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08-29-2018, 10:47 AM - 1 Like   #16
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QuoteOriginally posted by dick897 Quote
Thanks for that.
I've never seen a definitive answer to this question either.
Which led me to asking it.
I had presumed that there would be an answer though.
I'll experiment and see if I can find something that works for me or just use flash.

That is some post count.
I wouldn't have that much in the years I'm on here. But then I was a long time lurker
I enjoy helping and learning. I'm also not shy so I have a huge post count. I hope that's a good thing. Lol.

08-29-2018, 02:07 PM - 1 Like   #17
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QuoteOriginally posted by dick897 Quote
So, for example, if using 50mm of tubes, should the focal length just be increased by 50mm or is there a different formula because of the magnification factor ?
Your question inspired me to look for an answer - here's my take on this, I used this article as a source. Effective f/stop in macro can be approximated* as per following formula:


(1) effective f/stop = f/stop x (1 + magnification)

The formula for f/stop is simple:

(2) f/stop = focal length / aperture diameter.


It means that at given diameter, if we increase focal length twofold, f/stop will increase proportionally. Let's take a look at common macro lens as example: 100/2.8. Its aperture at 2.8 has diameter of roughly 36 mm, if we increase FL to 200mm, f/stop will be 200 / 36 = 5.6. If we compare it to (1), we can see that at 1x magnification effective f/stop becomes twice as high as original one (for instance f/16 instead of f/8), just as we were increasing focal length twofold. Putting all this together, we can derive formula for approximate focal length:

(3) effective FL = FL x (1 + magnification).

I wonder what your opinion is - please let me know if you find such reasoning correct or flawed.


*) precise value can be computed when pupil magnification is known, for details, please see the aforementioned Cambridgeincolour article.

Last edited by pentageek; 08-29-2018 at 02:12 PM. Reason: typo and clarification
08-29-2018, 02:22 PM - 1 Like   #18
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You know, I never really thought about this until you posted about it.
08-29-2018, 02:39 PM   #19
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QuoteOriginally posted by pentageek Quote
Your question inspired me to look for an answer - here's my take on this, I used this article as a source. Effective f/stop in macro can be approximated* as per following formula:


(1) effective f/stop = f/stop x (1 + magnification)

The formula for f/stop is simple:

(2) f/stop = focal length / aperture diameter.


It means that at given diameter, if we increase focal length twofold, f/stop will increase proportionally. Let's take a look at common macro lens as example: 100/2.8. Its aperture at 2.8 has diameter of roughly 36 mm, if we increase FL to 200mm, f/stop will be 200 / 36 = 5.6. If we compare it to (1), we can see that at 1x magnification effective f/stop becomes twice as high as original one (for instance f/16 instead of f/8), just as we were increasing focal length twofold. Putting all this together, we can derive formula for approximate focal length:

(3) effective FL = FL x (1 + magnification).

I wonder what your opinion is - please let me know if you find such reasoning correct or flawed.


*) precise value can be computed when pupil magnification is known, for details, please see the aforementioned Cambridgeincolour article.
I am delighted that you took the time to look this up, and come up with an answer, unfortunately, My maths is not good enough to understand your answer. Thats no fault of yours, just my rather poor education.

08-29-2018, 03:12 PM - 1 Like   #20
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You use SR? Unfollowing. I used to think you were cool... but now...

Nothing trumps the feeling of Man vs Machine and Man winning. It's not just about how good the photo turns out, it's about how the photo turned out. Ride that Aperture Adrenaline my friend!
08-29-2018, 03:21 PM   #21
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QuoteOriginally posted by BruceBanner Quote
You use SR? Unfollowing. I used to think you were cool... but now...

Nothing trumps the feeling of Man vs Machine and Man winning. It's not just about how good the photo turns out, it's about how the photo turned out. Ride that Aperture Adrenaline my friend!
Ha ha ha, No of course I don't, it's just a hypothetical question.
You can relax now.
Some of the times I don't even turn the camera on, preferring to try and imprint the image directly into my little brain
08-29-2018, 03:43 PM - 1 Like   #22
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QuoteOriginally posted by dick897 Quote
Ha ha ha, No of course I don't, it's just a hypothetical question.
You can relax now.
Some of the times I don't even turn the camera on, preferring to try and imprint the image directly into my little brain
Ok phew.. I'll re-add you <suspiciously clicks 'Add Friend'...>
08-29-2018, 07:34 PM   #23
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QuoteOriginally posted by dick897 Quote
Same as that.
Even more so with the bellows, as I'd have to carry a ruler as well.

---------- Post added 08-29-18 at 08:22 AM ----------



To be perfectly honest, I have never taken notes on what extension I've taken any shot at.
Iď have an idea of what I was at but with bellows it can change shot to shot
got a 2nd camera? take notes that way, even cell phone should be enough

08-29-2018, 09:22 PM - 1 Like   #24
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QuoteOriginally posted by dick897 Quote
I do a fair bit of macro shooting, using mostly bellows of late, but also with ext tubes.
My question is, what focal length should be input for the SR to function correctly.
So, for example, if using 50mm of tubes, should the focal length just be increased by 50mm or is there a different formula because of the magnification factor ?
Bellows then produce a different dilemma as it has varying degrees of extension.
Is it a case of trial and error, whatever works for you or is there an actual system for working it out ???
For most of my macro shooting, I use a ringflash and inputting the focal length + the amount of ext seems to work, I ask this question in relation to no flash being used

Any thoughts
For SR to really work for macro you need a camera with 5-axis SR, and for 5-axis SR to work you need a lens that report focus distance to the camera. Without focus distance information 5-axis SR will be limited to 3-axis.

I do not believe your equipment will support 5-axis SR so you will not have very efficient SR for macro.

The reason is that for high magnification shots it is horisontal and vertical shifts that dominates camera shake and it varies with magnification. On normal shots with lower magnification it is pitch and yaw camera shake that dominates and it varies by focal length.

You can try using longer focal length for SR than the lens have so it overcompensate for pitch a yaw, which may help for horisontal and vertical shift. Try 2-3x the lens focal length. How much you need to use will vary with magnification, so it is not very practical as you may have to change the focal length on the camera between shots. It may also vary on how you hold the camera so it will probably be difficult to find out which focal length is best to use for each shot.

Last edited by Fogel70; 08-29-2018 at 09:45 PM.
08-30-2018, 01:38 AM   #25
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QuoteOriginally posted by bwgv001 Quote
got a 2nd camera? take notes that way, even cell phone should be enough
I think it is unlikely that I will do this
The size and bulk of the
K1
short ext tube
Bellows
105mm macro
Ringflash
Diffuser
Handholding this lot requires 2 hands, which leaves me short a hand or 2 for taking notes, which is also veering off course for the original question, which was,

Is there a correct method for working out the focal length in relation to using ext tubes and SR.
Is it just the amount of extension, do you ignore the extension, is there an accepted standard way, or is it trial and error.

---------- Post added 08-30-18 at 01:56 AM ----------

QuoteOriginally posted by Fogel70 Quote
For SR to really work for macro you need a camera with 5-axis SR, and for 5-axis SR to work you need a lens that report focus distance to the camera. Without focus distance information 5-axis SR will be limited to 3-axis.

I do not believe your equipment will support 5-axis SR so you will not have very efficient SR for macro.

The reason is that for high magnification shots it is horisontal and vertical shifts that dominates camera shake and it varies with magnification. On normal shots with lower magnification it is pitch and yaw camera shake that dominates and it varies by focal length.

You can try using longer focal length for SR than the lens have so it overcompensate for pitch a yaw, which may help for horisontal and vertical shift. Try 2-3x the lens focal length. How much you need to use will vary with magnification, so it is not very practical as you may have to change the focal length on the camera between shots. It may also vary on how you hold the camera so it will probably be difficult to find out which focal length is best to use for each shot.
Well that at least makes sense to me, a very well explained answer.
It does raise some other questions

If using 2x or 3x fl for for SR input would 1x the fl guide for shutter speed apply,
So for a 100mm macro with whatever extension, need a shutter speed of 1/300th or there abouts.
I only ask as I thought that at higher shutter speeds the SR became redundant.

I will give it a go though and see if there is any difference.

As there seems to be no actual prescribed method, I wonder if the question shouldn't be what do you do ?
08-30-2018, 02:59 AM - 1 Like   #26
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Yes you are right.

I don't usually rely on SR for macro as I have cameras with 3-axis SR.
So if I have SR enabled I use shutter speed for what is needed without SR and and at least use twice as fast shutter as I normally would need.
So I try to keep shutter speed of 1/(focal length) x (crop factor) x2, So for 100 mm macro I try to avoid using shutter speed longer than 1/300s.

It is not that often I shoot macro with 1:1 or higher magnification handheld. I usually shoot at max magnification of 1:3 - 1:2 as it is mainly plants and flowers I shoot, and I'm using APS-C.
But when shooting outdoors wind can be an ever bigger problem than camera shake, so I often end up shooting at least 5-10 shots so I get one that I can use.

For shooting really high magnification I usually do it indoors and use tripod, as requirements for both shutter speed and focus become very difficult to handle using handheld camera.
08-30-2018, 03:44 AM   #27
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QuoteOriginally posted by Fogel70 Quote
Yes you are right.

I don't usually rely on SR for macro as I have cameras with 3-axis SR.
So if I have SR enabled I use shutter speed for what is needed without SR and and at least use twice as fast shutter as I normally would need.
So I try to keep shutter speed of 1/(focal length) x (crop factor) x2, So for 100 mm macro I try to avoid using shutter speed longer than 1/300s.

It is not that often I shoot macro with 1:1 or higher magnification handheld. I usually shoot at max magnification of 1:3 - 1:2 as it is mainly plants and flowers I shoot, and I'm using APS-C.
But when shooting outdoors wind can be an ever bigger problem than camera shake, so I often end up shooting at least 5-10 shots so I get one that I can use.

For shooting really high magnification I usually do it indoors and use tripod, as requirements for both shutter speed and focus become very difficult to handle using handheld camera.
I dont normally rely on SR for macro either, Most of my macro shots are with flash and I have never felt there was an issue, it was only when trying without flash to get some natural light shots that it came up as a question that I didnt know the answer to.

Almost all of my macro shots are outside in ditches and bushes, handheld, as a tripod is not viable in ditches
To give you an idea of the type of shots and level of magnification here is a link to a mini album on flickr , all taken with K1 and bellows, sigma 105mm, ringflash and homemade diffuser ( plastic mixing bowl ) all handheld

K1 + Bellows + 105mm macro | Flickr
08-30-2018, 04:36 AM - 1 Like   #28
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That is some really nice shots!
I can imagine you spend some time in the ditches.
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