BOGEN W.A. 40mm f3.5 ENLARGING LENS
I just picked up this wide-angle lens quite cheap on Ebay (notwithstanding how much it's costing to ship it here from the US!!). Of course I'll put it to work as soon as I get it, but I was wondering if anybody knew much at all about it? You know, reputation among lenses, its build, elements, etc etc. There's not much info about it at all out there on the Net. I kind of figured there wouldn't be much difference between this and any other WA lens within the enlarging limits of a Durst M605. I'm also wondering just how big can I go printing on an M605 with a WA lens before the easel starts smacking into the column. I'm sure my back is going to thank me when it comes to focusing!
Printing 35mm only, obviously, by the way. And when I say 'within the enlarging limits of a Durst M605', I mean with the head sitting normally on the column, not super-sized onto the wall or floor. The M605 has a relatively short column, which is why I jumped at the chance to get a WA lens without paying with blood through my nose for a Rodenstock or Schneider WA
It's the distance from the front of the column to the centre of the lens that dictates the potential size of the enlargement on the baseboard. If it is 7 3/4 " you will never get to 20 x 16 ". And don't forget the selvage of the easel. The focal length of the lens only helps up to a certain point. I understand the problem of a short column - I have limited height in my cellar.
Ahhh Youngrichard, what wouldn't I give to have a real cellar in which to build a darkroom!
Houses here don't have cellars... I really have often wondered why that is..
Maybe this is useful. The equation of the relationship between focal length of the enlarger lens (L), distance between negative and paper (D) and magnification ratio (m). All lengths in the same units, usually mm.
So if you want 16x enlargement, and lens is 40mm, then D=723mm according to the equation. It is slightly inaccurate because it assumes a "simple" lens without its own internal dimensions, but it will be quite close.
One way around insufficient column height is to remove the baseboard, then attach the column to the wall a bit higher than it was on the baseboard. Then you have more height, and the easel can move back under the column. There are still geometric limits, but it might get you enough magnification.
* means multiply
^ means to the power of, in this case to the power of 2, that is squared
Last edited by john_s; 02-05-2010 at 12:13 AM. Click to view previous post history.
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John, believe me I would've mounted it to the wall long ago, but for the fact that I'm renting
Finally I received this lens from the US. Never having used a wide-angle enlarging lens before, I was keen to see it's effect, so I grabbed a neg and popped the lens right in the enlarger.
WOW, the enlarger head is waaaay down yet the image is as big as the baseboard!!!!
Lovely. Now, there's just one problem. There is significant light fall-off in the top left corner of the image. For the record, I am using a Durst M605 Color with the Siriotub lens board doing just 35mm.
I tried all kinds of things, turned the lens board upside-down, tried the Siriopla too. Turning the lens doesn't change it either, so it can't be the lens, there's something about the enlarger, inside it, that encroaches into that corner of this now much-larger field of view, so to speak.
There are a couple of ways I found to get rid of that dark corner. One is to remove the wide-angle lens and put a normal 50mm back in!
The other is, with the wide-angle lens in place, if I was to slightly unscrew the lens board and ever so slightly move the lens board. Another way to picture what I mean is, you move the lens board as you loosen the tightening screw, in that direction. It doesn't have to move very far, you'll notice that dark corner will fill with light soon enough.
Having figured that out, it leaves me with two more questions:
Now that the lens board has slightly moved away from the two metal claws that grip it in place, how can I keep the lens firmly in that odd position?
Will moving the lens board slightly away from it's screwed-in position affect image quality/sharpness? For example, because the lens board has been loosened/moved and is now potentially 'off it's axis', is that going to make it blurry all down one side of the image or something?
I haven't actually printed yet to see for myself, my easel is busted anyway, I won't be happy until it's fixed! Anyway, I can't print with the wide-angle because I haven't figured out how to secure it in that off position.
Any advice is greatly appreciated. I'd love to be able to take advantage of this lens (provided it matches my Schneider generally - I'd love to test that too!).
For your light fall off issue, use the 6x6 or 6x7 mixing box (if you have it). If you don't, I know with the Omega enlargers, the 'wiggle room' is in the lightbox; in terms of centering it over the lens. How much play is there in your lightbox?
I have the Schneider 45mm HM and use it mostly for 16x20s and enlarging 16mm negatives. With smaller prints I can't even open my easel.
If you have a Schneider 50mm Componon or Componon-S I'll bet that will perform much better than the Bogen.
Personally I think a 40mm wide angle is just too much of a compromise to get good prints.
For example, your alignment will be even more critical with the 40mm, so, without that lensboard in its proper place, you are going to get a fuzzy corner.
On this enlarger there's a sliding lever from 'Box35' to 'Box66'. I'd forgotten all about it because it was taped over against light leak, I didn't anticipate having to move it again anyway.
I changed it, but I'm afraid it doesn't make any difference, the dark corner is still there.
Thanks for your advice though. I'd say you're probably going to be right too about this lens against the Schneider 50mm. With the wide-angle I can already see through the focus scope that the corners are not as sharp as the center. Well, it was worth the try
Thanks again, Paul
Ok, so the next thing to check is that lens axis is lined up with the center of the negative. Basically you already checked this and it was off (by moving the lens) but since the lens needs to stay fixed, how about being able to move the negative. One thing I do to center things is to use a larger glass holder and fiddle until the negative is in the center.
Originally Posted by gamincurieux
I do it by shining the laser right up at the lens and it makes a circular diffraction pattern when it is in the exact center. I mark this center on the baseboard and then move the negative carrier or the negative in the glass until the center of the image is where my center mark is on the baseboard.