Below lens or above? (contrast filters)

[tkamiya]

This is one of those things I wish I can test it myself but I'm not willing to destroy my filter to see how it will change things....

Commonly held wisdom is that less below lens (in enlargers) the better the print image quality. In this wisdom, it is said that below lens multi-grade filters degrade images if not perceptibly - at least theoretically.

There are statements found on internet, some firsthand, some second or third, that in reality, one will be hard pressed to see the difference in actual products even when filters are somewhat scratched. One on this forum has said, because the filter is so thin and close to the lens, it won't affect images.

I have two enlargers that currently, both are fitted with below lens Ilford filters. Personally, I have no seen anything objectionable but since I cannot test the other, I have no idea if it could be better.

Do we have anyone who has actually done tests in this regard? That is, comparison between above and below, then for below, pristine filters and scratched? If so, I would very much like to know what the experiences were.

For this thread, I am not so interested in how it *should be* based on theory alone. I'm more interested in actual accounts.

Thanks much!

[brucemuir]

I haven't done a direct comparison but used to use the below flip out type on my DII condenser set up.

I never noticed image degradation but I guess it has to happen. Whether it shows in the print is the main issue and I was quite happy with up to 11x14 (largest I did then). My filters were in decent shape.

I later went to above the lens and I'm now using a Dichroic diffusion head. The diffusion head definitely isn't as crisp as my below lens period so I think it all comes out in the wash

I wouldn't sweat using below lens filters if you are happy with your prints. I doubt you'd gain much.

[Greg Davis]

I've done both. As long as the filter used under the lens is fairly scratch free you will not notice a difference one way or the other.

[vpwphoto]

Without any doubt ABOVE... unless B+W makes filters and a holder that keeps them right in line with the lens... even if they did I'd still say above with no doubt.

If you were to measure lines of resolution in the print you would be able to quantify it. I won't even argue the point. If you are happy that is fine. But I am not projecting an image through a nice Rodenstock lens and then throwing those image bearing photons though a dusty piece of plastic with micro scratches. The light will scatter and reflect within the plastic. I have been using above the lens plastic 6x6 filters just below the cold light for 25 years.


For the record, my Ziess T* lenses bought new never had a skylight filter, and still have no ill effects on the elements from heavy professional use. Oh I did buy a B+W skylight filter on when I shot in rolling steel mills.
Only color correction minus blue and Orange filters when needed.

[Rick A]

Any time you add anything below the lens you have a reflective surface that can degrade the image. Definitly use above the lens filters.

[ic-racer]

I almost spent over $200 on 12" above the lens Ilford MG filters for my 8x10 enlarger based on that "above the lens" dogma. If you read the instructions for the smaller Ilford MG filters it says it is ok to use them under the lens, and I can say that indeed that is the case. I wound up getting the six inch below the lens filter set and saw no loss of quality (with grain magnifier and in prints) using the filters below the lens.

[tkamiya]

I understand, theoretically, above the lens is better. The filter is removed from the image path. But, my concern is more of practicality. Do any of you seen any degradation by placing one under? As I said in my original post, I would like to know if anyone have seen any difference, and if so, at what point (amount of scratch) did you notice the difference.

[MattKing]

I don't have anything but anecdotal evidence to rely upon, but here goes.

I have worked in darkrooms with multiple enlargers, where some use below lens filters, and others use above negative filters, and have seen no difference in results.

I have gone from using a below lens filter enlarger to one with a multi-grade head, and can see no filter induced degradation in the earlier prints.

It doesn't surprise me that this would be the case - the role that a below lens contrast filter plays in an enlarger's light path is very different than the role that a camera filter screwed on to the front of a lens plays.

[BetterSense]

It doesn't surprise me that this would be the case - the role that a below lens contrast filter plays in an enlarger's light path is very different than the role that a camera filter screwed on to the front of a lens plays.

How? It seems exactly the same thing to me.

The only change I think that below-the-lens filters cause is slightly increased flare. Since you are adusting the contrast anyway, I don't think it matters. I was too cheap to buy the nice plastic Ilford below-lens filters so I bought the 3" above-lens filters and I use them below the lens. It works.

[holmburgers]

If you've ever shot through a dusty lens, or an old fungus ridden lens, you'll be amazed at how the imperfections in the image path, but not in the plane of focus, have very little effect. Undoubtedly, there is an effect, but for most work I'm sure you'll scarcely notice a difference.