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12-13-2019, 03:45 PM   #31
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QuoteOriginally posted by swanlefitte Quote
Cropping the full photo and then enlarging it will change dof. Also printing larger or smaller than 8x10 will change Dof. And viewing from a closer or farther distance will change dof. Can you see when a point looks fuzzy or not is dof. Close up it's fuzzy at distance it's not. Large it's fuzzy and small it isn't. Dof is about perception of focus, not true focus.
?
But are the two photos (one in APS-C mode and one cropped to the same ) identical or not?

12-13-2019, 03:48 PM   #32
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QuoteOriginally posted by BruceBanner Quote
Ok... So I get that when we have a FA 77/1.8 on a K-1 we are seeing a FoV that is 77mm and we are getting f1.8 for aperture. When we place the FA77 on a KP we are now getting a FoV equivalent to using 115.5mm lens (if such a lens existed) on the K-1, but do we also now get an aperture that is more like f2.7 along with it?

Or another way to look at it, if we had a lens that was intended for FF and sat on the K-1 and was 115.5mm f2.7 lens (just pretending here), then if we had a KP right next to the K-1 with a FA77, would they be identical in terms of FoV and aperture/exposure performance (just megapixel difference)?

Or another way... if we had a crop sensor lens that was 51.3/1.2, would that be the same as a K-1 with a FA77/1.8 on it?

If that is the case... then if we have a lens intended for Crop, such as a DA 12-24, and we put it on FF, then does the aperture appear wider than f4 (like it's doing the same as above but in reverse lol).

Hehe...

TIA!

BB
To be honest, the answer is "no".

To expand the answer a tad, "I have always tried to get most of my photo in focus, so I have been down at those small numbers, like f/1.7, only when my film demanded more light."

The various parts of the "exposure triangle" have always been, in the words of computing, "over loaded" ..... they have always served two purposes.
* shutter-speed controls exposure and stops motion
* aperture controls exposure and controls DOF
* ISO value controls exposure and controls grain

I have always gone for a 'properly exposured' clear picture, so I have always gone for a middle aperture {on Kodachrome 25 film that meant f/8 or f/11 and at least 1/125} and I went with a larger opening only when I really needed the light, so I view this modern talk of "equivalent aperture" as being close to witchcraft, of confusing things.
12-13-2019, 03:58 PM - 1 Like   #33
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QuoteOriginally posted by BruceBanner Quote
Or another way... if we had a crop sensor lens that was 51.3/1.2, would that be the same as a K-1 with a FA77/1.8 on it?
Short answers here- in terms of FOV, yes.

---------- Post added 12-13-19 at 04:03 PM ----------

QuoteOriginally posted by BruceBanner Quote
we place the FA77 on a KP we are now getting a FoV equivalent to using 115.5mm lens (if such a lens existed) on the K-1, but do we also now get an aperture that is more like f2.7 along with it?
Only in terms of perceived depth-of-field issues, but it is still f/1.8 aperture so it will bring results accordingly for exposure and for related shutter speed availability.
12-13-2019, 04:08 PM - 2 Likes   #34
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QuoteOriginally posted by BruceBanner Quote
Ok... So I get that when we have a FA 77/1.8 on a K-1 we are seeing a FoV that is 77mm and we are getting f1.8 for aperture. When we place the FA77 on a KP we are now getting a FoV equivalent to using 115.5mm lens (if such a lens existed) on the K-1, but do we also now get an aperture that is more like f2.7 along with it?

Or another way to look at it, if we had a lens that was intended for FF and sat on the K-1 and was 115.5mm f2.7 lens (just pretending here), then if we had a KP right next to the K-1 with a FA77, would they be identical in terms of FoV and aperture/exposure performance (just megapixel difference)?

Or another way... if we had a crop sensor lens that was 51.3/1.2, would that be the same as a K-1 with a FA77/1.8 on it?

If that is the case... then if we have a lens intended for Crop, such as a DA 12-24, and we put it on FF, then does the aperture appear wider than f4 (like it's doing the same as above but in reverse lol).

Hehe...

TIA!

BB
As others have said, the focal length and aperture are properties of the lens and the lens alone. They don't change when you change the camera body or crop the image.

Likewise, aperture, shutter, and ISO are properties of an exposure level dictated by the light levels of the scene. They don't change when you change the camera body or crop the image. They don't even change when you change lenses, either. A light meter needs neither the sensor size nor the focal length to do its job.

BUT, if you ask "If I put a 77/1.8 on an APS-C camera, then what second lens do I need on FF to get the same FoV, DoF, and bokeh in final prints of the same size," then the answer is different. You would need a 115.5mm f/2.7 for the K-1 to match FoV, DoF, etc. (And you'd need to up the ISO half a stop to get the same exposure!)

The point is that it's not the lens that's changing when put on a different body. Instead, you need to change the lens if you change the body to get both images to look the same on FoV, DoF, bokeh ball size, etc. on two different format cameras. The pairs of this-lens-on-APS-C makes photos like that-lens-on-FF is what equivalence tells you but it's not about same lenses on different bodies but different lenses on different bodies.

12-13-2019, 04:09 PM   #35
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QuoteOriginally posted by bertwert Quote
?
But are the two photos (one in APS-C mode and one cropped to the same ) identical or not?
They are identical.
Let's say though you print the full photo to 8x10 and cut out the part that looks like the picture taken in crop mode and printed to 8x10. The cut out is smaller than 8x10. At the smaller size more looks to be in focus. So you are looking at pictures that are different sizes. If you now use an enlarger to the smaller one to make it also 8x10 you will also enlarge the fuzziness to where it's visible reducing the dof.

If a dof calculator say 7.54m printed at 8x10 then if you print 1.5x smaller and stand the same distance away, the dof is 14.66m.
Edit typos.

Last edited by swanlefitte; 12-13-2019 at 07:49 PM.
12-13-2019, 04:13 PM - 1 Like   #36
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QuoteOriginally posted by swanlefitte Quote
They are identical.
If they are identical, then the DoF is the same. Unless I am missing the complete fundamentals as to what the DoF is...

QuoteOriginally posted by swanlefitte Quote
Let's say though you print the full photo to 8x10 and cut out the part that looks like the picture taken in crop mode and printed to 8x10. The cut out is smaller than 8x10. At the smaller size more looks to be in focus. So you are looking at pictures that are different sizes. If you now use an enlarge to the smaller one to make it also 8x5 you will also enlarge the fuzziness to where it's visible reducing the dof.
Who said anything about printing?
12-13-2019, 04:37 PM - 1 Like   #37
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I used printing because if you print the crop to 8x10 and the full to 8x10 then crop, it shows the enlargement was different. Dof is about enlargement. How big can you enlarge the circle of confusion is dof. A coc of a certain size can be enlarged to a certain size and still look like a dot from a certain distance. A standard dof calculator uses a predetermined coc size, enlargement, and viewing distance. The dof is only that dof when the above three are used. Thus print to 24x36 and view at the same distance and it gave you the wrong dof. It's like saying how big a head can I see between my fingers at 3 feet away. If I change the size of the head or step closer the answer is different.
12-13-2019, 04:40 PM   #38
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QuoteOriginally posted by swanlefitte Quote
I used printing because if you print the crop to 8x10 and the full to 8x10 then crop, it shows the enlargement was different. Dof is about enlargement. How big can you enlarge the circle of confusion is dof. A coc of a certain size can be enlarged to a certain size and still look like a dot from a certain distance. A standard dof calculator uses a predetermined coc size, enlargement, and viewing distance. The dof is only that dof when the above three are used. Thus print to 24x36 and view at the same distance and it gave you the wrong dof. It's like saying how big a head can I see between my fingers at 3 feet away. If I change the size of the head or step closer the answer is different.
Still not getting it, let's agree to disagree. Though this gave me a big chunk of the posts for another raffle ticket

12-13-2019, 04:46 PM - 1 Like   #39
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QuoteOriginally posted by bertwert Quote
If they are identical, then the DoF is the same. Unless I am missing the complete fundamentals as to what the DoF is...

Who said anything about printing?
Photographs are usually taken to be observed. Technically, only a locus of points is in focus, but people agreed in the concept of "circle of confusion" {which is confusing, of course } to determine which points seem to be in focus to an observer ..... but this assumes that the observer is looking at the entire picture. As people peek at pixels, the whole concept comes apart, as it does more slowly if the observer enlarges the photo {as happens naturally if you go from a larger sensor to a smaller one}. In short, the whole concept is very contentious - just the the thing to discuss during a GiveAway month.
12-13-2019, 05:00 PM   #40
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I'm going to take a point and shoot camera with a tiny sensor, a super zoom point and shoot camera, my phone and my K-3.
I'm going to stage the shots so they're as close as possible and set the apertures so they all match (as open as the smallest aperture camera can go so it's all equal).
They all have different sensor sizes, then we'll see what the depth of field looks like.
12-13-2019, 05:02 PM   #41
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QuoteOriginally posted by Kobie Quote
I'm going to take a point and shoot camera with a tiny sensor, a super zoom point and shoot camera, my phone and my K-3.
I'm going to stage the shots so they're as close as possible and set the apertures so they all match (as open as the smallest aperture camera can go so it's all equal).
They all have different sensor sizes, then we'll see what the depth of field looks like.
Remember to have focal length the same as well as taking the shots from the same place. (Not equivalent the same, that defeats the experiment!) So you'll end up with 4 different field of views as well.
12-13-2019, 05:03 PM   #42
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QuoteOriginally posted by reh321 Quote
Photographs are usually taken to be observed. Technically, only a locus of points is in focus, but people agreed in the concept of "circle of confusion" {which is confusing, of course } to determine which points seem to be in focus to an observer ..... but this assumes that the observer is looking at the entire picture. As people peek at pixels, the whole concept comes apart, as it does more slowly if the observer enlarges the photo {as happens naturally if you go from a larger sensor to a smaller one}. In short, the whole concept is very contentious - just the the thing to discuss during a GiveAway month.
My brain is dead now.
12-13-2019, 05:18 PM - 1 Like   #43
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The forum members who helped me understand this are laughing at my attemps to use a different approach and having the same results.
Just trust that your dof calculator knows what it's talking about as per my post #25.
12-13-2019, 05:27 PM   #44
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QuoteOriginally posted by bdery Quote
The "crop factor" is only a crop. Nothing else.

See it this way. If you take a picture with your K-1, then crop it after the fact via software, you don't change the pixels which remain. You have the exact same image, only with pixels removed around the borders.

An APS-C sensor deos just that. Nothing more. It throws away part of the image, without changing what's left.



That's a dangerous way to see the crop factor equivalent, because of the kind of complications you are not writing about.

Sure, the FOV is equivalent, but nothing else is. Assuming so leads to mistakes.
Yeah I dunno... I can't see things from that way so easily. Usually because my position (where I'm physically standing) stays the same when swapping lenses or cameras in an event. I may decide that I want the full 24mp instead of 16mp crop on the K-1, so I take the FA77 off the K-1 and onto the KP and now I understand the FoV of what I am experiencing would be like what a 115mm lens would be like on the K-1 (that's useful for future lens buying decisions if I decide its a FL that I would like on the K-1). I know the aperture is still showing 1.8, but is it performing the same in terms of DoF that a 115mm/1.8 lens would on the K-1? That is really the point of this thread. Or am I seeing what is more likely a 115mm/2.7 lens (should such a lens exist) on the K-1. It's not dangerous, for me it's about getting an idea/impression of what certain lenses I don't own might be like (similar, not the exactly the same).


QuoteOriginally posted by Wasp Quote
The crop is 1.5. Multiply focal length by crop factor, i.e. 77x1.5=115.5mm. Make that 120mm for simplicity.

Multiply aperture by crop factor, i.e 1.8x1.5=2.7. Make that 2.8 for simplicity.

In short, the 77mm f/1.8 on APS-C will give the same angle of view and depth of field as a 120mm f/2.8 on full frame. Pentax made such a lens, once upon a time.

SMC Pentax-M 120mm F2.8 Reviews - M Prime Lenses - Pentax Lens Reviews & Lens Database
Thank you! So you are the first one here to actually confirm and address the question I am asking. I am simply looking to get a basic understanding of what a certain lens would/might be like, the impression of it etc. For example, if I shot the FA77 on the KP and I saw that the FoV was 115mm equivalent (for FF), and I am in the market to buying a tele lens for the K-1, then if I bought a 115mm/1.8 lens for the K-1 I would be expecting to get the same results (albeit more megapixels) to a FA77 on the KP, but in fact no... the f1.8 from the imaginary 115mm ff lens would actually give a far narrower DoF capability than what I would have experienced to date with the FA77/1.8 on the KP! A more accurate comparison would be a 115/2.7 ff lens! And thus I am now curious if it goes both ways... taking a crop lens not intended for FF (such as a HD DA 20-40 or DA 12-24) and using it on FF, does the f2.8/4 apertures it's capable of actually make that aperture appear less what what it really is?

QuoteOriginally posted by bdery Quote
Ohhh, that's a risky way of tackling this question!

Putting aside the fact that these are pretty big approximations, this line of reasoning supposes that a person wants to create the exact same image with a FF and an APS-C camera. That's a messy way to reason, because the equivalence will not hold for all apertures, subject distance, focal lengths, etc.

If you want to create a general rule this way, you'd have to take into account the pixel size since it influences the circle of confusion, which then influences the perceived DOF.

I repeat, it's a mess, and there are no general rules when going down this road.

A crop sensor simply removes the edges of an image, leaving the rest unchanged. It's much, MUCH simpler to reason that way. Any other trail will get people lost.
Might be risky way of thinking about things but it is my question lol, and how my head works.

You see... I don't really think of lenses in terms of FL, I think in terms of FoV. I have to, because I shoot lenses on two different sensor bodies. A 28mm on a K-1 is pretty much the beginning of a wide angle shot (group portrait), the same lens on the KP and it's a straight up portrait lens. I've come to learn and think of FF as being 'the scale' for me to reference things, so that a F28 on a KP and a FA43 on a K-1 is kinda duplicating a similar shooting experience, and is not covering a big difference in FoV range. And thus far in my journey I have only been considering FoV differences, but not aperture.

QuoteOriginally posted by Wasp Quote
Oversimplifying things doesn't help much. Smaller sensor means less depth of field. As long as you keep that in mind, you will be alright. It can be real deal breaker for those looking at Micro Four Thirds, but let's no dip into that can of worms, hehehehe.

The crop factor is a good way to compare things. It may not hold for every use case out there but it is still the easiest way to explain things. Unfortunately, it has turned into a bit of an obsession for the internet commentariat. Unless one owns, say, both a K1 and a K3, there is little reason for all the fuss.

If you have, as I do, a Kx with a Rokinon 85mm f/1.4, you get a certain kind of picture. Doing math with crop factors doesn't change my pictures, but using it has given me a feeling for the results that are possible. Using said oversimplified math I do know that if I ever get a K1, I will need a Rokinon 135mm f/2 to go with it to achive the same look and feel. It won't be exactly the same, but it is about the closest match that exists in the real world.
^^ This.

QuoteOriginally posted by jack002 Quote
Really? A sensor size affects the depth of field? So a f2.0 lens at f2.0 on different cameras has a different DOF? I never heard that. The field of view changes, yes, that's all. *confused*
Yep, I'm a bit slow to catch onto this also, thus far I was thinking only in terms of FoV differences. I get that the lens will still have the same exposure, f1.8 is 1.8 etc, but the DoF perception would not be the same to it's FF equivalent.

QuoteOriginally posted by Sandy Hancock Quote
With a given f-stop on different sensor sizes, depth of field only changes if you move backwards or forwards to get the same framing.

So back to Eddy's original question - your FA77 at a given aperture will give exactly the same exposure on a full frame, APS-C, micro 4/3 or Q body. If you don't change your position relative the to the subject, the depth of acceptable focus doesn't change either - only your angle of view.
So... pretend this scenario for one minute.

I'm shooting a gig. I can't move from the position I am at. I decide the FA77 is better on the KP than the K-1, instead of 16mp in crop mode on the K-1 I get 24mp on the K-1. Now... lets also pretend that a 115/1.8 lens exists, made for FF (FF coverage). I'm shooting happily with the FA77 on the KP at f1.8 but now I am hitting some buffer issues (because I am a terrible shooter who spams like an idiet), so I grab my lens bag and pull out the 115/1.8 FF lens and place it on the K-1 thinking I will now get a duplicate or very similar FoV to what I have had with the FA77 on teh KP (and that I decide that FoV is perfect for this long drawn out moment lol). But wait up... what's the deal here!? Once I place the 115/1.8 on the K-1 and put it to f1.8 I am experiencing an even shallower DoF! The shots are harder to nail! The DoF too thin! WHoly molly! It's cool and all that the bokeh could be even more pronounced with this imaginary 115/1.8 on the K-1 compared to what the FA77+KP combo can give, but if I want the same DoF slice as to what the KP+FA77 is giving me then I need to stop the imaginary 115/1.8 to f2.8.

True or False?

And so if I am correct in my above scenario, does the reverse also hold true for going the other way, using a crop lens on a FF body?

QuoteOriginally posted by swanlefitte Quote
Check on a dof calculator. Same distance, same fl, same fstop different sensor size gives different dof.
Yeah..
12-13-2019, 05:36 PM - 4 Likes   #45
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QuoteOriginally posted by bertwert Quote
If they are identical, then the DoF is the same. Unless I am missing the complete fundamentals as to what the DoF is...



Who said anything about printing?
Indeed!

There are two definitions of DoF: 1) a pixel-level definition (with a blur threshold measured in pixels) and 2) an image-level definition (with a blur threshold measured relative to frame height). Both are typically translated into a physical blur threshold measured in millimeters to go into a physical optics formula with focal lengths and other distances in millimeters.

The first definition is for pixel peepers. For pixel peepers, all sensors with the same pixel size have the same DoF with the same lens.

The second definition is for print makers or others who show images scaled to fill a widow of a display. Note that most DoF calculators use a frame height definition typically defined for normal viewing of an 8x10 print. For print makers, equivalence rules the roost.
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