Problem with printing from Medium format

[pge]

I wasn't sure if I should post this message under Medium Format or

under B & W Printing, but obviously I decided to post it here.

 

I am relatively new to Medium Format and less new to printing. I

have a Durst F60 enlarger which was set up for 35mm printing. I

purchase a medium format condensor lens (fesixcon 75) and a 75mm lens

so I could do Medium Format printing with my Durst.

 

I shot a test roll, all the same picture with the same exposure. I

made a contact sheet last night and it was definitely darker in the

center and lighter around the edges, you can actually see that it

fades out as the print gets closer to the edge of the paper. I am

getting more light near the center and less as you get further away

from the center.

 

This is no big deal with a contact sheet, it isn't that pronounced,

but clearly I need my enlarger to cast a consistent light over the

whole print area.

 

Am I doing something wrong, am I having an equipment problem, any

thoughts? Thanks for your help.

 

Phil

[john_banister1]

I think that there exist filters for wide angle large format camera

lenses designed for dealing with this same sort of problem. Perhaps

the problem is inherent in what the lens is trying to do, and using

a filter like one of those could fix it for you.

[david_goldfarb]

You should be getting even coverage. It's the job of the condensor lens(es) to do that, and you said that you are using the condensor set for medium format, so one possibility is that they are not installed properly.

 

Also, did you have a 6x6 or smaller negative carrier in place when you made your contact sheet? A condensor designed for use with 6x6 will normally only produce an even light distribution over the format it was designed for or smaller.

[andreas_carl]

If your enlarger is setup properly, there should be no problem whatsoever. For contact sheets, all you need to do is move the enlarger head higher (as if doing a bigger enlargment) to get more even illumination.

[sm. alec]

You may also want to check light distribution w/o any images on the paper, just expose for mid-gray and see what you get. Also, maybe stopping down (if you didn't already) as some lens' aren't so great wide open. Double check the light path for interference. Otherwise, it does sound like a condensor palcement/position issue.

[oskar_ojala]

To summarize, there are two things to check:

 

1. is the condensor aligned properly and the enlarger correctly installed?

 

2. is the lens stopped down properly (check the lens' manual for coverage details)?

[victor_lioce]

Check your owners manual and make sure you have the condensers in both the right order and right position. If, for example you have a single convex condenser lens with the flat surface down when it should, in fact, be flat surface up, it will change the pattern of the light distribution. Your owners or users manual will show how the condenser elements should be correctly placed inside the condenser housing.

 

-Victor

[steven_dowell]

On my Beseler 23c enlerger there is an adjustment knob that moves the condensor in relation to the lens. This is not the same as moving the entire unit up or down (for adjusting the size of your print).

You must move the condensor unit farther away from the lens (I think) when using medium format negs. This spreads the light out farther to cover the entire neg. If this is not done you'll get vignetting with lighter edges.

I don't know specifically about your Durst enlerger, but I think it's an adjustment issue.

Hope this helps,

Steve

[marck mcgill]

Hi Phil, I have a Durst F60. I will assume that the vignetting doesn't come from your camera, that is: your negative is PERFECT.<br><br>

First, project the light on the working table with no negative in the film holder and full opened diaphragm. Move the lamp of the enlarger up and down until the the square lighted area is as uniform as possible. You can move the lamp by grabbing the black cylinder that surrounds the hole in which the cable enters the head of the enlarger. It's just friction-mounted, so you can push and pull it freely up and down.<br><br>

 

Second, if you're using the Schneider-Kreuznach 75mm "Componar" lens that came as a standard companion to the Durst F60, remember that you must close it <b>AT LEAST</b> to f11 before printing to prevent vignetting and uneven focus over the projected area. Open it up to position the film and use a focusing aid only, but never print an image over f11.

[kparratt]

...or f8 with a Rodagon 80mm

[vatovec]

If You`re printing from negatives larger than 6x6 it may be that the lens doesn`t cover those or - does the problem arise in prints - in a contact sheet is possible tghat You haven`t raised enough the carrier/printhead?

[wyverndude]

As touched on in a few of these posts, my guess would be that perhaps if you are exposing the contact sheet <I>without</I> the negative carrier in place, you may be using an area outside of the intended illumination area.<P>If you do this with the 6X6 negative carrier (empty) in the enlarger, then it will mask down the illumination field to an area which the optics -if all are installed correctly- are designed to cover.

<P>

I always did contact sheets with the room light though.

[pge]

Thank you everyone for your suggestions, I have printed up your answers and I am heading for my darkroom, my basement bathroom.

 

My neg carrier was in place, and I am pretty sure that the condensor lens was correctly installed. The F60 is a pretty simple enlarger and if the condensor was upside down "Fesixcon 75" would be written upside down. I was using f8 which I thought was appropriate. Marck says that I must use f11 or smaller so I will definately be trying this.

 

I will double check the whole setup but I think it is correct. I don't doubt that raising the head would reduce the problem but it won't solve the problem once I get to the printing stage. It really isn't contact sheets that are the problem but I thought that making the contact sheet had identified a problem. Thanks again for your suggestions, I will look into them all.

 

Phil

[oskar_ojala]

Some Dursts (eg. the Laborators) that use several focal lengths have the other part of the condensor lens mounted upside down, so the way the text is doesn't necessarily tell anything (it might be ok, but it depends on the model - I'm not familiar with that one.)

 

Also, if the carrier is grossly misfocussed, you'll see a "vignette" effect on the light. Try to make an enlargment and set the aperture to f11 and see if the problem shows up there.

[marck mcgill]

No, the condenser is well mounted if the writing looks right. Just to make sure, check if the flat side of the lens is pointing down, almost touching the film holder. That's how it should be.

 

Yes, it could be that the enlarger was WAY out of focus. That would produce some vignetting. You should at least focus the film holder, when contact-printing...