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Lens Tests

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Flare Tests

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Brand and Grade Tradeoff Test

TOC

Introduction

Results

                                                                                Group A 50/1.4 and 28/1.8

                                                                                Group B 17-40 f4L and 300 f4L IS

Conclusions

Annex: Damaged Filters

 

Introduction

This test uses the standard bright light source to evaluate flare and ghosting. 

 

Group A Tests

In Group A two sample lenses are used, one the 50mm which is known to be very sensitive to filter induced ghosting and the other (28mm) which shows no obvious sensitivity with a high end filter. 

For additional interest to model the effect of damaged front elements two Canon UV filters have been damaged (I enjoyed that). Photographs of the damage is shown at the bottom of the page. These are intended to model the effect of a scratch on a front element, or front element microscoring due to poor cleaning techniques or excessive exposure to dust and grit.

 

Group B Tests

In Group B again two sample lenses are used, the 17-40 f4L and the 300 f4L IS. In this group both lenses are tested at f4 and f16 with a Hoya SHMC Pro 1 UV(O) and a Hoya MC Pro 1 Digital UV(O); there is no reference test with no filter as these can be seen in the main test section for these lenses, 17-40 and 300

The same exposure value has been used as for the Group A tests, but to improve sensitivity the background lighting level has been lowered. The white balance is derived from the Group A 50/1.4 no filter case for consistency.

 

The Test Severity and Method

Note as always these are very harsh test conditions, under normal conditions the differences between filters, or indeed no filter at all,  will probably not be noticeable.

For information on the test method and estimated test dynamic range please refer to main page for this section. In must be remembered when reviewing the test results that the test light source is extremely bright compared to the exposure level, particularly in the filament area.

 

Results  

Group A 50/1.4 and 28/1.8

Case

Specified

Reflectance

Sensitive Lens EF 50mm f/1.4 @ f/1.4 Sensitive Lens EF 50mm f/1.4 @ f/1.4 Crop of Ghost Insensitive Lens EF 28mm f/1.8 @ f/1.8
No Filter 0%  

Canon UV

(Single Coat)

~4%

Canon UV

(Single Coat)

Scratched [1]

?? ~4%

Undamaged

 

Canon UV

(Single Coat)

Abraded [2]

?? ~4%

Undamaged

 
Hoya MC Pro 1 Digital UV(O) ~2%
B+W MRC UV-HAZE 010 0.5%
Hoya SHMC Pro 1 UV(O) 0.3%

 

The Undamaged Filters

EF 50mm f/1.4 @ f/1.4

Interestingly the flare around the light source shows little difference across all the filters, or indeed without a filter. Even the single coat Canon UV seems to have similar performance to the three multicoat filters. Even in the shadow areas with +2 stops electronically boosted exposure there is no obvious difference.

However, the ghosting image intensity is higher (as well as a different colour) with the Canon UV compared to the three multicoat filters. Some of the responses are in slightly different positions, this is probably due to small differences in the distance between the filter glass and the front element. However what is surprising is that the difference is so little. Again curiously there is minimal difference between the three multicoats as far as the ghosting response in concerned.

Looking at the ghosting values more closely and assuming for this purpose an RGB to luminance weighting vector of [1 1 1] rather than the CIE 1931 human perceptive value of [0.3 0.6 0.1]:

We find the ghosting luminance difference between the Canon UV and the Pro 1 Digital is about a stop (using the ACR exposure control to match the luminance change). This does in fact match what is expected as the reflectance of these two filters are 4% and 2% respectively.

Using the same method the Pro 1 Digital and B+W MRC have a difference of about -0.15 stop, actually worse that the Pro 1 Digital despite the reflectance being 2% and 0.5% respectively. This is very surprising as the B+W MRC should be about 2 stops better than the Pro 1 Digital. This discrepancy is puzzling but may possibly be due to a geometry difference between the Hoya/Canon and B+W filters, however this explanation is unsatisfying.

Similar results are found with the Pro 1 Digital and SHMC Pro 1. The SHMC being also -0.15 stop worse than the Pro1 digital. Again most mysterious.

If this discrepancy was on just one filter then it could be dismissed as experimental error or a bad filter. However here we have two similarly specified filter responding very closely. However the two lower specified filters response relative to each other is more or less where expected. 

If the Canon filter was about 2 stops worse than the other filters we could say it was something special about the Hoya Pro 1 Digital, but this is not the case.

So the only conclusion can be is that the Hoya SHMC Pro 1 and B+W MRC are not performing to specification in this instance for ghosting.

 

EF 28mm f/1.8 @f/1.8

With the 28mm there is some slight veiling (low level flare over the whole frame) evident with the Canon UV compared to no filter, this is mostly a 0.3 stop blue increase, probably becuse the test light source has a higher colour temperature than the background lighting which the shots are white balanced for (all balanced for the no filter case). 

Another surprising result is the Hoya Pro 1 Digital actually has more veiling than the Canon UV despite being a better specified filter, however this is very small, about 0.4 stop on the blue channel relative to the no filter.

When either of the two high end filters are used the veiling is no detectable and the results are virtually identical to the no filter case.

Working with the shadow areas (and a 4 stop electronic enhancement) the following differences are measured:

Filter

Stops Shadow Difference Relative 

to no filter (Blue Channel)

Canon UV 0.50
Hoya MC Pro 1 Digital UV(O) 0.55
B+W MRC UV-Haze 101 0.35
Hoya SHMC Pro1 UV(O) 0.35

So here there is a small but measurable improvement with the high end filters.

 

The Damaged Filters

Although both the scratch and abrasion levels in these tests are deliberately high, the increase in flare in both cases is very significant. It seems reasonable to expect that a detectable loss of flare performance could be expected with damage a tenth of what is demonstrated here.

 

Group B 17-40 f4L and 300 f4L IS

Case Hoya MC Pro 1 Digital UV(O)

Specified Reflectance 2%

Hoya SHMC Pro 1 UV(O)

Specified Reflectance 0.3%

EF 17-40 f4L

@ 17mm f4

EF 17-40 f4L

@ 17mm f16

EF 300 f4L IS

@ f4

EF 300 f4L IS

@ f16

Case Hoya MC Pro 1 Digital UV(O)

Specified Reflectance 2%

B+W UV Haze MRC

Specified Reflectance 0.5%

EF 300 f4L IS

@ f4

EF 300 f4L IS

@ f16

 

The 17-40 f4L at 17mm

At f4 there is very little difference between the two filters. The ghosting in the upper right and small amount of flare on the left seem to be very close to the original no filter case. So it seems here the limiting factor is the lens and not the filter.

However, at f16 the situation is different. The original test used the Pro 1 Digital filter which added one or two second order responses on top of the naked lens, however the main responses (green ghosting upper right, red flare centre and upper right and most of the white ghosting near the light source) are due to the lens alone. These responses are very much the same with the higher performance SHMC Pro 1 filter but paradoxically this filter has added a few additional second order responses. 

Some of the Pro 1 Digital secondary responses have gone to be replaced by other with the SHMC Pro 1, overall the SHMC secondary responses are stronger.

In this case the Pro 1 Digital is, rather surprisingly again, the better filter for this lens. Suffices to say I was surprised enough to go back to the origional files and experiment notes and check the labelling using the file digitization time stamp - there is no mistake.

 

The 300 f4L IS

At f4 the Pro 1 Digital excites a quite bad green ghosting response lower left (this can be seen in the original test), the general flare around the light and flare response upper right seems to mostly be due to the lens alone. With the SHMC Pro 1 the green ghosting response is dramatically gone, otherwise things are very much the same with perhaps some reduction in the flare upper left.

At f16 the story is very much the same with the main difference between the filter being the green ghosting lower left, banished with the SHMC Pro 1.

The SHMC Pro 1 seems to be a large improvement for this lens over the Pro 1 Digital. The question is, is this due to small differences of geometry or the coating?

Both filters look the same, the mounts look the same thickness as does the glass. Both filters were screwed in all the way to fingerer tight. One can only assume that the improvement is indeed due to the superior coating.

The test was later repeated with a B+W UV Haze MRC (and a repeat of the Hoya MC Pro 1 Digital as a re-baseline) with very similar results.

 

Conclusions

On balance both the high end filters, Hoya SHMC Pro 1 and B+W MRC UV-Haze 101 can show  better performance but the difference is much smaller than expected considering the differences in specified light reflectance and inconsistent depending on the lenses tested. 

In one case the higher specification filter showed a dramatic improvement, in another two little or no difference and in a third it was actually worse that a mid range multicoat filter. 

The differences would show up in more extreme lighting conditions, but under such circumstances the filter is likely to be removed anyway. It is worth remember these test were done with prime lenses that are well controlled for flare. With zoom lenses, even good L zooms, the lens flare response has been shown to already be significant at this contrast level.

The single coat Canon UV showed a slightly worse ghosting image brightness and the 50mm and the Hoya Pro 1 Digital UV(O)  produced oddly high levels of veiling on the 28mm. The high end filters did not improve the ghosting performance significantly over Hoya MC Pro 1 Digital.

In summary single coat filters are probably best avoided but in many cases the difference between the medium and high end filters is not dramatic although going for a high end filter is recommend for lenses with very good flare resistance. NB that not all L zooms have equally good flare resistance. The 24-105 f4L IS has quite poor performance and information elsewhere on the web suggests that the 24-70 f2.8L is also prone to ghosting.

The results of the damaged filter tests illustrate that even much smaller levels of damage to a front element could easily introduce levels of flare more than even the lowest specified filter. This emphasizes the value of protective filter and / or the appropriate level of care required when cleaning front elements and using or storing lenses without protective filters fitted.

 

Annex: Damaged Filters

[1] Scratched Filter

A single scratch with a sharp object.

 

[2] Abraded Filter

Some microscoring added using wire wool. Not that obvious from a distance but is quite heavy if looked at close and at an angle.

 

Last Updated 27/04/2008

All Content 2005-16 Lester Wareham All Rights Reserved     

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