Discussion on cameras and lenses for UV

[Alex H]

double-doublet optical formula

 

Could you please elaborate what you mean by that. None of my many books on lens design and history of photographic lenses has this therm.

 

 

The same can be assumed of the opposing bi-convex / bi-concave doublet in the rear of the optical design.

 

What are the justifications for this assumption?

[JCDowdy]

Are you talking about having access to an actual high-resolution spectrometer ...

 

Absolutely, scanning double monochromator, integrating sphere, deuterium/tungsten stabilized source.

 

My laboratory runs mostly Gooch & Housego (formerly Optronic Laboratories) instruments.

 

I am putting the final touches on the assembly, working on the variable beam diameter collimator, but other work ($) keeps delaying completion.

 

- JD

 

[igoriginal]

Could you please elaborate what you mean by that. None of my many books on lens design and history of photographic lenses has this therm.

 

"Double-doublet" is simply another way of me saying a *two doublet* system. Two elements stacked together = doublet. And two doublets = double-doublet.

 

I understand that my way of stating it is not "official" in your book, but it's also not inaccurate. Just another way to word the same exact optical system. Whether "double-doublet", or "two doublet", it's the same exact thing, regardless.

 

The reason I prefer "double-doublet" with my wording, is because of the fact that the aperture is positioned precisely midway between each doublet, which is how the early two-doublet Petzval lenses were arranged. However, since this cine lens is not officially a Petzval lens, and therefore ... instead of calling it a "Petzval doublet", I choose to call it a "double-doublet." So, for me, this makes sense.

 

(If you like "two doublet" better, then that's fine, too.)

 

What are the justifications for this assumption?

 

 

My assumption is based on this reasoning: By finding that the two elements in the doublet up front are just "nested" together, it stands to reason that the rear doublet would likely be held together the same exact way, since it is an identical doublet, but facing in an opposing fashion to the first doublet. Although I cannot confirm the rear doublet's placement to any certainty (since I don't want to force the tiny little screws that hold the rear assembly together), there doesn't seem to be any logical reason why the manufacturer would nest the front doublet elements without adhesives, and not do the same with the rear (to keep production costs down, and make the manufacturing process efficient, as well as keeping all of element pieces interchangeable at will - to either front doublet use or rear doublet use - if necessary for salvaging individual elements from an otherwise defective batch).

 

Thus, I am almost certain that the two elements in the rear doublet are nested in the same fashion as the front doublet. Given the very steep curvature of the convex / concave merger between each element of a doublet pair, it makes sense why "friction fitting" (clamping) would be sufficient to hold them together.

 

Had the elements of each doublet been constructed with a less steep curvature, then perhaps then there would be the added need for adhesive to prevent slippage.

 

Conversely, if my logic / reasoning were reversed, then it would also stand to reason that if the rear doublet were actually glued together, then so would the front doublet be glued together. But, alas, the elements in the front doublet are not glued together.

 

Regardless, I never stated that I know for certain that the rear doublet is also joined together without adhesives. I said that I assume as such, based on logical / rational deduction. But, until I am able to actually disassemble the rear part, then it still remains an assumption, nevertheless.

 

(I also already expressed earlier in this string, that I am not an expert or trained optician.) However, I am in the process of forming hypotheses, based on observations and ongoing testing. I don't plan to make any claims of "absolutes", until complete confirmation. Hopefully, I can more easily disassemble another specimen of this very same lens, and finally figure out if the rear doublet is glued together or not.

 

For the time being, though (as already stated), I have absolutely confirmed that the front doublet is not glued together. Whereas, the status of the rear doublet remains an assumption, at best, until further notice.

 

Thank you for your questions. Good questions.

[igoriginal]

Absolutely, scanning double monochromator, integrating sphere, deuterium/tungsten stabilized source.

 

My laboratory runs mostly Gooch & Housego (formerly Optronic Laboratories) instruments.

 

I am putting the final touches on the assembly, working on the variable beam diameter collimator, but other work ($) keeps delaying completion.

 

 

That is awesome!

 

Well, then ... looks like I might plan a road trip in my foreseeable near future. :D

[JCDowdy]

Well, then ... looks like I might plan a road trip in my foreseeable near future. :D

 

I will let you know when I get all the bugs worked out!

[igoriginal]

I will let you know when I get all the bugs worked out!

 

I am also willing to pay you for your time, if that helps with your work. I believe that a man's (or woman's) work should always be fairly considered for a recompense.

 

Thus, let me know if I can slip you some cash, in exchange for testing my lens.

[Alex H]

"Double-doublet" is simply another way of me saying a *two doublet* system. Two elements stacked together = doublet. And two doublets = double-doublet.

 

I understand that my way of stating it is not "official" in your book, but it's also not inaccurate. Just another way to word the same exact optical system. Whether "double-doublet", or "two doublet", it's the same exact thing, regardless.

 

The reason I prefer "double-doublet" with my wording, is because of the fact that the aperture is positioned precisely midway between each doublet, which is how the early two-doublet Petzval lenses were arranged. However, since this cine lens is not officially a Petzval lens, and therefore ... instead of calling it a "Petzval doublet", I choose to call it a "double-doublet." So, for me, this makes sense.

 

(If you like "two doublet" better, then that's fine, too.)

 

I do not like "two doublet" either. Your definition is very confusing for anybody who studied lens design and history of camera lenses. In your "double-doublet" definition you merge such distinct types of lens design as: Petzval Protrait lens and its derivatives, Steinheil Aplanat / Dalmayer Rectilinear, Tessar, Dialyte / Celor, simple Double Gauss, simple Telephoto desings. All of them have two elements in front of the aperture and two elements in the back of the aperture, but all have very different opticalproperties and applications. For those interested, Kingslake's "A History of the Photographic Lens" is a good and easy read and describes lense designs that I had referred to above.

 

 

 

My assumption is based on this reasoning: By finding that the two elements in the doublet up front are just "nested" together, it stands to reason that the rear doublet would likely be held together the same exact way, since it is an identical doublet, but facing in an opposing fashion to the first doublet. Although I cannot confirm the rear doublet's placement to any certainty (since I don't want to force the tiny little screws that hold the rear assembly together), there doesn't seem to be any logical reason why the manufacturer would nest the front doublet elements without adhesives, and not do the same with the rear (to keep production costs down, and make the manufacturing process efficient, as well as keeping all of element pieces interchangeable at will - to either front doublet use or rear doublet use - if necessary for salvaging individual elements from an otherwise defective batch).

 

Thus, I am almost certain that the two elements in the rear doublet are nested in the same fashion as the front doublet. Given the very steep curvature of the convex / concave merger between each element of a doublet pair, it makes sense why "friction fitting" (clamping) would be sufficient to hold them together.

 

Had the elements of each doublet been constructed with a less steep curvature, then perhaps then there would be the added need for adhesive to prevent slippage.

 

Conversely, if my logic / reasoning were reversed, then it would also stand to reason that if the rear doublet were actually glued together, then so would the front doublet be glued together. But, alas, the elements in the front doublet are not glued together.

 

Regardless, I never stated that I know for certain that the rear doublet is also joined together without adhesives. I said that I assume as such, based on logical / rational deduction. But, until I am able to actually disassemble the rear part, then it still remains an assumption, nevertheless.

 

(I also already expressed earlier in this string, that I am not an expert or trained optician.) However, I am in the process of forming hypotheses, based on observations and ongoing testing. I don't plan to make any claims of "absolutes", until complete confirmation. Hopefully, I can more easily disassemble another specimen of this very same lens, and finally figure out if the rear doublet is glued together or not.

 

For the time being, though (as already stated), I have absolutely confirmed that the front doublet is not glued together. Whereas, the status of the rear doublet remains an assumption, at best, until further notice.

 

Thank you for your questions. Good questions.

 

I am sorry, but this is complete nonsence. Have you seen the optical scheme of Petzval lens with cemented front doublet and airspaced rear doublet? Some Petzval derivatives (Voigtländer's portrait lens) with both front and rear cemented doublets? Tessar with two airspaced elements in front of the aperture and cemented doublet in the back? Dialyte with all four elements separate? There are very good optical reasons for having cemented lens elements, jsut like for having them separated. And these reasons can not be negated by lovering the manufacturing costs or "salvaging individual elements from an otherwise defective batch". Again, I would recommend to start with something like "Field Guide to Lens Design" by Bentley and Olson to anyone interested in better understanding of optical properties of photographic lenses.

[igoriginal]

I do not like "two doublet" either. Your definition is very confusing for anybody who studied lens design and history of camera lenses. In your "double-doublet" definition you merge such distinct types of lens design as: Petzval Protrait lens and its derivatives, Steinheil Aplanat / Dalmayer Rectilinear, Tessar, Dialyte / Celor, simple Double Gauss, simple Telephoto desings. All of them have two elements in front of the aperture and two elements in the back of the aperture, but all have very different opticalproperties and applications. For those interested, Kingslake's "A History of the Photographic Lens" is a good and easy read and describes lense designs that I had referred to above.

 

Thank you for the suggested sources for reading. Clearly, you have much more experience and training with optics than myself. Which is why I am grateful for you pointing me in the right direction.

 

I am sorry, but this is complete nonsence. Have you seen the optical scheme of Petzval lens with cemented front doublet and airspaced rear doublet? Some Petzval derivatives (Voigtländer's portrait lens) with both front and rear cemented doublets? Tessar with two airspaced elements in front of the aperture and cemented doublet in the back? Dialyte with all four elements separate? There are very good optical reasons for having cemented lens elements, jsut like for having them separated. And these reasons can not be negated by lovering the manufacturing costs or "salvaging individual elements from an otherwise defective batch". Again, I would recommend to start with something like "Field Guide to Lens Design" by Bentley and Olson to anyone interested in better understanding of optical properties of photographic lenses.

 

Thank you for pointing that out. Again, as I have already stated, I am not sufficiently trained in optics. Hence, why I am going on assumption, for the time being, until I can test the rear doublet within the Velostigmat with certainty. However, I am always wanting to learn more, as my desire for knowledge is unquenchable, so I am grateful for your reading suggestions.

 

Much thanks!

 

(Note: I am still hoping that I can figure out the status of the rear doublet in my Velostigmat. I've searched the net, tediously, for some direct answers of optical design, but in vain. So, unless someone else knows of the certain design of this lens, then the only way to obtain a confirmed answer is to eventually find a way to disassemble the rear section, and remove the doublet for my own close inspection and confirmation. Here's hoping. :D )

[Andrea B.]

hmmmm.......I have 2 omegabob filters which aren't so great. So I'm not so sure.

No scratch/dig specs and they are very tiny (diameter) filters.

Not clear what he means by FIR either, so not sure of extent of blocking.

My two filters are fairly rough looking.

 

I suppose if all one is going to do is shoot a photo of them, it doesn't matter about the quality so much.

 

I would also like to use some narrow bandpass filters photographically - actually on a lens - so I've been looking on various optics manufacturers sites. A decent sized narrow UV bandpass filter is usually around $300 apiece.

Yikes !!

[Andrea B.]

Alex - It would be so cool if you posted a short list of recommended books on lenses and lens design in our Reference section ? I find myself more and more interested. I have the requisite math/physics background, but don't always want to sit down in the evening with formulas (!!) so the Kingslake history might be more interesting ?

 

Do you like or recommend anything else besides these two ?

"Field Guide to Lens Design" by Bentley and Olson

"A History of the Photographic Lens" by Kingslake

[igoriginal]

hmmmm.......I have 2 omegabob filters which aren't so great. So I'm not so sure.

No scratch/dig specs and they are very tiny (diameter) filters.

My two filters are fairly rough looking.

 

I suppose if all one is going to do is shoot a photo of them, it doesn't matter about the quality so much.

 

I would also like to use some narrow bandpass filters photographically - actually on a lens - so I've been looking on various optics manufacturers sites. A decent sized narrow UV bandpass filter is usually around $300 apiece.

Yikes !!

 

Hmmmm. That's odd. How long ago did you order them? Perhaps it depends on which category of filters you buy, based on his stock?

 

Mine are new "old stock", and still in original packaging. They all include detailed transmission information, and are sealed in desiccant. They all appear unused, untouched, no sign of any use at all. They also are neatly fitted into an anodized aluminum retaining ring, with very well-printed information about the filter on the side of the ring (ex: "325BP10", and even a directional arrow indicating which side faces towards the imaging sensor / film plane ... since there is a finely-polished "mirrored" side that needs to face outward, and a dark untreated side that faces inward. The kind of finish necessary for creating such a narrow-band "interruption" glass, I assume).

 

I am not sure about any of his other categories ... but all of the narrow-band "BP10" categories (Band-pass 10-nanometer transmission width) have all been newly sealed, and include detailed transmission data / specs.

 

Also, not all of them are that small. The sizes are very clearly listed, in the Ebay shop. He has diameters as wide as 25mm, and as thin as 10mm.

 

I opted for the 12.5mm diameter sizes, because in all due honesty, you really do not need for your narrow-band filter to fully cover your lens's image circle in order to simply conduct a transmission bandwidth test (and nothing else). You can just measure from the center.

 

The way I have my own project plan laid out (for my own home-made test coming up), I simply use a drill to create the sufficiently sized hole in a metal screw-in lens cap of a 52mm threading. Then, snap in a rubber grommet with a 12.5mm-diameter slot into the drilled hole. And finally push the 12.5mm filter into the rubber grommet. This will hold the filter inside of the screw-in cap securely, while also protecting its sides from being scratched up. My rubber grommet idea also creates a tight light seal around the filter's insertion into the metal screw-in cap, while still retaining my option to remove the filter if I ever wanted to use it for something else (rather than permanently sealing it into the cap with a silicone sealant).

 

This way, I can then screw in the 52mm metal lens cap unto the lens to be tested (and use whatever step-up or step-down rings on the lens threading to match), then conduct my test. Boom! Easy as that. In fact, I prefer having a black area ("porthole" region) surrounding the center of the transmission test, as a "black" reference to the exposed area in the center. But that is my preference.

 

Why pay $300 for a narrow-band filter ... especially with a larger diameter ... when I don't need to cover the entire image circle just to conduct a rudimentary transmission bandwidth test, based on measuring ambiance (light intensity) per unit of time / exposure, rather than forming an actual image?

 

My thoughts, anyway.

 

(Now, if you are interested in actual photography / imaging experimentation in narrow-band constraints, then of course you would need a filter diameter that would cover the entire breadth of your front element. But for my uses, it would be financial overkill to pay for an extra cut of glass that I do not need).

 

Not clear what he means by FIR either, so not sure of extent of blocking.

 

FIR = Far Infrared. So, the filter should have sufficient suppression through all bandwidths up to that region.

 

(Suppression all the way up to 15 µm [micrometers], or 15,000 nm [nanometers], which is the start of the "far infrared" bandwidth). You're more than adequately covered, since I do not know of any commercially-available Full-Spectrum-modded camera that can reach that far. :D

[colinbm]

Hi Iggy

I use a few different spectroscopes.

The best two for UV are...

USB Spectrometer http://www.ebay.com.au/itm/221370641970

Amici Prism Spectroscope http://www.ebay.com.au/itm/High-Quality-All-Metal-Prism-Direct-Vision-Gem-Spectroscope-in-Case-/161111573755?pt=LH_DefaultDomain_0&hash=item2582ff84fb

You can see some of my tests on Flickr http://www.flickr.com/photos/54724528@N06/sets

Cheers

Col

[JCDowdy]

I measure UV for a living and really would not advise anyone to use one of the inexpensive little spectrometers for UV testing. I know a lot of people use them but they are simply inadequate. I can assure that a lot of what many believe to be accurate lens transmittance is in fact not. Please no one take offense, as none is intended. Often one must make do with the tools at hand and I appreciate intent and effort. Problem is that any spectrometer with only a singe fixed diffraction grating and CCD or diode array detector will only achieve ~2.5 orders of magnitude single measurement dynamic range. Worse still, stray light rejection is often only 0.01 of out of band energy. Compare that to a proper double grating monochromator where routinely one may achieve 6-7 orders of single scan dynamic range with stray light rejection of 1E-08. The ISO standard for lens transmittance testing requires a double monochomator and that method is only for visible, requirements for UV measurements are generally more stringent.....

End of rant

[colinbm]

It is like a pregnancy test...........when you want to know, you want to know :D

But not a $500 test !

If you can just piss on a test strip & know.

Col

[Andrea B.]

JD, what kind of interior coating or surface is used in your integrating sphere for UV work ? Maybe PTFE or Spectralon or similar if indeed that stuff can be used as coating material ?

[Alex H]

Alex - It would be so cool if you posted a short list of recommended books on lenses and lens design in our Reference section ? I find myself more and more interested. I have the requisite math/physics background, but don't always want to sit down in the evening with formulas (!!) so the Kingslake history might be more interesting ?

 

Do you like or recommend anything else besides these two ?

"Field Guide to Lens Design" by Bentley and Olson

"A History of the Photographic Lens" by Kingslake

 

Here you go: http://www.ultravioletphotography.com/content/index.php?/topic/710-technical-references-lens-history-design-and-applications/

I do hope it will help forum members...

[Andrea B.]

Thank you Alex !!

[JCDowdy]

JD, what kind of interior coating or surface is used in your integrating sphere for UV work ? Maybe PTFE or Spectralon or similar if indeed that stuff can be used as coating material ?

 

My Optronic Laboratories spheres are pressed PTFE powder. Rather fragile stuff but superior performance to Spectralon.

My 2" and 4" spheres are robust enough to travel if well padded but my 6" spheres are to easily damaged

I think 10-12" is about the practical limit for compressed PTFE and larger spheres are usually Optolon or Spectralon depending on the mfg..

 

http://www.goochandhousego.com/products/instrumentation/integrating-spheres/

[JCDowdy]

It is like a pregnancy test...........when you want to know, you want to know :D

But not a $500 test !

If you can just piss on a test strip & know.

Col

 

When the test strip changes color what then does she do? She goes to the Dr for a proper blood test and an ultrasound.

 

I really like your analogy! Thanks, I needed a chuckle!

[igoriginal]

You people crack me up! :D

[colinbm]

Life is too short to be serious Iggy :D

Col

[rfcurry]

I don't know if Alex already mentioned "Lens Design = Fourth Edition" by Milton Laikin, but I found it easy to read and fascinating.

 

Igor, there are many other fine C-mount lenses. If you like Wollensac, they made the Cine Raptar until the 1960's. Here is the list of Wollensac from vademecum:

Cine Velostigmat f1.5, 25,50mm;

f1.9, 12mm; f2.7, 12, 25mm;

f3.5, 12, 25mm; A 1in (25mm) was noted on a Victor Animatograph in B.J.A. 1928, p744, and an RCA Sound camera in a 1937 advert.

Velostigmat f2.7 17mm This was noted for 16mm cine, noted (?about 1956) on a Kodak K100 turret.

 

Cine Raptar This seems to have come in 3 series, as f3.5, f2.5 and f1.9 and was made up to about 1960. It was noted as 9, 12.5, 13, 17, 25, 38, 76, 100mm (f4.5).

Cine Velostigmat This seems to have come in the same f1.9, f2.0, f2.5, f2.7, f2.8, f3.5, f5.0 aperture range, and has been noted in 13-50mm.

Cine Lenses for 16mm. The following are from many sources, including a Burke & James catalogue. High Speed Cine Raptar f1.5 12.7, 25, 40, 51mm,

Cine Raptar f1.9 25, 51mm

Wide Angle Raptar f2.7, f2.5 17mm Telephoto f3.5 51mm

Telephoto f2.5 51, 67, 75mm Telephoto f4.0 75mm,

f4.5 101, 152mm. Cine-Velostigmat f4.5 150mm.

http://www.bolexcollector.com/images/lens_wollensak.gif

Personally, I became fixated on triplets for their UV capability. Unfortunately, some use flint glass; those, of course, are not optimum for UV. But I tried many different triplets: first it was the Trinotar, then Ludwigs, then the Steinheil Cassar*s, and then the Pieskers. However, recently, I have looked for something crisper and have gone to modified Tessars. I do have one C-mount for my Lumix. It is an old 15-150 f1.5 zoom that weighs a ton... but it works on my tripod. And it came with a manual switch which threw a 2x lens into place, providing 30-300mm capability. All I did was substitute a UV bandpass filter (Andrea U) for the 2x and now I can toggle between Visible and UV shots.

 

So much GAS, so little money. :D

[JCDowdy]

Question:

 

Anyone have any experience or advice on Dr. Schmitt's X-series lenses?

 

He has recently announced what he is calling the X80QF, described as a made to order apochromatic 80mm f/3.2 Quartz Fluorite lens.

 

I know there were once other similarly named “X lenses” but there is seemingly little detail to be found about them.

[Andrea B.]

Don't know a thing about this recently announced lens other than what Klaus has posted on his blog.

My guess is he had a few models made up by a Chinese manufacturer as he did his

earlier helicoid offerings (which I have, they are nice).

 

Klaus makes it clear that the XQ80F is not the equal of a Coastal 60 or UV-Nikkor, but then what is??

But it might indeed be a very useful lens if the price is good.

Look carefully at the fotos Klaus has posted and write him about details and price.

 

With the understanding that quartz/fluoride elements can be "delicate", I suppose I would want to know more about how the elements are installed within the helicoid and whether they are well encased to prevent various kinds of damage including minor impacts. And I'd want to know what the proper storage and care should be. Also, if such a lens needs maintenance, is Klaus willing to provide it?

 

I am busy being broke right now, so cannot indulge in an investigative purchase of the X80QF until some time later.

[JCDowdy]

I do have one C-mount for my Lumix. It is an old 15-150 f1.5 zoom that weighs a ton... but it works on my tripod. And it came with a manual switch which threw a 2x lens into place, providing 30-300mm capability. All I did was substitute a UV bandpass filter (Andrea U) for the 2x and now I can toggle between Visible and UV shots.

 

What a marvelous mechanism! I would like to see it, is it posssible to post an image of how that works?

- John