Converting 5x7 enlarger to 8x10 enlarger

[ianrout]

Hi,

Some months ago I invested in a 8x10 camera, polaroid processor etc etc. Love it and have taken and processed various BW images, unfortunately the only 8x10 enlarger is about 1300km away.
Have sources a 5x7 enlarger and the plan is to convert. This all looks possible, using some well crafted housing to hold an LED light source (yes have looked all over internet to research), some good quality glass (no Newton rings) for holding the negs.

My question to the world is - how high should the 2 elements be, first being from existing 5x7 enlarger to where my negs will be held. The 2nd is how far should the LED source be from the negs?
Currently looking at a 240mm or 300mm lens, not sure if this will make a difference.

Thanks for any help!

Ian
Australia

 

[Dr Croubie]

1300km away, where's that?
Meanwhile, Welcome aboard!

I've also started designing (in my head, so far), a way to convert my 8x10 camera into a diffusion enlarger.
Is yours a diffusor or condenser?

First thing that I can answer, at least for diffusion, is that there's no real set distance for the light to film (as unhelpful as it is to say).
As long as:
a) it's far enough away to not heat the film too much (less of a problem with LEDs),
b) it's far enough away to make the light even enough (using a single-bulb in any flavour will make for unevenness, my plan is to use a few hundred LEDs on an 8x10" PCB, much more expensive but more even), and
c) it's close enough that exposure times are in seconds rather than hours.

 

[ianrout]

I live in Adelaide, the only other 8x10 enlarger I know of is in Sydney….
Thanks!

My design much the same as your, with some rough sketches. Will be a diffusor, think only option I have at the moment.

I'm not too worried about setting the light source distance, I know too far will effect exposure times, but from what I've read this isn't a huge issue. There's a place that makes LED light panels which I think will be perfect.
The main question is the 8x10 housing, which I'm making - how far the lens needs to be from negatives - i guess minimum. The 5x7 enlarger has bellows which extend. So my frankan-enlarger will basically be 2 boxes same size, one holding the negs (this is the part not sure how high needs to be) 2nd will go onto holding the LED. It might look ugly but the idea is to keep simple, light tight.

Cheers
Ian

 

[Dr Croubie]

There's one 8x10 enlarger I know of, although i haven't seen it. I was at The Analogue Lab visiting one night, they've got a 5x7 enlarger. Some guy came past and was talking about setting up his own lab somewhere near Hutt St, including an 8x10 enlarger. Didn't get his name though, maybe William (Polyglot here) or Alex can remember?

Distance lens to film is easy, especially as most enlarging lenses are near enough to symmetrical. A 300mm lens focussed at infinity will be 300mm from the film. At 1:1 repro it'll be 600mm from the film. For a 240mm lens that's 240mm at infinity, 480mm for 1:1. For enlarging, you'd want to be somewhere between those two, I'd say at least 250-500mm is a good range of movements. If you plan to enlarger 5x7s, 617s, 4x5s or smaller, with shorter lenses, then you should think about going closer again.

 

[DREW WILEY]

You need to be a lot more specific about which 5x7 enlarger you wish to start with, how high your ceiling is, how big the prints you wish to
make will be. I've successfully done it with a Durst 5x7, adding a 12X12 inch cold light, which is analogous to an LED panel in terms of fit.
The devil is in the details, including how you arrange the diffuser. I woudn't recommend anything shorter than a 300mm lens, though many
people do go down to 240 if they don't have enough headroom for a tall enlarger. It's easy to do up to 20x24 prints with a 300 mm lens with
only a standard 8 ft ceiling. Anything bigger won't work. But not all 5x7 chassis will accept a bigger easel anyway, unless you print horizontal.

 

[Mark Crabtree]

I converted a 4x5 Durst to 5x7 and started by running the numbers for bellows extension from the neg (that will include the extension box you make as part of the conversion), plus the the enlarger height vs focal length of lens choices. These are all standard formulas for varies magnifications. That should give you the dimensions you need. You do also need to look at the opening at the existing lens stage to make sure you don't block part the of the image - pretty easy to do that visually.

The shorter lens will probably end up being more practical.

 

[Old-N-Feeble]

Take this with a grain of salt: Many years ago I printed for professional labs. I was very concerned about center-to-corner image quality. Given a very high quality lens design , (in most cases) I deduced that ten percent shorter than normal focal length for the format was fine at 2x magnification but at 4x a normal focal length lens was needed for best quality. Beyond 4x (up to mural size) I preferred twenty percent longer-than-normal focal length for format, e.g., 180mm for 4x5 inch and 360mm for 8x10 inch (again, in most cases). None of the business owners cared enough to buy the proper optics for extreme enlargements but at least the longer focal lengths kept the corners nearly as sharp as the centers.

The smaller the print and larger the neg and longer the lens' focal length... the longer you'll need the bellows. Distance from light source to film isn't very important provided the film is kept cool enough and diffusion is sufficient.

 

[ic-racer]

Take this with a grain of salt: ...

Actually very good information. My experience also.

 

[ic-racer]

jp80874 APUG member has a converted 5x7 Durst for 8x10. He may chime in here. You can see his enlarger on his APUG page.
I believe the L138 has about 500mm of bellows.
You want the diffusion plate for the light source pretty close to the negative.

Realize that any point in the center of the negative gets light both from directly below the diffuser and light coming in from an angle from points all around (North , South, East, West). The edges of the negative will have less light falling on them unless the diffuser overlaps to some extent. This depends on how much angular light radiates from the diffuser and the distance of the diffuser to the negative. Trial and error will be of benefit in the design stages.

jp80874 has a 12" x12" Aristo head on the conversion.

My 8x10 Durst was not originally designed with the aftermarket cold-light source real close to the negative and it had a 14" x 14" Aristo head.

 

[DREW WILEY]

There were two outfits here in the US who routinely made 8x10 heads to fit the Durst 138 5x7 Chassis. There was plenty of wiggle room to
properly center the lens axis. The 8x10 cold light conversion for Beseler was a lot less glamorous, but some people found its limited capacity useful nonetheless. You always want cold light distinctly oversized for the sake of eveness of illumination, because the bends in the coils tend
to be less bright or predictable, even when substantial diffusion is involved. With an LED panel it's relative to the efficiency of the design.
Anyone remember Salthill, when they distributed the light using fiber-optic bundles?

 

[ianrout]

I hear they had one, rang them though and they said only unto 5x7, that was some months ago. I also heard there was an 8x10 kicking around at Kevin O'Daly's old studio, but its been sold. Have been trying all and any options...

The tech-specs, that's really helpful. Thanks!!

Other posts too - thanks for all the feedback and thoughts. Will be some trial and error.
Lens focal length has been noted too. Hopefully I can get this beast up and running.

There's one 8x10 enlarger I know of, although i haven't seen it. I was at The Analogue Lab visiting one night, they've got a 5x7 enlarger. Some guy came past and was talking about setting up his own lab somewhere near Hutt St, including an 8x10 enlarger. Didn't get his name though, maybe William (Polyglot here) or Alex can remember?

Distance lens to film is easy, especially as most enlarging lenses are near enough to symmetrical. A 300mm lens focussed at infinity will be 300mm from the film. At 1:1 repro it'll be 600mm from the film. For a 240mm lens that's 240mm at infinity, 480mm for 1:1. For enlarging, you'd want to be somewhere between those two, I'd say at least 250-500mm is a good range of movements. If you plan to enlarger 5x7s, 617s, 4x5s or smaller, with shorter lenses, then you should think about going closer again.