Why use Av instead of P?

Probably a stupid question, but here goes...

I've been getting to know my GX-10 a lot better of late. Having been used to aperture priority on film cameras, that's what I was using on the GX-10 until recently, when I started exploring the functionality rather more. I now tend to leave it in P mode most of the time, as it seems to me that it does exactly the same as Av mode if you want (one of the dials sets the aperture), plus you have the option to prioritize shutter speed instead with the other dial. Given this, why would I want to use Av mode? Or even Tv mode, come to think of it?

It makes no difference what mode you use, just use the one that suits.

However we dress it up, there are only three variables: aperture, shutter speed and ISO. Which one you choose to make the main variable that you take control of is up to you.

I use Av as the depth of field is critical to the final look of the image. It the shutter speed becomes too low I increase the ISO to compensate.

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Best regards, John

Sure, that's the reason I use(d) Av mode as well. My point is that P mode, as far as I understand it, gives you both Av mode and Tv mode, depending on which dial you adjust. So is there any reason why you would set your camera on Av mode, instead of leaving it on P and adjusting the rear dial?

Not all cameras have all options, so Av is pretty universal across all the cameras I use.

Let me ask the reverse question - if Av does all that's needed with all the cameras I use, why change it for something else on just a few of them?

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Best regards, John

I would say that Av & Tv are more 'active' modes for the photographer, and so the choices you make first up are likely to be more positive, a specific decision (eg to start with f1.8 for a portrait) than if you begin in P. With P you take the default (usually averaged) type of settings, then you need to take your active part. There is a risk this will therefore be too timid, and you will not achieve the full effect that may be possible or desirable (its a bit like the scene modes on 'entry-level' cameras I was talking about on the the other thread).

I believe that operating in Av or Tv will result in stronger and more positive user input than P - resulting therefore in stronger images.

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I think we're talking slightly at cross-purposes here. I'm not questioning why there are straightforward aperture priority and shutter priority modes on the camera - they certainly need to be visible there for anyone coming afresh to the camera, for familiarity's sake. My question is rather why would you, or another skilled and experienced user of these cameras, switch to Av instead of P? Does Av provide anything which P plus rear dial does not?

LATER: The above was in response to John Riley's comment.

Yes, a positive decision to retain full control from the outset. Starting with P isn't a positive decision in the same way as you start with whatever the camera offers.

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Best regards, John

Interesting idea! So more of a question of commitment, then, rather than any actual technical reason.

There is another mode, the Green completely automatic one, which I have never once used. I don't even really know what it does, but I assume that it makes decisions I would prefer to make myself. Might as well let the camera decide what to photograph.

You mean the camera with modes such as "Ansel Adams" and "Helmut Newton" included, plus the new Auto Composition feature.....

But if we go back to the 1980s and read articles in magazines speculating on what the future holds the amazing thing is that it's pretty much all happened. It's happened in a much better way as well.

In the happy days of childhood when I was reading books and comics with space walking in them, my parents said, "It's ridiculous of course, it will never happen."

Never say never.

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Best regards, John

So by logical extension of that thought process, the pinnacle is manual mode.

Which I would tend to agree with.

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You can see some of my photos here if you are so inclined

It's a means to an end. If I set the aperture and the camera indicates 1/250sec then there's no advantage to me setting that manually.

Av plus judicious use of exposure compensation will deliver any desired result. But then so will Tv if you wish.

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Best regards, John

One advantage of P mode is that, initially, you'll get a more useable combination of aperture and speed for a grab shot in darkish conditions. In Av, you're likely to risk a low shutter speed (or a high one in bright conditions) because you've set the aperture for the lighting that existed during an earlier "shoot".

I agree, there's an extra step involved in switching to aperture priority but this quickly becomes second nature. You also have the capability of switching to Tv almost instantly if the shot requires it. It all depends on what sort of photographer you are and your normal subject matter.

Technically, P mode can be set to operate in exactly the same way as Av. The only practical difference is that you'll lose your chosen aperture when you switch the camera off and must reset it when you switch on.

If Av gives you more self-confidence in your photography, that's fine, but it's more a question of mindset than practicality. Manual's fine too, but P mode can give you exactly the same settings if you're following the metered exposure or have factored in some compensation. Pure manual is good fun, though, and gives great control in very specific circumstances.


Al (who admits to using Av and manual from time to time)

me too.
the biggest advantage to knowing how to shoot manually and get pro results comes when you can pre-visualise the end result before you click the shutter and make the the shot the way you see it in your mind.
when you get there....

You make all the decisions that affect the image.

What has more processing power? Your bigger brain? or the chip in your camera?
figure that out, then let the smarter of the two make all the decisions.

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Fired many shots. Didn't kill anything.

Often it's better use the brain's processing power to make artistic compositional decisions and leave the computing of exposure settings to the camera.

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But it surely will always be better (or more advisable) to consider the subject type and any specific effect you might want and use the most appropriate mode for that. I doubt Smeggy you get many of your low DOF portraits shot wide open in P mode without having to crank the aperture open straight away, an extra unnessary step. It would make sense to begin in Av if this was the intention from the start - this does not involve any extra step if the dial is already set to Av. This would apply to landscapes also. If you're working in rapidly changing light then Tav could be better, or Tv if trying to control the effect of movement. I don't think my camera's computational power is going to be superior to my brain's processing in any of these situations

If you consider the 'priority' aspect of the shot, then you can decide on the most intuitive mode to use - eg : will the priority be a specific DOF effect (Av - shutter speed will vary), a specific shutter open time (Tv - aperture will vary), the need to lock both aperture & shutter speed values (Tav - ISO will vary), or the need to alter the ISO quickly for changing lighting or a specific noise effect (Sv - and I don't know what else changes!!)

You could get to the same settings in P mode, but not without more mental steps and visual references to the numbers, all of which will take more attention and be less intuitive. So the process in terms of the human / machine interface is very different indeed.

This is not to say that P mode has no use - it is good in situations where you have no clear identified 'priority' for capturing the shot, but where settings of an average nature will do - then it could be the more intuitive mode. For me these types of images are a minority though.

The OP asked about green mode above - this is very different to P again. Now you have absolutely no creative control at all - not aperture, shutter speed, iso, not even exposure compensation, and you can't even make the flash fire if it doesn't think it needs to.

It's worth mentioning the 'Program Line' setting (control panel on the K7 / K5). Here you can specify the bias that is applied to default P mode settings - speed, DOF or MTF (optimum aperture for quality on a DA lens). This could be useful I guess, but it won't apply the extreme settings that would give us the most effect we might need.

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My Guides to the Pentax Digital Camera Flash Lighting System : Download here from the PentaxForums Homepage Article .... link
Pentax K7 with BG-4 Grip / Samyang 14mm f2.8 ED AS IF UMC / DA18-55mm f3.5-5.6 AL WR / SMC A28mm f2.8 / D FA 28-105mm / SMC F35-70 f3.5-4.5 / SMC A50mm f1.7 / Tamron AF70-300mm f4-5.6 Di LD macro / SMC M75-150mm f4.0 / Tamron Adaptall (CT-135) 135mm f2.8 / Asahi Takumar-A 2X tele-converter / Pentax AF-540FGZ (I & II) Flashes / Cactus RF60/X Flashes & V6/V6II Transceiver