Out of focus at the edges medium format enlarging

dustym · Jan 18, 2006

I have a Dunco Model 2 enlarger and base board with a roganor - 2 50 mm 1:2,8
Im printing 6x6 negs , and I am experiencing out of focus on one side of the print , is this an alignment issue, if so how can it be cured as the enlarger bolts to its dedicated base board, is there a calibration method for this set up, or could the be a problem with the bellos track or focusing gear.

Bob Carnie · Jan 18, 2006

First problem is you are using the wrong lens 50mm for 6x6 negatives. Put a 80mm lens in the enlarger and some or most of your difficulties will be eleminated.
I also recommend a glass carrier, reg glass on bottom and anti newton on top for printing. This will hold the negative flat in the carrier and stop the middle of the negative drawing to the light source in longer exposures.
If these two things do not solve your problem then I would check the enlarger alignment and such.

haris · Jan 18, 2006

As Bob said, you need 80mm lens. Then apropriate condenser/mixing chamber for that lens/negative size. I don't know particular enlarger, but what I said are basic rules. I had similar problem last time, I simply forgot to change mixing chamber from 50mm lens to 80 mm lens chamber... You can as Bob said use glass carrier. I don't use it. And as Bob said, if those things don't work, then check alingment. One more thing. Maybe lens is not good at edges. I had one lens which made me similar problem as you have. When relpacing it for other lens my problems are gone.

photobackpacker · Jan 18, 2006

I agree with the longer lens statements. Additionally, as you move to larger negs, you will begin to run into film curvature issues. This will necessitate enlarger lens f-stops or f11 or smaller to give you sufficient depth of field to compensate for the lack of flatness in the film.

Neal · Jan 18, 2006

Dear Dustym,

The focal length of the lens is not your problem. If lenses that long can hold an 8x10 in focus from edge to edge they can certainly handle 6x6 negatives. While the lens could be defective, this definitely sounds like alignment. Procedure? Your manual should have that in detail. You should be able to get it pretty close with a good level, but a quality optical aid would be better. (Zig-Align and Versalab are the only two I know of.)

Neal

Bob Carnie · Jan 18, 2006

Hi Bruce

I have to disagree with closing down of lens to create depth of field for better sharpness.

All enlarging lenses that I have ever used are Flat Field lenses and therefore are designed to focus on a singular plane.
There is possibly some depth of focus issue, that may be present, but and image will be as sharp wide open as is closed down two stops.
Depth of field is apparent with image taking lenses in the camera.

I do recommend not using the smallest or narrowest apeture as the light will diffract and cause softness trying to get around the apeture blades.

Bob Carnie · Jan 18, 2006

Neil

As I see it , he is using a 50mm enlarging lens to print a 6x6 negative.
That indeed is the problem on the edges , then there could be secondary issues.

fschifano · Jan 18, 2006

In the world of enlarging lenses, the 50mm focal length is designed to cover the standard 24x36 mm frame. For the most part, they are optimized for making 10x enlargements give or take a bit depending on manufacturer. Similarly 80mm enlarging lenses are designed to cover the 6x6 cm. film format, though the optimum magnification factor is a bit less. If you are getting prints with a sharp central portion degrading out towards the edges with the 50mm enlarging lens it's no surprise. No amount of stopping down or enlarger alignment is going to fix that. You need to use the lens designed to cover the film format you are using. You also need to insure that the light source evenly covers the 6x6 cm format as well. If it doesn't, then your prints will be lighter at the edges because of the light fall off.

Once you get that sorted out the most egregious of your problems will disappear. Check for alignment problems by using a grain focuser. If the center and edges are both in focus at your working aperture (two or three stops down from wide open,) you're all set. There's no need for alignment or for glass negative carriers. If not, start by aligning the enlarger; making sure that the baseboard, lens, and negative stages are all parallel. Glass negative carriers would be a last resort for me. Using one is not a substitute for the proper enlarging lens and light source; nor is it a cure for an improperly aligned enlarger.

photobackpacker · Jan 18, 2006

Bob, I am not saying the image will be sharper when the lens is closed down. I am saying one will increase the tolerance for lack of flatness in the film plane. Depth of field and depth of focus stem from the same optical principle - the range over which the circle of confusion still appears as sharpness to our eye is increased at smaller apertures up to the point where diffraction begins to influence sharpness.

I used to print 4X5 in a glassless a carrier. Edge sharpness was an issue until the lens was stopped down.

Likewise, I can make slight corrections to perspective by tilting the easel. When doing so, however, it is necessary to stop the lens down to maintain sharpness across the easel.

Bob Carnie · Jan 18, 2006

Hi There

Depth of Field relates to camera taking lens and the circle of confusion is much larger in a camera taking lens then that of a flat field lens.
Depth of Focus relates to flat field lenses and is very small.

When enlarging we are using a flat field lens and the principles of depth of field do not come in play.
I would admit to notice a very , very minimal existance of depth of focus when projecting a negative but not enough to sharpen images at the edges.

A properly aligned easel board>lens>negative position> condensors> and light source are the considerations for sharpness.

A glass carrier is mandatory for my work. If I was only working with 4x5 negatives *thicker base* then I would consider glassless carrier.
for 35mm, medium format, polaroid negative a glass carrier is mandatory to keep the film flat through, longer exposures, split printing and complicated burn patterns. * the negative will rise in the middle towards the bulb with heat, which will cause pop negatives*

This is the case in my work and the pain of cleaning the glass is minimal compared to the suriety of sharp film along the whole print.

Others may have found a cure for popped negs other than glass, I have not.

fschifano · Jan 18, 2006

Bob Carnie said:
Others may have found a cure for popped negs other than glass, I have not.

Well there you go. I haven't found negative popping to be a problem with a diffusion type enlarger. Very little heat makes it to the negative stage. Condenser enlargers are a different story of course.

photobackpacker · Jan 18, 2006

Bob, I think we are actually in agreement. I admit that the depth of focus is extremely shallow (small) when compared to the depth of field. While I am not an optical engineer - I have always believed this to be a function short projection distances involved (not unlike the shallow depth of field experienced in macro work.)

Ron Wisner wrote of the flat field lens which I found to be informative and enlightening.

The point where we seem to disagree is whether the depth of focus is actually significant enough to resolve for a lack of flatness in the film plane. It has been my experience that it is (given my equipment and processes.) If that has not been your experience, I would certainly not try to invalidate that. I, too, switched to glass carriers because I have a broader range of exposure choices since I am easily bored with long exposures.

Good discussion. It is always valuable to learn of others' experiences.

Best regards.

Neal · Jan 18, 2006

Dear Bob,

Thank you for correcting me. I read his post as a 250mm lens.

Neal Wydra

Smudger · Jan 18, 2006

Out of focus on one side..

It's an alignment issue no question. As to glass carriers, I have only had to resort to double glass with 6x9 cm or larger pano. format on 120 film,because of the thin film base. 6x7cm or smaller is fine with a single glass above the neg : lets face it ; thats the way the camera holds the film..
And that must be some 50mm lens if you are not getting vignetting of the image.

Bob Carnie · Jan 19, 2006

Smudger

I really like the idea of a single glass above the negative, I tried this in the past with mixed results.
As others point out I use mainly condenser enlarger with a oversize 250w bulb which does push out a fair amount of heat. I find that I can close down 2 stops and print 16x20 fibres at 15 seconds.
With split printing and complicated burn patterns a shorter print time is really nice with the hotter bulb.
If I could make a single glass work well in my enlargers I would switch to that method in a heartbeat.

Out of focus at the edges medium format enlarging

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Out of focus at the edges medium format enlarging

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