Manual focus, diopter and glasses

Richard

The other day, I shot a bunch of pics in an aquarium. The light was dim enough that my Tamron f/2.8 28-75 was unable to achieve focus lock most of the time, so I switched to manual focus. While I got a few decent pics, most were out of focus, many more than I thought I had missed when I was shooting. Which got me thinking: I wear glasses all the time. I have the camera diopter adjusted so that the image appears sharp in the viewfinder. But could the combination of diopter and eyeglass lenses be giving me a different focus through the viewfinder than the focal plane of the camera? Is it possible to calibrate the diopter somehow to compensate? Or was it just lousy technique on my part? :scratch

Scott_Quier

Richard wrote:

The other day, I shot a bunch of pics in an aquarium. The light was dim enough that my Tamron f/2.8 28-75 was unable to achieve focus lock most of the time, so I switched to manual focus. While I got a few decent pics, most were out of focus, many more than I thought I had missed when I was shooting. Which got me thinking: I wear glasses all the time. I have the camera diopter adjusted so that the image appears sharp in the viewfinder. But could the combination of diopter and eyeglass lenses be giving me a different focus through the viewfinder than the focal plane of the camera? Is it possible to calibrate the diopter somehow to compensate? Or was it just lousy technique on my part?

The diotic adjustment has NOTHING to do with the focus of the shot on the sensor.

When you lens is properly focused, the image is (should be) sharp on both the focusing screen and on the sensor.

When you adjust the dioptic adjustment, you are simply focusing the light from the focus screen to match whatever focusing issues your eye might have.

When I made an adjustment to the dioptic adjuster, I look to the exposure information at the bottom of the viewfinder. When that's in focus, I know that the image I see on the focusing screen will be as sharp as possible and that any blur is the product of either poor technique or poor lens focus.

Qarik

Are you trying to actually manually focus by judging the clarity of the image in the diopter?

It would seem the best way is to lock a focal point then fram your subject on that focal point and .tweak tweak..till you see the in focus "green" inidcator in the dipoter and then snap?

As I am writing this..I had a thought..does the in focus inidcator not work in low light?

pathfinder

AF does not work in dim enough light, nor will the AF points acknowledge ( light up ) for correct focus is if is too dark.

I am wondering what shutter speeds Richard was shooting, if it was that dark? Are we certain the images were out of focus, as opposed to blurred due to movement, either of the camera or the subject?

It takes faster shutter speeds than one might think to stop swimming fish.

Richard

pathfinder wrote:

AF does not work in dim enough light, nor will the AF points acknowledge ( light up ) for correct focus is if is too dark.

I am wondering what shutter speeds Richard was shooting, if it was that dark? Are we certain the images were out of focus, as opposed to blurred due to movement, either of the camera or the subject?

It takes faster shutter speeds than one might think to stop swimming fish.

Right, sometimes the speed drops so low that all bets are off. But I'm not talking about those. I don't have a really good example, since I deleted all the junk, but this comes close:



This is SOC converted to JPG. f/2.8, 1/160, ISO 1600. He wasn't moving much, but I was very close. I would think 1/160 is fast enough, but maybe not. I usually try to keep the camera steady by having the lens hood touching the glass of the tank, but I don't know for sure that I did that on this one.

I think next time, I'm going to try shooting in Tv. What do you think the slowest speed should be to be safe?

Lord Vetinari

I use manual focus for all my shots (macro), I also have to wear reading glasses to see any of the camera settings but take them off for shooting. I have adjusted the dioptre as commented above so the image on the screen is as sharp as possible. Suspect your main problem here might be more to do with motion blur and very shallow DOF etc on moving subjects.
Brian v.

pathfinder

Richard wrote:

Right, sometimes the speed drops so low that all bets are off. But I'm not talking about those. I don't have a really good example, since I deleted all the junk, but this comes close:



This is SOC converted to JPG. f/2.8, 1/160, ISO 1600. He wasn't moving much, but I was very close. I would think 1/160 is fast enough, but maybe not. I usually try to keep the camera steady by having the lens hood touching the glass of the tank, but I don't know for sure that I did that on this one.

I think next time, I'm going to try shooting in Tv. What do you think the slowest speed should be to be safe?

Richard, part of your issue is shallow DOF - the head is in much sharper than the tail, and part may be movement - I think the dorsal fin is blurrier than the back of the seahorse, and the dorsal fin of a seahorse ripples with movement when I have seen them.

I agree that 1/160th should be fast enough, but shooting at f2.8 in the dark I find very tough without functioning AF and without a good split image focusing screen.

It is interesting as I have shot a few seahorses in the Chattanooga aquarium, and I found them hard to get critically sharp also. I think it is due to low light levels, the subject being close to the image plane, and large apertures, as well a creature movement all combine to create a challenging subject.