Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
11-01-2012, 08:06 AM   #1
Senior Member




Join Date: Feb 2012
Photos: Gallery
Posts: 120
Shooting IR

i am making a college project on IR photography. Both analog and digital. I would like to know if somebody has some experience on shooting IR. Since i am not keen on converting my K-r, i would like to know if TTL light meter is sensitive to IR light on my K-r? I noticed that if i put camera to P mode that even though i have IR filter on, camera decides to make shutter speed reasonable (around 1/15 - 1/30) that would be ok if my camera lacked low pass filter, and for IR film. But in reality i have to keep my shutter speeds no shorter than 60seconds.

Why i am asking this, well, if my light meter is sensitive to IR, than i can have a pretty good reference on how to set up my analog camera so my IR film gets a proper exposure.

11-02-2012, 06:46 AM   #2
Site Supporter
JimJohnson's Avatar

Join Date: Jan 2012
Location: Lake Superior - Michigan
Photos: Gallery
Posts: 2,270
The sensors on dSLRs all come with an optically transparent protective cover over the sensor. And if the camera is intended for general photography, virtually all of these covers have embedded UV and IR filters. That makes it pretty much impossible to do true IR photography with these cameras without making substantial modifications.This includes the Pentax K-r.

However, digital filters are available to create pseudo-IR images. I can't remember if a digital filter of this type is built into the K-r, but for sure one is available in the companion Pentax Camera Utility for use in post processing. You will find it as one of the monochrome conversion types.
11-02-2012, 09:46 AM   #3
Veteran Member




Join Date: May 2012
Posts: 698
The meter should not be sensitive to IR - it should have the same high pass filter as the one on the image sensor. I never checked whether this is actually so but I do hope it is (otherwise there are many situations where it would underexpose)

The reason you are gettiung 'reasonable' shutter speeds is most probably light leakage from the viewfinder. Once you put a dark filter (or even a cap) on the lens then the light leakage from the viewfinder becomes the dominant light source illuminating the exposure sensor.

Try repeat the test you did with the IR filter but this time make sure the viewfinder is completely covered. My guess is that you will get much slower shutter speeds. Try also comparing the IR filter with the lens cap - I think you will get almost the same exposure reading.
11-02-2012, 11:32 AM   #4
Pentaxian
Just1MoreDave's Avatar

Join Date: Feb 2007
Location: Aurora, CO
Photos: Gallery | Albums
Posts: 4,859
QuoteOriginally posted by zvon Quote
i am making a college project on IR photography. Both analog and digital. I would like to know if somebody has some experience on shooting IR. Since i am not keen on converting my K-r, i would like to know if TTL light meter is sensitive to IR light on my K-r? I noticed that if i put camera to P mode that even though i have IR filter on, camera decides to make shutter speed reasonable (around 1/15 - 1/30) that would be ok if my camera lacked low pass filter, and for IR film. But in reality i have to keep my shutter speeds no shorter than 60seconds.

Why i am asking this, well, if my light meter is sensitive to IR, than i can have a pretty good reference on how to set up my analog camera so my IR film gets a proper exposure.
I just tried metering a shot with the K-7, and the meter suggested settings that were about 10 stops underexposed from a useful digital exposure. I'll go out on a limb and say the meter's not accurate for IR.

Even when I use trial and error to get a better-looking histogram, the exposure wouldn't work for film. Digital sensors have filters to block IR while the film is meant to be sensitive to it. I think the film is sensitive to a spectrum further into IR than the filters I have, Hoya 72, which means 720 nm. The film should come with some advice on how to expose it properly.

With a stationary subject and a tripod, a normal K-r can take photos using the Hoya 72 filter. You should cover the viewfinder, it will leak light as mentioned, affecting the image. I'd set the white balance to Tungsten, the closest preset to the image. I use RAW to allow me to change white balance to something like 2000K, -50 tint later, but getting WB closer to that makes the preview image and histogram better. I use the RGB histogram to avoid overexposing the red channel. AF might work, CDAF might work too, live view is good for manual focus. Bracketing is a good idea because it's hard to tell if you have a good shot in the field, and IR images need processing anyway.

I took this test photo at 28mm, f4, ISO 100 and 15 seconds, but each sensor is different.



11-03-2012, 04:28 AM   #5
Senior Member




Join Date: Feb 2012
Photos: Gallery
Posts: 120
Original Poster
Yes. I get similar results.. Film manufacturer Efke suggested that i shoot the film as it was ISO50. But my first two rolls of film are a complete shot in the dark until I develop them, it is very frustrating to write down every shot i took so I can remember what I tried to get...
So i thought that maybe k-r light meter is metering IR properly when IR filter is screwed on. I bought zykkor IR850 filter and all my photos are in purple tones (the exact same color tone that you get from pointing a remote control to camera). So your yellow photo is due to 720nm filter? or you edited the photo that way?
11-03-2012, 01:25 PM   #6
Pentaxian
Just1MoreDave's Avatar

Join Date: Feb 2007
Location: Aurora, CO
Photos: Gallery | Albums
Posts: 4,859
Color is sort of meaningless once the IR filter goes on. I've read that the 720nm filters include some of the visible spectrum but an 850nm probably doesn't. The camera will show you colors because that's how it interprets the data. With Auto WB and my Hoya 72, I get a mostly red and black preview. When I apply the white balance I like (2000K, -50 tint) I like the result. Some people reverse the red and blue channels to get a blue sky. I like the false color look but it would be more accurate to use monochrome.

Here's a better image with slightly different processing:
11-04-2012, 05:06 AM   #7
Senior Member




Join Date: Feb 2012
Photos: Gallery
Posts: 120
Original Poster
great, thanks. I prefer it to be B/W, but adding color makes it look a bit dramatic like nuclear fallout or something .
Reply

Bookmarks
  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
analog, camera, film, filter, ir, k-r, kr, light, meter, pentax k-r, shutter
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Which Lens and Shooting Space is Required for a Fashion & Beauty Shoot? benjikan Photographic Technique 2 08-20-2009 10:12 PM
Shooting in Public Etiquette deludel General Talk 36 06-18-2008 04:04 AM
For Sale - Sold: IR Only K100D - w/ 760nm IR Filter frank Sold Items 39 05-29-2008 10:06 PM
IR effect on K10D Ash Post Your Photos! 2 05-01-2008 03:14 PM
IR with my new *st ds ... LaRee Post Your Photos! 3 01-16-2008 08:25 AM



All times are GMT -7. The time now is 06:02 PM. | See also: NikonForums.com, CanonForums.com part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top