Ghosts II

Hi All

Kingalew's recent post re ghosts reminded me of a problem I encounter every now and again...

If I have the sun top left of frame, either just in or just out of the frame, I sometimes get circular ghosting in the bottom right, or more occasionally top right of the photograph.

Below are a couple of unedited shots with the contrast pushed to show the problem:







It doesn't happen all the time, but it does specifically seem to happen on long exposures.

I use a K5 with a Sigma 10-20, slimframe Hoya UV filter, Lee wideangle filter holder, Lee 10 stop filter, and Lee grad on the outside...

My best guess so far is light somehow getting caught inside the set up and bouncing off a filter rim or something somehow (I can't use a hood on the lens due to the filters) ...

I'd be really very grateful if:

1. Anyone could help explain what is actually occurring here?
2. Anyone could help with a suggestion of how I might fix it?

Like I say it doesn't happen very often, but often enough to wish it didn't...

Thanks very much in advance...

Best

Hmmm, a mystery light streak. I sometimes get the same thing, get a streak across the middle of the frame, always the same place, and yes the viewfinder was covered properly.

I finally noticed like you have done, it was when the sun was hitting from a certain angle, so I started putting my hand over the 'sun' side which seemed to solve it. Mystified I investigated the lens (Sigma 10-20 I think) and noticed it doesn't sit entirely flush with the camera mount from about 7-8 o'clock, it could be light is sneaking in there?

Apart from that I'm stumped!

Thanks Sean... that's very interesting actually... it only happens with the 10 20... and like you I always cover the viewfinder... so it could be that... will definitely have a go with that next time I'm out...

Best

Pentax used to make very expensive Ghostless filters with curved glass to stop this happening. Light is being reflected back from the lens onto the filter.

Thanks for this Ken... I currently use a slim framed screw mount Hoya Multi Coated UV filter directly in front of the lens... is this a case of trying to get a better multicoating (ie Hoya Pro 1)? Is that likely to make a difference?

Or if light is actually going through the filter and bouncing off the lens onto the BACK of the filter during a long exposure, is there much I can do about it at all? Would it be better to remove the UV filter altogether?

Would be interested to know your thoughts...

Best

Get rid of the filter and test again.

Why compromise the carefully computed optical formula of a lens by adding an extra piece of glass in front of it. The only exceptions are where filters are needed, such as polarisers and grad filters.

But always use a lens hood, which helps to protect the lens from knocks and also reduces flare within the lens.

Hi John... thanks for the suggestion... as you say, will try without a UV filter and see what happens... unfortunately, as I mentioned in the original post, hoods are a non starter for me because of the nd filter set up I use...

Also the conditions I usually shoot in tend to be pretty tricky due to seaspray etc, hence the use of the UV filter in the first place to:

a) Keep sea spray off the lens
b) Make it easier to clean fast
c) Make it easier to swap out with a replacement when there's too much
salt built up on it to shoot (there comes a point where however much
you clean it there's still a layer of salt left on it)

But I take your point... will try shooting without one whenever possible...

Thanks again...

Best

Well those are certainly the best reasons to use a UV filter but if you are also using the ND then I think its unnecessary. It is light being reflected onto the back of the filter.

You see ghost images a lot in motion pictures where the use of a thick filter is part of the process of making the camera silent, usually in night shoots involving car headlamps.

Hi Ken... thanks very much for this... right... that settles it... the UV filter has to go... will get spares of the NDs instead to swap in and out...

Thanks again for your help...

Best