Ultracheap wide angle lens for UV?

[Alex H]

Depth of field links:

 

http://www.cambridgeincolour.com/tutorials/depth-of-field.htm

 

http://www.normankoren.com/Tutorials/MTF6.html

 

Please note his quotation: "While the phrase depth of focus was historically used, and is sometimes still used, to mean depth of field (DOF), in modern times it is more often reserved for the image-side depth."

My use of the therm "depth of focus" has the same meaning as modern use of "depth of field".

 

The simplest DOF calculations use only four variables: focal length, aperture ratio, object distance and maximum alowable circle of confusion. The latter depends from the imaging media used - size of photosites or film grain define the size of the circle of confusion. When the same sensor/film is used, lenses of same focal length, focused at the same distance and stopped down to the same aperture setting will produce the same DOF. Lens optical formula can affect circle of confusion through diffraction or spherical aberration.

[igoriginal]

Thanks for those links!

 

So, perhaps it is certain exploitative differences in the 'circle of confusion', which allows me to attain "everything-in-focus" (3 meters to infinity) on my 25mm F/6 UV lens. No? Even as this is impossible for me to do with any other 25mm prime which I currently own. Hmmmm.

[igoriginal]

I can tell you for certain that there is notable softness around the edges of my image frames (spherical abberation?), thus this could very well be the tell-tale signs of a maximally-pushed 'circle of confusion' on the lens design.

[colinbm]

Hi Iggy

Congratulations on this lens development.

It is a great idea & a very useful one too.

I would buy one from you, but at the moment the Aust dollar is very weak & I have a few projects I am saving for, so I'll have to wait till the new year.

Good luck

Col

[Alex H]

Let me ask you few more questions:

 

1) How did you measure the aperture value of your lens.

 

I would be happy to do so, once I have access to doing more tests. (I am not in a position to do it at this moment).

 

2) What about those test pictures you posted in your eBay add - surely you must have saved original RAW files from the camera?

 

I can tell you for certain that there is notable softness around the edges of my image frames (spherical abberation?), thus this could very well be the tell-tale signs of a maximally-pushed 'circle of confusion' on the lens design.

 

3) Do I understand this correctly: are you now saying that this lens does not produce usable image circle to cover M43 sensor? By "usable" I mean "with sufficient sharpness and resolution".

[igoriginal]

1) How did you measure the aperture value of your lens.

 

I went about determining this through multiple procedures, given the fact that since I do not possess advanced spectral testing equipment (which also involves other variables, such as refractive indices, light-transmission efficiency, etc.), then I have had to resort to the "poor man's" estimation of values.

 

My first step was to use the basic F-stop calculating principle of dividing the focal length (in millimeters) of the lens by the entrance pupil diameter (also measured in millimeters), using a digital caliper that I own.

 

Thus, 25mm / 4.3mm (estimated entrance pupil diameter) = F/5.81

 

But I understand that this is much too basic of a procedure to stop there (no pun intended, hehe), so I also pressed on to use other forms of testing.

 

My next procedure involved using other 25mm prime lenses that I own (with an already known F-stop rating), and then use my digital camera to meter against a steady light-source between my 25mm F/6 lens and the other 25mm primes. Given that some of these other 25mm primes that I own are preset-aperture lenses, I could estimate where F/6 would be, by first stopping at the F/5.6 marker, and then ever-so-slightly nudging just a bit beyond that point. Almost imperceptibly (although I could certainly leave it on F/5.6, given that my estimated F-stop on my 25mm F/6 is technically F/5.81, so close enough).

 

These metering comparisons were undertaken in a darkened room (at night), with curtains additionally drawn, and then using a steady artificial light source ... since outdoor metering comparisons can become significantly unreliable due to variables such as sun moving in and out of clouds, gradual changes in light-source angle (as the sun continues to move across the sky), and other potential factors.

 

The goal was to have all of my compared 25mm prime lenses set to the same (or close to) F-stop as my 25mm F/6, then check the metering values within my digital camera to determine if my prior F-stop calculation (above) was reliably derived. As it turns out, it was.

 

Granted, it should be noted that my metering tests were done strictly in VISIBLE wavelengths, since the other 25mm primes that I used for the comparisons are not UV-capable lenses (otherwise, I wouldn't be so determined to develop a 25mm UV-capable lens to begin if, if other 25mm UV-capable primes were plentiful).

 

My conclusion to "round off" my 25mm lens to F/6 was to simply be a bit more conservative with my estimates, just to not risk OVER-stating the "speed" of the lens. (And, the fact that listing it as a "25mm F/5.81" lens is just not very elegant, is it? :D )

 

2) What about those test pictures you posted in your eBay add - surely you must have saved original RAW files from the camera?

 

If I already had RAW files to use for your suggested 100%-crop publishings, I would have done it by now.

 

Alas, many of my earliest images were JPEGS (to save on hard-drive space), were primary hand-hand (and thus driving ISO up to less-than-ideal levels for a fair analysis of 100%-cropped sharpness test), and/or were done during times of the day when I didn't have an ideal landscape that was well-lit in both the infinity-distance region and the foreground. (Look at the images in my ad. There are many areas in shadow. For the record, I have crazy work-hours, and the only time I am usually free to do tests is either in the very early morning before work, or right when I come home at night. Rarely am I free to take test-shots mid-day, except on weekends).

 

Might I supply even BETTER images for my ongoing ad listing, in the near future? Sure. I plan on it, in fact. However, I did as best I could, given my immediate circumstances. And even if it turns out that my claims are not up to snuff to any of my potential buyers, they are free to return my lens without any drama, fuss, or hostility (as mentioned in my ad, too).

 

However, I did already have a few friends do some "beta-testing" for me, and were quite happy with the results. They even kept the lens. Clearly, then, I am not "blowing smoke" (or putting up mirrors), so to speak.

 

This should be a fair-enough indication that have no reason to deceive anyone, as well as the fact that my 100% Ebay rating should speak for itself. Does this mean that I am pretending to "know everything?" No. But this is ALSO reflected in my ad literature.

 

The point of the matter is that my endeavor is honest. Now ... if you feel that it is misguided, then I suppose that time will tell (and I would be the first to hold myself accountable, and make amends, as well as learning from the experience and improving on my endeavor in the process).

[igoriginal]

Do I understand this correctly: are you now saying that this lens does not produce usable image circle to cover M43 sensor? By "usable" I mean "with sufficient sharpness and resolution".

 

Now you are just entering the region of arguing semantics. ("Usable", "sufficient", etc.)

 

There are different levels and interpretations of what is "usable" and "sufficient." You being an optics expert, should know that more than anyone. Chiefly, that one person's "usable" may be another person's "unusable", and vice-versa.

 

(Ex: While some lenses are not "perfect", unlike the more expensive, computer-drafted and precision-cut glass of today, they exhibit their own unique characteristics. Sometimes those "imperfections" add to the lens's own "character." For instance, it is my understanding that some of the most "desirable bokeh" produced by certain lenses is due to the fact that the optical formula is LESS than "perfect." This is just one example that "perfect" is not always everything. Not to mention, photography "as an art" is subjective, in itself.)

 

Nonetheless, take the time to read my entire ad (and taking all of the images in full context with the ad literature), and I think it can be reasonably inferred what I have meant by "usable." (Factoring in the performance limitations of the lens, versus what I believe to be a fair price offering for what one can derive from the lens, I feel that the level of "usability" is already reflected).

 

Let me say this again: This lens has remarkable UV transmission, considering its very low price availability (something quite rare, for lenses of this price-point and focal length). It renders good enough images, when one's expectations are realistic and well-managed (although the center of the image frame is shockingly sharp, considering the primitive design). And, most importantly, it finally offers any "newbies" to the UV field (and even "seasoned pros" alike) with a cheap, simple, compact, and instant way to shoot UV-landscapes in a pinch (just pull the camera out of the bag, and shoot), and have fun doing it (without taking oneself too seriously, as opposed to more intensive work). This would also make this an excellent casual travel set-up (when one is not currently lugging around a full compliment of equipment, but unexpectedly stumbles upon a potentially interesting scene to photograph in UV). If remaining within the constraints of what I just mentioned, please tell me where the problem is?

 

Either this is good enough for you, or it is not. But since it is not you who is buying the lens (I have already had a few buyers, and they are awaiting the shipment of my next batch of assembled copies), then I should be using my time wisely to now prepare the materials for shipment in a timely manner ... rather than get drawn out into a dialogue that is clearly now bordering on frivolous :D

 

(To be fair-minded, I really respect you, Alex. And I stand to learn much from you, truly. Your own published works have inspired me to even be in this field of work, to begin with. Thus ... I wish to have kind relations with you, rather than under the cloud of a more "cynical" dialogue. I say this with sincerity.)

[igoriginal]

Hi Iggy

Congratulations on this lens development.

It is a great idea & a very useful one too.

I would buy one from you, but at the moment the Aust dollar is very weak & I have a few projects I am saving for, so I'll have to wait till the new year.

Good luck

Col

 

Much appreciated, Col! Thanks so much! It's been a while since we've chatted! Would be nice to catch up, sometime! :D

[Alex H]

Igor, I just want to understand for myself what your lens is capable of exactly. Unfortunately, your eBay ed does not porovide me with the answer that I seek. On the other hand, one full-resolution example picture would show me what I want to see, and would also avoid all the semantics issues. I am really surprised by your reaction. So, I will let this thread take its course without me prticipating in it. Good luck with your project.

[igoriginal]

I will provide the 100% out-of-camera crop examples, per your request and as promised, as soon as I get the chance (this weekend being what is feasible for me). It's just that there is no point to keep pressing the same issue, until I can do that. Thank you for keeping me on my toes, Alex. :-)

[Andrea B.]

Well, as they say, a picture can be worth a thousand words. :D

Igor, let's please start a new thread when you return with some fotos.

[igoriginal]

Well, as they say, a picture can be worth a thousand words. :D

Igor, let's please start a new thread when you return with some fotos.

 

Yes, Andrea, you are so right about that. :)

 

And you are also in vibe with my own recent notions ... that I should soon make a more "formal" post on my findings within the aforementioned areas (when I have more useful, and also more detailed data, as per Alex's suggestions).

 

Speaking of which, I have some exciting new "revelations", along my ongoing exploration and testing within the realms of what I have been recently preoccupied with. In fact, this one blew my mind (and I will also include this in my upcoming post, as well). But, for now, I just felt compelled to share it anyway (if only through a more preliminary tone):

 

As it turns out, among the "loose" lens elements ("odds and ends") that I have been playing around with - as obtained from the local parts supplier I am in contact with - and also making my UV-landscape pancake lenses with ..... some of them come fully "encapsulated" (already in a complete housing, as if ready to have been used in the apparatus they were designed for). And the complete lens-housing has them marked "F/5.5", thus it looks as if my own "estimations" of determining the aperture came very close. (F/5.5, versus my own estimation of F/5.8).

 

Additionally, these fully-encapsulated and air-spaced glass "triplets" were originally manufactured by a now-defunct arm of the "Eastman Kodak Co.", as stated on the storage packets they come individually sealed in. I was told (by my local supplier) that they were specifically made for using in cheap "point & shoot" (mostly "disposable") film cameras designed to be easy to use (only a shutter button, and no other function). No wonder these lenses have a "fixed focus" (focus-free) optical formula (just aim, frame, and shoot).

 

Amazing, that something manufactured in the 90's (when these were supposedly made) can transmit so much UV! Estimated to be down to about 330-340nm, according to my "Sparticle" narrow-band filter-array test (as originally proposed and popularized by Steve Smeed).

 

(What the heck is a "sparticle", anyway?! I wanted to know. Is it something like - "This is madness! Madness?! No! THIS - IS - SPARTICLE!!!" Sorry, couldn't resist. Teehee. :D :lol: )

 

But then, since these simple and fully-encapsulated lenses were made for very cheap and/or disposable cameras, then I suppose that the optical design (and coating use) was kept bare-bones. What an anomaly, indeed!

 

Then again, I suppose it should make sense, since the Eastman Kodak company DID once supply a lot of parts to many other photographic / imaging companies. (In fact, to date, isn't the former Eastman Kodak company the largest photographic corporation that has ever existed?)

 

Hence, it's quite possible that any number of cheap and/or disposable cameras implemented such simple lens designs. Of course, many of those bare-bones film cameras used plastic lenses, but the lenses that I have been using in particular (and also implemented and re-calibrated into a fully-assembled custom design for digital-camera UV-photographic use, per my first attempt at Ebay sales) are all-glass elements. So, I suppose these are "one tier" of quality above the more common all-plastic versions.

 

Not to mention, it's not always so obvious which one of those cheap point & shoots / disposables use glass elements, and which ones use plastic elements, until I personally would have each camera in my possession. (Data or specs on such stuff is now defunct, and not so easy to come by, as many of us already know all too well).

 

It has also crossed my mind that what I have in my possession were specifically made for "amphibious fixed-focus" film cameras (underwater film photography on-the-cheap), being fully encapsulated the way they are. In fact, I strongly suspect that (but I could still be very wrong).

 

Might I make this statement (for the sake of being honest and self-accountable) that my statements are admittedly still highly conjectural, of course. At least so early in my ongoing exploration within this area of current work.

 

Other points to consider: The Eastman Kodak company (at one time) was to film cameras what the Sony corporation today is to digital camera companies. Meaning, Kodak was once the king of all imaging-parts suppliers to other film-camera companies, just as Sony is now the dominant supplier of sensors for many other digital-cam companies. Is this not so? Very interesting stuff.

 

I suppose if I ever run out of the parts being sold to me through a local supplier acquaintance of mine for my ongoing projects in this area of work (although I hope that I do not run out of these parts) ... then, my next thing to do is to start buying up a bunch of random and cheap "fixed-focus" bare-bones and/or disposable film cameras, take them apart, and scavenge their lens-housings for UV testing. But not until I first run out of my sure-thing supplier, first. Because I imagine that there will also be a lot of wasted money just taking chances on random point & shoot / disposable film cameras, hoping that they yield a similar optical design (or even the exact optical design I now have found). Clearly, there is no guarantee in such an affair, because I would have to go through thousands upon thousands of many brands and models. It would probably spark off as big of a UV-lens "needle-in-a-haystack" search, as Dr. Klaus Schmitt (and Steve Smeed?) once sparked off for the "accidentals" in the focusible-lens-for-interchangeable-cameras realm.

 

But, hey, there is always room for other previously-unexplored frontiers to push our UV-pioneering wagons through, right? :D

 

 

In a final though (for now):

 

A friend of mine asked me this afternoon (in light of my shocking revelations in the areas I have been experimenting in): "Isn't it usually the coatings and glues that block UV? Not the glass?

 

"True", was my response. However, you'd think that even on the cheapest of disposable film cameras, the strong UV-blocking coatings would come standard by the mid-90's.

 

(From what I understand, the most basic of UV-blocking coatings are among the cheapest of materials to source along the entire world-flow of a lens's entire production line. Heck, even back in the 1940's and 50's, the Russians were applying very basic and yet fairly effective UV-blocking coatings on some of the cheapest of lenses at a time that the country's financial standings were stretched to the limit, fresh on the heels of the ending of WWII).

 

Thus, to find this anomaly among fairly "recent" lenses, is really amusing (and unexpected), to say the least.

 

To be sure, I have some cheap Russian (heck, even Polish) glass from the 40's and 50's, and some of those lenses (but not all of them) block just about all of usable UV. Even as such lenses are quite simple in optical formula (Tessar knock-offs, among others), they are just about useless in UV work. And yet, somehow, the Eastman Kodak company ends up churning out "accidental" UV-transmitting lenses made in the 90's, which apparently lacked UV-blocking coatings??? That's just fascinating stuff.

 

My only explanation for this paradox, is that given that the EK Co. was on the brink of complete bankruptcy and corporate dissolution of its chief operations, it must have "cut a lot of corners" in just about every area during its final years of mass-production projects. (Again, I am being mostly conjectural here, and not making any informed claims).

 

But, that may aptly explain why even with some optical parts that were manufactured as recently as the 90's, I just happened to run into surprisingly deeply-transmitting UV-capable lenses among disposable film cameras, of all places!

 

I guess it remains true that the UV-world is full of all kinds of surprises and epiphanies, along the way of hunting and exploring less-traveled roads.

 

To be continued.

 

(Note to Andrea: Maybe we'll end up adding a whole new section to our "UV-lens Sticky" - this one titled as: "UV-capable lenses scavenged and re-purposed from fixed-focus film cameras?" Hmmmm.)

[igoriginal]

Here are some (hopefully) better and more useful images taken with my 25mm F/6 lens, today, although our area was under a gray overcast all day long. I will be hoping for some sunlight, tomorrow, and perhaps then try again under more favorable conditions.

 

Thus, although these two comparison JPEG images (VIS and UV) were straight out-of-camera (per Alex's request) with absolutely no sharpness-increase or any other enhancements done (again, per Alex's request), I did "raise the shadows" a bit, before posting them (otherwise, the resulting image would once again not be as useful, given the very dreary and gray day). Note that raising shadows in both images produced some additional noise. (The Panasonic G2 is a fairly noisy device, to begin with, and its dynamic range does leave something to be desired).

 

The files were uploaded at full size (4000 x 3000), however I re-saved the JPEG image quality to "medium" instead of "high quality" before uploading these ... or Andrea would probably kill me.

 

Also note: The "softness" of the tree leaves in the UV image at the left of the frame is somewhat exaggerated, because the exposure was 5 seconds long and there was quite a breeze. For a better indication of sharpness, examine branches and distant tree bark (not withstanding the "haziness" created by a UV landscape image). Still, it remains obvious that at a native aperture of F/6 (or rather, F/5.5), the edges that this lens produces are significantly soft. But I personally do not mind this, if only as a "fun" aspect of the lens. (Though perhaps my next project should involve stopping down the lens with a custom-made iris, to sharpen up the entire frame?)

 

 

VISIBLE image. Camera: Panasonic G2 (full-spectrum-modified). Settings: Filter(s) 2.5mm-thick BG39; ISO 100; Shutter 1/80 sec.

 

 

UV-A image. Camera: Panasonic G2 (full-spectrum-modified). Settings: Filter(s) 1.5mm-thick ZWB1 + 2.5mm-thick BG39; ISO 200; Shutter 5 sec.

 

 

In the final image, below (out of curiosity's sake), I decided to "macro-push" my 25mm F/6 lens, by adding some macro-tubes to push the in-focus area much closer to my subject. The object in the photo is the top of a vintage Soligor-branded leather lens case, designed for small primes (2.8" diameter by 3.3" height). It appears (although I could be mistaken), that this lens sharpens up a bit, when pushed to do some macro work (since its "effective aperture" becomes smaller when the lens is pulled further from the sensor plane).

 

Thus, it seems to me, that I should next try some UV-floral tests with this lens (even though this was not part of my original project's intentions).

 

(This also makes me wonder that even when using this lens for my original intentions - doing UV landscapes - perhaps I should machine a smaller aperture, and attach it to the back of the lens in order to create a smaller pupil, hence very likely also sharpening up the lens even for landscape use. Now THAT is an idea that suddenly comes to mind. :D)

 

Also note that this photo is not "properly" color-balanced. (It was shot in "full-spectrum", indoors, with no filter).

 

FULL-SPECTRUM image. Camera: Panasonic G2 (full-spectrum-modified). Settings: ISO 200; Shutter 1/25 sec.

[JCDowdy]

I really got to hand it to ya Iggy, you are never at a loss for words!

 

Do you know if your repurposed lenses were from a 35mm or 110 disposable? A lens transplant from a 110 disposable onto a µ4/3 pan-focus mount might be fun.

[igoriginal]

Do you know if your repurposed lenses were from a 35mm or 110 disposable? A lens transplant from a 110 disposable onto a µ4/3 pan-focus mount might be fun.

 

I'm not certain, since I have only the lens-housing units in themselves with no reference as to which cameras they were manufactured for use in. I have learned, however, that this specific lens will cover a frame up to 30mm x 17mm, with no image edge-clipping. Thus, just slightly larger of an image circle over today's modern APS-C digital crop sensors. Definitely larger than 110, and even large enough to cover APS-C format with a few millimeters to spare. Yet, not large enough to cover Full-Frame.

 

But ... more to come (and I am sure I will also discover other vital things, along the way).

[igoriginal]

I really got to hand it to ya Iggy, you are never at a loss for words!

 

Yeah, I admit, I'm a "windbag."

 

But, I also have an over-active mind that just never seems to shut down or leave me at peace. Even while I sleep. Not sure if that's good or bad. Maybe a little bit of both? :D

 

( I find my brain trying to solve complex problems, even in my sleep.)

[igoriginal]

I should also mention, John, that I have other lens-housing units in my possession that I am in the process of testing. Some are even wider-angle than the 25mm F/6 (F/5.5) which I have been working with. For instance, I also have 24mm and 23mm focal-length lenses with F/7 aperture, and a 22mm lens with an F/8 aperture. I also have one rated at 27mm F/9 which will apparently cover a Full-Frame image circle. All of the above were manufactured by Eastman Kodak, and they all seem to transmit UV quite deeply, from some preliminary testing, aside from the 27mm F/9 which I have not physically tested for its UV transmission yet (though it looks promising, given its similar optical construction).

 

But let me not get ahead of myself, just yet. :D I want to first finish a fully-detailed report (and an associated UVP future posting) of my testing with this 25mm lens.

 

(Part of my next goal is to now implement a permanent focusing helicoid into the 25mm F/6, so that then it can become a fully-functional lens. As it stands, when using the helicoid of choice, I can focus it all the way from infinity to just close to around 1:1 macro, where the lens front is just an inch or so from the subject! Perhaps also add an iris, so it can sharpen up nicely. Of course, with this "updated" design, if I ever plan to sell it I'd have a higher asking price given the extra cost of materials used to make it).

[Andrea B.]

GET BUSY, IGOR !!! We would be happy to host that report here if you would like to do so. :D

 

A simple outline or bullet list of the facts with some supporting fotos is all that is required initially. This will keep you from being too wordy.