L-glass and Cokin filters - DPChallenge Forums

Sigma 35mm f/1.4 DG HSM for Canon

10/29/2007 04:43:18 PM · #1

I know the theory would go that putting a cheap piece of plastic in front of an expensive lens is fairly counterproductive, but does anybody have any links that actually look at comparisons of image degradation between a cheap filter and an expensive one? It could be for any type of filter; polarizer, ND filter, grad filter, etc.

Ubersteiny

Canon EOS-5D Mark II

10/29/2007 05:54:07 PM · #2

I don't have any comparisons but here is one of my photos with the 24-70 and a graduated tobacco filter and graduated neutral density filter

Canon EF 17-40mm f/4.0L USM

10/29/2007 06:32:43 PM · #3

So it's all just nasty rumor?

I'm afraid I can't tell much from you picture noisemaker because a) you don't link it and b) I have nothing to compare it to and c) it may not be 100% crop.

soup

Canon EOS-30D

10/29/2007 06:52:57 PM · #4

i guess A ;}

Originally posted by DrAchoo:

I'm afraid I can't tell much from you picture noisemaker because a) you don't link it and b) I have nothing to compare it to and c) it may not be 100% crop.

Canon EF 16-35mm f/2.8L USM

10/29/2007 06:56:56 PM · #5

You'll mostly see the difference on the margins of the light quality.

You'll get more flare, in situations when you'd get flare - because there is an extra piece of glass, because it is at the very front of the lens, because it may not be coated or might just be using a more reflective coating than you might have with just the lens optics or a more expensive coating material, or different glass composition.

In 'normal' operation, with 'normal' light it won't make much difference - maybe less contrast, maybe a slight colour shift.

But it is more about those marginal situations - shooting directly into the sunlight, or in a club at night with more direct light sources that could cause reflections.

Even then, those reflections and general loss of contrast aren't the classically tacky lens flare you can add in photoshop - just a general lowering of quality.

You can usually see that if you shoot with a lens that's in light compared to the same lens if you flag the light on it - the difference is very easy to see side by side, harder to see in a shot in general (otherwise everyone would use lens hoods)

So in general, the answer is, 'it depends'

it depends if you shoot in interesting light or not
it depends on if you use lens hoods or not
it depends on if you flag your lens in those sorts of lighting situations or not

The last glass I had over my lens was a pint glass, so I'm maybe not the best person to ask about concerns like that. Most of the time these days I seem to be trying to create flare, not get rid of it.

Message edited by author 2007-10-29 19:02:10.

Falc

Canon EOS-1D Mark III

10/29/2007 06:59:15 PM · #6

Doc, I used to use Cokin ND in front of my 16-35mm f2.8 L. I now use only Lee filters because of the colour cast produced by stacked cokin plastic. I say there is a huge difference in quality, though I cn't prove it.

10/29/2007 07:20:17 PM · #7

It's pretty amazing to me that there is a dearth of information about this when the difference in price between filters can be say from $50 for a 77mm polarizer to $250 for the same thing of "better quality".

Lee and Cokin are two more examples. You'd think somebody would have looked at this and posted some results when we are looking at $15 for Cokin and $100 for Lee grad filters.

10/29/2007 07:29:12 PM · #8

Originally posted by DrAchoo:

You'd think somebody would have looked at this and posted some results when we are looking at $15 for Cokin and $100 for Lee grad filters.

There are plenty of results out there. Its the same reason you bought 'L' lenses. Coatings, number of coatings, quality of coatings, transmission of light, resistance to flare, scratch resistance, potential for vignetting.

Message edited by author 2007-10-29 19:31:00.

10/29/2007 07:31:23 PM · #9

Originally posted by Gordon:

Originally posted by DrAchoo:
You'd think somebody would have looked at this and posted some results when we are looking at $15 for Cokin and $100 for Lee grad filters.

There are plenty of results out there. Its the same reason you bought 'L' lenses. Coatings, number of coatings, quality of coatings, transmission of light, resistance to flare, scratch resistance, potential for vignetting.

Link me up big boy. My googling has resulted in nothing other then anecdote.

10/29/2007 07:37:35 PM · #10

Originally posted by DrAchoo:

Link me up big boy. My googling has resulted in nothing other then anecdote. [/quote]

What do you want a link to ? Something that shows plastic is less optically pure than glass ? Go look through a plastic sheet and get back to me.

Something that shows that resin can be scratched more easily than glass ? Use a pointed bit of metal.

Are you looking for MTF charts for your filters ?

The value is in a whole lot of other aspects, just like L lenses. If you want to pay all that money for very expensively coated lens elements, to reduce the flare, internal reflection and contrast degradation, then put an uncoated bit of glass on as the last element where the lights going to hit it, then why bother buying all that other coated glass in the first place ?

I.e., if you think the coatings are worthless - don't buy L lenses.

Here's a starter for 10

Here's also an example of the differing effects of different optical coatings You get what you pay for, but you have to decide if its worth it to you. In many ways similar to the variety of types of glass and coatings available for framing work. Plenty of people use plastic, some use glass, others use anti-reflective glass, some pay for museum grade framing materials. Similar arguments in play.

You could also just fall back to optical physics. The lenses are designed to focus based on the actual number of air/glass boundaries between the groups and lenses within those groups. Adding a filter adds another two air/glass boundaries that will soften the results to a certain extent. The type of glass you use and the refractive index of it plus the coatings factors in as well.

Message edited by author 2007-10-29 19:47:10.

10/29/2007 07:44:46 PM · #11

My point is while I understand the theory behind it, if it really made a difference don't you think the expensive filter companies would proudly show concrete examples of superiority when they are asking 5x the price? My skeptical nature kicks in when you just can't find that stuff. It seems to me that if it were the case it would be easily findable because one side has an expressed business interest in making that info known. Take Canon lenses versus 3rd party lenses. You can find a dozen sites easily comparing everything possible between two lenses. We can easily see what the extra money a Canon lens costs either gets you or doesn't.

I'm not necessarily just talking about Cokin vs. Lee filters, although that's a great example. But how about a $40 polarizer versus a $250 polarizer?

Flare may also be the most obvious difference (and that makes sense to me), but I also wonder about pure image degradation. Does it occur? I can see why it would, but does it actually happen?

I'm not jumping on you Gordon, your answer is 100% in-line with what everybody else says, but nobody seems to ask why we can't see actual examples out there. Could it be there really isn't a difference and the Lee people are just selling a name?

Message edited by author 2007-10-29 19:45:59.

Nikon AF-S DX Zoom-Nikkor 16-85 f/3.5-5.6G ED VR

10/29/2007 07:49:08 PM · #12

Originally posted by DrAchoo:

I'm not jumping on you Gordon, your answer is 100% in-line with what everybody else says, but nobody seems to ask why we can't see actual examples out there. Could it be there really isn't a difference and the Lee people are just selling a name?

So how many sites are showing you side by side differences of the contrast/ colour improvements made using Canon L lenses compared to Sigma ? I don't actually think I've ever seen those either - yet 'everyone' claims its true.

Anyway - I already linked you to a set of graphs that show the difference you were asking for - I'm not quite sure what more you want. Lee/ cokin etc also publish that info in their literature.

You could always go to the font of all things technical, Ken Rockwell, for the pretty picture version, if you don't believe the science.

Message edited by author 2007-10-29 19:56:49.

talmy

Nikon D300s

10/29/2007 07:54:01 PM · #13

Glass quality doesn't matter when you use a Cokin filter. I found flare so bad with a Cokin graduated ND filter that I quickly stopped using them. Trouble is that just those cases where I would want to use them (bright sky, dark terrain) were just those where flare would be at the worst.

My other bad investment -- over $100 for a CP filter for my Sigma Bigma. Only brand I could find in a size that would fit was a Tiffen. It adds an ugly brown cast to everything I shoot with it and I have no idea how to remove a brown cast. (Maybe it was a Cokin tobacco filter in disguise?)

10/29/2007 07:58:37 PM · #14

Originally posted by Gordon:

Anyway - I already linked you to a set of graphs that show the difference you were asking for - I'm not quite sure what more you want. Lee/ cokin etc also publish that info in their literature.

What I want is something like Luminous Landscapes sending a dude out into the real world with a set of Cokin ND filters and a set of Lee ND filters and saying, "here is the same shot with a Cokin and with a Lee. Notice how the Cokin had a lot more flare and had poor contrast." That's what I'd like and that's what I can't find. I can't find it for Cokin vs. Lee, I can't find it for an expensive polarizer versus a cheap polarizer.

10/29/2007 07:59:12 PM · #15

Originally posted by DrAchoo:

Originally posted by Gordon:
Anyway - I already linked you to a set of graphs that show the difference you were asking for - I'm not quite sure what more you want. Lee/ cokin etc also publish that info in their literature.

What I want is something like Luminous Landscapes sending a dude out into the real world with a set of Cokin ND filters and a set of Lee ND filters and saying, "here is the same shot with a Cokin and with a Lee. Notice how the Cokin had a lot more flare and had poor contrast." That's what I'd like and that's what I can't find. I can't find it for Cokin vs. Lee, I can't find it for an expensive polarizer versus a cheap polarizer.

Okay, so don't believe the science then :)

10/29/2007 08:02:25 PM · #16

Originally posted by Gordon:

Okay, so don't believe the science then :)

I believe the science. I don't know if it makes a real-world difference OR if the difference is worth 5x the price. If I draw your blood and your white blood count is 6,500 or 7,500 does it make a difference?

I know enough from the medical literature that pharm companies that cannot show clinical differences in their medicines often rely on "technical" differences to show an edge for their product when it really doesn't matter at all. The cheaper generic works just as well as the expensive designer drug.

Message edited by author 2007-10-29 20:04:06.

Pentax DA 70mm f/2.4 Limited

10/29/2007 09:17:21 PM · #17

Originally posted by DrAchoo:

Originally posted by Gordon:
Okay, so don't believe the science then :)

I believe the science. I don't know if it makes a real-world difference OR if the difference is worth 5x the price. If I draw your blood and your white blood count is 6,500 or 7,500 does it make a difference?

I know enough from the medical literature that pharm companies that cannot show clinical differences in their medicines often rely on "technical" differences to show an edge for their product when it really doesn't matter at all. The cheaper generic works just as well as the expensive designer drug.

90% of the time it probably doesn't matter. The same with L lenses. It depends if you care enough about the other 10%

Same with anti-reflective coatings on glasses. And lens hoods, and all the other things you pay more money for.

From the little I understand the difference between generics and name brand drugs is entirely non-scientific though. They are chemically the same. Lens coatings are different - look at them in the right light and you can see the difference pretty easily.

It then comes down to a standard trade-off of if you care vs. how much you want to pay. If for example you don't bother with lens hoods either, then you probably really need more expensive filters, or you really don't care, then you could just buy untreated filters.

Qiki

Fujifilm X100T

10/29/2007 09:46:07 PM · #18

Originally posted by DrAchoo:

I think this is a very valid analogy Doc. 'Evidence based medicine' is gold standard and keeps folks honest in terms of claims being made. 'Evidence based photography' is far less common and leads to people making equipment decisions etc based more on hype and marketing than anything concrete.

Q.

10/29/2007 10:03:19 PM · #19

Originally posted by Qiki:

Look at your filter. Can you see it ? Then it isn't optically perfect. How much can you see it ? That's what you are paying for. Pretty easy evidence to gather.

Message edited by author 2007-10-29 22:03:40.

10/29/2007 10:04:14 PM · #20

I think what I ultimately want to know is where to spend my money. I really only consider buying L-glass and feel comfortable with that decision because I can see plenty of evidence out there that I'm getting value for the premium I pay. But my pockets are not bottomless and so questions like this creep into my mind.

It's just the way I work. Living and breathing a "show me" mentality in medicine makes you realize how much out in the rest of the world is taken for granted when there is little if anything objective to support it.

10/29/2007 10:16:23 PM · #21

Originally posted by DrAchoo:

It's just the way I work. Living and breathing a "show me" mentality in medicine makes you realize how much out in the rest of the world is taken for granted when there is little if anything objective to support it.

Yup, living in America brings that home every day ;) Though the evidence on filters is pretty trivial to see. You just have to look at them and then if that isn't enough, the various charts used to justify L lenses show the same thing for filters - coatings make a difference in both cases. Different lens materials make a difference in both cases.

The science is the same in each case, the visual evidence or lack of it is the same too.

Message edited by author 2007-10-29 22:21:14.

zeuszen

Canon EOS-1Ds Mark II

10/29/2007 10:31:36 PM · #22

Schneiders Optics (B+W)

Heliopan

Heliopan: The Making of Digital Filters (in German)

Message edited by author 2007-10-29 22:32:34.