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I am new to photography (just 3 to 4 months of experience) and I am looking to buy a new lens (either 35mm or 50mm, but mostly 35mm because I have already decided Sigma 85mm f/1.4 DG HSM Art Lens for the creamy bokeh) for general street photography.

I like my images to be as sharp as possible. I went through many websites and youtube videos and many of them mention that Nikon 1.4g is superior to Nikon 1.8g. At the same time they also mention that Nikon 1.8g is sharper. Why do they say Nikon 1.4g better when Nikon 1.8g is sharper ?

What did the reviewers say about why they chose one lens over the other? They have their own priorities and biases. You should evaluate the information they present and decide for yourself whether you agree with their conclusions.

Everyone tests lens sharpness because it's easy. Just photograph a resolution chart and read off the numbers. However, this method really tests lens-camera combinations.

• Beyond a certain level of sharpness, most pixel peepers should be satisfied. For me, around 65 lp/mm is "good enough". A lens that is at least that sharp gives me plenty of detail to work with in real images that are not of resolution charts or brick walls.




• The differences in sharpness among lenses that exceed sensor capabilities make no difference to final image quality.

There's more to lenses than sharpness.

How you prioritize these factors can result in a completely different lens being "better" for you than for me or anyone else.

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  veiling glare – I'm particularly concerned about veiling glare because it rapidly degrades images into uselessness.

  
  
  

  

  
  
  

  However, a bit of veiling glare can add character.

  
  
  

  

  
  



• contrast




• flare ghosts – Often used for artistic effect.




• focal length – 35mm, 50mm, and 85mm have different fields of view. Composing subjects similarly within the frame requires standing at a different distance from the subject with each lens. On a crop-sensor camera, 28mm or 35mm would work well from a few paces away. With 50mm and 85mm, you'll have to stand further back, unless you're trying to capture people's nose hairs.




• aperture – Lenses with larger apertures are usually more expensive and can produce more background blur, but...



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  bokeh (quality of blur) – There's more to "bokeh" than simple blurriness.

  
  
  
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    Shaped Bokeh – Why is the bokeh shaped like the aperture?
    
  
  
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    Swirly Bokeh – What swirly bokeh technique is this and how can I achieve it?
    
  
  
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    Bubble Bokeh – Besides mirror lenses, what can cause ring-shaped bokeh?
    
  
  
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    Donut Bokeh – What's so bad about a mirror lens?
    
  
  



• distortion – Usually only visible when photographing brick walls.




• chromatic aberration – Many well-regarded lenses have CA when used wide open, and wide open is the only way to get those perfectly round bokeh balls everyone is chasing after. As long as CA is not out of control and adds just a bit of color along some of the edges, it's part of the character of the lens. CA is typically reduced when the aperture is stopped down a bit. It can also be corrected by software during post processing.




• close focusing / macro mode




• color rendering




• technology – autofocus, image stabilization, etc.



• other factors – weight, size, price, water resistance, feel, etc. (as Davidmh notes)

I have two 35-105/3.5 zoom lenses from the 1980s that are quite sharp. The sharpness results are maybe too good and I wonder if I read the chart wrong. Regardless, the modern lenses still look just a bit better, but not because of sharpness.

Imagine these are 1"x1" crops from 40"x27" images. About the same level of detail can be seen in the clock regardless of lens, but the newer lenses have better contrast.

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  Canon EF 24-105/4L @ 24/4; Nikon 24-70/2.8E @ 24/2.8; Nikon 24-120/4G @ 24/4

  
  
  

  

  
  


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  Pentax-A SMC 35-105/3.5 @ 35/3.5 and 35/4.5

  
  
  

  

  
  

1) Sharpness is complicated.

Lens sharpness is just one aspect of the overall resolving power of a camera system. The appearance of crispness is separate from the rendition of detail. And a lens can be sharper in the center but not in the corners, or less sharp overall but consistent across the frame.

And that's not even getting into other factors that affect the system as a whole. Camera shake, subject movement, focus accuracy, diffraction — the list goes on. In fact, I'd go so far as to say that unless you are very meticulous with your technique, you won't ever notice a sharpness difference between these lenses, because any lens difference will be overwhelmed by the other things.

2) Sharpness is overrated.

It's fine if you like it, but recognize that sharpness is just one aspect of optical performance. All lens design is about compromise between various factors, and correction for one thing inevitably leads to compromise in another. See What image-quality characteristics make a lens good or bad? for a detailed look at this. Generally, though, when someone is saying that a lens is better than another even though the other is sharper, some of these other factors are probably at the forefront.

3) Don't forget that extra speed.

An f/1.4 lens can stop down to f/1.8. An f/1.8 lens can't open up to f/1.4.

4) But, finally, don't read too much into reviews — and don't get obsessed with "best".

There are basically three kinds of lens reviews on the Internet.

First, there are highly technical ones which measure the optical compromises and flaws using a workbench and special software and perhaps lasers. These are fun and can sometimes reveal useful information, but in general tend to emphasize small flaws and differences which rarely actually make a big difference to results.

Second, there are reviews by people who bought an expensive lens and need to tell everyone how great that lens is to help their internal justification. Since here we are comparing a $1700 lens to a $500 one — or a $200 one, if you are looking at the DX version — this may play more than a small part.

Third, there are subjective reviews from experienced photographers showing work they've made with a lens and talking about how it handles. These rarely mention technical details except in passing. These are the most useful in some ways, but you really have to read a lot to get a sense of whether you'll agree.

Overall, the best way to make this decision is to borrow or rent the lenses in question and try them each for a couple of weeks. (You need at least that time to really form a working relationship.) You'll probably find that you like the results you're getting with one better than the other — or if there is no clear winner, you can decide to go with the cheapest.

It's really easy to say "I clearly want the very best one!", but this is a trap. And, obsessing over technical reviews and measured sharpness play into that trap. What you want is a lens that fits your purpose — and your pocketbook.

You want the lens for street photography. The AF-S DX NIKKOR 35mm f/1.8G is a great lens for street photography for a DX-format body like your D5600. It's very sharp. It's also very affordable. An f/1.4 lens would give you a little more flexibility in lower light but it would cost almost 10 times as much. The image quality would be comparable. Since you're new to photography, it's understandable that you want to make sure you're spending your money wisely on good equipment. But don't get hung up on tiny technical details. It's very unlikely that you would be unhappy with either the f/1.8 or the f/1.4. You might, however, be happier having more money in your pocket.