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11-03-2014, 07:05 AM   #1
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Does size (lens elements/filter size) really matter?

I am wondering how important is lens element/filter when it comes to designing lenses? It seems to me that lenses made during the film era up to the DA Limited limited lenses are a great compromise between smaller lens body size (compared to Canon and Nikon) and largest aperture possible in that lens body size and still had very good to great IQ to boot, some even with pixie dust! For example, the Pentax A 50 mm F1.2 lens has a 52 mm filter size while the Canon 50L F1.2 lens filter size of 72mm and the IQ of both lenses is supposed to be similar. Pentax could have added screw drive to this lens and not have increased the filter size of this lens. The new Pentax HD DA 16-85 mm F3.5-5.6 ED DC WR lens has a filter size of 72mm which is the same size of the Sigma 18-35 mm F1.8 lens which is at least 5 times larger at the max aperture. What gives? Is it because Hoya fired all of its "Lens Elves" who used elfen magic to design Pentax lenses of the past?

11-03-2014, 07:15 AM   #2
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That's a good question...all I know is that the 43mm fa is a tny little thing and it is my best lens by far...so while size must matter, it ceratinly isnt a clear gauge of whats best....
11-03-2014, 07:39 AM   #3
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the filter does not matter at all, well except for the obvious reason that it should not give vignetting on the photo.

The same in theory goes for the front element, if all elements are created flawlessly you would only need exactly the diameter to cover the image sensor on the focal length and with the maximum F-stop the lens should be able to handle.

However, once you start adding more and more elements the need for precision gets higher and higher. And to get a bit more play you can increase the size of the front element. This will increase the size of all elements in the light path, making them easier to handle and making the permittable play between elements a bit larger. This is especially true when looking at aspherical elements.
11-03-2014, 08:16 AM   #4
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I imagine that, everything else being equal, engineering for small will drive up time and effort and thus drive up cost.

11-03-2014, 09:01 AM   #5
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Weren't many older pentax lenses 49mm filter size? I find that a beautiful system, since I can just bring one set of filters.
That aside, I think size is slowly becoming less of an factor as it used to be. The costs and practicality of big lenses probably limited the size factor back then. Nowadays it's more socially accepted. With the materials we have now, we can actually manufacture lenses that are practical and achieve top quality, and hence allowing for the bigger size factor. My 2c is that the filter size is just a side-effect of us wanting better IQ.
11-03-2014, 09:25 AM   #6
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Lenses designs nowadays are much more complex than before. An old 50 is made of 2 optical elements! Look at the Sigma 50 and Pentax 55 and you'll see how things have changed.

More elements call for larger elements or slower lenses.
11-03-2014, 11:23 AM   #7
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QuoteOriginally posted by V'cuz Quote
I am wondering how important is lens element/filter when it comes to designing lenses?
It depends and what the engineering team and marketing team are trying to make/sell. A lens design has specific flare characteristics, chromatic aberration, coma, and pincushioning. In general a larger design gives more opportunities to include other features. If size is the most important thing distortion might suffer.

The FA43 is a good example of a small lens from the Pentax lens elves of yesteryear. It gets so many optical characteristics correct and still manages to be very small. It has one flaw that most people will never see: a lot of coma distortion for astrophotography. Coma is invisible for most usage but pinpoint stars get stretched out by the distortion. Don't get me wrong - the FA43 is a great lens but no lens is perfect. If the FA43 was redesigned for minimal coma the size might suffer.

QuoteOriginally posted by V'cuz Quote
The new Pentax HD DA 16-85 mm F3.5-5.6 ED DC WR lens has a filter size of 72mm which is the same size of the Sigma 18-35 mm F1.8 lens which is at least 5 times larger at the max aperture. What gives?
Zoom range was more of a priority than size and aperture for the Pentax 16-85 design. The Sigma 18-35 sacrifices zoom range.
11-03-2014, 11:29 AM   #8
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QuoteOriginally posted by V'cuz Quote
The new Pentax HD DA 16-85 mm F3.5-5.6 ED DC WR lens has a filter size of 72mm which is the same size of the Sigma 18-35 mm F1.8 lens which is at least 5 times larger at the max aperture. What gives? Is it because Hoya fired all of its "Lens Elves" who used elfen magic to design Pentax lenses of the past?
The "Lens Elves" of the past didn't have to design 5.3x lenses.

11-03-2014, 01:17 PM   #9
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I was hoping that when Pentax would eventually make more primes, they would be compact as the ones they had in the past ( they have a lot of lens patents). They could use the new coatings and tweak the lens elements to improve the IQ. If you have existing patents on a lens, how hard is it to improve that lens? Does Pentax make their own lens elements?
11-03-2014, 03:01 PM   #10
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QuoteOriginally posted by Anthen Quote
The costs and practicality of big lenses probably limited the size factor back then. Nowadays it's more socially accepted.
I can't speak for everyone but Social acceptance is not my top priority when choosing photographic equipment
11-03-2014, 04:43 PM   #11
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Does it matter? Yes, of course it matters. The engineers who design lenses don't sit down and say "Let's design a lens with a 72mm filter. That will be cool!" I'm not an optical engineer, but there's surely a reason larger elements are used. You might think that smaller = less material, so less cost, but smaller elements may require tighter manufacturing tolerances that ultimately cost more than using more glass and plastic (both of which are not terribly expensive). I don't know the actual reason, but the engineers are most certainly making a trade off somewhere in the design process.

From the consumer perspective, it only matters when you start considering the cost of filters. Canon uses some 82mm threads on their lenses (the 16-35 f/2.8 is one of them); the cost for filters for that lens are outrageous. In fact, thread size influenced one of my purchases. I had the Sigma 17-70C and was looking for a faster lens. I considered the FA31, but since I'd have to replace my entire filter collection, the cost of it was nearly double the Sigma 18-35 f/1.8, which shares a 72mm thread with the 17-70C, when I was done with it all. That made the decision a lot easier.

QuoteOriginally posted by Anthen Quote
The costs and practicality of big lenses probably limited the size factor back then. Nowadays it's more socially accepted.
Film camera bodies were a lot smaller. A film SLR is only a bit larger than the roll of film it holds (that's about all it is, a holder of film + an optical path and a light meter, maybe some other sensors) and there's very little weight to them. A big lens would make it very hard to hold the camera, unless you put an automatic winder on there (the equivalent of a battery grip these days), but even that won't help much with balance.
11-03-2014, 05:31 PM   #12
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We have had a lot of discussions about lens / filter size.

Here's what matters. For telephoto lenses, ultimately the front element diameter has to be the focal length / f stop. And the filter needs to be the minimum of this diameter, with adjustment for the recess of the front element in the front of the lens,many the field of view

For wide angle lenses , especially ultra wide lenses and zooms, with huge curved front elements the lens design dictates how big the filter is, and because of the size of the front element and depth of curvature, you need a really big filter to avoid vignetting.

If you want a good idea of how small a front element can be look at a tamron 24/2.5 adaptall lens. It is about 10 mm in diameter, but the filter is , I think 52 mm just o avoid vignetting on a film dody considering the field of view
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