Flash and image sharpness question?

For the record I am only an occassional user of flash but would like to understand its usage to greater effect.

At the moment I have a most simple question, or so it seems to me

It was another dull day here in the UK but I wanted take a few more pictures in the garden with my 40D and I left the 70-300IS on it.

Well, with a shield bug I spotted I could get a 1/200 @ f8 @ ISO800 but the image a little too soft - ISO softness - a similar one taken at 1/250 @ f8 @ ISO 200 is very sharp by comparison. This flash image was surprisingly sharp straight out of camera compared to the non flash one.

Alright I was not trying under optimum comparison conditions but the results still intrigue me and I am a real noob when it comes working with flash.

What am I missing or not understanding that is likely blindingly obvious?

TIA

If the flash accounts for the large majority of the light used to capture the image, then it has the effect of freezing motion - both camera and subject movement. Think high speed strobe images. The actual duration of the flash pulse is on the order of milliseconds. But, as described that shouldn't have been the case in your garden, it may have been more a case of you holding more steady or letting the IS spin up and stabilize with the flash.

timbop wrote in post #4113811
If the flash accounts for the large majority of the light used to capture the image, then it has the effect of freezing motion - both camera and subject movement. Think high speed strobe images. The actual duration of the flash pulse is on the order of milliseconds. But, as described that shouldn't have been the case in your garden, it may have been more a case of you holding more steady or letting the IS spin up and stabilize with the flash.

Hmmm!!! this is why I like POTN because new (to me perspectives can be offered). Yes, I know to let the IS spin up!

The most pertinent feedback you give is the flash duration freezing all movement so even though a 1/200 or 1/250 is normally enough to get accurate focusing/sharp image with an IS lens the fact that was working at the closest focusing distance even at f8 the DoF would be quite slim so minor body movement could possibly account for it.

Oh for better light when I want to take pictures either that or I must/need to invest in faster glass....more money! And just possibly not work too often at the limits of what the camera and I am capable of

My (indoor) flash shots are always so tack sharp (compared to shots taken with large aperture lenses - e.g. my f/1.4), it makes me consider actually using flash more - but I hate the harsh shadows and the change in white balance (?) I think I may need to consider getting a diffuser (or building one myself!) since I don't think I'd use a Speedlite much.

The answer, my friend, is ceiling bounce. Forget the diffuser and point your flash up.

Thanks for the advice, JackProton.

Unfortunately, as I do not have a dedicated flash unit, I don't have the option to bounce. I figure since I am limited to the built-in flash on my 40D, that a diffuser is my best bet. Also, there are quite a few limitations to bouncing flash, aren't there? Colour of ceiling and distance come to mind - and these two are deal breakers for me in that I will mostly have a problem with both in the places I take my shots...

A dedicated flash unit and ceiling bounce made my flash photos look so much more professional that I won't use the onboard flash for anything but fill-flash or in case of a low-light emergency. Yeah, there are some limitations as you note. Though sometimes you can bounce off a neutral colored wall or bounce the flash behind you. One of my personal favorite images from my films days was a sepia toned portrait of a cat made by bouncing the flash off of a brown wood paneled wall.

fz_za wrote in post #4115757
Unfortunately, as I do not have a dedicated flash unit, I don't have the option to bounce.

Almost, not quite

Was that a marshmellow being used as an onboard flash diffuser?

It could be that your flash image looks sharper as it has more contrast and saturation as well.

Generally if flash looks sharper then I suspect my hand holding ability since I know that I am not as steady as I once was (sigh!).

Thanks for the info, guys. Hehe - gotta love DIY projects