| Moderated by: chrisbet, |
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| Depth of field | Rate Topic |
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| Posted by chrisbet: Tue Feb 12th, 2019 19:41 | 1st Post |
| Thanks to Roger & Eric for their contributions to my knowledge on the subject so far but, having been doing some reading and getting hold of a DOF calculator for my phone, I have a question - what is hyperfocal distance??
____________________ If it is broken it was probably me .... |
| Posted by jk: Wed Feb 13th, 2019 03:31 | 2nd Post |
| Definition of hyperfocal distance https://en.m.wikipedia.org/wiki/Hyperfocal_distance Notice the 'acceptable' word, doesnt mean that it is critically sharp or the like, just acceptably sharp which will of course vary between people.
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| Posted by Eric: Wed Feb 13th, 2019 04:28 | 3rd Post |
chrisbet wrote:Thanks to Roger & Eric for their contributions to my knowledge on the subject so far but, having been doing some reading and getting hold of a DOF calculator for my phone, I have a question - what is hyperfocal distance?? It's the closest point a lens can be focused, whereby everything behind that point will be in focus to infinity. It varies for lens focal length and aperture. Used for landscape photography mainly and a throwback from early plate camera days. These days you would be lucky to get infinity or even great distance into focus due to atmospheric fug.  Dof is more relevant to general photography. For many years, before apps and internet, I created a spreadsheet specific to my lens a**enal and their fstop range for set distances, which I was more likely to use. It was a sort of abridged version for my use to stop carrying around unnecessary data. I printed out a copy for my camera bag and used it quite a few times. But once you get the hang of a subject it sort of comes intuitively....until you change genre. I am at the moment struggling with dof on my bird shots because my seating position/location varies as does the need to fiddle with settings to handle low light levels whilst avoiding noise.... not to mention bird size and movement. Of course you can use the depth of field preview button on the camera to get a reasonable idea of where focus tails off. That's assuming you haven't assigned that button for another function....like me 
____________________ Eric |
| Posted by chrisbet: Wed Feb 13th, 2019 04:36 | 4th Post |
| I was confused by the variation in definitions - some say the closest point at which infinity is in focus and others say the point in the middle of closest focus and infinity. Are these the same thing? What has shocked me is using the DOF calculator shows how small the DOF is when focusing on a relatively close object. I am going to have to find an exposure combination that gives me the sharpness I want on the subject together with the bokeh I want in the background!
____________________ If it is broken it was probably me .... |
| Posted by Eric: Wed Feb 13th, 2019 05:49 | 5th Post |
chrisbet wrote:I was confused by the variation in definitions - some say the closest point at which infinity is in focus and others say the point in the middle of closest focus and infinity. The depth of field exists in front of and behind the point of focus ....typically 1/3 in front and 2/3 behind. So the considered wisdom is to focus 1/3 into the subject. In my experience it's not as precise as that and you still need to be careful you don't 'focus crop' key elements at the front or rear of the subject....that you WANT in focus. Then there is the fact that some lenses front or back focus....that's why later camera bodies have the feature to fine adjust lens focus position! I prefer to use longer lenses for a subject and stand further back. I've never actually compared dof figures to see if it is better than a shorter lens up close ...but I just seemed to have more control of the zone of sharpness by doing that.  Changing my wording on hyperfocal distance.....it is the point at which you focus on to get the greatest depth of field which extends from infinity back to a point nearest you. In other words the focus WILL extend in front of the hyperfocal focus point by an amount ....but NOT 1/3 V 2/3 as mentioned (....or everything in front of you AND BEHIND YOU to a total distance of 1/2 infinity would be in focus.  )It's a way of ensuring any spare foreground depth of field is used up so that everything from close to you to the far distance is sharp. Hope that hasn't confused you ....it has me. This puts it more succinctly..... “The hyperfocal distance is the closest distance at which a lens can be focused while keeping objects at infinity acceptably sharp. When the lens is focused at this distance, all objects at distances from half of the hyperfocal distance out to infinity will be acceptably sharp.†And it proves the point that the proportion of foreground sharpness varies, as in this case it is not 1/3 of the dof, like 'normal' photography ...but reaches forward only half way between the focus point and the camera.
____________________ Eric |
| Posted by chrisbet: Wed Feb 13th, 2019 07:10 | 6th Post |
| So - going back to my horse portrait, it would have been better to focus on say the rider's toes than the horse's chest and to stop down the lens to f11 to straddle the horse with the available DOF. Having said that, what lens focal length would optimise the background bokeh while giving the same DOF - bearing in mind I could get a bit closer to the subject?
____________________ If it is broken it was probably me .... |
| Posted by Eric: Wed Feb 13th, 2019 08:42 | 7th Post |
chrisbet wrote:So - going back to my horse portrait, it would have been better to focus on say the rider's toes than the horse's chest and to stop down the lens to f11 to straddle the horse with the available DOF. What you need to know is the distance you were from the horse and the focal length needed to fully frame the horse and rider how you want it (bearing in mind you can crop later). I would say you need 3m dof for a horse head on. So it's a question of stopping down to get just 3m. It seems from the exif you were 8m away from the subject. You've cropped the feet a bit so let's say 10m would be better distance. For example.... If you are 15m from the horse and have a 100mm lens you would need f3.5 to get 3m dof. But if you were only 10m away you would need to stop down to f8. Of course dof is all about the zone of acceptable sharpness. It won't suddenly go totally blurred at 9.5m and 13.5m. So it's about making a judgement call as to whether you use larger apertures and let the horses bum go soft to ensure the background is out of focus. Failing that you ensure nothing in the background is close enough to matter...or mask and use a blur filter on the background in software.
____________________ Eric |
| Posted by chrisbet: Wed Feb 13th, 2019 09:16 | 8th Post |
Eric wrote:Of course dof is all about the zone of acceptable sharpness. It won't suddenly go totally blurred at 9.5m and 13.5m. So it's about making a judgement call as to whether you use larger apertures and let the horses bum go soft to ensure the background is out of focus. Failing that you ensure nothing in the background is close enough to matter...or mask and use a blur filter on the background in software.Ahh - I have little option to get away from background unless I shoot towards the hills - then the horse is in such bright light it tends to flatten the image - seems like I need to do some PC work afterwards!
____________________ If it is broken it was probably me .... |
| Posted by GeoffR: Tue Feb 19th, 2019 06:25 | 9th Post |
Eric wrote:The depth of field exists in front of and behind the point of focus ....typically 1/3 in front and 2/3 behind. So the considered wisdom is to focus 1/3 into the subject. In my experience it's not as precise as that and you still need to be careful you don't 'focus crop' key elements at the front or rear of the subject....that you WANT in focus.Unless you happen to be using a Nikon 105DC or 135DC lens when the degree of defocus and the depth of focus within the area of acceptable sharpness is a variable. In the case of a portrait where one may well want the subject's nose and eyes sharp but be prepared to have the ears slightly soft these lenses allow that to be done. Great fun but much easier with the instructions that came with the lens.
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| Posted by jk: Tue Feb 19th, 2019 07:19 | 10th Post |
| I think that sometimes we try to be too formulaic on these things. If you want the horse in focus then focus on the nearest 'important' point on the horse - head on then focus on the nose/eyes, side on focus on a stirrup or its side. Then to get reasonable DOF use f8 if you are less than 10m away or f5.6 if you are further away. This will give you focus for all the horse it also depends on the focal length of the lens (that is an additional complication but let us assume a 50mm or 100mm lens). If the background is too focused/sharp you can always blur it in Photoshop or other editor that provided masking and gaussian blur. Remember always that even if the latest hype says that with AI you can get a sharp image form a fuzzy one in truth you cant, you can only make up what you think it would be if it was sharp. So getting a sharp image is always the way to go. You can then defocus or blur areas selectively in an editor.
____________________ Still learning after all these years! https://nikondslr.uk/gallery_view.php?user=2&folderid=none |
| Posted by chrisbet: Tue Feb 19th, 2019 17:06 | 11th Post |
| Thanks - I use GIMP on linux and it does indeed have masking and gaussian blur plus lots of other options but nothing quite like the bokeh produced by a lens. Masking off just the horse & rider is a painstaking and lengthy task even using "intelligent" scissors - and you can't overdo the blurring or it looks like you pasted the object on some crepe paper!
____________________ If it is broken it was probably me .... |
| Posted by Eric: Tue Feb 19th, 2019 18:18 | 12th Post |
chrisbet wrote:Thanks - I use GIMP on linux and it does indeed have masking and gaussian blur plus lots of other options but nothing quite like the bokeh produced by a lens. Absolutely! When I first set up my digital photography company 25years ago we had a saying “inside every good photograph is a great image waiting to get outâ€. We revelled in image manipulation for commercial clients who loved seeing their product advertised in “unusual†situations. The trick was to make them still look realistic. In retirement, I have to some degree tired of and turned away from, image manipulation. Burnt out old b*gger. I would so like to get it right “enough†in the camera...like the old days. 
____________________ Eric |
| Posted by GeoffR: Wed Feb 20th, 2019 05:55 | 13th Post |
Eric wrote:Whilst I can't disagree with that Eric, some times it just isn't possible. Yesterday I was presented with a low flying Red Kite at very short range*, no time to switch to spot metering or apply exposure compensation just point and shoot! The images appear to be silhouettes but there is detail there with a little work. *It was so close that at 200mm its wing tips were outside the frame.
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| Posted by Eric: Wed Feb 20th, 2019 07:40 | 14th Post |
GeoffR wrote:Whilst I can't disagree with that Eric, some times it just isn't possible. Yesterday I was presented with a low flying Red Kite at very short range*, no time to switch to spot metering or apply exposure compensation just point and shoot! The images appear to be silhouettes but there is detail there with a little work.I am finding that is the case with bird photography.
____________________ Eric |
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