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Lens focus The place to talk about your camera's glassware.

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Old 23rd November 2018
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Lenses: relative length & diameter

I am no expert in the physics involved in lens-making but always thought that with same-fit lenses having the same max apertures, the lens with a longer focal length would be longer and larger than the other one. If that is the case, how is it that the Sigma 56mm f1.4 DC DN is significantly shorter than the Sigma 30mm f1.4 DC DN (which I own and do NOT think is too big like some people do)?
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Old 23rd November 2018
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Re: Lenses: relative length & diameter

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Originally Posted by Loup Garou View Post
I am no expert in the physics involved in lens-making but always thought that with same-fit lenses having the same max apertures, the lens with a longer focal length would be longer and larger than the other one. If that is the case, how is it that the Sigma 56mm f1.4 DC DN is significantly shorter than the Sigma 30mm f1.4 DC DN (which I own and do NOT think is too big like some people do)?
It's quite trendy with lenses designed for digital sensors to be physically long. Look at, say, the new 50mm Nikon and Canon mirrorless lenses and compare them to something like a Zuiko (film era) 50mm lens - the new ones are more than twice as long.

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Old 23rd November 2018
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Re: Lenses: relative length & diameter

Iíve assumed itís down to the rise in resolution of sensors, plus the testing regimes of organisations like dxo, which push manufacturers to create more and more exotic lens designs with multiple fancy elements to reduce aberrations and increase Ďsharpnessí. You canít squeeze all that glass in to the same physical volume.

There are also several classic lens designs that tended to be used for particular focal lengths and apertures, some of which were and still are more compact than others.

Several full frame manufacturers have actually been working on the size and weight of their latest tele zooms, because the market has been pressing them on this, as well. I have been told recent Sony and Canikon 100-400 and 80-300 zooms are more compact, lighter and also better balanced in the hand than their earlier manifestations.

AF motors take a lot of space as well, especially the ones designed to produce the speed of response analysed by dxo etc.
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Old 23rd November 2018
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Re: Lenses: relative length & diameter

That sounds encouraging. What I'd love Sigma to do then is to design a 150-400mm f4.5-5.6 MFT lens that is only 125mm long and has no more than 72mm filter thread up front. With that, a weight of up to 500g would be fine.

Is that physically even possible?
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Old 23rd November 2018
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Re: Lenses: relative length & diameter

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Originally Posted by Loup Garou View Post
That sounds encouraging. What I'd love Sigma to do then is to design a 150-400mm f4.5-5.6 MFT lens that is only 125mm long and has no more than 72mm filter thread up front. With that, a weight of up to 500g would be fine.

Is that physically even possible?
Dunno. Thatís beyond even my armchair lens designer pay grade. Thereíd be thousands of experts on dpreview able to give you their definitive opinion, though...

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Re: Lenses: relative length & diameter

BTW the huge mount diameters in both the new Nikon and Canon full frame systems are necessary to meet the market demand for faster and faster lenses (one or other of them has an f0.95 50mm on the horizon, which is going to be huge and will weigh a ton). Never mind that real photographers are rarely going to need gear like this (and the Nikon hasn’t even got eye-detect AF, I believe, so most normal people won’t be able to get them in focus for portraits at full aperture, anyway).

As ever, people may regret what they’ve been asking for.

Since the bayonet end of the matching lenses are going to have to be large and heavy, this is going to work against them producing compact lenses, so Olympus may maintain more of a size advantage than many commentators have spotted.

The Sony EF full frame bayonet is much narrower and has apparently needed some optical compromises to cover the sensor, but this has allowed them to build more compact lenses (although looking at the new 400 f2.8 you’d wonder).
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Old 23rd November 2018
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Re: Lenses: relative length & diameter

My Panasonic 100-300mm f4-5.6 is 126mm long, has a 67mm filter thread and weighs just over 500g. That fits well into my camera bag inside its padded JJC case. The way I am thinking, that is a design over 6 years old, is a 3X zoom and a larger aperture range than what I am thinking of. It works very well in all departments.

That is what makes me wonder if Sigma (or someone similar) could design the 150-400mm f4.5-5.6 lens within the same dimensions - at least the length with the new tech available. It has less than 3X zoom.
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Old 23rd November 2018
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Re: Lenses: relative length & diameter

One thing that mystifies me is Olympus's 25mm and 45mm f/1.8 lenses. Both are lovely - but how come the 45mm is only fractionally longer, fractionally narrower, significantly lighter (116g vs 137 according to the spec) than the 25, and even more significantly cheaper (GBP199 vs 299 at Wex at the moment). It is the same aperture, nearly twice the focal length and of excellent optical quality so I would expect it to be bigger in all respects.

John
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Re: Lenses: relative length & diameter

I never had the Olympus 25mm f1.8 but having owned the 45mm f1.8 for 5 years, often wondered about its compact size. The price per se might be something to do with marketing policy, popularity etc. The 45mm f1.8 is certainly one of the best value great lenses around, as is the Sigma 30mm f1.4. I paid £239 at Wex for that one, NEW, soon after it came out.
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Old 24th November 2018
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Re: Lenses: relative length & diameter

Quote:
Originally Posted by Loup Garou View Post
I am no expert in the physics involved in lens-making but always thought that with same-fit lenses having the same max apertures, the lens with a longer focal length would be longer and larger than the other one. If that is the case, how is it that the Sigma 56mm f1.4 DC DN is significantly shorter than the Sigma 30mm f1.4 DC DN (which I own and do NOT think is too big like some people do)?

There are a couple of crafty lenses designs that were invented around 100 years ago:
Telephoto lenses use a design that allows the lens to be physically shorter than it's focal length. Today the term is often missused to just mean a long focal length lens. Not all long lenses are telephotos & some normal lenses are in fact telephoto.



The opposite arrangement retro focus designs allowed wide lenses to have more distance behind the lens that it's focal length would suggest. This was VITAL when you had to get an SLR's viewing mirror into the gap.
With modern mirrorless camera designs that reasoning for a retrofocus lens is no longer significant - but I suspect there are other advantages such as having the light more perpendicular to the sensor.


Todays lenses are often much more complicated & can be retrofocus at short focal lengths and telephoto at longer focal lengths.

There are practical advantages of compact lenses causing some designers to make smaller lenses even at the expense of slightly inferior optics.
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Old 24th November 2018
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Re: Lenses: relative length & diameter

Quote:
Originally Posted by Loup Garou View Post
...........how is it that the Sigma 56mm f1.4 DC DN is significantly shorter than the Sigma 30mm f1.4 DC DN (which I own and do NOT think is too big like some people do)?

Most 'long' lenses use the so-called 'telephoto' design, which makes the overall length of the assembly shorter than the focal length would suggest. Conversely, many wide angle lenses use a 'reverse telephoto' design, which makes the front lens smaller in diameter than would otherwise be needed to collect light out into the corners of the image but also makes the overall assembly longer than the focal length suggests.



In fact, 'fast' wide angles can be quite large, such that, for portrait photographers, who want a shallow depth of field, there is little advantage, in terms of size and weight, to be gained from using smaller formats. That's why we see lenses such as the 42.5mm f/0.95 lenses for MFT cameras, which provide similar values for both angle-of-view and depth-of-field to an 85mm f/1.8 lens on 'full frame'.
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