Building an Enlarger

[htmlguru4242]

So, yesterday afternoon I was sitting around looking at an enlarger lens that I've had forever, and I realized that it might not be that difficult to assemble an enlarger from scratch.

I built probably about half of it with a friend last night.
There's a lamphouse, made of 1/4" plywood, coated on the inside with reflective tape (that foil vapor-barrier tape). The whole enclosure is about 6" square, (well, 5.5" * 6"), and 9 or 10 inches tall - we didn't measure. Underneath that is a piece of Plexiglas that we frosted. There's a 2" square open space in the middle; the rest has foil tape on the inside.

The lens is held (for now) by compression into a 1/4" thick poplar board; we're going to need a way to mount it.

Nothing is mounted together or in a usable form yet, but that'll be coming next weekend. We've tested it out by holding everything the right distance apart, and it works really well. No prints yet, b/c its hard to hold 3 different pieces still enough to make a good print.

I'll post some pictures of what we've done so far for those who are interested.

 

[ben-s]

Sounds good!
What sort of lamp are you going to use?

 

[Nick Zentena]

If you have a monorail laying around much of the job is already done.

 

[Jim Noel]

This sounds a lot like the one I built in the late 30's. The plans were in one of the popular photo magazines of the time. I used aluminum foil for reflectance in the lamp house and a film pack camera for the lens and focusing mechanism. I used it until I saved up my pennies to buy my first "Real" enlarger a couple of years later.

 

[htmlguru4242]

At the moment, the bulb is a regular-old frosted 60-watt (actually a GE reveal) with the black logo / wattage info scraped off of the front. Once everything gets put together, I'm sure that there's a better bulb to use, though this one seems to work OK. I'm not sure what it's going to do to VC paper, but we'll see.

We started with a little 25 watt "flood" lamp, and that didn't work too well. You could see it, but it was uselessly dim.

The output is still pretty dim, so I think that the box we're using is a little long; seems almost like most of the light is being lost somewhere along the way. Having a diffuser there doesn't help too much with the light intensity either. What I really need is a good piece of ground glass.

 

[megamahi]

Hello, I'm the friend whose helping on this little project. Some pictures i took quickly of the assembly (as of monday, 7 hours since start of construction). The 'design' was hastily scribbled down by htmlguru witting in my car in front of Lowes on Sunday. Some changes from the original plan, but for the better (we hope). The idea of the project is how cheaply this can be built and how quickly (we needed an enlarger for another project starting in 2-3 weeks). So far about 30$ in parts from Lowes and scrap stuff laying around the house, and 6-7 hours build time; though a second unit would take probably half that.

This is the mount, seems like it'll work fine. Its manually adjusted using some lathed out 1" PVC couplers that were cut with pipe clamps on them.

The head. The box is going to be cut in half probably, a outer box will be made to go around it so that they can slide up and down. The tape is Shuretape for ducts, a little denatured alcohol was used to remove the red shuretape logos from the foil.

 

[htmlguru4242]

Hola Mahi.

I think that a bellows on a monorail type thing would probably be better than sliding box, but we can work that out.



On a side note, does anyone know if the reveal bulb is going to cause issues with variable contrast paper?

 

[ic-racer]

Great project. What format will this be?

Even though I don't like fluorescent lamps, one could really create a fire hazard by pumping a lot of tungsten wattage into a home made enclosure.

Using a fluorescent lamp and controlling light with the lenscap or a red filter is not that bad. In fact, even with a computerized timing console with closed-loop filtration control, I occasionally need to use the lenscap for timing when I'm dealing with negative popping.

 

[htmlguru4242]

At the moment, it's being built with 35mm in mind. There's no reason why it couldn't be used for 120 as well. The design isn't going to accommodate anything larger, and I'm not sure what the lens can do, though that's pretty easy to test.

Good point about the bulb being a fire hazard. We were intending to vent it somehow, but I'm not 100% certain how much that'll help; those bulbs do get pretty hot after awhile. Even holes and a fan might not be enough.

Fluorescent is probably how we'll go. The only issue I can see with a CFL is the warm-up time. They can take a good minute or two to get up to normal brightness, even after a hot-restart. I could see this causing issues with timing the exposure, if we were to turn off the lamp during exposures as I like to do. We could always just use a shutter or a red filter over the lens, as I believe was mentioned.

 

[megamahi]

The bulb is a incandescent(EDIT: oops i put halogen) (60W, 120VAC) GE Reveal, not a florescent (unless I'm missing something). It does put out a decent amount of heat though theres enough room in the top of the bulb housing (about 2 inches from top of the lamp holder to the tops of the sides) to put a blower fan, switch, and IEC power connector, and even a small microcontrolled timer and relay.

Warm-up time is an issue with any bulb that has a ballast. I use a 35W HID for dry-film exposure for copper clad board (UV exposure) and it takes a good 3 minutes for me to consider it 'warm'.

For the screw-in CFL bulbs, to test if its fully warmed I use a IR photodiode and wait for the amount of IR to drop below a certain point. Those screw-in CFL bulbs in my kitchen wreak havoc on the IR receiver on the cd-changer/amplifier for the first 10 minutes from a cold start before it's low enough that the remote works so thats how I figured that out.

 

[David Grenet]

Nice trick with the photodiode megamahi - thanks!

If you're going to go to all that effort anyway, why not go down the LED head route. There have been posts in the past if you're interested and I have a few ideas of my own...

 

[ic-racer]

For the screw-in CFL bulbs, to test if its fully warmed I use a IR photodiode

Yes, good idea. I do something similar with my coldlight. :http://www.largeformatphotography.info/forum/attachment.php?attachmentid=10274&d=1203349768

 

[Zach in Israel]

If you are worried about temperature try getting a probe meat thermometer. You can get one at the kitchen store and they are pretty cheap. You just set it to beep if it gets too hot. You may just want to turn the bulb on and leave it on for an hour or so with the probe in, see what temp it hits.

 

[megamahi]

@David: I'll have to take a look at doing a LED head. I'll have to search a bit for more info on that. Not sure about how bright the LED head would have to be to work well. Any idea on the light output or spectrum output that would be needed? Any ideas are welcome.
@Zach: Easy enough, haven't done much work on it this week as my schedule is packed, though there should be some progress this weekend.

I was able to obtain a Beseler 23C with a 23dga, color meter, and other assorted goodies on Monday. I'm not saying that we have abandoned this project (we haven't), but I'm cleaning that up a bit and making notes as to what I see that can be easily implemented into this enlarger. Going along with David's idea, would building a LED head with many colored or RGB LEDs work for making a form of dichro head?

 

[htmlguru4242]

I believe CMY LEDs would be needed for a dichro head; not sure what RGB would do in that respect.


It's a great idea, though.

 

[David Grenet]

Actually you'd want it to be RGB. CMY works with having a continuous spectrum and filtering parts of it out. LEDs have only a narrow emmission spectrum and thus are more suited to the additive approach.

The Phillips Tri One enlargers used an additive system using tungsten bulbs and filters (VERY inefficient).

You can look at the spectral sensitivity curves for the paper you use (they're all fairly similar anyway) to determine the best wavelengths.

Sorry for the short, fragmented reply - will post more when I get home tonight or tomorrow morning...

 

[David Grenet]

Ok, see (there was a url link here which no longer exists) for a previous thread which discusses an LED head for multigrade paper (green/blue LEDs). Just add red

Personally I'm not sure I'd bother with a microcontroller - I'd probably try a linear variable current source first with a 10 turn potentiometer or similar and ammeters to provide a value.

 

[Steve Smith]

Personally I'm not sure I'd bother with a microcontroller - I'd probably try a linear variable current source first with a 10 turn potentiometer or similar and ammeters to provide a value.

I wouldn't use a microcontroller either. And instead of a linear current source I would use a variable duty cycle switching circuit working at around 1 - 10 KHz.


Steve.