Lens for 20x30": could I make one?

[Alex Bishop-Thorpe]

A No. 1 close up lens has a focal length of 1 meter and will cover (I think -- you need an image circle of 900mm). Place the stop in front of the lens, with the concave side of the lens facing the subject. For extra resolution you can go the achromat route with either a 2-element close-up lens or something from Anchor optics.

You can combine a lens with a pinhole - the combination sharpens the image considerably but keeps the pinhole's 'infinite' depth of field.

If you want a process lens there is no reason getting anything fancy. A Brown or Ilex will provide more performance than you will need. However, process lenses are made for ~1:1 work and their coverage angle is small so you are going to need a really long one. And it is going to be huge and heavy. I have a 24" Dagor and it weighs about 10 lbs., making the lens support a major bit of work. Conversely, a close-up lens weighs an ounce at most.

I have a set of 58mm close up lenses that I got for christmas back in 2006. I knew there was a reason I never gave them up, even if I only used them twice...I just checked, and it looks like the no. 1 would easily cover. That's amazing. I never would have thought of that.

Surplus Shed is your friend. Check out the educational lenses as well as their fine lenses.

I never looked at the education lenses section of Surplus Shed, but they have a hell of a range. And that's a hell of a lot of possibilities.
(Oh great, now I'm gonna spend the whole evening browsing their catalogue again)
Can anyone reccomend a basic introduction to the topic that would help me understand what combining this element with that element might result in?
I'm generally from the "well let's just see what that does when I do this" school of science...

If you can find an ancient overhead projector the lens in that may work. The ones I remember from grade school were monstrous, and the image field was monstrous, too.

I've got an old overhead projector from a friend that I'm currently taking to pieces - it looks promising too, it seems to be a nice 255mm f/3 lens. That wont cover my format, but it will be good to play with.

Is focal length the main variable determining the image circle?

Again, thank you everybody for all of the information.

[Athiril]

If you want to aactually make one, che ckout dbOptic software for free design.



On a lathe you could cut a wooden 2D curve template and apply a cheap diamond tip glass cutter to cut the curve from the template, and fire polish the glass surface on the lathe too.

[michaelbsc]

Focal length alone has very little to do with image circle. For example a 250mm M42 mount lens will likely only cover the 35mm negative area. But a 250mm LF lens will cover much more.



There\'s far more about lens design that I don\'t understand to explain this. Maybe someone has a good reference work that can help.

[Andrew K]

Can I make a suggestion? Look for an old bromide/repro camera.

They are often given away/sold off really cheap. I picked up 3 lenses when the one we had at my old work was thrown out - all Rodenstock lenses that could cover just about 20 X 30.

I also have a Nikon 560mm APO Repro lens (and a Rodenstock APO Repro lens) at home as well - many of the repro lenses are a wide field lens that will cover far more than you could expect..send me a PM if you have any questions

[Alex Bishop-Thorpe]

Can I make a suggestion? Look for an old bromide/repro camera.

A friend of mine got his Ultraviolet exposure unit (with vaccuum back) through a local graphic arts supplier, one of their clients was getting rid of it and he picked it up for $150. I imagine old copy cameras could be found via similar avenues...surely there's some out there...
I'll start my experiments with this No.1 closeup lens and work forward from there, a real lens would certainly be nice.

[Athiril]

Focal length alone has very little to do with image circle. For example a 250mm M42 mount lens will likely only cover the 35mm negative area. But a 250mm LF lens will cover much more.



There\'s far more about lens design that I don\'t understand to explain this. Maybe someone has a good reference work that can help.

Many tele lenses do cover a lot more than 35mm in a lot of case.


And strangely... the Canon 17mm TS-E will cover the 645 format (and more) with a lot of movements.

[David Grenet]

Many tele lenses do cover a lot more than 35mm in a lot of case.

And strangely... the Canon 17mm TS-E will cover the 645 format (and more) with a lot of movements.

35mm lenses are generally designed to cover a 35mm frame, and that's about it. In fact if they did cover more it would potentially make them more vulnerable to flare. The TS lens needs to cover more to allow movements, although it sounds like it covers even more than it has to.

Now, for view camera lenses, a given lens design will have a consistent angle of coverage. As a longer focal length lens needs to be further from the film plane to focus it will cover more area of film.

This is all a bit off topic really though as I can't really help with which lenses will cover 20x30" sorry!

[ReallyBigCameras]

Many lenses will cover at 1:1, few will cover at infinity.

APO Artars, APO Ronars, APO Germinars and APO Nikkors 24" (610mm) or longer will cover at 1:1, as will 305mm and 355mm G Clarons and the 360mm WA APO Nikkor. f9 Computars in the 240mm, 270mm and 305m focal lengths will cover at 1:1, as will a 14" Goerz Blue Dot Trigor. Basically, any lens that has an image circle approaching 500mm, or more, at infinity, will cover 20x30" at 1:1. Process lenses that are optimized for 1:1 reproduction work will probably perform better than general purpose, or wide angle designs, but since you likel won't be enlaring (or will you?), that shouldn't matter much.

At infinity, you're much more limited. A 42" Red Dot Artar, or 1070 APO Ronar will probably cover, as will a 19" or 24" Dagor. A 1000mm APO Germinar should also cover 20x30" at infinity when stopped down.

I'm sure there are others I've missed, especially at 1:1, but that will give you a few ideas on what to look for.

Kerry