Depth of field concerns with a Yashica TLR

[tribal-warrior]

Sometime soon, I'm planning to shoot some star trails with my Yashica D TLR. Within my composition, I'm going to have a tree-lined hill in the foreground at the bottom of the frame with star trails streaking above it. I'll be shooting on a dark moonless night and I'll be selecting a pretty large aperture at around f4 or f4.5. So hopefully, I can get some separation between the hill and the sky. In other words, I would like the sky to appear lighter with some colour while the hill will record as a silhouette.

Yesterday, I was out at the shooting location during the day in the spot where I would be setting up. A number of times, I focused on the top edge of the tree-lined hill using the pop up critical focuser on my Yashica D and something really strange and unexpected occurred. Each time after I focused, I checked the distance on the focussing knob and it was different every time! It was really inconsistent. Sometimes, it would be right on infinity. Other times, it would be about 3 or 5mm away from infinity and even further like about 8mm or something like that. It was all over the place.

So when it comes to the actual shoot, I'm going to assume that my focusing of this hill is not going to be accurate (and I still cannot fathom why.) I just want some reassurance that the depth of field will be enough so that the hill will appear in sharp focus on the processed film. As most people know, depth of field increases with distance so I have that somewhat to my advantage. Though on the other hand, I will be shooting at a bit of a large aperture. I don't want to stop down further because I want a light coloured night sky separated from the hill.

Several years ago, I was shooting a semi-distant landscape with my Koni Omega Rapid 6 x 7 camera with a 90mm lens. And instead of focusing right at infinity, I deliberately set the focus a bit short of infinity like about 1 or 2mm away or thereabouts. The processed transparency was nice and sharp but I was probably stopped down a fair bit like around f8 - f11. I admit I haven't done the same thing with a large aperture.

By the way, this hill I'll be shooting is not super distant. It's not miles away or anything like that. It would be pretty quick to walk over to the base of the hill from the planned camera position.

Hmmm.....I guess I could do a test with a digital camera and a standard lens before the main shoot with the TLR. Go out to the same location (again during the day) and take a number of photos of the same hill (same distance) with the digital camera. Aperture would be set to f4 and the focus distance would be different for each shot but not too far from infinity. Then zoom in 100% on the computer to check focus.

 

[tribal-warrior]

The digital camera I will be using for the daytime test will be a Panasonic mirrorless M4/3. I'll be mounting a Canon FD 24mm f2.8 lens to it with an adapter (acting as a standard lens.) Another thing I will do is focus on the top of the hill through the EVF (while digitally zoomed in) and take note of the distance marking on the lens. That at least will give me an indication of the distance to my subject. I'll also take along a 35mm Canon SLR with a Canon FD 50mm lens and focus with that camera too and compare (to see if I get about the same distance.)

 

[tribal-warrior]

Today, I headed to the location with two cameras - a Canon T70 and Panasonic G7. With the T70, I focused on the top of the hill with a Canon FD 50mm f1.8 lens. I focused a number of times and there was a little bit of inconsistency at which focus distance I arrived at but not as much as with the Yashica TLR. The focus distance on the Canon FD 50mm lens was usually between 30 feet and infinity and often closer to infinity. At one stage, it was right on infinity.

Next, I focussed a number of times with the Panasonic G7 and a Canon FD 24mm f2.8 lens. Most of the time with this camera and lens combination, I got around 10 feet. I then stopped down to f4 and took a number of shots (adjusting the focus a bit closer each time.) The first shot didn't look entirely sharp surprisingly (focused at about 10 feet.) I then refocused again and this time, the distance on the lens was past 10 feet. I took another shot at this distance and the top of the hill looked very sharp when previewing the picture on the EVF. Once again, I took more shots and varied the focus but it didn't take much to get increasing soft images - even with small rotations of the focus ring. It just goes to show that even at this kind of long distance (likely over 30 feet) you still have to be pretty accurate with your focusing when shooting at a large aperture like f4.

 

[MartinN]

It just goes to show that even at this kind of long distance (likely over 30 feet) you still have to be pretty accurate with your focusing when shooting at a large aperture like f4.

That is exactly my experience, the curse of manual focus with medium format. I had once my Mamiya 70mm f2.8 LS sent for ’recalibration’ of infinity focus because I suspected some misalignment. Alas, when I got the lens back it was not any better or worse. The whole thing is that you have to have acute vision and a good ground glass, because in my opinion the ground glass view can be the most accurate. So I had to learn to focus really a lot back and forth and observe the ground glass. Still, it can be a miss or hit affair, so for critical shots I take a few and refocus between them. It needs a very good accuracy, but the fingers and vision are only so so.