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09-08-2008, 02:16 AM   #1
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Lens Filters versus Flare and Ghost Images

Flare Control

A shopping trip today led me to a non-coated 49mm Tiffen UV Haze-1 filter. It was not very expensive and it was the only 49mm one they had, so I bought it anyways. Not knowing much about it, I did some research online after I came home and I found some interesting information that would change the way I looked at UV filters for camera lenses.

My dad had always told me to put a UV filter in front of a camera lens as to protect it from the environments. Sounds reasonable enough. Afterall, I would rather damage a $30 filter than a $300 lens. But it seems this innocent piece of glass in front of the lens could do more damage to the image quality than if it were not there. I did a quick experiment.

The pairs of photos below are taken with a Pentax-A 50mm f/2 lens with SMC (Super Multi-Coating).

(Focused on the metal latch of the camera bag.)

(Focused on the door knob.)

(Focused on the Wimbeldon logo.)

As you can see, all these photos exhibited some amounts of flare from the light bulb. Unavoidable because of the way stray light entered the lens when the image was taken. This is where a lens hood would be useful. No hood was used in taking these pictures.

The surprising thing for me was what a non-coated UV filter would do to the images. The top photos were taken without a filter, and the bottom photos were taken with a filter. The un-coated piece of Tiffen glass certainly amplified the amount of flare in the images. It is quite noticable in all three cases. Clearly an unacceptable result then, but I also wanted to compare an un-coated filter to a coated filter.

Ghost Images

Aside from the increased flare with filters, I also noticed that there were cases of "ghost" images when i used a lens with a filter. The following are some pictures I took with and without filters.

Pentax-A 50mm SMC @ f/2.8 without filter. No ghost images. I tried shooting several different angles with this set up but was not able to produce a ghost image.

Pentax-A 50mm SMC @ f/2.8 with un-coated Tiffen UV Haze-1 filter. Pronounced ghosting! I could alter the location of the three ghost "lightbulbs" by shooting at different angles. Ghost image would not go away.

Sigma 24-60mm @ 50mm f/2.8 with a Hoya HMC (Hoya Multi-Coated) UV (N) filter. Much reduced ghosting but still visible.

Sigma 24-60mm @ 50mm f/2.8 without filter. Still some ghosting from this Sigma lens. However, at some angles, the ghost images did go away. The multi-coating on the Sigma lens is not the same as Pentax's SMC technology.

It's hard to compare exactly between coated and non-coated filters because I used different brand filters and different brand lenses. It was just the case of limited available equipment. But I think it is still fairly obvious at what a filter can do to an image. I am still quite used to having a filter on every lens, but I think after this little experiment, I'd be more inclined to using my lenses naked!

09-08-2008, 03:06 AM   #2
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Join Date: Aug 2008
Location: Cape Town, South Africa
Posts: 232
Wow, an interesting study and one Ive been curious about for ages. The old "to do or not to do" question.
Except for flare introduction, what other cons does using a UV filter have? The onyl reason im using one is for debris protection, and to rather clean the filter than wiping the front element all the time.

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