I want to expose film in a way to best reveal the underlying grain. I don't mean develop poorly to make big grain. I just what kind of technique to shoot, type of background or zone to be exposed in.
reveal grain
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OP
OP
Film size is not an option. I'm trying to trace down possible lens distortion issues for my Nikons. I need to verify I have good focus on the film surface to validate where my lens issues are.
Pushing could work....It's been a while. I think I still have some diafine hanging around....
Pushing could work....It's been a while. I think I still have some diafine hanging around....
What's wrong with Rodinal at 1+25? Maybe with HP5+?
OP
OP
My goal is also to use what I have. Although using a different developer than I normally use (pyro), I was looking for some optical tips to reveal the grain.
OP
OP
Looks like a middle grey card with something on it to focus the camera does the trick.
Grain is most obvious in areas with little detail like skies.
OP
OP
Thanks Gerry. I'll have to give that a whirl in the morning.
Printing with a condenser enlarging system helps to reveal the grain. Also develop using a non solvent developer and print on a harder grade of paper.
Examine your test negatives under a microscope or with a good enlarging grain magnifier. That should get you a good view of the grain.
I don't see how examining grain will show lens distortion. A negative will always have grain regardless of sharpness or focus and grain is so small that you would never see distortion in it. And grain orientation and shape is unknown so you couldn't see distortion by inspecting grain anyway. And you would never see focus in it unless you were testing enlarger focus which isn't what you asked.
To see distortion I would create on your pc and print out a square grid of fine lines. Then photograph it from fairly close up taking five images with the grid in each of corners of frame and in center of frame, preferably without moving camera and don't change any settings. It would be better to use 5 grid prints so that you only need to make one photo of them.
Then also make same photo at a distance of at least 10 times focal length.
Then develop to a higher contrast than normal or better still would be have a lot of light on grids so that they are high contrast to start with and develop normally which would be a better representation of real world practice.
Inspecting shape of grid will show distortion in corners of image if there is any. A normal neg loupe should show this.
If wet printing use normal or soft contrast which will NOT remove edge detail of grain (printing high contrast will remove grain edge detail and create false impression of grain sharpness and emphasize grain but not actual neg grain. Finely spread grain such as in shadows will be lost if printing high contrast which is opposite of what happens if developing to higher contrast).
If you are testing zoom lenses then you should repeat photographs of grids at different zoom lengths to find where distortion is pronounced or not so one image at minimum zoom, one at middle zoom and one at full zoom. And do both fairly near, say 2 meters and then again at least 10X focal length distance.
If you are scanning neg to check it, then scanner pretty much destroys film grain (depending on scanner) and creates its own so grain in scans is a product of scanner and not directly film so you can't really tell anything from scan grain.
You would see the grid distortion though.
If its also focus you are testing then see http://www.normankoren.com/Tutorials/MTF5.html
And perceived sharpness is also a function of edge contrast and not just lens focus. Increasing print contrast increases perceived sharpness and so does increasing neg development but that something different than increasing graininess of print.
And finally, most taking lenses are not designed to be flat field in the subject so the focus plane is not a real plane at all. I mention this because lens tests showing focus/sharpness/resolution falloff towards coners invariably don't mention this and don't specify whether they are testing flat field focus plane or not. With extensive testing you could determine the shape(approx ellipse) of fine focus but it would be a real pain to do it and is probably not necessary in 99.999999% of cases unless you are doing some very serious scientific measuring work.
MTF datasheets for lenses (if you can lay your hands on them) should show the distortion at different zoom lengths which is usually the case with zoom lenses.
Could you explain exactly why you suspect distortion in your lenses which would aid in suggesting best approach of how to proceed.
To see distortion I would create on your pc and print out a square grid of fine lines. Then photograph it from fairly close up taking five images with the grid in each of corners of frame and in center of frame, preferably without moving camera and don't change any settings. It would be better to use 5 grid prints so that you only need to make one photo of them.
Then also make same photo at a distance of at least 10 times focal length.
Then develop to a higher contrast than normal or better still would be have a lot of light on grids so that they are high contrast to start with and develop normally which would be a better representation of real world practice.
Inspecting shape of grid will show distortion in corners of image if there is any. A normal neg loupe should show this.
If wet printing use normal or soft contrast which will NOT remove edge detail of grain (printing high contrast will remove grain edge detail and create false impression of grain sharpness and emphasize grain but not actual neg grain. Finely spread grain such as in shadows will be lost if printing high contrast which is opposite of what happens if developing to higher contrast).
If you are testing zoom lenses then you should repeat photographs of grids at different zoom lengths to find where distortion is pronounced or not so one image at minimum zoom, one at middle zoom and one at full zoom. And do both fairly near, say 2 meters and then again at least 10X focal length distance.
If you are scanning neg to check it, then scanner pretty much destroys film grain (depending on scanner) and creates its own so grain in scans is a product of scanner and not directly film so you can't really tell anything from scan grain.
You would see the grid distortion though.
If its also focus you are testing then see http://www.normankoren.com/Tutorials/MTF5.html
And perceived sharpness is also a function of edge contrast and not just lens focus. Increasing print contrast increases perceived sharpness and so does increasing neg development but that something different than increasing graininess of print.
And finally, most taking lenses are not designed to be flat field in the subject so the focus plane is not a real plane at all. I mention this because lens tests showing focus/sharpness/resolution falloff towards coners invariably don't mention this and don't specify whether they are testing flat field focus plane or not. With extensive testing you could determine the shape(approx ellipse) of fine focus but it would be a real pain to do it and is probably not necessary in 99.999999% of cases unless you are doing some very serious scientific measuring work.
MTF datasheets for lenses (if you can lay your hands on them) should show the distortion at different zoom lengths which is usually the case with zoom lenses.
Could you explain exactly why you suspect distortion in your lenses which would aid in suggesting best approach of how to proceed.
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OP
OP
Simply put, by focusing on the grain verifies whether the image through the lens is in focus or not. The grain will always be there to focus on. I am not interested on "stock" data as I am trying to verify if some of my lenses need some "tuning" and needs to be cla'd.
Grain in negative is neither sharp nor soft (except solvent developers may smooth grain clump shape which some people call soft). It is a solid (for B&W film) embeded in the emulsion. What is sharp or soft is the percieved contrast over edges of differing densities of grain, which in the case of a ruler are the ruler markings edges. The concept of sharp grain should be reserved for prints only and relates solely to enlarger lens focus which is not what you're after by the sound of it. And enlarger lens depth of focus is quite large so wouldn't be suitable for testing taking lens focus plane anyway.
To test if lens is focussed on what you are pointing it at you take a ruler and put it on a table with nearest end touching table and far end raised at angle of approx 30deg up from table. You then photograph it from touching table end focussing on middle point of ruler with camera lens at same height as middle point of ruler using widest aperture (shortest depth of field) and see if your focus point is actually the best defined sharpness.
You should put ruler at decent distance from camera because close up you get much longer depth of focus (not field) so its harder to tell where the sharpest focus point is.
However, putting it too far from camera will increase depth of field so a happy medium would be maybe 6 to 10 feet but depends on focal length of lens.
Finding focus over the whole neg area is tricky since you don't know the surface profile of the in focus area which won't be a true plane. However, rotating the camera left and right and up and down without moving tripod position to get ruler at left, right, top and bottom in image without refocussing should tell you if sharpest point on ruler is same at left and right and top and bottom which if they are then lenses are in correct alignment although the level of accuracy you'll achieve is debatable.
Then you can repeat everything at different apertures to see if you have focus shift with aperture change.
To test if lens is focussed on what you are pointing it at you take a ruler and put it on a table with nearest end touching table and far end raised at angle of approx 30deg up from table. You then photograph it from touching table end focussing on middle point of ruler with camera lens at same height as middle point of ruler using widest aperture (shortest depth of field) and see if your focus point is actually the best defined sharpness.
You should put ruler at decent distance from camera because close up you get much longer depth of focus (not field) so its harder to tell where the sharpest focus point is.
However, putting it too far from camera will increase depth of field so a happy medium would be maybe 6 to 10 feet but depends on focal length of lens.
Finding focus over the whole neg area is tricky since you don't know the surface profile of the in focus area which won't be a true plane. However, rotating the camera left and right and up and down without moving tripod position to get ruler at left, right, top and bottom in image without refocussing should tell you if sharpest point on ruler is same at left and right and top and bottom which if they are then lenses are in correct alignment although the level of accuracy you'll achieve is debatable.
Then you can repeat everything at different apertures to see if you have focus shift with aperture change.
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Grain is always on the negative. More, less, focus, no focus. The grain is emulsion crystals, isn't it?
If you post process scan you could get grain revealed. If you print, using RC and deep contrast filter will bring the grain from the negative. I've just seen it earlier this week by printing same negative with #3,4 and 5 filters.
If you post process scan you could get grain revealed. If you print, using RC and deep contrast filter will bring the grain from the negative. I've just seen it earlier this week by printing same negative with #3,4 and 5 filters.
Peter, am I right with my interpretation, that those "possible lens distortion issues for my Nikons" concern your enlarger, or maybe scanner, and not so much your camera? What you look for appears to be some uniformly grainy patch of film, presumably 135 format, which you try to use as some sort of resolution target for evaluating sharpness of the whole frame at once, yes?
I my above assumptions are correct, here is what you should look for:
I my above assumptions are correct, here is what you should look for:
- most grain measurements in published literature focus on RMS granularity by itself. What you see as grain in your image, though, is RMS granularity divided by average density. While denser negs will generally have higher RMS granularity, they will not necessarily show up as more grainy in your enlargements/scans.
- The combination of weak exposure with strong development will likely exhibit stronger visible grain, since fewer latent image centers contribute to the developed image.
- vignetting of your camera lens can lead to non-uniform test negs: there is some vignetting due to imperfection of lens design, which is greatly reduced by stopping down your lens. However, there is also natural vignetting which is independent of aperture but dependent on distance between rearmost lens element to film plane (not necessarily focal length! ).
- A developer which depends on exhaustion phenomena will be more prone to non-uniform development, I'd recommend you use the most concentrated developer you can find for this test, and that you agitate a lot.
let me understand... you want to verify if your viewfinder agrees with the film plane?
put a ground glass on the film plane, the rails the film rides on. then with the camera on a tripod aimed at a well lit target, a news paper taped to a wall. focus the camera as critically as you can, even use a loupe in the view finder for the sharpest image. now check the film plane ground glass with the loupe to see if it as sharp as your view finder.
if it doesnt agree then you need an adjustment.
if you find certain lenses dont agree, they need service to be collimated. <sp>
i found an article for a diy test.
http://elekm.net/zeiss-ikon/repair/collimate/
and some interesting reading
http://www.garyseronik.com/?q=node/165
http://www.canonrumors.com/tech-articles/how-to-test-a-lens/
.
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