Peak BG filter for B&W enlarging
Today I went to our twice-yearly photographic flea market. One of the things I scored was a Peak enlarger focuser, 2000 (Model I)
Many years ago in another life whilst working in an industrial photo lab, I had the pleasure of using these grain-focusing units and believed them to be the best in the world. Well lady luck shone today and I picked one up, boxed and in new condition, with a BG filter.
Now I had never seen or heard of this filter before, so I trolled the web, came up with the Peak sight, and discovered this bit of information.
Use of the BG filter.
When you want to obtain more correct enlarging for the black and white film, use the focuser after fitting the BG filter to its eyepiece. The use of this filter will permit the coincidence between the wavelength sensitive to your eyes and that to be enlarged.
Upon getting home I decided to test this BG filter out. Firstly, I have to say as soon as I looked through the Peak I knew I was pretty much in darkroom heaven.
I printed a 12x16Ē enlargement as sharp and focused as I could to the best of my ability without the BG filter. I was very pleased with the result.
I then took out the BG filter, figured out how to attach it and looked at the grain, didnít really see much difference. However the BG filter is a push fit over the rubber eyepiece, there is a possibility that one could, or would, turn the dioptre eyepiece when fitting the BG filter.
My enlarger is a DeVere freestanding 4x5 with the drop table and the front focusing wheels. When the enlarger is set and locked, nothing moves so basically you can be assured if itís focused correctly it stays correctly focused.
Focusing was done with the filters removed from the light path, and the lens stopped down to the printing aperture.
After quite a number of test focusing, done with the Peak unit, with and without the BG filter, I concluded that there was a, ďjust perceptible differenceĒ in the two practices.
This was interesting; I then proceeded to make another print, with the focus set, using the Peak with the BG filter in place. This was the fourth print of the session; one print was 1/8 of a stop darker (first print).
I took the remaining three prints into the house for the final arbiter on my prints, the missus. I laid the three prints out under our normal print-viewing situation and asked her to pick the sharpest and/or best focused print. As I have rather poor eyesight these days, this is almost a standard practice, so she didnít know this was a test of equipment.
She picked the print focused with the BG filter in place!
Now, I am well past finding the silver bullet in my photography, but I did know that the Peak unit would aid my failing eyesight in the darkroom. The BG filter though, was completely unexpected and also completely unknown to me prior to today.
Have others out there experienced this little device and come up with similar results?
I did search the APUG forums but couldnít find anything about this filter, which I find rather fascinating at the moment.
By the way, the print my missus chose will be going into my local camera club competition. If Iím going to test materials or equipment, I see no reason why the test always has to be of a line or colour chart.
Hi, the short answer is not to use the filter because it introduces focusing error. Ref. Patrick Gainer, Photo Techniques Magazine.
Ralph Lambrecht and Chris Woodhouse reach the same conclusion in "Way beyond monochrome".
Originally Posted by Jon Shiu
Would the actual plane of focus obtained using the Peak BG filter and NO enlarger head filter, be the same as using NO BG filter and the enlarger head Magenta filter?
I am pleased that you have obtained such a nice piece of equipment and it is my hope that you continue to get joy from owning and using it.
As mentioned earlier using the filter to focus is a poor idea. I would guess though that the combination of using the filter may just possibly offset the shift of focus that one will sometime aquire due to the chacteristics of correction and sensitivity displayed by a lens and VC paper. Unfortunately this nice match would change with enlargement size and filter number.
I would advise that you continue to use the filter if it seems to work better in your case. I would stay alert to the possibility that if a print does not seem to be as sharp as you think that it should be, remake without the filter. The filter may also be helpful to you due to unusal conditions of your own sight.
Claire (Ms Anne Thrope is in the darkroom)
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Jon, do you know (approximately) when the information by Patrick Gainer appeared in Photo Techniques? I have been a subscriber for about 20 years and should be able to find this information and read it in context.
naaldvoerder, I will have to wait to read that book, it is currently unavailable in this country and ordering it over the net, is exhorbitant right now.
resummerfield, I cannot focus clearly under magenta filtration, so I cannot test your question.
Claire, I fail to see how this nice match would change with enlargement size. I think I know where you are coming from, but I fail to understand how moving the lens board up or down 300mm or so, would make that big a difference.
I think I understand how an aperture and filtration change, would make things different.
Interesting, more tests this evening will ensue.
Last edited by Mick Fagan; 10-08-2006 at 06:32 PM. Click to view previous post history.
Hi, I just looked it up in Ctein's book Post Exposure p. 67: Photo Techniques Jan/Feb 1997
Jon, many thanks for the edition of Photo Techniques. I do now remember reading this article, and especially remember the night picture by Chip Forelli on the lead page as extremely apt. By the way, the article starts on page 40.
I have now carefully read and re-read Patrick Gainer's article, like all well written technique and/or technical articles, it raises many questions and makes one wish to find out for one's self, that what in fact has been illustrated, is repeatable in your near identical environment by oneself.
I will now take into consideration many of the points made by Patrick Gainer and work on a test regime myself.
By the way, Patrick Gainer never states that it is an absolute, that you may/will have a focus shift under different coloured light, resulting in unsharp prints.
Under his conclusions section, it is apparent one will more than likely suffer from focusing differences under different light. Which would normally lead one to assume you will have unsharp prints, but it is not an absolute.
The whole article is in reality a scientific one, done to a level that most reasonably educated people should be able to follow and more importantly, understand.
I think the best part of the article is the last sentence where one is told:-
"All of the experiments can be repeated in almost any darkroom and in fact should be repeated, preferably by students who are not told what is going to happen but who are going to find out what does happen".
Well, I'm off to the darkroom after my session in APUG finishes, to work out just how I'll do some critical repeatable measurements.
From Gene Nocon (inventor of the F-stop Timer)'s book "Photographic Printing"..." I began experimenting with the blue filter attachment on the Omega Micro-Grain Focuser. When the blue filter was used there was a slight focus shift. Without the aid of the filter the picture actually looked out of focus. But when a print was produced it was pin sharp!.
I then tried printing from a chromogenic film, focusing with the blue filter, and that too became pin sharp."
He includes two enlargements from a frame that show the difference clearly.
Nocon was using multigrade paper. His rationale was that this is primarily sensitive to blue wavelengths, and,to a lesser extent,to green.
I have used a blue filter since , on principle.
Surely worth a try if you have a Rosco filter swatch lying around ?
Ian, that is interesting as last night I did a preliminary test and am warming to this BG (blue) filter supplied with the peak unit.
Tonight I will have someone else in the darkroom, a series of prints from both of us should be interesting.
Or to put it another way, a set of young eyes and mine.
I'll keep you posted.