DIY digital medium format photography?

Hi,


I've been thinking about making a DIY digital medium format camera myself to cut the price tag slightly.


There's a group of engineers at the university I attend who contract outside projects, and I'll be speaking to them about the technicalities, but I just want to get an initial impression from the photography community first.


Here's what I have laid out so far:


If I use two full-frame sensors (eg. from a Canon 5D, the cheapest available) side by side, then the total sensor area would be 36X48mm. Given that there are two sensors, I'm thinking parallel processing would be the best route: save the image from each sensor to a different file, and assemble them in post-production (to save the camera's battery and processor). The obvious potential flaw is that the sensors would have to be exactly aligned next to each other, and completely flat to the image plane.

Question 1: Is the entire sensor area exposed, or are there peripherals that are not exposed (eg. maybe 23x35mm exposure area)?


Obviously full-frame lenses would not cover a 36x48mm sensor, so I'd be using some 645 MF lenses, most likely the Mamiya 35/3.5N and 80/2.8N. Crop factor for this size sensor is 1.16X, so the 35/3.5 would look like a 25mm on FX; the 80/2.8 would look like a 58mm on FX.


The next issue would be that the 5D sensor resolves at around 3000dpi to give 12MP on FX. At this resolving power, two sensors would simply be 24MP.
I had a look at the DigMF sensors out there, and they resolve anywhere between 2800 and 4200dpi (with the outside being the 4890dpi of the IQ180).
Full-frame sensors resolve between 3000-5200dpi (5200: Nikon D800).
Crop-frame sensors resolve between 4200-5600dpi (5600: Canon 7D).
From these numbers, I think I can safely assume a resolving power of between 4000-4800 is not unreasonable, and at this size, would render 45-62MP images, which could be printed 300dpi at 19x25 to 22x30.
The difficulty there would lie in reprogramming the algorithm to something more akin to a crop-sensor's algorithm.

Question 2: is there any sort of interface to be able to play around with these type of details? I know of the firmware hacks that allow the camera to accept otherwise impossible settings, but I don't know if it can be extended to my project.

I've tried looking for retail image sensors, without real luck; however I think that simply buying the DSLR cameras would be a better option, as they already have the processors, body, etc.
Question 3: is there enough room in any FX body for a 36x48mm sensor with dual processors? I haven't been able to find detailed diagrams, just the see-through images of camera bodies from dpreview.com.

I think I can assume that, with the lens adaptor, the image circle would diverge at approximately the flange/mount. Given that the flange-sensor distance is 46.5mm, the angle of divergence would have to be 58.1*, assuming the full 41.5*56mm = 69.7mm image circle. 645 medium format lenses have an angle of divergence of 72.3*, so having a minimum required angle of 58.1* for full coverage, that looks like it would work.
For comparison, a normal FX lens covers 24x36mm with an end of lens-sensor distance of around 36mm (approximating using my Nikon 50/1.8D). The angle of divergence here is 42*.

Question 4: (out of curiosity) do different format lenses have different angles of divergence? I know that view cameras require the lens to be quite far away (from the large film sensor), and mirrorless 4/3s cameras have the lens very close to the (small) sensor.

Just to show the price range I'm looking at with this setup, two 5D bodies would come to around $2000, used (looking through the local classifieds); the two lenses would come to around $700, and the adaptor $80.

Materials cost is then $2800 or so.
Labour cost is as yet unknown, but I've heard the group at my university are quite reasonable, if you give them an interesting challenge.


Off-the shelf DigMF sensors alone are between $8000-$18000 for the dimensions I'm looking at, and offer between 22-50MP. So - significant savings, so I think I can deal with manual focusing.

If I wanted to extend this into the extreme, a 2X2 FX sensor system would give 90-120MP at 4000-4800dpi (or 47MP at 3000dpi), 1.08X crop on 6x7 lenses (if using 48x70mm rather than the full 48x72mm), and have a materials cost around $4600, but likely much more difficult in design and implementation.

Question 5: what sensor would you recommend for this venture? Using Canon's 5D II would give an easy 42MP without having to tinker with the algorithm, but at over double the price, plus tax. If buying the individual sensor and processor is an option, maybe I could simply insert that into a cheap body like the Nikon D90 - $500 used.


What are your thoughts?