Grain Focusing - any advice?

[jeroldharter]

I normally print 11x14 or 16x20 and have no problems focusing.

I use a Beseler 45VXL enlarger with the Dichro 45S light source and a Peak grain focuser.

Lately, I have been printing 8x10's from 4x5 TMAX 100 negatives. If I open the lens up to focus, I sear a hole from my retina to the back of my skull. The grain is so fine and the light is so bright that I rarely feel like I nailed the focus. If I stop the lens down a bit to see more comfortably, then the grain seems layered or imprecise and that does not work very well.

What do others do when trying to focus with a bright light source? Just occurred to me that I have an ND filter that will fit over my enlarging lens. does anyone do that?

 

[Claire Senft]

You could dial in a large amount of all three colors for focussing. This will cause neutral density.

 

[bdial]

Stop down for using the focuser. The range of "close to sharp" increases, because you get more depth of field, but "sharp" is still sharp.

 

[David A. Goldfarb]

I stop down a bit for small prints from big negs. If your lens has any focus shift it may be more accurate in any case to focus near the aperture you're using for the exposure.

 

[Doremus Scudder]

Jerold,

Stopping down will increase the depth of focus and make it harder to focus. Yes, sharp is sharp, but it is easier to find "sharp" with a very shallow depth of focus. I would use the ND filter and/or dial in neutral density with your dichro head.

If you are really a "sharpness freak," you might try printing with the ND, or reduced light intensity in order to keep your lens aperture close to optimum (usually 2-3 stops down from wide open). Stopping down a lot for small prints because of the brightness of the light source can introduce diffraction degradation.

Good luck.

Doremus Scudder

 

[ic-racer]

I have experienced this when the focuser lands on a light area of the negative. When I move to a dense portion of the negative then I can focus. My negatives tend to be denser, because I put the image on the straight portion of the cuve, so there is usually a reasonable place to focus. If your negatives are 'thin' with fine grain I can see how it can be challenging. Putting the blue filter on might dim it down and might help.

 

[Nick Zentena]

Don't focus on the grain. With 4x5 I look for lines etc. It's more like focusing a camera then getting the grain right.

 

[Jon Shiu]

Would it work to wear sunglasses?

Jon

 

[Mick Fagan]

I too use TMax 100 in 4x5" and enlarge onto 8x10" paper, I also enlarge onto Ilford Postcard stock, which is a metric sized stock of 150mm wide by 100mm deep or close to 6x4".

I also use a Peak focuser and had exactly the same problem, my course of action was to use the blue filter which came with the Peak focusing unit. Not only does it reduce light by about 2 stops, maybe a bit more, it aids focusing somewhat for me with my enlarger, which is a DeVere 504 with a dichroic head and single 250W globe.

So I think your idea of the ND filter would be quite good. For what it is worth, I also focus on lines or contrast separations between dark and light areas on the negative. At that magnification the grain is just barely focusable, so to speak, with this film.

I had the same problem when enlarging Ektar 25 professional colour negative material a couple of decades ago, unbelievably fine grained film.

Mick.

 

[Claire Senft]

When using a strongly colored filter for aerial image focus, one must be very careful. The properties of human sight are such that the strong blue color is likely to cause other than the best possible focus. I realize that this filters were sold with high quality magnifiers. I also believe that they were included as standard equipment with the sale of Apo El Nikkor enlarging lenses which I believe most people would consider to be a very high quality optic.

APUG member Mr. Patrick Gainer has done research and been published on this matter.

 

[Mick Fagan]

Yes, he had an article in Photo techniques, in January February 1997 which I have, and read when it came out.

I carefully tested my own filter and had others test the same filter equipped peak focuser, using my enlarger.

The enlarger is where I believe most problems come from, that is, most enlargers are not capable of exact fine focusing and locking of the negative stage.

I have a DeVere 504 free standing enlarger, I know what enlarger was used in the published article.

I have used a near identical enlarger as the one used in the testing for that article, I would agree with the results of the published article.

I have also read carefully Ralf Lambrecht and Chris Woodhouse's book, "Way Beyond Monochrome". In their book Ralf and Chris have one chapter called, "Sharpness in the Darkroom". This is an excellent chapter as it contains a multitude of tips, one of the sections in that chapter has a section called, "Accurate Focusing", there is a sub heading about "Focusing with Filtered Light", it is in this section that they make reference to using a blue coloured filter.

Their conclusion is the same as Patrick Gainer, it really doesn't work the best, mainly because a constant exact focus, is hampered by the human eye and it's poor light gathering capability in that part of the spectrum.

Basically I agree with both of them, however, and one does have to have the however. I do believe that there is a difference and various people (four to be exact) using my darkroom and my enlarger, have agreed that there is a difference, it is noticeably better, but it is dependent upon having equipment and lighting capable of harnessing this quite accurate focusing ability.

I have used some pretty interesting enlargers over the years, only a handful of these would be capable of utilising the power of very accurate negative stage movements with repeatable accuracy.

The top end Durst units, which includes most of the 8x10" models, but none of the 4x5 models I have used. All of the vertical tabletop and free standing DeVere 504, 507 and 810 enlargers manufactured in the last 35 odd years that are equipped with the front focusing wheels and locking knobs alongside the vertical column.

These are the only enlargers I have used, that would in my opinion, be capable of using a blue filter over a focusing lens, to obtain finer grain focusing.

Any other enlarger I have used, and certainly most I have seen pictures of, are just not manufactured to the exacting standards of what I call a very precise machine, for that kind of focusing precision.

I have spoken at length with my sister in-law's husband, he is an Opthalmic surgeon in Germany. He tested my filter and the wavelength of light that my blue filter passes, does present some difficulty with the human eye. Interestingly, the wavelength of my filter does correspond to that part of the spectrum the paper is subjected to (generally).

There is an interesting aside to this, which I have since tested in my darkroom, grades of paper contrast. I would humbly suggest that as you deviate from about Grade 3 and get closer to either Grade 1, or Grade 5, the accuracy of the blue filter seems to be ever so slightly off. It is this possibility I am now testing.

This is obviously an interesting subject, with many variables to consider.

Mick.

 

[Claire Senft]

That is really very interesting Mick. Thank you for posting that.

 

[jeroldharter]

Thank you all for the advice.

I dug out the odd sized 55mm Heliopan 8x ND filter that woould fit my Schneider 150 mm Apo-Componon enlarging lens. That worked very well. Also, as someone pointed out, the ND filter let me open up the lens 3 stops to avoid diffraction.

Then I tried to make a 16x20 of the same image. I use a Jobo Colorline 5000 analyzer in the integrated sensitometer mode to zero in on the appropriate exposure when I change enlargement ratios. That works pretty well, although the larger size still requires tweaks. Anyway, at the larger aperture of f5.6-8 that I was using, the image was horribly out of focus due to alignment issues. I unburied the Beseler alignment tool and made some minor tweaks but found no glaring alignment issues. I discovered that the issue is the lensboard for the Schneider lens. It is a big lens and requires a special lensboard (although it will fit on a standard board awkwardly). The special lens board does not have the two screws to lock down the board so it has a slight wobble which accounted for my sharpness problems. I swapped out the lens for a Rodagon 150 mm that I obtained "for free" as part of an Ebay indulgence and screwed down the standard lens board. I had never used or tested the Rodagon lens before. It is much smaller than the Schneider but my alignment issues were solved and the quality of the print was excellent with this lens.

I think I will continue to use the Rodagon for this project until I have time to re-mount the Schneider and compare the two side to side for a large print. I also have a Nikkor 135 mm that I might include in the test.

I know everyone talks about alignment being so important so I am careful about it. This is the first time I have had a problem but having seen the results I think alignment is perhaps the most important variable for getting sharp enlargements. I am not sure that I could discern any issues with diffraction though, so for this round of chaos at least, I think that alignment is a much more important issue than diffraction.

 

[phfitz]

Jerold,

glad you fixed it, the only other option I can think of is a "Magnasight", a image focuser not grain focuser. Very handy that most people can wear their glasses and still use it also.

 

[nworth]

In ancient times (when I was in school), I learned to us a green filter when looking at the grain of metal samples through the microscope. It took a lot of getting used to, but eventually I realized it helped. Something like that may apply here as well. For enlarging, I actually avoid my grain focusing tool. I never could get used to it. Instead, I use an ordinary magnifying focus tool. My favorite is the MagnaSight, but I have an old Durst model as well. Once I learned to look really hard, I discovered that I could see and focus on the grain with these, even doing an 8X10 from 120. Incidentally, I'm nearsighted, and age has taken its tool on accommodation, but if I take off my glasses it works fine.

 

[fschifano]

Stopping down a lot for small prints because of the brightness of the light source can introduce diffraction degradation.

Theoretically, that can be true. In practice, not so much. The enlargement factor is small and any degradation of the image will likewise be too small to notice unless you start examining the print with a magnifier.

 

[Claire Senft]

If one is using a smaller aperture with say a 4x5 inch print vs 16x20 from a given film format, the 4x5 print may have the larger effective aperture.

 

[dancqu]

Stopping down will increase the depth of focus ...

Just as with a camera depth of field does increase as the
lens is stopped down.

I focus using strong reading glasses, both eyes open and
the lens wide open. I fine tune the image until it is as
sharp as can be then stop down. I know the image
will be sharper yet for having stopped down. Dan

 

[jeroldharter]

I ordered some screw in B&W ND filters to fit my enlarging lens from Calumet. That definitely helps and solves the problem. Also, when I go from 8x10 up to 11x14 or 16 x20 I can adjust the ND amount and maintain about the same standard exposure times which I like.

 

[ic-racer]

I know everyone talks about alignment being so important .

I have been there. Nothing like high magnification enlargements to bring out any weaknesses in the system.

 

[gainer]

I have experienced this when the focuser lands on a light area of the negative. When I move to a dense portion of the negative then I can focus. My negatives tend to be denser, because I put the image on the straight portion of the cuve, so there is usually a reasonable place to focus. If your negatives are 'thin' with fine grain I can see how it can be challenging. Putting the blue filter on might dim it down and might help.

Do not use a colored filter except perhaps green. The human eye is not achromatic. There is a focus shift that increases the scatter of the focussing error and tends to bias it as well. White or green is best. It probably evolved that way through eons of hunting and living in forests. If you can find the Photo Techniques article "Haards of the Grain Focuser" you will see experimental proof. I seem to recall it was reprinted in www.unblinkingeye.com.

 

[Curt]

I didn't find it at the unblinkingeye, maybe it's elsewhere?

 

[Martin Aislabie]

Jerold, I too have a similar problem but tackled it slightly differently

I added equal amounts of C/M/Y from my colour head to act a neutral density filter.

I am still focusing under white light but without the searing intensity

Martin

 

[gainer]

It may still be in the archives of Photo Techniques which you can search on the net. Basically, what I showed is a focus shift with color of light of roughly 10 mm in one direction for blue and the other direction for red light, as well as increased scatter on either side of green. If you want to try green with dichroic filtering, mix cyan and yellow. Focus a well defined line, such as a hair stretched across the negative carrier, with white light, with the head about where it would be for an 8x10. Mark the location of the enlarger head on the column. Now switch to red, which you can get by mixing yellow and magenta. Do not use the focusing knob to refocus, but change the column height if necessary to restore focus on the hair. Mark the new location. Now switch to blue light by combining blue and cyan. Refocus, again using the column adjuster. You should see differences between the positions of best focus. To show the pictorial difference, make a print of the ame negative from each of the focus positions. These are the experiments I did, repeated a number of times so I could calculate the mean and standard deviation of error at different colors.

No modern lens of good quality will show the degree of color shift with color that the human eye does. This is not new knowledge. The usual dictum to focus with the color of light where the paper is most sensitive, thaereby compensating for focus shift of the lens, is not good for modern lenses, nor for VC papers.

 

[ic-racer]

If there is a focus shift of the projected image with different colored light then the enlarger lens has chromatic aberration.

When using a grain focuser with an arial image, if the reticle is in focus on the retina then chromatic aberration of the human eye will be compensated.