Best IQ - stop down or increase ISO?.

In this set of conditions what is likely to give best IQ especially sharpness. Pentax k-x, 55-300mm DAL ED lens at max zoom. I want to take a pic of a bird so I need, say 1/350th of sec shutter speed. Let's say for the given light I could either shoot at f5.6 (widest available) and ISO 400 or f8 and ISO 800. etc Which is likely to give best results. Or, put another way, in general is it best to get off the widest aperture in max telephoto zoom even if it means raising ISO by one stop?

Iso 100-400 is good on modern d-slrs, and the kx is perhaps the best at low light high iso...

I personally keep my cameras (k10's, ds2) at MTF priority (custom menu) to get the best performance from the lenses which is usually f8.
So I'd say stop it down between 5.6 and 11 and use higher iso's if needed.


even in the film days with my mz5 and 28-200 zoom I preferred iso 800 film, as the film didn't outperform the lens at 200mm where as velvia was capable of more sharpness than the lens at 200mm wide open...

In terms of bird photography the essential thing is usually sharpness and this means high shutter speeds to avoid not only camera shake but also subject movement. You might want the background out of focus to concentrate on the bird, so wider apertures will be very acceptable, especially as distances will not be very close.

That means that ISO may well have to be increased in duller weather, so I would happily increase it until suitable shutter speeds were obtained.

As for mode, AV is fine as as soon as the aperture is widened the shutter speed increases to compensate, so it makes no difference what mode you use. There are only three variables, all interlinked, shutter speed, aperture and ISO.

Any decent lens should perform well enough at wider apertures, especially a telephoto, and although f8 might be the optimum for lens quality that is no use if the picture is blurred.

Not when the noise level becomes unacceptable to you. Have a maximum ISO in mind.

High noise more noticeably spoils an image than slight softness from a good lens not being at its optimum aperture.

In general, I need to have an f5.6 300mm handheld lens wide open except sometimes in bright sunlight.

But it won't be blurred if the ISO is raised enough. What dcweather is asking is whether it's best to do that or use a larger aperture instead. It comes down to DOF and noise.

For (flying) birds even the 1/350th will be slow. If the noise performance of K-x is so good as test suggests and you have some average noise reduction programme, you can easily turn ISO up to 1600-3200 without problem to reach fast enough speed.

I'm with John on this - I would use whatever ISO, Aperture combination gives you the shutter speed. For a stationary bird (depending on the type) then you can get away with reasonably slow speeds (i normally try to have the shutter speed equivalent to focal length or better), but for one in flight I try and get above 1/1000 if I can - the faster the better - and in the British weather that normally means high ISO and biggest aperture... and still not fast enough! I use a K-7 and will happily go up to ISO800 and keep noise levels manageable. above that though I find the noise is more apparent. The only issue I find with the big aperture is that the DOF can become an issue, especially if shooting close-up or trying to get, say, more than one bird in a shot, but for a single bird I usually find it helpful for blurring out the background.

Mat

Thanks for the replies. It is pretty much as I thought and will just have to experiment with my new K-x to find out what is truly the max Iso vs noise level I am prepared to accept in the real world. I tend to shoot AV on max aperture and have previously tried to not go above Iso 400 but so far it looks like I might get away with iso 1600 which might get me the shutter speed on a cloudy day. Just have to see how good the Pentax 55-300mm is compared to my previous Tamron 70-300 on the k-m.
This was Iso1200, f5.6, 1/180th , hand held.
http://www.flickr.com/photos/dcweather/4219784254/
Dave

Nice Hedge Sparrow! I think you're right - you'll need to try it out and see what maximum ISO you find acceptable.