Canon 30D Tv Macro

[thierry nguyen cuu - nomad]

Hi there,

 

I'm playing around using a 30D body and a 100 mm f2,8 macro.

 

I wanted high speed macro shots and had to increase ISO to use speed over

1/1000.

 

I noticed that increasing ISO, to somewhere above 1250, stops down the lens

aperture.

I ended up with an aperture set to 32 (in Tv mode) ...

 

Any ideas?

[mark u]

If you want a high effective shutter speed for macro work, use flash. That way you can shoot at 100 ISO for best image quality, and still use an aperture that will get the best depth of field and sharpness compromise. Work in M mode and set the shutter speed to 1/200th. Flash durations should mostly be a lot shorter than 1/1000th anyway, and you will have minimal contribution from ambient light.

 

Incidentally, you should avoid using an aperture as narrow as f/32, since the image will suffer from significant loss of sharpness due to diffraction. On a 30D, I would be cautious about exceeding f/16, and maybe less. With static subjects and working on a tripod you could actually use a much wider aperture and take a series of images with slightly different focus, and then use software to combine them:

 

http://www.outbackphoto.com/workflow/wf_72/essay.html

 

So far as flash is concerned, I find that good results can be had using a regular EX flashgun on an off camera shoe cord, which allows flexibility in lighting angles and a greater flash to subject distance than you would get with a macro ring light - so giving more even illumination with reduced impact from inverse square falloff. However, it can sometimes be an advantage to light the background with a slave flash. Using simple reflectors and diffusers can also help to handle harsh shadows or overly directional lighting.

[tommyinca]

You can always lower the ISO (e.g.: 200) in direct sun-light and set it back up in the shade.

[thierry nguyen cuu - nomad]

Thanks for your answer.

 

My primary concern is the Aperture behavior when raising ISO in Tv mode.

 

Let's say that i want a speed of 1/1000 in Tv mode, and let the camera set the aperture. When the maximum aperture is reached, i have to compensate by raising ISO (otherwise, i'll under expose)

 

But when i raise ISO, in Tv mode, the aperture stops down, and i end up still under exposing :)

 

So, in Tv mode, can you really use the 1/8000 speed @ ISO 100, without shoting directly to the sun to get some "well" exposed shots ?

[mark u]

I don't understand why you think you might want to shoot macro at 1/8000th second ambient exposure. The camera offers the shutter speed to allow the use of very wide apertures such as f/1.4 in bright conditions. If you want to freeze action/motion (or even just to eliminate camera shake), you are much better to do it using flash, where the effective shutter speed can more easily be increased and to much faster speeds than are possible with a mechanical shutter in an SLR, while you will also have a measure of control over depth of field, without degrading image quality unnecessarily by using high ISO settings.

[valo_soul]

Well, at f/2.8 you're not getting enough light to use 1/1000th shutter and at the ISO setting that you increase it to, the lens stops down because you're getting too MUCH light. Solotion = don't increase the ISO as much. You don't need to go from 100 to 3200 or something... try 400 or 800 until it fits the bill. At least if I understand what you are saying.

[thierry nguyen cuu - nomad]

James, you got it.

 

 

Hum...

 

Just for fun: let's say that i wanted to understand how the camera, and the 100 f2,8 macro lens behave when they are stuck together.

 

These tests have been made with a 30D body, all in Tv mode.

 

When i set a "high" speed, the maximum aperture value blinks to tell me that i am under exposing.

If i want to keep the "high" speed, to compensate, i need to raise the ISO till the aperture stop blinking (good exposure)

 

 

Test 1. 30D + 10-22 EF-S

Raising ISO: MAX aperture stop blinking (@ an apropriate ISO value)

 

Test 2. 30D + 50 f1,4

Raising ISO: MAX aperture stop blinking (@ an apropriate ISO value)

 

Test 3. 30D + 24-105 f4 L IS

Raising ISO: MAX aperture stop blinking (@ an apropriate ISO value)

 

Test 4. 30D + 70-200 f2,8 L IS

Raising ISO: MAX aperture stop blinking (@ an apropriate ISO value)

 

Test 5. 30D + 100 f2,8 Macro

Raising ISO = aperture stops down.

The more i raise the ISO the more the aperture stops down.

 

So i will never have a good exposure (keep in mind that i want to keep my speed value)

 

Therefor, no matter what the purpose with macro and speed are for. The main concern here is the behavior of the 100 f2,8 Macro in Tv mode.

 

Sorry if i wasn't clear in my first question.