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Da Yi 6x17 back for 4x5 [Review]

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Old January 25th 05, 03:55 PM
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Default Da Yi 6x17 back for 4x5 [Review]

I kept seeing those Chinese made rollfilm backs that allow you to
shoot 6x17cm panoramas on 4x5 cameras, and wondering how
well one would work - so I decided to order one and find out.
Here are my first impressions for anyone else who's interested:

First off, for anyone who's never seen one of these and is screaming
"but 17cm is longer than 5 inches", I need to explain the principle.
Yes it is true that normally one thinks of 6x12 as the longest rollfilm
format that can be shot by putting a back on a 4x5 camera, and
that the only 6x17 backs available have been those (like the
Canham) made for 5x7 cameras. However, the Chinese have
taken a logical approach to 'solving' this limitation: how does a 5x7
format changing back fit onto a 4x5? Answer, by using a set of
tapering bellows in order to sit further back than the original 4x5
film plane, so that the light cone from the lens has room to spread
further before it meets the film. The Da Yi does basically the same
thing: it has a rigid body that fits into a 4x5 International back and
holds the film further back. There is also a separate ground glass
that fits in the same way, and with, of course, the same offset.

Obviously this approach introduces some problems - see below -
but it does provide a means to shoot 6x17 panoramas without
carrying a 5x7 camera, or investing in something as expensive and
specialised as a V-Pan or one of the Fuji or Linhof viewfinder
cameras for the format.

*** In the Box ***

The parcel arrived from Hong Kong, very quickly and well
packed. Inside the outer parcel was a smaller blue box which I
presume is the original retail packaging. This contained the film
back, the dedicated focusing screen in its holder, and two pairs of
format changing masks.

I didn't know the latter would be included: from pictures of the
back I had gathered that it was designed to shoot 6x9, 6x12 and
6x17, but no mention in the text had said that the masks were
included, they hadn't been in the pictures, and (to my chagrin) after
I ordered my back _then_ they started being mentioned as
included. In fact I have a Sinar Zoom back for doing 6x12 and
given the issues surrounding having to move the film plane back I
hadn't thought I'd want to use the Da Yi for anything other than
6x17 - but still, it was nice to get the masks as 'extras' and they
may turn out to have some use after all - see below.

There were no instructions, but the whole thing is obvious enough
not to need any.

One small black mark: no take up spool was included, so I had to
raid one from another back. Not a big deal, but annoying.

*** The Format ***

By my measurement the film gate is 57mm tall, and the length seems
to be just a hair over 170mm - so no short measure on size.

The format changing pieces are black aluminium masks that slip into
the film gate, resting just below the film plane and being secured at
each end by two screws. So they are easy to put in and take out,
but of course you can't do it mid roll - at only 8, 6, and 4 shots per
roll for the three formats that isn't a big deal.

Now for the interesting bit. The Chinese seem to have very literal
minds where format is concerned: in general 6x9 is actually
anywhere from about 78 to 84mm long, but on the Da Yi it is a
generous 92mm; 6x12 is normally 112mm long (except with Linhof
cameras and backs, where it is 120mm); with the Da Yi it is
124mm. These are the measurements on my example, of course
they may vary a bit between samples.

This is enough that I just might find I want to use the format
changing masks after all - probably not often, but it is enough that
I'm going to keep them safe rather than let them vanish into the junk

*** The Back ***

The back consists of two black anodised machined aluminium
castings. One attaches to the camera and holds the film chambers,
the gate, and the winder; the other is the back and clips on, this
bears the film pressure plates. I say plates, plural, because rather
than use one very long plate, the Da Yi uses a pair side by side,
each seemingly pushed forward by a centrally fitted spring. The
back clips on with two strong stainless steel spring clips: you slide it
on and then push down on the clips to make them pop over a pair
of studs. This attachment feels very secure and I have no worries
about it coming off in use or transit.

The dark slide is well forward of the film plane, about where it
would be on a 'normal' 4x5 back so there's a lot of air between it
and the film - maybe this would be a problem in very cold or humid
conditions, but I don't think it's a big issue. The slide is only just
slightly longer than the film gate - ie it starts to 'open' after being
pulled out only a few millimetres, so make sure it's always pushed
well home. It fits quite stiffly, but I think I might see about attaching
an elastic band or something similar just to make certain it stays all
the way in when in transit.

Loading is just dropping a spool into one end - the bottom lugs at
both ends can be pulled out against spring tension to do this - and
pulling the film across to the take up spool, threading it and putting
a few turns on the winder. Film counting is done through windows
in the back, so 220 film is a no no. Then just wind till the relevant
number appears in the right window. The back has three
windows, one for each format, and by each it tells you which
numbers to wind to: eg. for 6x17 you start by winding to the
number 2, and your other shots are at 5, 8 and 11. Logical

Because it's aluminium the whole things is lighter than it looks, given
that it is pretty big.

*** The Focusing Screen ***

This fits in the same way as the back, with the long narrow 6x17
ground glass set back in the same way. The glass is quite nice, with
a fairly fine grind on it, so it's brighter than I expected. No Fresnel
though, so when viewing it straight on the corners aren't very
bright. There are very simple markings in nice fine lines: an outline
of the whole frame, a central cross, and vertical lines for the edges
of the 6x9 and 6x12 fields of view.

One thing I hadn't expected was a nice bellows viewing hood. This
pulls out about five inches on two pairs of folding struts and stays
firmly put wherever you set it: it collapses small enough not to
impede my focusing loupe, and pulled out it offers quite effective
shading of the screen. It is attached, so far as I can see, with four
screws so could be taken off by anyone who didn't want to use it.

*** In Use ***

I only unpacked it yesterday, so this is a very preliminary
assessment: I haven't shot anything with it yet (lousy weather today)
so have no results to examine.

Overall the finish was a bit better than I'd expected. It's a simple
piece of equipment, and my sample wouldn't have passed QC at
Fuji, Linhof or Horseman - but there was nothing at all that I felt
needed 'fixing' before I could use it, and no sharp edges.

Loading was slightly awkward, with strong springs to work against,
but at least I know there'll be tension there to help keep that long
strip of film flat. Once I'd loaded the film in, but before winding
forward to the first frame, I took out the darkslide and carefully
looked at the film backing paper: it seems impressively flat, with the
twin pressure plates seeming to do a good job, and little sign of the
film curving away at the ends - this I'll examine closely once I have
some shots to look at.

Winding is by a knob, and one just slides up a window that covers
the holes for viewing the numbers on the paper backing, and winds
away. It feels smooth with a moderate amount of resistance -
basically it's nothing fancy, but neither is there anything that could
go wrong.

I like the ground glass - it really is quite nicely ground, and the
'sweep' of the 6x17 image looks very enticing on the glass. That
bellows shade over the GG is also a nice touch, and even when
using a dark cloth I expect I'll find the shade useful as it will help
keep the cloth 'out' from the screen.

All in all it gives the impression that it will 'do the job'.

*** Limitations of the Design ***

There are inevitable limitations when you shoot with a back that
sets the film back further than normal - the cost of having 6x17 on a
4x5 camera.

One set of these relates simply to the film being set back: wider
lenses may not be able to get infinity focus anymore, or you may
need recessed panels or bag bellows in order to get the lens to
focus and/or have any movements; and any rear swings and tilts
are now well off axis, turning around a point that is in front of the
film plane.

The first of these is probably not such a big issue as it seems: what's
the widest lens you have for your 4x5 that will actually cover 6x17
anyway? For me it's a 90mm, which won't focus to infinity on the
Da Yi while fitted to a standard panel, but it _looks_ to me like it
will once I've swapped it onto a recessed one. This limitation might
be a bigger limitation if you want to use the back for 6x12 - I have
65 and 38mm lenses that cover 6x12, but I very much doubt that
either will work with the format converting set on the Da Yi 6x17
back (they probably would with the 6x12 back that the same
company makes, since this is of 'conventional' design.)

The second one of these is a bit more of a nuisance, but if you're
used to working with base tilt, say, then having your axis swing and
tilt no longer 'on-axis' is at least a familiar thing to work with.

The second set of limitations relates to the fact that the 6x17 film
plane is now at the back of a 'tunnel' that reaches back from where
the 4x5 film plane would have been. At the 'ends' of the frame this
tunnel is necessarily only about 125mm long (5 inches) in order to
fit, and then flares out to the full 170mm. At the top and bottom of
the frame the tunnel could have started out four inches high and
tapered down, and a normal 4x5 sized darkslide could have been
used. Unfortunately the Da Yi designers didn't do it that way: the
tunnel starts 57mm high, just as it finishes.

To see why the 'length' - the taper of the tunnel at the ends of the
frame - is an issue, you need to think about the cone of light from
the lens. It is because this is a spreading cone that it is possible to
shoot 6x17 on 4x5 at all: the light passes through the 4 inch wide
opening at the back of the camera and continues to spread till it will
cover the 17cm long film plane further back. This is no problem
with wide angle lenses - the problem arises with lenses where the
cone tapers too 'slowly' for it to pass through the 4x5 opening and
then spread enough in the distance available to cover the full 6x17
frame: ie. longer focal lengths. Obviously the designers had to
make a choice he set the film further back and it is impossible
to focus wide lenses, make it too close to the original film plane and
the angle of the ends of the tunnel is too steep for longer focal
length lenses to cover the film plane. So this is, as I indicated
above, one of the inevitable 'costs' of making a 6x17 back that can
be used on 4x5, not a fault with this particular version of it.

I need to experiment to find out just what is the longest lens I have
that will still work with the Da Yi. Of course, as one exceeds this
length all that will happen is some vignetting at the ends of the
frame, so it may be that I'll find sometimes I use a lens that will still
let me cover 6x15, say and I'll just crop it. A 210mm is a 'normal'
lens for this format and I don't think that is going to be a problem:
it's the longer focal lengths I need to experiment with.

The parallel sides of the tunnel at the top and bottom introduce
another problem (actually it applies at the ends too, but is less likely
to arise there, in my use of the back anyway.) This is that moving
the lens off axis from the film will tend to introduce vignetting. Two
things could produce such off axis movement: shifting the lens or the
back, and tilting the back.

I did a little experimentation on these issues, just looking at the
ground glass, and neither seemed as bad as I expected them to be.
I used a 150mm lens, which is a moderate wide-angle for this
format (about equivalent to a 35mm lens on 35mm film). With this
I found I could apply as much rise and fall as my standard bellows
would allow with that lens focused at infinity - about 10mm - which
is a reasonable amount for landscape use. Next time I have some
time and daylight I'll put on the bag bellows and see how much
further I can go before I get vignetting. Next I looked at back tilt,
and found I could get at least 10 degrees with this lens before there
was any vignetting: again, as much as I'm likely to need in landscape

Now, this issue will be more acute with movement along the length
of the format, so swing or cross-shift with the back horizontal, or tilt
or rise/fall with it in portrait format will probably be much more
limited - but I'm likely to do this less often. I like vertical
panoramas, but there are few occasions when the 3:1 ratio of 6x17
is really suitable for such compositions and I'm more likely to use
6x12 (or the 1:2 2/3 ratio of the X-Pan).

Clearly I need to experiment a lot more, with different lenses and
with bag bellows (and also by swapping my base & axis tilt rear
standard for the base only one, which allows me to compress the
bellows a bit more), with putting my 90mm into a recessed board -
and with film in the back!

*** Conclusion ***

I like panoramas: I bought a Hasselblad X-Pan a couple of years
ago and love it, and since then have wanted to do more work with
panoramic formats on bigger pieces of film. But it isn't the mainstay
of my work, or central to my enjoyment of photography. Rather, I
often find myself working in a place where it would be nice to take
some panoramic shots as well as whatever else I'm there for, and it
will be one more string to my bow for the work I put with picture

In this context, the Da Yi is (subject to seeing some actuall results!)
looking like a winner. It was cheap, it isn't _too_ heavy or bulky,
there's nothing to go wrong with it, and the limitations imposed by
the design don't seem to be as severe as I thought they might be.

If I was committed to panoramic photography as my primary
interest I would get a V-Pan or one of the Fuji 617 models.
Likewise if it was the mainstay of my professional work. If I
wanted to shoot 6x17 with movements, but had no other use for a
4x5 camera I would, again, buy a V-Pan rather than this back plus
a 4x5. If I alredy had a 5x7 that I didn't mind taking into the field
I'd get a 'conventional' 6x17 back for it. If I was committed to
panoramic travel photography I'd get a Fuji 617, and if I was a rich
amateur enjoying playing with the format (nothing wrong with that)
I'd get any of the above, or a Linhof.

However, as a way to add this format to a camera I already own,
at low cost and for somewhat more occasional use, the Da Yi
works for me. For what I want from it, the price was right, and the
limitations are ones I can live with.


Now I just have to work out how to scan the slides.





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