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UltravioletPhotography

Lee 729 IR - West Green House garden


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Took the Lee 729 filter out today to try and get some red/blue IR shots. I had my multispectral EOS 5DSR and 17-40mm lens, with a small square of Lee 729 in the filter holder at the back. Custom white balance, but stupidly I did not select the Picture Style I had developed for the 'Faux Aerochrome IR' look. So this one isn't quite completely out of the camera. All I did was tweak the hue slightly, and then alter saturation and contrast (which would have been done in the custom Picture Style I created for the camera). Oh and I got rid of some flare as well.

 

post-148-0-15393600-1567366156.jpg

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A KG3 will 'clean it up' a bit, make grays less red, clouds less colored...

Running that pic there through Photoshop auto levels does it slightly for me, but KG3 will do it better and from the start.

Looks very nice though.

David Twede did it both ways and shows them here:

https://next-eyes.bl...tal-ir.html?m=1

 

Notice his first set of 729 shots, the sky is darker blue, then the second set using 729 + KG3, the sky is lighter blue, then compare whites, grays, etc....

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We are only using KG3 to reduce the higher IR, without removing the lower range IR that 729 transmits. KG3 is not used to reduce anything except higher IR. 729 suppresses red on its own.

I don't know what the Hoya 80C transmission plot looks like beyond 750nm, which is the important transmission range for using KG3 at all.

If anyone has an extended IR range plot for Hoya 80C, please post it. Without cutting the higher IR, there is no reason to use anything except the 729 alone.

 

Schott KG3 compared to Hoya 80C.

post-87-0-08245300-1567465283.jpg

 

Here is the KG3 beyond 800nm

post-87-0-25228300-1567468047.jpg

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I think Timber and Cadmium are forgetting that Jonathan has the 729 filter in a back of the lens gel holder. No way to add a IR cutter. So doesn't really matter.

 

Olympus cameras also have a color creator adjustment in camera. I will have to see if this works when I slide a 729 gel behind my Panasonic 7-14mm. Same issue, no room for anything but a single gel.

 

Oh, stock Panasonic 7-14mm don't have a gel holder. But you can get a replacement part for the 8mm fisheye and switch it on the 7-14mm to get a gel holder. Will fit 22mm square filters.

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Putty-mounting a smaller filter against the gel filter holder, with the Lee filter in place might be possible, if there is enough space margin to the mirror (EOS DSLR)

A thinner KG5 should work better for that. KG5, 1mm ≈ KG3, 2mm

 

Correction: KG5, 1.5mm ≈ KG3, 2mm

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As I said, the only point of stacking the KG3 with the 729 is to reduce upper IR which has more of a tendency to 'pollute' the other two Bayer channels (green and blue) with IR.

We have suppressed visual red from the Bayer red channel using the 729, because we want the Bayer red channel to be used for only IR.

We want the green and blue Bayer channels to be used for visual green and blue only, or as close to 'only' as we can get.

Below I have superimposed a typical Bayer color channel graph over the other graphs, this will show how the Bayer red channel is more sensitive to IR in the 700-800nm range than the Bayer green and blue channels are.

At about 800nm to 850nm the Bayer color channels all become more equally sensitive to IR.

The 729 + KG3 stack has a peak IR sensitivity in the same range that the Bayer red channel is most sensitive.

How much this works in our favor, I can't really say, I only know the difference in photos I have compared.

The point being, stacking KG3 works to concentrate more IR into the red Bayer channel and less IR into the blue and green Bayer channels.

David Twede has shown examples both ways, with and without KG3 (like Jonathan's, without KG3), I am just explaining the reason for the addition.

 

post-87-0-71464500-1567489805.jpg

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Haven't got any Lee 729! I suppose I could get some? I think I misunderstood your comment, though. When you said "upper" for some reason I was thinking you meant the 700-800 range, but I guess that's "lower."
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Yes, when I say upper IR I mean basically about 800nm there the Bayer channels become more even with each other.

Keep in mind we really don't know exactly what the 729 transmits about 800, I was hoping Jonathan would scan his and post it sometime,

but if we follow the trend of the 729 at 800nm it looks like it doesn't transmit much above 800nm. Would be interesting to know though.

(that crossed out part is wrong)

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Actually based on the Lee plot for 729, I bet it shoots straight up. Most Lee filters don't block any IR. I think the material used for the 729 is the same. So I would expect 50% at 850nm and near 100% just after 900nm.

 

Cadmium, Jonathan doesn't have a IR capable spectrometer. Only Ulf here does that I know. I maybe wrong, but I am fairly certain Jonathan's cuts off at 800nm.

 

Hopefully, Ulf scans his. I thought he was getting a sample pack a couple of months ago.

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Could you simply stack the Lee with some long pass that starts at 800nm and see how much gets through? Or, you know, Sparticle it?
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Not a bad idea. Cadmium if you stack a 830nm Lp with the 729, I bet you would not see any difference in the exposure settings compared to just the Lp830nm filter.

 

Ulf ordered his in March and should have gotten it in April. Just read through the old thread. But haven't seen any thing from him. I wonder if he got it.

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I am not going to do that, but you could.

Not sure if I sent any 729 to Ulf or not. Maybe just the PTFE, can't remember.

You did, a tiny bit, but without any comment of why. I forgot to ask.

I had already bought 100x more 729, that is less wrinkled and could be used for photo.

 

Have not had time for that too. I have too many balls in the air. :smile:

 

I'll try to get some time over to configure the optical bench for filter transmission measurements again and measure the Lee 729.

I hope to get some meaningful spectra from the Tiffen Haze 2A too. It arrived a few weeks ago

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I'm not planning on trying this with KG3 at the moment. I rear mounted the Lee 729, and it was on my wide angle which has a 77mm filter thread.

 

I think I can get to 850nm with my spectrometer, but no higher than that.

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Actually based on the Lee plot for 729, I bet it shoots straight up. Most Lee filters don't block any IR. I think the material used for the 729 is the same. So I would expect 50% at 850nm and near 100% just after 900nm.

 

Yes, your right, I was thinking of the other plot, the 729 is headed UP not down at 800nm.

I have never seen any transmission data on any Lee filter above 800nm. Do you know of any?

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I found that my filter transmission measurement components sat untouched on its own Arca-rail, ready to be used. :smile:

The transmission of my sheet of Lee Scuba-blue 729 looks like this:

post-150-0-67038600-1567507833.png

The curve is a result of 1000 spectra, with 37ms measurement time each.

I verified that 0% and 100% was OK before and after the measurement.

 

I suspect that the result below 400nm is partly due to crosstalk and the lowest values in vis below 1% might also be offset slightly upwards.

Neither of these limitations to the accuracy are affecting the result for the Aerochrome-like images we are trying to get with this type of filter.

 

Linear scale to be easier to compare with the Lee diagram:

post-150-0-51632300-1567508622.png

 

The last bit beyond 1000nm can be compromised too. I have never really looked into that end for accuracy issues.

I guess that if I combined the light source with a RG850 I would be able to focus on that end only.

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I have the Lee sample book and can measure other filter-types, if I find a good way to mount them, without taking the book apart.

I want to keep the book intact.

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