Recently, thanks to my good friend, Jon Robichaud, I had use of a borrowed Sony A9 and 200-600mm f/5.6-6.3 to use alongside an Olympus OM-1 and 300mm f/4 with either MC14 1.4x Teleconverter or MC20 2x Teleconverter to yield 420mm f/5.6 or 600mm f/8. See the image here for size comparison. The hood is attached to the 200-600 but retracted on the 300/4, so the difference is less than what the image shows.
The weight difference is about 1.5lbs. The Sony uses a stacked sensor of 24 megapixels and 36mm wide by 24mm tall in a 3x2 format whereas the Olympus uses a stacked sensor cropped to 1/2 the width of the Sony's at 17.3mm by 13mm and in a 4x3 format of 20 megapixels. The A9 debuted in 2017 whereas the OM-1 debuted in 2022. Both feature subject detections and tracking, though the Sony is the earliest version of this and does not distinguish among animals or choose the eye in non-human subjects, though it does seem to. The OM-1 can detect birds, dogs & cats, trains, automobiles, and airplanes/helicopters and track them. The Sony can continuously autofocus and follow subjects at 20 frames per second. This was uncanny in 2017. The OM-1 can do the same at 50 frames per second, though I usually set it to 25 frames per second except for very small fast birds. Both have very fast readouts so rolling shutter is not an issue with either camera. The Sony A9 was replaced by the A9II back in 2019, a little over 3 years ago, and I suspect the A9III will come out sometime this year. But the used market has Sony A9 cameras under $1900 in good condition and the 200-600 lens pre-owned for between $1500-1700, making this a top flight full frame kit for around $3400. The OM-1 is a new camera with used ones in short supply as it's much in demand, so expect to pay $1900+ for the camera and $2000+ for a pre-owned 300/4. Adding the teleconverters would add another $400-500, depending on the deal you make, so this kit would be about $1000 more than the older A9+200-600. BTW, the 200-600 does work well with the Sony 1.4x TC, making it a 280-840mm f/8-f/9 lens.
I had a few good days over the last couple of weeks with excellent light and action carrying both setups and got equally good images of cardinals, blue jays, woodpeckers, Northern Harriers, and Short Eared Owls, to where I’ve been able to examine hundreds of sequences and I have a much better feel of the pros and cons of the two systems. Either can be fine and both can also be fine. There isn’t a clear advantage as it depends on the physics of the shot. The Olympus OM-1 menu system is not unlike the Sony A9 menu system and so it was rather academic for me to learn how to configure the Sony to behave the way I want and there were some excellent Youtube how-tos related to my needs. The sensors are different sizes and proportions, but the output was similar in dynamic range and noise consistencies meaning they both performed well up to ISO12800 in good golden hour light, the best when photographing animals and birds.
As I noted above, both systems have potentially good results and we can compare the results in a number of ways that might give one format an advantage over the other but for the sake of simplicity, in this exercise I'm only considering the quality of details and sharpness of the main subject: the animal or bird we want to photograph and possibly print out at a reasonable size to hang on a wall or publish in a magazine.
MEGAPIXELS
Both sensors, though different sizes, have similar numbers of megapixels. The Sony has 24 megapixels and the Olympus has 20 Megapixels. But due to the different overall size of the sensors, at any given focal length and shooting distance from the subjects, the subjects will appear twice as large or twice as close in the Olympus view finder vs the Sony view finder. I can crop the Sony image twice as much, of course, when I download it, but then I am left with about half the megapixels as the Olympus would use for the same image. This might not matter for social media shares, but it could matter for enlarging and printing. So in some cases, the smaller 300mm f/4 with a teleconverter will actually get more of the subject to fill the 20MP sensor than I'd be able to do with the Sony unless I can get closer or use more telephoto than 600mm. The possibility exists in proximity to animals where the crop sensor camera will get a larger image of the subject by virtue of it's placing more of the subject on more megapixels than the larger full frame sensor camera might without significantly more focal length being added or significantly more megapixels (and much higher cost in money and size, in either case).
MAGNIFICATION FACTOR
Magnification increases with focal length with distance to subject affecting the capturing of details because every sensor and lens is affected by atmospheric distortion and various amounts of diffraction from a given distance, if it’s present in observable amounts. Thus, a bit more magnification will enlarge smaller details in spite of the loss of contrast, and if the first metric: megapixels per subject is not substantially diminished, the image magnified the most will appear more detailed. This affects nature and wildlife photography in a couple of ways.
First, for large birds and animals far away, greater magnification may recover details that can't be resolved simply by cropping to more megapixels. Some details can only be viewed if closer to the subject, or if we cannot safely get closer, by magnification of the subject using very good telephoto lenses. This case is mainly why some people spend a small fortune on really long lenses like 800mm and 1200mm lenses. In comparing the Sony A9 and 200-600 with the OM-1 and 300/4 with 1.4x or 2x teleconverters, it was rarely a case where there was much advantage at the long end for the Sony. Had the sensor been much higher megapixels, like the 50MP Sony A1, then there may have been some advantages for the Sony that were not apparent in the A9. However, basically, both kits worked just as well, or in some cases, just as poorly, when the subjects were too far away to fill the view finder adequately. Cropping more than 50% with either kit was possible, but also not ideal.
The second case is when subjects are close enough to frame with the Sony 200-600 at less than 600mm. If the subjects were close enough to more than fill the 600mm field of view, then the Sony had 600mm of magnification whereas I only had 300mm of magnification on the Olympus. However, the closer the subject, the more details resolvable by either lens and the less distinct difference. Even if a bird perched close by to where I had to zoom wider to 200mm, and on the Olympus I'd have to walk away to get the 300mm with it's 600mm field of view to compose similarly, there are really not clear winners in terms of details. In such cases I might use the 300/4 for a head shot and the 200-600 for a full body shot. The 300mm f/4 is such a sharp prime lens that even the very good 200-600mm Sony is not going to resolve noticeably more details at the working distances I employed. But ultimately, there is some advantage with the larger sensor giving a wider view such that using more telephoto increases magnification and though in reality, 300mm f/4 vs 600mm f/6.3 is very similar in overall subject separation in most cases I compared.
FIELD OF VIEW FACTOR
Finally, and most enlightening to me, a 36mm wide sensor can manage twice the focal length and therefore twice the magnification, of a 2x crop sensor at any given distance, if one has the glass available. I say ‘can’, but in reality, we don’t get to choose often with wildlife conditions. The wider sensor is an advantage up close because I can throw on a longer lens and still frame the subjects whereas a crop sensor pushes the photographer backward or forces a wider lens with less magnification. (as noted above, this isn't a problem when pretty close - closer is always better and every system is great up close) And by the same token, the larger sensor is at a disadvantage at a distance and has to compensate by doubling the pixel density (quadrupling the megapixel count), at least with current sensor technology which has leveled the playing field substantially between crop and full frame read out and dynamic range. In an ideal world, no matter what sensor and focal length we managed to use, we'd be able to get to just the right distance to frame and compose the subjects just the way we want. After using these two systems side by side, I found that the most similar performance occurred when comparing the Sony A9 with 200-600 with the OM-1 with 300mm f/4 and MC14 1.4x Teleconverter for a 420mm f/5.6. This gave a field of view of 840mm for 20MP sensor vs the Sony 600mm field of view on 24MP. It works out fairly close in terms of image pop and quality overall. With wildlife, zoom lenses are handy, but in reality, we are almost always using the long end and only zoom wide for environmental shots or when working in nature preserves where wildlife sometimes is very accessible.
FINAL THOUGHTS
This was a pretty basic and perhaps over simplified approach but one that for me at least works to alleviate the often academic exercises I read about or observe in countless YouTube videos making blanket claims that one format is always better than another. I liken the arguments to the old 'quality time vs quantity time' in relationships. In reality, both are necessary and there is no exact formula for every relationship. Quality Pixels are akin to the larger pixels on full frame sensors and Quantity Pixels are akin to the more densely packed and smaller pixels on the micro four thirds sensors and some APS-C sensors. It is a kind of an apples and oranges comparison and what seems best for one person may not appear to be the case for another as we all shoot different subjects on different days in different lighting and with different settings and techniques; we have different editing parameters and skills and we cannot, outside of the lab experiments, re-create situations in nature that will always give us an objective and measurable results to indicate a clear 'winner' every time. It ends up sort of best 2 out of 3 competition, then best 3 out of 5, then best 5 out of seven and it never ends so long as an infinite variety of conditions will exist on to infinity. When possible, it may be advantageous to own more than one format for the prolific outdoor nature and wildlife photographer.
I ignore in this article some other factors like depth of field and ISO because they aren’t technically involved as directly in the overall sharpness of an image in good light, but they do matter of course. A crop sensor using a 300mm lens to frame a subject vs 600mm on the full frame sensor, from a given distance, has greater depth of field, which may or may not be ideal. It depends on the physics of the scene and in wildlife work, scenes and lighting continually change over time. Other factors I do consider when choosing a system are the weight and image stabilization of respective systems. I also consider features such as the Olympus having ProCapture and able to autofocus continuously at up to twice the frame rate of some comparable full frame systems available today. Its weather sealing and image stabilization is second to none, which is very important in long treks in the wild where the elements and the fast moving wildlife require weather sealed systems that can be hand held for long periods of time. Being able to go all day without a tripod or monopod and able to stay hidden with a smallish camera kit is very helpful with keen eyed critters that notice everything unusual, including big white lenses. It has sometimes allowed me to get closer to subjects using a hand held kit than a physically larger lens along with the heavy tripod and gimbal might have allowed.