How Does Lens Coating Affect Colour?

Hi,

I ran some very unscientific tests on film the other day. I thought I was testing lens sharpness between my primes and zooms, but the most striking difference was colour.

I used my SFX on a tripod and focused on a collection of knicknacks in front of a pale yellow wall (about the colour of a hard-boiled egg yolk). The indoor lighting was from a mixture of window light and compact flourescents. (I'd guess 80% room light). The film was 100ASA Kodak Gold.

Skim the next details quickly;

I tested my 28mm SMC prime against an SMC FA 28-80 set at 28mm and a Samsung Xenon 18-55 set at 28mm. All were set at f4 and shots were about 1/4 to 1/2 sec.

I did the same test with a 50mm 1:1:4 Super Takumar, a 55mm 1:1.8 Super-Multi-Coated Takumar, a 1:4 Super-Multi-Coated Macro, an SMC 35 - 70mm Zoom, an SMC 28 - 80mm Zoom and the Samsung 18 - 55 Zoom. All set at 50mm, f4 and shot again at about 1/4 sec.

Then two Super Takumar 1:135 (f3.5 and 2.5) primes against an SMC 1:4.5 80 - 200 Zoom set at 135mm.

Here is what I discovered.

That pale yellow wall ranged from accurate, through bright yellow to pale orange and pale green.

Most of the SMC shots were in the bright yellow, the Samsung tended to pale green and the old Super Takumars seemed the most accurate.

I attribute the orange - tinted shots to slight underexposure on the SMC 80 - 200. (I'll try this again and give it another 1/2 stop).

I guess my question is if there is a difference between those grand old Super Taks vs SMC?

I saw a real difference with the Samsung Digital (pale green), but don't have the SMC version to compare.

I thought that flourescent lighting was closer to sunlight, but could this be what's triggering these variances? (Another advantage to digital, where you can control the white balance?)

Any and all comments most welcome.

Cheers!

The only real difference between the Samsung and Pentax equivalent lenses seems to be the coatings so yes, it's not suprising to see the Samsung/Schneider gives a different colour cast.

As for Pentax's own coating, it's been updated and tweaked over the years so again slight variations shouldn't be a suprise (although to a less marked extent).

You're right about it being less visible on digital, the camera chooses the white balance so they will all get adjusted slightly differently to give what the camera thinks is the right image, meaning they'd all look pretty much the same on a DSLR.

Interesting that the oldest were the most accurate though - perhaps the newer ones are coated to give a slightly "warm" feel which would account for the brighter yellows you see?

Thanks Hefty!

I'm going to do this test again under much more controlled lighting - ie: no window light.

I may run a series with AF280T flash as well. (I've just received a little sock-type diffuser to try out).

The more I think about it, the more I'm convinced that mixed lighting was the catalyst.

As to the Super Takumars vs SMCs, I remember reading an old article which lamented the upgrade. (A really OLD article). The author primarily complained about skin tone. Maybe there was something to it.

The reason I love these old Super Taks (and Screw Mounts in general) is their beautiful build quality and silky handling. They went out of production as much as 37 years ago and may be as old as 43 years.

The only thing I can relate the handling of these wonderful pieces of machinery to, are classic firearms.

I guess the limited lenses still have that quality, but are WAY out of MY grasp!

Anyhoo, I'll try this again and let you know.

Cheers

That is a print fillm if I recall correctly. Are you comparing the negatives or the prints? Tha vagaries of the printing process might have more to do with this than anything else - to do a 'proper' test you need to use either transparancies or possibly a DSLR with the white balance fixed

Compared to older Pentax SMC K, M and A lenses, I notice a tendency towards cooler colours with the modern Pentax 18-55, 16-45 and Samsung 50-200. This is with digital. My DS's auto white balance doesn't completey elimninate any difference in colour from a lens.

I'm not certain that Samsung lenses don't have Pentax's SMC coating. I've not seen any evidence of who actually makes the lenses and what the coatings actually are, only rumours and guesses.

I'm not sure what it will take to convince you then that they are all Pentax lenses. The identical construction, apart from cosmetics, the new Vietnam factory, the identical performance, the fact that it ain't no secret...

Anyway, one of the major advantages of keeping to a single range of lenses, such as Pentax, is that the colour across the range should be very consistent. When I first started in photography and bought independent lenses I soon noticed that my 135mm was very annoying because it looked blue, the focusing turned the opposite way and it took different sized filters. Three good reasons to regret buying an independent.

Of course with digital we can easily correct colours, but even so it makes sense if there is consistency up front. It could be a good idea to ditch AWB and use a constant value, perhaps the cloudy setting if you like warm images. It's a matter of what is required.

When I did a studio shoot with a friend I used Pentax's AWB and my images were nice and warm compared to his Fuji and the custom balance he set. Although the neutral colour from the S2 Pro was probably more "correct" it didn't look as attractive, just boring.

Colour used creatively doesn't always need to be accurate.

I am fairly convinced. My response was to those who think otherwise! People keep insisting the coatings (at least) must be different.

Mac,

Tony Milner is right. You can't draw any conclusions from print film. They probably had some computerised colour balancer changing the settings for each print.

Run the test again with a slide film and see what you get.

G

Tony and George,

You're absolutely correct with regard to the prints. I just talked to the kids at the mall and they said it's out of their hands - the developing machine is on full auto - they can't override it. Peering at the negatives, I don't see huge differences - in fact, I can't see ANY!

I'll run a slide film through in more controlled conditions - may take a while, but I'll get back to y'all.

John,

I didn't mean to imply that the Samsung isn't the same as the Pentax 18-55mm, I just didn't have a Pentax to compare, and was comparing it to older lenses It did really well on clarity - even against my beloved M42 primes at 28mm and 55mm.

I'm really happy that the Schneider and Pentax 18-55mm really are the same - saved me a bit of money.

Thanks for all your input, folks!

Excerpt from Amateur Photographer, 27 October 2007, pages 38-39 (lens test for Pentax SMC DA12-24mm f4 ED AL (IF) / Samsung D-Xenon 12-24mm f4 and Pentax SMC DA 50-200mm f4-5.6 ED / Samsung D-Xenon 50-200mm f4-5.6):

"...There is a difference in the colour reflected by the anti-reflection coatings, the Schneider having a strong bluish/green tinge and the Pentax a little paler..."

"...It is understood that the Samsung lens has Schneider coatings and the Pentax the firm's well known SMC (super multi coating) treatment. This may account for the Samsung having the marginally higher light transmission. Though technically an advantage, it is at a level unlikely to be of importance in everyday photography..."

Nobody is suggesting that the lenses are not optically and mechanically identical, nor that they're not built in the same factory from the same components, probably on the same production lines by the same people. But why do people find it such a stretch of the imagination to think they use different coatings, especially when the evidence of this is there for anyone who wishes to compare them side-by-side to see? After all, they're smart enough to stick different badges on them and change the rubber grips - I think the Vietnamese are cleverer than some people give them credit for...

I can imagine different coatings being supplied. I can also imagine them being the same. It would be nice to have some evidence beyond Amateur Photographer's "understanding", or at least to know where their understanding comes from. It's still just rumour and guesswork until then.

Comparing a Samsung 50-200 and a Pentax 18-55 side-by-side, the colours reflected by the coatings look the same to me.

They look the same to me as well.

Simple. It's costly to have to set up two coating systems instead of one, and nowadays companies are too savvy to spend extra money when they don't have to.

So, for me, the balance of probability is firmly on the side of the coatings being the same.

G