Digital BW, The Print

Hi-pass lets you choose which frequencies are passed to the sensor/film. works the same with low pass. The darkroom light is hi-pass. Can be like tone controls or rumble filters on a hi-fi.

This is just selective filtering and success depends on what you can find.  If you know any IR imaging engineers/designers for space orbit, you might get a line on good sources. The pass frequencies are critical.

gar


*********** REPLY SEPARATOR  ***********

On 3/14/08 at 2:46 PM c1asia wrote:

>--- In DigitalBlackandWhiteThePrint@yahoogroups.com, Sarah Thompson 
><sarah@...> wrote:
>>
>> Just my $.02 worth, as someone who likes to shoot B&W IR landscapes 
>with 
>> a Better Light scan back and a large format camera.
>> 
>> I'm quite fond of shooting infrared, partly (mostly?) because it's 
>> really easy to do with a a Better Light scan back. The Better Light 
>has 
>> no built-in IR filter, so you normally need to use an IR high-pass 
>> filter in front of or behind the lens for visible light work. I 
>like to 
>> swap this for a (visible light opaque) IR low pass filter, which 
>makes 
>> it possible to shoot very high quality IR.
>> 
>> The first thing I'll say is that I've not really seen any problems 
>with 
>> any of the glass I own with regard to IR -- whilst it would be 
>difficult 
>> to get a sharp result shooting IR and colour *at the same time*, 
>using 
>> an IR low pass filter and refocussing gives pin-sharp results. 
>There 
>> *is* a focus shift, however, which can be troublesome at times, but 
>the 
>> focus meter capability of the back makes it possible to tweak the 
>focus 
>> and get it right even though it's impossible to actually focus 
>> conventionally (i.e. no visible light to focus with). I've had the 
>> sharpest results with my 150mm Fujinon and my 90mm Super Angulon, 
>but 
>> then, they are my sharpest lenses anyway (not that my 47mm Super 
>Angulon 
>> XL or my 210mm Caltar are exactly blurred either, mind you). As 
>regards 
>> f stops, the usual 'stop down at least 2 stops from wide open, but 
>don't 
>> go too far or you'll get diffraction losses' advice works for IR 
>just 
>> fine, and (I suspect) even more so, because the longer wavelengths 
>> involved will be affected more by smaller apertures, at least in 
>theory. 
>> I've heard people say that IR gives dreamy, slightly blurred images 
>> inherently -- from experience, I can say for certain that this 
>isn't 
>> fundamental to IR because I've had some truly pin-sharp results. It 
>> probably *is* inherent in some IR shooting techniques, particularly 
>IR 
>> film, however. There's a bigish print on my office wall of Split 
>Rock at 
>> Joshua Tree National Monument where pretty much every grain in the 
>> house-sized rock is clearly visible.
>> 
>> My workflow is pretty simple: take the filter off, set the lens 
>wide 
>> open, focus and set shifts, swings and tilts conventionally (I use 
>a 
>> reflex finder as a matter of preference), insert the back, stop 
>down, 
>> put the filter in place, put the back in, refocus, shoot.
>> 
>> To return to the original point, rather than IR for a moment, depth 
>of 
>> field can certainly be an issue with large format cameras shooting 
>> landscapes. The best sharpness is generally found at around 2 to 4 
>stops 
>> narrower than wide open for most LF lenses, but this rarely gives 
>you 
>> depth of field that would have, for example, a meadow of flowers in 
>> focus from a couple of metres to the horizon. This is particularly 
>> noticeable with a 'standard' lens or short telephoto (150mm or 
>210mm 
>> with a Better Light, a bit longer than that for 4x5 film due to the 
>> slight crop factor), though it's still noticeable with a 90mm. 
>> Ultrawides like the crazy 47mm Super Angulon I use sometimes do 
>> obviously help, but you don't always want to shoot with something 
>that 
>> extreme. I've had very good results from using a 90mm Super Angulon 
>with 
>> a small amount of tilt to rotate the plane of focus  -- this is the 
>> *real* secret of pin-sharp large format landscapes. Stopping down 
>to 
>> f/64 will indeed give far more depth of field, but it does very 
>> noticeable soften the image. It's not so noticeable with film, but 
>it's 
>> *very* noticeable with a modern digital sensor, so tilts and swings 
>are 
>> where it's at in practical terms unfortunately. (And I mean 
>> *unfortunately* -- getting them right is difficult and time 
>consuming)
>> 
>> [s]
>>
>
>
>can you explain IR high-pass and low-pass filters to me?  i'm not 
>familiar with IR.  thanks.
>
>
>
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