Ultra 'Digital XPan' Image Quality and Multi-Format thoughts

In the last two posts I discussed my Ultra Digital XPan set up: using a Canon RF camera, a visible band R and an IR converted RP in my case, combined with Mamiya 645 film primes (35mm, 45mm, 80mm and 150mm), coupled together via two shift adapters - one of them with optics that result in a stop increase in focal length and aperture.

As photographers we are conditioned mainly through our available technology. For example the lens focal lengths and the sensor aspect ratio and size. which lead us to seeing the world through the system's 'field of view'.

For full frame cameras we 'see' through a 3:2 aspect ratio (AR) sensor. Whereas micro four thirds and digital medium format shooters usually see through a 4:3 AR.

As I evolved my Ultra Digital XPan I also saw it as an adaptable AR system. That is, not restricted to a 65:24 XPan AR.

Let's take the standard full frame sensor of 36x24mm as our baseline 3:2 AR and compare this to one of the best medium format camera systems, ie the Phase One IQ family. The Phase One sensor size being 53.4x40mm:

If we now add in the Ultra Digital XPan (flat stitched) sensor equivalent sizes, after using both adapters together, we see the following comparison:

One of the 'advantages' the Ultra Digital XPan set up is that we can rotate the camera (landscape/horizontal or portrait/vertical orientation) and independently rotate each adapter, giving the system multiple 'degrees of freedom'. We can also replace the Magic Shift Converter's optics with a 'simple' pass through adapter. Or, for example, we could 'just' use the MSC on its own, giving a 56x24mm or a 44x36mm stitched sensor equivalence.

As a final illustration of the sensor size adaptability of the set up, if we use the front shift in landscape mode of 30mm, which gets enlarged by the MSC by 1.4, and use the MSC's shift of 20mm in portrait mode, we arrive at a 78x44mm sensor equivalence, which, when compared to 35mm full frame and the medium format Phase One, looks like this:

To illustrate this 78x44 option, here is a (scaled for display) test image, taken with my 45mm Mamiya at 45x1.4mm because of the MSC, giving a 14903x8124 stitched image in Lightroom, ie some 135MP image:

Of course all the above adaptability must come at some cost.

I will ignore the obvious cost of buying the two adapters and a set of medium format lenses. A more important çost for many photographers will be the impact on Image Quality, but this is where it gets a bit subjective.

If you are a pin hole film shooter, your definition of IQ will be different to someone shooting with a Phase One IQ4 system. Thus I lean towards IQ being in the eye of the beholder. If it works for you, then all is right with the world :-)

After a very helpful exchange on the S&T DPReview forum (many thanks to those that chimed in) I decided to approach IQ in a very pragmatic way.

First, I decided to not 'worry' about resolution, as I can't change this, ie I'm stuck with using the Mamiya 645 film primes and the optics in the Magic Shift Converter. This decision allowed me to not get diverted by creating MTFs and using MTFMapper etc.

But I still wanted a 'feel' for how 'good' my set up was: so I elected to use a 'field map' approach:

• Set the aperture fully open
• Point the camera down at a flat surface with texture, eg a carpet (see set up image below)
• Place a reference object in the middle of the frame, to aid stitching. I used a ruler
• Set exposure and focus
• Capture your images for assessment
• Stitch if evaluating a pano frame
• Use the find edges filter in Photoshop to visualise the ‘IQ' across the image

The set up looked like this:

The RAW capture from one of centre pano captures looked like this:

After stitching, in this case using the full shift of both adapters with my 45mm Mamiya 645 lens at f/8, the resultant, Lightroom, (perspective) stitched capture (21216x4741) looks like this:
 

After applying the find edges filter I got this:

The stitched image in portrait mode, ie 86x36mm, looks like this:

On inspection, I am pretty content with what I'm seeing in both images. Of course there is some 'fall off' towards the edges, especially in the extreme case. But the overall linearity and ‘IQ', to me, looks OK.

As usual I would welcome any comments on this post, or any of my posts.