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Author Topic: focus stacking-move the camera (on a rail) or refocus?  (Read 7025 times)
Eric Brody
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« on: September 09, 2012, 05:14:12 PM »
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I am having lots of fun with some flowers and focus stacking using the fabulous 85mm PC-E lens on my D800E. I process in LR4 and PSCS6. I recently purchased a RRS macro rail and now am wondering whether it is demonstrably better to use the rail and move the camera without refocusing or just refocus from the near point to the far point of the object.

Here is my current technique. I mount the camera, with it located at the rear of the rail, and focus on the near point and make an exposure. I then slide the rail to the far point for an approximate focus and then fine focus on the far point using the screw to move the camera. Once I have the far point focus, I make an exposure and move the rail incrementally without moving the focusing ring on the lens, back until I get to the close point. All focusing is done with live view and a magnifier for accuracy. I focus actually only on the near and far points. I then bring the 10-12 images into Lightroom 4, correct the first image, synchronize the rest, and import as layers into Photoshop. I then select all the layers, go to edit-auto align, then edit-autoblend and after I have reviewed it and looked at it carefully, flatten what is often a 3-4GB file. I always have to do some cropping because there are always fuzzy edges.

Before I got the rail, the technique I used was to focus on the near point and then just incrementally refocus until one gets to the far point, and then do the import and processing as above. I have taped a piece of paper to the lens barrel with the near and far points marked so I know where to go as I move the focus. I am happy with the results from both, but wonder if I am missing or misunderstanding something.

I'd greatly appreciate comments and/or suggestions regarding these approaches.

Thanks.

Eric
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BartvanderWolf
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« Reply #1 on: September 10, 2012, 08:11:02 AM »
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I am having lots of fun with some flowers and focus stacking using the fabulous 85mm PC-E lens on my D800E. I process in LR4 and PSCS6. I recently purchased a RRS macro rail and now am wondering whether it is demonstrably better to use the rail and move the camera without refocusing or just refocus from the near point to the far point of the object.

Hi Eric,

Whether it makes a visible difference at all, depends on how the lens corrections are at this focus distance. I'm not familiar enough with the lens you mentioned
 to know if it uses floating elements/groups to focus at close range. One drawback of changing focus at close range is that the change in magnification will also slightly change the exposure for each successive focus bracket. How much of an exposure difference it makes, depends on the actual magnification factor. With a focus rail the magnification factor is fixed, hence the exposure per focus bracket is constant if the lightsource is constant.

It will probably be difficult to demonstrate any image quality difference between the 2 scenarios, unless the lens is a poor close-up performer. The dedicated focus stitching programs will also adjust for exposure differences between the focus brackets, I'm not sure what Photoshop does under the hood.

You may want to use a good DOF calculator (allowing to set the COC to the sensel pitch distance) to figure out how many bracketed exposures you really need at the distance/magnification you use. Since the magnification factor is constant when using a focus rail, you can pre-calculate the per-bracket-distance for a couple of magnification factors, and divide the total depth/distance by that per-bracket-distance if you want to know how many exposures are required. On the other hand, when you just start by focusing at the nearest distance, you can just step through the subsequent brackets with your pre-calculated interval until you reach the the other end of the range.

Cheers,
Bart
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elf
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« Reply #2 on: September 10, 2012, 08:35:42 PM »
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Either way is fine. 

Here's a thread on http://www.photomacrography.net that discusses different focusing methods for stacking: http://www.photomacrography.net/forum/viewtopic.php?t=7298

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FredBGG
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« Reply #3 on: September 10, 2012, 10:33:51 PM »
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Get your hands on ControlMyNikon. It does focus stacking automatically. You set the closest and furthest focus . It does the rest of the shooting.
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jawitto
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« Reply #4 on: September 15, 2012, 02:32:31 PM »
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My camera and lens are quite different, but the quest is the same. I have a Panasonic GH2 and a hybrid 'macro' set up: Fotomate camera rail; 7mm extension tube; 4/3 to Nikon lens adapter; and Nikkor-H 50mm lens purchased way back in 1969. This setup allows for extreme macro close ups, with an almost non existent DOF. A friend alerted me to your post about how you use multiple shots and Photoshop Auto Align and Auto Blend edits and I got an amazing result trying this with a photo of the back of a pocket-watch. I took seven photos (it would have been better with more) and was amazed at the result.  I've attached one of the seven series of shots I took, and the end result, and thanks for your post!.
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allegretto
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« Reply #5 on: September 19, 2012, 01:06:39 PM »
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I know this will sound dumb, but when you "stack", what happens to the blurry images?
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elf
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« Reply #6 on: September 19, 2012, 01:53:30 PM »
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A new image is created from the in-focus pixels.  The source images are not modified.
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allegretto
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« Reply #7 on: September 19, 2012, 04:35:36 PM »
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so, the software "knows"?
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jawitto
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« Reply #8 on: September 19, 2012, 05:14:49 PM »
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As Eric describes, there is some fuzziness around the edges so you have to crop the final result. After you have applied the Auto Align and the Auto Blend, each layer has a layer mask where you can see which parts of the original images have been used. Once you are satisfied with the result in Photoshop, simply flatten the layers and make your crop. The original images are not altered in any way. Then you can take this further in Photoshop or in Lightroom and apply additional edits if necessary, or to provide more oomph, take the image through Topaz Adjust 5.

Alex
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NigelC
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« Reply #9 on: November 14, 2012, 03:28:40 AM »
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Hi Eric,

 With a focus rail the magnification factor is fixed, hence the exposure per focus bracket is constant if the lightsource is constant.


Cheers,
Bart

I've been thinking about this too, especially as not overly keen to splash out for a decently engineered rail (which unfortunately does not include the relatively inexpensive manfrotto 454). Refocussing may change the image scale, but I really can't see how moving the whole thing on a rail doesn't do the same since you are changing the sensor to subject distance. I'd be using a Canon 100L lens with internal focussing BTW.
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BernardLanguillier
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« Reply #10 on: November 14, 2012, 03:49:59 AM »
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Get your hands on ControlMyNikon. It does focus stacking automatically. You set the closest and furthest focus . It does the rest of the shooting.

Thanks for the pointer. I was not aware of this option and it seems great.

Too bad they don't have an OSX version though.

Cheers,
Bernard
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A few images online here!
francois
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« Reply #11 on: November 14, 2012, 04:54:57 AM »
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Thanks for the pointer. I was not aware of this option and it seems great.

Too bad they don't have an OSX version though.

Cheers,
Bernard


Helicon offers a companion application to Helicon Focus. It's called Helicon Remote (link). I found that it works really well. Some versions were very crash-prone but tech support was always prompt and helpful. You might want to give it a try.
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Francois
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« Reply #12 on: November 14, 2012, 05:38:26 AM »
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I've been thinking about this too, especially as not overly keen to splash out for a decently engineered rail (which unfortunately does not include the relatively inexpensive manfrotto 454). Refocussing may change the image scale, but I really can't see how moving the whole thing on a rail doesn't do the same since you are changing the sensor to subject distance. I'd be using a Canon 100L lens with internal focussing BTW.

Hi Nigel,

When using a rail, once the 'bellows extention factor', or the required exposure increase ( (1+M)^2 ) due to the magnification factor M is set, it will stay the same. The magnification at the focus plane is the same for each focus bracket, and only those focused bits are used to composite the stacked result.

What will change during the software stacking procedure, is the magnification of each slice by resampling them to a size that allows to perfectly blend them together, foreground slices will receive higher upsampling than background slices because the subject is closer even though the optical magnification in the focus plane of the shot was identical by shooting from a longer distance. That's why e.g. Helicon Focus offers a choice of resampling methods that are well suited for small resizing changes. It also means that the final composition is usually cropped to the smaller (background slice) image size boundaries, important to remember when the composition has important elements close to the edge, especially relevant for Macro shots.

When changing the magnification of slices by refocusing, things work out differently, because the magnification is already in the images. The software will figure it out for you, including the required changes in average brightness between slices when manual exposure settings were used. Letting the camera's metering figure out the exposure compensations may or may not work, depending on the situation, so I always leave the software brightness compensation activated.

Cheers,
Bart
« Last Edit: November 14, 2012, 05:55:51 AM by BartvanderWolf » Logged
BernardLanguillier
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« Reply #13 on: November 14, 2012, 05:47:38 AM »
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Helicon offers a companion application to Helicon Focus. It's called Helicon Remote (link). I found that it works really well. Some versions were very crash-prone but tech support was always prompt and helpful. You might want to give it a try.

Thanks Francois.

Actually I have installed it but have not tried yet.

Cheers,
Bernard
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A few images online here!
francois
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« Reply #14 on: November 14, 2012, 06:00:08 AM »
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Thanks Francois.

Actually I have installed it but have not tried yet.

Cheers,
Bernard


Let me know it it works on your Mac(s).
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Francois
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« Reply #15 on: November 14, 2012, 08:58:06 PM »
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There is not much difference in stacking by moving the camera/lens together or moving the subject (using a stage). Stacking by changing the focus point manually in the lens is a little harder to get accurate steps and is prone to moving the camera if the tripod isn't sturdy enough.    You can also stack by changing the bellows draw.  This allows the the entrance pupil of the lens to remain stationary, so you can also do panoramas.  In other words, all of the shooting techniques work about equally, so do the one that's most comfortable to you.

All of the techniques will have some magnification changes, the stacking software will usually be able to handle this without difficulty.   

Here's a focus stacked macro panorama I did a few months ago by changing the bellows draw: http://photosynth.net/view.aspx?cid=39c28546-4202-4821-8b2d-4567cfceae6a
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John Nollendorfs
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« Reply #16 on: November 15, 2012, 10:15:06 PM »
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Very impressive shot of the spirea, Elf!
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Lupin
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« Reply #17 on: November 19, 2012, 10:21:51 AM »
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Get your hands on ControlMyNikon. It does focus stacking automatically. You set the closest and furthest focus . It does the rest of the shooting.

How well does it work Fred?
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