How does a DSLR measure brightness and sharpness of an image?

In mirrorless cameras, light reaches the image sensor all the time, so this data can be used by the camera to determine the correct focus, shutter time, aperture and ISO. Makes sense so far.

However DSLRs need to know all these parameters before the sensor gets hit by light and thus can’t use the sensor for that, so I imagine there must be some kind of additional measuring device to do the job. Assuming this assumption is correct, where exactly is this device located inside the camera and how does it work?

How do I get the high contrast sharpness seen in this B&W portrait?

I would like some help on achieving this image on my D7000:

enter image description here

the only lenses I have with me are: 50mm f/1.2, 80-200 AF f/2.8 and the 18-105 kit lens

I tried B&W with the built-in B&W conversion in the D7000 but I can’t get such sharpness.

So how can I achieve this level of sharpness with my D7000 and the given lenses?

How do I get the best sharpness from a Zeiss Jena Pancolar MC lens?

I’ve just ordered a Zeiss Jena Pancolar MC 50mm prime lens, and have been reading up as much as I can about how to get the best quality images from it.

It’s my intention to use it mainly with 3 different film SLRs, but occasionally with an APS/C Samsung mirrorless.

As I understand it, the sharpness on this lens is most crisp in the centre of the frame (as with my other 50mm lenses really), but I can’t find much information on the way the lens behaves at different f-stops with regard to sharpness around the edges of the frame.

I realise that it is very subjective to ask how to get high quality images, but I’m curious if anybody with experience of these lenses has any tips on how to ensure as sharp an image as possible.

Mostly, I tend to photograph scenes of industrial decay, landscapes, and various wild plants and flowers in reasonably bright sunlight, however as the uk weather tends toward dim days for a lot of the year, I find that I’m often taking shots in much lower light than I’d like.

When I’m photographing plants, I tend to place the subject close to dead centre so this isn’t too much of a worry for me, but when I’m photographing buildings or industrial scenes, I like to get as much of the edge of the frame in sharp focus as possible. One a session in Wales, it was fairly dark so I had the lens wide open (in this case, it was a Fujinon 55mm) and found that there was noticeable loss of sharpness at the edges of the shot. Stopping down a little and shooting for longer resolved this nicely.

I’d be grateful for any tips from anyone who has used one of these lenses in the past. I’m flying a little blind as on paper it seems like a superb lens, but I don’t know anybody personally who has used one to consult.

Do smaller apertures provide more depth of field past the diffraction limit, even if peak sharpness suffers?

In Understanding Exposure (3rd edition, on page 48), Bryan Peterson has what might be called a rant against modern on-line conventional wisdom about diffraction limits. Answers on this web site are pretty much in line with that conventional wisdom; see What is a "diffraction limit"? and What's the benefit of a tiny aperture?

But Peterson is particularly dismissive of “photography forum Web sites”, and says he “wants to set the record straight”. Is there a grain of truth to what he says, or is he totally off-base?

Particularly, he says that f/22 is “the smallest lens opening that, in turn, produces the greatest depth of field” with a wide-angle lens, and that f/22 is therefore the only way to record sharpness from front to back. Will stopping down beyond the diffraction limit give more consistent across-the-field sharpness, even if it isn’t absolutely as sharp, perhaps? Or does the diffraction limit mean that at certain point, far before f/22 on APS-C dSLRs, everything is as as sharp as it’s going to get, and beyond that, everything gets worse?

Peterson also says “The question of using f/22 was never an issue during the days when we all shot film, and it should not be an issue today.” In this answer on this site, jrista (convincingly, I thought) argues that the limit is a function of the recording medium. Does Peterson, despite credentials as being a best-selling photography author, not give enough credence to the difference between film and digital?

How will a teleconverter affect the sharpness of a lens at a given aperture?

If I have a 200mm f2.8 lens and apply a 2x teleconverter the effective focal length and aperture becomes 400mm and f5.6. However, I am unsure about the effect this has on other aspects, such as image sharpness (not of the teleconverter) related to the aperture. Say that my lens is very soft wide open at f2.8 and tack sharp when stopped down to f5.6. Will the added teleconverter give the same sharpness as 200mm f5.6 (minus the optical imperfections of the teleconverter and the effect of enlarging the lens imperfections) when shot at its widest (at f5.6), or will it be as soft as the 200mm f2.8 (plus the imperfections of the teleconverter)?

the best way to improve image sharpness on Canon 700D

I’m currently using a Canon 700D with a few EF-S lenses, I like the Canon system, the looks, feel and ergonomics but I’m not happy with the files I’m getting. Whenever I come across a photo that appeals to me from a technical point of view it happens to be shot on a full frame camera or some Sony sensor APS-C. The most important thing I miss in my files is sharpness, overall Canon crop sensor cameras lack in focus and / or sharpening ability when compared to Nikon / Sony / Fuji etc. Would you advise me to upgrade to a full frame 6D or to switch brands to Nikon D7100 / D7200 / possibly Nikon D610? I have just 4 basic lenses so the cost wouldn’t be very high. I don’t want to ask another question which brand is better, just some opinions on the best / the most efficient way to raise technical image quality. I know I can buy a professional lens like Sigma 18-35, but I have just one body which I’m going to upgrade soon, and I think maybe it would be more wise to buy the Sigma lens for a Nikon body to get optimal results.

Thanks for any replies.

What is the best way to downsample photos to increase sharpness

What is the best way to downsample photos to increase sharpness?

If I have a photo in raw format with a resolution of about 24MP. How do I best downsample it to increase sharpness if I think the original is soft? I’m avare that this will reduce maximum print size for a given dpi but I am wondering what the best downsampling method is.

My intuition tells me that scaling down by an integer factor using area avarage probably is quite good but can I use more information to get even better results?

Can the knowledge of raw pixel values before debayering be used for example?