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FORUMS Photography Talk by Genre Macro Talk
Thread started 23 Jan 2018 (Tuesday) 02:52
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Crop factor nonsense

 
Wilt
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Jan 24, 2018 10:51 |  #16

soeren wrote in post #18547876 (external link)
Hmmm we can agree that though 6x6, 6x7, 6x8 and even 6x9 shares og the same "short" side length only 6x9 will give you the "exact" same subject area at the same distance as 24x36?

YES! :lol:


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Wilt
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Jan 24, 2018 11:12 |  #17

Fordsabroad wrote in post #18547884 (external link)
Reading all of this excellent information is making me dizzy.
In laymans terms then. If I shoot a picture of, say a bird on a post with a FF camera and then a crop camera with the same lens then enlarged the FF image to the same as the crop would both images yield the same quality. (lets assume they have similar sensors). I ask this not to be argumentative but purely to know if it is worth hanging on to my 7D11 when I have a 1DXmk2.

Assuming both APS-C and FF camera had identical pixel pitch, if you took a 15mm x 22.5mm image area from each, the quality of the resultant image would be identical (assuming the same lens was mounted on each body for the shot). But read on


  1. Even with same pixel pitch sensors in both cameras (e.g. both a Canon 40D and a 6DII have 174-175 pixels per millimeter of sensor) the FF camera image will capture MORE TOTAL DETAIL because it captures a larger proportion of the lens' image circle! Lenses in past decades had test reports that measured lens detail resolution, and a good one might capture 100 line-pairs/millimeter onto very fine grain film.
    So a 24mm wide negative (135) would capture 2400 total line-pairs of detail. If the sensor is only 15mm wide, from the same lens it can only capture 1500 line-pairs of detail across the frame!

  2. Next, there is the fact that APS-C needs to use a different FL than FF uses, to capture IDENTICAL SUBJECT AREA with both...e.g. 50mm on APS-C vs. 80mm on FF. Assuming both lenses could deliver 100 l-p/mm to the sensors, then I have to accept the fact that what is captured across 1mm of APS-C sensor is captured across 1.6mm of FF sensor...the same subject area is captured with more total pixels on the larger format when the appropriate FL is used for each format.
    So something which is 1mm wide imaged at the APS-C sensor has 100 l-p of detail, but the same subject on FF sensor has 160 l-p of detail.

  3. Lastly, do not forget that the APS-C image has to be magnified by 13.5X to fill an 8" tall print, while FF image has to be magnified by only 8.5X to fill an 8" print.
    So the print from APS-C has 7.4 line-pairs per millimeter of print, while the FF print has 11.7 l-p of detail per millimeter of print.

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Dalantech
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Jan 25, 2018 01:35 |  #18

Fordsabroad wrote in post #18547949 (external link)
Dalantech

Thanks for your swift reply. My pictures are purely for personal use. I print my own and a few hang on the walls of my friends and family. I use an Epson SC-P800 and until recently printed at 300DPI however it was recommended that i tried printing at 180DPI and I have to say I cannot notice the difference.
As you say, I am sure someone will do the math and tell me that a crop v FF is better/worse.
The 1DXmk 2 is a very capable camera with excellent quality images but i suppose the real test for me would be to get of my backside and shoot some images with both cameras and see for myself. you never know I may just be able to sell the 7Dii and buy a new lens!!

It really comes down to what you're using the two cameras for, your style of shooting, and what the subject is forcing you to use. All of my gear choices are dictated by the critters I photograph and my need to keep everything as simple as possible so I can get the shots I want.


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Jan 25, 2018 02:03 |  #19

Wilt wrote in post #18548029 (external link)
....Lastly, do not forget that the APS-C image has to be magnified by 13.5X to fill an 8" tall print, while FF image has to be magnified by only 8.5X to fill an 8" print. So the print from APS-C has 7.4 line-pairs per millimeter of print, while the FF print has 11.7 l-p of detail per millimeter of print.

I know that this is gonna come across as "knit picking" but I think the proper term is "enlarged" and not "magnified". There is a real difference in those two terms, and mixing them up has caused a lot of confusion. I can't get more detail in an image by enlarging it, but I can get more detail by increasing the magnification (ignoring diffraction softening).

Although there's a difference in resolution (not sure if that's the proper term) would the increase to 11.7 l-p really make that much of a difference in a print? I guess it would depend on the level of detail in the area of acceptable focus and the viewing distance. I understand the math Wilt, but experience has taught me that most of it doesn't translate well. I could produce the world's sharpest highest resolution images but when I have a poster size print made on canvas it doesn't really matter, especially at the distance that someone would normally view a print that large.


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Wilt
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Post has been last edited 27 days ago by Wilt. 2 edits done in total.
Jan 25, 2018 17:55 |  #20

Dalantech wrote in post #18548469 (external link)
I know that this is gonna come across as "knit picking" but I think the proper term is "enlarged" and not "magnified". There is a real difference in those two terms, and mixing them up has caused a lot of confusion. I can't get more detail in an image by enlarging it, but I can get more detail by increasing the magnification (ignoring diffraction softening).

(...the blue text) Really?! Care to explain?

We have the real problem that DIGITAL shooters simply fail to understand the issue of getting a 15mm tall image to fill 8" vs. 24mm tall image to fill 8", and that it does entail any 'magnification' or 'enlargement' (no matter which term is more proper!).
That you state, " I can get more detail by increasing the magnification" is wrong if you consider 1500 line-pairs of detail going from 15mm to 8"...it still has only 1500 line-pairs of detail, neither enlargement nor magnification add any detail when the image is 'enlarged' or magnified' from 15mm sensor size to 203mm print size!

Dalantech wrote in post #18548469 (external link)
Although there's a difference in resolution (not sure if that's the proper term) would the increase to 11.7 l-p really make that much of a difference in a print? I guess it would depend on the level of detail in the area of acceptable focus and the viewing distance. I understand the math Wilt, but experience has taught me that most of it doesn't translate well. I could produce the world's sharpest highest resolution images but when I have a poster size print made on canvas it doesn't really matter, especially at the distance that someone would normally view a print that large.

Indeed difference from about 7 line-pairs/millimeter to 14 line-pairs/millimeter of detail is likely to be more than the human eye can perceive. But increase the print size from from 8" tall to 16" tall, and you end up with 3.5 line-pairs APS-C vs. 7 line-pairs FF, and the eye CAN see the ASP-C print as 'not sharp' while it sees the FF print as 'sharp'! The threshhold of human vision puts 5 line-pairs/millimeter as meeting nor not meeting that subjective standard in viewing a print.


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Post has been edited 26 days ago by Dalantech.
Jan 26, 2018 01:09 |  #21

Wilt wrote in post #18548922 (external link)
(...the blue text) Really?! Care to explain?

We have the real problem that DIGITAL shooters simply fail to understand the issue of getting a 15mm tall image to fill 8" vs. 24mm tall image to fill 8", and that it does entail any 'magnification' or 'enlargement' (no matter which term is more proper!).
That you state, " I can get more detail by increasing the magnification" is wrong if you consider 1500 line-pairs of detail going from 15mm to 8"...it still has only 1500 line-pairs of detail, neither enlargement nor magnification add any detail when the image is 'enlarged' or magnified' from 15mm sensor size to 203mm print size!

OK, but it doesn't sound logical and maybe you can help me understand it. Let's take those same 1500 line pairs and apply them to two different surfaces. Note: I'm gonna ignore diffraction cause there's no practical way for me to add that variable for this one, and I'm simplifying things quite a bit.

I take those same 1500 line pairs and I use them to resolve a surface that's 1500 millimeters. Now each line represents an area of 1mm.

Nothing changes except I'm going to increase the magnification so that the surface I'm trying to resolve is reduced by an order of magnitude (a power of 10).

I take those same 1500 line pairs and I use them to resolve a surface that's 150 millimeters. Now each line represents an area of .1mm.

So now each line represents a smaller amount of the total surface and you're telling me that I won't see more detail. If that were the difference in two satellite cameras then I'd go from monitoring traffic on a highway to reading the license plates...

Wilt wrote in post #18548922 (external link)
Indeed difference from about 7 line-pairs/millimeter to 14 line-pairs/millimeter of detail is likely to be more than the human eye can perceive. But increase the print size from from 8" tall to 16" tall, and you end up with 3.5 line-pairs APS-C vs. 7 line-pairs FF, and the eye CAN see the ASP-C print as 'not sharp' while it sees the FF print as 'sharp'! The threshhold of human vision puts 5 line-pairs/millimeter as meeting nor not meeting that subjective standard in viewing a print.

I don't think it's quite that bad Wilt. I've made some really detailed poster size prints from 12MP images -provided someone didn't stick their nose on the paper. I understand the math, but in my experience it just doesn't translate well. Most people don't even care about the detail in a photo unless the image as a whole grabs their attention.


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Post has been edited 26 days ago by Wilt.
Jan 26, 2018 01:25 |  #22

Dalantech wrote in post #18549150 (external link)
OK, but it doesn't sound logical and maybe you can help me understand it. Let's take those same 1500 and apply them to two different surfaces. Note: I'm gonna ignore diffraction cause there's no practical way for me to add that variable for this one, and I'm simplifying things quite a bit.

I take those same 1500 line pairs and I use them to resolve a surface that's 1500 millimeters. Now each line represents an area of 1mm.

Nothing changes except I'm going to increase the magnification so that the surface I'm trying to resolve is reduced by an order of magnitude (a power of 10).

I take those same 1500 line pairs and I use them to resolve a surface that's 150 millimeters. Now each line represents an area of .1mm.

So now each line represents a smaller amount of the total surface and you're telling me that I won't see more detail. If that were the difference in two satellite cameras then I'd go from monitoring traffic on a highway to reading the license plates...

I don't think it's quite that bad Wilt. I've made some really detailed poster size prints from 12MP images -provided someone didn't stick their nose on the paper. I understand the math, but in my experience it just doesn't translate well. Most people don't even care about the detail in a photo unless the image as a whole grabs their attention.

The line-pairs of resolution provided by the lens simply are divided into the full width of the subject which is captured within the frame dimension. Period.
So if you frame 10mm of subject, you have 1500/10 or 150 line-pairs per millimeter of subject, no matter how big the print is. Then if the original 15mm tall image is enlarged by 13.5X to fill an 8" tall print, you have (150/13.5) lines per millimeter of subject on print.
But if you frame 1000mm of subject, you have 1500/1000 or 1.5 line pairs per millimeter of subject, no matter how big the print is. Then if the original 15mm tall image is enlarged by 13.5X to fill an 8" tall print, you have (1.5/13.5) lines per millimeter of subject on print.
You only get 'more resolution' when you can image a smaller area of the subject, so that all of the lines of detail in the lens' image circle are allocated to the smaller area!


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Jan 26, 2018 03:41 |  #23

Wilt wrote in post #18549161 (external link)
You only get 'more resolution' when you can image a smaller area of the subject, so that all of the lines of detail in the lens' image circle are allocated to the smaller area!

Which is exactly what I was trying to get across to you in my last post. If you are imaging a smaller area then the magnification, and detail, have gone up. That's something that a simple enlargement won't do, and cropping creates an enlargement -it doesn't increase magnification...


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Wilt
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Jan 26, 2018 13:00 as a reply to Dalantech's post |  #24

OK, so we are both vigorously defending the same principle!
:-D


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Jan 26, 2018 13:03 |  #25

Wilt wrote in post #18549526 (external link)
OK, so we are both vigorously defending the same principle!
:-D

Indeed :-P


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