Not at all Peter, your statement sounds quite logical.

Pure instinct told me the result would be different though hence adding a filter. That is probably based on the fact that I know that years ago Nikon sold a IR/UV specific flash plus the relavent filters. In fact Andy posted a link in post no. 54 to that particular bit of kit. Nobody is going to make specialist kit like that unless there is a requirement based on experiences.

Just to confirm my instinct was correct I took a pic without the filter to compare later while I was at it.

Attached is a side by side screen grab of each Nef with it histogram. It is fairly large 1122 x 764 to give a reasonable view. Exposure on both is identical. White balance was custom, and taken from grass in sunlight. The difference I think you will agree is quite significant, hence I am going to do a job on my three portable flashguns.

As you are going to give it a go, and myself not being familiar with Canon lenses, does the lens you hope to use have an infrared focusing mark. I mention that, as with most lenses infrared focusses in front of the normal light distance. So it is a case of focus then manually refocus on the IR mark.
I will do a pic of one of my lenses to explain that.

Don

interesting stuff Don - looking at your image and thinking about it a bit more I guess that the 720nm filters cut out most visable light but not all, so by adding an IR filter to your flash you are reducing the amount of visable light 'contaminating' the IR image. But that might just be twaddle! If possible I'd like to meet up at somepoint and see your set up and get some tips on this, probably best to leave it until after the half term though!!!

No probs Peter, just PM me so I can e-mail you a map of where we are.

Today I got round to making the infrared accessory for my Metz 45CL3 flashgun. Image attached.

I have previously made a diffuser for the Metz which is almost never off it due to the quality of light it produces. Link to the thread and pics on making that.
http://www.worldphotographyforum.com...ead.php?t=1862

Instead of the bowl being attached to the mounting plate, I stuck velcro to the front on this one. The Cokin has a land 7mm wide on one side, and I made up and attached a velcro ring to that so as to allow the filter to be detatchable for safe storage. While light tight at the front there are some ventilation slots at the side to allow heat from the flash tube to eascape. The small amount of visible light that gets through those is not enough to degrade the IR image.

Don

Infrared focus and compensting for it.
 

Anyone using either Hoya R72 or Cokin 007 Infrared filters needs to be aware of the difference between the plane of focus of infrared light when compared to visible light, and the best way to demonstrate that is by showing it in a photo.

For this I drew a line chart, which is attached ( 1200 wide ), and can be printed on a sheet of A4 paper.

To demonstrate the effect I needed to have the shallowest depth of field I could get. As I am using the D100 for IR I chose to do the test with an autofocus lens so used an 85mm, set to f1.8 at near its minimum focussing distance. A Cokin 007 filter was used for the IR shots, but a Hoya R72 would have given the same result. I did not check the film filter but that is also probably in the same ballpark.

Method :
I firstly autofocussed on the centre mark and took a visible light pic.
Next, I turned A/F off to retain that point of focus, placed the IR filter on the lens and took another pic.
Lastly, I manually refocussed the lens to the IR index and took another pic.
All three were stitched together for the composite attatched.

For Canon users I am afraid I am not familiar with the lens markings, so assuming they are similar, I have attached a pic of Nikon lenses to give an idea of where a focus compensation mark may be found.

When using wide angle lenses its not that much of a problem. If you look at the focus scale on the 20mm lens in the pic you will see that f5.6 will cover everything from 2mtrs to infinity. It is a bigger problem though if you intend to do macro shots at 60mm plus, where depth of field is far shallower. Hence attaching the printable line chart so you can conduct you own tests, particularly if the lens has no IR compensation mark.

Don

Thanks for that Don, I've printed off the line chart already.

Well today was dull enough for an outdoor experiment with the IR attatchment on the Metz. So a Cokin IR filter on the Metz, and a Hoya R72 on the lens.
The composite shows the visible light version in comparison with the IR flash version. I tried direct and diffused flash. Adding a diffuser produced a rather soft image and also showed that I should really have bought a Metz CT60 all those years ago :rolleyes:. Never enough power when I want it ;). Light loss through the diffuser really required ISO to be ramped up to 1600. Not a good plot on the D100 as I think of NR as a detail killer, so never use it.

Fairly pleased with the experiment but it also put a thought in my head that I should try my Multiblitz studio job, as the flash duration is a lot longer and that may boost the IR effect.

For the gallery pic I which is a crop of the IR version here, I added a bit of tint and then boosted the whole effect with curves. Sort of Autumn rose.

To save going back to the gallery to compare, I have put it in this post.

Don

I like the tinted version Don. Now while I'm away on my holidays, how about trying various white balance setting:)

Harry

Hi Don, Harry and all IR on the not so cheap :D

Andy I see the burning enthusiasm at spectrum of IR.
Remember to sleep tonight as there is no usable IR once the sun is set and then there is a full day waiting for you tomorrow.

Enjoy your wonderful new toy.

Andy,

Welcome to the club. :)

Now you have your IR converted D100 I can reference some of my experiments from your pics if you give some details, paricularly WB setting. It would also be very helpful to post an unprocessed pic to reference that info.

Now we actually have some sun, I will be able to compare a double thickness film filter with Hoya or Cokin IR filter as they both have the same cut-off. Still not sure at what wavelength the film filter cuts off.

Don