PAS (not M) - Which do you use and why?

Started Sep 26, 2012 | Discussions thread
Agius FOTO
OP Agius FOTO Senior Member • Posts: 2,126
Re: PAS (not M) - Which do you use and why?

Wow, I have to absorb this, but I can't tell you how much I appreciate the effort you put into explaining this for me with examples. Thank you.

EinsteinsGhost wrote:

Any time! Here is my elaboration on the subject, with illustrations.

I primarily rely on Aperture Priority, as it provides very good control over depth of field, shutter speed and ISO. Here are some of the specific scenarios:

Landscape, with “infinite” depth of field (DOF)

This is when you might want virtually everything in focus, near and far. The concept of “Hyper focal distance” plays a role here. HFD is the minimum distance to focus, that results in everything beyond that point to be in focus (“infinite DOF”). Additionally, half the distance from that point, towards the camera is also in focus.

On a camera, HFD depends on focal length and aperture. Older lenses used to have DOF scale that provided a decent approximation. Now, you could use math, either on your own or smart phone apps like DOF Master or iDOF Calc. Do note that sensor size also plays a role but since we are considering one camera, we can ignore it for now.

Here is an example of my early experiments with HFD, in aperture priority mode. The camera involved is Sony A55 and the lens is Sigma 18-250mm f/3.5-6.3 HSM OS DC.

Supplying iDOF Calc with the focal length (28mm) and aperture (f/16) for A55 (APS-C sensor) calculates HFD as 2.45m (about 8 ft).

So, if I leave the lens focused at just over 8 ft (let us assume 8 ft for convenience), everything from 4 ft in front of the camera and beyond will be in focus for these settings. I have a “Focus Hold” button on my A55 which is used extensively for such compositions. I estimated about 8 ft, set the focus there, and with “focus hold” button pressed, I recomposed the scene and took the image.

Landscape, or Portrait, with a shallower DOF

If shallower DOF is desired (to blur the background and/or foreground), you want the aperture to be larger. This can allow “separation” of subject from the background/foreground which is very useful for portraits, and occasionally in landscapes. The same apps mentioned above, also calculate DOF, and like HFD, it depends on focal length and aperture. Additionally, it also depends on distance to the subject (focus point). For any focal length and aperture of the lens, closer distance will result in shallower DOF. Also worth noting is that larger sensors will deliver shallower DOF than smaller sensors, if everything else is kept the same.

Here is an example:

This was taken using Sony A55 and Sony 135mm f/2.8 STF. In this case, I did not want the “older” flower to be lost completely, but serve as a fainter backdrop. So, instead of using the lens wide open (at maximum aperture), I went with f/5.6. It was also a windy day so I didn’t want to go too small with aperture (or too high on ISO to compensate for it).

Using Aperture to control ISO/Shutter Speed

With a macro, for example, I would prefer to shoot at the best ISO setting. For a bee or a bird in flight, I might give up some of the ISO advantage to freeze the action. Sometimes, you may end up having to compromise. Here is an example where I had to compromise ISO and DOF:

In this case, Sony A55 was used with Tamron 90mm f/2.8 macro lens. This was going to be a handheld shot, in relatively low light, so I had to keep the lens wide open. I, personally, trust image stabilization for no more than 1-stop. So, with 90mm lens (or, 135mm equivalent on full frame), the minimum non-stabilized shutter speed would have been 1/135s. Going a stop down would mean, approximately 1/60s which I used here. With the lens at maximum aperture, my only choice was to bump up the ISO to 800, which I did.

ISO 800 wasn’t as much an issue (as you can tell) as was lack of DOF. I could get only a part of the butterfly in focus as a result (since it was angled somewhat, and I had a very shallow DOF to work with). If I had better light, I would have changed the aperture to f/5.6.

So, use of “A” mode gives a lot of flexibility to tweak and tune the composition/effect. In the following case, I was dead set to have 1/2000s (to try and freeze a bee in flight) at no more than ISO 400 (for better Dynamic Range, lower noise, and nicer color depth). I could have used “S” mode. But, I was also anxious to see the possibility of shooting with f/4 where the lens is even sharper than it is wide open (taken with Sony A55 and Minolta 200mm f/2.8 G APO HS). However, I realized that f/4 was halving the shutter speed, which I could compensate for by boosting the ISO to 800 (which I did not want). So, I opened the aperture and took this shot.

IMO, you should play with “A” mode first, and keep it all manual (do not pick Auto ISO). Investigate all possibilities.

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