Focus rail or focus ring?

[meow]

I just started to use Zerene and learn stacking. I'm basicially a total beginner to macro at large, so so far I stick to closeups to learn the technique. I run Zerene with the default settings, but I will of course dig deeper as I learn more.

I read at the Zerene site that using the focus ring often is better than using a focus rail. A tried to shoot some small flowers. With the rail and about 10 shots I got a horrible result. When using the focus ring I got a result I thought was quite good with only 5 shots. Used PMax for both.

The rail picture is horrible in so man ways, but it's one specific problem I want to ask about. Parts of the image have areas that are smudged and what looks like partly bleeding of colours and partly "double exposure". I think all my tries with the rail had similar areas.



Am I right in thinking that I tried to cover too large a depth and that this happened because the perspective changed too much as the camera got closer and closer? And that a rail is better suited for less deep stacks?

I now use the rail just for moving the base position of the camera and do the focusing with the lens. That works so much better! Thank heavens!

[Pau]

I think that the main problem with the posted picture is movement of the central group of flowers, because the left side flowers are well rendered.

IMO both taking methods can work well for this kind of subject if you have scale correction activated in Zerene

[rjlittlefield]

Am I right in thinking that I tried to cover too large a depth and that this happened because the perspective changed too much as the camera got closer and closer?

It's possible, but I suspect another cause.

Problems that are due to perspective change usually show up as a sort of smearing or doubling from center to edge along radial lines, what is sometimes called a "zoomburst" effect.

But In the image that you show, the doubling of petals seems to occur in many different directions. This is typical of flower parts moving from one shot to another, perhaps due to air movement or jostling of the table.

And that a rail is better suited for less deep stacks?

The main advantage of a rail for focus stepping occurs at higher magnification. Suppose you want to fill the frame with a subject that has the shape of a cube. Then if the subject is the size of a storage box you use the ring, but if it's a grain of table salt you use a rail. The general rule of thumb is that if you can use the ring then it's best to do that; otherwise use a rail.

--Rik

[meow]

I think that the main problem with the posted picture is movement of the central group of flowers, because the left side flowers are well rendered.

IMO both taking methods can work well for this kind of subject if you have scale correction activated in Zerene

OK. When you say movement of the central group do you mean, don't know how to express this, that as they got closer they got less central in the image, that I should have aligned the camera better? I should have mentioned that this is a crop from the right side of the image.

[meow]

Am I right in thinking that I tried to cover too large a depth and that this happened because the perspective changed too much as the camera got closer and closer?

It's possible, but I suspect another cause.

At least my thinking was it totally off...

Problems that are due to perspective change usually show up as a sort of smearing or doubling from center to edge along radial lines, what is sometimes called a "zoomburst" effect.

But In the image that you show, the doubling of petals seems to occur in many different directions. This is typical of flower parts moving from one shot to another, perhaps due to air movement or jostling of the table.

I guess that is possible. I used a flash with one of those cone like diffusers (like the Cygnustech, but a cheap ripoff). Possibly it brushed against the t-shirt I had placed the flowers on. I didn't noticed it did, but can't rule it out.

And that a rail is better suited for less deep stacks?

The main advantage of a rail for focus stepping occurs at higher magnification. Suppose you want to fill the frame with a subject that has the shape of a cube. Then if the subject is the size of a storage box you use the ring, but if it's a grain of table salt you use a rail. The general rule of thumb is that if you can use the ring then it's best to do that; otherwise use a rail.

Thanks. That's very useful information. After I gave up on focusing with the rail I still found it very useful for setting an "initial distance" and centering the subject (it's the two direction type). Easier than moving the tripod or the subject.

Maybe it's stupid to start learning stacking while still new to macro, but I find that approaching things from different directions often helps me understand, makes my brain click. And stacking of course doesn't need to be limited to macro. I'm looking forward to try landscape and interior stacks. I'll visit our beautiful cathedral one day and give that a try.

[Pau]

I think that the main problem with the posted picture is movement of the central group of flowers, because the left side flowers are well rendered.

IMO both taking methods can work well for this kind of subject if you have scale correction activated in Zerene

OK. When you say movement of the central group do you mean, don't know how to express this, that as they got closer they got less central in the image, that I should have aligned the camera better? I should have mentioned that this is a crop from the right side of the image.

No, I was just referring to central flowers actually moving during the shot session, not to any optical phenomenon.
If you browse sequentially the source frames you should be able to detect such movement if present

[Lou Jost]

It is not stupid to learn stacking and macro at the same time. I think it is actually beneficial to learn them together, so you treat stacking as a natural part of macro photography. And you will soon learn which subjects don't need stacking.

What you may have not thought about carefully enough here is the idea of controlled experiments to help you learn. You really need to keep everything constant except the variable you are testing. It may take some experiences, like this one, to learn all the relevant factors. You should use inanimate, immovable objects, and also make sure you have eliminated vibrations. The fact that you are using flash helps with the vibration aspect, so that was a good move. But flowers spread and wilt over the course of stacking.

You can only learn when you control ALL the variables except the one you are testing. These are not always immediately apparent. I (and other experienced stackers) have often been surprised by variables that I hadn't considered.

[rjlittlefield]

This is typical of flower parts moving from one shot to another, perhaps due to air movement or jostling of the table.

I guess that is possible.

I forgot to mention: there is a specific method for detecting movement in a stack. The trick is to process the stack, then put a checkmark on "Show as adjusted" at the top of the Input Files panel, then scroll selection back and forth through the list of source images while watching the image panel. With a well shot stack you will see nothing changing except focus, because all of the image shifts and scale changes will have been adjusted away during the alignment process. But if something has moved so as to cause a doubled edge in the result, it will be obvious in the adjusted image sequence. See https://zerenesystems.com/cms/stacker/d ... n_my_stack for more information.

--Rik

[meow]

Cool! I'll try that.

Since you guys are so helpful, can I ask another question? I read my first macro book yesterday and started on my second today. Yesterday's book was more tips and tricks, today's book goes deeper into theoretical things (today's book is "The Complete Guide to Macro and Close-up Photography" by Cyrill Harnischmacher). Both books describe the effects of crop sensors except when it comes to optimal aperture and diffraction.

I use m43 (OM-1) and as far as I have understood it crop is indeed something to consider when it comes to diffraction. Is there some mystical factor that I don't understand that makes this not true in macro land? Or are both authors just sloppy?

[rjlittlefield]

Both books describe the effects of crop sensors except when it comes to optimal aperture and diffraction.

I use m43 (OM-1) and as far as I have understood it crop is indeed something to consider when it comes to diffraction. Is there some mystical factor that I don't understand that makes this not true in macro land? Or are both authors just sloppy?

The topic is seldom covered well, despite the fact that the main message is pretty simple.

The optimal effective f-number scales in direct proportion to the linear dimension of the sensor.

So, if f/16 is optimal for your work on full-frame (sensor width 36 mm), then f/10 will be optimal on 1.6X crop (sensor width 22.5 mm), and f/7.7 will be optimal on m43 (sensor width 17.3 mm).

All this assumes that sensor resolution is not in play. For practical purposes that means equal megapixels in each format.

--Rik

[meow]

Thank you again. That's good (because I couldn't figure out why this would not be the case). And bad (because it would be very useful it it wasn't).

I'll try not to pester you with more questions for a while.