One for the techno wizards!

I have a K20D converted to 650nm IR.

This week I decided to try my Sigma EX DC 10-20mm f3.5, Pentax DA☆ 16-50mm & 50-135mm on it, and discovered an issue.

The images look like a film of vaseline has been applied to the lenses! They don't look out of focus.... just hugely soft.

I did find a compatibility list on the "other" Pentax site. These 3 were on it for the K20D! I have tried adjusting the focus but to no avail.

Any help would be muchly appreciated!

It would be helpful if you could post an example of an image?

Meanwhile, IR light will focus at a different distance to visible light and not many lenses are corrected for this. Some lense have an IR correction mark on the lens so this can be accounted for. Focus normally and then move the point of focus slightly closer and see if that helps.

Afternoon Spad,

I've a K5iis converted to 720nm, I vaguely recall reading somewhere that a cheap lens is ideal for IR, I've been using an old Sigma 18 - 200 but kit lenses are also recommended. I dont bother with any UV /Skylight filters on mine either.

Its produced sharp images from the day I had it converted, about 4 years ago now, a couple of examples as below.







Did you have it converted or did you purchase it converted, do you know if it was producing sharp images before conversion ?

Suggestion would be to try it with a kit lens if you have one

It was bought converted, and it shoots fine with all my other lenses...

Just not the 3 mentioned.

Try using a Polariser..... if "tuned" right it turns the sky black

I'll stick something up shortly..... need to fugure out how to get it of the camera n on to the tinterweb

Taken with Pentax DA☆ 16-50mm

Basically you are seeing what little bit of red can be shown as all the other colours have been removed. I would first convert that to monochrome. It needs a closer focus setting, which may well look out of focus through the viewfinder. It also needs a more defined subject to practice on. I would suggest an old black and white timber building, or anything with lots of sharp details. A museum, a set of houses or shops, just something inherently sharper than your landscape.

Then of course you need the light to have some IR in it, and as we can't see the IR light then that is variable. Try a bright sunny day with blue sky.

That should give you a starting point that you will be able to work with.

Righto.... and thanks John.

But.... it is not right. Images taken with any other are not like this.

But were they taken at f4 like the one above.
Try at f8-11
John