Calculating magnification of objective on telephoto lens

[Barrelcactusaddict]

Thank you. I figured it wouldn't do much if just mounted to the camera body. I'm curious to know what those "very few uses" might be, but I'm guessing it would be quite technical, and I'd better not ask. When I had purchased it, I thought an infinity-corrected objective would just project the image directly onto the sensor, but apparently that does not work; are there any finite objectives meant to be used with only 40-50mm of "distance between rear of objective and camera focal plane" (I don't know the term for that)?

[Doppler9000]

For less than $30, you could could get a Canon EF bellows on eBay. You could add some cheap finite objectives, use your adapter to mount them to the front, adjust the bellows, and get started. You might need to add a cheap extension tube to reach focus, depending on the bellows and the objective.

[Barrelcactusaddict]

For less than $30, you could could get a Canon EF bellows on eBay. You could add some cheap finite objectives, use your adapter to mount them to the front, adjust the bellows, and get started. You might need to add a cheap extension tube to reach focus, depending on the bellows and the objective.

That is true, that would be an option. Although, I've never used a bellows before, and I'm not sure how I'd mount it securely onto my makeshift copy stand. I would have to try to configure a horizontal setup, which I hadn't put as much thought into when considering the type of setup I wanted.

When I was initially trying to figure out what setup to make, I had thought of getting a miniature lab lift to place the subject on, as part of a horizontal setup. I then thought of going with a vertical setup, so I could make use of immersive media, as well as more easily take macro photographs of multiple small specimens; it seems I would also not have to worry as much about how to mount and securely position a subject. I think I may have also considered using a vertical setup, as it wouldn't take up as much horizontal space.

I wouldn't mind trying to use a bellows in the future, as my study space has very little atmospheric dust. It might be nice to experiment with one in the future.

[rjlittlefield]

are there any finite objectives meant to be used with only 40-50mm of "distance between rear of objective and camera focal plane"

I have never heard of a microscope objective meant to be used that way. The shortest standard tube length that I know is 150 mm, measured from the shoulder of the mounting threads to the focal plane.

There are a few other lenses that have RMS threads and could do useful work mounted directly on the camera. But these are specialized and uncommon. They would not match your application.

Regarding Rafcamera, it is important to understand that he plays the role of a machinist, not an optician. Other people tell Rafcamera what adapters they want, he designs and builds the adapter to their specifications, and finally he puts each new adapter into his catalog so that other people can order them as standard parts. As a result, he provides excellent descriptions of what each adapter is, but his descriptions of intended use are not always ideal. Most likely the person who commissioned the RMS-to-Canon-EOS adapter intended to use it with extension tubes or a bellows.

--Rik

[Scarodactyl]

Yeah, it would be handy for premade extension tubes like these https://www.ebay.com/itm/Auto-Focus-Mac ... 632-2357-0
I have tried a lomo 3.7x right up against the camera and it did cover aps-c. I didn't do any real testing but the image looked weird to me in a way my normal-photography-illiterate vocabulary can't describe, though oddly not awful.

[Barrelcactusaddict]

Regarding Rafcamera, it is important to understand that he plays the role of a machinist, not an optician. Other people tell Rafcamera what adapters they want, he designs and builds the adapter to their specifications, and finally he puts each new adapter into his catalog so that other people can order them as standard parts. As a result, he provides excellent descriptions of what each adapter is, but his descriptions of intended use are not always ideal. Most likely the person who commissioned the RMS-to-Canon-EOS adapter intended to use it with extension tubes or a bellows.

--Rik

Thank you, that does make sense, I hadn't considered that; I assumed he was also an expert macro photographer. Actually, I received today the two other adapters I had ordered a month ago from him (one male 49mm thread to female RMS thread for a SMC Pentax 100mm f/2.8, which I now don't intend to purchase, and a male RMS thread to female M26 thread for a Mitutoyo objective); I would have used the M26 for both of the RMS adapters meant for the 200mm and 100mm Pentax lenses. I'll photograph these two, and I'll be ready to post everything to Equipment Exchange, if that's okay.

Yeah, ir would be handy for premade extension tubes like these https://www.ebay.com/itm/Auto-Focus-Mac ... 632-2357-0
I have tried a lomo 3.7x right up against the camera and it did cover aps-c. I didn't do any real testing but the image looked weird to me in a way my normal-photography-illiterate vocabulary can't describe, though oddly not awful.

Thank you, that's interesting to hear that objective behaves that way. I did a search and came upon an article on closeuphotgraphy.com about that objective. I'm a little confused about the second paragraph of the section titled "Stacked or Coupled Lenses"; I thought a wider aperture results in lower depth of field, but this can't be what the author meant by "potential resolution", can it? Did he mean "wider" not in the physical sense, but as "higher" in the numerical sense? I'm not sure I understand what he meant by potential resolution.

Also, what are the numerical values of the "nominal aperture" for the objective itself and for its combination with the Makro-Symar 5.6/120? I solved for "X" in both cases, but couldn't find any matching info amongst the objective's specs in the author's provided link, and only found 3.56756756757 for the nominal aperture in the formula for the combination of lenses. Is the "nominal aperture" the actual settable aperture on the lens itself?

I'm probably shooting myself in the foot with this, but I would like to understand what the author meant in that particular paragraph, and how he attained those results with those formulas. I'm not questioning his correctness at all, I'm just confused as to what nominal aperture is and what their values were in those formulas.
https://www.closeuphotography.com/lomo-3-7x-and-sr120

[chris_ma]

Closeuphotography.com is a webpage provided by Robert who is also a frequent poster in this forum, and it's full of incredibly helpful and well researched information (which seems to be rarer and rarer these days on the internet).

That said, it seems to me from your previous posts that you shouldn't dive into stacked lenses at this stage of your journey. suffice to say that on high magnification one of the main limiting factor is diffraction due to light bending at the aperture, and stacked lenses have an advantage there since their effective aperture can be larger.

But back to your project:

You're most likely best of with getting the Laowa lens people have been recommending you and just start taking pictures - there will be enough to learn with stacking and post processing, specially considering that inclusions in amber is probably a very challenging subject.

[rjlittlefield]

I did a search and came upon an article on closeuphotgraphy.com about that objective. I'm a little confused about the second paragraph of the section titled "Stacked or Coupled Lenses"; I thought a wider aperture results in lower depth of field, but this can't be what the author meant by "potential resolution", can it? Did he mean "wider" not in the physical sense, but as "higher" in the numerical sense? I'm not sure I understand what he meant by potential resolution.

What Robert means by "potential resolution" is diffraction-limited resolution, that is, assuming the lenses have no aberrations.

In this case you can get more resolution from a cone of light with a wider angle, than you can from one with a narrower angle. A wider cone corresponds to a larger numerical aperture (NA) and a smaller f-number.

A conceptual explanation is that adding the rear lens allows the front lens to be closer to the subject, compared to getting the same magnification with empty extension. That closer distance accepts a wider cone of light, which is what gives the higher potential resolution.

If you need a refresher on diffraction, see viewtopic.php?t=6176 .

Also, what are the numerical values of the "nominal aperture" for the objective itself and for its combination with the Makro-Symar 5.6/120? I solved for "X" in both cases, but couldn't find any matching info amongst the objective's specs in the author's provided link, and only found 3.56756756757 for the nominal aperture in the formula for the combination of lenses. Is the "nominal aperture" the actual settable aperture on the lens itself?

I'm probably shooting myself in the foot with this, but I would like to understand what the author meant in that particular paragraph, and how he attained those results with those formulas. I'm not questioning his correctness at all, I'm just confused as to what nominal aperture is and what their values were in those formulas.
https://www.closeuphotography.com/lomo-3-7x-and-sr120

I think that you're talking about this paragraph:

You can predict the maximum possible resolution from a certain lens by using the simple fact that a wider aperture = higher potential resolution. The Lomo objective focused at 3.7x magnification by extension only would have an effective aperture of f/16.8 using the simple formula, effective aperture = nominal aperture * ( Magnification + 1 ). Now with the Lomo 3,7x mounted on the Makro Symmar 5.6/120 the effective aperture would be only f/13.2 using the formula effective aperture = nominal aperture * Magnification.

The analysis goes like this...

The Lomo is a finite objective, rated as 3.7X and NA 0.11. This means that it is intended to be used at 3.7X, on empty extension, and in that configuration, it will give NA 0.11.

There is a reliable formula that relates NA, magnification, and effective aperture:
effective aperture = magnification / (2*NA)
where NA describes the numerical aperture on the subject side, "effective aperture" is the working f-number on the image side, and magnification is the ratio between image size and subject size.

This formula is always true, regardless of what optics are involved.

From this formula we can immediately calculate that the effective aperture is 3.7 / (2*0.11) = 16.81818 .

So I agree completely with the statement about "effective aperture of f/16.8".

However, the paragraph then gets a bit scrambled. In fact we cannot get that 16.8 from the formula that effective aperture = nominal aperture * ( Magnification + 1), because we do not know the nominal aperture to plug into that formula!

But we can work backward, using the 16.8, plus that formula, to calculate what the "nominal aperture" of the Lomo objective must be, at least under the reasonable assumption that it behaves roughly according to that formula. The answer, given that 16.81818 = nominal aperture * (3.7 + 1), is that nominal aperture = 3.5783.

In other words, the Lomo 3.7 NA 0.11 objective is acting just the same as an ordinary f/3.5783 lens would act, if extended so as to give 3.7X.

Now regarding use with the Makro Symmar... With stacked lenses, when the rear lens is focused at infinity, it is always true that effective f-number on the camera side = magnification * effective f-number on the subject side [typo: used to say "sensor side"]. If we assume magnification 3.7 for the stacked pair, and f/3.5783 for the Lomo on the front, then we get effective f-number on the camera side = 3.7 * 3.5783 = 13.2397 .

--Rik

Nov 3, 2021, edited to fix typo.

[Barrelcactusaddict]

I did a search and came upon an article on closeuphotgraphy.com about that objective. I'm a little confused about the second paragraph of the section titled "Stacked or Coupled Lenses"; I thought a wider aperture results in lower depth of field, but this can't be what the author meant by "potential resolution", can it? Did he mean "wider" not in the physical sense, but as "higher" in the numerical sense? I'm not sure I understand what he meant by potential resolution.

What Robert means by "potential resolution" is diffraction-limited resolution, that is, assuming the lenses have no aberrations.

In this case you can get more resolution from a cone of light with a wider angle, than you can from one with a narrower angle. A wider cone corresponds to a larger numerical aperture (NA) and a smaller f-number.

A conceptual explanation is that adding the rear lens allows the front lens to be closer to the subject, compared to getting the same magnification with empty extension. That closer distance accepts a wider cone of light, which is what gives the higher potential resolution.

If you need a refresher on diffraction, see viewtopic.php?t=6176 .

Also, what are the numerical values of the "nominal aperture" for the objective itself and for its combination with the Makro-Symar 5.6/120? I solved for "X" in both cases, but couldn't find any matching info amongst the objective's specs in the author's provided link, and only found 3.56756756757 for the nominal aperture in the formula for the combination of lenses. Is the "nominal aperture" the actual settable aperture on the lens itself?

I'm probably shooting myself in the foot with this, but I would like to understand what the author meant in that particular paragraph, and how he attained those results with those formulas. I'm not questioning his correctness at all, I'm just confused as to what nominal aperture is and what their values were in those formulas.
https://www.closeuphotography.com/lomo-3-7x-and-sr120

I think that you're talking about this paragraph:

You can predict the maximum possible resolution from a certain lens by using the simple fact that a wider aperture = higher potential resolution. The Lomo objective focused at 3.7x magnification by extension only would have an effective aperture of f/16.8 using the simple formula, effective aperture = nominal aperture * ( Magnification + 1 ). Now with the Lomo 3,7x mounted on the Makro Symmar 5.6/120 the effective aperture would be only f/13.2 using the formula effective aperture = nominal aperture * Magnification.

The analysis goes like this...

The Lomo is a finite objective, rated as 3.7X and NA 0.11. This means that it is intended to be used at 3.7X, on empty extension, and in that configuration, it will give NA 0.11.

There is a reliable formula that relates NA, magnification, and effective aperture:
effective aperture = magnification / (2*NA)
where NA describes the numerical aperture on the subject side, "effective aperture" is the working f-number on the image side, and magnification is the ratio between image size and subject size.

This formula is always true, regardless of what optics are involved.

From this formula we can immediately calculate that the effective aperture is 3.7 / (2*0.11) = 16.81818 .

So I agree completely with the statement about "effective aperture of f/16.8".

However, the paragraph then gets a bit scrambled. In fact we cannot get that 16.8 from the formula that effective aperture = nominal aperture * ( Magnification + 1), because we do not know the nominal aperture to plug into that formula!

But we can work backward, using the 16.8, plus that formula, to calculate what the "nominal aperture" of the Lomo objective must be, at least under the reasonable assumption that it behaves roughly according to that formula. The answer, given that 16.81818 = nominal aperture * (3.7 + 1), is that nominal aperture = 3.5783.

In other words, the Lomo 3.7 NA 0.11 objective is acting just the same as an ordinary f/3.5783 lens would act, if extended so as to give 3.7X.

Now regarding use with the Makro Symmar... With stacked lenses, when the rear lens is focused at infinity, it is always true that effective f-number on the camera side = magnification * effective f-number on the sensor side. If we assume magnification 3.7 for the stacked pair, and f/3.5783 for the Lomo on the front, then we get effective f-number on the camera side = 3.7 * 3.5783 = 13.2397 .

--Rik

Okay, so I read, re-read, and re-re-read your post on diffraction; I think I can comprehend almost everything, except for what I'm looking at with the diagram and its captions (and some of the explanations that relate directly to it); so basically I get closer to the highest potential resolution the less I stop-down the lens' aperture, the more light I allow in?

So what is exactly the definition of "nominal aperture"? Is it just the lowest, unaffected aperture on a lens, or is it any kind of f-number possible by adjusting the aperture ring without the addition of a second, paired lens? I remember working backwards and finding the "3.5783", but I didn't think this is what would be used as the nominal aperture in the paired lens formula (I thought that that would have been 5.6, the base aperture of the Symmar lens): so the "nominal aperture" in the second part of the author's second formula is actually the "effective f-number on the sensor side" or "nominal aperture" of the Lomo objective "sensor" that you mentioned in the formula from your "working backward" section? So are "effective f-number" and "nominal aperture" interchangeable terms, or was this a typo? I'm confused by that.

So there are 3 different formulas, but please correct me if I'm wrong:
one involving numerical aperture to find effective aperture in microscope objectives
[effective aperture = magnification ÷ (2 * numerical aperture)]

one to find effective aperture in microscope objectives using the objective's nominal aperture and magnification
[effective aperture = nominal aperture * (Magnification + 1)]

and one to find effective aperture on the camera side using magnification and effective aperture on the sensor/outermost lens or objective side
[effective f-number "cameraS" = magnification * effective f-number "sensorS"]

--I think I understand, but could you please clarify if I was incorrect in my assessment on the section I typed in italics in my second paragraph? I thought that nominal aperture was different from effective aperture; if so, specifically how are they different (or in what conditions are they the same)?--

Thank you, I really, really appreciate everyone's patience with my ignorance and my questions, so very much. It really means a lot to me.

[Chris S.]

I'm probably shooting myself in the foot with this, but I would like to understand what the author meant in that particular paragraph, and how he attained those results with those formulas.

Thank you, I really, really appreciate everyone's patience with my ignorance and my questions, so very much. It really means a lot to me.

Kaegen,

Don't underestimate yourself--you're doing great! Keep up the good work.

Be aware that the issues you're currently grappling with make even expert heads explode on a regular basis. They are far from simple, and there is a lot of misinformation out there. If you followed the treatise on diffraction, you're way ahead of nearly everyone on the planet.

--Chris S.

[Barrelcactusaddict]

Closeuphotography.com is a webpage provided by Robert who is also a frequent poster in this forum, and it's full of incredibly helpful and well researched information (which seems to be rarer and rarer these days on the internet).

That said, it seems to me from your previous posts that you shouldn't dive into stacked lenses at this stage of your journey. suffice to say that on high magnification one of the main limiting factor is diffraction due to light bending at the aperture, and stacked lenses have an advantage there since their effective aperture can be larger.

But back to your project:

You're most likely best of with getting the Laowa lens people have been recommending you and just start taking pictures - there will be enough to learn with stacking and post processing, specially considering that inclusions in amber is probably a very challenging subject.

Definitely, thank you, I think when I do start again to pursue finishing my setup at some near-future date, I will purchase the Laowa 25mm Ultra Macro lens; that should be less complex than worrying about objectives and tube lenses and how those two interact.

I do have some experience taking photos of inclusions in amber, but they were only done using the 60mm f/2.8 macro Canon lens and combined 2x and 4x Hoya circular magnifying adapters: the results were very grainy because I had to photograph the amber with backlighting, due to its intense blue surface fluorescence under simple LED light (this constitutes "blue" amber) which obscures any detail. I'll post some links to the pics below; they are of two Pseudomyrmex sp. ants in a single 4.3g piece of blue Sumatra amber, as well as one unidentified winged individual in the same piece; there are literally only a handful of images of insect inclusions in Sumatra amber online, and only a couple species have ever been officially described, so I was shocked to discover this specimen's contents while working through my rough material. I'm not proud of the images, but they're the best I could do at the moment.

I don't really understand the concept of paired lenses, even at this point, but I can somewhat understand equations in this type of setting. I also still don't understand what effective and nominal apertures are or if they're identical, different, or are interchangeable terms in varying situations.

http://www.thefossilforum.com/index.php ... fm-~30-ma/
http://www.thefossilforum.com/index.php ... fm-~30-ma/
http://www.thefossilforum.com/index.php ... fm-~30-ma/
http://www.thefossilforum.com/index.php ... fm-~30-ma/
http://www.thefossilforum.com/index.php ... fm-~30-ma/
http://www.thefossilforum.com/index.php ... fm-~30-ma/

[Barrelcactusaddict]

I'm probably shooting myself in the foot with this, but I would like to understand what the author meant in that particular paragraph, and how he attained those results with those formulas.

Thank you, I really, really appreciate everyone's patience with my ignorance and my questions, so very much. It really means a lot to me.

Kaegen,

Don't underestimate yourself--you're doing great! Keep up the good work.

Be aware that the issues you're currently grappling with make even expert heads explode on a regular basis. They are far from simple, and there is a lot of misinformation out there. If you followed the treatise on diffraction, you're way ahead of nearly everyone on the planet.

--Chris S.

Thank you so much, that is most encouraging! I don't enjoy my broad lack of comprehension in regards to many concepts in optics, but I do think I'm beginning to understand just a little; not much, but a little. I do hope to improve.

Everyone's insight, experience, advice, and patience has been so, well, helpful; everyone here is of more help than they know, truly!

[Chris S.]

Everyone's insight, experience, advice, and patience has been so, well, helpful; everyone here is of more help than they know, truly!

Kaegen,

Here at PMN, we're moving ahead much faster as a group than any of us could move forward on our own. Discovery and disclosure, teaching and learning--these are central to PMN. Stick with it, Kaegen--my bet is that in time, you'll have a far bigger role as a mentor than as a one-time student. Can see your future posts: "I totally get where you are--was once frustrated myself. . . . Here's how you deal with it. . . ."

The practice of photomacrography has, over the past 15 years or so, undergone a great leap forward. Much of that leap has come from our own PMN community. And much of our contribution has come from folks who were once struggling newcomers. With time, assistance, and the light of their own talents, many once-newcomers have become significant contributors. In the long game, helping others puts us all ahead.

--Chris S.

[Chris S.]

. . . the results were very grainy because I had to photograph the amber with backlighting, due to its intense blue surface fluorescence under simple LED light (this constitutes "blue" amber) which obscures any detail. . . .

Kaegen,

I know nothing of "blue amber." But if surface fluorescence of your amber, occurring under illumination by full-spectrum LED, is obscuring photographic detail, the classic attack on this problem would be to filter your illumination to reduce portions of the spectrum that contribute to autofluorescence.

Remembering that when subjects absorb light photons and then emit other photons as autofluorescence, the emitted photons are "down-spectrum" from the absorbed photons, other than in highly contrived situations.

So my naive question is: Could you reduce or eliminate bothersome autofluorescence by filtering out of your illuminating light that portion higher in spectrum than the unwanted emissions?

--Chris S.

[RobertOToole]

Closeuphotography.com is a webpage provided by Robert who is also a frequent poster in this forum, and it's full of incredibly helpful and well researched information

Thanks!

(which seems to be rarer and rarer these days on the internet). ....

Yes, that was one of the main objectives for starting the site, but its come a long way since then. A few times I've used Google to search for a lens or objective or something I come across, and the search results have taken me to my own site, and I had completely forgot that I posted the info!

That makes me feel really old (I'm 52)

Best,

Robert