Why did I see sunlight reflection in viewfinder but not in final image?

I have a Canon 2000D DSLR with 55-250mm lens and no lens hood. Recently, I took a picture of a tractor that was in nearly the same direction the sun was shining from. However, the sun was sufficiently far away to be not in the picture.

When looking at the image through the viewfinder, I could see reflections of the sun and thought I need to purchase a lens hood. However, the final image was perfectly fine with no reflections of the sun.

Why is this the case? Why did I see reflections of sun through the viewfinder but not in the final image?

Is there a mirror actuation count limit in addition to shutter actuation count limit in DSLRs?

Every time you take a picture on a DSLR, not only does the shutter actuate but also the mirror actuates.

If using the LCD preview, and using phase detect autofocus, the mirror actuates too: the phase detect autofocus works only when the mirror is directing the light to the viewfinder. This time, the mirror is actuated when focusing, so if you need to focus multiple times before taking a photograph, the mirror actuates multiple times.

My questions are:

  • Is the mirror actuation count limited like the shutter actuation count?
  • Can you read the mirror actuation count somehow in modern DSLRs?
  • Which is a more limiting factor: a limited mirror actuation count or a limited shutter actuation count?

What’s the advantage of a DSLR’s “previewer” viewfinder, since I have observed that mirrorless cameras appear to have the same thing?

I have read some articles about DSLR and mirrorless cameras, and one thing all people insist on is that:

DSLRs use the same design as the 35mm film cameras from the past. A mirror inside the camera body reflects the light coming in through the lens up to a prism, and into the viewfinder for you to preview your shot.

source: beachcamera.com

But I have also seen that we can preview photos on the Canon M50, for example, which is a mirrorless camera. Here a photo of the Canon M50 with the previewer at the top of the device: https://www.imaging-resource.com/PRODS/canon-eos-m50/Z-M50-BACK.JPG

So what it is the point, when it seems also mirrorless camera also allows one to preview photo using a kind of lens, like a classic camera?

My question is slightly different to the possible duplicate proposals because I assume that this is the same thing, the other question already know it is a different thing, so my question begins from different assumptions, hence difference emphasizing in the answers. That said the two questions are complementaries I think, once you know why it’s different you can dive in the advantage of one or another.

Sigma DC 18-250mm 1:3.5-6.3 MACRO HSM

I have a Nikon D7000 and have used the Sigma 18-250mm F3.5-6.3 DC MACRO OS HSM lens since Feb 2017. Recently it will not unlock for manual focusing. What would cause this to happen?

I had it in for servicing and the paperwork indicates that the issue was switch operation and it was cleaned and repaired. However, the lens barrel is locked in AF mode and I cannot manually focus for pictures. The paperwork indicates it was repaired and working. However, when I put it on my camera it does not work. The lens manual focusing ability is not there. It will only work in AF and I lose the zoom capability of the lens.

How much should I consider lens mount when buying all-manual lenses?

I’m mostly shooting micro four thirds, and am looking at buying a set of primes. It occurs to me, that if I buy an MFT lens set, then those lenses can only by used with MFT cameras and those with shorter flange distances (like Sony’s E-mount). But lens adapters are cheap, and if I can buy a set of Nikon F-mount primes, then I can adapt that to Canon, MFT, Sony, any number of mounts. So if I’m shooting manual everything, is there any reason not to just buy a set with the longest flange distance and rely on adapters?

Is conventional wisdom about the mechanism of red-eye reduction flawed?

As an example for a typical explanation about red-eye reduction pre-flashes, the description in the Metz SCA3202-M7 flash adapter manual states

Red eyes are always the result of a physical effect. This arises whenever a person looks more or less straight into the camera, the ambient light is relatively dark and the flash unit is mounted on or directly next to the camera. The flash unit illuminates the back of the eyes, revealing the blood filled retina through the pupil. This is recorded by the camera as a red spot in the eyes.

The red-eye reduction function brings about a significant improvement in this respect. When this facility is used the flash unit triggers, prior to shutter operation, a few weakly visible preflashes which are followed by the main flash. These preflashes induce the pupils to close down, thereby diminishing the red-eye effect.”

So here are three flash photographs of my eye taken with one self-timer, distance probably 8m. Focus to approx half the camera distance

Focus on camera

Focus quite near

There is no significant difference in iris size: if any, there is a small overall reduction throughout the (chronologically sorted) sequence with photographs taken with a distance of about 1sec.

Nevertheless the last image not even looking in the direction of the camera (with the reflexes from the flash being almost or entirely off the pupil) clearly has the strongest red-eye, followed by the first image.

The middle image, in spite of having the flash reflex basically straight in the pupil, clearly has a minimal amount of red-eye.

What gives? The typical description of the red-eye effect strangely does not take into account that the eye is an optical system designed to create a sharp image of what you are looking at on the retina. If there is no overlap of the image of the flash on the retina and the image of the camera’s entrance pupil (the aperture as viewed through the front lens), no retina area lit by the flash will be visible from the camera’s entrance pupil and consequently the sensor.

So the main objective of a pre-flash to me appears to be making the eye focus on flash and camera so that their respective images on the retina are sharp and disparate. While reducing the iris size would also help by increasing the eye’s depth of focus (and thus decreasing blurring of the retina images), the effect seems minor compared to what the focus reflex can achieve here even with comparatively wide pupil.

So contrary to conventional wisdom, staring straight and focusedly at camera/flash (or a birdie waved at same distance) will do most of the work even without preflash. An urgently blinking self-timer lamp should be almost equally effective for red-eye prevention as a pre-flash.

Now the people writing about cameras and designing red-eye reduction systems know their place inside out optics. It seems preposterous to assume that they of all people would not consider the implications of the eye being an imaging device after which cameras have been modeled complete with lens, aperture, and sensor surface. And money is riding on it: basically every camera review tests for red-eye.

What am I overlooking?