What nm filter to go with?

MrMbss1 · Jul 16, 2016

Recently I got the idea to convert my old 50D to full-spectrum, and so I did, what I didn't think of was filters. Currently my main lenses are the 18-135 kit, a Canon 100mm macro and a 14mm f2.8 Samyang. Since the Samyang doesn't support circular filters and the 100mm is a bit too long for what I intend to use it for, I'm searching for a 67mm filter for the 18-135.

Tl;dr
My question is: what nm filter do I get/search for for infrared photography on a full spectrum Canon 50D?
(atm it's visible light + pretty much everything else, would like to block out visible light)

Bonus question: how much of the spectrum is the 50D actually able to catch? To me it doesn't seem like a whole lot more than infrared, as the photos look very redish with not much other in the mix.

I will post a couple of sample pictures as soon as the battery has charge enough for it, 10 min or so
EDIT: phone doesn't allow me to upload photos for whatever reason.

480sparky · Jul 16, 2016

There's no one 'gotta get' wavelength. Your choice will be driven by your desired results. The higher the nm rating of the filter, the less color data you will have to work with.

You might want to carouse a bit here.

Being a full-spectrum conversion, you have the option of buying more than one filter.

KmH · Jul 16, 2016

Now that your 50D is full spectrum it can capture and record wavelengths of light beyond the wavelengths of light humans can see.
Get a filter(s) that passes the wavelength(s) you want to photograph.
Infrared - Wikipedia, the free encyclopedia
The filters you have/had removed mostly kept the low end (red/infrared) of the spectrum from reaching the image sensor.

petrochemist · Jul 16, 2016

The most common filter for IR is the standard R72 type (720nm), which blocks just about all visible light, but you can get interesting effects with all sorts of normal filters on a full spectrum camera (nearly all will transmit IR).
One of the best is a variable ND filter, these let through IR & basically allow you to control the amount of visible light in the shot. Orange & red filters work for high colour type IR shots (560nm, 590nm etc).
More specialist filters that can work well include a Tiffen 47, U330 or if you can afford it the Baader U2 (UV only) but this can be very demanding of lenses etc.
Any IR filter above ~860nm will effectively be monochrome as all the channels of the Bayer mask transmit equally at those wavelengths.
There are also 'variable IR' filters available now, these are basically just the combination of a variable ND & a 560nm filter. With the ND darkened they come very close to a 720nm filter, the other end of the range is close to 560nm in effect, but intermediate positions don't really mimic intermediate filters.

For you bonus question normal digital camera sensors once converted can see from ~300nm to 1100nm. UV response is often quite poor, being blocked by glass (& by oxygen in the air below 190nm). Above 1150nm the silicon used in the sensor is transparent to IR.
To get further into the IR you need a thermal camera which will be quite expensive