Grain Focusing - discrepancies

[Mr Bill]

[from post #39] The filtration issue - blue filter, yellow filter - doesn't quite make sense to me. Here's the thing: when I focus with my eyes, it's very sharp on the easel. When I focus with the grain focuser, it's sharp but not *very* sharp on the easel. The prints I made on RC paper confirmed that to me. At the moment, this is all I'm worried about.

Marco, in the following post (#40), "Michael R 1974" explains things.

Let me try to be a bit more blunt. It is possible that your paper can be exposed by UV light, which you cannot see. The (invisible) UV image is probably out-of-focus. I suggest exposing through a UV filter, which will block the UV light, eliminating this possibility. This simple (if you own a UV filter) test can eliminate any need to hypothesize about whether or not UV light might be causing a fuzzy image.

I mention this possibility because the photographer/printer/writer Ctein reports that it has happened to him, and I do not take Ctein lightly. I don't have evidence that it IS your problem, only that it is a possibility that can be easily tested.

 

[DREW WILEY]

Bill - I don't guess at anything. I do tests and tests upon tests - but normally only on problems which affect me personally. I'm not interested in argument for argument's sake. Having done many
years of large format printing onto high-resolution materials like Cibachrome I have had the opportunity to isolate and fine-tune a lot of variables, and am simply making this info avail to others
from time to time, to save them similar heaches. When I speak of using a loupe, it's not just for the
groundglass or film. I want you to be able to walk up to a 30x40 print, spot a water drop a mm wide
on the actual print, and take a loupe to that!! Of course, not every original chrome or neg will be
that sharp to begin with, but sometimes they are, at least in key areas.

 

[AgX]

Now I use only the best one and hope that my progressively arthritic fingers
don't drop it like the cheaper ones! (Knowing it was expensive does make me a lot more careful!!)

Fix a line to it, with the other end fixed to the peak of the enlarger collumn and add some line enough to have it move around freely on the baseboard. Thus it cannot fall deep, if at all, if it is by accident wiped off the baseboard. Fix a box near the collumn as a savehaven for it.

 

[DREW WILEY]

Thanks. That's exactly what I do with the groundglass back to my view camera - a bit of lightwt
shock cord. But usually I don't lift expensive glass things in the lab very far off a surface. And once
I get away from computers awhile my fingers seem to get much better (get to retire from these
damn torture keyboards in a couple of years - but for now, got to use it all day!)

 

[sbattert]

These may be stupid questions, but what the hell:
Is it possible to callibrate the mirror on a grain scope? Or, perhaps can the enlarger be calibrated to the grain scope?

 

[ic-racer]

These may be stupid questions, but what the hell:
Is it possible to callibrate the mirror on a grain scope? Or, perhaps can the enlarger be calibrated to the grain scope?

The only adjustment on the Peak 1 is the viewfinder diopter adjustment. If it is not set correctly and you have presbyopia (inability to alter the focus of your eye), then your prints will be blurry.

The optical components are easy to disassemble and there is always the possibility that someone took it apart and buggered it up by not putting the focusing reticle in the correct location.

 

[Bill Burk]

The only adjustment on the Peak 1 is the viewfinder diopter adjustment. If it is not set correctly and you have presbyopia (inability to alter the focus of your eye), then your prints will be blurry.

The optical components are easy to disassemble and there is always the possibility that someone took it apart and buggered it up by not putting the focusing reticle in the correct location.

Oh! maybe they put the reticle in UPSIDE DOWN after cleaning! Thus making the focus off by the thickness of that piece of glass.

I just looked at my Micromega under a microscope. The reticle is on the outside surface of the lens. (You could put a fingerprint on the silver painted double rectangle if you touched it).

Also, by design I believe the visual projection of the reflection of the reticle should appear to be at the same plane as the paper surface, if you look down at the mirror with both eyes, so your left eye sees the reticle and the right eye sees the baseboard... I drew a rectangle on paper same size and placed it underneath so my eyes believed they were seeing one rectangle. The visual appearance was as if they are on the same plane. Parallax would show if they are out of place. Moving my head, the rectangles seem to stay visually in place. I suspect if the reticle was upside down (inside out), you might visually notice they are not in the same plane, and parallax would make the images move relative to each other when you move your head.

 

[pentaxuser]

The thing is Bill It seems as if all 4 of the OP's focusers are off compared to each other and his eye. It is very strange and I wonder as you will see from my previous post what were the circumstances of the OP's discovery of these faults.

pentaxuser

 

[DREW WILEY]

Of course there are ways to precisely calibrate such things, but is it worth it to set up instruments far more expensive than the only you're trying to fix? Been there, done that. I'm nitpicky, but at a
certain point, things can become overkill. Some of these magnifiers had paper shims in the base as
well as under the mirror. All it takes is a little bit of sloppiness in either and you've got an issue.
In most cases the casting aren't precise enough to dispense with the need of some manual adjustment during final assembly. And I never ever assume that a piece of equipment is precise without first checking it - well, maybe a machinist's quality instrument from Starret or Mitutoya
accompanied by a regiesterd certificate of accuracy - and I they'd have made on of these devices
it would have cost a lot more than what you paid for Peak. In fact they make instrumentation which
will read that front surface mirror and make a countour map of it several feet wide in millionth's of
an inch, just in case you need to see how flat it really is!

 

[ic-racer]

I'd put my Peak 1 focusers up against a Mitutoya any day. I'm surprised to hear so many people having trouble with them. I'll take any that are not wanted.

 

[scheimfluger_77]

Have a look at page 76 here:

http://ctein.com/PostExposure2ndIllustrated.pdf​

What? This book is available in PDF? Darn and I purchased a used one on Amazon.
Steve

 

[michaelbsc]

What? This book is available in PDF? Darn and I purchased a used one on Amazon.
Steve

Thinking out loud, I started building a collection of PDF and Kindle texts, but it's not the same without margin notes.

I know the electronic dodads let you "make notes" for a file. But it just isn't satisfactory in the end. At least not to me.

Luddite I guess.

 

[DREW WILEY]

What th' .... Ice Racer? Mitutoyo makes the instruments that measure the dies and machinery that
make things like Peak in the first place. They're a precision instrument and optics mfg - and obviously
have to been of a far higher quality control standard than the thing itself being made. I don't know what you're thinking of. You can buy something as simple as a digital caliper from them (and they
make some of the very best) or some advanced instumentation that will measure in angstroms!

 

[Steve Smith]

What th' .... Ice Racer? Mitutoyo makes the instruments that measure the dies and machinery that
make things like Peak in the first place.

Indeed. The manufacturer of the Peak focuser (do they make it themselves?) probably has some Mitutoyo equipment!


Steve.

 

[Nicholas Lindan]

My experience parallel's Marco's: I can focus more accurately [and far more quickly] without a grain focuser. It helps that I am terminally myopic. If you are far sighted I am sure a focuser is a great help.

The magnifiers' adjustment isn't for calibration but for adjusting to your eyesight so as to bring the reticle into focus. But you aren't making a print of the reticle. The proper calibration is to either move the reticle or to shim the focuser.

The Ctein article on focusing was discredited long ago.

 

[Steve Smith]

It helps that I am terminally myopic.

Yes/ Being short sighted has its advantages. Take off your glasses for good close up vision. Particularly good for ground glass focussing.


Steve.

 

[Sal Santamaura]

...The Ctein article on focusing was discredited long ago.

Where and by whom?

 

[RalphLambrecht]

The Ctein article on focusing was discredited long ago.

as far as i can tell, he was spot on. paper shims under he grain focuser are nonsense. the do f is huge! and covers many focusing issues, including wavy paper.

 

[Mark Crabtree]

And Ctein's method of determining the actual focus relative to the paper position is simple and reliable. To me, the main question here is "are the grain focusers giving accurate focus on the paper?"; and this can be clearly answered with a few sheets of paper using his method. Then if things are off, at least you have some solid footing to work from in figuring out the problem.

 

[Nicholas Lindan]

The Ctein article on focusing was discredited long ago.

I should qualify this: Ctein published an article in the early 90's advocating focusing through a blue filter, and claimed that not using a blue filter resulted in a 1/2" to 1" error in focus wrt the paper position. The claim was rebutted in letters to the editor and a subsequent article. I see Ctein no longer makes his original claim.

 

[Bill Burk]

I should qualify this: Ctein published an article in the early 90's advocating focusing through a blue filter, and claimed that not using a blue filter resulted in a 1/2" to 1" error in focus wrt the paper position. The claim was rebutted in letters to the editor and a subsequent article. I see Ctein no longer makes his original claim.

That limited refutation seems reasonable, of otherwise pretty decent information.

I don't want to open a can of worms but I believe there could be an error of focus with respect to ultraviolet vs visible in my system... which is quite different than the norm (though not an unreasonable system). I use graded paper and an Aristo grid bulb through a Xenar lens... I may have a system that is more susceptible to focus errors due to ultraviolet exposure than the more common tungsten sources used with multigrade paper through an APO lens.

Our Original Poster here, though, seems to have something very unusual going on, a gross error that really sounds like tampering, dropping, or possibly a bowed piece of paper.

 

[ic-racer]

What th' .... Ice Racer? Mitutoyo makes the instruments that measure the dies and machinery that
make things like Peak in the first place. They're a precision instrument and optics mfg - and obviously
have to been of a far higher quality control standard than the thing itself being made. I don't know what you're thinking of. You can buy something as simple as a digital caliper from them (and they
make some of the very best) or some advanced instumentation that will measure in angstroms!

They don't make a grain focuser. Peak 1 is the best out there. How would you improve it?

 

[ic-racer]

What th' .... Ice Racer? Mitutoyo makes the instruments that measure the dies and machinery that
make things like Peak in the first place. They're a precision instrument and optics mfg - and obviously
have to been of a far higher quality control standard than the thing itself being made. I don't know what you're thinking of. You can buy something as simple as a digital caliper from them (and they
make some of the very best) or some advanced instumentation that will measure in angstroms!

Peak 1 in conjunction with an enlarger will measure smaller distances than a consumer grade caliper.

In terms of focusing on the paper or the baseboard, I don't have an opinion on the matter, just the optical formula that predicts about a 2mm focus spread at f2.8 at 9x enlargement. This easily encompasses any photographic paper or film of which I am aware.

Modular transfer function focusing equation (equation #38 in Dead Link Removed) :
N_max ~ 20 / (1 + m) sqrt(dv)

N-max = F number
m = magnification
dv = focusing leeway on the baseboard
20 = constant for circle of confusion about 0.15mm on the print

 

[Steve Smith]

I think our enlargers are built the wrong way round!

They should have the light source, negative and lens at the bottom, projecting upwards onto a piece of ground glass for focussing which is then replaced by a paper holder for exposing in the same way as the ground glass and film in an LF camera.

Then we could check the focus with a loupe or even just our eyes without casting a shadow.


Steve.

 

[AgX]

Steve, on a large table/baseboard that means bending over the groundglass, maybe leaning even on it...
I'm the killjoy again.. But actually I like that idea!