Peak BG filter for B&W enlarging

Discussion in 'Enlarging' started by Mick Fagan, Oct 8, 2006.

  1. Mick Fagan

    Mick Fagan Subscriber

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    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 12x16” 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, didn’t 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 it’s 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, “just perceptible difference” 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 didn’t 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 couldn’t 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 I’m going to test materials or equipment, I see no reason why the test always has to be of a line or colour chart.

    Mick.
     
  2. Jon Shiu

    Jon Shiu Subscriber

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    Hi, the short answer is not to use the filter because it introduces focusing error. Ref. Patrick Gainer, Photo Techniques Magazine.

    Jon
     
  3. naaldvoerder

    naaldvoerder Member

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    Ralph Lambrecht and Chris Woodhouse reach the same conclusion in "Way beyond monochrome".
     
  4. resummerfield

    resummerfield Subscriber

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    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?
     
  5. Claire Senft

    Claire Senft Member

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    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.
     
  6. Mick Fagan

    Mick Fagan Subscriber

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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.

    Mick.
     
    Last edited by a moderator: Oct 8, 2006
  7. Jon Shiu

    Jon Shiu Subscriber

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    Hi, I just looked it up in Ctein's book Post Exposure p. 67: Photo Techniques Jan/Feb 1997

    Jon
     
  8. Mick Fagan

    Mick Fagan Subscriber

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    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.

    Mick.
     
  9. Smudger

    Smudger Member

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    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 ?
    -Cheers,Ian.
     
  10. Mick Fagan

    Mick Fagan Subscriber

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    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.

    Mick.
     
  11. Mick Fagan

    Mick Fagan Subscriber

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    Well another evening in the darkroom, another interesting development with the BG filter.

    My second set of eyes was unable to turn up, so the experiment I was envisaging, didn't happen. Instead I enlarged two negs for two prints.

    I'm using 35mm and 12x16" paper. One neg is full frame on the paper, and approximately 11 times enlargement. The other is a cropped print with the enlargement approximately 15 times.

    The most amazing thing is the 15 times enlargement, it is pin sharp, and that is an understatement! Mind you the other smaller enlargement is also pin sharp.

    I cannot wait until I have another set of eyes to back up my findings.

    Regardless of that, I am reasonably sure that using the BG filter with the peak focusing unit, in my darkroom, with my methods, is giving me more accurately focused B&W prints, than I have been able to do since I don't know when.

    I will post more results, when I'm able to get another set of eyes to confirm my findings.

    Mick.
     
  12. pentaxuser

    pentaxuser Subscriber

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    Mick. I have read G Nocon's book and seen the print which he says proves the point about the filter. Maybe it's just my eyes or the book's reproduction but with due consideration now I really don't think I could see any difference. At the time and because Gene had said which was the sharper, I was looking for the difference and if pressed would have said that it was marginally sharper but I think this was due to conditioned thinking. I knew what I had to look for so I found it.

    Barry Thornton in his "Elements" book is quite unequivocal about claiming that this belief in the benefit of the blue filter is wrong and he goes into some detail as to why and says that in 25 out of 25 times a print focused through the blue filter then without brought the focusing knob to exactly the same marked position. In a blind test of prints both using the fliter and not, he and other viewers couldn't distinguish. Presumably he marked the backs and then shuffled the prints so neither he not his viewers knew which were which.

    Maybe you could try the Thornton focussing test and the blind print test and let us know if there was a difference that could not be accounted for by chance.

    I wonder if Gene Nocon's position remained the same? However it if works for you then that's all that counts.

    pentaxuser
     
  13. Mick Fagan

    Mick Fagan Subscriber

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    Well some time has passed and I took great care with some enlargements doing prints with and without the BG filter on the Peak Focuser.

    When I am doing prints in my darkroom with the BG filter attached to the Peak Focuser I am definitely getting pin sharp prints.

    The time arrived when I had another set of eyes in the darkroom. My student came for another session. She developed her 35mm film, then made contacts. A negative was picked out for enlarging, test print done, some adjustments made; she nailed it on the second print. She also made positive comments about the Peak Focuser.

    I then asked her to humour me by using something different for focusing. I attached the BG filter and asked her to check the focus, adjust if necessary, but ensure that it was as good as she could get.

    Nothing else had changed, the neg had not been touched, the negative stage movement remained locked, the only change made was the lens was moved up and down slightly whilst attaining critical focus. This was then locked and another piece of paper was exposed.

    When we had dried the print and put it alongside the first print her first comment was, “How much does one of those Peak Focuser things cost?”

    In short, there was a real and quite significant difference in the BG filter print.

    Sharp is not correct, pin sharp is what came to mind.

    We brought the prints into the house for the missus to decide. There was no problem as whilst the first white light focused print looked very good, the BG focused print was outstanding. Razer sharp comes to mind.

    Now I have had a bit of time to reflect upon the apparent mystery of why some people say the BG filter works, whilst most say it doesn’t.

    I think that the changes made to the focusing part of an enlarger are so minute, that it is possible that only very well manufactured enlargers are capable of effecting these changes, and, more importantly, able to hold and lock the change in position.

    I would consider the LPL 7700 enlarger with the fine focus accessory a possible contender for this type of accuracy, as long as the negative stage was tightened up enough to eliminate any sag, once final focus has been attained or set.

    I did not measure the movement of the lens, the lens stage, or anything else on my enlarger. All my student and I did was to carefully focus the grain with the aid of a BG filter attached (crudely) to a Peak Focuser, nothing more, nothing less.

    Enlarger used: DeVere 4x5 free standing with drop table and single globe colour head

    2.8 50 Componon S lens.

    Ilford MGIV RC paper

    Film Neopan 400 35mm all cases.

    Negatives from two cameras and two photographers, with each photographer enlarging their own negative(s)

    I would be extremely interested to hear from anyone else who has one of these Peak Focusers with the BG filter and has tried the filter.

    If anyone in the Melbourne area wishes to come to my darkroom to see and try this, you're most welcome. The way I see it, the more minds able to see this and work out the pros and cons, the better.

    Mick.
     
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  15. Jerevan

    Jerevan Subscriber

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    It's an interesting thread, and I've followed it along, trawled the net a bit for information, but I can't figure one little detail... the "BG" part. :D

    Is it a shorthand for blue-green or is the filter of some other colour?
     
  16. Mick Fagan

    Mick Fagan Subscriber

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    Jerevan, it is a very dark blue filter which slips onto the rubber eyepiece. It doesn't slip on too easily either!

    http://www.peakoptics.com/product_info.php/manufacturers_id/1/products_id/62

    That is the manufacturer's own site explaining the filter. I don't know what the G stands for, it could be Blue Green, I just don't know.

    I do know though, I'm a bit excited at the way my printing has been transformed by the addition of this piece of equipment to my darkroom. However one does really need to have an enlarger capable of the minute adjustments one makes to ensure they are transposed to your print.

    Mick.
     
  17. Claire Senft

    Claire Senft Member

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    I think that this thread has done a fine job of showing that relying upon the statements of others that are well intended and that has been shown to be true in their own cases does not mean that you will not end up with different results from your own work.

    When I carefully and thoughtfully make tests and I end up being perfectly satisfied to believe my own eyes but hopefully I do not disparage what others have found to work for them. It is also true I believe to retest my assumptions every once in awhile to make sure I still are use what will work best for me.

    Good thread Mike! I am glad those lovely Australian snakes did not get you.
     
  18. Mick Fagan

    Mick Fagan Subscriber

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    Jereven, I have been doing a bit of trawling for information about this BG filter. I found this piece of information on one of APUG's members site.

    "Variable contrast papers (VC) are coated with a mixture of separate emulsions. All components of the mixed emulsion are sensitive to blue light but vary in sensitivity to green light. Exposure to blue light produces a high contrast image, and exposure to green light produces a low contrast image. By varying the proportion of blue green light exposure, any intermediate paper contrast can be achieved."

    Source:- Calibration of dichroic heads to ISO paper grades, by Ralf W. Lambrecht


    Using the above information, one logically comes to the conclusion that the Peak manufacturing company calls the BG filter so, because it is used to focus light in the blue green part of the spectrum.

    I would be quite interested to know anyone else's explanation.

    Pity you don't live on the same continent, you could drop in and test it out yourself.

    For what it's worth, my student, after seeing how well the Peak Focuser worked on my enlarger, is now going to test it on her LPL 7700 enlarger, if the outcome is the same, she is going to purchase a Peak Focuser with the BG filter, the difference is that good.

    Mick.
     
  19. Smudger

    Smudger Member

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    B/G filter..

    Given that some posters have difficulty in finding any difference with this filter,I occurs to me that it may be a result of variations in colour perception in the eye (a.k.a "colour blindness).
    This is a surprisingly common condition,and,unless profound,most people will never notice a slight deficiency in colour vision. I find a benefit in using the filter,but my colour perception has been tested by my optometrist.
    I also use a common or garden Paterson grain focuser, so I would suggest you don't really need a Peak model.
     
  20. Mick Fagan

    Mick Fagan Subscriber

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    Smudger, that is very interesting news, do you have a source or name, of the actual filter that you use?

    Until very recently I was also using the Paterson el-cheapo grain finder. If this can be converted to the accuracy of the very much more expensive Peak Focuser fitted with the BG filter, then the darkroom for some people could be made much better.

    What differences have you noticed?

    Mick.
     
  21. dancqu

    dancqu Member

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    Your lens is not well color corrected. Your student's
    lens may be more or less well color corrected. If her
    lens brings to the exact same focus all wave lengths
    from deep blue through red then her white image
    focus will be the exact same as seen using the
    BG filter. The better the print's sharpness
    with the BG the worse is the lens' color
    correction.

    BUT, your's and your students lenses may be Damn
    Good at producing a blue only image. Switch to blue
    sensitive only Graded paper and have your self prints
    sharper than pin sharp.

    More than one have posted, better to set the BG aside.
    They can say that because of the more precise color
    correction of their lenses.

    There are several fine points relating to focus and
    and filtering such as UV and violet sensitivity, filtering
    for, and other matters. I've Ctein's article on the
    subject but should review. I've a suspect lens
    myself that needs evaluation. Dan
     
  22. Mick Fagan

    Mick Fagan Subscriber

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    Dan, that is a point I had not considered, makes good sense. I will borrow a friend's Apo enlarging lens and see how that goes.

    I have been producing exceptionally sharp colour RA4 and EP2 prints from negatives, for around 20 years with this lens.

    I was of the understanding that this lens was, or should be alright for B&W. It could be though, that it has limitations with the latest VC papers.

    I have produced quite stunning pictures over 15 years ago with this same lens, but that was single B&W graded paper.

    I am learning a lot from this thread, makes life interesting, eh?

    Mick.
     
  23. dancqu

    dancqu Member

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    I've been looking for that article by Ctein. I recall it being
    in an issue of Photo Techniques. Very thorough. I gave it
    a couple of good readings but that was years ago.

    He analysis the problem light source to paper spectral
    sensitivity, condenser and dichro. IIRC, he does suggest
    the use of a UV type filter in the light path. At least B&W
    papers have an extended, exaggerated, blue-violet-UV
    sensitivity. Similar to films.

    Personally, I consider the BG filter a useful tool. Ctein
    tested it as well as other deep blue filters. He measured
    differences in focus by shimming the easel. I think it must
    have been one of his most laborious under takings.
    I'll keep looking. Anybody know which issue? Dan
     
  24. Claire Senft

    Claire Senft Member

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    In Ctein's later writing on the subject he conceded that a part of his focus error was due to this filter..approx. 4-5 mm at the easel if I remember correctly.
     
  25. dancqu

    dancqu Member

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    I've no context within which to place that remark.
    Mick has made it plain that there is much improved
    focus when he uses the deep blue BG filter.

    Perhaps focus error was the norm with whatever filter
    Ctein used. There is a spread of spectral wave lengths
    to which papers are sensitive. There is a band width to
    the filters used. Focus can be off some due to a
    paper's very short wave length response.

    Ilford's Oriental paper has a band width sensitivity of
    350 to 500 nano-meters and is most sensitive from 400
    to 450 nano-meters. IIRC the BG is most transmissive at
    470 nano-meters. Papers vary in their spectral response.
    Light sources vary.

    Ctein's article is rather involved and very exhaustive.
    The testing included a number of variables. I'm still
    looking for my copy of his article as I've a suspect
    105mm Nikkor which should be tested. Dan
     
  26. Matthew Gorringe

    Matthew Gorringe Member

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    That's a nice score Mick,
    the Sydney market was pretty bare 2 weeks ago. I was looking for one of these there but found very little of interest. I was offered a multigrade 500 head with all extras for $150 but apart from that there was almost nothing really. If you find another one of these (the model 1) don't hesitate to buy it and I'll forward you the money.

    Are Bromide/Chloro-bromide graded papers more finely attuned to the blue wavelengths and would the filter possibly work better with graded papers?

    Regards, Matt.