[Rob Payne]

Hi Pentaxians,
I am relatively new to the camera world but I have mastered the basics and can take a technically competent picture (correct exposure, desired depth of field etc etc) but one thing makes me scratch my head...
and that is the choice of lens, focal lengthwise.

I know the extreme examples, wide for landscape and zoom for catching the far off but in between drives me mad.

When I take the camera out I usually have no idea at all what I plan to shoot so I usually take my sigma 28-300 super wide lens which in good light gives me great pictures, of various types.
But I am aware that this is a bit of a blunderbuss approach, and I may be sacrificing some sharpness by using one lens.

I have a dozen or more pentax lenses ranging from 28/50/135 primes to a host of 35-80/28-70/35-105 etc.
This last category of medium zooms gives me the headache as I really dont know what are the best uses for each.
To a certain degree I guess its a matter of personal choice but I cant find any fixed logic to hang a preference from.

I would be very interested to hear your opinions and reasons for choosing which medium zooms you choose under which circumstances.

All the best
Rob

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Last edited by Rob Payne; 07-20-2021 at 03:02 AM.

[Sandy Hancock]

Find a perspective which gives the desired spacial relationships for your foreground and background elements.

Select your focal length to give you the framing you want.

[Bertrand3000]

First, we need to know what the crop factor is, which means, are you full frame (K1) or APS-C?

Conventional wisdom is 50mm (in fact 43mm) is "human point of view" for full frame. On APS-C, this is between 28 and 35mm.

For portrait, it is usually done with short telephoto: around 80mm full frame, or 50mm for APS-C.

But focal length is not the only factor. Maximum Aperture is also very important, and autofocus speed can be key for long lenses if you are going to shoot wildlife.

[jersey]

What is the need for medium zooms? Same as for any other lens. You get them when you need such focal lengths. There is not much philosophy around them. Not everyone needs long reach, so shorter zooms make more sens for them. Some need fast lenses, so they get two (normal/long) zooms as with shorter range you usually get faster aperture. Etc. It is strictly technical.

I use Sigma 17-50 and Pentax 55-300 that complement each other. 55-300 I bought for ultra fast autofocus and range, it was and still is only Pentax offering with long range and really fast AF motor. 17-50 because I needed something wide and faster then 18-55 WR or 15mm Ltd. Why not 28-300 from Sigma? Because I need weather resistance for longer lens (for shorter too) that Sigma lenses don't have.

If I had so many lenses as you I would most likely chose what I like and use most and sold rest. There is little reason to keep overlapping lenses.

[ProfessorBuzz]

It's all about the angle of view, and that determines how much you see in the image and how close you have to be to the subject.

Don't confuse Zoom and Telephoto - a zoom lets you run through a range of focal length. Zoom gives you flexibility - carry 1 lens instead of 2 or 3.


A long lens will isolate the sujbect, and will appear to compress distance.
e.g. shoot a street in your town, and you'll see the cars/cyclists/street light poles are all compressed.
e.g. focus on a person in a busy scene - it will be just them in focus.


Why? A telephoto lens will help you isolate a subject, as it has a narrow field of view - it has a narrower angle of view.

Take a day and just shoot at the maximum focal length of your longest lens. Snap birds, people, cars, trees, mountains. Get used to what it does.
If you treat it as a zoom, you may never get the difference.

[Fogel70]

IMO the best images can be when going against tradition.So try to be a bit creative and you may capture more interesting images.
Like using telephoto or medium zooms for landscape, wide angle for portraits, or fish-eye for sports.

Sometimes it is best to limit yourself to just one lens and then try to capture all sorts of images with it. Then you may discover something new.

[Bruce Clark]

Suggestion; take one lens out for a day and use it for everything you like to photograph. Next day take a different one and so on. Experience and understanding will kick in.

[Wasp]

Interesting question. Firstly, focal length determines framing. If you have the luxury of moving around to do this, you can get by with only one lens. In the real world this is seldomly the case. The landscape of your choice usually have obstacles that get in the way. The animal might decide to move away if you get too close, or even to attack you. In sports you can't be on the playing field. Et cetera.

So you reach for a telephoto or wide angle to get the framing of your choice. This brings up the second thing that changes with focal length is depth of field. Wide angles have lots of it. Telephoto have less, making accurate focus a challenge.

The next thing is camera shake. Telephotos need a faster shutter speed to keep this at bay. Modern cameras have things like Shake Reduction to help with this,but there are limits.

Finally, there is perspective. Wides exaggerate it and teles compress it.

There are few hard and fast rules about focal lengths. The only one I can think of is to use a short telephoto for close up portraits. Using a wide or standard lens means that their noses appear large and their ears small - not a good look.

[Kozlok]

I did a series where I took the “same” photo with different focal lengths. Did maybe 30 different subjects. It gave me a lot of insight on which FL to use for whatever effect I’m going for.

[RICHARD L.]

Suggestion : Put your zoom on a tripod and take various pictures at all significant focal lengths. This way, you will learn the picture potential of your lens and what you like the most. You can also try an assortment of fixed focal length lenses to compare their field of view. Here are a few examples : 1) Three pictures of a river taken with a K1 + DFA* 70-200 mm f/2.8 @ 100, 140 and 200 mm. 2) Three images of the same river in winter taken with a 645Z + P67 45 mm f/4, P67 90 mm f/2.8 and P67 165 mm f/2.8. You will learn to anticipate the results that can be obtained by each this way.

Pentax K1 + DFA* 70-200 mm zoom






Pentax 645Z + various P67 lenses

[bdery]

When I take the camera out I usually have no idea at all what I plan to shoot so I usually take my sigma 28-300 ultra wide lens which in good light gives me great pictures, of various types.
But I am aware that this is a bit of a blunderbuss approach, and I may be sacrificing some sharpness by using one lens.

Learning is about making mistakes, and understanding them. You mention your "blunderbuss" approach, I think having such a wide focal range on your lens lets you learn.

Experiment with it, try to frame differently, and then look at your images, see which you prefer, what are the repeating patterns, etc. You'll find out which focal lengths you like best.

In general, on full frame 50-85mm is seen as ideal for portraits, 20-30mm for landscapes, wider for specific uses or cramped spaces, longer for subject isolation and distant subjects. Of course these are not fixed rules, just guidelines.

On APS-C, divide the focal lengths by 1.5 to get an equivalent feel.

You'll also find that in many cases the aperture plays an important role. For instance for portraits a shallow DOF is more important than a precise focal length.

[othar]

While there are certain focal lengths that are usually more common for certain situations, there are multiple examples available with unusual focal length / subject combinations that look fabulous (full-body portraits with a wide angle lens, or landscape pictures with a long telephoto lens,...).
The key in my opinion is, understanding how certain focal lengths influence the resulting image differently, then you can deside whether a certain focal lengths suits your needs or not.

For portraits typical focal lengths are normal (~30mm for APS-C; ~50mm for FF) to shortish telephoto lenses (up to 135mm maybe 200mm), because wide angle lenses might distort the head shape and with too long lenses your working distance to the model gets awkwardly big (the resulting image with very long lenses can also create a voyeuristic feeling). As mentioned before can you still use wider or longer lenses to do portraits, but you should be aware of how they influence the image.

My usual genre is landscape photography. For mountaineering I usually have my F 35-70mm lens on the camera (K-3; APS-C) and either my Cosina Cosinon-T 135mm or my F 80-200mm lens in the bag (sometimes I also bring my A 50mm f1.7 lens instead of the F 35-70mm lens).
I prefer normal to short telephoto lenses over wide angle lenses (like my DA 18-55mm lens) because I don't have to choose focal length that carefull when taking pictures of my companions (to avoid distortions of wide angle lenses) and if I need a wider field of view I can stitch multiple images together later.

[photoptimist]

Here are a three of ways of looking at it:

1. How big is the subject and how far away are you from it: If you are a short distance to a very big object (e.g., skyscraper across the street), you'll need a very short focal length (ultra-wide angle) lens. If you are a long distance from a very small object (e.g., a bird up in a tree), you'll need a long focal length or telephoto lens. If you like, there's some really simple geometric math (known as similar triangles) for figuring out the lens to use: Focal_Length = (Width_of_Sensor)*(DIstance_to_Subject)/(Width_of_Subject)

2. How much perspective do you want: Focal length enables creative control over the relative visual size of foreground objects, the mid-ground subject, and background objects. Shorter focal length lenses (wide angle) tend to exaggerate the perspective. For example a ultrawide angle lens can make a foreground bouquet look larger relative to a mid-distance bride who looks larger than the distant wedding chapel. Longer focal length lenses (telephoto) flatten perspective so that objects tend to retain their relative sizes. The flip-side is that perspective also exaggerates distance. The strong perspective effects of a wide angle lens make background object look farther than then are and foreground object look closer than they are. Telephoto lenses are said to "compress" distance with all foreground objects, mid-ground, and background objects seeming to be at the same distance.

3. Practicality and intentions: If you don't want to change lenses but need to shoot diverse kinds of subjects (from birdies to buildings), bring a superzoom like the Sigma 28-300. If you can't change your distance to the subject matter, bring a zoom or a bag of prime lenses. If you don't want to have a big, conspicuous camera, bring a smaller lens. If you know you only want to shoot landscapes, bring just a wide-angle prime. If you know you only want to shoot portraits, bring just a short telephoto prime. If you want the sharpest possible pictures bring a good prime or very good zoom.

P.S. Small correction on terminology: A lens that helps enlarge small distant objects is known as a "telephoto" lens, not a "zoom." A "zoom" is just a lens that can vary the focal length, not a reference to any particular focal length. There are "ultrawide zooms" (e.g., the Pentax DFA 15-30mm ) and there are "telephoto zooms" (e.g., the Pentax DFA 150-450mm ). Also note that "ultrawide" tends to refer to lenses shorter than 24mm on full frame cameras or 16mm on APS-C cameras. Your 28-300 is not ultrawide but it is a "super zoom".

[VictorDA]

ake one lens out for a day and use it for everything you like to photograph. Next day take a different one and so on.

I like to do exactly that! When photogrtaphy is a hobby and you don't actually "need" to get optimal pictures at the end of the day, I found it's the best way to really get intimate knowledge of the lenses and what they can and can't achieve. Especially interesting exercise with prime lenses (1 fixed focal length).

I think having such a wide focal range on your lens lets you learn. Experiment with it, try to frame differently, and then look at your images, see which you prefer, what are the repeating patterns, etc. You'll find out which focal lengths you like best.

Personally, I would not recommend this approach so much. In theory yes, it makes sense, but: I find a superzoom makes me lazy, often using one end of the range or the other and generally avoiding any challenge, therefore any reflexion (it might be just me though).
If the OP already has a solid collection of lenses, I would suggest taking out primes and short-range zooms (x2, x2.5: things like 35-70, 20-40, 24-50, 28-70...), they'll force him to think about the composition and really learn the field of view/focal length relationship
And the most important: have fun! Otherwise there's no point...

[swanlefitte]

As said the subject to background/foreground is the main composional reason for a focal length when given a choice.
Where you can stand in relation to your subject will limit your choice.

These 2 things allow for subject size in the frame and how much else is in the frame.

I did a demonstration on cows. Post 10 shows how if you double the fl and distance your subject is virtually the same but the background both grows and moves out of frame. https://www.pentaxforums.com/forums/173-general-photography/420755-my-though...mposition.html