Chroma 679 - Medium Format System

[stevelmx5]

But what's with the SD card holders?

[emoji23] Well, I’ll lose them if I don’t have somewhere to keep them..

It was a test design to integrate a strap lug on the top of the grip, which I’ve now removed again.

 

[stevelmx5]

Some more progress on the new system;

This is my Kiev88 6x6 back, the same mount fits a Hasselblad A series back, so long as you use a Series 1/2 version which allows you to wind on the film manually;









I’ve just taken an updated grip off the printer which is hollow to allow for a roll of 120 to be stored inside it [emoji1303]

There’s also a matching magnetic ground glass back, which allows for the original Kiev/Hasselblad popup shade and glass to be fitted;

View attachment 295350

 

[stevelmx5]

Today I’ve printed a rear body/plate and ground glass frame for a Mamiya RB Pro S 6x7 back too;







This plate has an integrated tab to press the darkslide locking pin, so you can actually remove it :0)



I’ve flipped the rollfilm back upside down, to allow for the darkslide to be removed.

Both rollfilm back options use the same main body, helicoid plate and grip, giving flexibility of format without having to swap everything over. They also both have the same film plane, meaning the lens can be marked up once for both formats.

Next job is to get hold of a Mamiya Press rollfilm back and design a mounting plate for that too.

 

[steveo_mcg]

What are you using for a gg on the rb set up?

 

[stevelmx5]

What are you using for a gg on the rb set up?

For this one (because I haven’t got an RB WLF to mount), I’m going to get a custom ground glass cut to size.

 

[steveo_mcg]

For this one (because I haven’t got an RB WLF to mount), I’m going to get a custom ground glass cut to size.

I don't have a spare I can send. Think the only thing that would be missing is the magnifier though can always use a loupe. Would need a chimney of some description, don't want to try and carry a tiny little dark cloth.

 

[RaglanSurf]

Some more progress on the new system;

This is my Kiev88 6x6 back, the same mount fits a Hasselblad A series back, so long as you use a Series 1/2 version which allows you to wind on the film manually;

View attachment 295346

View attachment 295347

View attachment 295348

View attachment 295349

I’ve just taken an updated grip off the printer which is hollow to allow for a roll of 120 to be stored inside it [emoji1303]

There’s also a matching magnetic ground glass back, which allows for the original Kiev/Hasselblad popup shade and glass to be fitted;

View attachment 295350

What about 65mm Fuji 5x4 lens, with a Hasselblad 6x6 back mounted to a Chroma style “Flexbody” adapter?

 

[stevelmx5]

What about 65mm Fuji 5x4 lens, with a Hasselblad 6x6 back mounted to a Chroma style “Flexbody” adapter?

So long as the rear element of the Fuji lens fits through the helicoid (<61mm diameter), that won't be a problem at all

 

[RaglanSurf]

So long as the rear element of the Fuji lens fits through the helicoid (<61mm diameter), that won't be a problem at all

About 48mm wide and protrudes 28mm from the back of the lensboard.

 

[stevelmx5]

About 48mm wide and protrudes 28mm from the back of the lensboard.

Spot on, no problem at all Nick [emoji1303]

 

[stevelmx5]

I’ve had the opportunity to do an interesting comparison;







I never realised that the SWC was a little brick [emoji3]

Obviously the Hasselblad is slightly wider than mine (38mm vs 47mm).

 

[RaglanSurf]

I’ve had the opportunity to do an interesting comparison;

View attachment 296354

View attachment 296355

View attachment 296356

I never realised that the SWC was a little brick [emoji3]

Obviously the Hasselblad is slightly wider than mine (38mm vs 47mm).

I’m liking how this is evolving Steve

 

[stevelmx5]

I’m liking how this is evolving Steve

Me too Nick. The updated grip now has a hollow centre, large enough to hold a roll of 120.

I’m quite surprised about the weight of the SWC though.

 

[RaglanSurf]

@stevelmx5

I do have a spare Mamiya Press back and an RB wlf I can lend you while you’re at the testing/design stage, I’m not sure how good the light seals in the back are are but you’re welcome to borrow it.

 

[stevelmx5]

@stevelmx5

I do have a spare Mamiya Press back and an RB wlf I can lend you while you’re at the testing/design stage, I’m not sure how good the light seals in the back are are but you’re welcome to borrow it.

They would both be great Nick, if you don’t mind. They’re the next priority for me in terms of adaptor designs.

I’ll send you a pm with my address, and cover postage of course [emoji1303]

 

[RaglanSurf]

I’m working all weekend but will sort them out next week.

 

[stevelmx5]

I’ve made some more progress on this system. I’ve now got a fully complete back for the Kiev88 rollfilm body, along with 95% complete backs for Hasselblad and Mamiya RB67 bodies.

The mid-body of the system now has 2 coldshoes integrated into the top, along with mounting points on either side for L/R handed grips, and an additional plate for 2 more cold shoes. The grip is also hollow, to include a compartment to store a spare roll of 120.



I’ve just put together a pinhole lens board too, to give another option on top of standard lenses.





All three of the current film backs have the same film plane, meaning they can be swapped out without needing to refocus. I’ve also got a dedicated ground glass back, with integrated frame/cover, which I’ll be printing next.





I’ve got a Mamiya Press rollfilm back on the way (thanks Nick [emoji1303]), so I’ll design a body to mount that too, giving a full range of formats from 66, 67 and 69, on one single system.

The next task is to design a new rear body for the Carbon Adventurer/Advanced45 field cameras, to allow for the same rollfilm bodies to be mounted to those cameras as well.

 

[stevelmx5]

I haven’t completed the RB body yet, but this will mount in the same way as the Kiev body above.



The mid-body can be printed in any depth, according to the lens being mounted. This one is only 10mm thick, as it’s designed to mount my Schneider 47/5.6.

The front plate, with the metal helicoid, is also detachable from the mid-body, secured with 4 thumbscrews (I’ve got black ones on order). This can then be swapped out for other lens mounts, including Mamiya Press, which are next on my list.

 

[stevelmx5]

There’s also a tripod mount integrated into the base of the grip;

View attachment 297113

The grip is secured using keyhole mounts, with the camera clicked down from the top, meaning that the weight of the camera is always pushing down into the locks, so it won’t come out when secured to a tripod (or in your hand);

 

[RaglanSurf]

Fantastic work Steve, great to see this system evolve

 

[stevelmx5]

Fantastic work Steve, great to see this system evolve

Thanks Nick. I printed the ground glass body last night, so that’s almost ready to go. Next job is to design the body around the 6x9 Mamiya Press back you sent over.

 

[stevelmx5]

Some more progress today;





I’ve now got a nicely secure Mamiya Press back on its’ own body [emoji1303] It has fixed mounting plates on the top edge, which slide into the cold shoes on the mid-body, as well as a pair of rotating mounting cams on the bottom edge.

As the distance between the face of the Mamiya Press holder and its’ film plane is around 4.5mm further than the Kiev/Hasselblad/RB backs, I’ve adjusted them to make sure the film plane matches on all 4 backs. As a result, all backs are fully interchangeable with the mid-body/lens, meaning that the frame size can be switched without having to refocus.

Also, as the Mamiya Press film holder is much larger than the others, the standard camera grip is removed before fitting it. It’s not an issue with regards to holding the camera, as the film holder becomes the grip itself, but it does mean that the tripod mount thread is removed with the grip. Therefore, I’m making a small change to the Mamiya Press back to integrate its’ own tripod thread instead.

 

[ChrisR]

Grappling with how this all works, @stevelmx5 ... Am I right, the lens is bog standard, the film back is bog standard, the "body" fits between and is dependent on both the lens and back?

If so, would you be trying to offer a "body" for each combination, or simply print bodies on demand?

Also if so, a body would be unlikely to have much resale value, given the difficulty of finding a customer with the same back/lens combination?

So I think I must have misunderstood! Maybe it's each back/focal length? Still confused! Hang on, spacers!!!

Therefore, I’m making a small change to the Mamiya Press back to integrate its’ own tripod thread instead.

Does that mean you're modifying the MP back, or are you in fact changing the design for the body that matches the MP back?

Confused of... somewhere!

 

[stevelmx5]

Grappling with hw this all works, @stevelmx5 ... Am I right, the lens is bog standard, the film back is bog standard, the "body" fits between and is dependent on both the lens and back?

If so, would you be trying to offer a "body" for each combination, or simply print bodies on demand?

Also if so, a body would be unlikely to have much resale value, given the difficulty of finding a customer with the same back/lens combination?

So I think I must have misunderstood! Maybe it's each back/focal length? Still confused! Hang on, spacers!!!



Does that mean you're modifying the MP back, or are you in fact changing the design for the body that matches the MP back?

Confused of... somewhere!

Sorry Chris, I've probably added confusion with talk of backs/bodies

Essentially, a complete setup would comprise (front > back);

- Lens/shutter - Currently only mounts for standard Large Format lenses, but I'm working on a Mamiya Press lens mount too.
- Lens board - Standard aluminium threaded lens board, as used on my SnapShot
- Helicoid Plate - Standard metal helicoid, as used on my SnapShot, mounted to an acrylic plate which attaches to the front of the printed mid-body (and is removable)
- Mid-Body - Printed body, which integrates two cold shoes. This can be printed in any thickness, depending on the lens being used, as it determines the adjustable flange depth (as per the steel spacer bars on a SnapShot). The grip attaches to this section.
- Rear Body - Various options, depending on the rollfilm holder you want to use. I currently have four versions ready to go, Hasselblad, Kiev88, Mamiya RB Pro S and Mamiya Press. All rear bodies are designed to mount the film the same distance back from the front edge, meaning that all rear bodies are interchangeable, without having to refocus.
- Ground Glass Body - Again, this has been designed to mount the ground glass in line with the same film plane as the four different rear body options.

As the helicoid ranges from 17-31mm depth, there is a certain amount of flexibility with the mid-body thickness, as many large format lenses will rack from nearest>furthest focusing within around 10mm of movement. With my Schneider 47/5.6, for example, the mid-body is only 12mm thick, and it racks focus in only a couple of mm of helicoid moment.

Like with my SnapShot, the thickness of the mid-body can be calculated by taking the flange depth of the lens you want to mount, then subtracting the other components.

e.g. Schneider 47/5.6

Lens Flange Depth 52.2mm - Subtract 37.75mm (15.75mm Rear body, 17mm Helicoid minimum, 5mm lens board) = 14.45mm Mid-Body thickness

Like with the SnapShot spacer bars, I always make them shorter, to allow for a little movement in the helicoid focus before reaching infinity, so the mid-body for the Schneider 47/5,6 is 12mm thick, allowing for 2.45mm movement to infinity.


The only section you'd need to swap out to mount different lenses is the mid-body, to account for different flange depths. The helicoid is mounted on an acrylic plate, that screws onto the front of the mid-body.

 

[Harlequin565]

Great explanation - I was trying to wrap my head around all the combinations...

Very excited for the RB67 variant with Mamiya Press lenses.

 

[stevelmx5]

Great explanation - I was trying to wrap my head around all the combinations...

Very excited for the RB67 variant with Mamiya Press lenses.

No problem Ian, I'm glad it helped. I've got an updated ground glass body and Mamiya Press Body on one of my printers now, so will have those ready to photograph tomorrow.

With regards to Mamiya Press lenses, they all have the same flange depth (53mm), along with their own integrated focusing helicoids, so they will all mount to the same mid-body.

 

[steveo_mcg]

RB67 lens board?

 

[stevelmx5]

RB67 lens board?

I’d certainly like to add the option, but I don’t currently have an RB lens to design the board around!

Also, are there specific interlocks on the back of the lens, that need to be engaged by the body, before the shutter in the lens can be fired/cocked? I’ve never looked close enough at an RB lens to know.

 

[stevelmx5]

Looking at this video, whilst it’s possible to cock/fire the RB lenses off camera, it’s not a simple process (mechanically) so will take some thought to figure out a way to work around it.

View: https://youtu.be/9jB0udZ7Z34

 

[steveo_mcg]

I’d certainly like to add the option, but I don’t currently have an RB lens to design the board around!

Also, are there specific interlocks on the back of the lens, that need to be engaged by the body, before the shutter in the lens can be fired/cocked? I’ve never looked close enough at an RB lens to know.

Shows how long it's been since I've looked at it. The lever on the side of the body cocks the lens and there are a couple of pins which the body moves to do that, its a pita to do manually off the camera.

Besides an rb lens weighs a ton.

 

[excalibur2]

I’d certainly like to add the option, but I don’t currently have an RB lens to design the board around!

Also, are there specific interlocks on the back of the lens, that need to be engaged by the body, before the shutter in the lens can be fired/cocked? I’ve never looked close enough at an RB lens to know.

Congrats on your entrepreneurism... but am I right in that your design would only work if the lens has internal focusing, A RB lens will only focus using bellows.

 

[StephenM]

Large format lenses also use bellows. But see post (NOT f/ ) 64.

 

[excalibur2]

Large format lenses also use bellows. But see post (NOT f/ ) 64.

Well I try to keep up to date on ideas\designs etc but find it hard going reading the posts

 

[stevelmx5]

Well I try to keep up to date on ideas\designs etc but find it hard going reading the posts

As Stephen said above, the RB lens would be mounted via a separate Helicoid, as I already do with large format lenses on my SnapShot;

 

[stevelmx5]

Ok, I now have the following components finalised;

- Acrylic helicoid plate, with M65 mount threaded lens board (as used on my SnapShot)

- Threaded pinhole lens board for helicoid mount.

- Multi-size mid-body, adjustable for any focal length, with mount points on either side for left/right handed grip or additional twin cold shoe plate.

- Removable hollow grip, with pass through hole for cable release, along with a lidded storage section for a roll of 120.

- Ground glass rear body, with acrylic protector plate which doubles as a light shield.

- Kiev88 mount back

- Mamiya RB Pro S mount back

- Mamiya Press mount back

- Hasselblad A series mount back

I’ve printed all of the components on my FDM (filament) printer, but am currently waiting for a set of resin print components too, so I can compare the results.





















The film backs are attached to the mid body with the same magnets I use for the back on my Chroma field cameras, so they’re not going anywhere unless you want to remove them :0)

Once the resin components arrive, I’ll take some proper photographs and will be looking to launch this system.

 

[steveo_mcg]

Cool, sign me up for a dohicky box, a LF lens board thingy an RB lens boardy thing.

So, my order ready yet

 

[stevelmx5]

So, my order ready yet

I’ll get the invoice raised [emoji6]

 

[ChrisR]

This does now appear to be a Thing, or set of things, you can actually buy! Also appearing in Kosmo Foto, and DP Review.

Steve or anyone, somewhere I remember seeing a comment to the effect that LF lenses are fine for... larger formats (d'oh!), but suffer in comparison to lenses specifically designed for smaller formats. Is this likely to be an issue for some LF lenses?

My only LF lens is a coated Fujinon 135, so I'm hoping it would be fine, but I'm interested in the general question. I'd have thought that a LF lens on a smaller format has the advantage that the film is at the centre rather than the edges. Perhaps it's the dreaded "sharpness" that's potentially at issue, based on higher magnification from the smaller film formats?

 

[stevelmx5]

This does now appear to be a Thing, or set of things, you can actually buy! Also appearing in Kosmo Foto, and DP Review.

Steve or anyone, somewhere I remember seeing a comment to the effect that LF lenses are fine for... larger formats (d'oh!), but suffer in comparison to lenses specifically designed for smaller formats. Is this likely to be an issue for some LF lenses?

My only LF lens is a coated Fujinon 135, so I'm hoping it would be fine, but I'm interested in the general question. I'd have thought that a LF lens on a smaller format has the advantage that the film is at the centre rather than the edges. Perhaps it's the dreaded "sharpness" that's potentially at issue, based on higher magnification from the smaller film formats?

Hi Chris. I've been meaning to get back to the thread to post a link to the camera on my website all week, but have sent most of the week camped in my workshop!

679 – Modular Medium Format System

The brand new “Chroma 679” is a modular medium format system, assembled with a combination of magnetic interchangeable sections to build a camera around your own style. It is…

chroma.camera

679 – Multi format Camera System – Chroma Cameras

679 Medium format camera system

chroma.camera

I'm not an optical engineer, but as far as I understand it, using a lens with a larger image circle on a smaller format essentially means that you're cropping a large format frame down to a smaller format. Of course, like all enlargements, starting with a larger negative will give you more scope for larger results (without losing fine detail), but that's a result of the negative size rather than the optics used.

On the whole, I haven't seen any major issues with using LF lenses on smaller formats, as you're basically using the sharpest part of the image circle from the centre.

 

[StephenM]

I can give a quick reply, but it's not quite clear cut. If you're measuring in lppm as the sole criterion, LF lenses will have a lower value. But not that much! All lenses are designed for their intended use, and miniature camera lenses are designed for high resolution (they really need it!). LF lenses don't need it so much.

I can supply a link where you can download, or even just view, an example I used in a talk where I start with a view of the whole 5x4 negative, and successively crop and enlarge to show that a small black blob is a car, ending with a decipherable number plate. This from a 1950s lens.

If not decentred, any reasonable lens should be diffraction limited when stopped down, and that hammers resolution like nobody's business.

If you're using medium format size negatives, it's a non issue.

More details - and figures for resolution - if you want, but I don't carry them in my head.

One thing you might like to play with is the Katz empirical formula for combined resolution of film and lens. It comes in two varieties, the second more accurate but the first easy to do in your head.

If a lens can resolve r1 lppm and the film r2 lppm, the resolution on the film r3 will be given by 1/r3 = 1/r1 + 1/r2. Example: film resolves 100 lppm, lens the same, result of the two together 1/100 + 1/100 = 1/50 so 50 lppm.

Hence, film choice is a big drag too. It's harder to get resolution figures now, but assume about 100 for a 100 ISO black and white film - possibly a little more.

Hmm. Not as quick as I intended.... Proof: Steve's post above appeared while I was tapping.