Infra-red filter on dichroic head?

[Poco]

I recently got a Chromega E Dichroic II enlarger by way of an ugly Ebay transaction. The enlarger arrived with a smashed infra-red filter on the diffuser box, which I have temporarily replaced with plain glass. Is the Ifra-red filtering really necessary for the proper functioning of the Dichro head? I haven't had any experience with one before and haven't a clue. Initially, I plan only to enlarge B&W, but may give color a shot some day.

Any input appreciated...

-Michael

[clogz]

An ifra red filter is certainly necessary for colour printing. On the other hand it depends on the coating of your enlarging lens as this may protect against IR light waves. So I think you'd better replace the smashed-up filter.

Good luck

Hans

[Poco]

Thanks, Hans.

I suppose I'll have to hunt for the replacement part, or for some appropriate substitute.

[Donald Miller]

I have not encountered an IR filter on any of the three enlargers that I have owned and the countless others that I have seen or used. Are you talking about a red filter that is usually placed into the light path (most commonly beneath the lens)? If this is what you are asking about then you can very easily do without it.

[Donald Miller]

If, however, this is a filter that is pertinant to the E model, then I would check with the folks at Focal Point, (a search will locate them for you), since they deal with a number of different enlargers, parts, and accessories. Hope that this helps. Good luck.

[Poco]

The filter is basically a 1" diameter piece of clear looking glass that the light enters the diffusion box through. Originally I thought it was just meant to shield the interior of the box from the heat of the halogen bulb, but then I noticed the glass had a faint opalescence to it ...and then a note on the diffusion box itself that said it was equipped with a "infra-red filter." Presumably it's meant to filter out infra-red rather than meant to mimic the effects of infra-red film.

I will indeed do the search you suggest.

Thanks.

[Thilo Schmid]

Michael,

you will only need an IR Filter in your dichroic head, if you are processing color paper. The cyan forming layers of most color papers is sensitive down to ~750nm. Since almost all enlarger lenses are not corrected for IR, part of the paper "sees" an unsharp image. BTW: the same happens with the UV Portion of the light on all papers (including B&W). Fortunately, most of the UV Light is absobed by the lens (which is not the case with IR Light). Good dochoic heads do have both IR and UV filters.

[Ed Sukach]

A "Dichroic" filter is better described as a "heat glass", ... an Infrared filter for *really invisible* infrared radiation, otherwise known as "heat".

Its function is to absorb heat in the optical path and keep the negative stage relatively cool to prevent "popping" out of focus, or in extreme cases (and not ALL that extreme either), damage to the film.

You CAN get away without it. Personally - I wouldn't try.

[Thilo Schmid]

</span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (Ed Sukach @ Apr 9 2003, 10:50 PM)</td></tr><tr><td id='QUOTE'>A "Dichroic" filter is better described as a "heat glass", ... an Infrared filter for *really invisible* infrared radiation, otherwise known as "heat".</td></tr></table><span class='postcolor'>
A Dichroic Filter is based on light inference instead of dyes. This is the reason why the don&#39;t wear out (except from getting dirty). Whether a Dichroic Filter absorbs, reflects or passes IR light, depends on the characteristics/specifications of the filter. Not all Dichroic Filters cancel IR nor are all "hot mirrors". Even if they would be, the effect would be dependent on the amount of filtration dialed in.

[Ed Sukach]

</span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (tschmid @ Apr 10 2003, 03:17 AM)</td></tr><tr><td id='QUOTE'></span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (Ed Sukach @ Apr 9 2003, 10:50 PM)</td></tr><tr><td id='QUOTE'>A "Dichroic" filter is better described as a "heat glass", ... an Infrared filter for *really invisible* infrared radiation, otherwise known as "heat".</td></tr></table><span class='postcolor'>
A Dichroic Filter is based on light inference instead of dyes. This is the reason why the don&#39;t wear out (except from getting dirty). Whether a Dichroic Filter absorbs, reflects or passes IR light, depends on the characteristics/specifications of the filter. Not all Dichroic Filters cancel IR nor are all "hot mirrors". Even if they would be, the effect would be dependent on the amount of filtration dialed in.</td></tr></table><span class='postcolor'>
"Poco" described the filter in question to be "on the diffuser box", which would indicate to me that it had, in fact, a heat attenuation purpose. I don&#39;t infer any "adjustablilty" from the original post.

I&#39;ve checked the "Spectral sensitivity" information I have (I only have the data sheets from Agfa) and color paper does have a greater "range" than black and white. Agfa black and white papers drop off to *very little* after about 550 nm, a consideration for safelight use. With their color papers, Spectral and Color sensitivity of the cyan layer end at about 720 nm.

I think some of the confusion here may stem from the term "Infra Red" filter. The filters for use with IR film <on the camera> *PASS* IR and filter out everything else (yeh, I know - oversimplication), while IR filters in OPTICAL PATHS (sometimes referred to as "dichroic filters" or "heat glass, or "heat mirrors" are there to *REMOVE* Infra Red radiation.

I&#39;ve printed color for some time, now, and the idea of controlling IR for some effect or other has never ben a consideration. I&#39;ve never heard anyone critique one of my prints by saying "Needs more IR."