Calculating magnification of objective on telephoto lens

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Barrelcactusaddict
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Re: Calculating magnification of objective on telephoto lens

Post by Barrelcactusaddict »

JKT wrote:
Fri Oct 29, 2021 11:36 am
You don't want to use the Laowa in immersion even if you could. The optical formula is not designed for that. It is designed for air. You may get away with the amount of effective immersion in the amber, but you definitely don't want to multiply that amount.
I'm sorry, I'm not sure what you mean by "effective immersion", and what it means to "multiply that amount". But yes, I wouldn't want to risk damaging a (relatively) expensive lens, so I wouldn't immerse it unless I had a fool-proof, tried method to protect the end of the lens.

Lou Jost
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Re: Calculating magnification of objective on telephoto lens

Post by Lou Jost »

JKT:
You don't want to use the Laowa in immersion even if you could. The optical formula is not designed for that. It is designed for air.


You:
I wouldn't immerse it unless I had a fool-proof, tried method to protect the end of the lens.
A big part of your confusion is due to not reading carefully what people are telling you. JKT has told you that the Laowa lens has an optical formula that is not designed for immersion. You would make things worse, not better, by filling the space between the amber and the lens with oil. DON"T DO THAT.

Barrelcactusaddict
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Re: Calculating magnification of objective on telephoto lens

Post by Barrelcactusaddict »

Lou Jost wrote:
Fri Oct 29, 2021 8:11 pm
JKT:
You don't want to use the Laowa in immersion even if you could. The optical formula is not designed for that. It is designed for air.


You:
I wouldn't immerse it unless I had a fool-proof, tried method to protect the end of the lens.
A big part of your confusion is due to not reading carefully what people are telling you. JKT has told you that the Laowa lens has an optical formula that is not designed for immersion. You would make things worse, not better, by filling the space between the amber and the lens with oil. DON"T DO THAT.
I see nothing on Laowa's site's description that says the lens cannot be used in this manner; in fact, I sent them a query about this earlier today, as I mentioned in one of my previous posts today. I'm not sure if JKT owns this lens, or is a distributor for Venus Optics, so I cannot authenticate his claims; like I said, I studied the lens' description on the company site, and I've submitted a query to them for confirmation and advice.

I may not have clearly stated it, but I did not intend to immerse the lens directly in oil, and there would be a space of glass, maybe with some air as well, between the lens and the oil: I would in effect be photographing a solid piece of amber in the shape of a petri dish, albeit at a very close distance. The refractive index of cedar oil and amber are extremely similar (1.516 vs. 1.539-1.545), far better than air (1.000293); an acquaintance of mine uses it in all his shoots, and not with a dedicated oil-immersion lens, at that (somehow he protects the lens during shooting, but I have not asked him any specifics); it is a very common medium used in amber research.

I read all posts very carefully, and do my research.

Lou Jost
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Re: Calculating magnification of objective on telephoto lens

Post by Lou Jost »

I think you are missing an important optical principle. Lens design has to take into account the medium it is shooting through. The Laowa lens (which I own) is designed to shoot through air, as JKT told you. If you remember, I wrote above that the Laowa was a good choice for you because it can be stopped down. This reduces the effect of the medium (amber and/or oil) on the image quality. That is the most obvious way to minimize the bad effects of shooting through a medium.

A very thin layer of oil can help eliminate surface irregularities. But every mm of oil depth makes the image worse. So again, JKT is right, you would not want to use a thick layer of oil. His reason for this has nothing to do with protecting the lens.

There are other ways to shoot through media. My favorite is to use a reversed Micro-four-thirds lens on a telephoto lens. Micro Four thirds cameras have sensors with a thick glass filter on them. Therefore a Micro four thirds lens is designed to take into account the thick glass that the image has to go through before being captured by the sensor. When it is reversed, these same design considerations mean it is correctd to shoot through a thick layer of glass or similar material. This works very well.

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Re: Calculating magnification of objective on telephoto lens

Post by rjlittlefield »

Barrelcactusaddict wrote:
Fri Oct 29, 2021 8:30 pm
Lou Jost wrote:
Fri Oct 29, 2021 8:11 pm
A big part of your confusion is due to not reading carefully what people are telling you.
...
I read all posts very carefully, and do my research.
Barrelcactusaddict, I expect that Lou is inferring process based on results. Without watching your eyes, it is impossible to tell the difference between not reading carefully, and reading carefully but getting a scrambled interpretation. I apologize for being blunt, but it seems clear that you have scrambled several interpretations very badly. As one example, it seems from reviewing previous posts that at one point you were convinced that combining a 5X objective and a 200 mm telephoto would give 20X magnification, the rationale being that 200 mm is a "4X" telephoto, and 5*4 = 20. To those of us who know the technology well, this is obviously not correct. But when Scarodactyl tried to explain to you how things actually work (HERE), you actively argued with him, referencing another person (holdinghistory) whose techniques you did not understand correctly either. I think you hit the nail on the head a few posts ago, when you wrote that "I thought I knew what I was doing, but it seems it was all wrong." Yes, it was all wrong, and since I don't see that much has changed except for that realization, I am not optimistic about the future.

Stepping back and wondering what is the best advice I can give, I think the best way forward is for you to continue realizing that you don't understand the optics and it is at best very risky to act as if you do. In particular, buying individual pieces of equipment in hopes of fitting them together later is likely to be a waste of time. Instead, you should carefully specify what you want to accomplish, plan the whole setup to achieve that, and then ask "Will this work?". That approach is not guaranteed either, but it's safer than what you have been doing.

--Rik

Lou Jost
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Re: Calculating magnification of objective on telephoto lens

Post by Lou Jost »

Another suggestion would be to just do exactly what people here suggested and hope that you will learn the details over time. Many of us started that way. The Laowa lens is a very easy option.

You will of course have to learn to stack images though.

Barrelcactusaddict
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Re: Calculating magnification of objective on telephoto lens

Post by Barrelcactusaddict »

I don't understand, all I know is that I'm confused by everyone's information and explanations, right from the beginning. I can't wrap my head around what everyone is saying. Don't get upset with me because I'm an idiot and can't comprehend even the basics of "optics". I'm using every ounce of my energy to comprehend what others are talking about here, and it simply doesn't work. If my posts contradict themselves, it only proves my confusion. I'm doing the best I can to make sense of what others are telling me, and I'm sick of getting shot down and getting nowhere.

I have enough stress in my life (I just found out I'm developing serious health issues), and now it's found its way into my hobbies. In the last few years, due to unforeseen circumstances, I now have a very low income, and every penny counts, and it takes forever to finance anything for my hobbies.

Why do I even bother? Maybe I should just forget about photography and stick to what I know: lapidary and paleobiology. This is only stressing me out more; why should I even bother to purchase the Laowa if I'm not mentally capable of understanding how lenses work. It's like putting a computer in the hands of an infant, it's pointless. I'm so sick of this, I quit. :cry:

Lou Jost
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Re: Calculating magnification of objective on telephoto lens

Post by Lou Jost »

It's not that bad, even a child uses a computer nowadays, even though they know nothing about its innards. And I think that also applies to nearly every one else who uses a computer. How many people know enough quantum mechanics to understand how transistors work? You don't need to know that in order to use a computer. It is another matter entirely if you are trying to improve or design a computer... or if you want to argue with someone who does.

You don't need to know much to use the Laowa....and you will learn if you take your time.

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Re: Calculating magnification of objective on telephoto lens

Post by rjlittlefield »

Speaking only for myself, I'm not upset at all. I'm just scratching my head trying to figure out how to help. So far none of my usual approaches have worked.

So then, I have one more idea. Instead of trying to do the photography yourself, consider making friends with somebody local to you who already has some or all of the required equipment and skills. I did a Google search on Rexburg Idaho photography club , which found https://www.facebook.com/groups/757016101057280/ , Rexburg Photography Group, public, 514 members. Most of those people will be into scenics, people, pets, and cars, but the number is big enough to suggest that somebody in there might be interested in photographing small exotic stuff like polished amber. It's worth considering, anyway.

--Rik

Barrelcactusaddict
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Re: Calculating magnification of objective on telephoto lens

Post by Barrelcactusaddict »

:(

Thank you. I don't know what to think, I'm just so exhausted.

Thank you for reassuring that it could be possible for me to learn how to use the Laowa; I'm going to have to take some time before I pursue anything further with my setup. I'll just try to sell my lens and adapters for now.

Thank you for suggesting a photography Group, I had not considered that. I've now placed a request to join that Group, but from their questionnaire, I get the vibe that they are looking for competent, experienced photographers. Maybe they'll let me join, I'm not sure.

I wish I was capable of understanding all this, it would make my life so much easier. I'm just going to take some time to work on my material, maybe study some research publications, and put aside any plans for the setup for perhaps a couple weeks or more.

Thank you.

-Kaegen

Chris S.
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Re: Calculating magnification of objective on telephoto lens

Post by Chris S. »

Kaegen,

For whatever it’s worth, I suspect that only a small percentage of photographers would understand what's been discussed in this thread. At this forum, we get into the weeds; but in the outside world, plenty of people don’t and still take great pictures. So if this level of optics discussion isn't your thing, no big deal--go forth and take pictures. If something doesn't work, ask us geeks and we'll try to help.

I doubt that Shakespeare understood the physics of ink, but he could sure write.

This said, will you let me have one more try at explaining ink theory? Here goes.

A problem in the way you were trying to calculate magnification is that you were mixing two metaphors of magnification that don’t play well together. Perhaps this is because earlier mentors told you to do so. In any case, it led you astray.

One understanding of magnification is how typical users of telephoto lenses, such as bird photographers, look at it. If you put a 50mm “normal” lens on your camera and take a picture of a bird, the bird will usually be too small in your photo, because most birds are small and pretty far away. So the bird photographer switches out his 50mm lens for, say, a 300mm telephoto lens. With the 300mm, the bird looks larger in photos. Indeed, the bird will be six times larger with the 300mm lens than with the 50mm lens. This is where the “divide focal length by 50 to get magnification” concept comes from. And for things like bird photography, it’s a decent rule of thumb.

By the way, 50mm is not entirely arbitrary. A 50mm lens was a so-called “normal lens” because most people used cameras for which a 50mm lens captured about what human eyes see. So once upon a time, if you bought a 35mm film camera, if often came with a “standard” 50mm lens. If you then bought a telephoto lens for bird photography, it was natural to compare it with the standard lens considered "normal" for your camera.

Our modern digital cameras have inherited many standards from the film days.

But this concept of magnification is emphatically inappropriate for understanding the magnification you’ll get with a microscope objective. For microscope objectives, cast aside the “divide by 50” concept and never visit it again.

You’ve read that microscope objectives can be divided into two types: finite-corrected and infinity-corrected. The difference between these two types is that finite objectives can do their job alone, without any additional optics. Infinite objectives, on the other hand, can only do their job with another lens behind them. This is super important, so I’ll say it again: An infinite objective must be paired with another lens, and does nothing useful without a second lens behind it.

That behind-the-objective lens, by the way, is supposed to be focused at infinity. This is a designed-in requirement of infinity-corrected objectives. If you notice the phrase “infinity-corrected objective” sounds a lot like "this second lens should be focused at infinity," yes, there is a correlation.

Manufacturers of microscopes have different words for this second lens. Most call it a “tube lens”; at least one calls it a “telan lens”; and I seem recall one calling it the "secondary objective"; I often refer to it as a “converging lens.” For simplicity, I’ll continue with “tube lens.”

Manufacturers of microscopes also make different choices for the focal length of the tube lens. Most common is 200mm, but at least one manufacturer uses 180mm. Other focal lengths likely exist. No matter, the actual focal length they choose isn’t very important.

A bit of history: It was right here in our forum community that people developed and popularized the practice of using microscope objectives directly on cameras, without involving an actual microscope. This brought a quantum leap to high-magnification macro photography. At first, we used only finite objectives and mounted them on a bellows or lens tube of empty air, with our cameras behind that air.

Eventually, we realized that we could also work with (the newer) infinity-corrected objectives. But not on a tube of empty air, of course--infinity-corrected objectives don't work that way. We needed to mount infinity-corrected objectives on a lens focused to infinity. Crucially, we also realized that we didn’t need an expensive, official tube lens from a microscope manufacturer. Many regular camera lenses would work very well as tube lenses.

We also learned that infinite microscope objectives aren’t very picky about the focal length of the tube lens—use a tube lens of a different length than the manufacturer intended, and the objective will often work just fine. This said, changing the tube lens’ focal length does alter the image.

The biggest such alteration is magnification on the camera sensor. If you have a 5x objective and want it to deliver 5x on your camera’s sensor, you need a tube lens of the same focal length the manufacturer had in mind when designing the objective.

If your tube lens has half the focal length the manufacturer intended, you’ll get half the magnification. If your tube lens is twice the intended focal length, you’ll get twice the magnification.

Since Mitutoyo (and, I believe, Nikon) designed their objectives for a 200mm tube lens, you get half the rated magnification with a 100mm tube lens. A 150mm tube lens is ¾ as long as 200mm, so gives ¾ of the rated magnification.

But in optics, one rarely gets something for nothing. There are trade-offs to using longer or shorter focal length tube lenses. Knowing when to change the focal length of the tube lens in your use is a matter of understanding those trade-offs. But that’s a subject for another lecture, if this one works for you and you want another.

So, does this make any sense?

If not, how about: "Sod the ink physics, Will—write us a play!"

Cheers,

--Chris S.

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Re: Calculating magnification of objective on telephoto lens

Post by rjlittlefield »

Chris S. wrote:<lots of highly technical stuff>
For whatever it's worth, now my eyes are glazing over too! :lol:

Of course I'll read Chris's discussion very carefully for review and crosschecking, but not until after I've had some more coffee.

--Rik

Chris S.
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Re: Calculating magnification of objective on telephoto lens

Post by Chris S. »

I thought I was writing a story--a story that starts where I think Kaegen is, and goes to where I think he wants to be. There many words, but it's a journey of many footsteps.

I hope that if looked at paragraph by paragraph, it's not all that technical. (And I've made a few edits for clarity.)

--Chris S.

Barrelcactusaddict
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Re: Calculating magnification of objective on telephoto lens

Post by Barrelcactusaddict »

Thank you Chris, I truly appreciate the time, thought, and effort you've put into composing your post. I think I can understand some of what you explained.

When I first started out, I do remember reading articles about using bellows with finite objectives, and how for some, dust accumulation becomes an issue, which is why I thought I should go the route of getting a telephoto lens and infinity-corrected objectives; from there, I've been laboring under a delusion. Indeed, perhaps it would be best for me to instead use a lens that can communicate with the camera itself, as well as exert less weight on my makeshift copy stand.

Hopefully, in coming months I'll find the enthusiasm and faith in my quite-limited ability to finish the setup, maybe with just using the Laowa lens; really my main concern with that is, I do not know if Laowa has Canon-level customer service should, heaven-forbid, the lens need repair of some sort after its 3-year warranty is ended; or, if other companies would be willing/able to repair that lens. That is my greatest concern.

I do have one question to re-visit, though; would the female RMS thread to Canon EF-S mount adapter I purchased from RAF Camera even work at all with an infinity-corrected objective? It sounds like without a tube lens, this would not work. I think the length from mount to focal plane indicator on the camera body is 44mm, if that matters at all. The listing does also mention bellows and extension tube compatibility, but first mentions for use directly with the camera body. Is the adapter worthless for direct-to-camera use? https://rafcamera.com/adapter-rms-canon-eos

I suppose in the end, I really can only appreciate Shakespeare's works. Metaphors aside, The Taming of the Shrew is a classic and is my personal favorite.

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Re: Calculating magnification of objective on telephoto lens

Post by rjlittlefield »

Barrelcactusaddict wrote:
Sun Oct 31, 2021 8:54 pm
Is the adapter worthless for direct-to-camera use? https://rafcamera.com/adapter-rms-canon-eos
This adapter has very few uses direct-to-camera.

I'm sure that I could dream up one or two configurations that would do something useful, but the vast majority of applications would add bellows or extension tubes to move the objective farther from the camera sensor.

The main use is with a finite objective and around 100 mm of additional extension, which will place the objective about 150 mm away from the camera sensor. Except for the physical shape of the adapters, this configuration would be just like the one shown in the first image at viewtopic.php?t=12147 ("FAQ: How can I hook a microscope objective to my camera?").

--Rik

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