EIR / Aero Photos: Filter Question

[Cadmium]

Oops! I didn't realize there was more than one page. I will read more then.

[Andy Perrin]

Colin, for imaging vegetation, there are a LOT of special "indexes" that are in common use, and I just found a nice article with a summary of them:

https://eos.com/blog/6-spectral-indexes-on-top-of-ndvi-to-make-your-vegetation-analysis-complete/?utm_source=Email&utm_medium=educational_content&utm_campaign=button

[bvf]

Yes, I was looking for Hoya 80C charts....

 

This may be of relevance, Colin, or it may not!

 

If you look at the "Hoya Color Filter Glass" catalogue, it doesn't show many of the Hoya filters we are familiar with. R72 is there, but others like O(G), Y(K2), R25A and 80C are not: perhaps these filter designators are used by the Hoya department or spin-off that makes finished products, whereas the catalogue is from the department that manufactures glass.

 

However, there are glasses in the catalogue that seem to do the same thing as those filters we are familiar with. In the catalogue, the LB series of glass are blue light-balancing filters. The LB80 has a mired shift of -80 (+/- 5), which corresponds closely to the 80C (mired shift of -81). It could be that the 80C filter is made using LB80 glass. The catalogue gives curves and data for the LB80 covering the range 200-5,000 nm.

 

PS: you can find references on the internet to Hama light filters KB 9/ LB-80/80c - may just be co-incidental, but it suggests a link between LB80 and 80c.

[dabateman]

Bernard,

You might be on to something. This Midpoint optic Lb-080 spectrum does look similar to a 80C one I have, both around 25% at 700nm.

 

https://midopt.com/filters/lb080/

[colinbm]

Thanks Bernard

Sounds logical, I will look...

[Cadmium]

Go here:

https://hoyaoptics.c...-filters-la-lb/

 

Here are some of the Hoya 'light balancing' filters.

 

Here is a graph of 80A, 80B, and 80C.

 

Here is an overlay of the two graphs above.

Like Bernard was saying... Some similarities...

I think this also helps to answers the question about how the 80A/B/C filters transmit in the IR range. Kind of the opposite of KG3 in a way, the transmission actually increases as the IR nm gets higher,

and has its strongest IR suppression in the 700nm to 800nm range, right where you want the IR to be strongest.

[colinbm]

Thanks Steve

[colinbm]

Colin, for imaging vegetation, there are a LOT of special "indexes" that are in common use, and I just found a nice article with a summary of them:

https://eos.com/blog...campaign=button

Yes, thanks Andy, I am trying to digest this site, but I haven't come across what filters they are using yet, or their set-up ?

[Andy Perrin]

Yes, thanks Andy, I am trying to digest this site, but I haven't come across what filters they are using yet, or their set-up ?

 

Oh, they are talking about using satellite imagery to take the photos, which means the equipment will be very different from ours. The point is that how you process the data matters as much as which bands you image in. So say you want to compute the "GCL" index, which they claim lets you estimate leaf chlorophyll in different species. For that one, the formula is

 

GCI = (NIR) / (Green) – 1

 

So one way to do that would be to use a Tiffen #12 filter to get the NIR/Red/Green data, and then process it using the above formula, which could be done in photoshop by rewriting it as (NIR - Green)/Green and then using the Channel Mixer for the subtraction, and then use Layers to do the division by the green.

 

For some of them, you need NIR, Red and Blue, which probably requires taking two photos, a visible and a pure infrared (say with a 850nm long pass filter).

[colinbm]

Thanks Andy

I am happy with juggling filters on a full spectrum cameras, & basic processing....but juggling software in Photoshop is beyond me.

First I don't have Photoshop, except Elements. & my age is showing trying to learn & remember new software tricks....:-(

Cheers

Col