How to adjust a grain focuser?

[Loren Sattler]

I picked up a second grain focuser (by Thomas Instrument) recently and compared it to my old Accura model that I have used for years. See photo. I discovered they do not agree, the Thomas Instrument is more accurate when enlarging at full aperture (2-1/4 sq negative at 11 x 14 print size, Nikor lens at f5.6). The print is noticeably sharper.

Are these focusers adjustable? How?

Thanks in advance.

 

[Newt_on_Swings]

the one on the right is not adjustable, the one on the left should be be adjustable. easiest way is to load up a negative into the enlarger, make it unfocused, and put your eye up to the reticle, inside you should be able to see a line, or box, adjust your eyepice by rotating it until that line or box is sharp. Then you can focus your image as normal, but use an area that close to the line, or place the grain inside the box for best results. Move the grain finders around the image as well, and also check corners.

 

[Hilo]

The previous post answers your question almost completely.

I would just like to add something perhaps very subjective, but nevertheless from years of experience: when I place the grain finder (Peak in my case) in the middle of the image it is easy to see everything, but in the final print the grain in the corners may not always be as sharp as in the middle of the image. When I place the grain finder in a corner it is a little harder to see the grain, but in the final print both corners and the middle of the image have perfectly sharp grain.

So, I always place the grain finder in a corner.

I think the reasons for this are in the lenses. With my Focomats 1C and 2C came first-version lenses. I could only get the grain sharp doing what is described before. Later on I got later-version lenses (Focotar-2 50mm and 100mm) and with these it seems easier to almost always get sharp grain from corner to corner, even when not stopping down.

 

[Mr Bill]

I don't know about the adjustability of either, but an option to keep in mind is that you can raise the focus tool. If this is the right direction to "correct" the tool, just write the needed correction on the bottom. Back at a time when I was crudely prototyping equipment, I often used pads of Post-it notes for shims; this would be a convenient way to raise a focus tool by some arbitrary amount.

 

[Seele]

I always use mine with the lens set at working aperture, it should take care of the possibility of focus-shift. I mainly use Paterson's but also use a Bausch & Lomb parallax focusser.

 

[Loren Sattler]

What brought this to light is I recently started using some Fomatone MG warm tone paper which is a very slow chlorobromide paper. To reduce exposure times to under 20 seconds I have made a number of 5 x 7 prints at full aperture (f5.6 for med format and F4.0 for 35mm). I noticed the enlargements have not been as sharp as I am accustomed to, so I tried the Thomas Instrument unit on a bigger enlargement. The test print was significantly sharper than a test print made wide open with my old (Accura) grain focuser. In the past I have rarely made prints wide open, usually two to three stops closed from wide open. Obviously I have gotten by because of the depth of field provided with these narrower apertures.

I am going to need to find a smaller grain focuser since the Thomas Instruments unit is physically too large to work with 5 x 7 prints. It is too tall to fit under the lens stage.

Thanks to all for the responses.

Looking at the Peak units, there are three models (1,2, and 3) available ranging in price from about $60. to $350. Any comments on the merits of the three models?

 

[Newt_on_Swings]

I use the peak 1, its my go to grain focuser. It has the largest mirror of the three, and the adjustable angle eyepiece lets me get an image from any corner of the print easily. It is built very well, and the stand looks as if it was machined out of a solid block of metal. Blue filter makes focusing easier but thats a whole other bag of worms. (You can search about it, and its debated)

They dont come up for sale used that often, i mostly see the smaller 2 or 3 pop up, i guess its a testament to how much people like them.

You may be able to get by with a magnifying pair of reading glasses, or a handheld magnifier at an enlargement of only 5x7. Its probably the cheapest way.


Sent from my iPhone using Tapatalk

 

[Hilo]

Peak grain finders are great. One just sees much more easily with them. I don't have the cheapest model, but do have the middle and the top model. Both are better than anything else I ever used and the top model is still worth the extra cost. Sorry, but I am always confused about their model numbers. I think you can find the most expensive model for less than $130. A tip: the mirror is two sided, you can turn it around if one side is scratched !

I would reconsider trying to reduce your enlarging times. I print up to 20X24 on fiber papers and exposure times of 60 seconds and more are very normal. All my lights go off while exposing, I think that is a must. But stopping down the enlarging lenses is essential, with all respect.

 

[paul ron]

BTW when focusing, be sure to use a piece of the same paper under your focuser.
Height makes a difference.

 

[pentaxuser]

BTW when focusing, be sure to use a piece of the same paper under your focuser.
Height makes a difference.

I have seen a lot of posts backed by experiments carried out by the posters that have concluded that this is a myth.It is to do with the DoF which gives a range of focus that well exceeds the thickness of the paper

OP, do a search of posts on APUG and then decide for yourself

pentaxuser

 

[jscott]

Yes, it was a surprise to me but I took a B&W course from a leading photographer and this came up. He focused without paper on the platform and when I mentioned that there was no paper he responded "nobody ever sued me because my prints were out of focus". That's all he said about it. He never explained any more than that but I think the point is that the depth of field will take care of it....

 

[paul ron]

That's one i haven't seen. But when focusing, notice how sensatve n delicate you make your adjustments? DOF?... I'll have to give that a try...

Oh but without paper in my easel i won't be able to see my image for a rough focus n composing on the black or yellow empty easel base.

 

[Tower Photo Art]

I picked up a second grain focuser (by Thomas Instrument) recently and compared it to my old Accura model that I have used for years. See photo. I discovered they do not agree, the Thomas Instrument is more accurate when enlarging at full aperture (2-1/4 sq negative at 11 x 14 print size, Nikor lens at f5.6). The print is noticeably sharper.

Are these focusers adjustable? How?

Thanks in advance.

 

[Tower Photo Art]

I found that compensating the height of the fine grain mirror to easel was 5 cm....I lowered the enlarger head 5cm so that it was in focus to the print....not fine grain mirror, and it does make a visual difference.

 

[Doremus Scudder]

A couple of observations/comments.

1. Prints made at maximum aperture may not be as sharp as prints made stopped down a couple stops just because the lens won't be as sharp at maximum aperture.

2. Unless you're getting sharper prints using one grain magnifier than the other, having used both on the same print at the same aperture (and making sure nothing moves in between, such as negative popping etc.), you're not comparing apples to apples.

3. If you are getting sharper prints from one magnifier, the other is likely not focusing as accurately, or you are having difficulty focusing with it. In the former case, you can try shimming the bottom of the magnifier to make it agree with the better one. This only works if the error is in that direction, i.e., the mirror on the magnifier is too low. If the error is the other way around, you're likely out of luck. Ditch the magnifier; it's not worth the effort to try to fix it. I don't know of a single grain magnifier with adjustable mirror height. (Note, that if a front-surfaced mirror on a magnifier has been replaced with a back-surfaced one, there will be a substantial error that could be corrected by shimming the bottom of the magnifier to correspond to the thickness of the glass.)

4. Adjusting the eyepiece so that the reticle is sharp is what focuses your eye on the image. If your magnifier does not have a screen on which the image is projected, the image is an aerial one. If you don't have a reticle to focus on and your eyesight does not agree with the way the magnifier is focused, you may, indeed have a focus discrepancy (I'm assuming here, perhaps incorrectly, that eyesight will affect the perceived focus of an aerial image; I'd love to have more info on this - anyone?). If there is no way to adjust the eyepiece in such a case, the magnifier is simply unusable by you. Pass it on and get a better one.

Best,

Doremus

 

[Dali]

Yes, the Scoponet focuser can be adjusted. I have the user's manual somewhere written in French. If you want, I can pm you a quick and dirty translation.

 

[ic-racer]

How to adjust a grain focuser?

Add or subtract material from the base.

The stamped steel support of the wavy line on the right hand pictured focuser can easily be bent, causing it be out of adjustment.

 

[Pieter12]

So you have a nice grain focuser that produces noticeably sharper prints. I don't see any issues or need to make adjustments that are probably not necessary in the first place.

 

[Mark J]

4. Adjusting the eyepiece so that the reticle is sharp is what focuses your eye on the image. If your magnifier does not have a screen on which the image is projected, the image is an aerial one. If you don't have a reticle to focus on and your eyesight does not agree with the way the magnifier is focused, you may, indeed have a focus discrepancy (I'm assuming here, perhaps incorrectly, that eyesight will affect the perceived focus of an aerial image; I'd love to have more info on this - anyone?). If there is no way to adjust the eyepiece in such a case, the magnifier is simply unusable by you. Pass it on and get a better one.

Best,

Doremus

Yes, I wouldn't use one without a reticle. It opens up a lot of potential for error, from eyesight and eyesight+colour filter changes.

ps. I would also focus at full aperture too. That way the focus setting is more accurate. All modern enlarging lenses should be corrected to have the full-aperture focus very close to the stopped-down focus, that's the way they are intended to be used.

 

[Pieter12]

Yes, I wouldn't use one without a reticle. It opens up a lot of potential for error, from eyesight and eyesight+colour filter changes.

ps. I would also focus at full aperture too. That way the focus setting is more accurate. All modern enlarging lenses should be corrected to have the full-aperture focus very close to the stopped-down focus, that's the way they are intended to be used.

I generally focus wide open, then double check stopped down, center and corners. A little harder to do with a dense negative or big enlargement.

 

[ic-racer]

The average adult human eye is somewhat of a doublet, with a variable focal length around 17mm at infinity. There is an adjustable aperture from about f2 to f11. It can focus from about 2 feet to infinity by releasing tension on the "lens," causing it to bulge and increase strength. The "lens" has less power than the cornea. The cornea is a lens which serves as the main light bending structure. Due to the adjustable focal length of the system, aerial image focusing is not going to be reliable for persons with normal eyes. As the eye ages (presbyopia) the lens focal length becomes fixed.

A further confounding issue for grain focusing is the human eye's pronounced chromatic aberration. This is counteracted by stopping down the human eye in daylight, but in dim light, or after pharmacologic iris dilatation, the chromatic aberration is severe.

One way to minimize the percieved effects of the eye's chromatic aberration is to filter the light before it hits the retina. This has the theoretic potential to sharpen ones perception of the focus reticle. This becomes more important if one's iris is wide open (dim enlarger light). A blue filter is provided with the Peak 1. It is easy to try and see if it has any benefit.

 

[Mark J]

I would agree with most of the above, but why is the graph drawn with a waveband in the near infra-red ?
The eye is only barely sensitive past 0.7µm.

 

[ic-racer]

I would agree with most of the above, but why is the graph drawn with a waveband in the near infra-red ?
The eye is only barely sensitive past 0.7µm.

Excellent point. The graph came from a research paper on infra-red, not a descriptive physiology text.

 

[Philippe-Georges]

Linhof made an easy to use one (and perhaps other companies too):