Enlarger sizing

[peter brooks]

I'm going to build a 5x7 enlarger but I also want to print 5x4, 120, and possibly even 35mm.

I have seen posts about using a LF camera in reverse as an enlarger (with a light source behind the neg).

Light bulb moment... Does this mean I can get any 'neg to lens' and 'neg to bed' dimensions required by simply putting the relevant enlarger lens on a camera, using an appropriate film size mask on the ground glass, and paper size outlines stuck to a wall?

That would be great - but maybe there is some other arcane magic at work with an enlarger?

Thanks,
Peter

[Tin Can]

More less, it is a simple thing

Then people get nuts

Just start and try something with 4X5

Use 135 or 150mm lens, any lens

The trick is getting everything aligned

Lamp Light, Neg, Lens, Paper

Draw it first and use cones aka triangles

[peter brooks]

Thanks Randy. The camera thing is just to get the relevant design parameters for the different formats.

I've already got a 210mm enlarger lens (for 5x7), plus a 7.5" Ektanon and some very useful bits from an Omega or MPP (see What enlarger is this from).

The idea is birch ply, homemade big square bellows, Openbuilds V-Slot rails and wheels, Acme lead screw for fine focus, and Marco's LED light unit and controller. Horizontal or vertical orientation (aka hung on the wall to get it out of the way).

Yep, I always make full size drawings, saves lots of pain later.

[Tin Can]

All good!

I am also working with V-Slot and wheels with Horseman parts to try and make Auto Focus Portrait camera

The tech is ready and sold cheap from China

[peter brooks]

All good!

I am also working with V-Slot and wheels with Horseman parts to try and make Auto Focus Portrait camera

The tech is ready and sold cheap from China

That sounds interesting... How will the auto-focus work?

(Realisation that I have no idea how auto-focus works - and I might be hijacking my own thread here )

[Conrad . Marvin]

Sounds like a really fun project! Make sure that all surfaces between the lens and the negative are flat black. I have had an enlarger from a rather well known company (Xxxxx) that had medium gray interior paint which did cause irritation with any lens.

[peter brooks]

Sounds like a really fun project! Make sure that all surfaces between the lens and the negative are flat black. I have had an enlarger from a rather well known company (Xxxxx) that had medium gray interior paint which did cause irritation with any lens.

Thanks for the tip!

[Len Middleton]

Peter,

One can calculate the distance from the negative stage to the paper stage for various lenses to better understand maximum magnification.

Useful when one has limited headroom to raise the enlarger head.

Let me know if you want that spreadsheet calculation.

Len

[peter brooks]

Peter,

One can calculate the distance from the negative stage to the paper stage for various lenses to better understand maximum magnification.

Useful when one has limited headroom to raise the enlarger head.

Let me know if you want that spreadsheet calculation.

Len

Thanks Len, yes that calculation would be really useful - if possible, could you post it here?

(I replied here rather than by PM because it may be useful to others in the future who find this thread).

[Len Middleton]

Thanks Len, yes that calculation would be really useful - if possible, could you post it here?

Peter,

It is simply the magnification equation...

Enlarger Negative Stage, Lens & Baseboard Distances => u=v*F/(v-F)=F*(M+1)/M or v=u*F/(u+F)
where,
u = lens to negative distance (inches)
v = lens to baseboard distance (inches)
M = Magnification
F = lens focal length (mm)
u+v = negative to baseboard distance (inches)

I have a spreadsheet where I put that into a single sheet, and ran some numbers for different focal length lenses to determine magnification, given that my enlarger head was hitting the bottom of a floor joist and constraining the maximum u+v value even with the drop table.

Good luck with it,

Len