conkerwood

I absolutely agree in the scenario you described and for general landscapes it works. But in those cases you can get a huge depth of field anyway so focus stacking may seem a lot of work for a little gain. But imagine a long receding landscape with a fencepost a couple of metres in front of you and you want that that to be in focus too shooting at a low angle so that the fence post dominates the pic from base into the sky. You shoot receding focal points at say f22 so that you have plenty of overlap in the foreground and mid ground to avoid blooming. But when you move to the top of the fencepost where the only thing behind it is the sky and distant hills, even at f22 there will be no shots containing intermediate mid ground to provide the overlap. In this scenario, and this was the type of pic I was trying to take, you will not have a blooming problem where the fence post covers the mid ground because at f22 there will be a shot which has the them both in relatively sharp focus, but you will have the blur around the fencepost where the foreground covers the distant background. But now that I see that you are into numbers and the maths of the thing I will sit down tonight and do the maths to show you what I mean.

Catch you soon.

Peter

conkerwood

These are the numbers I came up with, they are based on DOFmasters online depth of field calculator.
Lets use the scenario I suggested, a fence post, 2.5 metres away with a receding landscape behind it to say 1000m which really isn't that far for a background. And assume that the pic is taken from a low angle so that the fence post protrudes over areas of both mid ground and the furthest points of the background ie 1000m away. You suggested a narrow aperture so I am assuming a sunny day and no wind and going for f22 which is as tight as my 24-105 L series will go on my 7D. If I set my zoom to 50mm, the furthest point I can focus to and keep the post in acceptable focus is around 3.5 metres but this will only give me around 8.5 metres behind the fencepost in acceptable focus. The closest point that I can set the focus so that the 1000m distant object is in acceptable focus is around 10 metres. But at this distance 4.5 metres is the closest limit which is well beyond the fencepost at 2.5 so it will be quite blurred. If I combine these two shots in a stack I will end up with blooming around the fencepost where it covers over the most distant parts of the scene. No shots taken in between can change this. A shot taken at 6m for example may have minimal blooming but it would only be in focus for a distance of about 28 metres beyond the fencepost which is of no use considering that we are trying for acceptable focus 1000metres away.

Obviously at f22 the problem worsens if the fencepost is closer than 2.5 metres, and also if you zoom beyond 50mm. Conversely if you move further away or bring the zoom back then the problem lessens. In fact if you bring the zoom back to 45mm you don't need focus stacking at all because from 2.44 metres to infinity will be in acceptable focus. Equally if you take the aperture down to say f/32 then you don't need focus stacking either unless you go past 55mm. But once you start to get beyond 60-65 mm with the scenario I described then blooming starts to happen again. All of this assumes of course that you have ideal circumstances ie plenty of light and no wind, but so often it seemed that I didn't have those circumstances. So f22 always meant winding up the ISO which to me defeats the purpose because past a certain point you are simply choosing another way to degrade the pic. Certainly you can do some really good focus stacking landscape work and there are some great exponents out there, way beyond my ability, but I am yet to see examples with very close foreground elements protruding over distant background unless of course they have done a little cloning repair work. So the solution is to avoid the scenario I described which for me was a problem because it was precisely that scenario that I was interested in. So I gave up and moved onto something else. But in the end you are essentially correct that the problem is minimised by reducing the size of the aperture but how often do we want to or are we able to be going down to f/22, f/32, particularly because the 24-105 performs best in the range f/8 to f/11
Please convince me I am wrong because I would love to find a way around it.

Peter

Chinaman Loc: Adelaide, South Australia, Australia

Thanks Peter for your detailed explanation. I am not doubting your issues and I won't continue to press you as I am not using this technique yet, and don't want to waste your valuable time. One of these days I'll have to come up to your place and tackle this fence and focus stacking together!

conkerwood

No, more important, one day you will come unto my place and I will sit down with you and try and figure out why the hell you have such a great natural eye and a natural feel for a pic and I have to work my butt off to get close. But as always it is fantastic to talk. Lets see some more of your posts, your stuff is always inspiring.

Peter

Chinaman Loc: Adelaide, South Australia, Australia

Ha, Ha!. Hate to shatter your wrong impression of my 'natural eye'. It's 35 years of learning and practicing!! Bet you feel happier now as anyone can do it after all that time. I'm highly confident you will do it in far, far less time. I promise to post soon as my Uni course assignment (and the course) will be over in a few days time! This last few weeks have been so distracting with the Christmas & New Year festivities, the 5 day and 1 day Test cricket series against England, the national 20/20 Bash, lots and lots of summer events, the Tour Down Under just underway, the Clipsal 500 about to start. Where can one find the time to go to work 5 days a week?!! Talk to you again.

Chinaman

LoneRangeFinder Loc: Left field

Peter is quite right: the "blooming" is a product of focus stacking-- of which I've done more of than HDR. I've never combined the two....