Calculating magnification of objective on telephoto lens

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RobertOToole
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Re: Calculating magnification of objective on telephoto lens

Post by RobertOToole »

rjlittlefield wrote:
Tue Nov 02, 2021 6:37 pm
Barrelcactusaddict wrote:
Tue Nov 02, 2021 3:18 pm
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.

....................

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
Fantastic detailed answer Rik!

Before I answer any more PMs from Kaegan (with these exact same questions he asked here) I'm going to check your last 10 posts before I respond. I'll never get those 20 minutes of my life back and you did a better more thorough answer anyway #-o

Did anyone mention that it is a little strange that in the case of the Lomo 3.7, a finite lens, performed better stacked? At least I've never seen that before. It really did fantastic on the Makro-Symmar but I did get lucky with the magnification/FL working out the way they did.

Best,

Robert

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Re: Calculating magnification of objective on telephoto lens

Post by Barrelcactusaddict »

Chris S. wrote:
Tue Nov 02, 2021 10:00 pm
Barrelcactusaddict wrote:
Tue Nov 02, 2021 9:07 pm
. . . 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.
Thank you so much, I really do hope to be able to contribute more in the future, rather than only asking questions. :)

That's an excellent question and it has a few solutions, which I hadn't thought of using at the time of the shoot. About amber fluorescence, it's all due to the presence of aromatic hydrocarbons within the amber; with "blue" amber, there is an unusually high concentration (or a high ratio to non-fluorescent compounds) of fluorescent, aromatic hydrocarbons. This observable fluorescence is limited to the surface and for a few millimeters beneath it, depending on clarity; a natural blue base color in amber is extremely rare, but it is known from Sicilian amber (Simetite).

For Sumatra amber, the excitation spectrum range begins roughly at 360nm and ends slightly above 700nm with the highest peaks of excitation at around 420nm and 530nm (the LED lighting I was using, and typically use, is of a common yellow phosphor that emits light between 440-470nm). I'm not sure why, but I didn't think of using my Hoya HRT circular polarizing filter (52mm) while taking the pics with the Canon 60mm f/2.8 macro lens. The emission spectrum of Sumatra amber has its highest peaks at around 370-440nm, so perhaps the filter would have worked (I can't find the specific range of wavelengths that this filter "absorbs"). The other option I had considered was using incandescent light for the setup, but excessive heat can damage amber (especially if prolonged, or as a sudden change), and I was leery about using that on such a rare piece. It could definitely be possible, though, as long as I had a fan running on the specimen. I just wasn't thinking at the time of the shoot, but there definitely are ways to limit that fluorescence.

I do hope to take better pictures in the future, particularly of the inclusions in that specimen.

Here's a link to one of my more favorite articles, that explains in depth the chemical and spectroscopic signatures of Sumatra and Bitterfeld amber; sections in pages 6 and 7 are especially relatable to my situation: https://www.nature.com/articles/s41598- ... rigin=ppub

This specimen is extremely unique, in that it contains intact insect inclusions in blue amber (these are usually destroyed by heat-related processes during diagenesis; those processes can contribute to the formation of the "blue" variety). Alan Simpson, the fellow photographer of amber inclusions that I had mentioned (uses cedar oil and petri dishes in his photographic setup) actually has a specimen of Sumatra amber with insect inclusions, but he did not mention if it is of the blue variety; he mentioned to me this summer that he had hoped to work on it and take photographs, but he hasn't produced them yet. He posts mainly on Instagram as part of his personal blog. https://www.instagram.com/fossilsinamber/

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Re: Calculating magnification of objective on telephoto lens

Post by rjlittlefield »

Barrelcactusaddict wrote:
Tue Nov 02, 2021 8:47 pm
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?
More like the latter. For example, suppose we have an EL Nikkor 50 mm f/2.8 enlarging lens, which we mount on enough extension to give 0.5X magnification. If we set the aperture ring on the EL Nikkor to f/2.8, then we have nominal aperture f/2.8 and effective aperture f/4.2 (=2.8*(0.5+1)). But if we set the aperture ring to f/8, then we have nominal aperture f/8 and effective aperture f/12 (=8*(0.5+1)).
(I thought that that would have been 5.6, the base aperture of the Symmar lens)
In the case of paired lenses, usually the limiting aperture is provided by one or the other, but not both. Whichever lens does not provide the limiting aperture, the nominal aperture of that lens does not matter because it does not affect what light gets through the system. In the case of Lomo+Symmar, the hole in the Lomo lens is so much smaller than the hole in the Symmar at f/5.6 that the 5.6 does not matter.
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?
I assume you are asking about "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."

In that formula, "effective aperture" refers to all the optics, as seen by the sensor, and "nominal aperture" refers to the Lomo alone. This formula assumes that the limiting aperture is provided by the front lens, so it is the nominal aperture of that lens which matters.

Please note that there was a typo in my explanation: at one point I wrote "sensor side" when I meant "subject side". I have edited my earlier post so that it now says
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"].
So are "effective f-number" and "nominal aperture" interchangeable terms, or was this a typo?
No, these are not interchangeable terms. "Effective f-number" always describes the angle of a cone of light, usually at the sensor. "Nominal aperture" usually refers to the f-number of some part of the system in isolation.

But as always, there are exceptions. Modern Nikon systems have a clever interaction between camera and lens, such that the f-number you set on the camera body is taken as being the effective aperture that you want, and the camera and lens collaborate to adjust the lens iris to make that happen. Canon has no such thing; whatever you set on the camera body just gets transferred directly to the lens. This leads to some huge confusions, because "1X and f/11" on a Canon system then ends up meaning about the same thing as "1X and f/22" on a Nikon system. When a Nikon shooter marvels at how his Canon friends get more DOF with the same settings, it's because of this confusion.
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)]
These two look correct. More precisely, the second formula applies to lenses on empty extension, so it works for finite objectives but not for infinite objectives.

Then
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"]
This appears to have inherited my typo that substituted "sensor" for "subject". The proper formula would be

[effective f-number "cameraS" = magnification * effective f-number "subjectS"]

--Rik

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Re: Calculating magnification of objective on telephoto lens

Post by Barrelcactusaddict »

Thank you for correcting me, I think I can now somewhat understand what effective and nominal apertures are. I guess it's okay that I don't fully grasp the concept, since I don't plan on using paired lenses any time soon.

Heading back a bit, perhaps it would be wise for me to postpone selling my adapters and lens until I see how the Laowa performs with inclusions in amber. I don't especially use telephoto lenses by themselves at all, as I don't get out much. :)

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Re: Calculating magnification of objective on telephoto lens

Post by rjlittlefield »

Barrelcactusaddict wrote:
Wed Nov 03, 2021 7:29 pm
I think I can now somewhat understand what effective and nominal apertures are.
A general way of looking at the terms is that "Nominal is what you set; effective is what you get."

(Oh, cool! Google reports "no results found" for that quote!)

Recapping earlier explanation, "effective" describes what the light does, "nominal" describes some component or setting within the overall system.

--Rik

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Re: Calculating magnification of objective on telephoto lens

Post by Chris S. »

Agree with Rik, but can't resist a bit of constructive pedantry.

[pedantry on]

"Nominal" comes from the Latin "nominis"--"of name." Knowing this etymology serves us well in optics and other sciences, because "nominal" is so often some form of "as named" or "as superficially labeled."

We sometimes say things like "to achieve nominal magnification with an infinity-corrected objective, use it on a converging lens of the same focal length as the manufacturer intended; if you use a tube lens of a different focal length, you will get a different effective magnification." In this case, "nominal" is "as the objective is labeled, and "effective" is "as set up."

Economics also makes substantial use of "nominal" vs. "real." In a common example, "nominal profit" is how much more you sell a stock for than what you paid for it, often after holding it for many years. But during the years you held this stock, inflation was likely at work. So "real profit"--nominal profit minus inflation's effective reduction of that profit--is a more correct measure of actual stock gains.

And it appears that the "as named" or "as labeled" sense of the word "nominal" is highly conserved across many sciences.

[/pedantry off]

--Chris S.

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Re: Calculating magnification of objective on telephoto lens

Post by Barrelcactusaddict »

rjlittlefield wrote:
Wed Nov 03, 2021 8:28 pm
Barrelcactusaddict wrote:
Wed Nov 03, 2021 7:29 pm
I think I can now somewhat understand what effective and nominal apertures are.
A general way of looking at the terms is that "Nominal is what you set; effective is what you get."

(Oh, cool! Google reports "no results found" for that quote!)

Recapping earlier explanation, "effective" describes what the light does, "nominal" describes some component or setting within the overall system.

--Rik
That does make more sense, and I do like that quote, it makes it quite easy to remember. :)

My problem in general definitely is understanding how and why optics work, but I'm starting to come to terms with the fact that it's not really critical for me to know why or how; maybe I should be more concerned with experimenting and learning how to manage the different components of a paired lens setup to get the best results. Knowing the "why" and "how" would make it markedly easier, but maybe my mind just needs a hands-on approach.

I'll just have to wait and see what the next few weeks are like, as life is a bit hectic at the moment. I had hoped to start stacking and editing photos before the year's end, but hopefully it won't be long before I can manage something.
Chris S. wrote:
Wed Nov 03, 2021 9:55 pm
Agree with Rik, but can't resist a bit of constructive pedantry.

[pedantry on]

"Nominal" comes from the Latin "nominis"--"of name." Knowing this etymology serves us well in optics and other sciences, because "nominal" is so often some form of "as named" or "as superficially labeled."

We sometimes say things like "to achieve nominal magnification with an infinity-corrected objective, use it on a converging lens of the same focal length as the manufacturer intended; if you use a tube lens of a different focal length, you will get a different effective magnification." In this case, "nominal" is "as the objective is labeled, and "effective" is "as set up."

Economics makes substantial use of "nominal" vs. "real." In a common example, "nominal profit" is how much more you sell a stock for than what you paid for it, often after holding it for many years. But during the years you held this stock, inflation was likely at work. So "real profit"--nominal profit minus inflation's effective reduction of that profit--is a more correct measure of actual stock gains.

And it appears that the "as named" or "as labeled" sense of the word "nominal" is highly conserved across many sciences.

[/pedantry off]

--Chris S.
That's very true. As it happens, I do remember being rather confused when trying to find a suitable diameter of steel pipe when constructing my copy stand. The fact that pipe is measured by "nominal pipe size" had me confused, and it still does, compounded by the fact that there are also the national pipe taper thread measurements to think about. Test fitting at the local hardware store solved the physical issue, but the whole measurement systems still throw me for a loop; it's too bad such things can't be standardized/simplified even more than they already are.

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Re: Calculating magnification of objective on telephoto lens

Post by Chris S. »

Barrelcactusaddict wrote:
Wed Nov 03, 2021 10:14 pm
Knowing the "why" and "how" would make it markedly easier, but maybe my mind just needs a hands-on approach.
I think that's a learning style common to many of us. We can study theory for a while, and learn much from it. But at some point, our brain gets full, and we benefit more from switching to hands-on work. After working hands-on for a while, going back to the theory and reading becomes effective again--often more effective than before. This works until our brain is full again, at which point it's time for more hands-one work.

I suspect that alternating between reading and hands-on work is a commonly effective learning strategy.

--Chris S.

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Re: Calculating magnification of objective on telephoto lens

Post by rjlittlefield »

Chris S. wrote:
Wed Nov 03, 2021 10:32 pm
I suspect that alternating between reading and hands-on work is a commonly effective learning strategy.
It is the only one that I have ever found to work very well. Reading and thinking are faster than doing, but they're quite vulnerable to cascades of misinterpretations, excessive approximations, and outright errors. Every once in while I need to see if what I think will happen is what actually happens, to catch my MEAAOE's. (Did I just hear a cat in here?)

--Rik

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Re: Calculating magnification of objective on telephoto lens

Post by Chris S. »

rjlittlefield wrote:
Wed Nov 03, 2021 11:18 pm
Every once in while I need to see if what I think will happen is what actually happens, to catch my MEAAOE's.
Perhaps I'm missing something obvious, but I don't know what "MEAAOE" means, and searching with Google several times has not enlightened me. Can you do so?

--Chris S.

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Re: Calculating magnification of objective on telephoto lens

Post by rjlittlefield »

Apologies -- I have violated the First Principle Of Initialisms -- "make it explicit on first use". :oops:

Misinterpretations, Excessive Approximations, And Outright Errors -- MEAAOE's.

--Rik

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