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10-04-2007, 06:00 AM   #1
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Infrared Filter help? Bad filter and technique

I'm looking for some real help here. I recently picked up an IR filter on Ebay:
Infrared Filter (IR) for Cokin A Holders (89B R72) - (eBay item 7591990174 end time Oct-11-07 05:08:16 PDT)
for my Cokin P holder. So I read the other threads and I'm doing something drastically wrong of I have just bought a very bad filter.

The picture below is about the 20th attempt just of some trees in my back yard. The shot was taken at ISO 400 61 seconds f4 and without the filter the camera says 1/400th @ISO400 f4.0. So the exposures are very long in comparison.

Others have posted shots at 15-30 seconds that look bright and the green leaves look white and so on. Even some at 1-3 seconds and in these light conditions I tried short exposures and those shots are totally black. Are all these shots heavily post processed to get the unique whites and blues in the shot?

Another thing of note is this filter is very thick. I'd say about 3mm. Is that typical? How thick is the Hoya R72 version? I think I've set up the camera right with the rear viewfinder cap on, covering the Cokin holder with a black cloth to avoid stray light from the front. The sky was grey and overcast as well. I noticed that many other posts that look so good appear to be on sunny days. That may have a lot to do with the results.

Is the filter a dud? Has anyone tried this filter? What other advice could you guys offer?

I converted the shot to B&W as well. BTW I shot at 6MP on the K10D just to speed up write times as I was testing it but even in RAW the results seem similar but the lower resolution/long exposures would account for the noise I assume.

I feel like a complete newbie doing this.

Edit: Sorry images removed to free up some space.


Last edited by Peter Zack; 11-27-2007 at 06:44 PM.
10-04-2007, 07:28 AM   #2
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Some thoughts:

The K10D is *very* insensitive to IR. All of my IR shots are done with the *ist D. If you look at this excellent site you will see that the K10D is about 15 stops less sensitive to IR light with a Hoya R72 filter. It looks like the *ist D/DS only lose about 7 stops with the same filter.

You really need to shoot IR in RAW.

It helps significantly to set the white balance manually. My last post was about how even in RAW, setting a manual white balance produces different results than either Auto or Tungsten WB.

And also, shooting in bright daylight is perfectly fine. Apparently mid-morning is a great time because the light is richer in IR, but I like shooting IR because it gives some interest in the middle of the day.

Jens R (a Pentax user) has some great IR tips on his site.
10-04-2007, 07:42 AM   #3
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Thanks Carpents. I'll do some more reading and experimenting. It would appear that the filter does what is it's expected to do but I have to learn how to set the camera correctly and of course choose the right things to shoot. Looks like some more reading... BTW I assume you are using a Hoya 72. Is the filter really thick like this one seems to be? I'm just curious if that is any issue with allowing light through.
10-04-2007, 07:50 AM   #4
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QuoteOriginally posted by Peter Zack Quote
Thanks Carpents. I'll do some more reading and experimenting. It would appear that the filter does what is it's expected to do but I have to learn how to set the camera correctly and of course choose the right things to shoot. Looks like some more reading... BTW I assume you are using a Hoya 72. Is the filter really thick like this one seems to be? I'm just curious if that is any issue with allowing light through.
Yes, I'm using a Hoya R72. It isn't any thicker than a normal filter, but I don't think your experience is being caused by a 'thick' filter. I don't use my K10D for IR because of your very predicament - it takes enormously long exposures to get anything out of it. With the *ist D I can take shots at ISO 400, 1/25th second at f/3-something, like this shot here. This makes it really hand-holdable for most of my purposes. The K10D wouldn't even be close to hand-holdable for the same scene.

10-04-2007, 10:15 AM   #5
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Welcome to IR with a K10D *grin*

Seriously though, nothing looks wrong - just perhaps not a great subject? I've shot a bunch of IR w/ the K10D and an R72 (Cheap-o hoya R72) and have got mixed results. I've gotten exposure times from 1s to 2min, and it all depends on light and subject.

Once you've got the light and the subject down, you'll need to work on your PP. 60% or more of IR shooting with a camera like this is in your PP technique.

Firstly, almost never should you be using 'convert to grayscale' or 'de-saturate'. These will most undoubtedly result in poor output for most IR shots (and for most color->b&w digital conversions).

Take this shot: it's with the K10D, R72 filter, ISO 100, F/8 and 2s exposure:

Last Stand Shutter Drone

The trick with this one was "where is the sun?" it's directly behind me and just over-head == the whole scene awash in IR light, shorter exposure time.

(I used no CWB as an earlier poster mentioned - it would've probably made the photo better if I had, however)

But, it really came to be in PP:

Step 1: I used ACR to 'pull' the image slightly (histogram balanced to the left) - this lets me push the highlights more in the next steps w/o too much blowout; keeps dramatic shadows.

Step 2: Used new adjustment layer -> channel mixer to handle B&W conversion, selecting as much from each channel as I liked. One trick when converting to B&W here, is you _definitely_ need some blue and green channel data here to bring out detail in images. I don't know exactly why, but you can't just retain the red channel only, it comes out 'mushy' - in this one, IIRC, I kept a decent amount of green [15%] and reduced blue quite a bit to get detail in the leaves.

Step 3: Place a new adjustment layer between the background and the channel mixer, make this one a levels. Now tweak the compression on the individual channels (red, green, blue - not the RGB combined) until you get the detail and feel you want. Don't worry too much about blowing out highlights.

Step 4: used dodge/burn to correct highlights and adjust details where you want.


This may seem fairly standard color->b&w conversion, because, for the most part, b&w IR on digital is a fairly standard color->b&w process. I hope this helps some! I've yet to have an IR image from the K10D that didn't require a LOT of work in photoshop, but each has been worth it in the end.

!c
10-04-2007, 01:55 PM   #6
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These tips have been a big help. I can see this will take some practice and time to get the feel for both the shooting and the editing. Thanks for the insights.
10-05-2007, 04:02 PM   #7
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To me it looks like the filter is not really an R72. It is possibly just a very strong dark red filter. That would explain the awfully long exposure.

I can take hand-held shots at ISO 1600, 1/16 or 1/30 with a Kood R72 on the K100D in moderate sunlight. Even losing 7 stops more would give you about 4-8 seconds exposure, not 60.
10-11-2007, 01:57 AM   #8
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Hi, I use the same combination of camera (K10d) and filter (Cokin 007 = 089b = Hoya R72). My experience is that taking photos is not the problem, apart from the relatively long exposure times. But that can be used artisticely, so I don't really mind.
My real problem with the cokin set-up is that the dark filter is reflected in the front lens and that I can see a reflection of the lens in the picture. My remedie is to make sure that no direct sunlight falls on the filter and lens. But this is a bit of a hassle. Any suggestions?

Roger.

10-11-2007, 02:40 AM   #9
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My only suggestion is using the hood and that system allows a second hood to be clipped on the first one if you are using a long enough focal length. AS for ricardobeat's comment he might be right. I'm not very happy with this setup and As Carpents noted his filter is much thinner than the version I have. But it's only usable on very bright days in many circumstances.
10-11-2007, 06:58 AM   #10
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As several have mentioned, Peter, the Pentax K10D incorporates two infrared filters (low pass and sharp-cut) over the image sensor, making this and similar cameras particularly insensitive to infrared light. This is done to increase image quality with normal images (reduced red-component noise, improved blacks, etc), and is, or will soon be, standard in all higher-end image sensors.

In other words, the camera is the root of your problems here. Because of these filters, the K10D requires really long exposures for the same amount of infrared light to reach the sensor as another camera without these filters. And, even then, the resulting images will not be the same as those from a camera without filters as the K10D's built-in infrared filters attenuate some parts of the infrared spectrum greater than others. This means that some parts of the infrared light will reach the image sensor easier then other parts (the image would need to be virtually over-exposed for all parts of the infrared spectrum to reach the image sensor).

So what does all this really mean to you? Well, it means the K10D can take infrared images if you're willing to tolerate the slower exposures you've already experienced and the slightly different look to the resulting infrared images. Otherwise, you may want to consider another camera for infrared images, simulate the effects of infrared images using computer software, or give up on infrared images entirely. Since I'm not that overly impressed with infrared images, I chose the latter.

stewart
10-11-2007, 01:55 PM   #11
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Stewart, I had heard some things along these lines but your comments make this much clearer. Thanks. I have a *ist D on the way. I'm getting it for a second body to shoot special event stuff and weddings. I just can't part with my AF400T flash system, quantum battery and all. (pissed that Pentax decided to abandon the TTL setup on the K series but that's another rant). Plus the *ist D is laid out much like the K10D (thumb wheels etc). So I'll give that a try. If it continues to be that much trouble with the *ist D then I may just sit back and enjoy others efforts. What I most liked about the process wasn't so much the IR stuff although some shots I've seen look very good but the B&W conversions from the IR original. The B&W versions have a look that can't quite be duplicated any other way.
10-16-2007, 04:42 AM   #12
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FWIW, i found the results from my K10D sdisapointing, similar to your example in the first post.

I decided to keep my istD and use it as my IR camera. Instead of exposures in the hours(lol) i can do exposures around 1/4 second or so.

Just a thought

Dave Brooks
10-16-2007, 04:55 AM   #13
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Thanks Dave, i'm looking forward to trying that camera. It should also be a better camer for astrophotography as well since the K series cameras would naturally filter out some of thee colours as well. Someday I'd like to get decent telescope to give that area of photography a try.
10-16-2007, 06:52 AM   #14
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QuoteOriginally posted by pentkon52 Quote
FWIW, i found the results from my K10D sdisapointing, similar to your example in the first post.

I decided to keep my istD and use it as my IR camera. Instead of exposures in the hours(lol) i can do exposures around 1/4 second or so.

Just a thought

Dave Brooks

I think the K10D is OK for IR work... i use the Hoya R72 for a lot of B&W work, sure you need a long exposure and sure you need a rock solid tripod and definitely make sure to both block the VF and that there is no gaps between lens and filter.

But I have made some pretty decent B&W photos thanks to the K10D and hoya R72.

Sure I prefer the DS for IR, but the K10D with its low IR sensitivity actually komes to a decent use, if you like me like to do long exposure work.
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