Fixed focus camera?

[jb7]

The advantage of the 65mm ƒ/8 is that it will fit in a smaller helical-
in fact, using one of the Schneider helicals would require an extra board in order to be able to use this lens-

With regard to focus testing, trying to find infinity on an ƒ/8 lens would be a very inexact way to approach things,
and would invariably end up with focusing error in the close range.

The same might even be true for the faster lenses...

Making (and printing) a focusing scale for a helical mount is actually one of the more straightforward parts of camera building,
since you can use the optical formula for conjugate distances-
and the focus throw and rotation distance is easily measured.

If you can get accurate focus at the closest point on your helical, and your flange/focal distance is reasonably accurate,
then it need be no more fiddly than trying to set up a dedicated helical at infinity.

A £10 digital caliper is a very useful tool when it comes to this stage of the operation...
as well as for making a focusing screen with an accurate T dimension-

I suppose it comes down to approach, but whatever the method you choose to mount your lens,
your biggest challenge for a point and shoot camera will be parallelism, in my opinion-
again, precision machining will help to keep things manageable,
but if you don't have access to that,
you may end up shimming to correct for machining inaccuracies,
even if you choose to go down the route of purchasing a dedicated helical-

Of course, the big advantage of the dedicated helicals is their ability to accommodate the faster lenses-
but given the choice, I think I'd leave it as a last resort-
for the reasons given above-
part of the attraction of building cameras is in overcoming the difficulties of making it work, in your own way- ultimately, it's about expression.

Of course, if you have random parts lying around, then it might seem odd to try to reinvent the wheel,
and if your budget stretches to outsourcing expensive processes and components,
then these observations are hardly relevant anyway-

Hope you manage to find your parts-


joseph

[Steve Smith]

With regard to focus testing, trying to find infinity on an ƒ/8 lens would be a very inexact way to approach things,
and would invariably end up with focusing error in the close range.

I know, I tried it!

I found the best plan was to use the data from Schneider's website and set the back of the shutter 70.5mm from the film plane. I then ran a roll of film through my test camera (an old 6x6 folder with the bellows and front removed and the 65mm lens put in place) and took some photographs at various focus settings along with detailed notes.

From my initial findings, the infinity setting appearted to be correct and a setting of around 12' on my adapted Olympus focusing helix gave me hyperfocal distance.

As I will be using this on a tripod, usually at f16 or f22 I expect that this 12' setting will be the most commonly used. I could probably just set the lens in this position and not bother with the helical - which was my original intention!


Steve.

[jb7]

Yes, a much better way-

I worked these out by calculation, after a little testing, and they seem reasonably accurate-
I printed it out on a sticky label, and applied it over the nicely engraved numbers on the barrel-
I wonder if my 3.5 is anywhere close to your 12?

[Alan Clark]

I am beginning to feel a little sorry for Dave Dawson, the original poster. All he wanted to do was make a simple wooden fixed focus camera using a 90mm Super Angulon lens. He has been told he will need a very expensive or home-made focussing mount or will need to shim the lens board to overcome his inability to focus the test camera at infinity, and unless he uses CNC equipment he won't, in any case, be able to make a box accurately enough in length or parallel front to back.

A few years ago I actually made a fixed focus camera for a 90mm Super Angulon using simple hand tools and accurate measurements with a steel rule marked in millimetres. No shims, no focussing mount, no worrying about curved fields, no reference to charts, lens tables, formulae or anything remotely technical. It was very easy to do and I described earlier how I did it. ( If for some reason you can't focus at infinity at f45, then focus your test camera at something 8 feet away at F8, and use this for the front to back measurement) And guess what? The camera works really well. 20 x 16 prints are very sharp. This is why I built the camera. Does anything else matter? Why complicate things?

I appreciate that we all use cameras in different ways and that my camera would not suit everyone. I am just a little concerned that getting over-technical could put some people off getting started.

Alan

[Steve Smith]

I am beginning to feel a little sorry for Dave Dawson, the original poster. All he wanted to do was make a simple wooden fixed focus camera using a 90mm Super Angulon lens. He has been told he will need a very expensive or home-made focussing mount or will need to shim the lens board to overcome his inability to focus the test camera at infinity, and unless he uses CNC equipment he won't, in any case, be able to make a box accurately enough in length or parallel front to back.

I think we are just expressing our own experiences in the hope that some of the information may be of use.

His simple box camera with a hyperfocal placed lens will be just fine. There are only two important things to get right however simple or complex the camera is:

1. Keep it lightproof

2. Get the lens and film the correct distance apart.

Anything else is just an added bonus.


STeve.

[Alan Clark]

Hi Steve,
I apreciate your comment, and didn't mean to denigrate your previous comments. After all, I might wake up one morning and find that I have a desperate need for a camera with helical focussing. ( You know how it is!) Then your work on a home-made focussung mount will be very useful.

Alan

[Dave Dawson]

"I am beginning to feel a little sorry for Dave Dawson"

Well Alan, It's been a VERY long time sinse anyone has felt a little sorry for me Although I'm not sure how to take it when the misses says she feels sorry for me

When I do get around to making the fixed focus camera I'm thinking of painting it bright canary yellow, putting it on a tripod at the side of the A1 and watching smoke coming from all four tyres as the drivers hit the brakes (wicked ain't I?)

Seriously though ALL suggestions have been noted but like Alan I think it shouldn't be too hard to get good results with a modest box type camera with a Super Angulon shoved on the front.

Cheers Dave

[Dave Dawson]

Well my fixed focus camera project hasn't got off to a very good start I haven't been able to find an old 5x4 international back or a #0 shutter at a reasonable price I keep getting outbid)

Has anyone got either of the above please? The back doesn't have to be pretty and can have a broken/missing gg screen. The shutter doesn't have to be anything fancy either.

I don't have a proper International back but I do have one which I made: http://stevesmithstuff.blogspot.com/ (first picture).

It's been sitting around for a couple of years so if it's of any use to you whilst you are in an experimental stage, you can have it. Then replace it with a proper back when you get one.


Steve.

If your offer still stands Steve....Please PM me.

Cheers Dave

[Alan Clark]

That's the spirit Dave!

Alan

[Steve Smith]

I have made a bit more progresss on mine and updated the web page a bit: http://stevesmithphoto.webs.com/pano612.html


Steve.

[Emmanuel Bigler]

http://stevesmithphoto.webs.com/pano612.html

Superb work, nice wooden camera body.... thanks for sharing the work in progress with us.

Since you have designed and built your own rollfilm holder (impressive !) I would like to mention that in all rollfilm cameras and rollfim backs I know, the (film + backing paper) is not actually pressed against the film gate by the pressure plate. The pressure plate rests against some precisely machined parts of the film holder, leaving a certain gap between the film gate and the pressure plate. Same applies alos to 35 mm cameras, if you look at the film gate and check where and how the film pressure actually plate "presses" on the gate.
In the 6x6 Rolleiflex TLR, the plate-to-gate gap is 0.45 mm. Hence if the 120 film is not totally free to run between the film gate and the pressure plate, there is some amount of functional gap to be optimized. The gap of 0.45 mm determined for the Rolleiflex might not be the same for a panoramic holder, though.
There is an exception to this, some versions of the Rolleiflex TLR had a plane glass in the film gate. In this case, the film was actually pressed against the flat glass, but for winding the film to the next image, there was a lifting pin in action in order to separate the pressure plate from the film and allow a free film tranport. The plane glass device was abandoned since it generated more drawbacks (dust, parasitic haloes of light, etc) than real advantages in terms of image sharpness.
Another remark regarding film flatness in panoramic backs is that it seems to be better for film flatness to sacrifice some film width, for example to reduce the film gate to 50 mm width instead of the standard 56 mm.
In the Hasselblad film magazine, which is the exact contrary of a panoramic back, the film gate is slightly cropped down to 54x54 mm, and I'm sure that this helps the film to stay flat. Resolution tests on test targets have shown that 120 rollfilm with its infamous backing paper was capable of resolving about 100 cycles/mm, in a well-tuned 6x6 Rolleiflex or in the 6x6 Hasselblad with a good film back. Even higher results have been measured by Chris Perez on a 6X7 Mamiya rangefinder camera.
If bulging or some other horrors were the rule, those results could hardly be ever reached.

Good luck for the continuation of the project !

[Steve Smith]

I would like to mention that in all rollfilm cameras and rollfim backs I know, the (film + backing paper) is not actually pressed against the film gate by the pressure plate. The pressure plate rests against some precisely machined parts of the film holder, leaving a certain gap between the film gate and the pressure plate.

This is something I have been thinking about. At the moment, the rails the film registers to are the same height as those which the pressure plate registers to. I think I need to laminate some strips of polyester to the outer rails so that there is a gap just slightly larger than the film and backing paper thickness. I have plenty of sheet adhesives and polyesters at work so that shouldn't be a problem.

Another remark regarding film flatness in panoramic backs is that it seems to be better for film flatness to sacrifice some film width, for example to reduce the film gate to 50 mm width instead of the standard 56 mm.

That's worth considering. I will stay with a 56mm width for now but I only have to re-cut one part to change this if needed.


Steve.

[jb7]

very good, looks great, can't be far off making pictures-

[Steve Smith]

very good, looks great, can't be far off making pictures-

I just need to make the back which is a much slimmer version of the front. The problem is that the only piece of oak I have is warped so I think I will make a temporary back out of 9mm MDF and if it all works out o.k. I can get some more oak.

The beauty of a CNC cutter is that I can just run the programme again and make an identical piece.... or modify it if necessary.


Steve.

[jb7]

Sounds wonderful-
can I send you some walnut and a drawing?

Don't worry, only joking...