macro and flash but why so noisy?

[JonSadler]

Hello all,

I have been playing around with flash and my Sigma 150 (a replacement for the 180 which met with a terminal accident at the hands of my son). The camera is a 30D and I am using the on-board flash on manual set at 250 shutter and 13 aperture. Why is it so noisy? And why does the camera register a -2 exposure compensation?

As I said I am playing but the manual is not helping at all. I am sure I am doing something very silly wrong. The image is a brown carder bee:

http://www.wildaboutbritain.co.uk/ar...m/IMG_4012.jpg

Any help very gratefully received!


Regards

Jon

[BillyPilgrim]

I'm only guessing but I'd say the noise is there because the photo is under-exposed?

Maybe the -2 indicates 2 stops of under-exposure? Have you tried some test shots at larger apertures? It could be that you have gone beyond the limits of the built-in flash. I have the 30d and rarely use the flash because the results have never been too good.

[matt_xyz]

Hi Jon,

Much of the 'noise' appears to be dirt on your sensor. At high levels of magnification and small apertures this becomes very apparent. Any additional noise would be caused by the fact the background is underexposed and has perhaps been lifted slightly in Photoshop? Also, you don't mention what ISO setting you used. An ISO of 400 or above would tend to cause noise in an underexposed background that has been 'lightened' in PS.

Presumably you have selected -2 exposure compensation at some point. The shot looks about right exposure wise but you may get away with -11/3 (one and a third) exposure compensation.

Matt

[JonSadler]

Hi Matt

Doh! I had the darn thing set at ISO 1600! No idea why or how it happened!

Still - I have learned something today!

Less haste more speed.

Thanks both.

Jon

Originally Posted by matt_xyz

Hi Jon,

Much of the 'noise' appears to be dirt on your sensor. At high levels of magnification and small apertures this becomes very apparent. Any additional noise would be caused by the fact the background is underexposed and has perhaps been lifted slightly in Photoshop? Also, you don't mention what ISO setting you used. An ISO of 400 or above would tend to cause noise in an underexposed background that has been 'lightened' in PS.

Presumably you have selected -2 exposure compensation at some point. The shot looks about right exposure wise but you may get away with -11/3 (one and a third) exposure compensation.

Matt

[Steve S]

Jon,

I’m not sure if I have the answer to your entire question, flash macro photography is something that I do very little of, but here goes anyway.

I suspect that your camera is registering a -2 exposure because of the closeness of your subject compared to the distance to the background. You are using the camera in manual, so you have made sure that the exposure on your main subject is correct. And it looks just about spot-on to me (no burnt out highlights and nice detail in the shadows such as the bees’ legs).

Your cameras’ light meter is trying to meter for the whole scene and as light intensity decays rapidly the further it travels from the source, it sees the background as under exposed - by as much as two stops in this case. You don’t need to worry about that. You have done the right thing and concentrated on getting the main subject correct.

The digital noise is a product of under exposure and a dirty sensor. Where areas of your image are under exposed (or just dark) there is only a small amount of information being recorded by your camera sensor. Background electrical noise is always present, but usually so low compared to the main image being recorded it is not relevant. In low light levels that may not be the case and it becomes much more of a factor. It can be minimised by using as low an ISO setting as possible, but under some circumstances it can’t be eliminated completely (time for some post-capture processing).

The big blobs of noise are actually specks of contamination on your sensor. Close focus with a small aperture means a large enough depth of field to include your sensor. This has allowed these specks of dust to be noticed in your photograph. If you were to use a telephoto lens wide open you probably wouldn’t see them at all.

I hope that makes sense to you and has been of some help.

Nice shot by the way.

Steve.

It looks as if others were already on the case while I was writing this.....

[matt_xyz]

Originally Posted by JonSadler

Hi Matt

Doh! I had the darn thing set at ISO 1600! No idea why or how it happened!

Still - I have learned something today!

Less haste more speed.

Thanks both.

Jon

That'll be it! There is also dirt on your sensor though, time to give it a wipe perhaps.

Matt

[Meta menardi]

Originally Posted by JonSadler

Hi Matt

Doh! I had the darn thing set at ISO 1600! No idea why or how it happened!

Still - I have learned something today!

Less haste more speed.

Thanks both.

Jon

Less speed, better picture?

[JonSadler]

Thanks for the additional advice, it is definitely helpful. I will check out the threads on cleaning the sensor!

Regards
Jon