Advice on enlarger problem

[Casey Kidwell]

Hello all. I'm having an enlarger issue and was hoping for some help. I have a Beseler 67c XL. It's the head with the twist-lock vs crank. Basically I'm getting a shift in focus during longer exposures. I've ruled out enlarger shake because after inspection I had to refocus. I don't use a glass carrier but I have adhered film with drafting tape to reduce negative "pop". It's really not a hot lamphouse anyway. I could certainly be wrong but I think the focus assembly is shifting somehow. I've tightened down the tension but I think I'm missing something. Ultimately I would like a better enlarger but I just cant justify it right now. So I need to make this one work correctly. I'm hoping someone has run into this. Thanks

 

[Bob Carnie]

Your neg is most likely popping even if you are using tape, I only use glass carriers for this very reason.

 

[Mike Wilde]

Longer exposures as in as in how long. more than 20 seconds or more than two minutes. I think you know what I am getting at.

What sort of aperture are you printing at?

Is the lens you use matched to the negative format being projected?

Also what size of negs are you noticing this on? Just one, or multiple?

Is it just one type of film, or just one neg carrier, or all the ones you use in different formats?

Is the enlarger on its own baseboard, or is it bolted to the wall, with the baseboard separate, or a hybrid; ie on baseboard, but with top of column braced to the wall.

I'm not a Beselar expert; I sold my 23xl about 6 years ago. I seem to recall it used a bowed friction spring on the lens stage bellows to keep it from moving. Could it be possible that the spiring has broken or is not properly aligned to push on the pinion assembly to keep it in place after it is adjusted?

These are just ideas to get your own scientific method brain working.

 

[fschifano]

I had a similar problem with my Omega D4. After making sure that the head wasn't shifting, it turned out to be the fine focus adjustment. I tightened it down a bit and problem solved. Maybe there are some worn parts in the focusing mechanism. Looks like there's a rubber wheel against a metal shaft. These old rubber wheels get hard and slick with age, so that may be the problem. Look on page 7 of this document for an illustration.

 

[Casey Kidwell]

Mike, usually 30 second plus exposures are most notable. Or on a subsequent burn in. I generally print around F11. I've noticed this shift on 6x7 as well as 35mm with multiple lenses. This enlarger has a sloping single column support (large I-beam) on a base board. Different from the 23c and 4x5. Sorry, I can't find a picture of the albatross at the moment. The lens platform is geared with a fixed vertical row of plastic teeth and a cog on the fine focus knob. I'm looking for wear on the vertical row and trying to make it slip but if it is, it's so small I'm missing it.
Bob, I certainly shouldn't rule negative pop out. I'm trying to ignore that particular little voice right now because I can't find glass carriers and I'm not convinced the lamphouse is getting hot enough. Thanks everyone. Some great comments. It's so very nice to see such a vibrant community like the one here at APUG.

 

[Worker 11811]

I vote for the negative popping.

I have a hard time believing that only a minute's worth of radiant energy from a 75 watt incandescent lamp can cause a cast metal lens carriage to heat up enough to expand and shift focus.

Cinema projectors do exhibit this effect but we're talking about 2,000 watt (and sometimes up to 6,000 watt) xenon lamps which burn at an external temperature of several hundred degrees Celsius. Even in that case, it takes a few minutes for the focus to start shifting and the machine probably takes 10 minutes or more to reach equilibrium.

If you're seeing a focus drift in a few seconds or even up to a minute or more, I can't see where thermal expansion of the enlarger chassis could be the cause.

Put the your grain focuser on the easel and focus the image well. Leave the lamp on for whatever time it takes your focus to start drifting. I'll bet you can actually watch the negative popping through the grain focuser. To me, it looks like a wave of blurriness washing over the negative. It's a strange effect to watch until you get used to seeing it.

If thermal expansion was the cause it would take several minutes to go away. Once the metal heats up in a movie projector it takes 15 minutes or more for it to cool down again with the exhaust fan running full time. If heat was expanding your enlarger's chassis it would take a while for it to cool down, too.

Solution #1: Glass negative carrier.
There ain't no way that negative's going to move when it's sandwiched between two sheets of glass.

Solution #2: Preheat the negative before making your final exposure.
Get your exposure worked up the way you want. When it's time to make your final exposure let the film heat up and pop before you fine tune the focus one last time. When you're ready to make the print, use a piece of heavy cardboard to block the lens and make one "false" exposure to heat the film and force it to pop. Since you already popped the negative before you focused, it should pop INTO FOCUS. Quickly remove the cardboard and hit the button to start your clock. Since the film is already hot it should already be in focus, too.

I have an older Beseler 23C enlarger with the integral filter drawer cast into the lens carriage. I don't use those filters. I use the large gel filters that fit in the top slot, up above the condenser. So, what I did was cut a piece of sheet metal to fit into the lower filter holder. I use that to block the light when I want to make a false exposure to compensate for negative pop.

 

[Bob Carnie]

That little voice is correct , unless it is an obvious mechanical problem it is the neg popping.

Mike, usually 30 second plus exposures are most notable. Or on a subsequent burn in. I generally print around F11. I've noticed this shift on 6x7 as well as 35mm with multiple lenses. This enlarger has a sloping single column support (large I-beam) on a base board. Different from the 23c and 4x5. Sorry, I can't find a picture of the albatross at the moment. The lens platform is geared with a fixed vertical row of plastic teeth and a cog on the fine focus knob. I'm looking for wear on the vertical row and trying to make it slip but if it is, it's so small I'm missing it.
Bob, I certainly shouldn't rule negative pop out. I'm trying to ignore that particular little voice right now because I can't find glass carriers and I'm not convinced the lamphouse is getting hot enough. Thanks everyone. Some great comments. It's so very nice to see such a vibrant community like the one here at APUG.

 

[Casey Kidwell]

Thanks Worker. No, I'm sure the actual carriage isn't heating up. I thought the gear might be slipping on the plastic teeth. I just don't think the film is getting hot enough to pop. Especially when it's adhered by drafting tape. Good suggestion to leave the focuser under the lamp till focus goes out. Should have thought of that. I'll post up when I get a definitive culprit.

 

[Worker 11811]

It's kind of an old timer's trick used in the projection booth. You focus the image when the projector is hot. Then, when you start the next show, the image will come INTO focus as the machine heats up instead of the other way around.

I only transferred the trick from the cinema to the darkroom but I bet other people have thought of it before me.

It doesn't take much heat to make the film warp. The emulsion and base layers of the film act like a bi-metallic strip inside an old style "coil spring" type thermomenter. It doesn't take much movement of the bi-metallic spring to make a large movement of the needle.

One side of the film is made of finely divided particles of silver. The other is made of what is, for all intents and purposes, a piece of plastic. Plastic and metallic silver heat and expand/contract at different rates. The amount of movement involved might only be a fraction of a millimeter but that would be enough to throw the image out of focus.

Not saying that it has to be negatives popping but that is my first suspect and it's easy to test for.

Just focus when the film is hot and let it cool down. Without touching the focus knob, read the image with a grain focuser and watch to see if the image pops into focus when you turn the lamp on for half a minute or longer.

 

[MattKing]

A 67c is a pretty good enlarger - I used mine for almost 3 decades (bought it new) and still have it in storage, pending a bit larger darkroom space or a return to printing colour.

There is/was a heat absorbing filter available as an accessory for them - if negative popping is the culprit, you may want to investigate that.

Beseler sell a replacement elevation lock kit, in case that is the source of your problem.

As I recall it, the focus adjustment system is fairly robust. Certainly I never had any problem with it slipping.

If it isn't a problem with the negatives popping, I would concentrate on the elevation lock.

By the way, what size negatives are you enlarging from? If it is 35mm or smaller, you might check that the bellows is compressing easily.

 

[winger]

I've had negs pop in my 23C during a 25 second exposure. It only happened in the winter in my old darkroom and when I was split filtering.

 

[fotch]

The negative is very flexible and directly in the light (heat) path. The tape will only keep if from sliding around, it cannot support the middle of the negative. That is why it still pops.

An easy way to prove this is go to a glass dealer (hardware store?) and get a piece of picture frame glass cut to fit where the negative holder goes. Then put a scratch on the glass and fill the scratch in with a marker. Or, just draw a fine line in with the marker.

Focus it and see if it goes out of focus. If it does, then its a mechanical problem, if it does not, its negative pop.

I suppose you could get 2 sheets and sandwich your negative between them, if there is enough space as another way to prove this to yourself.

 

[Bob Carnie]

This is a pretty good idea

The negative is very flexible and directly in the light (heat) path. The tape will only keep if from sliding around, it cannot support the middle of the negative. That is why it still pops.

An easy way to prove this is go to a glass dealer (hardware store?) and get a piece of picture frame glass cut to fit where the negative holder goes. Then put a scratch on the glass and fill the scratch in with a marker. Or, just draw a fine line in with the marker.

Focus it and see if it goes out of focus. If it does, then its a mechanical problem, if it does not, its negative pop.

I suppose you could get 2 sheets and sandwich your negative between them, if there is enough space as another way to prove this to yourself.

 

[Casey Kidwell]

Fotch, great idea. I cut a piece of glass to fit the enlarger and made some marks with a fine point sharpy. Tested it for 30 seconds for several intervals. Then I cursed at it for another twenty and slapped it lightly a few times. Stayed in perfect focus.

I'm not finding a glass carrier for this enlarger. Guess I'll have to make one or buy the accessory heat shield and hope it works. Someone suggested pre-heating before I expose paper which should work fine but I would prefer a more permanent fix.

What drives me crazy is that my lamphouse just doesn't get very hot. The glass I placed in it for the test was heated up for a minute and was barely warm. And the 75 watt bulb and film are separated by 2-3 condensors and VC filter. Might be the humidity change. Thanks again everyone.

 

[richard ide]

If you can do it; try one piece of glass on top of your negative. The negative will be held very flat because of the direction of film curl.

 

[Worker 11811]

Although heat is the main cause for the effect it's not really the whole problem.
Differential expansion of dissimilar materials is the culprit, behind the scenes.

The cellulose triacetate base and the gelatin/silver emulsion expand and contract at different rates when heated or cooled. The uneven expansion of the two substances is what causes the warping.

I said above, the bi-metallic strip inside a coil spring type thermometer works on the same principle. A very small difference in the expansion of the dissimilar materials inside the thermometer can cause a large movement in the needle of the thermometer.

Reducing heat will reduce the problem. And, as explained, reducing heat even by a small amount can give a comparatively large reduction in film warping.

Heat absorbing glass will help. It did make a difference on my Beseler 23C.
Getting a better negative carrier can help. Getting a glass negative carrier is best.

 

[tlitody]

could be negative popping, especially if enlarger type is condensor with bulb vertically above film. The diffusion enlargers with bulb off at 90degs to film aren't so bad as you only get light from mirror and not direct heat.

But another potential problem is cause focussing up rather than down. i.e. if the focus movement moves the lens stage up as its last movement it can sometimes settle back down a little. Always try and make last focus movement down so there is no downward settlement of lens stage afet focus.

 

[MattKing]

I'm not aware of there being a glass carrier for the Beseler 67 series enlargers.

You mentioned that there was a VC filter above the condensors. Do you have the same focus shift problems if you print without a filter?

Is the head seating correctly on top of the negative carriers?

Does this happen if you don't tape your negative in?

 

[fotch]

Heat absorbing glass probaly will solve your problem, however, if humimidy is also playing a part, then you may consider a De-humidifier. One other fix would be to reduce wattage of the bulb.