Question about focusing

Mats_A

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When using a focusing aid on the easel should you (in theory) place a paper under the equipment you are using? If you focus on the easel you will be off-focus when you place the paper. Since it is slightly higher.

Or am I overanalysing this?

r
 

Anscojohn

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shimoda said:
When using a focusing aid on the easel should you (in theory) place a paper under the equipment you are using? If you focus on the easel you will be off-focus when you place the paper. Since it is slightly higher.

Or am I overanalysing this?

r
Click to expand...

***********
No
 

tkamiya

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I actually experimented with this quite a bit.

I used MagnaSight and MicroSight for this test. MagnaSight is an image focuser with X8 magnification and MicroSight is an grain focuser with X25 magnification. I was using f/5.6 which is wider than my usual f/8 or f/11. I can bring the image to sharp focus, then lower or raise the focuser about 1/4" without seeing any difference. This test was done using both 35mm and 645 negatives projected to 8x10 equivalent size.

Go ahead and try it.... use a notebook or something and white sheet. Focus, then remove the notebook. Focus then add another notebook. See if there are any difference. I couldn't see any.
 

JBrunner

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I always do it. I have samples of the papers I use labeled and in a box by the enlargers. I think a focusing error on my part is more likely to intrude than the paper thickness, so it just gives me that much more margin, and I like that.
 

RalphLambrecht

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shimoda said:
When using a focusing aid on the easel should you (in theory) place a paper under the equipment you are using? If you focus on the easel you will be off-focus when you place the paper. Since it is slightly higher.

Or am I overanalysing this?

r
Click to expand...

Theoretically yes, practically no need. The depth-of-field around the paper plane is enormous compared to the paper thickness (at least 10 mm even at modest enlargements and apertures). So, there really is no need for the paper whatsoever.

Nevertheless, I use a piece of paper for different reasons. My easels are all painted flat black to avoid light bouncing back from the easel surface into the emulsion during exposures (this is an issue with white easels). Unfortunately, the black surface makes it impossible to compose or focus on. Consequently, I use a white piece of paper to compose, which I leave there until focusing is done. Two birds with one stone!
 

RalphLambrecht

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JBrunner said:
I always do it. I have samples of the papers I use labeled and in a box by the enlargers. I think a focusing error on my part is more likely to intrude than the paper thickness, so it just gives me that much more margin, and I like that.
Click to expand...

You are kidding yourself. An 0.1mm margin inside a 10mm tolerance band?
 

Arvee

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If my feeble memory serves, I believe Ctein also supports what Ralph has stated here.
 

JBrunner

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John Wiegerink

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Many years ago our class instructor contact cemented a piece of printing paper to the bottom of all of our grain focuser's and trimmed the excess paper off. I guess he did that so we wouldn't forget to do as he told us. Of course we all used the same paper in class and never changed. If you stuck to one paper you'd be fine with that method, but who sticks to one paper. JohnW
 

Steve Smith

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But what if the manufacturers of the grain focusers have already accounted for the paper thickness and built this into the base?

Does anyone have any manufacturer's instructions which state if paper should be used or not?


Steve.
 

richard ide

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Steve,
Then how would you account for different thicknesses of paper?
 

Steve Smith

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richard ide said:
Steve,
Then how would you account for different thicknesses of paper?
Click to expand...

Average out the range available. It can't be much more than a 0.15mm difference.

The reason I ask this when the subject is raised is because in his book 'Darkroom Printing' Gene Nocon suggests not using paper as it is not needed. He states that using the blue viewing filter is the most important thing with these viewers.


Steve.
 

RalphLambrecht

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Steve Smith said:
But what if the manufacturers of the grain focusers have already accounted for the paper thickness and built this into the base?

Does anyone have any manufacturer's instructions which state if paper should be used or not?


Steve.
Click to expand...

Manufacturer's instructions state that the bottom of the base is the focusing plane. In other words, they assume that you are placing the focusing aid on top of whatever you're to focus on. Consequently, there is no need to make any assumption about paper thicknesses.
 
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