Homemade SLR Camera by Denis MO (in English!)

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Homemade SLR Camera by Denis MO (in English!)

Nouveau messagede Pierre-Yves P le Sam Mar 20, 2010 2:07 am

:Hello: Since this thread has gained a lot of attention from people all over the world, we have decided to translate it in English.
Please bear in mind that English is not my native language, and that I lack a sound technical background to translate this project with a pinpoint precision! I apologize for any mistakes or misspelling.
Thanks!
Pierre-Yves

PS/ We have an “English speakers' corner” on the forum, if you want to join us!
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Re: Homemade SLR Camera by Denis MO

Nouveau messagede denis MO le Sam Mar 20, 2010 2:10 am

:D After a short discussion with Sylvain [the webmaster] who agrees 300% with me, I will show you my new crazy home-made challenge:

My project consists in creating a 24x36mm reflex all by myself – no more, no less. I have had this project in mind for the past 25 years, but I didn’t master the technique nor did I have the knowledge necessary to complete it until now (I’m almost 42).

- The aim is not to use pieces scrapped from existing cameras, except for the shutter curtain fabric, ball bearings and screws; I have already found a solution for manufacturing the mirror, the focusing screen and even the prism.

- This camera will not be a copycat of an existing camera, but a new design that allows me to use my workshop equipped with model-making machine tools. Of course, the design will be drawing from existing solutions, such as the focal-plane shutter of the Leica II.

- I didn’t find anything like this on the web, even on Anglo-Saxon websites, and they do like DIY a lot, I will therefore be facing the teething problems.

- This project does have some difficulties :gratgrat:, this wouldn’t otherwise be interesting. The most hindering issues for me will be the light proofness and the focal-plane shutter. As regard the light proofness, I will be bypassing this issue by drawing from the bottom-loading design of Leica, Zenit 1, Zorki… The only difference is that the bottom plate and the casing will be removable in a single piece. As regards the shutter, I scrutinized a Zenit 1 as well as a Zenit E from every possible angle to understand the operation, I have had some issues understanding it, but it now clear to me.

- Lastly, my camera will have to be reasonably sized in comparison with existing cameras. The technical level will be more or less on par with the one of the 1950s, I don’t think I’ll be able to implement an instant-return mirror, for example, but if one is too greedy from the start, the project fails and end up unfinished in a box.

Of course, I will be listening to you and taking your comments & criticisms into account. :hurle:
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Re: Homemade SLR Camera by Denis MO

Nouveau messagede denis MO le Sam Mar 20, 2010 2:12 am

In a project like this one, room is crucial: there isn’t a single half-millimetre to be wasted.
Even though I started industrial design using pencils & rulers, I will use more convenient tools, such as 3D Computer-aided Design (CAD).

Let’s now introduce the project itself. The camera body isn’t represented here for clarity purposes. The shutter curtains are here in the cocked position.
Image
[Note: “dent” is the French for tooth. “25 dents” therefore means a gear with 25 teeth]

Starting from the take-up spool, there is firstly a 24-tooth gear meshing with two 20-tooth gears, which are in turn meshing with the 25-tooth gear of the film sprocket. This equals to a 24/25 gear ratio, the middle gears do not influence this ratio. Given that the film sprocket will do a complete revolution, the take-up spool 24-tooth gear will shift by one tooth every time, in order to implement the film counter. My system will be limited to 24-exposure film, because I am using 0.5-module sprockets, which are slightly larger than regular cameras, but this facilitates the calculations. If I was to use 36 exposures film, I would have needed a 39/40 ration.
E.g. for two 20-tooth gears, the gear diameter is 10mm, with a 10mm gear spacing.

Now the bottom view:
Image
The film sprocket drives a 15-tooth gear that meshes with a 30-tooth gear, the latter being limited to a 180° rotation. Given that the ratio is 1/2, the sprocket does a full revolution, which insures that the film will advance without overlapping exposures.
The 30-tooth gear meshes with the shutter curtain drum through a 20-tooth gear, hence a (30/20)*180 = 270° rotation of the drum.
The drum has a 18mm diameter: 18*Pi*(270/360) = 42.5mm of curtain linear movement.
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Re: Homemade SLR Camera by Denis MO

Nouveau messagede denis MO le Sam Mar 20, 2010 2:15 am

Manufacturing of the Leica II-like focal plane shutter.


Cutting the bottom part of the 1st curtain drum:
Image

Grooving of the upper part of the 1st curtain drum:
Image

Components of the drum:
- axis
- 1st curtain parts
- 2nd curtain drum
- the other parts are used in the retaining tab of the 2nd curtain
Image


The drum assembly:
Image

More difficult now: manufacturing of the spring-loaded winding drums.
- the axis has a 4mm diameter
- the drum is an aluminium tube (8mm external diameter; 6mm internal diameter)
- the ring are 1mm thick, and I have to drill a 0.6mm hole in this millimetre to hook the spring into
Image

All of this is assembled using Loctite. The axes aren’t cut to their final size yet.
The dark (Nylon) parts on the second winding drum will be used for binding the 1st curtain straps to the 2nd curtain drum.
Image
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Re: Homemade SLR Camera by Denis MO

Nouveau messagede denis MO le Sam Mar 20, 2010 2:17 am

Let’s draw the curtain over the curtains.

It should look like this:
Image
Image

I use strong but repositionable glue to glue the curtains, starting with the 2nd curtain.
Image

Once wound up, the curtain has to be aligned with the drum retaining tab. By the way, this tab has been modified, it is now using two smaller bearings.
Image

I am checking the winding of both curtains, using clothespin as a ballast to simulate the spring tension.
Image
Image
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Re: Homemade SLR Camera by Denis MO

Nouveau messagede denis MO le Sam Mar 20, 2010 2:20 am

Gears 1/2

For the project, I needed a dozen of 0.5-module gears, which cost 15 to 20€ apiece: this is expensive for mini gears, and I can’t buy a module milling-cutter either, for I’m not richer than Croesus.
I first manufactured a fly cutter (which sort of a milling cutter with only one tooth).
The fly cutter is hand made, using HSS 6 steel.
Image

No difficult calculation here, but just a grinder and a plastic gear to check the shape.
Image


Passage au diviseur pour un 20 dents, je tangente et rentre dedans de 1.25mm en une passe, comme c'est du laiton.
Image

This is a helicoidal hob, something like a milling cutter without teeth. You need to hold the gear axis with both hands, perpendicular to the thread, a 700 to 1000rpm lathe will do the rest. A M10 screw can be used instead of the hob.
Image
On the left a "raw" gear, in the middle a gear lapped with a M10 screw and on the right a gear that has been lapped several minutes on the homemade hob.
Image

And that is a tiny gear salad!
Image
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Re: Homemade SLR Camera by Denis MO

Nouveau messagede denis MO le Sam Mar 20, 2010 2:23 am

Gears 2/2

I used the following website to create my hob; Anglo-Saxon use this milling cutter to create gears profile, regardless of the number of teeth.
http://www.helicron.net/workshop/gearcutting/involute/

In this case, I drew from the profile that looks like a rack-and-pinion shaped like a helicoid, for a 0.5-module.
The thread is therefore 0.5*Pi = 1.58, with a 1.70mm depth.
This is like making a screw, but with a 40° angle tool.

Without this tool, one could use a M10x150 screw for lapping, or even better a screw with 16 threads per inch (1.587).

In fact, what I have built is just like a leadscrew without teeth. If I would go further, like explained on the website linked above, I could make teeth, quench them and obtain a 0.5 module leadscrew that cost 500€.

I drilled this plate to check the good operation of the gears, as well as the gear spacing.
Image

Since these gears are trial-and-error made, I think that result is good – much better in any case than the macro ability of my digital compact!
Image

Working with the divider implies a perfect centering of the gear, I use a gauge.
Image

I am here making the groove that is going to limit the rotation of the 30-tooth gear to 180°. I drilled a hole in the end of the groove in order to be able to adjust with a round file, if needed.
There is a very tiny ball bearing (2x5x2.5) in the center of the 30-tooth gear.
Image
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Re: Homemade SLR Camera by Denis MO

Nouveau messagede denis MO le Sam Mar 20, 2010 2:25 am

Since I’m moving, my workshop is closed, so I did some more CAD.

Here are some thoughts on the mirror:
- the flange-to-film of a m42 lens is 45.5mm
- 21+24.5mm = 45.5mm so the total is good, from the lens mount to the focusing screen. I didn’t use a Fresnel lens under the focusing screen, since I don’t know how it affects the distance. I can however place a convex corrective lens on top of the focusing screen – I don’t know if this will be useful.
- the circle represents the rotation of the mirror: it can’t collide with the back of the lens.
- I think that a plastic prototype will be necessary to validate the viewing system.
Image

The project as of today: I am still working on the general architecture – that is, the way to place the different parts in a limited space. I am not working on the looks of the camera yet, aesthetics consideration will be the last part of the project.
Image
Image
Image

The mirror issues completely emptied my brains! I’m going back to addressing the shutter and film transportation issues, for which I have much more precise ideas.
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Re: Homemade SLR Camera by Denis MO

Nouveau messagede denis MO le Sam Mar 20, 2010 2:26 am

I made a focusing screen out of a 2mm thick glass. I rubbed this glass with a larger glass and some grinding powder.

Then, I removed the focusing screen of a Zenit E (which focusing screen also has a corrective lens effect), and replaced it with my own.
It looks a bit rough, but this improves when focusing – just like it does with mircroprisms.
Viewing through this ground glass without a corrective lens is acceptable for a homemade project; there is no light falloff. I tested both a 50mm and a 200mm, there a little bit of a luminosity loss when taking pictures inside, but not much – even though I have only tested “small” apertures of 1:3,5 (Industar) and 1:4.5 (Pentacon), it should be much better with a 1:1.8 Helios, but everything is packed right now!

I might be able to enhance the ground glass, I saw that grounding gel is available.
I don’t see the point of a correcting lens above the focusing screen for this homemade project: even on the Zenit E you can see it a little bit in the viewfinder.
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Re: Homemade SLR Camera by Denis MO

Nouveau messagede denis MO le Sam Mar 20, 2010 2:28 am

Resuming of the project

I started to tackle with the shutter release.

When the shutter release button is depressed, the small gear at the bottom will disengage from the film sprocket, and the first curtain will fire, thus making this small gear rotate fully, and taking the same position again.
Image

Simultaneously, pressing the shutter release button will switch a latch that will block the 2nd curtain tab.
Image

The brown axis shown below rotates with the 1st curtain, and drives the blue parts along.
It is the dark blue part that is going to fire the 2nd curtain, by releasing the aforementioned latch.
Image

The 2nd curtain is now released:
- 1/30 is achieved when the 1st curtain travels all the way
- 1/60 is achieved when the 1st curtain travels 1/4th of the way
- 1/60 is achieved when the 1st curtain travels 1/8th of the way
- etc.
- Bulb: the 2nd curtain is never released: only when the shutter released button stops being pressed will the latch be switched.
Image

If you have trouble understanding, it’s normal, it took me some time too to figure out the refinements of a Leica II-like shutter.
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Re: Homemade SLR Camera by Denis MO

Nouveau messagede denis MO le Sam Mar 20, 2010 2:29 am

Enough with the theory, let’s put into practice:

The film sprocket is made using a lathe.
Image

That’s like the dentist!
Image

The shape of the film sprocket teeth will be completed with a hand file.
That’s something unique with this project: each part is hand-finished!
Image
Image
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Re: Homemade SLR Camera by Denis MO

Nouveau messagede denis MO le Sam Mar 20, 2010 2:30 am

It’s good to see that there are still people passionate about precision mechanics in these where nobody is surprised by nothing anymore; as a matter of fact, I think that we are losing our capability to be surprised – hopefully there still some aesthetics-loving camera collector like us. You want more, and I’ll give you more:


I have finished the base plate, only the corners will require some rounding. Don’t worry I will cut the axes to the right length, it’s not a porcupine camera!
Image
Image

I feel like I’m taking a 50 years step back (I wasn’t born by that time) and living what the prototyping engineers of the Leica might have lived; my means are identical, I just replaced the drawing board with a computer.
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Re: Homemade SLR Camera by Denis MO

Nouveau messagede denis MO le Sam Mar 20, 2010 2:32 am

Another step of the project.

This tricky step consist in gluing the curtains to the winding drums (the screw that protrudes at the back is only temporary, for assembly purposes).
Image

Another image with the top plate in place:
Image

I tried manipulating the curtains, there is some friction, particularly for the 1st curtain; some adjustment with tailored washers will be necessary. The big central drum that winds the 2nd curtain is a bit too large diameterwise and I will certainly have to replace its Nylon components with micro bearing so as to reduce friction and to allow for the 1st curtain to fire more smoothly.

That means more fitting and tuning to come.

I have a question for you: have you heard of reflex cameras that need their mirror pulled down manually, i.e. independently from the film advance? I might chose this solution: cocking, then pulling the mirror down using a lever, then, when I press the release button the mirror goes up and the shutter is tripped; I could just pull the mirror down to use the viewfinder, without cocking the shutter or advancing the film.
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Re: Homemade SLR Camera by Denis MO

Nouveau messagede denis MO le Sam Mar 20, 2010 2:33 am

I often have to create some tools, like this homemade square that I use for holding delicate parts like the film guide.

Image

The film guide is used to assemble the top & bottom plates, I still need to create the sides.

Image

You are going to make fun of me, but I already stamped the serial number. As you can see I limited myself to 1000 pieces. More seriously, I stamped the serial number now because this part is still sturdy, it will be weakened by later machining.
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Re: Homemade SLR Camera by Denis MO

Nouveau messagede denis MO le Sam Mar 20, 2010 2:33 am

I modified the shutter parts: while it’s not obvious, I reduced the second curtain drum (here on the left hand side) from 16 to 15mm, the drum thickness is therefore only 0.5mm. This drum is now mounted on mini ball bearings. The sides of this drum, that are used to wind the 1st curtain, are also modified in such a way that the 2nd curtain once wound doesn’t touch them. The spring-loaded winding drums are also modified from 8 to 7mm, which makes them 0.5mm thick too.

In this project, there isn’t any wasted room, all parts are 1mm apart, and often 0.5mm only.

In order to glue the curtains, I had to create another DIY tool.

Image
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Re: Homemade SLR Camera by Denis MO

Nouveau messagede denis MO le Sam Mar 20, 2010 2:34 am

Technical progress of the day: I added a small, complicated part under the film sprocket, which first aim is to prop up the sprocket when the shutter button is being pressed. The other aim of this part is to prevent any light leaking from the chamber through the gears assembly.

I have designed a temporary plastic latch (on the bottom plate), I will make a sturdier one once its shaped is finalized.

Image
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Re: Homemade SLR Camera by Denis MO

Nouveau messagede denis MO le Sam Mar 20, 2010 2:35 am

Summary of this week-end’s work:

I have drilled 4 notches in order to maintain the film pressure plate. These should have stopped 0.2mm short of the film slides, so that the film could move freely, but I made a mistake. Instead of re-engineering this whole part, I will make a 0.2mm groove in the film pressure plate.

Image

On the top: the winding gears; the gear just above the sprocket will slide, so as to allow rewinding.

Image

This is the 2nd curtain latch.

Image
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Re: Homemade SLR Camera by Denis MO

Nouveau messagede denis MO le Sam Mar 20, 2010 2:36 am

Today I tackled with the take-up spool, which is made of 4 parts and which is driven by a friction spring: it is the film sprocket that controls the film advance.
On the bottom of the picture, a film advance & spacing test, using an old film.

Image

I tested winding up a 36 exposures film, to see if nothing jams (you can see my beautiful digital compact in the reflection).

Image
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Re: Homemade SLR Camera by Denis MO

Nouveau messagede denis MO le Sam Mar 20, 2010 2:37 am

This week-end I cut the reflex cage – don’t worry I do get out my garage!

I started with an aluminium block hand-cut in a 20mm plate pffff! I then rounded the block using my milling-cuter, and I also hollowed a 12mm hole in the center of the block.

Image

I could have used a milling cutter to drill a larger hole, but my lathe is much sturdier.
I fastened the block in a 4 independent clamps mandrel and used to previous 12mm hole to center the new hole.

Image

I then refined the centering using a dial gauge.

Image

The reflex cage for the time being – there is much more work to do on this part.

Image
Image
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Re: Homemade SLR Camera by Denis MO

Nouveau messagede denis MO le Sam Mar 20, 2010 2:42 am

I already know that you will ask: “Why lenses are you going to use?” I don’t have the arrogance to create a homemade lens – I might make one alright, but just for fun. The simplest way for me is to make a standard 42mm screw mount. What’s more, I have all a range of lenses in this mount.

I could have used a M42 mount from a for-parts Zenit (I have some of those), but where would be the masochist pleasure of the homemade craftsman, who doesn’t want to use any existing parts?

Now, that what you call heavy duty: 60mm tubing, 10mm thickness… I took me some time to cut this with a hand saw!

Image

Then some work on my prehistoric-but-sturdy lathe number 1.

Image

I then did the threading on my prehistoric-but-sturdy lathe number 1 – this one is more advanced but really old, the security standard are ancient too, one should be aware of catching his hand in the gears. I’m 42 and I still have all my fingers, knock on wood.

Image
Image

The ring was then cut, and by that time it was too brittle to be clamped on the divider, so I had to make-do with another cylinder. Of course, you need to use a lens to spot the right orientation of the lens once it is screw on the mount!

Image

The mount is fixed with five M2 screws. Why 5? Well, I like it, I think it looks better than 4, and nobody can accuse me of using a Zenit mount!

Image
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Re: Homemade SLR Camera by Denis MO

Nouveau messagede denis MO le Sam Mar 20, 2010 2:47 am

I’m waiting for the end of the project to remove any extra material, I might need some at some point, but I’m not sure yet, so I let it be for the time being.

Talking about flange-to-film, I check it using a gauge, I should have 45.5mm – here I have 45.3mm so the paper shims should do the trick, just like back in the old days!
Image

Test with a makeshift ground glass made from Plexiglas with a Pentacon 50, even the picture doesn’t do the result any justice:

Image

Mmmm there might be a problem, the image is upside-down! :mrgreen:
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Fabrication d'un appareil télémètrique et d'un réflex homemade (rubrique : réparation et entretien)
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denis MO
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Re: Homemade SLR Camera by Denis MO

Nouveau messagede denis MO le Sam Mar 20, 2010 2:47 am

Here I am working on the project, the picture was taken by Thierry

Image

On the left, you can see a Praktica waiting for better times – it was salvaged, by the way.
My repairs are Boolean, it’s either a complete success or a complete failure. My success rate is about 50%.
Collectionneur de Zenit et objectifs Russes
Fabrication d'un appareil télémètrique et d'un réflex homemade (rubrique : réparation et entretien)
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Re: Homemade SLR Camera by Denis MO

Nouveau messagede denis MO le Sam Mar 20, 2010 2:48 am

Thanks to Web, there are some overseas French-speaking folks reading me on the other side of the ocean!

I started to reassemble the shutter; it does take a lot of fine tuning for everything to work correctly. During testing, when I cocked the shutter, the shutter release button became very stiff, stiffer than the one in a sand-filled Zenit! I took me a while to figure it out, but now I understand my mistake:

Image

1) This is the first system, where everything is concentric. As a result, when the shutter is cocked, the gears push the film sprocket sideways, therefore jamming the shutter release spindle.
2) The enhancement: the film spool now rotates using a ball bearing; the force of the gears will now not jam the spindle. [note: jeu = backlash]
3) Given that the sprocket is a complicated part, I didn’t want to make a new one, so I just glued a tubular part on it using strong Loctite (the green one).

I didn’t see this problem coming, what really matters is finding a solution without breaking anything.
Collectionneur de Zenit et objectifs Russes
Fabrication d'un appareil télémètrique et d'un réflex homemade (rubrique : réparation et entretien)
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denis MO
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Re: Homemade SLR Camera by Denis MO

Nouveau messagede denis MO le Sam Mar 20, 2010 2:48 am

I don’t know if the DMflex will be finished for Christmas, but it has clicked for the first time!
http://dailymotion.com/video/xav5p4_fon ... du-dm_tech
I adjusted the spring tension using nothing but intuition; I have 1/28th for the 1/30th setting, which is good enough since it is within tolerances. For the time being, these parts are only prototypes, I will need to rework some of them.
I tried the 1/30, 1/60 and 1/125 and the linearity of these speeds is correct. I can tell because I control the curtains operation on 3 spots (right, middle, center). I think I may add 1/250 as well.

See the topic viewtopic.php?f=37&t=11&p=55537#p55537 about controlling shutter speeds.
Collectionneur de Zenit et objectifs Russes
Fabrication d'un appareil télémètrique et d'un réflex homemade (rubrique : réparation et entretien)
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Re: Homemade SLR Camera by Denis MO

Nouveau messagede denis MO le Sam Mar 20, 2010 2:49 am

I started to work on the speed selection assembly:

Image

I did the pale blue part on the picture above following the theoretical calculations et here is the result:
1/30 ok
1/60 = 1/90
From 1/125 on, nothing, there isn’t any space between both curtains.

I therefore added 2 holes, one before the 1/60 to try to get the 1/60, one just after to try to get the 1/125.
For the time being, I have 1/30 1/60 1/125 with a good linearity. I can drill a hole after the 1/125 to get the 1/250 speed, but I didn’t try so far. I don’t think 1/500 will work on this project. On most Zenit cameras, the 1/500 setting usually gives a slower speed, roughly 1/380 or maybe 1/400. I also noticed that the higher speeds are more accurate on rotating speed dial Zenit.

For the moment, I can find the right speeds but only using trial and error: as a result, this speed selection ring is starting to look like Swiss cheese, I will need to make a new one.
Collectionneur de Zenit et objectifs Russes
Fabrication d'un appareil télémètrique et d'un réflex homemade (rubrique : réparation et entretien)
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