How do you calculate the reach advantage? Sony A900 vs Nikon D3S

Started Apr 19, 2010 | Discussions
Dave Oddie Veteran Member • Posts: 4,138
Re: Reach advantage = pixel density advantage?

Robsphoto wrote:

Thanks very much Dennis for your thoughtful reply. At a first glance, you would think that, when a 300mm lens is on two full frame cameras, there can be only one answer, that is, the reach of the two cameras is the same! And it certainly is the same if the pixel density of the two cameras is the same.

There is only one answer that the reach is the same and that it isn't related to pixel density.

They have the same reach because when taking the photograph if you filled your frame with the mythical duck mentioned below you would be stood on the same spot whichever camera you used.

But, after participating in a Canon thread that touched on the topic of “reach”, one poster said that, clearly, “pixels per duck is the only thing that makes sense”.

http://forums.dpreview.com/forums/read.asp?forum=1032&message=35045202

And, when you compare the Sony A900 with the Nikon D3S, because of its 42% higher pixel density, the A900 would have more “pixels per duck”, and therefore has a 42% reach advantage.

No it doesn't. I means the A900 duck is a higher resolution duck than the one captured by the D3s. That is all.

99% of the time people will compose their photos in the viewfinder taking advantage of the entire frame on both cameras. So the duck would fill the frame on both.

If you then cropped the A900 image to the pixel size of the D3S the duck would lose vital parts of its anatomy.

People won't routinely crop while composing using the A900 as a 12 mega-pixel camera. You could do this if stuck without your 500mm mirror lens only having say your 70-300 with you but that is not how most people will routinely use the camera. They will fill the frame with their composition on both cameras and hope to crop minimally if at all to aid composition during PP.

Dave

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Dave Oddie Veteran Member • Posts: 4,138
Re: How do you calculate the reach advantage? Sony A900 vs Nikon D3S

Cyrus84 wrote:

Dave Oddie wrote:

Robsphoto wrote:

In these circumstances, would you agree that the "reach advantage" in favour of the A900 is about 42%, which is also equal to the 42% pixel density advantage (in linear terms)? This 42% reach calculation was explained in my opening post.

There is no reach advantage. If you crop the A900 image but end up with an identical photograph to the D3S shot, you would have to have been further away in the first place (for the A900 shot) given you were using lenses of the same focal length.

You have gained nothing because you have ended up with two identical photos of the same pixel dimensions.

I disagree with this. First, you did gain something-- you took the same picture but from a greater distance (however far you had to back up to take it). If you go forwards instead of backwards, that is like taking a picture of something 100 yards away when the other camera has to walk forward 25 yards to take the same picture. You gained that 25 yards of "something."

I disagree. Taking the picture from a greater distance means you are using the A900 as a 12 mega pixel camera and composing your picture using the centre of the viewfinder. This is a compromise to not using a longer lens (if you want to be further away from the subject).

But more to the point if you fill the frame of the A900 as I am sure most users do 99% of the time you do not gain any reach over a D3S because you simply can't crop the image down that much without losing vital parts of it. What you gain with the A900 is a higher resolution image.

Secondly, as I said in another post, the perspective will completely change, so there is no way to have the same exact perspective when you use the same field of view and resolution. One of the three has to change-- either different perspective, or different field of view, or you can't crop to the same resolution.

You will end up with your subject the same size in the final output and the final output will be of the same pixel dimensions so in that sense there is no advantage. Different perspectives may or may not be appropriate for the subject.

Dave

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Mike CH Veteran Member • Posts: 9,631
Re: Cropping power of the Sony A900

Cyrus84 wrote:

Mike CH wrote:

Cyrus84 wrote:

I think "reach" means the focal length to most... 400mm has more reach than 300mm. You can't just crop to get the same field of view without changing the perspective.

Are you sure about that?

If you change from 400mm to 300mm and also change you position to maintain the same the scene, then perspective changes.

Exactly. That is what I am saying-- you cannot just crop to get the same field of view without changing the perspective.

There is no crop involved in my description above. You change the lenses, then you change your shooting position until say the width of the scene is the same. This will change the relative positions of the objects in the scene wrt to you and the camera and thus the perspective will change (the relative sizes of the objects have changed).

But if you stay in the same place (rather, the optical center of the lenses stay in the same place), do the lens change and then crop to get the same scene, then perspective should stay the same.

See, I think it is similar to another poster above. You can't do that-- if you have 24 MP versus 12 MP, when you crop down to the same resolution, you aren't getting the same scene. Therefore, the higher MP camera has to back up to get the same FOV with the same resolution.

We are not (well, I am not) talking about FF vs APS-C, but about two FFs with different pixel densities. With FF vs APS-C you are right, I think, but not with FF vs. FF.

You take two FF cameras, one with low and one with high pixel density, and use the same focal length lens of both cameras to take images from the same position. Now you crop out part of the high density image. This should be roughly equivalent (same perspective) to an image from the low density camera, but with a longer lens.

Cropping out part of an image does not change the relative sizes of the objects in the image, and thus the perspective should stay the same.

The optical center has to stay the same. Small variations will not be noticable in larger scale images, say when you are using 300mm to 400mm teles on distant subjects. Macro is different, where small variations will be more noticable.

Regards,
Mike
--
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tompower53 Veteran Member • Posts: 4,261
Can't see the forrest because there are to many trees

Dave Oddie wrote:

The A900 gives you the ability to crop more aggressively compared to a D3S that is all. Talk of a reach advantage is misleading and unhelpful in my opinion.

So tell me - what is the difference between reach advantage and cropping power when you are looking at a photo of a duck flying by?

Yes the peripheral elements in the photo will have a different perspective but we are looking at the duck.

For practical purposes for most people who are using telephoto lenses on APSC the "reach advantage - cropping power" are the same thing and helpful when printing an image, framing a shot and especially buying the gear. Must have a high quality lens though.

This whole discussion is lost in the confusion of scientific fact versus practical application. Forests and trees. But factually speaking for sure there is not a "reach advantage" just as a push up bra does not make breasts bigger. Tell that to a young woman going out on a hot date though and she will say - WTF are you talking about? My boy friend sure thinks there is a difference!

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Cyrus84 Senior Member • Posts: 1,862
Re: Can't see the forrest because there are to many trees

tompower53 wrote:

Dave Oddie wrote:

The A900 gives you the ability to crop more aggressively compared to a D3S that is all. Talk of a reach advantage is misleading and unhelpful in my opinion.

So tell me - what is the difference between reach advantage and cropping power when you are looking at a photo of a duck flying by?

Yes the peripheral elements in the photo will have a different perspective but we are looking at the duck.

For practical purposes for most people who are using telephoto lenses on APSC the "reach advantage - cropping power" are the same thing and helpful when printing an image, framing a shot and especially buying the gear. Must have a high quality lens though.

This whole discussion is lost in the confusion of scientific fact versus practical application. Forests and trees. But factually speaking for sure there is not a "reach advantage" just as a push up bra does not make breasts bigger. Tell that to a young woman going out on a hot date though and she will say - WTF are you talking about? My boy friend sure thinks there is a difference!

I give up debating it... I agree with you. There is some confusion as to what we are talking about here.

To the posters who quoted me before-- couple of thoughts.

1- There is no difference between the APS-C and cropping with a FF. So you can compare APS-C and FF and whatnot-- The point of it is if you have a higher resolution image zoomed out, you can crop in and get the same resolution image "zoomed in."

2- Forget changing perspective. The OP point is that with a 200mm lens and a 12 MP FF, you can take a picture of 4 bushes and get this image: XXXX

Now, with 24 MP FF and the same lens, but backing up, you can get this image: XXXXXX. Now, cropping on just the middle XXXX, you get the same image as the 12 MP FF but from a greater distance.

Is this that hard to understand? I don't know why anyone is talking about filling the viewfinder-- while that might be how people shoot when composing a landscape, we are talking about distant objects that you CAN'T fill the viewfinder with. So by cropping, you CAN.
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Cyrus84 Senior Member • Posts: 1,862
Re: Cropping power of the Sony A900

Mike CH wrote:

Cyrus84 wrote:

Mike CH wrote:

Cyrus84 wrote:

I think "reach" means the focal length to most... 400mm has more reach than 300mm. You can't just crop to get the same field of view without changing the perspective.

Are you sure about that?

If you change from 400mm to 300mm and also change you position to maintain the same the scene, then perspective changes.

Exactly. That is what I am saying-- you cannot just crop to get the same field of view without changing the perspective.

There is no crop involved in my description above. You change the lenses, then you change your shooting position until say the width of the scene is the same. This will change the relative positions of the objects in the scene wrt to you and the camera and thus the perspective will change (the relative sizes of the objects have changed).

Perspective is dependent on distance, not lens. If you back up and shoot with a 300mm lens, instead of a 400mm lens, but then crop to the same FOV as the 400mm lens, the perspective is identical.

That is probably why we are confusing each other in talking about it. Instead of phrasing it this way, we can say that if you aim at a distant building with both cameras, the 24 MP can shoot at 300mm and crop to the same FOV and perspective as the 12 MP at 400mm*. ( Not sure the exact focal length, but you get the gist of it)

But if you stay in the same place (rather, the optical center of the lenses stay in the same place), do the lens change and then crop to get the same scene, then perspective should stay the same.

See, I think it is similar to another poster above. You can't do that-- if you have 24 MP versus 12 MP, when you crop down to the same resolution, you aren't getting the same scene. Therefore, the higher MP camera has to back up to get the same FOV with the same resolution.

We are not (well, I am not) talking about FF vs APS-C, but about two FFs with different pixel densities. With FF vs APS-C you are right, I think, but not with FF vs. FF.

I am talking about cropping from a full frame camera, which is exactly the same as having an APS-C sensor. The pixel density makes a difference as well, but you can't separate the crop factor in what we are talking about.

You take two FF cameras, one with low and one with high pixel density, and use the same focal length lens of both cameras to take images from the same position. Now you crop out part of the high density image. This should be roughly equivalent (same perspective) to an image from the low density camera, but with a longer lens.

Cropping out part of an image does not change the relative sizes of the objects in the image, and thus the perspective should stay the same.

The first paragraph above says that the 24MP sensor can be cropped to mimic the 12 MP sensor with a longer lens. That is what I am saying. That is more "Reach", although reach is a bad word for it.

Now, the second paragraph is where we look at it differently. My point is that you are trying to bring a distant object into focus, so you can be further back to get the same FOV as the 12 MP with the same lens. Therefore, different perspective.

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Dennis Forum Pro • Posts: 18,963
Half semantics, half calculations

Half the issue is semantic. You can argue that shooting with a higher res sensor lets you crop therefore giving you the same image that you'd get with a longer tele. I certainly understand the concept, but don't like suggesting that it gives you more reach.

The other half is in the calculations and none of Robs replies have addressed this. Just because you have 42% more pixels in each dimension doesn't mean you've captured 42% more detail. DPReviews tests show that the A900 captures only 22% more detail in each dimentions, and that's under ideal conditions, not with a long tele lens under possibly sub-optimal shooting conditions. So even if you wanted to say that the extra detail-recording capability of the high res sensor effectively gives you more reach, you'd be incorrect in basing the amount of added reach on the pixel counts.

  • Dennis

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copejorg1 Senior Member • Posts: 1,626
Re: Half semantics, half calculations

Dennis wrote:

Half the issue is semantic. You can argue that shooting with a higher res sensor lets you crop therefore giving you the same image that you'd get with a longer tele. I certainly understand the concept, but don't like suggesting that it gives you more reach.

The other half is in the calculations and none of Robs replies have addressed this. Just because you have 42% more pixels in each dimension doesn't mean you've captured 42% more detail. DPReviews tests show that the A900 captures only 22% more detail in each dimentions, and that's under ideal conditions, not with a long tele lens under possibly sub-optimal shooting conditions. So even if you wanted to say that the extra detail-recording capability of the high res sensor effectively gives you more reach, you'd be incorrect in basing the amount of added reach on the pixel counts.

You stated the concept very well. However, I personally don't mind the suggestion that a higher pixel density gives you more "reach", because in a practical sense, that's exactly what it does. But I do agree that calculating the actual increase in reach is far more complicated than simply ratioing the pixel dimensions, and would also change for different shooting conditions.
--
Greg

Mike CH Veteran Member • Posts: 9,631
Re: Cropping power of the Sony A900

Cyrus84 wrote:

Mike CH wrote:

There is no crop involved in my description above. You change the lenses, then you change your shooting position until say the width of the scene is the same. This will change the relative positions of the objects in the scene wrt to you and the camera and thus the perspective will change (the relative sizes of the objects have changed).

Perspective is dependent on distance, not lens. If you back up and shoot with a 300mm lens, instead of a 400mm lens, but then crop to the same FOV as the 400mm lens, the perspective is identical.

That is probably why we are confusing each other in talking about it. Instead of phrasing it this way, we can say that if you aim at a distant building with both cameras, the 24 MP can shoot at 300mm and crop to the same FOV and perspective as the 12 MP at 400mm*. ( Not sure the exact focal length, but you get the gist of it)

Yes. We basically mean the same thing (apart from one little quibble below).

Those discussions always come from different terminology. One of the reasons why I didn't like Robs new use of reach

But if you stay in the same place (rather, the optical center of the lenses stay in the same place), do the lens change and then crop to get the same scene, then perspective should stay the same.

See, I think it is similar to another poster above. You can't do that-- if you have 24 MP versus 12 MP, when you crop down to the same resolution, you aren't getting the same scene. Therefore, the higher MP camera has to back up to get the same FOV with the same resolution.

You take the shot and then crop. The crop and the original do not show the same scene, of course. But the crop shows a part of the original scene, enlarged if you want. The cropped image thus has the same perspective as the original.

The first paragraph above says that the 24MP sensor can be cropped to mimic the 12 MP sensor with a longer lens. That is what I am saying. That is more "Reach", although reach is a bad word for it.

Right to both parts.

Now, the second paragraph is where we look at it differently. My point is that you are trying to bring a distant object into focus, so you can be further back to get the same FOV as the 12 MP with the same lens. Therefore, different perspective.

No, the crop part changes that.

Regards,
Mike
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Robsphoto
OP Robsphoto Senior Member • Posts: 1,219
Images that show the relationship between A900 and D3S

Cyrus84 wrote:

Mike CH wrote:

Cyrus84 wrote:

I think "reach" means the focal length to most... 400mm has more reach than 300mm. You can't just crop to get the same field of view without changing the perspective.

I really appreciate the time people have put in to give their views on this topic. I thought it might help the discussion if I put on my site three photographs that show the differences between the images we have been talking about. So, I have quickly prepared this temporary page:

http://www.robsphotography.co.nz/reach.html

The images on the above page are approximately to scale.

Image 1 was taken with a 300mm lens and it has dimensions of 6048 pixels x 4032 pixels (Sony A900 dimensions).

Image 2 was taken with a 300mm lens and it has dimensions of 4256 pixels x 2832 pixels (Nikon D3S dimensions).

Images 1 and 2 have the same field of view, but because the pixel density (in pixels per linear centimetre) of the A900 is about 42% greater than that of the D3S, Image 1 is 42% wider than Image 2.

Image 3 is a crop of Image 1. It has been cropped from 6048 pixels x 4032 pixels to 4256 pixels x 2832 pixels. This cropped image effectively increases the "reach" of Image 1 by 42% from 300mm to 426mm (6048 pixels / 4256 pixels x 300mm = 426mm).

From what I can see, we need to have a definition of the term "reach" that most people are happy with. How would you define the term "reach"?

Perhaps the term "field of view" might be more understandable? In other words, when describing the cropped image (Image 3), we could simply say that it changes the field of view (as shown in Image 1) from 300mm to 426mm. Would you be happier with this description? Or is there some other terminology you prefer?

Thanks very much for your feedback.

Regards
Rob
http://www.robsphotography.co.nz/focal-length.html

Article about the advantages and disadvantages of cropping images to gain extra reach

Robsphoto
OP Robsphoto Senior Member • Posts: 1,219
Re: A900 vs A700: reach advantage of A700 is 7.9%?

copejorg1 wrote:

Robsphoto wrote:

I agree that the "extra reach" of the A700 over the A900 is not very significant, in fact it is only 7.9%, as shown on this web page:

http://www.robsphotography.co.nz/crop-factor-advantage-s700-s900.html

Tell us whether or not you agree with the following calculations:

I agree in principle; but your numbers are off by a little bit, because you're using a pixel size that's inferred from sensor size dimensions that are not precise, rather than using the actual pixel sizes published by the sensor manufacturers.

The 7.9% gain in reach (in favour of the A700) arises only because the pixel density of the A700 (in pixels per linear centimetre) is 7.9% greater than that of the A900 (1818 / 1685).

The actual gain is more like 8.2%. The A700 pixel size (as published by Sony) is 5.49 microns. The A900 pixel size (also as published by Sony) is 5.94 microns. So, rather than go to the trouble of (imprecisely) calculating some figures for pixels per centimeter, all you really had to do was ratio the sizes of the pixels themselves. And this ratio of 5.94/5.49 is equal to 1.082, or a gain of 8.2%.

Calculation of reach advantage: Reach of A700 with a 300mm lens = 458.3mm (300mm x 35.9/23.5).

The effective sensor width of the A900 is only approximately 35.9mm, just as the effective sensor width of the A700 is only approximately 23.5mm. That's the source of the small error in your calculations. Using the actual pixel size eliminates the need even to know the sensor size, or to calculate "effective" focal lengths (as you did below) when calculating the "reach advantage" being discussed. But if you did want to calculate the effective sensor size accurately, you would do it this way ...

For the A700:

Sensor width = 4272 pixels * .00549mm/pixel = 23.45328mm
Sensor height = 2848 pixels * .00549mm/pixel = 15.63552mm

For the A900:

Sensor width = 6048 pixels * .00594mm/pixel = 35.92512mm
Sensor height = 4032 pixels * .00594mm/pixel = 23.95008mm

For the Nikon D3S:

Sensor width = 4256 pixels * .00845mm/pixel = 35.9632mm
Sensor height = 2832 pixels * .00845mm/pixel = 23.9304mm

All a bit pedantic, I know -- but if you're going to be reporting an "advantage" or whatever, down to a tenth of a percent (as you are), you need to be calculating it the right way.

Reach of A900 when an image is cropped to the same image width as A700 = 424.7mm (6048 / 4272 x 300mm).

Gain in reach of the A700 = 7.9% (458.3mm / 424.7mm)

Regards,
--
Greg

Thanks very much Greg for this interesting information. The source of my information was the specifications for the A700 and the A900 that are published on the DPR web site:

http://www.dpreview.com/reviews/compare_post.asp?method=sidebyside&cameras=sony_dslra900%2Csony_dslra700&show=all

I see that the DPR summaries of camera specifications are widely used by people on these forums.

I guess roundings are always going to have a small effect on the final answers you arrive at. For example, I see from the figures you provide, that the crop factor of the A700 is in fact 1.5318 (35.92512 / 23.45328).

But, if you use the DPR figures quoted above, the sensor width of the Sony A900 is given as 35.9mm, and for the A700 it is 23.5mm. This gives a crop factor of 1.528, so the difference between 1.528 and 1.5318 isn’t that great, particularly if you round them both to 1.53!

But, it's interesting that everyone actually uses a crop factor of 1.5 for the A700, so we seem to accept roundings for this!

The examples I have given are purely to illustrate the principles involved, so it might be better to stick with "theoretical cameras", where the mathematical relationships can be precisely set, as in this example:

http://www.robsphotography.co.nz/crop-factor-advantage-appendix-3.html

With an example like this, you can (hopefully) see at a glance that the calculations are correct and make sense!

Regards
Rob

Dennis Forum Pro • Posts: 18,963
Re: Images that show the relationship between A900 and D3S

I'm not sure why you're pushing this flawed concept so much.

42% more pixels does not mean 42% more detail, and additional detail is the only thing that matters in your arguments. You can always upscale a D3S image and the whole argument goes away unless you can demonstrate that it has less detail.

Putting dummied up photos to demonstrate the concept (a D3S "sized" image shot with an A900) only helps to illustrate the concept, not to prove anything.

More pixels on the sensor = potential to capture more detail which is always beneficial in large prints and/or crops. But that added detail isn't guaranteed (it depends on the lens and long teles don't tend to hit Nyquist frequencies for high res sensors the way 50's do) and it isn't proportional to the increase in photosite density (as demonstrated by dpreview resolution tests). If you're not capturing substantially more detail, just uprez the D3S files by 42% in each dimension and you match the A900.

That's all we're talking about here. I don't see where anyone benefits from an alternate way of looking at it, especially when you provide math to suggest "reach" equivalents based on flawed assumptions.

I applaud your efforts to put up pages like this for the purpose of educating people, but in this case, you're spreading misinformation.

  • Dennis

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copejorg1 Senior Member • Posts: 1,626
Re: A900 vs A700: reach advantage of A700 is 7.9%?

Robsphoto wrote:

Thanks very much Greg for this interesting information. The source of my information was the specifications for the A700 and the A900 that are published on the DPR web site:

http://www.dpreview.com/reviews/compare_post.asp?method=sidebyside&cameras=sony_dslra900%2Csony_dslra700&show=all

I see that the DPR summaries of camera specifications are widely used by people on these forums.

And that's fine, as long as it is recognized that those figures are approximations, based on approximate sensor sizes. Thus, calculations of other properties deriving from that data (crop factor, pixel size, "reach", etc) will have errors inherent to them. That's the only reason I called you out on your "7.9%" figure in the OP of this thread. If you'd said "8%", there would've been no issue, and I wouldn't have commented. But since adding the next significant digit made the true answer to be 8.2%, your 7.9% figure was definitely incorrect at that level of precision.

I guess roundings are always going to have a small effect on the final answers you arrive at. For example, I see from the figures you provide, that the crop factor of the A700 is in fact 1.5318 (35.92512 / 23.45328).

Well, sort of. But here's a minor point: I wouldn't use the A900's sensor size as the baseline for calculating crop factor. I would use the nominal frame size of 35mm film for that -- 36mm X 24mm. Thus, the crop factor of the A700 would have been more properly stated (IMO) as 1.5350 (36 / 23.45328, or alternatively, 24 / 15.63552).

Another minor point: I prefer using the sensor height (the short dimension) for calculating crop factor (and for other purposes, such as calculating CoC size for use in DOF calculations, etc), because for some odd reason, most non-Canon DSLR sensors have "extra" pixels in the long direction -- giving them an aspect ratio a bit greater than the true 3:2 aspect ratio of 35mm film. And since most print formats have an aspect ratio either equal to or less than 3:2, those "extra" pixels in the long direction are usually going to end up being cropped away, anyhow (either deliberately by the user, or automatically by the print driver, to prevent white borders along the long edges of the print). So, the short direction is the only one in which you would consistently be actually making use of all of the available pixels.

For example, Nikon masks the 12MP APS-C Sony sensor in their 12MP "DX" DSLRS (D300, D90, D5000) differently than Sony did for the A700, resulting in an output resolution of 4288 X 2848 -- the same as the A700 in the short direction, but with an extra sixteen pixels beyond the true 3:2 ratio in the long direction. Or another example (out of many others I could have chosen), would be the 14MP sensors in the Sony A380 (CCD) and A550 (CMOS) -- both of which have output resolutions of 4592 X 3056. In these, the long dimension contains an additional eight pixels beyond the true 3:2 ratio. I don't know why they do this, but they nearly always do.

And now, an exception to the above (before someone even more anal about this stuff than I am points it out to us): The 10MP Sony CCD sensors used in various Sony, Nikon and Pentax DSLRs went the other way, using fewer than 1.5X as many pixels in the long direction as in the short direction. In this case, the output resolution is 3872 X 2592 -- with sixteen fewer pixels in the long direction than would be dictated by a true 3:2 ratio.

I guess the lesson we can take from the above is, if you really want an exact 3:2 aspect ratio in your DSLR sensor, then buy either a Canon or a Sony A700/850/900 or a Nikon D3X (no other DSLR I'm aware of meets that criterion). Or, just do the sensible thing and don't worry about the small discrepancy in all those other cameras.

But, if you use the DPR figures quoted above, the sensor width of the Sony A900 is given as 35.9mm, and for the A700 it is 23.5mm. This gives a crop factor of 1.528, so the difference between 1.528 and 1.5318 isn’t that great, particularly if you round them both to 1.53!

True.

But, it's interesting that everyone actually uses a crop factor of 1.5 for the A700, so we seem to accept roundings for this!

And that's certainly close enough for practical purposes, but it isn't exact. The discrepancy will often make a difference of a few millimeters in the "equivalent" focal lengths calculated for crop-sensor DSLRs. For example, the "equivalent" focal length of a 200mm lens used on an A700 would be 307mm when using the actual sensor dimensions -- not 300mm, as is usually calculated via the 1.5X approximation for CF.

The examples I have given are purely to illustrate the principles involved, so it might be better to stick with "theoretical cameras", where the mathematical relationships can be precisely set, as in this example:

http://www.robsphotography.co.nz/crop-factor-advantage-appendix-3.html

With an example like this, you can (hopefully) see at a glance that the calculations are correct and make sense!

Agreed. For illustrating basic principles, it's a lot easier to use rounded numbers for sensor sizes and resolutions, pixel dimensions, etc. As long as it's pointed out that in the "real world", the actual calculations won't be as clean and nice as that.

And I'll also note (as Dennis has been pointing out in this thread) that there's a lot more that goes into a true calculation of "extra reach", or "extra croppability" (which is basically the same thing), than ratioing the pixel density alone. Other factors, including relative low-pass filter strength, diffraction effects at higher F-numbers, and so on, will also play into it.

Regards,
--
Greg

(unknown member) Senior Member • Posts: 1,181
Pointless article...

which adds to an already long list of pointless articles. Not sure if that generates the traffic you're craving for.

Robsphoto
OP Robsphoto Senior Member • Posts: 1,219
How do you calculate the reach advantage? Sony A900 vs Nikon D3S

JulienA wrote:

which adds to an already long list of pointless articles. Not sure if that generates the traffic you're craving for.

I am certainly craving for knowledge that is based on fair and balanced reasoning. As for traffic, I have no interest in that because the site is purely a hobby site. Now, come on JulienA, be kind to people, it doesn't really hurt! You could make the same comment about most photography articles that have been written, but as long as they make you think, they are far from pointless. Have a nice day.....

Cheers, Rob

Robsphoto
OP Robsphoto Senior Member • Posts: 1,219
Re: Images that show the relationship between A900 and D3S

Dennis wrote:

I'm not sure why you're pushing this flawed concept so much.

42% more pixels does not mean 42% more detail, and additional detail is the only thing that matters in your arguments. You can always upscale a D3S image and the whole argument goes away unless you can demonstrate that it has less detail.

Putting dummied up photos to demonstrate the concept (a D3S "sized" image shot with an A900) only helps to illustrate the concept, not to prove anything.

More pixels on the sensor = potential to capture more detail which is always beneficial in large prints and/or crops. But that added detail isn't guaranteed (it depends on the lens and long teles don't tend to hit Nyquist frequencies for high res sensors the way 50's do) and it isn't proportional to the increase in photosite density (as demonstrated by dpreview resolution tests). If you're not capturing substantially more detail, just uprez the D3S files by 42% in each dimension and you match the A900.

That's all we're talking about here. I don't see where anyone benefits from an alternate way of looking at it, especially when you provide math to suggest "reach" equivalents based on flawed assumptions.

I applaud your efforts to put up pages like this for the purpose of educating people, but in this case, you're spreading misinformation.

Thanks for your comments Dennis, but in my humble opinion, I am not misinforming anyone. Rather the opposite, because I am seeking in a fair and balanced way the views of people on how they interpret the term “reach”. This thread seems to show that there is not just one way of interpreting this term, and this is why some people will interpret the information I have given in a different way to others.

I realise that, when deciding whether to buy a 12mp or a 24mp full frame camera, there are hosts of quality issues that need to be assessed when you are making a decision as to whether you should purchase one camera or another.

But, “all things being equal”, if you buy a 24mp full frame camera, this undoubtedly gives you the scope to crop a 24mp image to the same image size as the 12mp image, and in doing so, gain a “greater telephoto field of view” than you can get from the equivalent 12mp image.

Now, whether or not this “greater telephoto field of view” should be defined as a “reach advantage” and whether this “advantage” can be properly measured, is what this thread is about.

How do you think the greater magnification that is obtained from the cropped 24mp image should be defined?

You talk about upscaling, or uprezzing images, but doesn’t this raise as many potential quality / technical issues as cropping an image does? I feel safer cropping the larger image to the size of the smaller image, and this is why my notes have been based on this approach.

Regards
Rob
http://www.robsphotography.co.nz/focal-length.html
Advantages and disadvantages of cropping images to gain extra reach

Robsphoto
OP Robsphoto Senior Member • Posts: 1,219
Re: A900 vs A700: reach advantage of A700 is 7.9%?

copejorg1 wrote:

And I'll also note (as Dennis has been pointing out in this thread) that there's a lot more that goes into a true calculation of "extra reach", or "extra croppability" (which is basically the same thing), than ratioing the pixel density alone. Other factors, including relative low-pass filter strength, diffraction effects at higher F-numbers, and so on, will also play into it.

Regards,
--
Greg

Thanks for an informative post, your feedback is appreciated. You talk about a “true calculation” of extra reach. Can such a thing be done in a mathematical way? At least, when “ratioing the pixel density” it gives you some idea of what the “magnified field of view” is compared with an uncropped image.

In my opening post, I said that:

“If you apply the principles in the article linked to above, do you agree that, when an image from the A900 is cropped to the same image width as the D3S (4256 pixels), this effectively increases the “reach” of an A900 image by 42% from 300mm to 426mm (6048 / 4256 x 300mm).” Do you agree with this calculation? Even if the word “reach” is debateable, do you agree with the calculation of 426mm?

I have made a temporary web page that shows the relationship of these images:

http://www.robsphotography.co.nz/reach.html

Wouldn’t you agree that Image 3 on the above page is approximately equivalent to what you would get if you were to use a 426mm lens on the Nikon D3S?

By cropping the 24mp image to the same size as the 12mp image, the field of view in Image 3, IMHO has changed from its initial field of view of 300mm to 426mm, and this principle is worth knowing when you are choosing between a 12mp and a 24mp full frame camera. Perhaps I should just state this fact, that the “field of view” has changed from 300mm to 426mm, and leave the debate as to whether or not this a “reach” advantage to PhD scholars?

With regard to the specifications published by DPR, I didn’t see anywhere that they were only approximations and that you should go to the manufacturers’ own specifications rather than placing reliance on the DPR ones. So, IMHO the maths I have given is accurate based on the DPR specs!

Regards
Rob

Dennis Forum Pro • Posts: 18,963
Re: Images that show the relationship between A900 and D3S

Robsphoto wrote:

How do you think the greater magnification that is obtained from the cropped 24mp image should be defined?

As a crop. Again, you can crop a D3S image as well. The 24MP sensor gives you the potential for greater detail, but it's not a simple mathematical formula based on pixel counts.

You talk about upscaling, or uprezzing images, but doesn’t this raise as many potential quality / technical issues as cropping an image does?

My point in raising it was to bring up the quality issue. Having more MP is only beneficial than few MP for cropping to the extent that the more MP captures more detail. And 42% more pixels doesn't capture 42% more detail. How much it captures varies widely; dpreviews test shows a 22% gain with a good, sharp prime (usually a 50mm is used) while (many) long teles don't resolve as much detail as that to begin with, so in practice, you may very well capture nearly as much detail with a D3S as an A900, depending on the tele lens.

I feel safer cropping the larger image to the size of the smaller image, and this is why my notes have been based on this approach.

I agree, but the article and the math provided suggest a 42% pixel count provides 42% more detail for cropping and that's misleading. I'd love to see a demonstration using actual D3S images (and not A900 images sized to D3S specs).

  • Dennis

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Dennis Forum Pro • Posts: 18,963
Also

Cropping gives you the equivalent of a smaller sensor image, meaning lower signal-noise ratio, than using a longer lens, so that's another sense in which the ability to crop is not the same as 'reach'.

  • Dennis

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Dennis Forum Pro • Posts: 18,963
Re: A900 vs A700: reach advantage of A700 is 7.9%?

Robsphoto wrote:

By cropping the 24mp image to the same size as the 12mp image, the field of view in Image 3, IMHO has changed from its initial field of view of 300mm to 426mm,

"If you shoot 300mm and crop 24MP to 12MP your FOV changes to that of a 426mm lens uncropped".

Assuming the math is right, THAT I can agree with !

and this principle is worth knowing when you are choosing between a 12mp and a 24mp full frame camera.

I think everyone understands that a higher res sensor gives you more room to crop. But how much is variable & depends on the shot. Cropping 24MP to 12MP may result in too little detail and/or too much image noise for your taste.

Perhaps I should just state this fact, that the “field of view” has changed from 300mm to 426mm, and leave the debate as to whether or not this a “reach” advantage to PhD scholars?

Sounds like you'll be eliminating the parts that are debatable

  • Dennis

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