Clear answer on longer lens over crop body?

Hi I'm a wildlife photographer and I find the hardest thing to do is fill the frame with the subject, Although I do have places I can get close shots I find often I'm having to crop in a lot even when I'm only 10-15meters away from small birds.

My Current wildlife set up is a 7D and a 400mm F5.6 L, and I'm almost always cropping my final image so it's under 10 megapixels, often around 5Mpx. I've looked at images from a local wildlife photographer who shoots wtih a 1Dmk4 but use to shoot with a Mk3 and a 500mm F4 L, and he gets images that seem much more detailed and appear much less cropped than mine do. Working it out I figured it must be my technique as the 400mm x 1.6 crop would equal 640mm and the 500mm and 1.3 crop of the 1Dmk3/4 equals 650mm.

But now however from working things out and briefly reading over things I believe that what is true is that crop factor will help to fill the image or "magnifiy" onto the frame what i see with the 400mm and the 7D, but because this guy is using a 500mm lens the subject is bigger in the frame already and is "magnified" less by the 1.3 crop but this doesn't matter as much as the 500mm is obviously bringing out much more subject detail with that extra 100mm, than I'm getting with the extra crop of the 7D, as it's really just cropping in the field of view and not actually magnifying detail of distant subjects at all really.

Could someone please confirm that is true but keep it fairly simple, even though I don't think I have in the question lol If I had a a pair of different sensor size camera's I'd test this out but I don't sadly.


**Note** I have noticed the X-factor thread but all of the posts seem over complicated to the simple answer I am curious to know.

Longer lens will always win over simply cropping and enlarging

If the images are being cropped a lot from the original size they were shot with, then it doesn't matter what size the sensor was (FF, 1.3 or 1.6), it matters what the properties of the sensor are "per area" as well as the technical skills of the operators both in taking and processing the images. This is where the pixel size, microlens array etc make a difference as well as the operator being able to get the shutterspeed high enough for the tripod support being used, the aperture large enough so diffraction blur is minimized, focus technique is critical etc etc The 7D and the 4005.6 is a very good combination but requires a high degree of skill in the whole chain from set-up to processing to make the most of.

Let's use your exact comparison...400mm on APS-C vs. 500mm on FF. Let's assume a 1' tall object is 1000' away. With APS-C it will see a 37.45' tall area, while FF will see a 47.92' tall area. The 1' tall object will be 1/37.45th of the 15mm frame on APS-C, while covering 1/47.92th of the 24mm frame on FF (yeah, I know 7D is 14.9mm, not 15mm, but my frame capture software assumes 15mm tall APS-C frame!). So the object is 0.4005mm on APS-C and 0.5008mm on FF sensor.

Let us also assume that the 400mm lens and the 500mm lens both have identical detail resolution and contrast, and both deliver 100 line-pairs/mm of resolution (a superb lens) to the sensor plane. So the APS-C image is portraying the 1' tall object with 40.05 ll, while the FF image is portraying that same object with 50.08 lines. So at the sensor the FF is already winning with 20% more detail delivered by the lens.

But wait, we still have not made a print! So we enlarge both images to 8x12". The FF image uses 8.47x enlargement to make the 8x12, while the APS-C image uses 13.55x enlargement. So the FF sensor yields 11.8 lines of resolution per mm on the print (100/8.47 = 11.8 ), while the APS-C sensor yields 7.3 lines of resolution per mm on the print (100/13.55 = 7.3). So the eye will also perceive the 8x12 from the FF as 'sharper'.

So we are evaluating the lens-delivered performance above. Next we deal with the sensor and its pixels...

We saw that we used 0.4005 of the APS-C sensor and 0.5008 of the FF sensor to capture the 1' tall object which is 1000' away. The 7D would have 92.9 pixels to portray that 1' tall object, while the 1DsIII would have 78.1 pixels. So the 7D actually has 18.95% better pixel count to capture that 1' tall object. This demonstrates the so-called 'better reach' of APS-C based on pixel count alone (at least, for the two cameras chosen for this analysis). But let's now factor that along the effective lens resolution...we have a 25% advantage of FF for lens-delivered resolution which is then offset by 18.95% advantage of APS-C for pixel count, so FF still wins the detail 'war' by 5%! And it still has the magnification print resolution advantage, too.

Wilt, the other guy was using a 1.3x 1D, not full frame. I don't know for certain but I'd assume the crop 1D has a lower pixel density and would probably be at a disadvantage to the 7D in this case.

The Ran wrote in post #10891838
Wilt, the other guy was using a 1.3x 1D, not full frame. I don't know for certain but I'd assume the crop 1D has a lower pixel density and would probably be at a disadvantage to the 7D in this case.

Well, I ain't gonna do that analysis over again! The 1DIII has a smaller sensor to factor in, too. The proof of that comparison is left to the student to perform.

Ok, I'm gonna relent...

400mm on APS-C vs. 500mm on APS-H. Let's assume a 1' tall object is 1000' away. With APS-C it will see a 37.45' tall area, while FF will see a 47.92' tall area. The 1' tall object will be 1/37.45th of the 15mm frame on APS-C, while covering 1/38.14th of the 27.8mm frame on APS-H (my frame capture software assumes 27.8mm tall 1DII APS-H frame!). So the object is 0.4005mm on APS-C and 0.7288mm on APS-H sensor. So the APS-H image of the 1' tall object uses 100 pixels on APS-H vs. the 92.9 pixels of APS-C. Advantage 7.6% better pixels in APS-H, and advantage is 25% better for APS-H on lens resolution on print, too.

[edit] I re-ran the numbers in a later post...I used some wrong figures in a hurried calculation. The proof is still left to the student to determine of the 'teacher' goofed later! I admit this goof.

The 500/4 is better than the 400/5.6, too...more resolution to start with.

Wilt wrote in post #10891990
Ok, I'm gonna relent...

400mm on APS-C vs. 500mm on APS-H. Let's assume a 1' tall object is 1000' away. With APS-C it will see a 37.45' tall area, while FF will see a 47.92' tall area. The 1' tall object will be 1/37.45th of the 15mm frame on APS-C, while covering 1/38.14th of the 27.8mm frame on APS-H (my frame capture software assumes 27.8mm tall 1DII APS-H frame!). So the object is 0.4005mm on APS-C and 0.7288mm on APS-H sensor. So the APS-H image of the 1' tall object uses 100 pixels on APS-H vs. the 92.9 pixels of APS-C. Advantage 7.6% better pixels in APS-H, and advantage is 25% better for APS-H on lens resolution on print, too.

Is that assuming the same pixel density though? To match the 7D's 18mp the 1Ds would have to have around 22mp, which I assume it doesn't as I think the full frame version has about 24mp and I believe the 7D and 550D are the highest for crop.

Wilt wrote in post #10891990
Ok, I'm gonna relent...

400mm on APS-C vs. 500mm on APS-H. Let's assume a 1' tall object is 1000' away. With APS-C it will see a 37.45' tall area, while FF will see a 47.92' tall area. The 1' tall object will be 1/37.45th of the 15mm frame on APS-C, while covering 1/38.14th of the 27.8mm frame on APS-H (my frame capture software assumes 27.8mm tall 1DII APS-H frame!). So the object is 0.4005mm on APS-C and 0.7288mm on APS-H sensor. So the APS-H image of the 1' tall object uses 100 pixels on APS-H vs. the 92.9 pixels of APS-C. Advantage 7.6% better pixels in APS-H, and advantage is 25% better for APS-H on lens resolution on print, too.

I'm confused by something here. The bold bit doesn't look quite right, Wilt. If the image of a 2 foot tall duck from a 400 mm lens is ~0.8 mm on a sensor (or any surface really), then, with the same duck viewed from the same place, the image from a 500 lens should be ~1 mm, on any sensor, no? The 7D would have 160 pixels (from the 400mm lens) while , say, the 5D2 would give 156 pixels (from the 500 lens - or 125 with the 400 lens)To make a print of this duck that will be 1" tall we will enlarge from either 0.8 or 1 mm to ~25mm i.e. a 31x or a 25x enlargement. The difference in enlargement is due to the use of two different lenses, not the different sensors. In post #4 you talk of making an 8x12 print, but in this situation, that is very unlikely , IMHO - therefore we should ignore the parts of the image that are not relevant - the parts that have been cropped. Therefore the size of the whole sensor is eliminated from calculations and we are just left with sensor and lens resolution. Clearly if one takes the same lens on the two different cameras, the one with the higher pixel density will capture more detail - not necessarily in proportion to the pixel size difference (it will be limited by the lens's MTF fall-off curve) but it will be more, assuming diffraction is not relevant and the taking skills are excellent etc.....

Back to the OP
If cropping is happening in both your case and your friend's case, then the SIZE of the sensor (crop, X or "format" factor) does not play a role.

Maximono wrote in post #10891636
Working it out I figured it must be my technique as the 400mm x 1.6 crop would equal 640mm and the 500mm and 1.3 crop of the 1Dmk3/4 equals 650mm.

But now however from working things out and briefly reading over things I believe that what is true is that crop factor will help to fill the image or "magnifiy" onto the frame what i see with the 400mm and the 7D, but because this guy is using a 500mm lens the subject is bigger in the frame already and is "magnified" less by the 1.3 crop but this doesn't matter as much as the 500mm is obviously bringing out much more subject detail with that extra 100mm, than I'm getting with the extra crop of the 7D, as it's really just cropping in the field of view and not actually magnifying detail of distant subjects at all really.

It appears to me that you don't really understand the "crop factor" basics, so I will try to help.

In your first paragraph above, you are calculating what's known as "35mm equivalent focal lengths". This is fine, as long as you understand what's happening. What you are doing in both cases (APS-C and APS-H calculations) is determining what focal lengths would give you the same field (angle) of view on a 35mm film format camera (which includes several so-called "full-frame" DSLRs).

Your second paragraph, however, is where I get the idea that you don't understand the facts. There is no "magnification" going on when you use different format cameras. The term format, by the way, refers to the size of the film frame or digital sensor in a camera.

Please read the following carefully. It is a bit long, but should help you understand what the "crop factor" is all about. Then, I'll get to the points you need answered.

- - - - - - - - - - - - - - - -
The "crop factor" is a reference number that relates to the difference in film or sensor size (known as the camera's "format") between two cameras like the Canon 7D and a 35mm film (or a so-called "full-frame" digital) camera. Let me list the facts:

35mm film cameras and so-called "full frame" DSLRs have a film frame or sensor size of approximately 24mm X 36mm, while the Canon 7D has an APS-C sized sensor, measuring approximately 14.9mm X 22.3mm. The other Canon APS-C format cameras - starting with the D30 in the year 2000 and progressing through all of the "digital Rebel" xxxD series, the xxD series, and today's 7D - all have sensors that are sized similar to that in the 7D.

When camera manufacturers started designing digital SLRs (DSLRs), they decided that the DSLR bodies should be about the same physical size and configuration as their 35mm film SLRs. For that reason, they concluded that they could use the line of lenses they already had for their 35mm SLRs on the new DSLRs.

All lenses designed for 35mm cameras project an image circle onto the film that covers a 24mm X 36mm rectangle. The 35mm camera records the portion of that image circle that is defined by the opening behind the shutter for the film (24mm X 36mm in size). A digital SLR with an APS-C sized sensor only records the smaller area (approximately 14.9mm X 22.3mm) of the image circle projected by the same lens.

When you put a 100mm lens on a 35mm film camera and make a photograph, then put the same lens on a DSLR such as the Canon 7D and make a similar photograph - same subject, same position for the camera, and same focal length - and then enlarge both photographs to the same size print (4 X 6 inches, for example), it will appear as though the photo from the Canon 7D was taken with a longer lens. That is because the image recorded by the Canon 7D was of a SMALLER PORTION of the image circle projected by the lens - cropped, if you will - compared to the image recorded by the 35mm camera.

The special lenses for the Canon 7D (and other Canon APS-C cameras starting with the 300D - the first Digital Rebel) are called the EF-S series. These project a smaller image circle, making the lenses less expensive to design and produce in wide-angle and extreme wide-angle formats. The EF-S lenses also project deeper into the camera than the EF specification allows (the "S" referring to "Short back focus), allowing for less expensive wide-angle lens designs. However, an EF-S lens set to 40mm will produce the exact same image as an EF lens set to 40mm if both lenses are used on the same APS-C format body and both lenses are focused at "infinity". Focal length is focal length, period.

Now to the primary point that I want to make: NOTHING about lens EVER CHANGES when you put it on different format cameras. Focal length never changes. Aperture range never changes. The only thing that would change is the apparent field of view, and that change is not a function of the lens but it is a function of the size of the sensor or film that will record the image.

The "crop factor" calculation for "35mm equivalent focal length" has only one valid use. That is for comparing lenses used on two different format cameras.

Here's one common example: Joe took a photo of Mount Rushmore with a 35mm camera from a particular place using a 200mm lens. You want to replicate that photo with your Canon 7D. What focal length do you need to do that from the same location that he took his photo? Divide the 200mm by 1.6 and you get the answer - 125mm.

Here's another popular example: Mary Sue has been using a Canon SX120 IS point-n-shoot camera and is wanting to use a Canon 50D DSLR. She is, of course, interested in what focal lengths she would need to keep the versatility of the SX120 camera's 10X super-zoom lens. The SX120 lens is actually a 6.0mm to 60.0mm lens, but the advertising also shows the "35mm equivalent" focal length range as 36mm to 360mm. To know the focal lengths needed for the 50D, merely divide the "35mm equivalent" values by 1.6. In other words, Mary Sue would need 22.5mm on the short end and 225mm on the long end for the 50D to have the same field (angle) of view coverage as her SX120 IS camera.

The "crop factor" is NOTHING MORE than a REFERENCE between the two camera formats that lets you compare the field of view of particular focal lengths between the two formats.

The "crop factor" (as related to using lenses essentially designed for 35mm SLR cameras) is always given assuming that the 35mm format (24mm X 36mm) is the reference master. Something to realize, though, is that the 35mm film format is not, never has been, and never will be the master" format against which all other camera formats are referenced. It is simply the format of the cameras that have also evolved into today's commonly used digital SLRs.
- - - - - - - - - - - - - - - -

Now that you have the basics, there are a couple of things that need to be added into your thinking about the combinations of camera formats and lens focal lengths.


One thing you need to consider is the resolution of each digital camera's sensor. That relates to the number of pixels in the camera's image files. In your comparison of the 7D and the 1D MkIV, you need to know the relative sizes of the sensors.

• The sensor length or width in the 1D MkIV is 1.25 times the size (in each direction) of the sensor in the 7D.
  
• The area of the 1D MkIV sensor is 1.56 times the area of the 7D sensor (1.25 squared).
  
• The number of pixels in a 7D file is 17,915,904.
  
• The number of pixels in a 1D MkIV file is 15,980,544.

• 400mm on the 7D gives the same field of view as a 644mm lens on a 35mm film camera (400 x 1.61).
  
• 500mm on the 1D MkIV gives the same field of view as a 645mm lens on a 35mm film camera (500 x 1.29).

AJSJones wrote in post #10892272
I'm confused by something here. The bold bit doesn't look quite right, Wilt. If the image of a 2 foot tall duck from a 400 mm lens is ~0.8 mm on a sensor (or any surface really), then, with the same duck viewed from the same place, the image from a 500 lens should be ~1 mm, on any sensor, no?

OK, running the numbers again from scratch as I type (I think I used some wrong values in my prior computationops...note the calculations are complicated (and not adjusted) by the fact that 1D2 sensor is different size than 1D3, but my FOV calculator assumes 1D2 dimension.
APS-H (1D2) using 500mm lens of object at 1000' sees area 38.14' high. So item 1' tall is 1/38.14 of the frame, which is 19.1mm high (1D2), or the subject is 0.5008mm tall on sensor. The 1D3 is 18.7mm tall with 2592 pixels, or 138.6 pixels per mm, so 1' tall object at 1000' is 69 pixels tall. So the 7D APS-C sensor has 35% better number of pixels, while having a 19% disadvantage on lens resolution delivered on print.

I think the guy with the 1D Mark IV and a 500mm f/4.0L pictures will come out better because his equipment is better. I'm sure if you gave the guy your 7D and 400mm f/5.6L lens and shot the same picture his 1D Mark IV and 500mm will still win. I bet your 7D and a 500mm f/4.0L would be a killer birding kit. I say go and buy the 500mm f/4.0L lens.

Take Care,
Cheers, Patrick

Let me toss out a couple of practical matters -- first is that if you browse the wildlife/birds sections, you will see that the 500 is a "favored" lens -- that extra reach counts, no matter what your sensor size. But one huge plus with the 500 f/4 is that it will work well with a teleconverter.

On a 7D/1.6 cop body, you can use a 1.4x TC and work with an f/5.6 aperture, which will allow the 7D to achieve AF. But, and this is a huge but, on a 1D body you can actually use a 2x TC, giving you f/8, and the 1D body can actually achieve AF with an f/8 aperture.

So, those are pretty compelling reasons for why the 500 is loved by say birders (and others), and you can see from the images that it has excellent IQ.

But, of course, you are looking at a pretty huge expense. I myself ran out of a "big photo spending" budget a couple years ago. I've been using the 100-400 with a 1.4x TC (meaning at f/8 I can AF with my 1D3) and I content myself. But, if I could, would I grab a 500? Dang right I would -- there's nothing like more reach. And, as I pointed out, you can use a 1.4c TC on a 7D or a 2x TC on a 1D -- what's not to love about that??!