Thread: Image resolution in cameras used on hunting trips

Here then to kick things off is a comparison between two Canon cameras; the 50x zoom “bridge” SX50 at 595 grams that I have used for the last 10 years and is quite a performance benchmark — inasmuch as many NZHS Forum members seem to either have one or have used one in the past — and the physically much more “Compact” 40x zoom SX740 weighing half that at 299 grams and that I had hoped would be a light weight replacement.




First up the sizes of the captured images can be compared. The SX740 compact produces the larger image of the two, 20.1MP over the 12MP of the SX50 from the same 1/2.3” sized sensor. Of interest is that when each are set to maximum zoom, the difference between 40x and 50x working in the opposite direction to the ratio of the respective image sizes, comes close to restoring the subject matter to much the same size. Actually this is very helpful for this particular comparison, as common features can be cut from the images and compared directly, with them being depicted by a very similar number of pixels, as can be seen below. Resizing would inevitably modify the image. No issue with downsizing though when only looking at relative image size rather than image quality, in this case both to the same 25% for uploading to the Forum pages.




Of course image size is meaningless in and of itself. Any image can be re-sized. So now to the nitty–gritty; below I’ve cropped out portions of the original photographs showing parts of the pole fuses. It may well be clear depending on what device is being used to view this thread, but the SX740 has given up significant detail to the SX50. It’s as if the ISO was cranked right up. Compare the difference in the fuse hinge, the softness in the lines of the cabling, the light reflecting off the insulator and the writing on the strainer termination. There is also more colour fringing from the smaller camera that surely must be a product of the lenses and in spite of the more advanced internal image processing, as the sensors are both the same 1/2.3 size, but others better versed in such matters may wish to offer their thoughts?



For those who might not be able to easily zoom in to the detail in the above, here are close-ups of the strainer and the fuse hinge I mentioned. The split pin is better defined and writing is clearly present in the image from the SX50 on the left but missing in the matching portion of the image from the SX740 on the right. As mentioned earlier; these have been cropped from the original images and not had re-sizing applied in a way that could have modified their relative appearance.



A closer inspection finds detail is present down to the pixel level from the SX50. So other than making each pixel a truer representation of the light entering the lens from that direction (through less noise, better dynamic range etc) it appears to my untrained eye that the potential resolution from the 50x lens in creating the full 4000 x 3000 12MP image is close to being utilized. I’m sure this is a simplification, and photography buffs on here will be ripping their hair out, but you get the general direction of my thinking.

On the other hand it is my assessment from the power pole image that the 5184 x 3888 dimensions from the SX740 could each be halved without any meaningful loss of recorded visual information. In other words 5MP rather than 20.1MP would be sufficient to store the resolved image through this lens at 40x and internal processing used. This begs the question: why the advertised combination of 40x and 20.1MP when they are not able to be utilized together. Disappointing.


For a resolution comparison that focuses on contrast, I’ve photographed text from a Lentle and Saxton book at a distance of twenty metres, cropped portions from the SX50 on the left, SX740 on the right. I used a number of different exposures and tried to match the images for background brightness. The conditions were heavy overcast. Both cameras were set for automatic white balance. I think the SX50 page white is the truer representation of the conditions, though this can of course be corrected either at the time the camera is used or later. Despite what appear to be considerable compression artifacts around the letters, the difference is still pretty clear.




Another day, same 11kV fuses. Here I’ve taken a cropped image shot at 40x with the SX740 (top) and then reduced the resolution in the way mentioned in one of the earlier posts, by first re-sizing the dimensions down by 50%, and then re-sized back up by 200% to the original size. The modified image is now made up of blocks of 2x2 identically coloured pixels, each block a colour average of the original four. In a camera that utilizes its full resolution at maximum zoom, the lower image, being at half the resolution, should appear degraded.



Again for those who can’t easily zoom into the above, immediately below are a couple of portions of these images cut from the above to compare, and then cropped again to resolve down to the individual pixel level on the left, and the blocks of four identical pixels on the right.




I’ll refer back to my original question; has any meaningful resolution actually been lost? I would say no.

Assuming my sample SX740 is performing to specification, either the 20.1MB image size promises resolution that the camera cannot actually deliver, or the 40x zoom, while optically occurring, has not the necessary attributes of lens quality and mechanical precision to translate into an improved resolution beyond the 20x setting. I haven’t looked into this further to determine which, though it is probably just a softer lens. One way perhaps would be to retract the lens back to a 24mm focal length equivalent setting, and see if the photographs taken then produced detail down to the pixel level. If so the limitation would — by elimination — lie with the lens when extended out to the long focal length.

In light of this finding I have reservations about recommending the SX740 for game photography without also saying that perhaps Forum members should moderate their expectations from what is implied by the published specifications. While the SX740 is small and typical in weight to other compacts, and I enjoy using it, there may well be alternatives at a similar price–point where the actual still–image performance comes closer to meeting the manufacturer’s claims.


Which leads back to the original request; if you could please consider posting to this thread those comparative images or photos that demonstrate the ultimate resolution of your camera according to the methods outlined? I realize this isn’t a Camera & Photography forum, but I think there will be a bit of interest in making a few such comparisons across camera models available.