December 14, 2017, 05:32:34 AM

Author Topic: Need Source for Equivalent f-stops, pls  (Read 10005 times)

Talys

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Re: Need Source for Equivalent f-stops, pls
« Reply #30 on: September 09, 2017, 11:32:55 AM »
It seems very esoteric, indeed. Could you please describe a setup or even better show an image that would have suffered from having been shot with a crop camera with a slightly shorter focal length, correspondingly lower magnification and larger aperture, with output size, viewing distance, and observer visual acuity fixed?

Yes, it's very esoteric and not a very useful from a practical perspective, because, most people with a crop camera will not stand in exactly the same spot as they would with a full frame camera, using a lens set at the same focal length.

Instead, with a crop camera vs full frame, they will change FL with zoom, or move nearer or further away as they would with a full frame, or use a different lens, to frame the same shot.  The crop factor -- 1.6 -- is just too a huge change in composition.  And as you change distance to subject and/or focal lengths, your depth of field is going to change.

The whole thing is mostly academic.

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Re: Need Source for Equivalent f-stops, pls
« Reply #30 on: September 09, 2017, 11:32:55 AM »

privatebydesign

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Re: Need Source for Equivalent f-stops, pls
« Reply #31 on: September 09, 2017, 01:14:08 PM »
It seems very esoteric, indeed. Could you please describe a setup or even better show an image that would have suffered from having been shot with a crop camera with a slightly shorter focal length, correspondingly lower magnification and larger aperture, with output size, viewing distance, and observer visual acuity fixed?

Yes, it's very esoteric and not a very useful from a practical perspective, because, most people with a crop camera will not stand in exactly the same spot as they would with a full frame camera, using a lens set at the same focal length.

Instead, with a crop camera vs full frame, they will change FL with zoom, or move nearer or further away as they would with a full frame, or use a different lens, to frame the same shot.  The crop factor -- 1.6 -- is just too a huge change in composition.  And as you change distance to subject and/or focal lengths, your depth of field is going to change.

The whole thing is mostly academic.

It isn't academic.

Say I took a scouting shot with my phone or P&S. I can work out what focal length and aperture I'd need for a bigger camera.

Say I saw a particular image on line of a place I was going and wanted to get a very similar shot. If I understand equivalence I can reverse engineer what I could retake that perspective with from the EXIF data of the image even if it was a phone.

Say I have the 'wrong' camera with me or my main fails and I have to finish a session with a different sensor size, if I understand equivalence I can maintain consistency throughout the shoot.

Say I am working a crop and ff camera at the same time. If my battery dies or the flash stops working I can instantly understand what I need to do to get the 'same' image from my other camera.

It isn't academic for many shooters; it is for many others. But core understanding and knowledge can be applied in so many areas it is very good to have. Conversely all the incorrect 'knowledge' out there leads to so much confusion it is farcical.
Too often we lose sight of the fact that photography is about capturing light, if we have the ability to take control of that light then we grow exponentially as photographers. More often than not the image is not about lens speed, sensor size, DR, MP's or AF, it is about the light.

Talys

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Re: Need Source for Equivalent f-stops, pls
« Reply #32 on: September 09, 2017, 01:35:44 PM »
It seems very esoteric, indeed. Could you please describe a setup or even better show an image that would have suffered from having been shot with a crop camera with a slightly shorter focal length, correspondingly lower magnification and larger aperture, with output size, viewing distance, and observer visual acuity fixed?

Yes, it's very esoteric and not a very useful from a practical perspective, because, most people with a crop camera will not stand in exactly the same spot as they would with a full frame camera, using a lens set at the same focal length.

Instead, with a crop camera vs full frame, they will change FL with zoom, or move nearer or further away as they would with a full frame, or use a different lens, to frame the same shot.  The crop factor -- 1.6 -- is just too a huge change in composition.  And as you change distance to subject and/or focal lengths, your depth of field is going to change.

The whole thing is mostly academic.

It isn't academic.

Say I took a scouting shot with my phone or P&S. I can work out what focal length and aperture I'd need for a bigger camera.

Say I saw a particular image on line of a place I was going and wanted to get a very similar shot. If I understand equivalence I can reverse engineer what I could retake that perspective with from the EXIF data of the image even if it was a phone.

Say I have the 'wrong' camera with me or my main fails and I have to finish a session with a different sensor size, if I understand equivalence I can maintain consistency throughout the shoot.

Say I am working a crop and ff camera at the same time. If my battery dies or the flash stops working I can instantly understand what I need to do to get the 'same' image from my other camera.

It isn't academic for many shooters; it is for many others. But core understanding and knowledge can be applied in so many areas it is very good to have. Conversely all the incorrect 'knowledge' out there leads to so much confusion it is farcical.

When I say that it's academic, I'm talking about the specific, and very narrow case that I took a test shot of -- depth of field of a FF and a crop sensor, both with identical lenses, taken from exactly the same focal distance.  On the full frame image, the depth of field of any part of the image available on the crop is identical to the depth of field on the crop image. 

But the only scenario that this would be useful for is if you had an 80D set up to take shots on a tripod, and it died; then you could swap in a 5DSr and get exactly the same shot, and just take the crop area.  You'd get essentially identical depth of field in the images.  The reverse is more likely, and even technically true but it's totally useless, because if you swap out a 5DSr with a 80D without moving and using the same lens, you'd lose 40% of your image, and one assumes that's not desirable.

I certainly don't mean that the understanding of focal length, aperture, distance to subject as it relates to depth of field is academic.  It most certainly isn't!

okaro

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Re: Need Source for Equivalent f-stops, pls
« Reply #33 on: September 29, 2017, 03:03:04 AM »
[When I say that it's academic, I'm talking about the specific, and very narrow case that I took a test shot of -- depth of field of a FF and a crop sensor, both with identical lenses, taken from exactly the same focal distance.  On the full frame image, the depth of field of any part of the image available on the crop is identical to the depth of field on the crop image. 

You get less DoF on a smaller sensor if you use same lens. If you later crop the FF image then you will naturally get identical results.

Quote
But the only scenario that this would be useful for is if you had an 80D set up to take shots on a tripod, and it died; then you could swap in a 5DSr and get exactly the same shot, and just take the crop area.  You'd get essentially identical depth of field in the images.  The reverse is more likely, and even technically true but it's totally useless, because if you swap out a 5DSr with a 80D without moving and using the same lens, you'd lose 40% of your image, and one assumes that's not desirable.

I certainly don't mean that the understanding of focal length, aperture, distance to subject as it relates to depth of field is academic.  It most certainly isn't!

One naturally would use a different lens in the crop sensor or open the zoom more.

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Re: Need Source for Equivalent f-stops, pls
« Reply #33 on: September 29, 2017, 03:03:04 AM »