How to reduce sunspots in Infra-red

[isaac4130]

Hi guys,

I'm relatively new to infrared photography - and am currently using a Canon 400D with a Cokin A 007 Infrared filter.

My problem is, every now and then my images get sunspots on them - little hexagonal shaped flared spots that are randomly scatted over the picture.

I have noticed that they are worse in direct sunlight, and am assuming that they might be caused by light refracting off the filter.

My question is - is this something common in infrared photography, or would I be best with another filter? I ask because the likes of Hoya r72 and Heliopan 720 / 780 or Wrattern 89B seem to be the standard in IR work.

Would changing to one of these screw on filters as opposed to the Cokin system help eliminate these sunspots?

Do you have any other suggestions as to how to reduce these spots?

Many thanks for your replies!!

 

[OzSavage]

Sounds like flare to me. You might want to try using a lens hood.

Do you have an example?
--
Dave Savage
GMT +9:00 hrs

 

[Tony D]

Unfortunatly flare is a big issue in infra-red photography as most lenses are optimized to prevent issues only in the visible region, multiple internal reflections (main source of the shapes you see) are not well controlled in the infra-red region - add to this more 'lens' elements (read filters) then the reflection issue increases dramatically. I'd try a screw on filter (near to the lens so reflection generally less of an issue) and definatly use a good lens hood. Take all the additional steps you would to prevent flare in the visible region (Please also be aware the lens itself can cause issues - most of my Canon 'L" lens are worse in IR than my old 35-105 non-L lens so switch lenses are see if this helps (goggle digital infra-red photography and investigate what's out there on the best lenses). I gave up with filters and went with a permenent mode to my old unused 10D - ordered the sensor filter from LifePixel.com and installed it myself (not a complex upgrade but dust is the killer issue, had to remove and clean the filter once which meant taking the camera apart again). Doing this has meant I can take real time (focus and exposure metering is the same as for visible as no filters on lens) and there is definatly less issues with flare than with filters (still there but less with all lenses and almost non-exsistant on the non-L lens above). Still playing as I only converted the camera 3 weeks ago.

 

[JeanDorais]

You don't mention which lens you are using...

I shoot on both a 20D and 30D and Hoya R72 filter, the key is lens flaring. I can't shoot on any of my Sigma Pro lenses or Canon L glass either. I shoot of my little, inexpensive Canon 50mm f/1.8 (nifty fifty) and get great results.

As mentioned above, lenses are coated for the visible spectrum of light- not the IR side of things.

Hope that helps,

Jean D.

 

[isaac4130]

I'm just using the standard 18-55mm kit lens that came with my camera, no fancy glass here.

Yeah, sounds like flare is the problem, I haven't been using a lens hood, so that, along with a screw on filter, will be my next purchases, and hopefully that will improve things

OK - I'm having a go at posting an example image, but my html skills aren't that crash hot:

 

[isaac4130]

example:

http://www.imagedump.com/index.cgi?pick=get&tp=484685

 

[Max Pixl]

Flare should be a straight line pointing towards the sun. Are the spots always in the same composition on your images? Dust makes darker and soft spots. As yours are lighter & hexagonal it has something to do with false light reflecting inside your lens & filter-system. Little scratches on your filter? As far as i know Cokin is an open filter-mounting-system, so direct sunlight can get between filter and lense. These two things can cause the problem imo. In that case maybe a good lens hood, replacing the filter or putting the shade of your hand or body over the camera can solve the problem?
Hope this helps.

Kind regards,
Max
S85/F828-IR/R1