Filter ghosting? I GOT PROOF!

[rburgoss]

All of my lenses have UV filters on, permanently, as protection. But since I switched to digital, I´ve been noticing a bit of "softness" in my pictures. Few days ago, while shooting at night with my *ist D and FA 200/2.8, I noticed some "extra lights" that were not in the original scene (via LCD screen). I wondered where did those extra lights came from and decided to make an experiment. Remove the filter and shoot again.

Here are the results:

Attachment 13967

Besides the extra lights, that obviously are "ghosts" originated from the two main bulbs (real) in the scene, you can notice an overall softness.

I know that the Cokin filter is not a super prime quality filter. BTW, this is not a plastic square one but its a regular glass screwon as any regular filter.

Has anyone noticed similar results?

RB

[séamuis]

I have personally never noticed any ghosting or softness with any of my hoya filters and I use UV's as protection for all of my lenses as well.

[Tom S.]

It would be interesting to see the shot redone after rotating the filter to see if it's a "gerneral" reflection or caused by a flaw in the glass.

[volosong]

So, that's what those little green Martians are! Last year on our Italy tour, I took some nighttime shots in Assisi that exhibited a bunch of those little green gremlins. Never would have imagined they were caused by my filter. Thanks for the analysis and warning.

[rburgoss]

Originally Posted by Tom S.

It would be interesting to see the shot redone after rotating the filter to see if it's a "gerneral" reflection or caused by a flaw in the glass.

In fact I did, and results where the same. It seems that the "ghosts" shift position accoding to the shooting angle in relation to the light source. Of course, this is no surprise since it is supposed to do so. The only way to get rid of the ghosts is to shoot with the light source exactly in the middle of the frame. This means the ghost is not really gone, but rather it is superimposed to the real light source.

RB

[lithos]

Maybe they're ghosts, but not filter ghosts.

Isn't there a movie that's just come out that's about Pentaxes capturing ghosts?

[davef]

I've noticed similar results over the years on both film and digital. I have only ever noticed it with low end filters and have always attributed it to flaws in the coating or grinding process on cheap filters. I'm not familiar with Cokin screw ins. Over the years, I have gotten good results with Tiffen, Hoya MC, Sigma MC, Rodenstock, B&W, etc. Dave

[Tom S.]

Originally Posted by rburgoss

In fact I did, and results where the same. It seems that the "ghosts" shift position accoding to the shooting angle in relation to the light source. Of course, this is no surprise since it is supposed to do so. The only way to get rid of the ghosts is to shoot with the light source exactly in the middle of the frame. This means the ghost is not really gone, but rather it is superimposed to the real light source.

RB

Interesting! Could you detect them in the viewfinder?

[reeftool]

Remember "They Live!" when Rowdy Roddy Piper put on his sunglasses and could see the alien invaders? Maybe you have proof.

[rburgoss]

Originally Posted by Tom S.

Interesting! Could you detect them in the viewfinder?

Nope, no visible ghosts in viewfinder. That means the reflections are acting somehow with the low pass sensor filter. Such thing never happened with film. It is just with digital SLRs.

RB

[alohadave]

This is a well known effect of using filters at night. The extra lights are reflections off the back side of the filter being sent towards the sensor.

You can see that the reflections are exactly opposite the light sources through the center of the frame.

[OniFactor]

oh em gee! a free-roaming, vaporous, full-torso apparition!

[georgweb]

Hi RB,
thanks for letting us know!

I've had the same discussion about this picture,
Missglckt: Reflexionen durch altes Objekt

It is from an SMC-M-1.7/50 an a Pentax DSLR and NO UV filter (shot wide open).

Still, you can see exactly the same behaviour, reflected lights around the image center.

My conclusion: Ghosts will occur, but it's good to know how to reduce them or avoid them. I personally love them, but that's just the other way around of getting them to know :-)

Georg

[christinelandon]

RB, a question and a couple comments:

Is your Cokin filter the model 231 UV or the 235 UV multi-coated? If the former, you're possibly getting a bit of light bouncing between the rear surface of the filter and the highly polished surface of the built-in filter over your sensor, which may be enough to produce the "ghosting" evident in the image. The multi-coated filter should be less prone to that, as is film vs. sensor capture. In either event, your shot setup looks like the sort that is likely to produce just such "ghosting."

You mention that you've only recently shifted from film to digital capture. I don't know if you've read much about the differences, but digital sensors tend to produce RAW (unprocessed capture) images that are a bit softer than those recorded on film; in-camera JPEG processing of the RAW data usually applies some degree of sharpening to compensate. It may be that you are detecting that inherent difference between film and sensor sharpness, especially if you view RAW image files with no sharpening applied in post-processing.

[rburgoss]

Originally Posted by christinelandon

RB, a question and a couple comments:

Is your Cokin filter the model 231 UV or the 235 UV multi-coated? If the former, you're possibly getting a bit of light bouncing between the rear surface of the filter and the highly polished surface of the built-in filter over your sensor, which may be enough to produce the "ghosting" evident in the image. The multi-coated filter should be less prone to that, as is film vs. sensor capture. In either event, your shot setup looks like the sort that is likely to produce just such "ghosting."

You mention that you've only recently shifted from film to digital capture. I don't know if you've read much about the differences, but digital sensors tend to produce RAW (unprocessed capture) images that are a bit softer than those recorded on film; in-camera JPEG processing of the RAW data usually applies some degree of sharpening to compensate. It may be that you are detecting that inherent difference between film and sensor sharpness, especially if you view RAW image files with no sharpening applied in post-processing.

In fact I moved to digital about 4 yrs ago, but since rarely use my FA 200/2.8 at night, then such ghosting was not happening to me. In fact, I´ve noticed this only with my FA 200/2.8.

As for RAW or JPG images, both were shot using JPG *** setting. I also rarely use RAW when shooting outdoors. I only use RAW for "studio" situations.

RB