Da Yi 6x17 back and ground glass quality

[kryn_sporry1]

Currently I'm using a Shen Hao 4x5 with a Da Yi 6x17 back. Nowadays

I'm in Taiwan so I can make some interesting exotic shots. However,

I find it extremely difficult to view the scene on the ground glass.

The center is ok, but teh corners are just black. Can't see anything

in there (mind you, the days are bright). I use a 90 Nikon f8 SW

lens, so brightness isn't exactly brilliant. Is there a way of

making the view finder better to see? SHould I replace the ground

glass with something better?

[michael_briggs2]

I don't have this particular back, but it a general characteristic of wide-angle lenses that the corners are darker. One reason is that these lenses deliver less illumination off-axis than compared to the center, particular wide-open. Another reason is that the rays to the corner arrive at an angle to the ground glass -- while the ground glass scatters the rays somewhat, only a small fraction of the corner rays are redirected to the photographer's eye at the center. The technique that I use is to move my head around, viewing the corners at the angle that gives the brightest view. Sometimes you have to build up the image in your mind. Or you can try adding a Fresnel lens, which will act to focus the rays towards your eye, centered behind the ground glass. Or for the most expensive possible approach, you could buy a faster lens.

[mikestacey]

Kryn, I have the exact same back and also the same lens, on a Horseman Woodman. I can just see the edges if I move my head around a bit under the dark cloth. Otherwise, I love this back with the LF camera as I have enough movements to tweak focus most of the time.

[vinny_walsh]

Most office supply stores sell 9x12 inch magnifier sheets for maps. It's a series of

concentric circles similar to a fresnel you'd buy for much more than the 7 dollars i spent.

Cut to fit over your ground glass using the center point as the middle. I replaced my

shenhao gg with a satinsnow gg and i can't tell much of a difference. the cheap fresnel

make a hell of a difference with my 90mm though.

I've got the shenhao 6x12 roll film back and i can't get sharp results because it's too heavy

for the camera. Are you getting sharp negs with your 6x17?

[mikestacey]

The cheap fresnel is a good idea. Yeah the slides are pin sharp. My tripod is a lightweight Manfrotto 390 I think. The whole rig wobbles a bit but with a firm hand on the centre of the tripod it all seems fine. I also have the 6 x 12 Da Yi back and it works well too, probably better but I don't like the format nearly as much.

[paul_owen]

Go down the cheap fresnel route! I use an A4 page magnifier - a very flexible and cheap (about ﾣ3GBP)alternative. I measured and cut out the central portion and mounted it to the screen using clear, self-adhesive photo corner mounts. The difference was amazing! I've just fitted the same type of fresnel to the screen of a Tomiyama Art Panorama 6x17 Camera - same improvement - those dark corners simply "open".

[kryn_sporry1]

Thanks for the advice guys. I too had sharp results before with the 6x17 on the Shen Hao45, unfortunately I used a benbo tripod, which is now going out the door. The results were sharp but the horizon was angular. I think this is because the benbo is actually not stable/stiff enough for this combi. (trekker mk2). I just ordered a velbon CF530 (I think it's CF, carbon anyway, for only 124 GBP!!!) I'm on holiday now so don't have it with me. I nstead I am now using an old aluminium Velbon tripod, no head, for maximum stability. Lack of a good head makes it a little less practical, but it is stable like a seaman during still waters! (It weighs a ton as well!!!)

 

As for the ground glass, I'll try to get hold of a fresnel lens magnifier paper thingy and try that. It actually makes sense with a wide angle lens to have dark corners. Focussed at infinity the lens is very near the film plane/ground glass in the centre, but ofcourse that means that in teh corners it is miles away, which again explains why you should also use a centre spot...