Focus Stacking

Hippo_MC

Hippo_MC

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Ray
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I understand the concept of focus stacking, but I have a couple of questions. :thinking:

I read that people use macro rails to move the camera forwards or backwards to change the point of focus, but wouldn't that also change the composition/size of the image in the viewfinder slightly as well?

Wouldn't you keep the camera static, but adjust the focus?

Also I have come across this photo on flickr
http://www.flickr.com/photos/kliton77/5733328063/in/pool-21563296@N00/

How do you focus stack on something that is very unlikely to be holding the pose long enough for you to fire of 3 shots with different focal points?

TIA
 
Hippo_MC said:
I read that people use macro rails to move the camera forwards or backwards to change the point of focus, but wouldn't that also change the composition/size of the image in the viewfinder slightly as well?
Click to expand...
If the focus isn't changed then the magnification will remain constant

Hippo_MC said:
Wouldn't you keep the camera static, but adjust the focus?
Click to expand...

As above.....adjusting the focus will change the magnification.

Focus rails and stacking software are the way forwards.

Bob
 
Perspective will change but the magnification at the focal plane will remain constant if the focus is not adjusted.

An example....
Take a cigarette (or pencil if you're cleaner living than me) and position along the optical axis. Focus on the nearest point and take a shot. Refocus on the farthest point (without moving the camera/lens or cigarette/pecil) and take another. The width of the subject will be greater for the first shot.
Repeat the test but move the camera/lens until the far end is in focus (don't adjust the focus) and you'll find that the cigarette/pencil is the same width at each end...which it is in reality.

Bob
 
ok, so the idea is the point in focus on any given shot is the same magnification

anything not in focus may be a different magnification but that doesn't matter as it won't be used once stacked?
 
If you think about it, if you are moving the camera to change which part of the subject is sharp, the sharp part is always the same distance from the camera if you haven't moved the focus ring.
 
Thanks Bob, that now makes sense to me also :D It still doesn't explain how the focus stacked image was possible on the spider, unless it was frozen :thinking:

So the next question, is what focus rails should I invest in. Any suggestions :wave:
 
Like most things, you get what you pay for and, more likely, what you're prepared to pay.

£400-700 will get you something truly wonderful but I suspect that your enthusiasm doesn't warrant such an outlaw.

I currently use a Novoflex Castel Cross-Q (a shade over £300 nowadays). A very stable platform with an Arca plate mount under and over that securely holds a 1srs body. Little or no backlash worth mentioning and very well engineered.

If sub £100 is nearer your budget then I'd recommend a Velbon Super Mag Slider (£60'ish). Works fine with an ungripped xxD size body but lacks a movement scale (useful but not essential).

£30 will get you something from an Ebay seller that'll do the job but leave you wanting or wondering about something better.

Bob
 
Bob, really appreciate your response. I will take a look at the Velbon.

Cheers
 
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