Enlarger contrast filters: over or under lens?

[marke]

I'm using a Beseler 23c II enlarger in my photo class, and just picked one up for my own darkroom I plan to build this winter. In class we are using the over-the-lens filters, but I also see that Ilford makes ones for under the lens. What's the advantage of under the lens? Isn't that a sure bet to degrade the projected image much more than an over-the-lens filter?

 

[Al Kaplan]

A lot of enlargers have a filter drawer over the condensers so they're out of the image forming part of the light path. In theory that's better for sharpness. Also, in theory, delicate easily scratched gelatin filters don't degrade the image. Plastic ones do. Back to practical reality!

Using a holder below the lens lets you buy a set of fairly small filters. You can often pick up a set for very little money second hand, a few dollars perhaps. Several brands are/were available and they all work the same way so you don't have to use Ilford filters only with Ilford paper. Kodak Polycontrast is likely the most common. Ansco briefly made some. DuPont, who came out with the first variable contrast paper, Varigam, made Varigam filters. Later when they introduced Varilour they came out with Varilour filters.

Ilford filters are available in half grades, plus they make a #00 (double zero) ultra low contrast. The DuPont Varilour filters incorporate a bit of neutral density. Find the correct exposure for the lighter middle tones and you can increase or decrease contrast without changing exposure time EXCEPT that the #4 requires twice the exposure. Hit the button on the Time-O-Lite twice so you don't jiggle anything out of place while changing f-stops.

The biggest advantage of a below the lens arrangement is the ease of switching filters while making a print without disturbing anything. You can, for instance, make an overall 12 second exposure through a #2, then give it 3 seconds through the #4 to "punch up" the blacks without affecting much else, then burn in some bright areas through a low contrast filter to get a hint of tone. Some people like the effect of giving part of the exposure through a #4 and part through a #1, doing a bit of burning and dodging in each exposure, but not in the same places. No exposure at all is made through the "normal" #2. See, it's just as versatile (and complicated) as Photoshop and your hands get to smell like hypo (but there's no dirt under your fingernails). And you end up with a gorgeous gelatin silver print!

If the under the lens filter degrades the image I've yet to notice it.

http://thepriceofsilver.blogspot.com/

 

[tmfabian]

i like using a plain old color enlarger for b&w printing and adjusting contrast through the color correction wheels for the same thing you stated. Plus I really like working with diffusion enlargers so dust and scratches don't pop up so much.

A lot of enlargers have a filter drawer over the condensers so they're out of the image forming part of the light path. In theory that's better for sharpness. Also, in theory, delicate easily scratched gelatin filters don't degrade the image. Plastic ones do. Back to practical reality!

Using a holder below the lens lets you buy a set of fairly small filters. You can often pick up a set for very little money second hand, a few dollars perhaps. Several brands are/were available and they all work the same way so you don't have to use Ilford filters only with Ilford paper. Kodak Polycontrast is likely the most common. Ansco briefly made some. DuPont, who came out with the first variable contrast paper, Varigam, made Varigam filters. Later when they introduced Varilour they came out with Varilour filters.

Ilford filters are available in half grades, plus they make a #00 (double zero) ultra low contrast. The DuPont Varilour filters incorporate a bit of neutral density. Find the correct exposure for the lighter middle tones and you can increase or decrease contrast without changing exposure time EXCEPT that the #4 requires twice the exposure. Hit the button on the Time-O-Lite twice so you don't jiggle anything out of place while changing f-stops.

The biggest advantage of a below the lens arrangement is the ease of switching filters while making a print without disturbing anything. You can, for instance, make an overall 12 second exposure through a #2, then give it 3 seconds through the #4 to "punch up" the blacks without affecting much else, then burn in some bright areas through a low contrast filter to get a hint of tone. Some people like the effect of giving part of the exposure through a #4 and part through a #1, doing a bit of burning and dodging in each exposure, but not in the same places. No exposure at all is made through the "normal" #2. See, it's just as versatile (and complicated) as Photoshop and your hands get to smell like hypo (but there's no dirt under your fingernails). And you end up with a gorgeous gelatin silver print!

If the under the lens filter degrades the image I've yet to notice it.

http://thepriceofsilver.blogspot.com/

 

[Roger Hicks]

If the under the lens filter degrades the image I've yet to notice it.

Dear Al,

Ilford's research indicated exactly the same thing. Even when they deliberately used scratched filters, the effect on sharpness was imperceptible, though with REALLY badly scratched filters, contrast suffered.

Incidentally, it was Ilford who invented the concept of VC paper. At that time, Ilford was not imported into the USA, and the heads of research at Ilford and Du Pont were friends, so Du Pont borrowed the Ilford technology -- I think they even used Ilford-synthesized dyes at first -- to bring out Varigam. Commercial introduction of the Ilford material was delayed by WW2, which of course started a bit earlier in the UK than in the USA.

Cheers,

Roger

 

[marke]

Dear Al,

Ilford's research indicated exactly the same thing. Even when they deliberately used scratched filters, the effect on sharpness was imperceptible, though with REALLY badly scratched filters, contrast suffered. Roger

Now I'm REALY confused! 😕

Wouldn't this mean that your enlarger lens could be pretty scratched up too, and it wouldn't be noticable? Or is this comparable to the fact that a scratch on the outer element of a camera lens has nowhere near the effect on IQ as a scratch on the inner-most element of the lens?

So if this is the case, would there be ANY advantage to using the (more expensive) over the lens enlarger filters?

Thanks for everyone who has answered.

 

[Roger Hicks]

So if this is the case, would there be ANY advantage to using the (more expensive) over the lens enlarger filters?

Mainly in theory, and if you're careless with your filters: fingerprints, scratches, etc., won't lower contrast at all if they're above the negative, and given that we're dealing with contrast filters here, lowering contrast and reducing the predictability of the contrast filters is not a good idea.

Look after your filters and no, there's no disadvantage whatsoever.

Cheers,

R.

 

[Fred Burton]

Under the lens filters are fine. They are so close to the enlarger lens that damage to them, because they are so out of focus, simply disappears. There's a bunch of math to explain all of it, of course, but I'm math disinclined; but, my practical experience confirms it.

 

[David Goldfarb]

Modern Ilford MG filters also use ND, so you can change filters from 00 through 3.5 without changing exposure, and add one stop for 4 and higher. This is a major convenience compared with older systems or using color printing filters or a dichro head, because you can expose for the highlights and adjust filtration to get the blacks where you want them without changing the exposure.

I like to keep the filters out of the image path, but I've used under the lens filters in the past, and they work fine. Under the lens filters are particularly convenient if you don't have a filter drawer (for instance with a cold light head) or if you are enlarging really big negs.

That said, I usually prefer graded papers, but for MG papers I sometimes put a 6" MG filter between the cold light head and the negative carrier of my Omega D-II, and that works as well.

 

[marke]

Under the lens filters are fine. They are so close to the enlarger lens that damage to them, because they are so out of focus, simply disappears. There's a bunch of math to explain all of it, of course, but I'm math disinclined; but, my practical experience confirms it.

Thanks for your answer, Fred. But I'm wondering, wouldn't an out of focus scratch result in things like a drop of contrast in that particular area of the image?

 

[marke]

I just want to say thank you to everyone who answered my question. I decided to just get whatever came along at the best price. It was able to get the winning bid on an ebay printing kit that included several other things I also needed, such as an easel and grain focuser. The Ilford over the lens filters are like brand new, as are the other two items. I got these 3 items (in addition to MANY more items I'll probably never use) for $58.

Now as soon as I install my wife's new dishwasher, I can get started building my darkroom!

 

[Roger Hicks]

I just want to say thank you to everyone who answered my question. I decided to just get whatever came along at the best price. It was able to get the winning bid on an ebay printing kit that included several other things I also needed, such as an easel and grain focuser. The Ilford over the lens filters are like brand new, as are the other two items. I got these 3 items (in addition to MANY more items I'll probably never use) for $58.

Now as soon as I install my wife's new dishwasher, I can get started building my darkroom!

Great news! Use it in good health!

Cheers,

R.