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06-04-2013, 10:47 PM   #31
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There is another issue to consider. A while back, someone asked about depth of field, when changing lenses / focal lengths and recompense ting for the change in focal length by repositioning. I did some work and found that depth of field remained, to a first order, constant for any aperture when doing this, it became apparent that depth of field is only a function of magnification ratio (isubject to sensor/film) and aperture and nothing else. But I would agree with many arguments that when changing sensor size , if you are going to fill the sensor, it becomes an issue.

However, having shot wildlife for over 30 years, and considering that you are never as close as you would like to be, and unless you set up in a situation where you have a blind, and sit and wait, it is unlikely that you are going to be close enough to make any difference between full frame and a crop sensor and rendering for low DOF a real issue, you are always going to be cropping the image, therefore much of the difference is lost, and once you a cropping the image depth of field calculations go out the window, because you need to go back to the origin of the circle of confusion calculation, and what it really equates to is acceptably sharp, when printed on an 8" x 10" print. Or more specifically a point of light being portrayed as a circle smaller than 1/100 of an inch or 0.25mm on the 8x10 print.

Cropping in, or over enlarging has just as much impact as aperture on depth of field.

Quite honestly, I prefer APS-C sensors for wild life due to the pixel resolution over full frame

Add to these arguments, that full frame camera evolution/ cycle time is quite slow to APS-C and you can literally be years behind in sensor development, although this is improving, but you are generally behind the 8 ball in the development of high ISO performance for most of the life time of a full frame body, compared to the latest APS-C sensors, so for wild life and most tele applications, I think cropped sensors are the way to go.

This is aside from any arguments about weight savings, and cost advantages ease of packing etc, that you will get with newer bodies on cropped sensors,

Taken to the extreme, consider a Pentax Q. I can put a 135/2.5 on the Q and have a 750mm full frame equivalent with F2.5 speed in under 700 grams including the camera.

Although the Q sensor is not quite there yet with absolute quality compared to the K5 for example, in terms of ISO and noise, you can still do exceptional things with it, and when considering ease of transport, it becomes interesting., but thatis another days discussion

06-05-2013, 04:57 AM   #32
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QuoteOriginally posted by normhead Quote
Exactly... so while DoF changes with F-number... and the DoF will be different across systems, the F-number with the same shutter and ISO will remain the same across all systems. F 2.8 on one system when looking at exposure, because the F-stop is one of the units by which exposure is measured. DoF on the other hand is the distance between the closest and furthest points in acceptable focus. It is not a measure of available light as is an f-stop, but is a distance measured in inches or mm. The cost of confusing these two measures is endless confusion, incorrect assumptions and misleading arguemnts that while factually correct in a limited perspective, create semantic juxtapositions that create factual confusion.

How's your head?

If we use the F-stop as a measure of the intensity of the light transmitted through the lens and the DoF as a distance between two points, the confusion will be eliminated. The fact that DoF changes with aperture doesn't make DoF the same as aperture. As soon as you wrap your head around that, you can see a lot of the gobbly gook around "equivalency" for what it is. Confusion caused by trying to condence two different concepts into one term.
Here is what you posted :
"you do understand that an F -stop is a measure of light transmission and doesn't directly relate to DoF don't you?

You have three camera setting choices :
shutter speed
iso
aperture

Take a guess what setting is directly related to DOF.
F stop DOF example

Last edited by jogiba; 06-05-2013 at 05:54 AM.
06-05-2013, 06:29 AM   #33
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QuoteOriginally posted by jogiba Quote
Here is what you posted :
"you do understand that an F -stop is a measure of light transmission and doesn't directly relate to DoF don't you?

You have three camera setting choices :
shutter speed
iso
aperture

Take a guess what setting is directly related to DOF.
F stop DOF example
Take a guess.
YOu need to buck up on your basic terminology.

Start with what is exposure.

Exposure is the combination of ISO (sensitivity) Shutter Speed and Aperture.

Any definition of Aperture that ignores the absolute irrefutable fact that it is an element of exposure is misleading.
Any definition of Aperture that would lead to confusion in exposure is a misuse of the term.

F 2.8 on APS-c is F 2.8 on any format. Get used to it.

Once you've got that under control... the rest will be easy.

As discussed else where you can argue rough equivalency in terms of field of view for lenses, but it doesn't really exist. There are characteristics of a 35 mm lens, that are not changed by what size sensor is behind it, and those characteristics are formed by many factors. The number of elements, the shape of the elements etc. If you think I might be in error, try and take a picture with a simple lens. Or better yet, get a lens from one of those old cheap throw away cameras. The parabolic lenses in those will totally destroy your concept of the link between F-stop and DoF forever. So while for the purposes of understanding the relationship between DoF and Aperture may be a great teaching tool, there are so many elements in lens design it doesn't address, it's not practical as more than a teaching concept. When I see a DoF chart that includes the number, shape, and composition of the elements for a given lens, I might pay a bit of attention to it. It doesn't matter how your graph is linked. When you use such an imprecise measure as describing one of your units with a simple lens, it's pretty meaningless, except in a conceptual way.

If you want to talk about DoF fine, measure it. It's measured in inches or mm. It's a distance.
If you want to talk about Aperture, think of it a a level of illumiation that's consistent across all systems.
If you want to think about different lenses, think about distortion, CA, vignetting etc.

Trying to bundle those three things, each of which come with it's own variables, and is an area of design unto itself, reducing them to their simplest form, and combining them into one concept is a recipe for mis-understanding.
06-05-2013, 09:59 AM   #34
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QuoteOriginally posted by normhead Quote
Take a guess.
YOu need to buck up on your basic terminology.

Start with what is exposure.

Exposure is the combination of ISO (sensitivity) Shutter Speed and Aperture.

Any definition of Aperture that ignores the absolute irrefutable fact that it is an element of exposure is misleading.
Any definition of Aperture that would lead to confusion in exposure is a misuse of the term.

F 2.8 on APS-c is F 2.8 on any format. Get used to it.

Once you've got that under control... the rest will be easy.

As discussed else where you can argue rough equivalency in terms of field of view for lenses, but it doesn't really exist. There are characteristics of a 35 mm lens, that are not changed by what size sensor is behind it, and those characteristics are formed by many factors. The number of elements, the shape of the elements etc. If you think I might be in error, try and take a picture with a simple lens. Or better yet, get a lens from one of those old cheap throw away cameras. The parabolic lenses in those will totally destroy your concept of the link between F-stop and DoF forever. So while for the purposes of understanding the relationship between DoF and Aperture may be a great teaching tool, there are so many elements in lens design it doesn't address, it's not practical as more than a teaching concept. When I see a DoF chart that includes the number, shape, and composition of the elements for a given lens, I might pay a bit of attention to it. It doesn't matter how your graph is linked. When you use such an imprecise measure as describing one of your units with a simple lens, it's pretty meaningless, except in a conceptual way.

If you want to talk about DoF fine, measure it. It's measured in inches or mm. It's a distance.
If you want to talk about Aperture, think of it a a level of illumiation that's consistent across all systems.
If you want to think about different lenses, think about distortion, CA, vignetting etc.

Trying to bundle those three things, each of which come with it's own variables, and is an area of design unto itself, reducing them to their simplest form, and combining them into one concept is a recipe for mis-understanding.
Are YOU for real.

06-05-2013, 10:48 AM   #35
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actually, what i'm reading from norm and on that wiki article just feuls the fun debate of APS-C vs FF.

one of the factors cited in DOF was focal length and that focal length (magnification and field of view) has a great effect on realized DOF.
I think we can all agree that a wide angle lens (20mm?)(less magnification greater FOV) at f2.8 for example will give greater DOF than a 200mm lens at f2.8.
so if you have a 200mm lens at f2.8 on and APS-C format, you should get the a nearly identical DOF as a 300mm lens on a FF because of the (magnification and FOV)

now my next point.. why we are arguing of DOF for wildlife shots, especially if the difference is 3" at 30 feet??? usually DOF is intrinsic to foreground anchoring and such, and honestly I don't want a foreground in my wildlife shots. so the relevant point norm makes, and makes sense to me, is that light transmission, (needed to elevate shutter speed for wildlife) is the same at f2.8 for any format. therefore, the OP comparison of f2.8 lens on APS-C vs FF is a valid argument.

you can argue noise etc, but that's as much a result of firmware and other factors. I could bring in the same argument about using FF glass on APS-C sensor and that it gives me better corner to corner results because of the extreme nature of making FF glass extremely sharp across the entire image circle. yes, some 8k lens can do that, but if a 1500 FF lens on an APS-C format sensor gives me the same corner to corner sharpness because the "bad" corners are already cropped for me, and I get the same light transmission (ie same iso and shutter speed to reach correct exposure), I say score one for the APS-C side

plus, I can make a counter argument (based on several articles I've read that have even more math in them that I want to weed through) that the pixel density of APS-C is going to give you better image quality than most FF. so maybe its worth dealing with a little noise for better detail. here's my thread on that topic I started:

https://www.pentaxforums.com/forums/general-photography-industry/224430-aps-c...ame-305-a.html


to answer the OP original question, I'd go with the APS-C 200 f2.8 as my winner and take the savings and get a 300 f2.8 to ALSO have a 450mm equivalent lens!....lol

Last edited by nomadkng; 06-05-2013 at 11:33 AM.
06-05-2013, 10:55 AM   #36
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QuoteOriginally posted by jogiba Quote
Are YOU for real.
That's for me to know and you to find out...
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