Depth of Field

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Ste_S

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Having trouble getting used to depth of field and manual focusing with a Pentax ME Super with 50mm f2 lens. Mostly walkabout shooting on city streets, and end up getting shallow depth of field when opening up the lens for lower light. I presume f8 is the sweet spot, and opened up wider than that I'll get shallower dept of field ?

I've perhaps been ruined by auto-focus crop sensor digital cameras and zone focus film compacts....
 
Yep!
Open it up - shallower depth of field.
If you want to shoot at 5.6 or 8 just use a faster film. 400 instead of 100
 
The wider the aperture (the lower the 'f number') you use, the shallower depth of field (depth of focus) becomes. This is useful when isolating objects from their background/foreground, but be aware that your focussing will have to be more accurate to capture the point you want in perfect focus. This is fairly easy when shooting static objects, but can be harder to achieve if trying to capture faster moving objects such as people walking quickly towards you on a busy street (as you've probably found out).

This can make using a manual focus camera more challenging, but makes it all the more rewarding and satisfying when you get 'that' shot. If you want to increase your depth of field then use a smaller aperture (perhaps f8 or above) but, as you may have found, unless it's sunny and bright, this may drop the shutter speed too low to freeze moving objects or avoid camera shake. If so, as Ken says, try using a faster film such as 400 ISO to give you a higher shutter speed, if you're still struggling then you could perhaps try some Kodak Portra 800 ISO, it's not cheap but I find it's a nice-looking film for the ISO it gives. Hope this is useful, and let us know how you get on. (y)
 
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Thanks both. I have been using the camera at 800 ISO with Tri X pushed one stop, and Fuji Neopan 400CN shot from 200-800 ISO.
I suspect it's mostly user error / not understanding the variances of depth of field. I've been so used to cameras that have auto focus and wider depth of field due to crop sensors and slower kit lenses.

This shot below for example. I did open up the lens (can't remember if f2 or f2.8), as I did want to blur the background. I didn't perhaps realise just how shallow dept of field is at wider apertures on 35mm/full frame



Attachment-1.jpeg
 
Yes, you'll notice a difference between a film SLR (or FF DSLR) and crop sensor DSLR in terms of DoF, particularly using a wider aperture lens. It's like anything, you just need to get to know the camera and lens set-up you're using. Does the ME Super have a depth of field preview button? If so, maybe use that for a bit until you get used to what DoF at each f stop looks like on the lens you're using? If not, someone posted a link to a useful video in this thread https://www.talkphotography.co.uk/threads/focus-issues-photographing-fish.666621/ which demonstrates the principles of DoF when using a DSLR, and how this moves depending on where you focus.

You could perhaps modify this technique, placing the bit of tape (or other highly visible item to act as a focal point) at the range you usually take you street photos, then shoot a series test shots (using a tripod, and making careful notes of the f stop you've used for each shot - you could perhaps put a bit of card with a reference number written on it in each photo so there's no chance of mistaking each one). You could then refer to your notes and each photo to familiarise yourself with how much DoF your camera and lens gives you at a set distance (or two) with whatever lens you're using. If you use a 36 exposure film you could probably get three or four test sequences on it, and as long as you keep very careful notes as to which shot was taken on which setting this should give you a good reference point. A hi-resolution lab scan of the film would probably be best for this, as the sharper the scan of the negs you get, the more you should be able to tell from it. Hope this suggestion is useful. :)
 
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Ste_S said:
I presume f8 is the sweet spot
Click to expand...
There is no 'sweet spot'. Dof is a variable, and is influenced by aperture, the focal length in use, and your closeness to the intended subject. But it sounds as if you're getting a feel for it. A problem with dof preview levers is that their operation darkens the vf image thus making it harder to assess. Experience is the best teacher.

As mentioned it's best to gauge the film speed to the intended use, but remember that shallow dof can be a compositional tool.
 
Ste_S said:
Thanks both. I have been using the camera at 800 ISO with Tri X pushed one stop, and Fuji Neopan 400CN shot from 200-800 ISO.
I suspect it's mostly user error / not understanding the variances of depth of field. I've been so used to cameras that have auto focus and wider depth of field due to crop sensors and slower kit lenses.

This shot below for example. I did open up the lens (can't remember if f2 or f2.8), as I did want to blur the background. I didn't perhaps realise just how shallow dept of field is at wider apertures on 35mm/full frame
Click to expand...

You have got a lot of mixed up thoughts. You need to slow down and understand what you do. E.g. the sweet spot refers to the f stop where a lens produces its best possible sharpness (edge to edge) and usually that is somewhere towards the middle of the range.

You can open the diaphragm to let more light in when there is not enough light or you can drop the speed if you want to keep the small aperture.

The photo you show, I assume you focused on the second subject so correctly the camera has blurred the near person (depth of field works in front and behind the point of focus). But you sound as if you wanted the front person in focus but you focused on the second person.

As you use a single focal length lens when you focus on the scale of metres/feet you are likely to have some aperture numbers ... they show for a given a aperture what distance is going to be in focus (someone else could explain it a lot better)...

If it helps a little.
 
Learn to read the focus scale.

Untitled-1.jpg

This image shows the lens focused at just over 15ft (~ 5m). And the f/8 marks show that everything from ~ 4m to 10m will be w/in the DOF if the lens is set to f/8. The f/4 marks show the DOF if set to f/4 to be ~ 4.5m to 6.5m (est). And if set to f/22 it would be ~ 2m to infinity.
However, the manufacturers use a rather lax definition of "acceptable sharpness/DOF" in determining these markings, and the scales are rather coarse, so you might prefer to use the next shallower aperture markings in practice.
 
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