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Aperture

P_H_I_L_L
Posted 29/03/2011 - 20:41 Link
This has probably been discussed a thousand times, but this thought has just entered my head and I thought I'd better mention it before it swiftly leaves.

If I am taking a shot of something in the distance, on infinity focussing, does the aperture still effect how sharp the image will be?
gartmore
Posted 29/03/2011 - 20:46 Link
Techically yes, in reality probably not. However, aperture affects more than depth of field, for example, lenses will perform better at apertures some way between fully open and fully stopped down.

Far better to caluclate the hyper-focal distance for a given aperture and len combination.
Ken
“We must avoid however, snapping away, shooting quickly and without thought, overloading ourselves with unnecessary images that clutter our memory and diminish the clarity of the whole.” - Henri Cartier-Bresson -
Smeggypants
Posted 30/03/2011 - 00:14 Link
It will affect it yes. It's difficult to get all the light from a wide open to lens to focus exactly on the same place. That's why stopped down lenses tend to be sharper. This is nothing to do with DOF, but imperfections of the lens itself.

With zooms it might also be a function of focal length as well as aperture. My Sigma 135-400 lens ahs a stunning IQ. up until 350mm. After that it rolls off a bit. So much so that I get better IQ by shooting at 350mm and cropping than I do shooting at 400mm.
[i]Bodies: 1x K-5IIs, 2x K-5, Sony TX-5, Nokia 808
Lenses: Pentax DA 10-17mm ED(IF) Fish Eye, Pentax DA 14mm f/2.8, Sigma 17-70mm f/2.8, Pentax-A 28mm f/2.8, Sigma 30mm F1.4 EX DC, Pentax-A 50mm f/1.2, Pentax-A 50mm f/1.4, Pentax-FA 50mm f/1.4, Pentax-A 50mm f/1.7, Pentax DA* 50-135mm f/2.8, Sigma 135-400mm APO DG, and more ..
Flash: AF-540FGZ, Vivitar 283
MrCynical
Posted 30/03/2011 - 04:38 Link
Yes: lenses tend to be at their sharpest (ie capable of resolving the most detail at the in-focus area) when stopped down, however this depends on the lens's maximum aperture. For example the DA 18-55 kit lens, or the Sigma 10-20, are best at about f8 while the FA43 is sharpest at f4 because it has a larger maximum aperture (f1.9 compared to f3.5 and f4 for the two zooms)
Dangermouse
Posted 30/03/2011 - 11:09 Link
Definitely makes a difference, even with very well regarded lenses. The Pentax-M 28mm f3.5 I keep raving about turns sharp enough for very severe crops if you stop down to about f8 at infinity for a landscape/cityscape.

This is why I can never fathom the shutter priority mentality. I know people who set shutter speed once then change aperture to balance it, which to me is very strange. I set the aperture to get the sharpness/DOF I want then the shutter speed is matched, although obviously if in low light I'll sacrifice DOF to avoid camera shake.

Tv mode does have its uses, such as aircraft where you either want the camera locked to the fastest possible speed for jets or 1/125 or so to avoid frozen propellers.
Matt

Shooting the Welsh Wilderness with K-m, KX, MX, ME Super and assorted lenses.
Algernon
Posted 30/03/2011 - 11:46 Link
Dangermouse wrote:
This is why I can never fathom the shutter priority mentality. I know people who set shutter speed once then change aperture to balance it, which to me is very strange. I set the aperture to get the sharpness/DOF I want then the shutter speed is matched, although obviously if in low light I'll sacrifice DOF to avoid camera shake.

Tv mode does have its uses, such as aircraft where you either want the camera locked to the fastest possible speed for jets or 1/125 or so to avoid frozen propellers.

Strangely it was shutter priority that made Canon popular with the AE1 (no remarks please about Canon users being dim ).
Half Man... Half Pentax ... Half Cucumber

Pentax K-1 + K-5 and some other stuff

Algi
Dangermouse
Posted 30/03/2011 - 13:15 Link
I think it says a lot that Pentax only bothered fitting it to the Super A, of all their manual focus bodies!

Weirdly it does have a use there. If you want to fiddle around proving that some DA lenses are full frame capable then shutter priority will allow you to change the aperture in a rather roundabout manner.
Matt

Shooting the Welsh Wilderness with K-m, KX, MX, ME Super and assorted lenses.
gillbod
Posted 30/03/2011 - 15:19 Link
generally you'll be ok as far as depth of field go. but the lens should gain in terms of the sharpness it can provide at apertures around f/8, typically.
k7, 15/4, 31/1.8, 70/2.4, 200/2.8, Metz 58
Dangermouse
Posted 30/03/2011 - 16:46 Link
I also remember reading in "The Asahi Pentax Way" that when shooting at infinity with a lens with the correct markings (like the K, M or A series) you should set the infinity mark to the left hand mark for the aperture used.

The theory went that otherwise you were also focusing on things beyond infinity (as DOF extends further behind the subject than in front), whereas by doing this you use the hyperfocal distance to have far closer objects in focus.
Matt

Shooting the Welsh Wilderness with K-m, KX, MX, ME Super and assorted lenses.
Algernon
Posted 30/03/2011 - 17:44 Link
That's correct Matt? Makes you wonder why they removed the markings on later lenses
Half Man... Half Pentax ... Half Cucumber

Pentax K-1 + K-5 and some other stuff

Algi
Dangermouse
Posted 30/03/2011 - 19:05 Link
I suspect they weren't being used by many people. DOF seems to be considered quite advanced in point and shoot circles, meanwhile I always recommend newbies find a decent article on the subject and learn about it as their first step in serious photography. I notice the focal distance markings have been left off the DA L lenses, and I can't really believe this is due to cost.

I find it much, much easier to turn an aperture ring and read the DOF scale than it is to twirl a thumbwheel and guess the DOF!
Matt

Shooting the Welsh Wilderness with K-m, KX, MX, ME Super and assorted lenses.
Edited by Dangermouse: 30/03/2011 - 19:06

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