Grain Focusers

[Curt]

I got the focuser today and it came with a separate blue aberration filter. When do you use the blue filter? I haven't use one of these in years, it's going to be a great addition to my darkroom. The two I use now are going on the shelf for a long deserved rest.

 

[greybeard]

The grain focusers must be accurately adjusted to the user's eyesight, or they will result in out of focus prints.

This is true for a groundglass focuser because accommodation by the eye can compensate (to some extent) for error in the focal plane. But proper use of an aerial image focuser involves adjusting the focal plane so that there is no relative movement between the reference marks and the aerial image when your eyepoint is moved laterally; this relative movement is caused by parallax, and is affected by eyepiece focusing only to the extent that the reference marks become indistinct.

An appallingly cheesy Bausch and Lomb focuser that I have actually works just fine, in part because the reference marks are actually the instructions to adjust until there is no relative movement between the lettering and the image! (The tiny field of view, however, really stinks.)

 

[Martin Aislabie]

Paterson v Peak

Setting aside for the moment the fact that the Peak focuses into the corners which the Paterson doesn't, is there any difference between a print that was "Paterson focused" and one that has been "Peak focused". If so,does this difference manifest itself at all enlargements or is there a minimum size beyond which it begins to show?. For a scientific answer I suppose this question really has to be addressed to those who have both models and may have used both to produce two identical prints from the same neg.

Thanks

pentaxuser

Pentaxuser raises a good question - a very good question.

I now own both.

I started with the Paterson, which was fine for 35mm & 6x6 - I could see the grain easily on 35mm enlargements and just about on 6x6.

However, I then moved up to 5x4

Grain on a 5x4 Neg was way beyond the Patersons capabilities - well with my eyes anyway.

Following advice from a thread I posted on APUG requesting advice, I then started to use the Paterson to focus on details (twigs/leaves/edges/anything) when using the 5x4.

However, as been stated before, the Paterson only works in the middle bits of a print.

If my details on the 5x4 were outside the operating area of the Paterson - I was stuffed

Hence the move to the Peak, not only can I see into the corners of the print but I can now once again see the grain - even on a 5x4 - yeah!

So, in answer to Pentaxusers question, are you going to get sharper focused (better) prints from a Peak than a Paterson, then the answer is probably not.

If you are using a Paterson and it works for you then getting a Peak won't offer you any advantage,

I bought a brand new metal Peak from Robert White and it cost me about £150 (but I fully intend to be fumbling in the dark for this thing for at least the next 30 years )

It is easy to use, has a very bright image plus its rigidity and weight give it a very nice tactile quality that cannot be easily quantified.

But, and it is a major BUT, it only focuses the negative on the paper.

If I was a professional printer I would buy one without hesitation but as an enthusiastic amateur I would only buy one out of necessity

Martin

 

[Curt]

Now that I have three I can compare them, they are all accurate, the Peak is a little brighter, the inexpensive very old Prinz works but is hard to focus with. The Omega is the most ergonomic. The Prinz cannot see the corners of the easel. The Omega has a nice eye adjust rectangle. I'll be using the Micromega most of the time now.

 

[ozphoto]

The british printer Gene Nocon recommends using a blue filter with the grain focuser to ensure sharpness. I can't recall the details exactly but it had something to do with wavelength of light I think (of course I could be wrong ). I've used a blue filter but since changing to the Peak, I no longer use it - maybe I should try again.

-Nanette

 

[Steve Smith]

The british printer Gene Nocon recommends using a blue filter with the grain focuser to ensure sharpness. I can't recall the details exactly but it had something to do with wavelength of light I think (of course I could be wrong ).

It's because different wavelength (colours) of light focus in slightly different places. Photo emulsion is sensitive mainly in the blue and green region so viewing with a blue filter allows you to see what the paper sees.

Gene Nocon also suggests not using a piece of scrap paper under the focuser. Something which was argued at length on a previous thread but not this one...... so forget that I mentioned it!


Steve.

 

[Martin Aislabie]

There is also a strong school of thought that says our eyes focus different wave lenghts incorrectly.

This is a topic that seems to come up bi-monthly

The general concencus is - focus with white light with a piece of paper under your focus finder

As someone pointed out - if you have an APO Enlarging Lens - white or any colour all focus on the same plane anyway.

Martin

 

[Curt]

What is the argument for not using a piece of the same paper under the focuser? I've always done it and never considered doing otherwise.

 

[Steve Smith]

I will have a look at his book again tonight as I don't remember the reason.

The only reason I can think of now is that the manufacturer has already accounted for the paper thickness in the calibration of the device. I know that if I was designing one, that's what I would do.



Steve.

 

[Steve Smith]

The following quotes are from the book 'Photographic Printing' by Gene Nocon.
ISBN 1-85227-015-2 1987

On blue filters:

"Using the blue filter on the Omega Micro-grain focuser at this enlargement* the grain can be seen to be pin sharp on the print. The image projected onto the easel will actually appear out of focus after focusing with the blue filter but the print produced will be sharply focussed".

(* text illustrated with an image).

He also explains about the blue filter showing the image that the paper sees.


On paper under the grain focuser:

"There is a popular belief that focussing on a sheet of photographic paper placed on the baseboard will give you a more accurate result because it compensates for the thickness of the print. This is nonesense. Save your paper".

Unfortunately he does not give his reasoning.


Steve.

 

[pentaxuser]

Thanks Martin for comprehensive reply to my question. Nice that there is someone out there who has used both focusers and answers what was asked.

pentaxuser

 

[fschifano]

I will have a look at his book again tonight as I don't remember the reason.

The only reason I can think of now is that the manufacturer has already accounted for the paper thickness in the calibration of the device. I know that if I was designing one, that's what I would do.

Steve.

You could, if you could count on all paper being the same thickness. In the real world, that ain't so. Double weight fiber, single weight fiber, resin coated - they're all different. Heck, you can't even count on all resin coated papers being the same thickness. The Foma paper I use is noticeably thinner than the Ilford, Agfa, Kentmere, and Kodak RC papers I've used. In reality, it doesn't make a whole lot of difference if you focus with the lens wide open, then stop down two or three stops for the exposure.

 

[Steve Smith]

It's a pity Gene didn't explain his reasoning in the book and that's the only reason I can think of. Personally I have never put paper under the focuser and I don't think I have ever had a focusing issue.

Gene Nocon is a much better printer than I will ever be so I will just go along with his suggestion.

I have not tested this theory but it could be possible that focus at the enlarger stage i.e. lens position is more critical than height of the paper (especially when closed down a couple of stops). I recently printed a couple of prints on Ilford postcard paper right to the edges so the paper was just sitting on the easel but was bowed upwards, probably about 4mm higher in the middle. The image which was focussed onto the easel baseboard was still sharp on the print. I can see very small detail in it if I look closely and I can't imagine it being any sharper.

As for differences in paper thickness, in reality if you found out what the thickest and thinnest papers available were, and worked out the difference, then if the grain focuser manufacturer compensated for the middle paper size in his design, the maximum error would only be + or - half that difference. Probably not very much.


Steve.

 

[Claire Senft]

The basic thing is that the difference is too small to been seen. Make two prints. Make 1 print that is focused with the magnifier on top of the paper. Make a second print with focussed with the magnifier on the easel. Develop them together. Can you tell any difference in sharpness?

If you cant see a difference then repeat 10 times "What, me worry".

That being said I always focus with the magnifier on thop of a piece of paper...just can't help myself...obsessive, compulsive...and a worry wart.

 

[Steve Smith]

That being said I always focus with the magnifier on thop of a piece of paper...just can't help myself...obsessive, compulsive...and a worry wart.

Perhaps you will now worry that it may be sharper without the paper!




Steve.

 

[marke]

Perhaps you will now worry that it may be sharper without the paper!Steve.

I know that I will!:rolleyes: