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Macro ratio per sensor and lens reversed.
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Jun 11, 2021 21:29:28   #
danniel Loc: North Port, Florida
 
I most often use my Pentax 100mm Macro lens for my smaller subjects.
It is classed as a 1 to 1 ration. But since I am using a crop sensor of 1.5 wouldnt that give the lens a FOV of 150mm>
And if so would that change the ratio ?.

I also use a 35mm and 50mm reversed for much smaller subjects.
So I am curious as to what ratio's those would be on full and crop sensors.
This is math and knowledge beyond my means mates . Perhaps someone here will have them smarts and satisfy my curiosity.

Thanks

2 from my 100mm
Pentax K3

Spider of some sort, and 2 thorny Tree Hoppers, perhaps (horny) tree hoppers.


(Download)


(Download)

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Jun 11, 2021 21:36:55   #
Robert1 Loc: Davie, FL
 
You are right with the focal length changing to 150mm.

If I'm not mistaken your ratio does not change, your perspective change to that of a 150mm lens.

If you reverse the lens then, I think that the ratio changes. If I'm wrong someone will correct me.

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Jun 11, 2021 21:53:33   #
CHG_CANON Loc: the Windy City
 
The lens focal is 100mm and does not change regardless of the camera / sensor where the lens is mounted. Original full-frame 'film' lenses project a circle of light sized to cover the size of the 35mm frame of film or similar sized digital sensor. That same lens on a cropped sensor body projects the exact same sized circle. Nothing changes about the lens, nor how far the lens sits from the sensor, nor the size of the circle of focused light the lens projects.

The difference of a cropped sensor body is the sensor is smaller than the geography of the original 35mm film frame size. The idea of an equivalent focal length identifies the 35mm full-frame focal length needed to create that field of view on a full frame camera with no cropping. Most APS-C cameras (Nikon and Sony) are a 1.5x factor, Canon is 1.6x, meaning 100mm x 1.5 = 150mm or 100mm x 1.6 = 160mm. The Pentax K3 is also a 1.5 crop factor.

The crop factor does not magnify the image. So the 1:1 ratio remains the same. Smaller subjects will 'fill the frame' of the crop-sized sensor, but again, the subject is not magnified nor differently sized than it would appear on a full-frame sensor. If you take the image from the cropped sensor and place that image over the middle of a full-frame image of the same subject with the same lens at the same distance, the image within the area of the overlay will be identical.

Sometimes there's confusion about DX style lenses. These lenses still have the same focal length as measured in millimeters. However, the lenses are designed to create smaller image circles that more closely correspond to the cropped sensor size. This is done by allowing the lens to sit closer to the sensor while still retaining infinity focus. But, the focal length remains unchanged. For a given crop body, whether the lens is a full frame 100mm or a DX / EF-S style lens at 100mm, both yield the same image when used on the crop body.

The magnification ratio of the reversed lenses again is an attribute of the lens, not the sensor size.

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Jun 12, 2021 00:42:46   #
danniel Loc: North Port, Florida
 
CHG_CANON wrote:
The lens focal is 100mm and does not change regardless of the camera / sensor where the lens is mounted. Original full-frame 'film' lenses project a circle of light sized to cover the size of the 35mm frame of film or similar sized digital sensor. That same lens on a cropped sensor body projects the exact same sized circle. Nothing changes about the lens, nor how far the lens sits from the sensor, nor the size of the circle of focused light the lens projects.

The difference of a cropped sensor body is the sensor is smaller than the geography of the original 35mm film frame size. The idea of an equivalent focal length identifies the 35mm full-frame focal length needed to create that field of view on a full frame camera with no cropping. Most APS-C cameras (Nikon and Sony) are a 1.5x factor, Canon is 1.6x, meaning 100mm x 1.5 = 150mm or 100mm x 1.6 = 160mm. The Pentax K3 is also a 1.5 crop factor.

The crop factor does not magnify the image. So the 1:1 ratio remains the same. Smaller subjects will 'fill the frame' of the crop-sized sensor, but again, the subject is not magnified nor differently sized than it would appear on a full-frame sensor. If you take the image from the cropped sensor and place that image over the middle of a full-frame image of the same subject with the same lens at the same distance, the image within the area of the overlay will be identical.

Sometimes there's confusion about DX style lenses. These lenses still have the same focal length as measured in millimeters. However, the lenses are designed to create smaller image circles that more closely correspond to the cropped sensor size. This is done by allowing the lens to sit closer to the sensor while still retaining infinity focus. But, the focal length remains unchanged. For a given crop body, whether the lens is a full frame 100mm or a DX / EF-S style lens at 100mm, both yield the same image when used on the crop body.

The magnification ratio of the reversed lenses again is an attribute of the lens, not the sensor size.
The lens focal is 100mm and does not change regard... (show quote)


Yes, I understand the FOV between full and crop, I had just forgotten it to be honest, I don't know why I asked that lol. Even after years and after explaining the FOV vs crop vs full to others, I still get lost in the mind thought even though I know better.

However does reversing a lens create an entirely different dynamic for the ratio, or, FOV. Or are FOV and Ratio interchangeable terms in that case ?
I have heard speculation that a reversed 50mm might = a 2:1 or even a 3:1 ratio. Would this hold true, or would it come down to FOV ? again, just curious :)

As far as my experience with DX on some FF cameras, I have noticed the IQ and or resolution to be sub par to an actual cropped sensor. Perhaps due to the larger photo-sites, which would look fine at the distance of a FF shot vs the same photo-site size at a Crop image distance, that's if they change. Just my opinion mind you.
Not sure if I am getting my idea across.

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Jun 12, 2021 00:54:22   #
CHG_CANON Loc: the Windy City
 
danniel wrote:
Yes, I understand the FOV between full and crop, I had just forgotten it to be honest, I don't know why I asked that lol. Even after years and after explaining the FOV vs crop vs full to others, I still get lost in the mind thought even though I know better.

However does reversing a lens create an entirely different dynamic for the ratio, or, FOV. Or are FOV and Ratio interchangeable terms in that case ?
I have heard speculation that a reversed 50mm might = a 2:1 or even a 3:1 ratio. Would this hold true, or would it come down to FOV ? again, just curious :)

As far as my experience with DX on some FF cameras, I have noticed the IQ and or resolution to be sub par to an actual cropped sensor. Perhaps due to the larger photo-sites, which would look fine at the distance of a FF shot vs the same photo-site size at a Crop image distance, that's if they change. Just my opinion mind you.
Not sure if I am getting my idea across.
Yes, I understand the FOV between full and crop, I... (show quote)


I don't know that there's a chart of standard focal lengths that when reversed become a standard / consistent magnification ratio. It seems 50mm is consistently around 1:1, less than 50mm can achieve 2:1 or 3:1, where the shorter the lens, the more the magnification when reversed. Over 50mm drops below 1:1.

Field of view and magnification ratios are not interchangeable terms. Again, the smaller sensor just yields a cropped image from the image circle. If an ant was physically 10mm long and filled the frame of a 22mm wide APC-S sensor, there's your 2:1 magnification. The crop factor is not involved. That 2:1 magnification applies whether the ant image is captured on a crop sensor or a 36mm wide full frame sensor.

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Jun 12, 2021 05:07:24   #
danniel Loc: North Port, Florida
 
CHG_CANON wrote:
I don't know that there's a chart of standard focal lengths that when reversed become a standard / consistent magnification ratio. It seems 50mm is consistently around 1:1, less than 50mm can achieve 2:1 or 3:1, where the shorter the lens, the more the magnification when reversed. Over 50mm drops below 1:1.

Field of view and magnification ratios are not interchangeable terms. Again, the smaller sensor just yields a cropped image from the image circle. If an ant was physically 10mm long and filled the frame of a 22mm wide APC-S sensor, there's your 2:1 magnification. The crop factor is not involved. That 2:1 magnification applies whether the ant image is captured on a crop sensor or a 36mm wide full frame sensor.
I don't know that there's a chart of standard foca... (show quote)


I was thinking the terms might be interchangeable when mounted in reverse, not forward.
Perhaps the laws of physics are not willing to change for me lol.

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Jun 12, 2021 06:32:02   #
Peterfiore Loc: Where DR goes south
 
danniel wrote:

Perhaps the laws of physics are not willing to change for me, lol.



A realization many a daredevil sadly have learned the hard way—some with the ultimate price.

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Jun 12, 2021 07:33:07   #
Drbobcameraguy Loc: Eaton Ohio
 
I used this to remember that a crop sensor lens or a lens on a crop sensor camera simple crops the full frame image at a ratio of the crop factor.

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Jun 12, 2021 09:47:28   #
sippyjug104 Loc: Missouri
 
Very well taken images so job well done. The "lens" determines the amount of magnification, not the size of the sensor. The size of the sensor relates to the field of view. I equate to it this way: I look over a short fence at a bed of flowers. Then I bend down and look through a knothole in the fence at the bed of flowers. Of course I can not see as many left to right nor up and down for my "sensor" has been cropped in comparison to the other view.

Field of view changed, magnification did not.

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Jun 12, 2021 11:44:21   #
BassmanBruce Loc: Middle of the Mitten
 
An easy way to determine the magnification of a setup is to take a picture of a mm rule at minimum focus distance and divide no. of mm shown in pic into width of the image sensor.
If your pic shows 26.6mm of the ruler on an aps-c sensor you are at 1:1 and so forth.
Hope this helps.

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Jun 12, 2021 12:53:43   #
cbtsam Loc: Monkton, MD
 
CHG_CANON wrote:
The lens focal is 100mm and does not change regardless of the camera / sensor where the lens is mounted. Original full-frame 'film' lenses project a circle of light sized to cover the size of the 35mm frame of film or similar sized digital sensor. That same lens on a cropped sensor body projects the exact same sized circle. Nothing changes about the lens, nor how far the lens sits from the sensor, nor the size of the circle of focused light the lens projects.

The difference of a cropped sensor body is the sensor is smaller than the geography of the original 35mm film frame size. The idea of an equivalent focal length identifies the 35mm full-frame focal length needed to create that field of view on a full frame camera with no cropping. Most APS-C cameras (Nikon and Sony) are a 1.5x factor, Canon is 1.6x, meaning 100mm x 1.5 = 150mm or 100mm x 1.6 = 160mm. The Pentax K3 is also a 1.5 crop factor.

The crop factor does not magnify the image. So the 1:1 ratio remains the same. Smaller subjects will 'fill the frame' of the crop-sized sensor, but again, the subject is not magnified nor differently sized than it would appear on a full-frame sensor. If you take the image from the cropped sensor and place that image over the middle of a full-frame image of the same subject with the same lens at the same distance, the image within the area of the overlay will be identical.

Sometimes there's confusion about DX style lenses. These lenses still have the same focal length as measured in millimeters. However, the lenses are designed to create smaller image circles that more closely correspond to the cropped sensor size. This is done by allowing the lens to sit closer to the sensor while still retaining infinity focus. But, the focal length remains unchanged. For a given crop body, whether the lens is a full frame 100mm or a DX / EF-S style lens at 100mm, both yield the same image when used on the crop body.

The magnification ratio of the reversed lenses again is an attribute of the lens, not the sensor size.
The lens focal is 100mm and does not change regard... (show quote)


Ya got me confused, Paul, something I'm uncomfortable with despite having to have grown familiar with it over the years. I understand that the FF lens doesn't change when mounted on a cropped sensor camera, so its focal length doesn't change. However, suppose I mount my 100mm FF macro lens on my FF camera, and it focuses to 1 foot to get 1:1, and that setup virtually fills the frame with my 0.9 x 1.3 inch subject. Now, suppose I take the FF camera off the tripod and replace it with a cropped sensor camera, install the same lens, focused again at 1 foot. As you point out, the crop sensor will only record part of the lens' image circle, so wouldn't it only record part of the subject, thus effectively getting me closer than 1:1? And, if not, what exactly am I missing?

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Jun 12, 2021 13:05:51   #
CHG_CANON Loc: the Windy City
 
cbtsam wrote:
Ya got me confused, Paul, something I'm uncomfortable with despite having to have grown familiar with it over the years. I understand that the FF lens doesn't change when mounted on a cropped sensor camera, so its focal length doesn't change. However, suppose I mount my 100mm FF macro lens on my FF camera, and it focuses to 1 foot to get 1:1, and that setup virtually fills the frame with my 0.9 x 1.3 inch subject. Now, suppose I take the FF camera off the tripod and replace it with a cropped sensor camera, install the same lens, focused again at 1 foot. As you point out, the crop sensor will only record part of the lens' image circle, so wouldn't it only record part of the subject, thus effectively getting me closer than 1:1? And, if not, what exactly am I missing?
Ya got me confused, Paul, something I'm uncomforta... (show quote)


The cropped image that shows less of the subject, it really is nothing more than an image that shows less of the same sized subject. The subject isn't magnified on the smaller sensor when you make no change to the focal length (lens) and distance to subject.

Let's take the idea of a slice of bread. Imagine a small plate where the four counters of the bread reach just to the edges of the plate. The bread is the sensor, the plate is the image circle from the lens, and the image is just the bread portion of the larger circle.

If you take a sharp knife and trim the crust, remove the crust and place the bread back onto the plate. There's less bread, but nothing about what remains of the original slice of bread is bigger or different from before the cropping. The 'cropped bread' just uses less of the same image circle. If the bread had been magnified by the lens, still within the same image circle, the bread slice would now be larger than the image circle (i.e, magnified to become larger than the plate / image circle). But, a cropped sensor with the same lens and distance and subject does not relate to magnification, the cropped sensor does not impact magnification.

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Jun 12, 2021 13:35:46   #
Drbobcameraguy Loc: Eaton Ohio
 
CHG_CANON wrote:
The cropped image that shows less of the subject, it really is nothing more than an image that shows less of the same sized subject. The subject isn't magnified on the smaller sensor when you make no change to the focal length (lens) and distance to subject.

Let's take the idea of a slice of bread. Imagine a small plate where the four counters of the bread reach just to the edges of the plate. The bread is the sensor, the plate is the image circle from the lens, and the image is just bread portion of the larger circle.

If you take a sharp knife and trim the crust, remove the crust and place the bread back onto the plate. There's less bread, but nothing about what remains of the original slice of bread is bigger or different from before the cropping. The 'cropped bread' just uses less of the same image circle. If the bread had been magnified by the lens, still within the same image circle, the bread slice would now be larger than the image circle (i.e, magnified to become larger than the plate / image circle). But, a cropped sensor with the same lens and distance and subject does not relate to magnification, the cropped sensor does not impact magnification.
The cropped image that shows less of the subject, ... (show quote)


Excellent example!!!!!! I wish more folks would use such good examples.

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Jun 12, 2021 14:56:41   #
cbtsam Loc: Monkton, MD
 
CHG_CANON wrote:
The cropped image that shows less of the subject, it really is nothing more than an image that shows less of the same sized subject. The subject isn't magnified on the smaller sensor when you make no change to the focal length (lens) and distance to subject.

Let's take the idea of a slice of bread. Imagine a small plate where the four counters of the bread reach just to the edges of the plate. The bread is the sensor, the plate is the image circle from the lens, and the image is just the bread portion of the larger circle.

If you take a sharp knife and trim the crust, remove the crust and place the bread back onto the plate. There's less bread, but nothing about what remains of the original slice of bread is bigger or different from before the cropping. The 'cropped bread' just uses less of the same image circle. If the bread had been magnified by the lens, still within the same image circle, the bread slice would now be larger than the image circle (i.e, magnified to become larger than the plate / image circle). But, a cropped sensor with the same lens and distance and subject does not relate to magnification, the cropped sensor does not impact magnification.
The cropped image that shows less of the subject, ... (show quote)


Thanks for your attempt to help me, Paul, but my shrinking brain is still confused. If the bread in your example is, as you describe it, the sensor, I wasn't thinking of magnifying the sensor, I was thinking about magnifying what appears on the sensor. So I was thinking that if the FF sensor showed the whole spider, but the cropped sensor, showing less of the image circle, showed only the spider's head, that seems a lot like greater magnification to me.

Of course, the lens isn't functioning differently, magnifying the spider more, it's just that the result is a smaller piece of the spider filling my frame, AS IF I'd gotten closer to the spider, or AS IF the spider had been magnified more. And my 1:1 image on the FF sensor is just the spider's whole body, while the result from the same lens, same distance on the cropped sensor is just the head, AS IF the lens on the cropped body magically attained a different macro ratio, making it more magnifying, while the reality is that the spider's head is 1:1 on the crop sensor, while the body is 1:1 on the FF. Just like the 100mm lens doesn't become the 150mm lens on a cropped body, it just gives the same image on the cropped body that a 150mm lens would on the FF body (due to a smaller piece of bread).

Again, I'd appreciate any correction you might provide if I am mistaken here; you generally seem to understand lots of technical things like this much better than I do.

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Jun 12, 2021 15:27:32   #
Drbobcameraguy Loc: Eaton Ohio
 
cbtsam wrote:
Thanks for your attempt to help me, Paul, but my shrinking brain is still confused. If the bread in your example is, as you describe it, the sensor, I wasn't thinking of magnifying the sensor, I was thinking about magnifying what appears on the sensor. So I was thinking that if the FF sensor showed the whole spider, but the cropped sensor, showing less of the image circle, showed only the spider's head, that seems a lot like greater magnification to me.

Of course, the lens isn't functioning differently, magnifying the spider more, it's just that the result is a smaller piece of the spider filling my frame, AS IF I'd gotten closer to the spider, or AS IF the spider had been magnified more. And my 1:1 image on the FF sensor is just the spider's whole body, while the result from the same lens, same distance on the cropped sensor is just the head, AS IF the lens on the cropped body magically attained a different macro ratio, making it more magnifying, while the reality is that the spider's head is 1:1 on the crop sensor, while the body is 1:1 on the FF. Just like the 100mm lens doesn't become the 150mm lens on a cropped body, it just gives the same image on the cropped body that a 150mm lens would on the FF body (due to a smaller piece of bread).

Again, I'd appreciate any correction you might provide if I am mistaken here; you generally seem to understand lots of technical things like this much better than I do.
Thanks for your attempt to help me, Paul, but my s... (show quote)


The FF pic of the whole spider is the same magnification as the crop sensor. If you place them side by side the head will be the same size as the head in the full frame image. You just have a smaller piece of the FF pic with the crop sensor.

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