Prints partially underexposed

glbeas

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I've also seen this happen when a filter holder was not set square in the enlarger. Under the lens holders are the worst about this but an internal holder can be the problem just as easily.
 

glbeas

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Another thing to check is whether the factory bulb has a shorter neck than the replacement. This changing the distance to the condensor can have serious effects on the illumination.
 

RalphLambrecht

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You did not answer the question yet if this was from day one or a recent occurrence.
 
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mindcircus

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You did not answer the question yet if this was from day one or a recent occurrence.
Click to expand...

I noticed the problem last week when I made some large prints (30cm x 40cm) and saw it on my smaller prints too that made later. But after that day I've printed a couple of photos that are uniformly exposed. That is, it happens from time to time. This means that either the problem appeared last week or I put the negatives in different position on the carrier (which is for 6x6 negatives).

There is one more parameter that I forgot to mention earlier (sorry about that)... When bought the enlarger had a Belar lens on it. Recently I bought an El Nikkor lens, but I don't remember if I made any prints with it to test it. I don't know if it's important or not, but it shouldn't be.

You should better wait for 3 hours (when the sun will set here, so I can use my darkroom). I'll make some experiments on changing the lens, the bulb and the position of the negative to see what happens. I'll come back then to give you some more clues.
 
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mindcircus

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The experiment:
I tried three different lenses, the El Nikkor 50mm, the Bellar 50mm and a Rokkor 80mm. I put no negative in the carrier, though the lenses were focused.

The results:
All the lenses have the same problem, though in my 80mm it is not so much obvious.

As I've mentioned before I've changed the bulb I had initially with a different one, but the problem remains.

So, what do you think? What do I do next?

Edit: I thought that 80mm lens doesn't have this problem, but I had exposed the paper more and had become black. Sorry for those who read the thread before the edit
 
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mindcircus

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Ok, I'll do that

Thanks everyone for your time and your interest
 

Nicholas Lindan

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Too see if it is uneven illumination in the household bulb you might try turning the bulb 90 degrees and seeing if it is now the top/bottom that shows the exposure discrepancy. Changing the bulb may not show a difference: bulbs are produced on automated machinery and it is likely if one bulb has a misplaced filament all the bulbs from that machine will have exactly the same error in filament placement.

Enlarger bulbs really are special and although you can get a household bulb to work in a pinch it is as likely to result in headaches as prints.
 
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mindcircus

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I can't rotate the bulb because its base is fixed... I've changed it with one that has different shape/size and was made by a different manufacturer, so it could have worked...

Anyway, I'll find an enlarger bulb. It's easier this way. Guessing what would happen if I had one doesn't really help...
 

RalphLambrecht

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I think Nicholas meant to unscrew it for half a turn, unless it makes an iffy electrical contact that way.
 
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mindcircus

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By unscrewing it 90 degrees (even if it still has electrical contact) I will put the bulb about 1-2mm closer to the condenser. I don't think that that would make any difference. The second bulb I used was about 1cm longer than the first one, but the problem remains.
 

glbeas

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Have you checked the condensor set to verify that it is mounted in its place properly and not set askew? I can remember some cheap enlargers I've owned that had a lot of room to move the parts around.
 
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mindcircus

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It seems to be in the right position. Actually there are no options about its position, neither on the horizontal axis nor on the vertical.

The horizontal isn't a problem. Having printed the whole 6x6 negative carrier (which is square obviously), there is more light intensity in the center and less in the sides (symmetrically) . There is no misalignment between the bulb and the condenser.

On the vertical axis, the only parameter I can change is the bulb size.
 
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Nicholas Lindan

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mindcircus said:
there is more light intensity in the center and less in the sides (symmetrically)
Click to expand...

I'm a bit confused here: In the first post you said the problem was on the right side...

If the problem is symmetric about the center then the problem is not using the proper enlarger lamp.
 

Ian Grant

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That quite typical; of what happens when you use a household bulb, and exactly what happened when I used one in my Durst.

Ian
 
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mindcircus

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First of all, for those who aren't aware of it, Meota Opemus 6 was made for 6x6 film format. It has a 6x6 negative carrier and a condenser that covers the 6x6 negative. That means that if you put a 35mm film there is no problem, but you will project an area of 24x36mm on your papers instead of a 6x6 area.

I'm a bit confused here: In the first post you said the problem was on the right side...
Click to expand...

I began the thread when I saw that some of my photos did not get evenly exposed to light. I had put 35mm negatives (on the 6x6 negative carrier) and noticed that the right side sometimes does not get the same amount of light.

A couple of days later, I projected the whole 6x6 negative carrier on my papers, not just one part of it that covers a 35mm negative. I know that a 50mm lens doesn't cover the whole 6x6 area, so I tried a 80mm lens too.

What I wanted to make sure in the last test, was whether the 6x6 was lit evenly or not.

So why I had problem only on the right side? It's just a matter of lack. If I had put the 35mm negative in a different position on the negative carrier I would have problem on the left side or at the bottom or at the top (of my photo)...

I hope you get my point.

If the problem is symmetric about the center then the problem is not using the proper enlarger lamp.
Click to expand...

Why symmetry can't be caused by the enlarger bulb? If the household bulbs transmit more light at the center of the condenser than at its sides, it will give me more light at the center of the 6x6 negative carrier. This may have been caused either by the size or by the shape of the bulb. It's not probable that coating plays any role here...

Enlargers are very simple in their construction. I've opened it many times this week and I wonder what else can be wrong... It has a bulb, the filter carrier (that has a diffusive glass), the condenser, the negative carrier, the folders and the lens. Which of these may be defective or have gone out of adjustment? I remind you that condenser and bulb have a fixed position...

That's why I'm almost sure that it's the bulb that causes the problem. But I can't be totally sure about it until I find one and try it.
 
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R gould

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Just to clarify something you say that you lay the 35mm negative on the 6x6 carrier,do you have the 35mm meopta insert?, I did once experiment with printing a 35mm neg without the proper insert, just for fun, laying the 35mm neg across the 6x6 frame, without a 6x6 insert and the lighting across the frame was very uneven, using the correct inserts and no problem,using a meopta 6, my standard enlarger,also, try btaking out the glass diffuser from the filter draw, that can cause uneveness with a meopta,Richard
 

smieglitz

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Gary has already mentioned that the problem could be an under-the-lens filter holder. This is very common. So common in fact that I've removed all such holders from the enlargers in the community darkroom at the college where I work. Do you use such a filter holder? If so, check to see if any of the projected light is being intercepted.

If you are going to buy a new enlarger bulb, I would purchase at least one spare. Isn't there a European Union mandate to eliminate incandescent bulbs in the near future?
 
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mindcircus

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No I don't use any 35mm insert... In fact I've never heard of it. But the problem stil remains if I want to print a 6x6 negative, so I don't think this is a solution. You are right, I won't have unevenness on the 35mm films, because in the center it seems to have an area evenly lit, but it still doesn't sound as a solution.
I'll try to take off the filter holder, but without this diffusion I will probably make things worse.


No, Opemus 6 has a filter carrier above the condenser. There is nothing beneath the lens.

If you are going to buy a new enlarger bulb, I would purchase at least one spare. Isn't there a European Union mandate to eliminate incandescent bulbs in the near future?
Click to expand...

Yes I was thinking of it, but it probably refers to household bulbs. If not I should buy about 100 bulbs in case my grandchildren decide to shoot with film
 

Nicholas Lindan

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mindcircus said:
If the household bulbs transmit more light at the center of the condenser than at its sides .... It's not probable that coating plays any role here...
Click to expand...

It is the coating that is the key.

A standard bulb is 'frosted', and there is a bright spot at the center because the frosting lets most of the light through in a sort-of-straight path and only deflects a small part of the illumination at large angles.

An enlarging lamp uses 'opal' glass (or sometimes opal paint). The bulb shows no bright spot in the middle but is instead uniformly bright at the center and at the edges. Opal glass is made by suspending a pigment, usually Titanium Dioxide, in the glass or coating. None of the light can take a straight path from the filament to your eye without being bounced around by zillions of little particles of TiO2.

The condensers can be seen as imaging the bulb onto the back of the lens (not strictly true, as they are made to image a very fuzzy image of the bulb). The light exits the condensers in a cone, passing through the negative, and on to the lens. An enlarging bulb, being uniformly bright illuminates all parts of the negative equally. A household bulb illuminates the corners and edges poorly as they are lit from the light at the edge of the bulb.

There are enlargers that move the position of the negative in the cone of light to illuminate various negative sizes. The distance from the condensers to the back of the lens is held (somewhat) constant and the position of the negative carrier in the light cone is adjusted for different negative sizes.
 

R gould

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I use a meopta opemus 6 enlargter and have done so for some time,and the negative carriers in these require a metal insert in them for each format used, I print 6x6,645 and 35mm, with a condenser head, I suggest that you get an insert for your 35mm, and take out the diffuser from your filter draw,Try and get a enlarger bulb,and then try, The inserts should be fairly easy to obtain, at least in the uk they are.Without the correct inserts your negatives will not be held correctly in the negative carrier, and that alone, with the diffuser, in my experiance, can cause problems with the enlarger, they are very good and strong enlargers and give very little problems as long as you set them up properly, I have had nor problems.Richard
 

R gould

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Another thought, have you made sure that the enlarger is correctly allinged,? if the enlarger is even slightly out then then one side is higher than the other, one side of the paper gets a little more exposure than the other, check that the lamphouse is level with a spritlevel, I once altered the allingnment of the lamphouse and had similer problems to you, Check these things out and try again,Richard
 

MartinP

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In many markets (possibly not the UK?) the standard negative carrier for the Meopta Opemus 6 is a double-glass 6x6 holder, with anti-newton glass on the top.

There are posts which move slightly in order to position the back edge of 135 or 120 film such that the centre of the neg is in the centre of the neg carrier. There are also adjustable masking strips under the carrier to block out unwanted light. The film is held very nicely flat by this device, with only the usual dust problems from the four extra surfaces to worry about.

It sounds as though the original poster has this sort of multi-format negative carrier. As many people have suggested, the lighting problem is most likely due to the bulb, unless there is a dead moth between the two condensers of course ! (Had to get the bug joke in there somewhere....).
 
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mindcircus

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MartinP said:
As many people have suggested, the lighting problem is most likely due to the bulb, unless there is a dead moth between the two condensers of course ! (Had to get the bug joke in there somewhere....).
Click to expand...

Ha Ha! I wouldn't be surprised even if there was an elephant inside my enlarger!

Anyway, I've tried an enlarger bulb, but that was not the problem... Sorry guys

MartinP said:
In many markets (possibly not the UK?) the standard negative carrier for the Meopta Opemus 6 is a double-glass 6x6 holder, with anti-newton glass on the top.
Click to expand...

Yes, I have the double-glass 6x6 negative holder, that's why I was confused when I heard about 35mm negative carriers.

It seems that putting the negatives in the center of the negative carrier solves partly the problem, but it's not very easy to find exactly the center. A slight transposition gives another wasted paper.

I tried to remove the diffusion glass, but things got worse. Then I removed both the condenser and the diffusion glass and I saw that the bulb was projected on my paper (I had a white circle surrounded by a black square). When I put the diffusion glass (without the condenser) I saw that the light was quite uniform, but the difference between the center and the sides was noticeable. Putting again the condenser I noticed that what it really does, is to project the center of the diffusion glass enlarged. So I guess that if the diffusion glass isn't uniformly lit, the negative carrier will not be either.

RalphLambrecht, I didn't give the necessary importance to your suggestion about more diffusion. Sorry about that. As far as I can see that's the solution. I think the best position to put it is beneath the bulb, but now I have to find a proper material...

"Frosted plastic foil"? Sorry, but as you can see English is not my native language and I am not sure if I know what this is...

I wonder if a piece of frosted glass would help. Anything I put must be heat resistance, because I've put a 150watt bulb.

Your ideas are welcome again
 
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