dealing with negative popping

[cliveh]

I have never had a problem with popping, because my enlarger is never on long enough due to the fact that I don't faff around.

 

[DREW WILEY]

That's the advantage you have specializing in 35mm contact prints!

 

[M Carter]

It can be a big issue for lith prints with exposure times in the minutes.

I just drilled the film-holding pins out of a 6x7 carrier and taped a piece of glass to it; then I tape the neg down flat to the glass with litho tape. Between that and the heat absorber, I haven't had problems, and haven't used a top glass. But I can get kinda ghetto...

 

[Loren Sattler]

Excessive curl with Kodak 35mm film?

I recently bought a Zeiss Focomat 1C for 35mm work. What a beautiful piece of equipment. In addition to the autofocus feature (which is a big time saver) the Focomat's condenser lays on top of the 35mm negative to flatten it out similar to a glass negative carrier (with top glass only). What an improvement over the 35mm film holder used in my Beseler 23C enlarger!

This is especially helpful with Tri-x film which I believe curls more than other films. After a few months in a Print File negative sleeve the curl is gone, but I usually want to print shorty after developing negatives. Do other people find a lot of curl with Kodak 35mm film? I do not find Kodak's 120 film curling nearly as much as the 35mm.

 

[BetterSense]

I find kodak has more longitudinal curl than ilford et.al. and it seemed more when I was running tri-x than with TMY which seems flatter.

Oddly, tye longitudinal curl seemed to help with the popping issue...

 

[Neil Grant]

Unsupported areas of film a never going to lie perfectly flat - but some will sag more than others. A bit of heat from the lamp may encourage them to go flatter or even 'pop' towards the lens. I usually focus after the neg has warmed up had a chance to stabilise. I prefer a slightly 'long' lens for each format - which increases depth-of-focus. Sounds like the OP needs a bit more than fine-tuning though.

 

[BetterSense]

At the same magnification, and same exposure time, lens focal length does not impact depth of field or depth of focus. The only way a longer lens will increase your DOF is if you stop down and use a longer exposure time with the long lens, and stopping down the shorter lens to the same exposure time would have the same effect.

 

[Neil Grant]

At the same magnification, and same exposure time, lens focal length does not impact depth of field or depth of focus. The only way a longer lens will increase your DOF is if you stop down and use a longer exposure time with the long lens, and stopping down the shorter lens to the same exposure time would have the same effect.

Are you sure? I've just run a quick test using a 35mm neg and two lenses: 60 and 90 mm. With the 90mm a 7 in wide print corresponds to a 11.5 cm bellows extension measured from front of standard to film plane (sorry about the mixed units). Using the 60mm instead for the same print width needs a bellows extension of only 9.5 cm measured similarly. So I think for depth of focus to be the same the bellows extension would need to be the same too. Whats wrong with my thinking?

 

[AgX]

DOF is only dependant on image scale.

 

[MattKing]

At the same magnification, and same exposure time, lens focal length does not impact depth of field or depth of focus. The only way a longer lens will increase your DOF is if you stop down and use a longer exposure time with the long lens, and stopping down the shorter lens to the same exposure time would have the same effect.

DOF is only dependant on image scale.

What they say.

f/stop and magnification are the determinants. Using the two different lenses with two different extensions of the bellows just gives you two different ways to get to the same magnification.

One lens may behave better than the other at that magnification and f/stop. And the working distance (lens to easel) may be better for one than the other. But depth of field (and light intensity) will be the same if the f/stop and the magnification are the same.

 

[DREW WILEY]

I leave popping to snack stands in movie theaters, which I also wisely avoid.

 

[Neil Grant]

What they say.

f/stop and magnification are the determinants. Using the two different lenses with two different extensions of the bellows just gives you two different ways to get to the same magnification.

One lens may behave better than the other at that magnification and f/stop. And the working distance (lens to easel) may be better for one than the other. But depth of field (and light intensity) will be the same if the f/stop and the magnification are the same.

I think depth of focus will only be the same if the 'cones of light' from the 'neg side' of the lens are the same angle. If a neg is further from the lens, then the light reaching it is more parallel. I think this means a small change in neg postion means less difference to focus.

 

[MattKing]

Depth of focus has nothing to do with the focusing mechanism. It is a measure of how the optical system performs - think circles of confusion.

 

[Neil Grant]

Depth of focus has nothing to do with the focusing mechanism. It is a measure of how the optical system performs - think circles of confusion.

Yes, optical paths and the angles sub tended at film planes. Shallower with a longer lens and a given print size.

 

[mr rusty]

No substitute for a glass carrier

Unless you have a cold light source, in which case negative popping doesn't exist and glassless carriers rule.

 

[DREW WILEY]

I do have a cold light on one of my enlargers, and I would never ever ever go glassless even with that, or else I would never ever have a
truly sharp print, sharp edge to edge. But paper itself can pop, so to round out this discussion, one should include vacuum easels in certain
situations. Often, however, the tendency of fiber-based paper is to maintain some of its curl down away from the emulsion, where it is less
flagrant. Still... just depends on how nitpicky your standards are, how big you print, and how long your exposures are. Paper can be expensive, so I'd rather not gamble.

 

[BetterSense]

I found an LED that appears it will work with my enlarger and contrast filters. It's only 4 Watts, so it never gets detecably warm, and is probably doubly safe against negative popping because it's not putting out the majority of heat as IR. This seems even better than a cold light because my experience with cold lights is they require warm-up for consistent light, and don't work perfectly with contrast filters either.

(there was a url link here which no longer exists)

 

[AgX]

But paper itself can pop, so to round out this discussion, one should include vacuum easels in certain
situations.

A makeshift solution would be doublesided adhesive tape.

 

[DREW WILEY]

Gotta be careful with that idea. What you'd want is the 3M tape that is high tack only on one side, but repositionable "Post-It" adhesive on the other. If you grab just any double-sided tape, your print will probably get ripped up somewhat. I don't recall the product number at the moment, but do use it for my adhesive filmholders. Gudy probably makes something equivalent in the EU.

 

[MartinP]

That sounds like an interesting and useful product. An alternative could be sticking down a few pieces of post-it note, probably around the centre of the easel, using easily available double-sided tape.

 

[AgX]

Gotta be careful with that idea. What you'd want is the 3M tape that is high tack only on one side, but repositionable "Post-It" adhesive on the other. If you grab just any double-sided tape, your print will probably get ripped up somewhat. I don't recall the product number at the moment, but do use it for my adhesive filmholders. Gudy probably makes something equivalent in the EU.

Basically you are right. There are tapes of different tack. (There was/is a low tack glue-stick.) And backs of papers have different surfaces too.
One has to try.
There also was a easel that had stick tape.