted with a 300mm lens in terms of Field of View, this is fact, take all your depth of field arguments and put them in your pocket, it was not asked, and, why, I was very particular to always talk in terms of Field of View. The only equivalence ever decided on, by the manufacturer was, field of view, this is why Pentax made, the 16-50, and the 50-135 zooms, when others didn't, to make lenses with the most popular fields of view, solely for APS-C format. Too many people get fooled into the depth of field arguments, that have nothing to do with the particular question that the OP asked and are completely irrelevant to the particular question the OP asked, and understood, some 2 pages ago.

Absolutely. We are dealing with practical real-world use here, not anything abstract or unreal.
04-23-2019, 04:22 PM - 1 Like   #45
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QuoteOriginally posted by oh_9000 Quote
Cheers guys, this is all very helpful. Appreciate all the background insight as well!
Bottom line for me, will try and go for DA*200mm rather than 300mm if there is a good one to be found.

Ondrej
Thanks for dealing with us. I hope you feel confident moving on.
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