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Andrew Reid

Lenses

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6 hours ago, Stab said:

Yes, that makes sense. With a crop factor of 2x you multiply the focal length and the f-stop by 2x to get a similar FOV and DOF.

Got it.

But, on the DOF calculator that I used, I didn't want to match any framings. I just put the same lens on 2 different bodies. And the MFT sensor had a shallower DOF than the Full Frame sensor. If that is correct, then why is that?

Same distance to subject, same lens, same everything.

you just compare 2 things that are not the same. sorry it's just the way it is. crop factor does exists. so in your test you're not compairing 2x 70mm but a 70mm a 2.8 and a 140mm at 5.6

2 hours ago, thebrothersthre3 said:

I've seen androidlads comparisons and thats good enough for me 

he prefers hlg so you should try it

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EOSHD Pro Color for Sony cameras EOSHD Pro LOG for Sony CamerasEOSHD C-LOG and Film Profiles for All Canon DSLRs

That's quite a surprise..

To my way of thinking, it should be like this:

I have a (hypothetical) 55/1.8 lens on my (hypothetical) a7R IV. This gives me a DOF of (let's say) 80 cm. 

The framing is a bit wide for me, so I turn on S35 (APS-C) mode. I don't get any closer to the subject, don't change the aperture - everything stays the same apart from the fact that I'm using a smaller crop of my sensor. 

Do my DOF change? 

No. 

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1 hour ago, heart0less said:

That's quite a surprise..

To my way of thinking, it should be like this:

I have a (hypothetical) 55/1.8 lens on my (hypothetical) a7R IV. This gives me a DOF of (let's say) 80 cm. 

The framing is a bit wide for me, so I turn on S35 (APS-C) mode. I don't get any closer to the subject, don't change the aperture - everything stays the same apart from the fact that I'm using a smaller crop of my sensor. 

Do my DOF change? 

No. 

I was trying to figure out why we were wrong, the optical system hasn’t changed so the depth of field hasn’t changed - this is pretty fundamental in optical systems I have worked on.

 

The bit that we were missing, as Kye says with the circle of confusion, was that while the optical system hasn’t changed, the viewing conditions have. The depth of field ( effective to the viewer of the output ) is the same for any size sensor as long as the output is scaled similarly to the input I.e. FF35 is viewed twice the size of M43. The circle of confusion is related to both the input and output size and scaling that changes the visible depth of field. I think of it like zooming into 100% , I can see whether something is actually in focus but I couldn’t tell when scaled to fit the screen, the difference won’t be as apparent as that example though.

 

This is interesting to me because it explains why FF35 looks so good on a phone but can be too shallow on a big screen, and may explain some of the rush to the bigger sensors - as the images we view get smaller we need shallower depth of field to match the depth of field we see ourselves or are accustomed to in media.

 

What I haven’t quite wrapped my head around yet is whether it changes the absolute level of blurriness of the out of focus areas. My initial thought is that it doesn’t, it just changes the rate of transition between acceptable sharpness and out of focus but not the absolute blurriness ( I’m sure there’s better terms for this :) ) Anyone got any pointers on that ?

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24 minutes ago, Otago said:

I was trying to figure out why we were wrong, the optical system hasn’t changed so the depth of field hasn’t changed - this is pretty fundamental in optical systems I have worked on.

 

The bit that we were missing, as Kye says with the circle of confusion, was that while the optical system hasn’t changed, the viewing conditions have. The depth of field ( effective to the viewer of the output ) is the same for any size sensor as long as the output is scaled similarly to the input I.e. FF35 is viewed twice the size of M43. The circle of confusion is related to both the input and output size and scaling that changes the visible depth of field. I think of it like zooming into 100% , I can see whether something is actually in focus but I couldn’t tell when scaled to fit the screen, the difference won’t be as apparent as that example though.

 

This is interesting to me because it explains why FF35 looks so good on a phone but can be too shallow on a big screen, and may explain some of the rush to the bigger sensors - as the images we view get smaller we need shallower depth of field to match the depth of field we see ourselves or are accustomed to in media.

 

What I haven’t quite wrapped my head around yet is whether it changes the absolute level of blurriness of the out of focus areas. My initial thought is that it doesn’t, it just changes the rate of transition between acceptable sharpness and out of focus but not the absolute blurriness ( I’m sure there’s better terms for this :) ) Anyone got any pointers on that ?

Let's cut to the chase with an example.

If I set up a lens and adjust focus so that the blur on some writing is just enough to make it unreadable, then it doesn't matter which crop factor or how much resolution I digitise the projection from that lens at, the text will remain unreadable.

If I then adjust the lens so that text is just readable, then it will be readable regardless of crop factor and resolution (except if the resolution is too low to resolve the detail in the text).

Does that make sense?

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4 minutes ago, kye said:

Let's cut to the chase with an example.

If I set up a lens and adjust focus so that the blur on some writing is just enough to make it unreadable, then it doesn't matter which crop factor or how much resolution I digitise the projection from that lens at, the text will remain unreadable.

If I then adjust the lens so that text is just readable, then it will be readable regardless of crop factor and resolution (except if the resolution is too low to resolve the detail in the text).

Does that make sense?

Yes, it's pretty obvious when you state it like that 😀 

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2 hours ago, Otago said:

I was trying to figure out why we were wrong, the optical system hasn’t changed so the depth of field hasn’t changed - this is pretty fundamental in optical systems I have worked on.

 

The bit that we were missing, as Kye says with the circle of confusion, was that while the optical system hasn’t changed, the viewing conditions have. The depth of field ( effective to the viewer of the output ) is the same for any size sensor as long as the output is scaled similarly to the input I.e. FF35 is viewed twice the size of M43. The circle of confusion is related to both the input and output size and scaling that changes the visible depth of field. I think of it like zooming into 100% , I can see whether something is actually in focus but I couldn’t tell when scaled to fit the screen, the difference won’t be as apparent as that example though.

 

This is interesting to me because it explains why FF35 looks so good on a phone but can be too shallow on a big screen, and may explain some of the rush to the bigger sensors - as the images we view get smaller we need shallower depth of field to match the depth of field we see ourselves or are accustomed to in media.

 

What I haven’t quite wrapped my head around yet is whether it changes the absolute level of blurriness of the out of focus areas. My initial thought is that it doesn’t, it just changes the rate of transition between acceptable sharpness and out of focus but not the absolute blurriness ( I’m sure there’s better terms for this :) ) Anyone got any pointers on that ?

circle of confusion yes but also the photosite size has a real impact on dof.

dof on digital is not the same as on film

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3 hours ago, thephoenix said:

circle of confusion yes but also the photosite size has a real impact on dof.

dof on digital is not the same as on film

I don't understand how the photo site size can change the dof, unless it is massive and there are so few samples to judge sharpness from. I could sort of see how it could be true for film, a flat CCD or CMOS with micro lenses vs a multilayered sheet. I'm obviously out of my depth with the maths behind all of this, is there a book or paper that you know of to explain it all ? 

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28 minutes ago, Otago said:

I don't understand how the photo site size can change the dof, unless it is massive and there are so few samples to judge sharpness from. I could sort of see how it could be true for film, a flat CCD or CMOS with micro lenses vs a multilayered sheet. I'm obviously out of my depth with the maths behind all of this, is there a book or paper that you know of to explain it all ? 

i have documentation but in french 😕

not sure you do read french ;) but maybe google translate can help ( i doubt it on technical stuff)

https://artfx.school/profondeur-de-champ-capteurs-numeriques/

 

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6 hours ago, Otago said:

I don't understand how the photo site size can change the dof, unless it is massive and there are so few samples to judge sharpness from. I could sort of see how it could be true for film, a flat CCD or CMOS with micro lenses vs a multilayered sheet. I'm obviously out of my depth with the maths behind all of this, is there a book or paper that you know of to explain it all ? 

Wikipedia is all you should need.  https://en.wikipedia.org/wiki/Circle_of_confusion

Basically, if I make a scene with three points, the first one is perfectly in focus, the second is a one inch behind the focal plane and is a bit blurry and the third is two inches behind the focal plane.   Then I project that image onto two sensors, one is low resolution and the other is high resolution.  

On the low resolution sensor the point source hits one pixel (one photo site) and the second one is a bit blurry but the photo sites on this sensor are so large that it still only hits one photo site.  The third point is so out of focus that it hits more than one photo site.  On this sensor the first two points are in focus and the third is out of focus, therefore the DoF is between 2 and 4 inches.  

On the high resolution sensor the point source hits one pixel (one photo site) and the second one is a bit blurry and because the photo sites on this sensor are so small that it hits multiple photo sites.  The third point also hits more than one photo site.  On this sensor the first points is in focus and the second and third are out of focus, therefore the DoF is between under 2 inches.

This is because the definition of what is in focus and what is out of focus is related to the resolution of the sensor / film-stock.  This is what Circle of Confusion is referencing.

Also from wikipedia:

Quote

In photography, the circle of confusion (CoC) is used to determine the depth of field, the part of an image that is acceptably sharp. A standard value of CoC is often associated with each image format, but the most appropriate value depends on visual acuity, viewing conditions, and the amount of enlargement. 

In digital photography, what is acceptably sharp would be based on the resolution (which is why people pixel-peep by zooming into 100%) and the visual acuity of a digital sensor is its resolution.

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21 hours ago, thephoenix said:

you just compare 2 things that are not the same. sorry it's just the way it is. crop factor does exists. so in your test you're not compairing 2x 70mm but a 70mm a 2.8 and a 140mm at 5.6

he prefers hlg so you should try it

Yeah but he doesn't claim it offers an entire stop more. People generally prefer Log for delivery so I almost always shoot log or Eterna. Might shoot HLG once I get the S1 as maybe they'll match better than the logs from either camera.

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I have never really used 35mm (FF angle of view) lenses very often, not something I every really wanted I guess and my only lenses that covered that are/were zooms.

I have never got what many saw in it to the point some use it as their ONLY lens.

That said, I have started putting my ancient Canon FD 24 1.4 L on my little APSC (1.5x crop) Sony Nex and I think I am really going to like it.

I do like it on FF at 24mm but I think it will get used a lot more now on crop.

Way too shallow DOF close in for video for me at 1.4 or even f2 I think but fine for stills and stopped down will have its uses for video.

I should have stopped this down a bit I think.

 

 

DSC02023.jpg

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On 9/7/2019 at 11:09 AM, noone said:

I have never really used 35mm (FF angle of view) lenses very often, not something I every really wanted I guess and my only lenses that covered that are/were zooms.

I have never got what many saw in it to the point some use it as their ONLY lens.

Nice pic!

I really like the 35mm FF equiv focal length.  That said, I really think that any focal length is very personal and it depends on what you shoot, how you shoot it, and under which conditions you shoot.

For example, I shoot holiday videos of my family, which is essentially environmental portraiture.  In this sense, I want to see my family members interacting with the environment they are in. This could be people or the place itself.  In this sense, I want a FOV that allows for two or three people in the frame.  I also shoot fairly close as we're in public, so the lens has to be at the wider end, otherwise I couldn't get far enough back / people would walk in-between.  

Also, I have discovered that when doing portraiture, we tend to frame up the people in the shot in roughly the same size, and when we do this over different focal lengths the distortion of that focal length comes into play.  Lenses longer than 'normal' create a distant feeling with a compressed background and lenses wider than normal create a 'you are in the scene' / up close and personal feeling.  In my videos I want them to feel like you're there with us, rather than somewhere nearby watching us, so I like a lens wider than normal, but not too wide.

Here are a couple of examples I've shared previously from a 35mm FOV lens:
Japan5_1_32.1.thumb.jpg.abc5d39be93d7932d2947aebdff0a68a.jpg

Japan6_1_86.1.thumb.jpg.4919101d3460765cad18a2ff0d2475fc.jpg

In terms of using this as your ONLY lens, I guess you could, but you'd either have to have the ability to create the set around the lens, or be the kind of film-maker who is looking for subjects that fit that lens and ignore great shots that don't work on it.

I've worked out for me that my kit is equivalents of a 16mm, a 35mm and an 80mm.  The feel of those lenses is exactly what I want - the 16mm gives those WOW shots, the 35mm gives those "you're here with us" environmental portraits, and the 80mm gives a feeling of looking at that thing over there, wether that thing is something in the distance, or if it's a stolen moment from a bit further away when no-one saw you watching.

In this sense, the lenses give the same feeling as you get in person, so for me they match what I shoot (people I love in interesting situations), how I shoot it (while I'm there enjoying the experience with them - and also enjoying the film-making immensely too), and under the conditions that I shoot (in public, often in crowded or restrictive circumstances where you don't have freedom to get into the right spot for the right composition).

In terms of what is right for everyone else, that's not for me to judge, but for anyone who hasn't already worked out what focal lengths they like, I would encourage them to think about the feeling they want to create and look for the lens that gives that feel while composing how they like to compose.

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11 hours ago, kye said:

 

Also, I have discovered that when doing portraiture, we tend to frame up the people in the shot in roughly the same size, and when we do this over different focal lengths the distortion of that focal length comes into play.  Lenses longer than 'normal' create a distant feeling with a compressed background and lenses wider than normal create a 'you are in the scene' / up close and personal feeling.  In my videos I want them to feel like you're there with us, rather than somewhere nearby watching us, so I like a lens wider than normal, but not too wide.

 

In this sense, the lenses give the same feeling as you get in person, so for me they match what I shoot (people I love in interesting situations), how I shoot it (while I'm there enjoying the experience with them - and also enjoying the film-making immensely too), and under the conditions that I shoot (in public, often in crowded or restrictive circumstances where you don't have freedom to get into the right spot for the right composition).

In terms of what is right for everyone else, that's not for me to judge, but for anyone who hasn't already worked out what focal lengths they like, I would encourage them to think about the feeling they want to create and look for the lens that gives that feel while composing how they like to compose.

Thanks,

Yeah focal length choice IS personal and I agree about framing to the same size.

Just remembered I HAVE had a 35mm prime- I had an old MF Nikon 35 1.4 briefly but it was one I got cheap as it had some issues and I never really got on with it anyway.

I usually use a wider lens for environmental portraits.    For stills portraits I usually use (on both APSC and FF though without FF for now) 50/55mm, 150mm 2.8 and 300mm 2.8 lenses though I also love 85mm (pretty much any lens 70mm and up) but do not have any of those to use right now (I do have an FD 85 1.2L I love but it still needs repair as the focus throw is very loose due to dissolving bearings and I still have to find somewhere to repair it in Australia and then afford the repair cost).    My favourite lens for groups of people is my 17mm tilt shift though I also like using longer lenses from further back when I have the room.   24/55/85/150/300 I will pretty much have the same sort of framing for portraits including both head shots and full body.     It is not so easy to carry around and in crowds it makes me a bit self conscious but I do love using my old MF Tamron 300 2.8 for stills portraits outdoors.     For VIDEO, I really only use shorter focal lengths unless it is something specific that will be used on a tripod.     I have a one day festival next month and will probably take this 24 1.4, my 55 1.8 for an AF lens and the 300 2.8 (plus a little superzoom Canon camera for day time use).

Since it seems I am pretty much now going to be stuck with APSC, I should get  FD to E and EF to E focal reducers ASAP.

 

 

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