Cleaning LF Lens

compur · Jul 15, 2016

The mistake is thinking that each individual point of the subject is rendered into an image by an individual point in the lens. If that were true then, yes, the point in the subject “covered by” the speck would be blocked by the speck and would be rendered as a speck in the negative.

But, fortunately, camera lenses don't work that way.

The reality is that each individual point of the subject is rendered into an image by the entire lens which focuses that point into a point in the image. So, the speck becomes an infinitesimally small part of each infinitesimally small point in the image and so can't be seen by a human eye.

Flaws in a lens have to be gross to create a perceivable difference in the image. For example, haze in a lens usually covers the entire surface area so it would have a perceivable effect in the image because it would affect the rendering done by every point in the lens.

SoulfulRecover · Jul 15, 2016

thank you all for the information!

unpopular · Jul 15, 2016

thanks @compur I couldn't quite articulate it as well as you had.

@SoulfulRecover there are actually enlarging lenses that exploit this by adding overlapping solid color filters that slide into place to provide color correction. When you turn the knob, each filter fills more of the aperture. Looking through the lens you can see clearly these filters where they gap. However, when focused at a distance they are indistinguishable and appear to be the composite of all the filters.

I actually own one, and I am curious how these filters will affect bokeh. As an enlarging lens it's not an issue, but in macro photography it might have some interesting effects. Unfortunately, the lens is too large to fit onto my bellows without interfering with the rail.

Dave Colangelo · Jul 27, 2016

As has been mentioned the specs will most likely have no impact on the image but like you I would want to clean them out so,

These older style lenses can be opened fairly easily. I would assume those notches are for spanners, however many of these lenses can be opened by hand since they are generally not that tight. If you are afraid of causing damage you can use a lens opening tool like this one. They will grip the lens pretty well and allow you to screw it off. I like to set my aperture wide open and my shutter to bulb (opened) when I do work on these kinds of things. This generally keeps all the blades tucked away in the sides of the lens while you remove the elements, once you have it apart you can release them for cleaning etc.

If I were a betting man I would say those are tiny spots of old oil that has been thrown around by the shutter. I have found Naphtha to be a good cleaner for this kind of stuff as it thins the old oil and drys out fast. If you slower shutter speeds are not working as well the Naphtha may also help that issue when it gets worked into the mechanisms. Any good lens cleaning solutions will be able to clean these up no problem.

You should take special care around any grouped elements as some older grouped elements were held together with balsam cement or other similar things which can react with household cleaners.

Regards
Dave