[hjoseph7]

I'm not a glass-worker and don't know much about the lens making process, but I often wondered what makes certain lenses produce more contrast than others ? If I compare all of my lenses, some produce better colors and/or better contrast than others. For example I just started testing my Takumar 35mm f3.5 which arrived in the mail a few days ago. This lens produces extremely saturated colors especially the red, brown and greens. Perfect for landscapes I would say, but how did the folks at Pentax arrive at this formula ?


Is it the lens coatings, maybe but even some older lenses with single coatings can produce very colorful images. I don't mean to sound stupid, but when I look through the lens everything looks clear to me.


Once I read a review on a lens, I forget which one and the reviewer claimed that Pentax purposely oversaturates the image on their cameras to produce brighter, more saturated pictures. if this is true then that would mean that they manipulate the sensor, but that still does not answer the question of why some lenses produce more contrast than others ?

[MadMathMind]

Technically speaking? It has to do with the glass's ability to resolve high frequency components. It's optical dynamic range, basically. The more dynamic range of light frequency components the lens has, the darker the dark parts and the brighter the bright parts. Low frequencies are no problem; it's resolving the high stuff that is always hard. In the digital domain, the equivalent result is the Shannon-Nqyist Sampling Theorem. It's basically the same idea with lenses; if the lens doesn't damp high frequency content, then it will have better contrast.

[Adam]

This might prove to be an interesting read:
All About SLR Lens Coatings - Articles and Tips | PentaxForums.com

[dms]

1) (better) Lens coatings further reduces flare, as does having fewer glass-air surfaces, and the flare has a general veiling affect--reducing contrast.
2) Also the higher the resolution the less neighboring (differing color/intensity) light beams are mixed--leading to higher contrast/micro contrast.
3) Vis-a-vis (above 2) it is also true some lenses have very high contrast and yet not so great resolution (The FA* 24mm is reputed to be one)--and I am not sure why this is the case.

[rrstuff]

I'm not a glass-worker and don't know much about the lens making process, but I often wondered what makes certain lenses produce more contrast than others ? If I compare all of my lenses, some produce better colors and/or better contrast than others. For example I just started testing my Takumar 35mm f3.5 which arrived in the mail a few days ago. This lens produces extremely saturated colors especially the red, brown and greens. Perfect for landscapes I would say, but how did the folks at Pentax arrive at this formula ?


Is it the lens coatings, maybe but even some older lenses with single coatings can produce very colorful images. I don't mean to sound stupid, but when I look through the lens everything looks clear to me.


Once I read a review on a lens, I forget which one and the reviewer claimed that Pentax purposely oversaturates the image on their cameras to produce brighter, more saturated pictures. if this is true then that would mean that they manipulate the sensor, but that still does not answer the question of why some lenses produce more contrast than others ?

Lens designers have two ways to make the contrast higher - increase the transmittance and decrease the number of interfaces between air and the lenses. Many of the pentax primes have very few elements and they historically had good coatings that transmitted a lot of light.

Let's say that 99.7% of the light passes through each lens. If you have 5 lenses with air-glass interfaces, then total transmitted light is 99%, then 0.99^5 = 95.1%. If you have 10 interfaces it is already 90.4%, and many zoom lenses have more. So fewer elements is better for contrast. If you have better coatings, you could lose less light at each interface and for 99.5% transmission and 5 elements 0.995^5 = 97.5%, and for 10 of them = 95.1%. The best lenses these days have 99.7-99.8% transmission for each lens, and it varies a little for different colors. See Fa 43mm for an example: Pentax smc FA 43 mm f/1.9 Limited review - Ghosting, flares and transmission - LensTip.com

Now look at the block diagram of the 35 F3.5 Tak: https://www.pentaxforums.com/lensreviews/data/20/Super-Multi-Coated_TAKUMAR_35_3_5_optics.jpg
And compare that to a zoom lens: SMC Pentax-FA* 28-70mm F2.8 AL Reviews - FA Zoom Lenses - Pentax Lens Reviews & Lens Database

Even with poorer old coatings, takumar has much easier job to do with just a few glass pieces in there.
I hope this makes sense, cheers.

[dms]

Perhaps it will help to explain that increased light transmission is "by itself" not going to affect the contrast. The light that is not transmitted is either reflected or absorbed--and it is the reflected light that causes the "veiling flare" (i.e., reduced contrast). This because the light is (first) reflected forward but then it is partially reflected back again off the rear of another glass surface.

BTW I don't mean to say increased light transmittance doesn't improve contrast--it does--but I wanted to clarify by what mechanism it does so! Greater transmittance means less reflected light, and thus less reflected light subject to a second (multiple) reflection back to the film plane/sensor.

[derekkite]

When light hits the first element it is bent and refracts, or separates into the different wavelengths. The combination of other elements essentially puts it back together, allowing the designer to accentuate certain wavelengths to create the quality desired. Different glass composition, coatings as well as combinations of convex and concave lens surfaces make up the result.

There was an interesting series of articles on the lens rental site describing the history of lens design.

LensRentals.com - From Petzval's Sum to Abbe's Number

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Last edited by derekkite; 08-31-2015 at 08:38 PM.