70mm Why?

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Wayne
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What is a 70mm focal length "perfect" for?

I have not heard of many 70mm primes, yet plenty top class glass ends or starts with 70mm. 24-70, 70-200 etc.

Am I missing out on something?
 
The only one I know of is the Pentax 70mm DA (for the crop cameras), guess that equates to 105mm which is a popular FL for headshots.
 
Why does a focal length have to be good for something.

24-70 and 70-200 is just a focal range. They have to start and stop somewhere. Perhaps there is some scientific reason why they chose 70mm but who cares.

The types of photographers using zoom lenses (usually landscape) will zoom in and and out until they get the frame they want. They don't care if is 62mm, 68mm or 70mm and if they need more reach they switch to the longer focal range.
 
[my uneducated guess]

Lenses are limited by physics and also what the market will bear. That's why we don't have a 14-14000mm f/1 yet.

If a lens is too big or too expensive, people won't buy it. If people won't buy it, people won't make it.

70mm is probably a very good starting/stopping point for cost vs size vs practicality and allows companies to make (for example) a 28-70mm and 70-200mm meaning that 2 lenses gives you 28-200mm (depending on your budget and weight/size requirements). I would imagine if they chose (for example) 55mm or 135mm, the lenses in either category would mean more expense or size on one of them. Optical quality is probably also a factor, but likely lesser.

I would imagine the hobbyist market makes up the most income for the big lens makers and that is where they aim their sweetspot. "Get these two reasonably priced & sized lenses and you're done"

Take the 28-70 f/2.8 & 70-200 f/2.8. Both are big, heavy and expensive. But if you made a 28-135 f/2.8 & a 135-200 f/2.8, the former would be much more expensive & bigger whilst the latter would offer a perceived "short" zoom range and yet likely be just as expensive. A 28-200 f/2.8 would likely be a monster in terms of weight/size and wife agro.

[/uneducated guess]
 
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Why does a focal length have to be good for something.

24-70 and 70-200 is just a focal range. They have to start and stop somewhere. Perhaps there is some scientific reason why they chose 70mm but who cares.

The types of photographers using zoom lenses (usually landscape) will zoom in and and out until they get the frame they want. They don't care if is 62mm, 68mm or 70mm and if they need more reach they switch to the longer focal range.
This^^
 
The only one I know of is the Pentax 70mm DA (for the crop cameras), guess that equates to 105mm which is a popular FL for headshots.

There's also the Sigma EX DG 70mm f2.8 macro, sharp as a razor with an AF motor that sounds like a lawnmower. Really good for portraits too.
 
70 is double 35. just saying :p
 
Similar to what @ecoleman posted I believe the rule of thumb for a quality zoom is that 3x is the best optical compromise, and the 200mm and 24mm 'other end' are fairly 'good' focal lengths. though personally I'd prefer a 28-85
 
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There are two Pentax 77mm lenses, the DA f1.8 for crop and FA f1.8 for FF. The DA one would give circa 115mm which is a good portrait focal length, the FA lens on FF is also good for portraits but a bit closer. But as Elliot, Ian and Phil have said, it's not that significant.
 
What is a 70mm focal length "perfect" for?

I have not heard of many 70mm primes, yet plenty top class glass ends or starts with 70mm. 24-70, 70-200 etc.

Am I missing out on something?
Zooms are usually worst at the extreme ends of their zoom range, so 70mm wouldn't be the best focal length zooms.

I don't think there is really a perfect use for any focal length. Most compositions work well over a moderate range of focal lengths, subjects can have an much grater range of acceptable focal lengths. Despite portraits having a 85mm focal length recommendation, they can be done successfully with a 200mm or (if surroundings are included) with at 28mm...
 
Everything in photography is a compromise- take a look at the Canon 24-105 f2.8. At 24mm, uncorrected, the lens doesnt project an image circle quite big enough to cover a full frame sensor. All of these things are constrained by cost, weight and physics and balancing between all of those. I actually think 70mm is quite a nice focal length for headshots and mid length portraits - but ideal world would be a 24-85 f2 or f1.4. Problem is, laws of physics kick in and you end with something what is just too heavy to be practical for every day. What I like about 24-70 f2.8 zooms is they are workhorse lenses that aren’t too big and heavy and that matters a lot.
 
Why any focal length? We talk about primes and 28, 35, 50, 80 etc. I have a lens
That covers every single one of those, and everything in between. *Mod edit* - learn to use a civil tongue please - there's no need for that.
 
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70mm is genuinely useful. From landscapes to closeups to some portrait applications. I find my 70mm ART macro very useful, only shame it has such a nasty stm motor
 
Thank you all for your considerations and replies: Educated me there, which was my original intention.

I had been considering that it might be something to do with distance compression within the image and that 70mm was some kind of sweet spot which I was not aware of.

Kind of with the old chestnut use 50mm and move your feet. From my investigations there is far more nuance to focal length selection than just moving closer too or farther away from the subject.

Thanks again.
 
Problem is, laws of physics kick in and you end with something what is just too heavy to be practical for every day.
Laws of physics certainly cannot be denied, but we also find with time that we just weren't too great pushing and bending them so far. Take a look at the new Sony 28-70mm f/2 GM. By all metrics including size and weight it obliterates a few year old massive and relatively soft design by Canon. This was considered "impossible" yet is available on the shelves today. In fact I find it rather tempting as long as I can find ways to account for its pricetag
 
Personally I've always found 70mm on a 24-70mm to be too shot for my style of shooting, thats why I normally go for the 24-105mm or the ever so slightly longer 85mm prime (on FF) But that said we all shoot diferently (and I dont use the 85mm much if I'm honest).
 
I think a good way to see if something is useful or not is to give it a try.

I mostly like 28/35/50mm lenses with only very occasional use of 24/85 and even rarer uses of other focal lengths but when I first bought into MFT I used a 50mm lens giving an equivalent fov of 100mm in FF terms and I've taken a lot of pictures with that combination.

So Wayne, if you struggle to see a use for 70mm why not give it a try? That's not as hard as it sounds as no matter what format you have you can get to 70mm or pretty close for eg 35mm on MFT = 70mm fov, 50mm on APS-C (other than Canon) = 75mm fov (near enough?)
 
Personally I've always found 70mm on a 24-70mm to be too shot for my style of shooting, thats why I normally go for the 24-105mm or the ever so slightly longer 85mm prime (on FF) But that said we all shoot diferently (and I dont use the 85mm much if I'm honest).
Presumably you are doing portrait and events work... This gets you nice full to maybe 3/4 length shots, small group shots, great in studio, not too great for subject isolation or long reach, certainly not ideal for headshots. It was always presumed you will have 70-200mm along to go longer whenever needed, ideally on a second body. Or as you mentioned any combination of longer primes...
Now there is a choice of 2x-105 2.8 zooms and is arguably a better choice for some instead of the two conventional zooms. There is even 35-150 from tamron which is likely very questionable at the wider end, in any case more than the alternatives.

I rather now have 28, 35, 50 and 85mm f1.4 primes, so 70mm was a true pain point. I just had to get that sigma
 
Personally I've always found 70mm on a 24-70mm to be too shot for my style of shooting, thats why I normally go for the 24-105mm or the ever so slightly longer 85mm prime (on FF) But that said we all shoot diferently (and I dont use the 85mm much if I'm honest).


I feel the same, so I went for the slower but longer option - the 24-120 (on Nikon FF). On the Fujis, I use their 18-135 which is about the same as a 28-200 on FF.
 
Presumably you are doing portrait and events work... This gets you nice full to maybe 3/4 length shots, small group shots, great in studio, not too great for subject isolation or long reach, certainly not ideal for headshots. It was always presumed you will have 70-200mm along to go longer whenever needed, ideally on a second body. Or as you mentioned any combination of longer primes...
Now there is a choice of 2x-105 2.8 zooms and is arguably a better choice for some instead of the two conventional zooms. There is even 35-150 from tamron which is likely very questionable at the wider end, in any case more than the alternatives.

I rather now have 28, 35, 50 and 85mm f1.4 primes, so 70mm was a true pain point. I just had to get that sigma
Yes I do always have a longer lens on a second body on a serious shoots
I always used to shoot primes with film, but the modern zooms are a lot better than the early film ones. I still carry a few for fast or wide open stuff though.
 
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Old zooms were designed by humans, drawing multiple optical pathways whereas modern ones are designed by computer, following many more paths to get an improved final design. Some current primes still use the same optics as the older MF designs so the IQ difference is narrowing. As Wayne says, it's still worth having some [primes] for specialist usage but zooms are plenty good enough in most instances.
 
If you think of lenses as stops of focal length with 1 stop being 1.4x and 2 stops being 2x then you get the following series for the most common focal lengths (50mm=0)

24mm -2
35mm -1
50mm 0
70mm 1
100mm 2
135mm 3
200mm 4

If you use primes, this can be a useful way of thinking about lenses and the way things scale up when you change focal length.

I guess zooms were made to match the primes people had.
 
If you think of lenses as stops of focal length with 1 stop being 1.4x and 2 stops being 2x then you get the following series for the most common focal lengths (50mm=0)

24mm -2
35mm -1
50mm 0
70mm 1
100mm 2
135mm 3
200mm 4

If you use primes, this can be a useful way of thinking about lenses and the way things scale up when you change focal length.

I guess zooms were made to match the primes people had.
A stop is a halving or doubling. Which means 24-50mm would be one stop not two as would 50-100mm.

I’m not sure I see any benefit of thinking of focal lengths as stops.
 
A stop is a halving or doubling. Which means 24-50mm would be one stop not two as would 50-100mm.

I’m not sure I see any benefit of thinking of focal lengths as stops.
Focal length, like apertures, square when it is used to determine light levels. So doubling the focal length with the same aperture diameter would mean you increase the aperture number by 2 stops (eg from /2.8 to f/5.6). This makes sense dimensionally as the same amount of light spread over a rectangle which was 1/2 as big along each side would be 4 times brighter (2 stops).
 
Focal length, like apertures, square when it is used to determine light levels. So doubling the focal length with the same aperture diameter would mean you increase the aperture number by 2 stops (eg from /2.8 to f/5.6). This makes sense dimensionally as the same amount of light spread over a rectangle which was 1/2 as big along each side would be 4 times brighter (2 stops).

My thinking wasn’t so technical.

You half or double light or you half or double speed was my thinking and therefore you”d half or double focal lengths.

Thank god we don’t think of focal lengths in stops.
 
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