Bellows Design for 8x10 enlarger.

Kshaub103 · Oct 2, 2017

Im working on converting a Durst 138 to 8x10 enlarger. I have a few question about bellows design and want to see if anyone had suggestion. Main question is how to calculator the size of bellow opening / exit needed for 8x10. Was trying to see if the tapered bellow that came installed would be sufficient or will some of image be cut off due to size of the bellows.

John Koehrer · Oct 2, 2017

The negative/top opening?

Kshaub103 · Oct 2, 2017

Yes, Throw to the len stage.

ic-racer · Oct 2, 2017

http://www.largeformatphotography.i...-5x7-to-8x10&p=1280623&viewfull=1#post1280623

Kshaub103 · Oct 2, 2017

Yes I saw this enlarger is weekend converted by Michael Mutmansky. It is a very nice design. My question is about bellow design the opening and the exit size required not to interfere with the projected image. I’m planing on basically some of my design off johns enlarger but with a few modifications.

ic-racer · Oct 3, 2017

I believe the bellows on John's enlarger is the original 138 bellows. From what I recall he did not use a 300mm lens. Maybe 240mm.

Kshaub103 · Oct 4, 2017

No he uses a 300mm lens with his set up

John Koehrer · Oct 4, 2017

A bit of trial & error using construction paper as basic pattern might be of help.

ic-racer · Oct 4, 2017

Kshaub103 said:
No he uses a 300mm lens with his set up

Yes, it has been many years since I have seen his enlarger. Did I read your prior post correctly, you saw his enlarger just last week?

Here is a post he made a few years ago:

I use a 300mm Rodagon and only enlarge to 20x24 though there is room to go much larger either by lowering the table or switching to the 240mm Rodagon. I havent wanted to wrestle with larger paper in a high sink with a 7' 2" ceiling. The floor awaits that effort, but I am making 7x17 contact prints instead now.

Kshaub103 · Oct 5, 2017

Yes I did get to meet john and see his enlarger last week. Im not just trying to build the same enlarger. I would like to be able use it for 8x10 and smaller formats as well. Also the ability to use the built in masking blades. My Question is how to calculate bellow for different formats (size need), i am looking at ordering custom bellows and don't know where to start. I was told by another member that "The requirements for bellows is simple. Light from any of the four corners of the format must travel in straight lines to any exposed part of the rearmost glass surface." im not sure I understand. How do i calculate the amount of bellow drawl need for different format prints. Sorry if I'm not making this as clear as it should be. the drawling might help explain what I'm trying to articulate.

John Koehrer · Oct 5, 2017

I believe it's going to depend on fl.
since you have the 138, just measure the draw you need to focus the respective format. Glenview may be able to give you a hand
with information.
I've attached some information from his site mentioning sizing problems with custom bellows made to the correct size. Hope this helps out.

Durst L184 bellows. You can buy bellows made to approximate size, but no one will make them ready to install today. Installation is tedious. It helps to have them sized perfectly with required holes precut. Durst bellows are held onto the enlarger with metal strips with holes in them. Screws go through the metal strips, the bellows, and into threaded holes in the enlarger. These bellows are a perfect size and in perfect alignment. Any other bellows you buy probably will not be. I have had many bellows made for Durst enlargers. Some were so poorly made that they would not work. These are used bellows off of an 8X10 Durst L184. They will fit any 8X10 Veritcal Durst enlarger I have dealt with. They had a few holes that I patched with bellows material according to instructions given to me by Jack Deardorff. The repairs are not visible from the outside and barely visible from the inside. $400

ic-racer · Oct 6, 2017

The simple lens formula should get you in the ballpark with your measurements:

1/p + 1/q = 1/f
p = lens to negative
q = lens to paper
f = focal length lens

In general, your problem of using short focal length lenses for small formats might not be the bellows, as even a very long bellows will collapse very small. The issue will probably be that the bellows can't fold in on itself. You might think about a recessed lensboard. I know the 8x10 enlargers used the HOTUB and the LARATUB. I'm not sure if either of those fit the 138. I can measure my HOTUB and LARATUB if you like.
Use caution, as with any home-made thing, bad things can happen. That is, the HOTUB could allow the back of the enlarging lens to contact and break the glass negative carrier.

Kshaub103 · Oct 6, 2017

Yes here is the formula. Thanks ic. Sorry for all the confusion. But yes bad things can happen hopefully they won’t. This formala with help me in the design so I can work those types of problem out before the construction. Tho I’m sure there will be changes as I continue the conversion. Measurements of the recessed lens boards would be of interest.

DREW WILEY · Oct 6, 2017

No need for a new bellows. You just need a box-shaped spacer between the original bellows top mount and your new 8X10 negative carrier position - basically a cube about a foot in each dimension. Test for fit by making a foamcore board prototype first. I've done this, and can easily make 20X24 prints from 8X10 using a 305 lens and a 12X12 cold light.

Kshaub103 · Oct 6, 2017

I have seen these types of modifications but I’m not sure that is the best way especially since I want to use the enlarger for multi formats. Tho I was thinking if I where to go with the spacer I will design two negative stages one for 8x10 other for 5x7 and smaller. Foamcore will be good for test purpose thanks for that suggestion. I’m just trying to work the detail out on paper because I was told that you measure twice and cut once.

DREW WILEY · Oct 6, 2017

Yeah, trying to print small negatives with a modified unit will be tricky, though you could resort to longer than normal lenses relative to these formats. If you do need a special bellows, I strongly recommend Custom Bellows in the UK.

ic-racer · Oct 6, 2017

Just to elaborate on the HOTUB and LARATUB. One is for L184 and the other is for L1840. The difference is that they are each of the exact proper depth to focus a 50mm lens for a wall projection, but won't allow the back of the lens to hit the negative carrier when the bellows is fully collapsed. If your enlarger does not have the fixed turret, these recessed lensboards for the 8x10 enlargers will fit your enlarger. One of those might be just enough depth inside your bellows to allow you to focus a short lens and only have the single negative stage.

DREW WILEY · Oct 11, 2017

Any bellows long enough for 8X10 film is not likely to scrunch up enough for short lenses typically used for small film formats anyway. A recessed system for these is probably going to be mandatory. But they're fairly easy to find for Durst.

kosuke · Mar 18, 2024

hello does anyone know the maximum length of the bellows of durst 2506 10x10 enlarger ?

thank you

ic-racer · Mar 18, 2024

The bellows on a 10x10 Durst L1840 extends to about 685mm. I suspect the 2506 would be similar.

kosuke · Apr 5, 2024

Than you so much ic-racer !

Bellows Design for 8x10 enlarger.

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