Reduce magnification

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Garymicheal
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Reduce magnification

Post by Garymicheal »

Hello my mitutoyo 10x objective has finally arrived wow !@# and its much harder to use than I expected
If I want to reduce magnification is it best to shorten my bellows with the raynox 150 attached or to swap the the raynox 150 for the 250 ? I have both
And to increase magnification is it as simple as increasing the tube length ( bellows) as you would with a macro lens and extention tubes ?
Many thanks Gary
P.s I know I should have done my research before buying
God knows how people take photos with a 20x or more 🙃😵💫🤔
Last edited by Garymicheal on Fri Jan 17, 2025 12:36 am, edited 2 times in total.

Scarodactyl
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Re: Reduce magnification

Post by Scarodactyl »

You need a shorter focal length tube lens to push down the mag. You can do a bit by changing the focus of the tube lens from infinity but pushing objectives out of spec like this can have variable results

rjlittlefield
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Re: Reduce magnification

Post by rjlittlefield »

Another "be aware" type caution: reducing the magnification will get you little or no increase in depth of field.

DOF is determined solely by the working NA of the objective, at least until your resolution becomes limited by the digital imaging system instead of the optics.

--Rik

Garymicheal
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Re: Reduce magnification

Post by Garymicheal »

rjlittlefield wrote:
Fri Jan 17, 2025 12:56 am
Another "be aware" type caution: reducing the magnification will get you little or no increase in depth of field.
Thanks for the reply
It's not the depth of I'm trying to change
( or is it )
at 10x yesterday it took me 30 minutes to find a bees foot 😵💫 so I was thinking if I reduced the magnification to get use to the objective and lighting it etc

iconoclastica
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Re: Reduce magnification

Post by iconoclastica »

I use this objective with Raynox-150 in front of a bellows. The bellows gives it some zoom-capacity. Reducing to c. 70% works well, with more reduction the image circle becomes limiting and vignetting becomes apparent.
--- felix filicis ---

JKT
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Re: Reduce magnification

Post by JKT »

Garymicheal wrote:
Fri Jan 17, 2025 12:14 am
And to increase magnification is it as simple as increasing the tube length ( bellows) as you would with a macro lens and extention tubes ?
Not quite. As discussed, you can decrease the magnification by using shorter focal length tube lens. That works in the other direction as well, so using longer focal length tube lens gives more magnification. In order to keep the tube lens focused at infinity, it ALSO needs more extension, but that comes from the increased focal length.

When going in that direction, your microscope objective will give you larger coverage, but your tube lens might not. That depends on your tube lens. What you will likely see is that your images will be softer. That is because the increased magnification does not increase the microscope objective resolution. You are simply projecting the same data on larger area. The problem with those basic Mitutoyos is that there is practically no reserve resolution when used with current cameras. You'll quickly see the softening.

Darionett
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Re: Reduce magnification

Post by Darionett »

Garymicheal wrote:
Fri Jan 17, 2025 1:09 am
rjlittlefield wrote:
Fri Jan 17, 2025 12:56 am
Another "be aware" type caution: reducing the magnification will get you little or no increase in depth of field.
Thanks for the reply
It's not the depth of I'm trying to change
( or is it )
at 10x yesterday it took me 30 minutes to find a bees foot 😵💫 so I was thinking if I reduced the magnification to get use to the objective and lighting it etc
This post may help you https://www.photomacrography.net/forum/ ... 25&t=47935

in my case, between the tube lens and the microscope objective I installed a microscope turret, so to search for the point of my interest, I use the microscope objective with the lowest magnification, then I select the turret to the desired magnification.

iconoclastica
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Re: Reduce magnification

Post by iconoclastica »

We all are challenged to locate the subject in the finder occasionally. This topic might be a help: Laser aiming and focus in photomacrography.
--- felix filicis ---

IMAGOμM
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Re: Reduce magnification

Post by IMAGOμM »

rjlittlefield wrote:
Fri Jan 17, 2025 12:56 am
Another "be aware" type caution: reducing the magnification will get you little or no increase in depth of field.

DOF is determined solely by the working NA of the objective, at least until your resolution becomes limited by the digital imaging system instead of the optics.

--Rik
I think that the search for the "right" DOF for stacking is always a fascinating topic, like the search for the Holy Grail. The hunt for a concrete but unfindable, elusive and, ultimately, extremely metamorphic object.

I guess that with the previous statement RiK means to say that, by decreasing the M factor, the effective NA increases - therefore the DOF decreases - but it is applied to a smaller image - due to the lower magnification - and the two factors compensate each other (more or less). The same, but in reverse, I suppose happens in the case of pushing-up. Or am I wrong?

I wonder if there is a complete treatment of these optical phenomena in the bibliography, both in the case of tube lenses with different focal lengths and with the same lens pushed up/down. In any case, thanks to Rik who very recently illustrated, with excellent simulations, some dynamics of the objective/tube lens systems. And I understand why he has given up, at least for the moment, on formulating a program that calculates the DOF taking into account every (too many!) variable.
Last edited by IMAGOμM on Fri Jan 17, 2025 2:57 pm, edited 1 time in total.

Pau
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Re: Reduce magnification

Post by Pau »

iconoclastica wrote:
Fri Jan 17, 2025 9:26 am
We all are challenged to locate the subject in the finder occasionally. This topic might be a help: Laser aiming and focus in photomacrography.
This method is very good (I also use it) but only works with DSLRs

For mirrorless cameras here you have some ideas https://www.photomacrography.net/forum/ ... 31#p301831

But 10X is very doable without those kind of help, just sufficient practice will do in most cases
Pau

rjlittlefield
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Re: Reduce magnification

Post by rjlittlefield »

IMAGOμM wrote:
Fri Jan 17, 2025 10:07 am
I guess that with the previous statement RiK means to say that, by decreasing the M factor, the effective NA increases - therefore the DOF decreases - but it is applied to a smaller image - due to the lower magnification - and the two factors compensate each other (more or less). The same, but in reverse, I suppose happens in the case of pushing-up.
Sorry to say, it's the reverse of all that. If you decrease the magnification by reducing the bellows extension, then you'll have to increase the distance from objective to target in order to maintain focus. That increased front distance will decrease the effective NA, which increases the DOF. At the same time, you're increasing the information density on the sensor, which makes it more likely that sensor resolution will come into play, which also increases the DOF. All effects push in the same direction.

If you decrease the magnification by swapping in a shorter tube lens, leaving the tube lens focused at infinity, then there will be no change to the front focus distance or the effective NA. Only the effects at sensor will be in play, if you've pushed far enough for that to happen.
I think that the search for the "right" DOF for stacking is always a fascinating topic, like the search for the Holy Grail. The hunt for a concrete but unfindable, elusive and, ultimately, extremely metamorphic object.
I assume that "right DOF" means "best step size". I like your description "extremely metamorphic", because the answer depends on so many things including the particular user's willingness to trade off capture+processing time against changes in image quality.

In the whole area, I know of only one question that has a (nearly) crisp answer. Ironically it's a question that hardly anybody ever asks!

That special question is this: given a specified step size, what's the best aperture setting?

Phrased in this way, and limiting the concerns to diffraction and geometry, the answer turns out to be "whatever aperture puts the specified step size right on the lambda/4 criterion for DOF". An aperture that gives much less than 1/4 lambda will make a stack that's blurred from diffraction; an aperture much larger will make a stack that exhibits focus banding. There's a well defined peak in the quality curve that's only about 1 f-stop wide, depending on exactly how you want to trade off maximum sharpness against consistent sharpness.

This is very different from the usual question that asks the other way around: given a specified aperture, what's the best step size? This more common question does not have a well defined peak in the quality curve. Decreasing the step size will always give less blur, so the answer becomes a judgement call of what step size makes the most acceptable tradeoffs.

In any case, thanks to Rik who very recently illustrated, with excellent simulations, some dynamics of the objective/tube lens systems. And I understand why he has given up, at least for the moment, on formulating a program that calculates the DOF taking into account every (too many!) variable.
Thank you for the kind words and understanding. There will be no such program. :)

--Rik

IMAGOμM
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Re: Reduce magnification

Post by IMAGOμM »

rjlittlefield wrote:
Fri Jan 17, 2025 8:01 pm
IMAGOμM wrote:
Fri Jan 17, 2025 10:07 am
I guess that with the previous statement RiK means to say that, by decreasing the M factor, the effective NA increases - therefore the DOF decreases - but it is applied to a smaller image - due to the lower magnification - and the two factors compensate each other (more or less). The same, but in reverse, I suppose happens in the case of pushing-up.
Sorry to say, it's the reverse of all that. If you decrease the magnification by reducing the bellows extension, then you'll have to increase the distance from objective to target in order to maintain focus. That increased front distance will decrease the effective NA, which increases the DOF. At the same time, you're increasing the information density on the sensor, which makes it more likely that sensor resolution will come into play, which also increases the DOF. All effects push in the same direction.

If you decrease the magnification by swapping in a shorter tube lens, leaving the tube lens focused at infinity, then there will be no change to the front focus distance or the effective NA. Only the effects at sensor will be in play, if you've pushed far enough for that to happen...
First of all, thank you for finding the time, desire and patience to write this long clarification.

1. Tube lens.
Let's see if this time I have correctly understood the dynamics of the objective/tube lens combination.
To summarize:

a. Push up/down of the tube lens.
Pushing down the lens the working distance increases, the NA decreases and the DOF increases (and consequently the stacking step). The opposite for pushing-up.

b. Variations of the focal length of the tube lens.
The NA remains unchanged and so does the stacking step.
I have to say that this surprises me: it seems like the optical equivalent of perpetual motion. Not very nice in the case of a short lens but very convenient in that of a long lens.
I would really like to delve into these topics. Are there any bibliographical references?

2. Step size.
Maybe there is a reason why people don't ask what is the best aperture for a specific step. In Photomicrography.net, as in general worldwide, there are many professional members but also many hobbyists. For the former, who often need to maximize working time, it is important to reduce the image creation time and consequently the duration of a stacking and the number of shots generated. For hobbyists this aspect is not relevant and they can afford the luxury of dedicating themselves to the search for maximum quality, whatever the meaning of this term. Otherwise, there would be no explanation for the large amount of threads on this site that discuss the differences between various lenses even when their visualization requires an eagle eye and a lot of experience. Not to mention the randomness due to ancillary but not negligible factors such as production tolerances, stability and precision of the rigs used, lighting, vibrations in the environment and so on.
Perhaps the most useful question is: what is the best step and the best aperture (for lenses with a diaphragm) to obtain the most balanced result? Ultimately, this is the principle that the late Robert O'Toole adheres to in his countless lens tests.
As for the best step for stacking, you also have to take into account the real world. For the virtual world, your suggestion of the λ/4 condition is certainly very useful in maximizing the time needed to create the image, even if in the 2014 white paper "What's the depth o field..." you suggest adopting the λ/8 criterion. However, rails and stepper motors are not perfect, so - as you know perfectly well - most people stick to the λ/12 criterion and many prudently choose λ/16. It is certainly not by chance that in the DOF Calculator that you inserted in Zerene Stacker the user can set the overlap of the steps as he likes more.

However, there is no more confusing topic than this. Over the years I have accumulated many books dedicated to macro/micrography written by photographers in the field, even with academic references (few are those dedicated to scientific photography, a little-frequented topic, which are reduced to the usual Morton and Lawson - very dated - and the more recent Savazzi, a highly appreciated member of this forum). Well, in almost all of them there is a DOF table depending on the magnification and aperture. There are no two tables that report data that are not identical but at least consistent with each other. Indeed, the differences are often wild. Evidently everyone has their own ideas on the matter. This says a lot about the harshness of the subject.

3. Pixel pitch.
This term normally refers to the distance between the pixels of the sensor measured in rows and columns. It is also the data provided by the manufacturer. However, it is not unusual to find a different measurement criterion, namely PP=PP*√2. In fact, it seems right to consider the minimum resolution of the sensor (theoretical) as that calculated along the diagonal, rather than that according to rows and columns. I would like to know your opinion on this.

4. Transfer of the maximum resolution from lens to sensor.
In all the discussions and papers I know of, it is assumed that the MTF of the lens (often, unfortunately, only theoretical: the equipment to measure the practical one is expensive and not very widespread) can be transferred as is to the sensor. In the "pioneering" times of film, when practice was very important and theory was little (not for nothing Ansel Adams has become a legend) there were some VERY approximate formulas that intended to define the relationship between the l/mm of the lens, the film and the resulting image. However, one thing was known for sure: even using the best film (personally I often used Technical Pan) you could hope to transfer to the film a maximum of 80/90% of the resolving power of the lens. I believe that something similar also happens in the digital world, and therefore we overestimate - and not by a little - the sensor's ability to offer adequate image transfer of the lens. (Something different here:https://photomacrography.net/forum/view ... =8&t=47956
I have in front of me, as I write, a print of an ootheca (egg sac deposited by some insects) extraordinarily sharp, taken at the beginning of the century with a Canon 100/2.8 lens (not extraordinary in itself) on Technical Pan developed in Technidol. The resolution of this combination, which exceeded 200 l/mm, could be considered completely superfluous for a glass that, closed to nominal f/16, exhibited much lower performance. Yet I can assure you that there was no history in the comparison, in the same conditions, with the excellent Velvia 50 or Tmax 100 or Pan F. So, we have to be careful when talking about "empty magnification". May be that the lack of enhancement depends on other factors that interfere with image formation. I think it would be interesting to discuss this topic with other members of this forum. Note that for M>10 the situation could be substantially different due to diffraction.

Lou Jost
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Re: Reduce magnification

Post by Lou Jost »

IMAGOμM wrote:
Sat Jan 18, 2025 12:41 am
rjlittlefield wrote:
Fri Jan 17, 2025 8:01 pm
IMAGOμM wrote:
Fri Jan 17, 2025 10:07 am
I guess that with the previous statement RiK means to say that, by decreasing the M factor, the effective NA increases - therefore the DOF decreases - but it is applied to a smaller image - due to the lower magnification - and the two factors compensate each other (more or less). The same, but in reverse, I suppose happens in the case of pushing-up.
Sorry to say, it's the reverse of all that. If you decrease the magnification by reducing the bellows extension, then you'll have to increase the distance from objective to target in order to maintain focus. That increased front distance will decrease the effective NA, which increases the DOF. At the same time, you're increasing the information density on the sensor, which makes it more likely that sensor resolution will come into play, which also increases the DOF. All effects push in the same direction.

If you decrease the magnification by swapping in a shorter tube lens, leaving the tube lens focused at infinity, then there will be no change to the front focus distance or the effective NA. Only the effects at sensor will be in play, if you've pushed far enough for that to happen...
First of all, thank you for finding the time, desire and patience to write this long clarification.

1. Tube lens.
Let's see if this time I have correctly understood the dynamics of the objective/tube lens combination.
To summarize:

a. Push up/down of the tube lens.
Pushing down the lens the working distance increases, the NA decreases and the DOF increases (and consequently the stacking step). The opposite for pushing-up.

b. Variations of the focal length of the tube lens.
The NA remains unchanged and so does the stacking step.
I have to say that this surprises me: it seems like the optical equivalent of perpetual motion. Not very nice in the case of a short lens but very convenient in that of a long lens.
I would really like to delve into these topics. Are there any bibliographical references?

2. Step size.
Maybe there is a reason why people don't ask what is the best aperture for a specific step. In Photomicrography.net, as in general worldwide, there are many professional members but also many hobbyists. For the former, who often need to maximize working time, it is important to reduce the image creation time and consequently the duration of a stacking and the number of shots generated. For hobbyists this aspect is not relevant and they can afford the luxury of dedicating themselves to the search for maximum quality, whatever the meaning of this term. Otherwise, there would be no explanation for the large amount of threads on this site that discuss the differences between various lenses even when their visualization requires an eagle eye and a lot of experience. Not to mention the randomness due to ancillary but not negligible factors such as production tolerances, stability and precision of the rigs used, lighting, vibrations in the environment and so on.
Perhaps the most useful question is: what is the best step and the best aperture (for lenses with a diaphragm) to obtain the most balanced result? Ultimately, this is the principle that the late Robert O'Toole adheres to in his countless lens tests.
As for the best step for stacking, you also have to take into account the real world. For the virtual world, your suggestion of the λ/4 condition is certainly very useful in maximizing the time needed to create the image, even if in the 2014 white paper "What's the depth o field..." you suggest adopting the λ/8 criterion. However, rails and stepper motors are not perfect, so - as you know perfectly well - most people stick to the λ/12 criterion and many prudently choose λ/16. It is certainly not by chance that in the DOF Calculator that you inserted in Zerene Stacker the user can set the overlap of the steps as he likes more.

However, there is no more confusing topic than this. Over the years I have accumulated many books dedicated to macro/micrography written by photographers in the field, even with academic references (few are those dedicated to scientific photography, a little-frequented topic, which are reduced to the usual Morton and Lawson - very dated - and the more recent Savazzi, a highly appreciated member of this forum). Well, in almost all of them there is a DOF table depending on the magnification and aperture. There are no two tables that report data that are not identical but at least consistent with each other. Indeed, the differences are often wild. Evidently everyone has their own ideas on the matter. This says a lot about the harshness of the subject.

3. Pixel pitch.
This term normally refers to the distance between the pixels of the sensor measured in rows and columns. It is also the data provided by the manufacturer. However, it is not unusual to find a different measurement criterion, namely PP=PP*√2. In fact, it seems right to consider the minimum resolution of the sensor (theoretical) as that calculated along the diagonal, rather than that according to rows and columns. I would like to know your opinion on this.

4. Transfer of the maximum resolution from lens to sensor.
In all the discussions and papers I know of, it is assumed that the MTF of the lens (often, unfortunately, only theoretical: the equipment to measure the practical one is expensive and not very widespread) can be transferred as is to the sensor. In the "pioneering" times of film, when practice was very important and theory was little (not for nothing Ansel Adams has become a legend) there were some VERY approximate formulas that intended to define the relationship between the l/mm of the lens, the film and the resulting image. However, one thing was known for sure: even using the best film (personally I often used Technical Pan) you could hope to transfer to the film a maximum of 80/90% of the resolving power of the lens. I believe that something similar also happens in the digital world, and therefore we overestimate - and not by a little - the sensor's ability to offer adequate image transfer of the lens. (Something different here:https://photomacrography.net/forum/view ... =8&t=47956
I have in front of me, as I write, a print of an ootheca (egg sac deposited by some insects) extraordinarily sharp, taken at the beginning of the century with a Canon 100/2.8 lens (not extraordinary in itself) on Technical Pan developed in Technidol. The resolution of this combination, which exceeded 200 l/mm, could be considered completely superfluous for a glass that, closed to nominal f/16, exhibited much lower performance. Yet I can assure you that there was no history in the comparison, in the same conditions, with the excellent Velvia 50 or Tmax 100 or Pan F. So, we have to be careful when talking about "empty magnification". May be that the lack of enhancement depends on other factors that interfere with image formation. I think it would be interesting to discuss this topic with other members of this forum. Note that for M>10 the situation could be substantially different due to diffraction.
I strongly agree with you, and I think most of us do. My favorite formula for combining lens and film resolutions was a version of the same formula used to add the combined effects of random noise from two independent sources:
Total resolution = 1/{SQRT [1/lens resolution)^2 + (1/film resolution)^2]}
and I think something similar might apply to a digital sensor. In film days, improving film resolution always increased overall resolution, and the final resolution was always less than the highest input resolution. In the days of film, the idea of matching lens resolution to pixel resolution was wildly incorrect. A lens that resolved 100 lpm coupled with a film that resolved 100 lpm would produce an image that resolved about 70 lpm. It was impossible to capture the full lens resolution, regardless of the film resolution, but the total resolution approached the lens resolution as film resolution became very large. For example, a film resolution of 200 lpm gives a total resolution of almost 90 lpm. I strongly suspect that the situation is similar in the digital world, and I think the idea of matching pixel size to lens resolution is deeply wrong. I haven't proven this, though. I'd be interested in anyone else's experience with this.

IMAGOμM
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Re: Reduce magnification

Post by IMAGOμM »

Lou Jost wrote:
Sat Jan 18, 2025 7:17 am


I strongly agree with you, and I think most of us do. My favorite formula for combining lens and film resolutions was a version of the same formula used to add the combined effects of random noise from two independent sources:
Total resolution = 1/{SQRT [1/lens resolution)^2 + (1/film resolution)^2]}
and I think something similar might apply to a digital sensor. In film days, improving film resolution always increased overall resolution, and the final resolution was always less than the highest input resolution. In the days of film, the idea of matching lens resolution to pixel resolution was wildly incorrect. A lens that resolved 100 lpm coupled with a film that resolved 100 lpm would produce an image that resolved about 70 lpm. It was impossible to capture the full lens resolution, regardless of the film resolution, but the total resolution approached the lens resolution as film resolution became very large. For example, a film resolution of 200 lpm gives a total resolution of almost 90 lpm. I strongly suspect that the situation is similar in the digital world, and I think the idea of matching pixel size to lens resolution is deeply wrong. I haven't proven this, though. I'd be interested in anyone else's experience with this.
Yes! The formula I was referring to is exactly this one. I have been tempted several times to conduct the test you are referring to. I have a Nikon Z8 with 45 Mp and 100 Mp in pixel shift; possibly a Lumix M43 with 25 Mp and 100 Mp; several very stable and very heavy rigs resting on anti-resonance feet on massive marble slabs anchored on three sides to concrete walls in a basement far from traffic vibrations (and without dust :lol:). It is true that I live near the top of an (active) volcano :shock: but in the last fifty thousand years it has not given much trouble... I also have Mitutoyo HRs, MGenossen FL0530 etc. Maybe I lack the cheap lens for comparison but that can be easily remedied :wink: . In reality what I lack are high quality and reasonably cheap charts to conduct tests up to 10x (a problem addressed, even recently in many threads of this site). I don't want to spend hundreds, if not thousands of $ for this project and I don't want to dedicate too much time to it, taken away from other activities that are priorities for me: after all, the "mission" that I have given myself is to create a certain type of images, not to conduct technical tests. For this reason I have never followed up on good intentions. But never say never.

ray_parkhurst
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Re: Reduce magnification

Post by ray_parkhurst »

Garymicheal wrote:
Fri Jan 17, 2025 1:09 am
at 10x yesterday it took me 30 minutes to find a bees foot 😵💫 so I was thinking if I reduced the magnification to get use to the objective and lighting it etc
There is certainly no issue with shortening the bellows extension in order to make "finding" your subject easier. Once found, you can gradually and iteratively increase the bellows length and shorten the WD until you are back to correct optical positioning. If using a bellows with both standards adjustable, the process can be very quick. And while there is some reduction in IQ when mag is incorrect, you can judge for yourself how much you can tolerate. I think mostly the issue happens in the corners, though I have not pushed any of my Mitties to extremes.

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