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Pentax Lenses for IR Photography

bforbes
Posted 30/09/2016 - 21:21 Link
I've read that while a lens may have no issue when used for the normal light spectrum, if it's used for the IR spectrum it can exhibit internal reflections or "Hotspots".

Is there anyone with experience of Pentax lenses to avoid for IR photography, or indeed any Pentax lenses they would recommend, either modern or legacy?
johnriley
Posted 30/09/2016 - 23:10 Link
I've not found a Pentax lens yet that's been a problem in that way, but I doubt that any of us have tried them all with IR in mind.

Manual lenses tend to have IR focusing marks, so that could be useful. A series lenses would be the most convenient as they will meter and stop down correctly without any hassle. However, some AF primes may also have IR marks, so they can be used manually anyway.
Best regards, John
Blythman
Posted 30/09/2016 - 23:27 - Helpful Comment Link
Alan


PPG
Flickr
derek897
Posted 30/09/2016 - 23:58 Link
Blythman wrote:
There's this list

http://kolarivision.com/articles/lens-hotspot-list/

Nice one Alan, I had seen that list and it was wrecking my head trying to remember where i had seen it.
I know what i like, If not always why.
bforbes
Posted 01/10/2016 - 09:26 Link
thanks guys
petrochemist
Posted 02/10/2016 - 10:18 Link
johnriley wrote:
A series lenses would be the most convenient as they will meter and stop down correctly without any hassle.

On most converted DSLR's the metering is not measuring IR at all. Metering usually being done by a separate sensor by the prism. I've never heard of a conversion adjusting the metering wavelength but no doubt it's possible.
Mirrorless cameras & some in liveview mode will meter from the main sensor and will be measuring the same wavelengths the image gets recorded from.
Mike
.
Pentax:K5ii, K7, K100D, DA18-55, DA10-17, DA55-300, DA50-200, F100-300, F50, DA35 AL, 4* M50, 2* M135, Helicoid extension, Tak 300 f4 (& 6 film bodies)
3rd Party: Bigmos (Sigma 150-500mm OS HSM),2* 28mm, 100mm macro, 28-200 zoom, 35-80 zoom, 80-200 zoom, 80-210 zoom, 300mm M42, 600 mirror, 1000-4000 scope, 50mm M42, enlarger lenses, Sony & micro 4/3 cameras with various PK mounts, Zenit E...
Far to many tele-converters, adapters, project parts & extension tubes etc.

.[size=11:].FlickrWPFPanoramio
bforbes
Posted 02/10/2016 - 14:30 Link
Is there a convention to follow regarding lens hoods with IR - needed more, needed less, makes no difference.
johnriley
Posted 02/10/2016 - 19:50 Link
Always use a lenshood, regardless. As fr metering, I meant the camera would meter as designed to. With IR, we never know how much IR light is p[resent anyway, so there is a certain amount of trial and error.
Best regards, John

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