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I\'m too tired to think math..
Old 01-02-2006, 04:45 AM   #1 (permalink)
JohnPaul
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Ok... it's 3:30AM... I have taken 3 sleeping pills... but I want to make a point, but I forget how to do this..

What is the "magnification" / "cropping factor" of a 1/1.8" sensor which is 7.18mm x 5.32mm on a DSLR body that would accept 36mm x 24mm "full frame" lenses?

What am I looking at is IF there was ever a 1/1.8" sensor on a DSLR body....that would use 35mm format lenses, say like from Canon or Nikon..what would that be?

Gosh, when I was a kid, I could do this in my sleep.. [img]/ubbthreads/images/graemlins/frown.gif[/img] Now,...I'd have to look up that stuff in those old dusty books..

Thank you in advance..

JP
 
 
Re: I\'m too tired to think math..
Old 01-02-2006, 06:51 AM   #2 (permalink)
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I forgot how to do that (give me math with letters and funny squiggly lines and I can do that - I'm more of a theorist - sosumi).

What I do remember though, is that you have all of the variables to make the comparison.

You have the length and width, so you have what you need to find the diagonal measurement (that's the process that I can't remember).

Then divide one way or the other with 35, and you should have your size ratio.
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Re: I\'m too tired to think math..
Old 01-02-2006, 08:47 AM   #3 (permalink)
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Taking the simple route, the mag factor in relation to a 36mm x 24mm frame would be ~4.83X and you would lose about 15% of the width. I'm thinking in terms of geometry, not optics. I'm not sure if other stuff figures in or not.

Diagonals:

24mmx36mm = 43.27mm (remember pythagoras?)
7.18mmx5.32mm = 8.84mm

8.84X = 43.27
X = 43.27 / 8.84
X = 4.89

The apsect ratios are not proportional to each other though. A 36x24 frame is an aspect ratio 1.5:1(3:2); the 7.18x5.32 is close to TV at 1.35:1(4:3)... but not exactly. It will crop off about 15% of the width.

Read military history, better than sleeping pills, try Rick Atkinson's books.

Chip
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Re: I\'m too tired to think math..
Old 01-02-2006, 10:00 AM   #4 (permalink)
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John Paul,

You may know much of the information below but I would like to share it with the masses as some are not aware of some of the technical reasoning behind the answer.

As I am an engineer and have a degree in mathematics, I believe I can be overly helpful. As I mentioned, this same sensor size issue is one that effects me greatly as a Nikon D2X guy wanting the same shallow Depth of Field as a full frame piece of film. One interesting point to those that don't know is to note that a 35mm piece of film does not measure 35mm in either direction. It really measures 24 x 36mm in film as it is double frame (height) of the old 18 x 24 movie film.

I think it is also important to note that magnification is done through the lens and the cropping factor (something invented by communists like Nikon / Sony to keep costs down and customer bases up) simply means the same size image comes through the same lens but some of that image spills past the edges of the sensor and into "nowhere" land off the sensor. An advantage of smaller sensors, aside from cost, is the edges of the lens (full frame sensors will see this) will vignette / darken as they can not disburse the light as efficiently as the center glass can. Simply understanding the concept of why fiber optic lines require a sheathing layer helps explain this refraction issue.

Besides sensor cost, please note that smaller sensors require smaller lens, also keeping lens cost and weight down. The issue of economics drives is what drives digital cameras anyway. Let's face it, if we really cared about Depth of Field or image quality, we would be shooting medium format Hassleblads!
In cameras like my D2X, it makes sense that the image quality is high, not because of any cropping factor, but simply that the receptors on the CMOS sensor are very small and close together. Nikon offers the highest image definition of any digital camera on the market simply because the sensors provide a finer image. Nikon leaves Canon in the dust when measuring resolving power simply because of this reason. The D2X has the highest resolving power of any digital camera. One note to remember is the Glamor business doesn't want resolving power as we don't want to see flaws in skin anyway. Black scarf filter anyone? NASA on the other hand uses D2X's to shoot the bottom of the shuttle as they do want resolving power. Something about things hanging off the bottom of their vehicle and 17,000 mph. The problem with the smaller sensors is when an image is "stretched" to be the same image size as a full frame camera it looks as if the resolving detail is not the same quality as the full frame camera. This effect was demonstrated in a previous post where two images (one D2X and one Mark II DS) where shown next to one another. The flaw in that remonstration is the Nikon camera would have to be further away or the image cropped to give the same starting point image.

To answer your question about sensor size cropping factor, the issue is slightly more complex that just that of sensor size as, for example, the Nikon has a sensor height of apx. 24mm and a Mark II DS has a sensor size of apx. 36mm. Simply dividing 36 / 24 gives you 1.5, or an apparent 1.5 crop factor. Just like horsepower of a car, you can measure power at the tire or the engine. You get different numbers depending on the point of measure. With cameras, you can measure the image at the sensor or on the final digital file. The only issue to keep in mind is that the image size has little to do with sensor size and more to do with pixel size and pixel count. Just as an example, there is an interesting article explaining this resolving power at:

http://www.lonestardigital.com/D2X.htm

To underscore the issue, please note that neither Nikon nor Canon define their image size by sensor size but rather by pixel count. To calculate a true comparison, you would need to know the pixel count and the pitch size of each photosite on the sensor.

All that being said, if the pitch size is somewhat similar in your question, simply 24 / 5.32 for an answer of around 4 1/2 or 5. I would dare to add that a sensor so small would undoubtedly have as fine a pitch count as the full frame camera as I suspect price / cost was a driving force to manufacture such a small sensor in the first place.

I still want a Canon D5 because the pixel count and photosite pitch size allow me to fit the image I want onto the sensor at a closer range than my Nikon therefore, blurring the background (similar to 1 1/3 greater stops) at a wide open F Stop.


Too much information?

[img]/ubbthreads/images/graemlins/grin.gif[/img]
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Re: I\'m too tired to think math..
Old 01-02-2006, 12:05 PM   #5 (permalink)
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More, more, Wow. I have never heard all this. I recently took a class at Western KY University, known for Photojournalism. The class was titled "Electronic Technology in Photojournalism". It was suppose to cover Photoshop and the whole digital workflow. I was really disappointed with the professor (Chad Stevens). There were other professors much more knowledgable of the workflow that should have been teaching the class. The majority of what I learned came from lynda.com tutorials that we subscribed to as students. Everytime we went to class we had to discuss current events, when we should have been learning about the difference in sensor sizes, lens sizes and how that relates to depth of field, etc. If I wanted current events...I would watch Fox News[img]/ubbthreads/images/graemlins/grin.gif[/img] or CNN depending on your bias.

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Re: I\'m too tired to think math..
Old 01-02-2006, 12:54 PM   #6 (permalink)
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They never told you about this in class? Since I used to take 35mm slide film (C-6) and enlarge them up to 30 inch prints, the differences from one size media to the other size media are very noticeable. Simply talk to a photo lab that does wedding photography and develops medium format images and they would be happy to show you examples of the effect. If your class was photojournalism, they may have just thought that holding a shallow DOF was not needed and therefore, not in need of mentioning.
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Re: I\'m too tired to think math..
Old 01-02-2006, 01:46 PM   #7 (permalink)
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Yeah I understand the difference in media size and the limitations respectively. I was talking more specifically about the the sensor size in digital when being used with identical lenses. Say for instance Canon 5D {fullframe sensor) vs 10D (APS size sensor)... if you shot the same image with the same f/stop same canon L lens. Would there a be a noticable difference in depth of field between the 2 sensors and if so is it constant or only noticable in one dircection? I hope that makes sense.
Bottom line is I was a 35 mm user and have a very good understanding of the "general rules" to apply when shooting 35mm... specifically aperature effects for depth of field, shutter speed (motion, avoid camera shake, stop action) and how these each apply to different lens selections. Now with digital I feel like the "general rules" that apply have changed, or shifted slightly. I am just trying to figure out what I need to be aware of.
I spent all morning looking over the information you linked to and really appreciated it. One of the things that has already bitten me once with digital is shutter speed with hand holding different focal lengths. I didn't know you were suppose to double it with smaller digital sensors from 35mm standards. This is one of the things that should have been approached in my class regarding digital usage. Oh well I am learning more from this board then the class recently. I thank I will save some money on classes and just get a lifetime membership on the board. [img]/ubbthreads/images/graemlins/grin.gif[/img]
Thanks again Brad!
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Re: I\'m too tired to think math..
Old 01-02-2006, 02:14 PM   #8 (permalink)
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Thank you for your reply! I'm glad those links and information helped! I honestly hadn't thought it all through until I kicked out $5,000 on the D2X body, took some pictures and said "what the hell is going on here?" I can also understand the issue of doubling the hand holding rule (i.e. 200mm lens means don't hand hold slower than 1/200th) as, since you have increased the distance between yourself and your subject, camera shake now accounts for a higher mathematical angle of shift during exposure. With the old 35mm format, you could get the same picture up close and a 1/2 of a degree shake wouldn't mean that much as far as where the image would hit the recording media. I haven't given the hand held rule much thought but now that you brought it up, it makes perfect sense.

Hell with classes... just join GG! [img]/ubbthreads/images/graemlins/laugh.gif[/img]
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Re: I\'m too tired to think math..
Old 01-02-2006, 06:39 PM   #9 (permalink)
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[ QUOTE ]
Taking the simple route, the mag factor in relation to a 36mm x 24mm frame would be ~4.83X and you would lose about 15% of the width. I'm thinking in terms of geometry, not optics. I'm not sure if other stuff figures in or not.

Diagonals:

24mmx36mm = 43.27mm (remember pythagoras?)
7.18mmx5.32mm = 8.84mm

8.84X = 43.27
X = 43.27 / 8.84
X = 4.89

The apsect ratios are not proportional to each other though. A 36x24 frame is an aspect ratio 1.5:1(3:2); the 7.18x5.32 is close to TV at 1.35:1(4:3)... but not exactly. It will crop off about 15% of the width.

Read military history, better than sleeping pills, try Rick Atkinson's books.

Chip

[/ QUOTE ]

Yawn.... it's 5:33pm...and I'm still waking up.. [img]/ubbthreads/images/graemlins/crazy.gif[/img]

Thank you Chip for your help!! [img]/ubbthreads/images/graemlins/smile.gif[/img]

JP
 
 
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