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I do a lot of photography that focuses on tiny details usually with marine animals such as coral. I am in need of a camera that produces a photo, that even when enlarged from a macro point, it retains clarity.

I realize getting closer is often the answer, but there is a limit to how close I can get to the subject. One, they are often under water, two there is a pane of glass between me and the subject.

This is for biological details. Yes a nice picture for other applications is nice, but the most important feature is the ability for me to enlarge the photo to the point where tiny details can be seen to record.

So here's my question: How much of a difference is there between the enlarged photos of a D610 and D810? And will the difference be enough to affect details. I have enclosed a photo of the type of clarity I need and how large I need a photo to be to get those details. Enlarged macro shot of coral

The entire coral in this picture is less than three inches tall. I don't know that exact limb, but I'd say a half inch at the most. The polyps are about 1/3 the size of a grain of rice. And no the depth of field on this one isn't terrific, however the sharpness of the photo, where it is in focus, is. I did not take this photo, it was done by a lab with a DSLR camera.

The distance from the subject in that photo is probably 9-15 inches. I didn't measure it when they did them, but it wasn't right up on the coral which was submerged in water. Also, this picture isn't cropped. This is the entire picture that was in the frame of the shot.

The camera I currently use is a D90, tripod, timer, 60mm macro lens, low ISO. When I enlarge my photos to match the size of this one, they don't pixelate. Rather they become noisy and details blur out.

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    What lens are you using? What technique; macro lens, zoom + tubes? Hand-held, tripod, macro rail & stacking? [I'm assuming not the latter] tbh, it's hard to tell from such a small picture what you consider 'sharp'; that doesn't have the greatest depth of field & the picture's too small to tell how sharp the centre is. There's the additional consideration that 24mp on a crop frame will already gain magnification. [I don't have the tech knowledge to know whether that would be sharper than 36mp on FF] Also - how big is that coral? & distance from lens? – Tetsujin Dec 17 '19 at 18:12
  • @Tetsujin Both the D610 and D810 are full frame so the comment about crop sensors is irrelevant. What lens is very relevant as I think it would take a good one to resolve more than the D610's 24 megapixels. – Eric Shain Dec 17 '19 at 19:16
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    The entire coral in this picture is less than three inches tall. I don't know that exact limb, but I'd say a half inch at the most. The polyps are about 1/3 the size of a grain of rice. And no the depth of field on this one isn't terrific, however the sharpness of the photo, where it is in focus, is. I did not take this photo, it was done by a lab with a DSLR camera. The camera I currently use is a D90, tripod, timer, 60mm macro lens, low ISO. When I enlarge my photos to match the size of this one, they don't pixilate rather they become noisy and details blur out. – MixedFruitBasket Dec 17 '19 at 19:28
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    The distance from the subject in that photo is probably 9-15 inches. I didn't measure it when they did them, but it wasn't right up on the coral which was submerged in water. Also, this picture isn't cropped. This is the entire picture that was in the frame of the shot. – MixedFruitBasket Dec 17 '19 at 19:31
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    The D90 is an old 12mp crop frame. A decade later, it can probably be considerably out-performed by the entry level D3xxx series. Link to a question I posted a while back, not completely relevant but it links to an image done on a D5500 with nothing but a nifty fifty & some extension tubes, not even a real macro lens - photo.stackexchange.com/questions/110547/… – Tetsujin Dec 17 '19 at 19:35
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What kind of lighting are you using? I think that is where a lot of potential for improvement lies. With textured subjects, the angle(s) of your light source(s) with regard to the camera's optical axis can make a significant difference in contrast and the amount of detail you can see.

Using flash will also allow you to "kill the ambient" and freeze any motion caused by the water moving around in the tank. Even though your shutter duration may be fairly slow (at your camera's flash sync speed), if the only light that makes a major contribution to the image is from your flash(es), then the short duration of the flash will freeze the motion.

The fact that your subjects are usually inside aquariums does present additional challenges, but they're not insurmountable. Much of what is discussed regarding lighting in this question about photographing fish in an aquarium would also apply to your situation.

Your 12 MP APS-C D90 has the same pixel density as a 27 MP FF sensor would, so you'd actually be losing a bit of ground with the D610 at 24 MP, but the 6% linear difference would be negligible. You'd just get more in the frame with the same lens. The D810, on the other hand, has a 36.3 MP sensor. In terms of linear resolution, that's a 23% increase over the 90D which could be significant if your lens is up to the challenge.

Which brings us to the lens choice, which is where all macro photography should start.

We should probably pause here to define a few terms:

  • MFD - Minimum focus distance is measured from the subject to the imaging plane. That is, the focus distance is measured from the film or digital sensor to the subject.
  • WD - Working distance is measured from the front of the lens to the subject. Working distance can be defined as the minimum focus distance less the distance from the imaging plane to the front of the lens when the lens is fully extended at MFD. If a lens has an MFD of 8" and it is 5" from the sensor to the front of the lens when the lens is focused at MFD, the WD would be the remaining 3".
  • MM - Maximum magnification is the largest the lens can project a focused image of the subject onto the film or sensor. If a lens has a MM of 1.0X, it can project an image of the subject that is the same size on the sensor as the subject is in real life. If a lens has a MM of 0.5X, it can project a half-size image of the subject onto the sensor. This magnification is measured at the sensor.
  • RR - Reproduction ratio is another way of expressing the amount of a lens' maximum magnification. It is the ratio of the size of the projected image compared to the size of the subject. 1:1 is the same thing as 1.0X MM. 1:2 is the same as a 0.5X MM, 5:1 is the same as a 5.0X MM (very specialized lenses), and so on.
  • Enlargement ratio - When we view images from most of our cameras, we enlarge the resulting image far beyond the size of the sensor or film. If we have a full frame camera (36x24 mm sensor or film) and a lens with a MM of 1.0X, when we view the image at even 4x6 inches, we've used an enlargement ratio of about 4.25X (linear), so the subject will appear 4.25X wider and taller on a 4x6 inch print than its actual size. It would appear 8.5X it's actual size for an 8x12 inch print, and so on.

Most macro lenses are only capable of 1:1 reproduction at their minimum focus distance.¹ If you have to shoot from further away, you lose some of that magnification. The further back you have to shoot from, the smaller the subject will be in the frame.

  • If you are using the AF Micro-Nikkor 60mm f/2.8D lens you have an MFD of 8.7" and a working distance of 3.56 inches.
  • If you are using the AF-S Micro-Nikkor 60mm f/2.8G ED, Nikon lists the MFD at 7.2" which leaves a working distance of only about 2 inches when the lens is extended at MFD.

The density of the glass through which you are shooting will affect this somewhat, and the density of the water on the other side of the glass will affect it even more. The refraction due to the air/glass/water interface will increase magnification, which will also reduce MFD slightly.

To be able to use maximum magnification with subjects that are more than 2-3 inches from the side of the aquarium, you'll need a longer focal length macro lens than your current 60mm lens.

The following working distances are for each lens at 1.0X (1:1) maximum magnification:

Tamron 90mm Macro (there have been several well regarded versions - I'm using the Model F017 specs) has a working distance of about 5.1"
Nikon AF-S 105mm f/2.8G Micro has a WD of about 5.3"
Sigma 150mm f/2.8 EX DG APO HSM Macro has a WD about 7.3"
Sigma 180mm f/2.8 EX DG OS HSM Macro has a WD of about 10"

Other macro lenses in each of the focal length ranges are similar. The longer the focal length, the greater the MFD at 1:1 and, assuming the lens lengths are relatively proportional to their focal length, the greater the working distance.

There are plenty of other questions/answers here regarding technique for doing macro work, but we'll mention a couple of things that many folks new to macro work can easily miss:

  • To get maximum magnification the lens must be set at the minimum focus distance. Typically one manually sets the lens' focus at MFD and then moves the camera forward or backwards until the subject comes into focus.
  • To get maximum detail a sturdy tripod or other solid camera mount is required. When using the MFD technique mentioned above, a macro rail between the tripod and the camera can be invaluable. Macro rails can range in price from around $20-30 to several hundreds of dollars, but you can find pretty good ones for less than $100.

¹ There are some macro lenses that have higher reproduction ratios than 1:1. With such lenses, the highest reproduction ratio is always at MFD, and 1:1 would be at a longer focus distance than MFD.

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There will be minimal difference; particularly for macro type photography where the aperture generally has to be stopped down in order to achieve a usable depth of field.

The D610 has a pixel size of 5.95um and the D810 has a pixel size of 4.87um. In order to resolve all visible light wavelengths to that size requires a (theoretical) perfect lens used at f/2.8 (red 4.8um, green 3.8um, blue 2.7um). At f/4 the same lens would project red light at 6.8um in diameter. And at f/8 even the blue wavelengths would be at 7.8um. But we can safely assume that the lens in use is not perfect, and the results will be at least one stop worse.

When the size of the airy disk exceeds the size of the pixel contrast is reduced. Whereas smaller details require greater contrast in order to be discernible. And when the airy disk becomes significantly larger than the pixel (2x), recorded resolution decreases.

If I use DXO's measurements of a very good long macro lens such as the Sigma 150mm, it shows that the lens is sharpest at f/4 and delivers 18MP on the D610 and 23MP on the D810 when at f/4. By f/11 it is near 12MP on both sensors. The higher resolution sensor always gives some small gain in recorded resolution due to oversampling, but it is seldom anywhere near what the specs would indicate.

But you are also indicating that you don't actually need much recorded resolution at all. The attached image is less than 0.41MP in resolution, and the amount of detail it contains is significantly less than that.

In this scenario a camera of even less resolution like a 12MP D3 might actually be more beneficial due to it's much larger pixel size (8.4um)... However, another consideration is that only the D810 does not have an AA filter which gives it another potential advantage. And when operating with settings/situations that do not allow you to maximize the D810's resolution, the recoded images are still not any worse. That's why I own/use a D850, even though I seldom actually benefit from it significantly.

https://www2.uned.es/personal/rosuna/resources/photography/Diffraction/Do%20sensors%20outresolve.pdf

EDIT: Based upon the added information of camera/method used, I would say your main issue is lighting and shutter speed, or rather, shutter speed which better lighting will help with. When working with longer SS's there are many things that can contribute to a lack of sharpness... mirror slap, floor vibrations, etc. And even if you mitigate all of those things you are still going to have an issue.

That's because there is a current in the aquarium... the corals require it to survive. And the current causes movement in the subject; even if it doesn't cause movement in the subject it can cause minor changes in the diffraction/focus as the water moves between the lens/subject.

My best suggestions to improve your results: Make certain the lens axis is exactly perpendicular to the glass face of the tank. Get the SS up to at least 1/250 if at all possible (or use off camera flash). Turn off the current/pumps if possible.

The pumps and SS are somewhat reciprocal; you can probably get away with a lower SS w/ the current/pumps turned off. But the first point is pretty critical... I suspect a lot of your noise/blur is actually due to off axis diffraction.

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