Using grains focuser with or without paper on the easel

[faberryman]

Thank you for the time and effort you put into this experiment.

Any chance the grain goes from blurry to sharp to blurry, or was that what you were looking at with the 30x microscope that was not satisfyingly sharp?

 

[Bill Burk]

Thank you for the time and effort you put into this experiment.

Any chance the grain goes from blurry to sharp to blurry, or was that what you were looking at with the 30x microscope that was not satisfyingly sharp?

Blurry to less blurry to blurry.
Here are three examples. The best is from the real 11x14 glossy. The blurry is #1054 and the not as blurry #1026. There’s about 50 prints in the stack on Matt paper #999 to #1054. I believe lesser sharpness is a normal attribute of Matt paper surface, but it’s the paper I had enough to spare for the test.

 

[Pieter12]

(even the best print is a little degraded from what you can see in the grain focuser

Could that be from UV light as discussed earlier in this thread?

 

[Bill Burk]

Could that be from UV light as discussed earlier in this thread?

It may be the surprise once we look at them all together. The point of best focus might be sheet #1015. It “seems” to me the sharpness is skewed higher up the stack than I expected, but that’s too soon to tell. At some distances they all look the same.

 

[faberryman]

Blurry to less blurry to blurry.
Here are three examples. The best is from the real 11x14 glossy. The blurry is #1054 and the not as blurry #1026. There’s about 50 prints in the stack on Matt paper #999 to #1054. I believe lesser sharpness is a normal attribute of Matt paper surface, but it’s the paper I had enough to spare for the test.

The blurry to less blurry to blurry is the sequence we were looking for even if none are actually sharp.

 

[Bill Burk]

The blurry to less blurry to blurry is the sequence we were looking for even if none are actually sharp.

Ok I will get closer for the series

 

[faberryman]

Ok I will get closer for the series

No need. It appears from you description you have proven the point.

 

[wiltw]

Got the copy stand out and ready to make the presentation.
Stack is 3/4 inch with focus at 3/8 inch. From a normal viewing distance they all look sharp. From a fairly close examination the slight out of focus towards sharp and back can be seen but only the extremes seem unsharp. Under 30x microscope they all look unsharp so you see revealed detail and obscured detail but never satisfyingly sharp (even the best print is a little degraded from what you can see in the grain focuser).

Wow, thx for the time and not-insignificant expense of that stack of enlargements! My takeaway, (paraphrasing to make sure of no misinterpretation)...

• The entire stack appeared 'sharp' to the naked eye, but at close examination you could tell the difference near the extremes of the distance range
• Under magnification, even the 'ideal height' print wasn't perfect but it was better than the others

Q: So if focus shift makes 'farther from plane of focus' to be closer to 'correct focus'( correcting for Ctein observed 2-12mm of error, what (if anything) might be your observation relative to that focus shift error phenomenon? (I realize that A) you could be using paper less prone to shift, B) be using Grade less susceptible to shift, and C) your enlarger might not be so prone to focus shift!)

 

[Bill Burk]

Video of the stack of prints.

 

[Bill Burk]

Q: So if focus shift makes 'farther from plane of focus' to be closer to 'correct focus'( correcting for Ctein observed 2-12mm of error, what (if anything) might be your observation relative to that focus shift error phenomenon? (I realize that A) you could be using paper less prone to shift, B) be using Grade less susceptible to shift, and C) your enlarger might not be so prone to focus shift!)

Farther from plane of focus, sharpness falls away as expected. Above the plane of focus is unexpectedly sharp for quite a few prints.

 

[Bill Burk]

I calipered the stack and estimate that the 32nd frame is the focused point.

In the video that appears to me as nearly the last frame of the region of best sharpness.

So it feels to me there is a skew in good results, favoring a point above where I focused.

It can’t be skewed up due to blue/uv shift. That would be farther. For example using a Pentax to focus on anything and throwing focus opposite the direction of the IR red mark… moves the focus to a longer distance.

I don’t have an explanation why the range of sharpness seems to be centered above where I focused.

Maybe it’s because after focusing… I did not move the enlarger up and down to determine the center. Maybe I left it at an edge of sharpness. That’s a good “Occam’s Razor” explanation.

 

[Bill Burk]

If it is wavelength-related/LCA, blue/violet focal plane would tend to closer to the lens than the average “visual” focal plane. Red would be further than visual.

Why does my Pentax test tell me the opposite?

 

[Bill Burk]

It’s possible your grain focuser isn’t correct. We are working under the assumption that the mirror to eyepiece distance is the same as the mirror to easel distance, but maybe it isn’t.

You could try setting the focus to the sharpest height according to the prints, then move the focuser to the easel plane (or easel plus one sheet if you prefer) then focusing the eyepiece until it’s sharp.

Anyone have a Peak- type grain focuser? Can you tell me whether the reticle is supposed to be silver out or silver in? It’s possible to disassemble to clean and reassemble wrong. The silver is out on mine now, and I have at some point disassembled it and cleaned it.

 

[Pieter12]

I bought my Peak used, so it is possible a previous owner may have disassembled it. Having said that, it looks like the silver is in (not facing the mirror).

 

[Bill Burk]

I don’t understand what you mean in the Pentax test. When you focus a film camera visually on a target plane, assuming no correction for longitudinal chromatic aberration, longer wavelengths will have focal planes behind the film (and shorter wavelengths will have focal planes in front of the film). With an infrared focusing index, you approximate a correction for this by slightly increasing lens extension.

And conversely you correct for UV by decreasing lens extension, right?

 

[Bill Burk]

I bought my Peak used, so it is possible a previous owner may have disassembled it. Having said that, it looks like the silver is in (not facing the mirror).

Oooh interesting. It’s only a small amount but it’s the direction I see a shift…

 

[Bill Burk]

What model lens are you using?

I have one and will check the mirror when I get home

It’s the Omega branded “peak”

 

[Bill Burk]

Yes. Basically, you approximate corrections for dispersion by “pretending” the subject is closer to the camera than visually apparent (in the case of long wavelengths) and vice versa for short wavelengths.

Don’t get me wrong - I’m not saying blue/violet LCA is necessarily responsible for your observations. It could easily be other things like error/imprecision in the grain magnifier, focus shift when stopping the lens down. Who knows.

No worries I am just trying to figure out the direction…

 

[Bill Burk]

Both my Micro Sight III (25x) and Peak Model 1 (10x) have a front surface mirror with the slivering closest to the eyepiece.

The main mirror yes is surface up. But the surface of the reticle, as I have it now, faces the surface of the mirror. In other words, there is no glass between the two points.

The lens is a 50mm APO-Rodagon f/2.8 but not N

 

[Bill Burk]

I saw this on a good ad for one, so that makes it seem correct silver facing silver for the reticle and mirror.

I have the blue filter that comes with it. I could try.

But my best guess for the skew is that I snap to focus in one direction or the other, and either way I probably skew to the edge of the direction I am coming from. This could be verified by a few experiments without printing.

For the print series itself, we can say it covers the entire range of sharpness, so I am happy how that came out

 

[Sirius Glass]

In the end the question was whether a single piece of paper makes a difference and think we can safely say “no”.

But I will still use it because additionally it lets my see how the negative is positioned on the paper. Please feel free to do all the testing you want, it will help keep you off the streets.

 

[Pieter12]

I saw this on a good ad for one, so that makes it seem correct silver facing silver for the reticle and mirror.

I'm not sure you can tell which side of the glass has the reticule from a single photo. Depending on how I angle the lens, it can look like it is on either side because it is silvered.

 

[Sirius Glass]

I'm not sure you can tell which side of the glass has the reticule from a single photo. Depending on how I angle the lens, it can look like it is on either side because it is silvered.
View attachment 280055

An easy way to find our if you have a first surface mirror: Get your finger dirty will grease, put a finger print on the mirror, scrub the mirror hard with cleanser and steel wool. If the mirror then does not reflect as well, you have a first surface mirror.

 

[Pieter12]

An easy way to find our if you have a first surface mirror: Get your finger dirty will grease, put a finger print on the mirror, scrub the mirror hard with cleanser and steel wool. If the mirror then does not reflect as well, you have a first surface mirror.

Not about the mirror, but the reticule used to focus on the mirror. But go ahead and test all your mirrors--we're looking forward to the results.

 

[Bill Burk]

@Pieter12 The left hand one casts a shadow… it’s surface slivering.

Meanwhile all my tests prove that I skew to the edge of the tolerance when I focus my lens. So although the tolerance is nearly 3/8 inch, my act of focusing does not place the focus in the best place. After lens focusing I should easel focus up to edge, down to edge and then settle to the center between the edges.