Does a cheap polorizer degrade image? examples

[Steve M]

Just saw this on the net:

"But don't filters rob sharpness?

No. This was an old-wives tale from the 1950s.

Proper filters cause no loss in sharpness.

The additional exposure required due to the loss of light can increase motion induced blurring due to longer exposure times, or accentuate a poor lens' loss of sharpness at larger apertures, or simply cause smaller depth of field at the larger aperture. This is probably what led to the old wives' tales still spouted today by junior high school photo teachers about filters lowering sharpness.

It is easy to test your filters if you are worried about a defective filter desharpening you image. Just look through it with any binocular or small telescope. The image ought to be sharp. If there is any defect in the flatness of the filter it will be obvious through the magnification of your binocular (one-eyed) or telescope. Hold the filter half over the front of the binocular; you should see a single, not double, image. If there is a problem it will be obvious through the scope.

I have seen perfectly good plastic Cokin filters, and also bad expensive glass Hoya and B&W polarizing filters. This binocular test makes clear exactly what you have and eliminates all uncertainty."

Source: http://www.kenrockwell.com/tech/filters.htm

 

[D.P.]

I use a Hoya Pro Digital Polariser. How dou you all rate those??

These are very good but are at the lower end that I would consider using for my personal work. I started out on cheaper Hoyas but they gave a colour cast, softened the image slightly and had flare problems. I moved to a Hoya HD CPL which are supposedly excellent but it broke before I ever used it. Since Then I have been using B+W religiously. However, I recommend my GF but a Hoya PRo 1 Digital as a good compromise since the better filters are only marginally better and the price goes up considerably, so these Hoyas are the good value. I played with them briefly, seemed very good. However, when Screwing them on or off a lens I really feel a difference in the lovely brass rings of B+W F pros.

 

[D.P.]

Just saw this on the net:

"But don't filters rob sharpness?

No. This was an old-wives tale from the 1950s.

Proper filters cause no loss in sharpness.

The additional exposure required due to the loss of light can increase motion induced blurring due to longer exposure times, or accentuate a poor lens' loss of sharpness at larger apertures, or simply cause smaller depth of field at the larger aperture. This is probably what led to the old wives' tales still spouted today by junior high school photo teachers about filters lowering sharpness.

It is easy to test your filters if you are worried about a defective filter desharpening you image. Just look through it with any binocular or small telescope. The image ought to be sharp. If there is any defect in the flatness of the filter it will be obvious through the magnification of your binocular (one-eyed) or telescope. Hold the filter half over the front of the binocular; you should see a single, not double, image. If there is a problem it will be obvious through the scope.

I have seen perfectly good plastic Cokin filters, and also bad expensive glass Hoya and B&W polarizing filters. This binocular test makes clear exactly what you have and eliminates all uncertainty."

Source: http://www.kenrockwell.com/tech/filters.htm

Rule 1 of the photography on the internet.. don't quote Kenrockwell.

Anyway, it is clear that poor glass can affect sharpness, otherwise cheap lenses would be just as good as professional lenses.

Besides that, my complaints with cheap filters are little to do with sharpness, more to do with colour casts, flare, contrast, build quality and materials.
I've seen cheap UV filters shatter and cover the front elements with razor sharp glass, the last thing you want. Cheap polarisers & ND filters tend to give a brown colour cast. Cheap filters noticeable flare. Cheap filters tend to get crossed threads, or get jammed to the lens thread.

 

[Steve M]

Rule 1 of the photography on the internet.. don't quote Kenrockwell.

Ha ha, why's that then?

 

[D.P.]

Ha ha, why's that then?

For starters:
http://www.kenrockwell.com/about.htm

This website is my way of giving back to our community. It is a work of fiction, entirely the product of my own imagination.
...
I feel like the Forrest Gump of photography
...
Apparently the world finds my opinions very useful, but remember, they are the opinions of one man. I have a big sense of humor, and do this site to entertain you (and myself), as well as to inform and to educate. I occasionally weave fiction and satire into my stories to keep them interesting. I love a good hoax.

Then there is this :

"* Ken Rockwell is the Chuck Norris of photography

* Ken Rockwell's camera has similar settings to ours, except his are: P[erfect] Av[Awesome Priority Tv[Totally Awesome Priority] M[ajestic]
* Ken Rockwell doesn't color correct. He adjusts your world to match his.

* Sure, Ken Rockwell deletes a bad photo or two. Other people call these Pulitzers.
* Ken Rockwell doesn't adjust his DOF, he changes space-time.

* Circle of confusion? You might be confused. Ken Rockwell never is.

* Ken Rockwell doesn't wait for the light when he shoots a landscape - the light waits for him.

* Ken Rockwell never flips his camera in portrait position, he flips the earth
* Ken Rockwell ordered an L-lens from Nikon, and got one.

* Ken Rockwell is the only person to have photographed Jesus; unfortunately he ran out of film and had to use a piece of cloth instead.

* When Ken Rockwell brackets a shot, the three versions of the photo win first place in three different categories

* Before Nikon or Canon releases a camera they go to Ken and they ask him to test them, the best cameras get a Nikon sticker and the less good get a Canon sticker

* Once Ken tested a camera, he said I cant even put Canon on this one,thats how Pentax was born
* Rockwellian policy isn't doublethink - Ken doesn't even need to think once

* Ken Rockwell doesn't use flash ever since the Nagasaki incident.

* Only Ken Rockwell can take pictures of Ken Rockwell; everyone else would just get their film overexposed by the light of his genius

* Ken Rockwell wanted something to distract the lesser photographers, and lo, there were ducks.
* Ken Rockwell is the only one who can take self-portraits of you

* Ken Rockwell's nudes were fully clothed at the time of exposure

* Ken Rockwell once designed a zoom lens. You know it as the Hubble SpaceTelescope.
* When Ken unpacks his CF card, it already has masterpieces on it.

* Rockwell portraits are so lifelike, they have to pay taxes

* On Ken Rockwell's desktop, the Trash Icon is really a link to National Geographic Magazine
* Ken Rockwell spells point-and-shoot "h-a-s-s-e-l-b-l-a-d"

* When Ken Rockwell went digital, National Geographic nearly went out of business because he was no longer phyically discarding photos
* For every 10 shots that Ken Rockwell takes, 11 are keepers.

* Ken Rockwell's digital files consist of 0's, 1's AND 2's.

* Ken Rockwell never focus, everything moves into his DoF

* Ken Rockwell's shots are so perfect, Adobe redesigned photoshop for him: all it consists of is a close button.
* The term tripod was coined after his silhouette

* Ken Rockwell never produces awful work, only work too advanced for the viewer

* A certain braind of hig-end cameras was named after people noticed the quality was a lot "like a" rockwell

* Ken Rockwell isn't the Chuck Norris of photography; Chuck Norris is the Ken Rockwell of martial arts.
* Ken Rockwell never starts, he continues "

 

[Steve M]

What a legend!

 

[juno_first]

Ok, I just spent ages getting these 2 shots as close as possible to compare a cheap CP filter against without.

18-105 @ 105
Selected from a 1ev bracketed shots & adjusted the brighntess of the white label on the non cp filter shot to match the cp filter shot which is nicely clipping around 255.

Original image (no CP) at best aperture f5.6.

no CP

with CP

Should I spend £50 on a Jessops CP filter is the question?

 

[rG-tom]

my example of a jessops UV filter was to show an example of a cheap one by the way :s

 

[juno_first]

my example of a jessops UV filter was to show an example of a cheap one by the way :s

Not as cheap as £16.30 for this:

 

[D.P.]

Ok, I just spent ages getting these 2 shots as close as possible to compare a cheap CP filter against without.

18-105 @ 105
Selected from a 1ev bracketed shots & adjusted the brighntess of the white label on the non cp filter shot to match the cp filter shot which is nicely clipping around 255.




Should I spend £50 on a Jessops CP filter is the question?

There are too many variables here. The18-105 lens is good but it wont be sharp enough to show sharpness differences between filters, especially at 5.6. Try a 50mm 1.4 or 1.8 prime stopped down to f5.6 to f8.0. Making sharpness tests will require to know the ISO, the camera model, the lighting condiitions, etc. Also, to do a sharpness test one would have to make sure you are using a very solid Tripod (not a cheap flimsy thing) combined with a solid head with a solid camera bracket). MAke sure the photo was taken with the mirror up. You should also check different fous distances to be sure. And focus is a whole new issue. You will have to be sure to focus multiple time (like expsoure bracketign but change the focus) using liveview and also focus the lens from minimal focus distance (MFD) and backwards from infinity (you will find depending on whcih way the lens will focus the exact focus point will vary due to tolerences). Out of 20 or so near identical shots with slight focusing differences you should select the sharpest to compare.

I say this because those 100% crops do not look very sharp too me so there could be a number of factors here hiding any effects.

Moreover, you are ignoring any other effects. You said you changed the WB. Well one of the issues with cheap filters is a colour cast so this is an unfair test. You also need to look at things such as flare and reduced contrast, which are much bigger issues than the very slight sharpness reduction.

Next is somewhat destructive, tap a cheap filter with a a hammer. Does the glass shatter and splinter into thousands of tiny pieces (seen it done to a friends fcheap hoya filter), or does the filter suffer a small and harmless crack (seen it happen to a top end Hoya).

My opinion, keep to your cheap filters since you already have them. When you are progressing your skills and lenses then look to upgrade to a Hoya pro 1 or B+W. I would skip a cheap Jessops filter since you already have a cheap filter.

 

[juno_first]

I say this because those 100% crops do not look very sharp too me so there could be a number of factors here hiding any effects.

Interesting you mention the sharpness, as Ive not really been enthralled with the sharpness of shots with the D90 so far, maybe its the 18-105 or DX sensor, I dunno. Maybe I should try use the 50mm prime as much as possible.


Wow thanks for the info. A lot to figure out.
My 50mm 1.8 has a different thread mount & I didnt want get a CP filter for a 50mm on a APS-C sensor as the filter would primarily be used for landscape scenes.
I suppose Im limited by cash atm, so Im thinking a battery pack would be more useful for now and then a descent 28 or 35mm lens.

As I cant really tell a difference between the 2 shots I may as well keep the cheap CP filter until I maybe go full-frame one day & get some good filters too.
Being as you say the Jessops is cheap too & I cant guess at this point if it will improve IQ significantly.

 

[juno_first]

Phew, Ive done this before but this time Ive been as accurate as possible: old 50mm vs 18-105@50mm @f5.6.
The darn cheapo tripod kept moving between changing lenses/zooming, but I did the best I can & its yielded interesting results.
Corrected the RAW in Lightroom with lens corrections/CA & added sharpness until just before halos appear around contrasty lines, as the D90 shoots a bit soft by default.

Even with the C.Aberrations fix, the 18-105 still shows more flaws which I presume is normal.

A bit off topic, but comparing 50mm vs 18-105@50mm (considering the CP filter fits the 18-105)

full 50mm

Comparison