35mm lens vs 50mm lens: An In-depth Comparison of 5 Optical Differences

When comparing 35mm lenses with 50mm prime lenses, what are the differences apart from focal length? Let’s dig a little deeper and discuss 5 optical characters that set them apart, so you will know for sure which lens to use in every situation.

Are you deciding between a 35mm and a 50mm lens to add to your collection? I suggest you read this article first.

1. Depth-of-Field (DOF)

For those new to photography, it may be intuitive to think that an object can be either ‘in-focus’ or ‘out-of-focus’. While this is absolutely correct (and usually validated by the red dot on your DSLR viewfinder accompanied by an assuring beeping sound), the reality what is ‘in-focus’ and ‘out-of-focus’ is determined by more than the autofocus function of a camera. If you have never heard of the term ’depth of field’, it essentially means the distance from the camera within which everything is in focus.. You may have already learnt that a faster lens (f/1.4 or f/1.2) provides a lot of bokeh: the blur produced in the out-of-focus parts of an image produced by a lens. This is because a large aperture decreases the depth-of-field, bokeh is essentially what’s captured by a lens outside of the depth-of-field.

Aperture is not the only factor that determines depth-of-field. A smaller aperture, shorter focal length, and smaller sensor size will increase depth-of-field (meaning more things will be in-focus). On the other hand, a larger aperture, longer focal length, and larger sensor size will decrease depth-of-field (meaning less things will be in-focus).

Comparing a 35mm f/1.8 lens and a 50mm f/1.8 lens, if both are used to take a photo with aperture wide-open, the 35mm f/1.8 lens will have a larger depth-of-field. This is very desirable in situations where auto-focusing is not possible. For example, street photographs often wish to shoot as soon as holding up his camera in a candid scenario, so that the person he is taking a photo of does not react in an unnatural way. A usual setting for the pro street photographers with a 35mm lens in manual mode is an f/8 aperture and 1/250 shutter speed. Usually, if he manually fixes the focus at around 5 feet (1.5m), everything between 3.87 ft (1.18m) and 7.06 ft (2.15m) will appear in focus in the photo. This is an ideal depth-of-field for street portraits to have people on the street in focus without engaging any autofocusing function. It is a technique called ‘pre-focus’. On the other hand, the same setting with a 50mm lens will have a depth-of-field between 4.38ft (1.33m) and 5.82 ft (1.77m), a narrower Depth of Field which makes it harder for objects to appear in focus.

If a bokehous photo is what you are after, given a 35mm lens and a 50mm lens, by all means, pick the 50mm.  With a smaller Depth-of-field, there will be bokeh in the photo will be prominent which makes the subject ‘pop’. Some call this ‘the 3D effect’.

2. Aberrations: beyond the ‘purple edge’

aberration visible at the edge of this photo

Aberrations are images distorted by a lens (or a group of lenses), that changes its shape, color and sharpness. Aberrations affect the fringes and corners of photos most due to the nature of the spherical shape of the lens. Light enters a spherical lens on the side and at a large diagonal is more likely to land on the camera sensor with a degree of aberration.

There are two types of aberrations, chromatic aberrations and monochromatic aberrations. If this sounds too theoretical, just remember Chromatic aberration is like how a prism turns sunlight into a rainbow, therefore showing incorrect color in the photo. Monochromatic aberration is the incorrect loss of sharpness of an image.

As mentioned above aberrations is caused by the spherical shape of the lens. Light enters the lens from the fringe of the lens at a diagonal is so complex that it cannot possibly be corrected with the lens itself. So lens designers need to add a second lens to correct aberration caused by the first lens, which in itself, causes another type of aberration. A classic and successful lens structure, such as the Tessar, has 4 lenses (called ‘elements’ by lens engineers) in 3 groups. While a Sonnar lens structure has 7 elements in 3 groups. An extremely well designed (and more expensive) lens such as a Zeiss Otus 55mm f/1.4 has an amazing 12 elements in 10 groups. There is a great deal of correction involved to eliminate aberration as much as possible.

Unfortunately most commercially available and commonly used lenses are affected by aberration to a certain degree. A 35mm lens, wider than a 50mm lens, accepts more light from the edge of the lens at different diagonals and is more likely to be affected by aberration. (Aberration is even worse in super wide angle lenses, if not effectively corrected.) The degree of aberration may be tolerable for most photographers there, especially among modern lenses built with the aid of computerised optical engineering.

In case you are deciding between a 35mm and a 50mm vintage lens, remember technology such as aspherical lenses were not widely available back in the days and manufacturers did not have effective means to control and correct aberration. If image quality both at the centre and at the corners of a lens is important to you, a safe bet is a 50mm lens. Years ago I bought a Pentacon 35mm f/1.8 lens on eBay, the image it took had so much aberration around the edges that I thought it was faulty and returned it to the seller. Lucky the seller accepted my return.

If you already have a 35mm vintage lens that is affected by aberration, many post-processing software such as the Adobe Lightroom and Camera Raw have chromatic aberrations correction functions. This does not fix all the problem but at least it will take ‘the purple edge’ away easily. For sharpness issues, using a smaller aperture usually helps. Unfortunately, there is no much you can do beyond this.

3. Distortion: why is my nose so big?

In which part of the world is a big, strong nose considered attractive? Well, at least I cannot think of any. If your photography style is portrait and especially you like to take close-up photos of a model shoulder-up, avoid a 35mm lens and go for at least 50mm or longer.

To take a ‘head and shoulder’ shot of a model with a 35mm lens on a full frame camera, the camera has to be about 3 feet (1m) away from the model for her image to fill the frame. This is so close that the distortion of perspective (fish-eye effect) became apparent. The degree of distortion varies from one lens to another, however in general due to the short distance from the camera to the model, it affects 35mm lenses more than 50mm lenses.

I included a signature photo of street photographer Eric Kim , ‘the laughing lady’, shot with a 28mm lens. You can tell because he was literally 1 foot away from the old lady (Kudos to Eric), the lady’s mouth and nose appear much larger than her eyes, causing this dramatic distortion effect. You probably don’t want to do the same if the subject person is an attractive young lady, or god-forbidden, your dear wife or girlfriend. For a more flattering portrait, take my advice and get yourself a lens 85mm or longer if you are using a full frame camera. If you have an APS-C camera, use lenses at least 50mm or above should ensure the photos are not affected by the big-nose syndrome.

4. The Technicality of ‘the Boring Focal Length

50mm focal length
50mm focal length

This is a controversial topic among photographers. A 50mm focal length is seen by some as ‘the boring focal length’. Optically this is because a 50mm lens offers a field-of-view very similar to human visions which is 40 degrees horizontal, therefore photos taken by a 50mm lens may seem plain and uninteresting. A secondary reason that many forget to mention is that a 50mm lens can be made so accurate that it is free from the most distortions. The distortions in other lense may add interest to photos if used aesthetically.

The possible argument from those disagree with this view is that many photography Masters use 50mm lenses. To this I say this is exactly why they are masters, they make the impossible possible.

A good experiment to see if you have the eye for 50mm is to examine the photos you took with a standard zoom lens (that is 24mm – 70mm on full frame cameras, or 17mm to 50mm on APS-C cameras).  Now count how many of your favourite photos are taken around the 50mm focal length. In my case, I can tell you the answer is ‘not many’. Human eyes are attracted to views that are a bit ‘different’ to what we normally see, such as ‘birds-eye view’ of extra wide-angle lenses and portraits of wild animals using telephoto lenses. A 50mm lens is unfortunately designed to take photos of the most common view, therefore is the most difficult perspective to impress audiences.

In comparison, 35mm is slightly wider than the field-of-view of the naked eye. A good photographer with a 35mm lens would recognise this difference in field-of-view and pre-frame a photo accordingly. For a novice, the pre-framing is easier and more intuitive to do with a 50mm lens.

5. Lenses Sizes: Small is Beautiful

Pentax DA Limited lenses
Pentax DA Limited lenses

Holding everything constant, to achieve the same exposure, the wider the lens, the smaller the diameter of the optical lenses required. This is because, with wide angle lenses, a larger amount of light is allowed through the lens itself from near and afar. While telephoto lenses are designed to take in light from a very narrow area in the field of view, therefore to achieve the same exposure value, the diameter of the optical glass needs to be a lot bigger.

Some may be quick to point out that this theory does not hold true at the super wide-angle end. The reason is that aberration becomes very apparent in this focal length which requires larger diameter optical lenses to correct. 20mm – 40mm lenses hit the ‘sweet spot’: they allowing ample amount of light in but they are not impacted too much by aberration issues. As a result, the lens size can be made very small. This is especially so among APS-C only lenses, as the light is only required to cover a smaller sensor size, making further room to reduce the light intake requirement.

Pentax DA Limited lenses are designed for the Pentax APS-C DSLR users. The DA Limited lenses are famous for their pancake design. Although the Pentax DA Limited 35mm Macro lens is not a pancake due to the macro ability requiring it to aggressively correct aberration with 9 elements, 8 groups, the Pentax HD DA 40mm f/2.8 Limited lens has a thickness of an amazing 0.6 inch (15mm) and weights a tiny 3.2 oz (89 g). Inside the lens is 5 elements, 4 groups of optics and a beautiful 9 blades automatic aperture ring. The Pentax HD DA 21mm F/3.2 limited follows with a thickness of 1 inch (25mm) and weights 4.2oz (134g)  containing an amazing 8 elements of glass in 5 groups. This is truly outstanding lens engineering.

Share your opinion below

What do you like or dislike about 35mm and 50mm lenses? Please do not hesitate to share with me your thoughts. I read and reply to all comments so please be sure to leave yours below.

 

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