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# How do zoom shooters actually calculate their shots?

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Re: How do zoom shooters actually calculate their shots?
1

deednets wrote:

Pixel Pooper wrote:

With the same framing, you will get the same DOF at the same f-stop regardless of focal length. Changing your framing will change your DOF whether you do it by changing your focal length, your subject distance, or both. There is no "DOF issue" and you can use the same approach for shooting with a zoom as you would with a prime.

Ok, I play: at ff 85mm and 2 meters distance the dof is around 6cm at F1.8 and a touch less than 40cm at F11. 40cms typically gets all of a head in focus. So as long as I stick to 85mm I have a reasonably accurate idea as to what I am getting here regarding dof.

You will also get the same DOF at 50mm and 1.2 meters distance or at 200mm and 4.7 meters distance because the framing is the same. As long as you keep the same framing you will get the same DOF at the same f-stop, so a tight head shot requires the same f-stop regardless of focal length.

But on a zoom I have no strategy, apart from looking, what the dof is at, say, 110mm and F2.8. Tables help, but zooms have too many variables hence my question as to how people approach this.

The trick is to think in terms of framing. At a given f-stop you can't change the DOF without changing your framing. If you change your framing by changing your focal length or by changing your distance, the effect on DOF is the same. Whether you use a zoom or a prime, the only variables that affect your DOF are framing and f-stop.

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Re: A few thoughts on that…

Tuonov2 wrote:

deednets wrote:

So how do you - as a zoom shooter - "calculate" any of the above shots?

Mini-challenge??

Deed

In exactly the same was as you would calculate for a prime, is there any other answer?

A bit too simplistic. My original post wasn't about using a zoom at an EXACTLY the same focal length as a prime, but using it as a framing tool. Like you stand in front of a group of people and then crop by zooming.

The DOF changes as you do this, in contrast to:

using a prime or

using the zoom at particular focal length without changing.

I have no idea as to how else to explain what I am after, but it seems this is really a difficult enough question for most.

Now, since you responded to the post with the examples, how would YOU zoom in (not using 35mm F2!) and get this "look" when your framing is somewhere further away and you zoom in?

Deed

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Re: How do zoom shooters actually calculate their shots?

Pixel Pooper wrote:

deednets wrote:

Pixel Pooper wrote:

With the same framing, you will get the same DOF at the same f-stop regardless of focal length. Changing your framing will change your DOF whether you do it by changing your focal length, your subject distance, or both. There is no "DOF issue" and you can use the same approach for shooting with a zoom as you would with a prime.

Ok, I play: at ff 85mm and 2 meters distance the dof is around 6cm at F1.8 and a touch less than 40cm at F11. 40cms typically gets all of a head in focus. So as long as I stick to 85mm I have a reasonably accurate idea as to what I am getting here regarding dof.

You will also get the same DOF at 50mm and 1.2 meters distance or at 200mm and 4.7 meters distance because the framing is the same. As long as you keep the same framing you will get the same DOF at the same f-stop, so a tight head shot requires the same f-stop regardless of focal length.

But on a zoom I have no strategy, apart from looking, what the dof is at, say, 110mm and F2.8. Tables help, but zooms have too many variables hence my question as to how people approach this.

The trick is to think in terms of framing. At a given f-stop you can't change the DOF without changing your framing. If you change your framing by changing your focal length or by changing your distance, the effect on DOF is the same. Whether you use a zoom or a prime, the only variables that affect your DOF are framing and f-stop.

I am aware of all this, have just been using a 16-35/4 Zeiss extensively by using the lens as an array of mainly 4 focal lengths: 16-20-24 and 28 mm. Never used the 35mm.

This is just the way I shoot, dialing in 20mm and then frame a shot and NOT standing somewhere and then zooming in to get my frame.

Spot the difference?

Deed

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Re: How do zoom shooters actually calculate their shots?
1

deednets wrote:

Maybe they don't at all and simply shoot what they see without too much of a worry??

Thanks

Deed

Hi, I don't. Yes, one has an idea that at f2.8, on my 16-55 or f5.6 on my 100-400, I'll have relatively shallow depth of field, other factors depending, and that at, say f8+, the DoF will be longer. Other than than, I'd say I focus more on composition and accurate focus - and enjoying the moment.

If I were into calculating DoF, I suspect that it would be for a serious project, which as a hobbyist I don't do, and use a prime. But even when using a prime, such as my 50/f2, I just go by feel.

Not answered the exam question, I know, but outside the World of professionalism for a specific project, I wonder how many people do calculate DoF precisely.

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Re: How do zoom shooters actually calculate their shots?
7

deednets wrote:

Pixel Pooper wrote:

The trick is to think in terms of framing. At a given f-stop you can't change the DOF without changing your framing. If you change your framing by changing your focal length or by changing your distance, the effect on DOF is the same. Whether you use a zoom or a prime, the only variables that affect your DOF are framing and f-stop.

I am aware of all this,

Oh, your OP and subsequent comments sure made it seem like you were not aware.

have just been using a 16-35/4 Zeiss extensively by using the lens as an array of mainly 4 focal lengths: 16-20-24 and 28 mm. Never used the 35mm.

This is just the way I shoot, dialing in 20mm and then frame a shot and NOT standing somewhere and then zooming in to get my frame.

Spot the difference?

As far as DOF is concerned, no difference.

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Re: How do zoom shooters actually calculate their shots?

At this point I am afraid one has to either crop or resample the file. This is the other way left to control the DOF if you have some margin as to the resolution of the display device of course.

I am assuming here that the camera is fixed and the zoom is used to change the framing. Changing the sensor size will also change the framing if we keep the same lens. This is done by cropping the sensor,

Cropping is like using a smaller sensor. A 23mm lens frame can be re-framed as a 35mm lens by using just a portion of the sensor. The result is the same as if using a a 23mm with a smaller sensor: more DOF.

Resampling changes the resolution and a decrease of resolution increases the DOF. Resampling is done automatically when viewing high-res pictures anyway.

You may be afraid of loosing resolution by cropping but you will be loosing effective resokution anyway to diffraction if you have to resort to using a very small aperture to get a deeper DOF at longer focal lengths.

It is still about framing but doing it with the sensor instead of using the zoom.

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Re: A few thoughts on that…
1

When I use a zoom and have to consider DOF, I just hit the DOF preview button.  It all goes very fast and easy.  I personally can’t imagine agonizing over calculating the DOF.  If it looks like I want it to, I hit the shutter.  If it doesn’t, I don’t.

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Re: How do zoom shooters actually calculate their shots?

Pixel Pooper wrote:

deednets wrote:

Pixel Pooper wrote:

With the same framing, you will get the same DOF at the same f-stop regardless of focal length. Changing your framing will change your DOF whether you do it by changing your focal length, your subject distance, or both. There is no "DOF issue" and you can use the same approach for shooting with a zoom as you would with a prime.

Ok, I play: at ff 85mm and 2 meters distance the dof is around 6cm at F1.8 and a touch less than 40cm at F11. 40cms typically gets all of a head in focus. So as long as I stick to 85mm I have a reasonably accurate idea as to what I am getting here regarding dof.

You will also get the same DOF at 50mm and 1.2 meters distance or at 200mm and 4.7 meters distance because the framing is the same. As long as you keep the same framing you will get the same DOF at the same f-stop, so a tight head shot requires the same f-stop regardless of focal length.

But on a zoom I have no strategy, apart from looking, what the dof is at, say, 110mm and F2.8. Tables help, but zooms have too many variables hence my question as to how people approach this.

The trick is to think in terms of framing. At a given f-stop you can't change the DOF without changing your framing. If you change your framing by changing your focal length or by changing your distance, the effect on DOF is the same. Whether you use a zoom or a prime, the only variables that affect your DOF are framing and f-stop.

If we limit the discussion to the geometric DOF - the physical distance between the nearest and  farthest points in a scene which appear in acceptable focus - what you've written is accurate.

However depth of field is a perceived quality in a photograph, itself a two-dimensional representation of three-dimensional physical space. At the same distance from the subject and with the same perspective on the subject, any two photographs made with the same entrance pupil diameter - regardless of focal length, framing, and f-stop - will be perceived by most viewers as having the same depth of field.

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Re: How do zoom shooters actually calculate their shots?
4

deednets wrote:

Martin_99 wrote:

deednets wrote:

Martin_99 wrote:

Thank you for your interesting question. It show to me again, how different are people on the world, with different mind sets and opinions.

I shoot with both primes and zooms on apsc. And my answer is simply I don't calculate it, because it's not necessary either on prime or zoom. In case of doubts I simply check the photo in critical area and shoot again with different setting or distance.

I can ask you the same question regarding primes - how do you calculate DoF? The most critical parameter is camera-subject distance. Do you measure it before shooting?

No, I don’t measure it, but have a set of figures memorised e.g. the dof of 6cms at 2 meters distance at F1.2. It means that in a portrait I can get eyes and nose in focus when the eyes are on the same focal plane. At F8 it's 40cm ... I find it helps.

56/1.2 given as an example.

Deed

Question for me - is it really relevant/important? You mentioned portrait. From my perspective, important is to nail a focus on eye, if DoF is 6cm or 20cm not matter much to me. Of course, that you will want to get certain "look", but you would know it roughly from experience, no need to calculate cm.

Do you find it important also for other photography genres?

EDIT: one note - I shoot only for fun and for my family, so if I ruin some photos (I remember some group photos, where I got too narrow DoF), nobody care. I can imagine, that for PRO's it's more critical.

Well if you don't care then the question wasn't for you.

My idea was to comfort you to be not afraid to use zooms because of false reasons 😉

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Re: A few thoughts on that…
1

tdwesbo wrote:

When I use a zoom and have to consider DOF, I just hit the DOF preview button. It all goes very fast and easy. I personally can’t imagine agonizing over calculating the DOF. If it looks like I want it to, I hit the shutter. If it doesn’t, I don’t.

Sp you think there is no place for a quick calculation then? Like you want to have a woman's hairpiece as well as the dress in focus and maximise out of focus blur. You can tell, maybe, that by pressing the dof button that everything looks ok, but would it really be agony to know you have 60cm in focus when using the 56 at a certain distance, rather than using F11 just to be sure?

In the studio when you work with strobes, the shutter speed is of no importance as long as it's long enough to expose the whole sensor. The aperture is then set in fine increments typically starting at some ridiculous 1/128 or longer of the total power. If you need,say, 120cm in focus for a mini group shot, you might end up at f8 or f13. I use a Sekonik flash meter for that, rather than using a maximum aperture as there are some side-effects from using super small apertures as I am sure you will know,  like diffraction. Maximum sharpness is often achieved at F4-F8 so you want to kethe aperture close to those values.

And you do this by pressing the dof button? Well, I have to admit that I can't reliably predict the whole frame. If you can, yhen good for you.

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Easy
5

I use my Depth of Feeling calculator: subject, lighting, mood. Then adjust my settings accordingly

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Re: Easy

Pocket Lint wrote:

I use my Depth of Feeling calculator: subject, lighting, mood. Then adjust my settings accordingly

Yes!

But not many here seem to do that. In fact, having shot large format cameras and weddings seems to be equally good ... good for them who can "see" the scope of their DOF, but I can't.

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Re: A few thoughts on that…
4

tdwesbo wrote:

When I use a zoom and have to consider DOF, I just hit the DOF preview button. It all goes very fast and easy. I personally can’t imagine agonizing over calculating the DOF. If it looks like I want it to, I hit the shutter. If it doesn’t, I don’t.

Exactly how and why I use zooms exclusively. If you have to faff about and consider DOF and all the other math being sullied around here its highly likely your image is gone, especially if you are working on wildlife or street shooting. Priority is framing and composition.

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Re: Easy
2

deednets wrote:

Pocket Lint wrote:

I use my Depth of Feeling calculator: subject, lighting, mood. Then adjust my settings accordingly

Yes!

But not many here seem to do that. In fact, having shot large format cameras and weddings seems to be equally good ... good for them who can "see" the scope of their DOF, but I can't.

Deed,

You do know that the image plane is infinity thin.  There is nothing in focus outside the image field.  DOF is an artificial construct that arose for film - primary printing.  The equation of DOF contains a constant - the photography equivalent to Plank's constant except it does not have the same physical meaning as Plank's constant.  It is the "Circle of Confusion." To be precise the equation for DOF is

DOF = (u/f)^2 * 2*N*CoC, where u is the distance to the focal plane, f the lens focal length, N the f-number and CoC the Circle of Confusion.  Everything in this equation is a physical element and measurable.  The CoC is a constant based is not such a parameter. However, the circle of confusion arises out of physics along with human visual perception.  A point source of light does not image through a lens and aperture as a point.  It images as a disk - even one from the focal plane.  One reason is diffraction because of the finite lens and aperture.  This disk size will increase when the point source is outside the focal plane.  The more out side the larger.  As you move away from the focal point the disk between two point sources get larger and larger and eventually merge.  The CoC is the size of the circle that a human viewer can differentiate two point sources in the image.  It is different for a print of an image viewed and the "standard viewing distance" and someone pixel peaking with their nose one inch from the monitor.

In printing part of the calculation is in the enlargement ratio - a 4x5 negative for a given print has a much smaller enlargement ratio than a 35 mm negative.  This impacts the CoC estimation.  So for one that prints, the CoC will be different than for one who pixel peaks.  For a pixel peeker it would be on the order of about two times the pixel pitch before the the Rayleigh limit is reached because of diffraction.

So DOF is not an absolute concept simply because it is different based on how the image is to be viewed simply because one key factor is depending on how the image is to be viewed.  For viewing at 100% with the nose to a display - it is one number.  For viewing a printed image at about 2.5 times the diagonal of the print - it is a different number.

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Re: (wrong place) Aha, now I know what you were asking...
2

Nilsa wrote:

... this means changing framing, why should it not. I believe the use case is like this: I have memorized the DOF for 16mm and 35mm FL @F4 at a given distance. However, standing at the same distance I want to zoom/frame to 24mm and want to know what DOF that would give me.

If you want tp change framing but make a photo having the same perceived DOF as the original wider or more narrow angle of view, simply maintain a constant entrance pupil diameter. For example if you like the DOF at 70mm f/2.8 but prefer the more narrow angle of view at 200mm, use an f-stop corresponding to the same (70/2.8=25) 25mm entrance pupil diameter produced at 70mm. At 200mm focal length, that would be f/8.0.

https://www.dpreview.com/forums/post/64536294

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Re: (wrong place) Aha, now I know what you were asking...
1

Bill Ferris wrote:

If you want tp change framing but make a photo having the same perceived DOF as the original wider or more narrow angle of view, simply maintain a constant entrance pupil diameter. For example if you like the DOF at 70mm f/2.8 but prefer the more narrow angle of view at 200mm, use an f-stop corresponding to the same (70/2.8=25) 25mm entrance pupil diameter produced at 70mm. At 200mm focal length, that would be f/8.0.

That will only give you the same DOF if the 70mm shot is cropped to the same field of view as the 200mm shot.

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Re: (wrong place) Aha, now I know what you were asking...
1

Pixel Pooper wrote:

Bill Ferris wrote:

If you want tp change framing but make a photo having the same perceived DOF as the original wider or more narrow angle of view, simply maintain a constant entrance pupil diameter. For example if you like the DOF at 70mm f/2.8 but prefer the more narrow angle of view at 200mm, use an f-stop corresponding to the same (70/2.8=25) 25mm entrance pupil diameter produced at 70mm. At 200mm focal length, that would be f/8.0.

That will only give you the same DOF if the 70mm shot is cropped to the same field of view as the 200mm shot.

Incorrect. See the post I linked to.

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DOF Scale in Viewfinder
1

DOF calculator functionality is built right into the distance scale in the viewfinder...  Not super precise, but it seems to just do the math based on aperture and focal length to display the range of distances in the current field of focus.

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Re: (wrong place) Aha, now I know what you were asking...
2

Bill Ferris wrote:

Pixel Pooper wrote:

Bill Ferris wrote:

If you want tp change framing but make a photo having the same perceived DOF as the original wider or more narrow angle of view, simply maintain a constant entrance pupil diameter. For example if you like the DOF at 70mm f/2.8 but prefer the more narrow angle of view at 200mm, use an f-stop corresponding to the same (70/2.8=25) 25mm entrance pupil diameter produced at 70mm. At 200mm focal length, that would be f/8.0.

That will only give you the same DOF if the 70mm shot is cropped to the same field of view as the 200mm shot.

Incorrect.

It is correct as the DOF calculator below confirms. For the DOF to be the same, the subject would have to be displayed at the same size which requires the 70mm shot to either be cropped to the same FOV, or displayed 2.85 times larger than the 200mm shot.

See the post I linked to.

That's just another post by you repeating the same mistake.

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Re: (wrong place) Aha, now I know what you were asking...
1

Pixel Pooper wrote:

Bill Ferris wrote:

If you want tp change framing but make a photo having the same perceived DOF as the original wider or more narrow angle of view, simply maintain a constant entrance pupil diameter. For example if you like the DOF at 70mm f/2.8 but prefer the more narrow angle of view at 200mm, use an f-stop corresponding to the same (70/2.8=25) 25mm entrance pupil diameter produced at 70mm. At 200mm focal length, that would be f/8.0.

That will only give you the same DOF if the 70mm shot is cropped to the same field of view as the 200mm shot.

You are absolutely right. You are using term DoF as a property pertinent to the whole image and that's how it should be used.

Bill is trying to introduce a new concept he calls "perceived DoF", which I think is neither DoF nor "perceived". It does serve a useful purpose though.

If I say "to make equivalent images on different formats one should shoot from the same subject distance using equivalent focal lengths and equivalent apertures", the statement is correct but has three e-words in it and people don't like the e-word.

I can get rid of two e-words by saying "to make equivalent images on different formats one should shoot from the same subject distance and match the viewing angle (= match the framing on the subject) and use the same aperture diameter (as measured in mm, for example)". Note that we can adjust the framing or "crop" the image in three different ways: (i) by using a different sensor size, (ii) by using a different focal length (iii) by cropping the image in post processing. Let's lump these three together and think for a moment what "two images taken from the same subject distance and using the same aperture diameter" have in common. Well, they will look like one of them might be a crop of the other one - they will have the same background blur relative to the subject. If we crop these two images to the same field of view, they will be equivalent.

I think Bill describes the above property as "two images having the same perceived DoF". I am sure he will correct me if this is not what he means by "perceived DoF" as opposed to "DoF".

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