infrared filter


abesad

Link Posted 12/08/2009 - 18:08
I bought a cokin infrared filter to use on my pentax k20d, I tried it out, but no picture, have I done something wrong or does my pentax camera not take infrared. Thanks for any help.
susan

greynolds999

Link Posted 12/08/2009 - 18:13
Your K20d has an IR blocking filter in front of the sensor. You can take IR shots but you will need MUCH longer exposures. Best thing is to keep experimenting!
My Photobucket

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johnriley

Link Posted 12/08/2009 - 18:16
All digital cameras are very sensitive to IR so the manufacturers put a filter in front of the sensor to remove some or all of the IR. It can cause colour shifts and loss of contrast.

The *istDS is not too bad in this respect and will work quite well with IR, but the K10D filtered quite aggressively and wasn't so good. The K20D I have not tried.

The technique is to put the camera on a tripod, compose your image, refocusing manually to the IR marker if there is one on your lens. Then put on the filter and let the camera calculate the new exposure. You won't see through the viewfinder at this stage because the filter removes all the visible light.

When the (possibly quite long) exposure is done you will be able to view the very red image on the camera screen. This then needs converting to black and white either in camera if it does it or in Photoshop or similar.

That's it in a nutshell, but there are plenty of books on IR imaging. It can look fantastic with the right sort of subject.
Best regards, John

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jackitec

Link Posted 12/08/2009 - 18:24
There is an infrared setting on the K20 it's not that good but it does work.

abesad

Link Posted 12/08/2009 - 18:44
greynolds999 wrote:
Your K20d has an IR blocking filter in front of the sensor. You can take IR shots but you will need MUCH longer exposures. Best thing is to keep experimenting!

So how long exposure are we talking about. I don't understand this bit about an IR blocking filer in front of the sensor though.

abesad

Link Posted 12/08/2009 - 18:45
johnriley wrote:
All digital cameras are very sensitive to IR so the manufacturers put a filter in front of the sensor to remove some or all of the IR. It can cause colour shifts and loss of contrast.

The *istDS is not too bad in this respect and will work quite well with IR, but the K10D filtered quite aggressively and wasn't so good. The K20D I have not tried.

The technique is to put the camera on a tripod, compose your image, refocusing manually to the IR marker if there is one on your lens. Then put on the filter and let the camera calculate the new exposure. You won't see through the viewfinder at this stage because the filter removes all the visible light.

When the (possibly quite long) exposure is done you will be able to view the very red image on the camera screen. This then needs converting to black and white either in camera if it does it or in Photoshop or similar.

That's it in a nutshell, but there are plenty of books on IR imaging. It can look fantastic with the right sort of subject.

I composed my photo and had while it was on timer, I put the IR filter on before it took the shot.

abesad

Link Posted 12/08/2009 - 18:49
jackitec wrote:
There is an infrared setting on the K20 it's not that good but it does work.

I like the idea of using a filter rather than the one inside the camera,although I have used the inside one, but thanks anyway.

greynolds999

Link Posted 12/08/2009 - 18:55
Basically, the filter you have bought only allows IR through, but the K20d (in common with most DSLRs) has a filter designed to block IR. Therefore the two cancel each other out.

Because you now have hardly any light entering the camera you need to use a very long exposure. Just keep experimenting with longer and longer exposures until you start to see something.
My Photobucket

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johnriley

Link Posted 12/08/2009 - 18:56
Quote:
So how long exposure are we talking about. I don't understand this bit about an IR blocking filer in front of the sensor though.

Generally, internal reflections within a lens can cause flare and loss of contrast. Because the sensor is sensitive to IR light any IR that is being scattered will affect the sensor even though we can't see it. This causes colour shifts and lack of contrast, so it is filtered out by a "hot filter" in front of the sensor.

Leica found this to be quite a problem in their rangefinder digital R8.

Canon also filter out IR very aggressively, so Canon cameras are unsuitable for IR photography.

It is possible to have the hot filter removed by a repairer and replaced by clear glass, thus creating an IR sensitive camera. Fuji actually market IR versions of their S5 and S9600 cameras.
Best regards, John

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grahamwalton

Link Posted 12/08/2009 - 19:43
Susan

When you say that you have a Cokin Infrared filter, is it a screw-in circular filter or a square slide-in type. I ask this because to get good infrared images you need to stop all unfiltered light from reaching the lens. A Cokin square filter may allow daylight to reach the lens down the side; if this is so then you may want to apply some black tape at the edges.

To take infrared photographs on your Pentax K20D, I would use a tripod and take a trial exposure in Manual setting, at 1/15 sec at f8 using 400 ISO. This assumes good sunlight. Be prepared to alter this to 1/8, 1/4 or 1/2 at f8, with ISO settings of 400, 800 and 1600. The higher ISOs will produce plenty of noise and this makes the images look very soft.

I have not tried infrared on my K20D but have taken plenty on my istDL2.

Best of luck with the experiments.
Friendly Regards
Graham

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Hardgravity

Link Posted 12/08/2009 - 19:52
There's an old thread here that might help.

There again...
Cheers, HG

K110+DA40, K200+DA35, K3 and a bag of lenses, bodies and other bits.

Mustn't forget the Zenits, or folders, or...

I've some gallerieshere CLICKY LINK! and my PPG entries.

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abesad

Link Posted 12/08/2009 - 20:29
grahamwalton wrote:
Susan

When you say that you have a Cokin Infrared filter, is it a screw-in circular filter or a square slide-in type. I ask this because to get good infrared images you need to stop all unfiltered light from reaching the lens. A Cokin square filter may allow daylight to reach the lens down the side; if this is so then you may want to apply some black tape at the edges.

To take infrared photographs on your Pentax K20D, I would use a tripod and take a trial exposure in Manual setting, at 1/15 sec at f8 using 400 ISO. This assumes good sunlight. Be prepared to alter this to 1/8, 1/4 or 1/2 at f8, with ISO settings of 400, 800 and 1600. The higher ISOs will produce plenty of noise and this makes the images look very soft.

I have not tried infrared on my K20D but have taken plenty on my istDL2.

Best of luck with the experiments.

Hi its one you slide into the holder.

abesad

Link Posted 12/08/2009 - 20:30
Thank you everyone, I read all these comments more thoroughly and try again tomorrow depending on the weather.
regards susan

Conky

Link Posted 13/08/2009 - 15:22
My attempts at this involved 20 or 30 second exposures with apertures in the f5.6-9.5 range (and 100 ISO). As the guys on here pointed out, it's an uphill struggle given the effectiveness of the sensors' IR filtration. It's worth a try though and I'll have another go if the sun ever comes out again.
In use: K7 & M35/2.8, FA50/1.4, M200/4, M100/4 Macro, DA 16-45/4, DA* 50-135/2.8, DA-L 55-300/4-5.8
Non-Pentax: Sigma 24/2.8
Gathering dust: K10D, K1000, MX, ME Super

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jackitec

Link Posted 13/08/2009 - 18:09
This was taken with the infrared filter built in to the K20, I don't know how it compares to a proper filter or an infrared camera, any comments.
Jack.


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