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UltravioletPhotography

Clone Wars - Newcomers are the Casualties


bvf

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... The Lithagon 28mm is better than the Lithagon 24 mm, but the Nikkor 24 mm is much better than any Lithagon/Porst I tested.

My tests with the Lithagons: http://savazzi.net/p...naLithagon.html

 

Thanks, Enrico. Your material ("This lens is the best 28 mm I tested so far in UV") actually played a part in my decision to buy the Lithagon, together with Klaus Schmidt's chart.

I didn't go for a 24mm lens partly because of cost (AI-S Nikkor at about £175 vs. £40 for the 28mm Lithagon) and partly because I didn't know how it would work with the Baader U (i.e. whether you'd get edge effects). I tried the Baader U with my Canon 28mm/2.8 and didn't get any problem, so hopefully I'll be OK with the Lithagon.

 

PS: in one of your links you say "The optical scheme probably uses 6 elements in 6 groups". That supposition is supported here: Enna Lithagon 3,5/28 mm

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UPDATE:

 

I'm going to mark the Sticky with an Under Edit note to indicate that it is not currently stable.

 

I purged the "no data" lenses, but that resulted in the loss of some we all use and know to be ok. So I'll have to think about how to add those back in.

 

I was thinking also that I could keep the original list and mark entries with some kind of flags or colours to indicate OK, No, or "Caution".

 

Igoriginal lenses will not be listed given that each is an individual production.

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There is nothing wrong with the lens sticky, it is perfectly fine.

I would not remove lenses from the sticky,

I believe the information there is more than 99% accurate and useful.

 

No it is not perfectly fine at all!!

It is a list of more or less usable UV-capable lenses that likely work in some situations for UV-photography.

 

It is still valuable as a list of candidates to be properly verified and I think it should be kept intact.

The list can be used as a base for something better.

 

However it is absolutely NOT 99% accurate. Instead it is mostly full of beliefs and opinions from many different sources.

Therefore it is not possible to compare any two lenses capability as the statements are based on different test methods and interpretations.

 

The "truths" are often misinterpreted.

 

I discussed this problem with Andrea a few months ago and want to help improving the quality of the collected information.

I have some ideas of how I would like to approach the problem with a suitable structure of the information.

However I got flooded with work and obligations and have not been able to pull it any further. I'm sorry for that.

 

Maybe now is a good time for a joint effort?

If there is an interest, I can describe how I think it should look like.

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This is an important resource and anything to make it more usable would be valuable. I don't know what you're thinking of, Ulf, but in principle I'm happy to put some effort into this as part of a collaborative activity.
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I would like to have a list of the lenses, maybe the current sticky-list can be used.

 

For each lens there should be a link to a separate topic for each lens in the list.

 

The first post in each lens-topic should have a standardised format for several possible parameters and could be working a bit like Wikipedia.

To get this function I would like to have essential parameters added back to the first post when they eventually, when new data is found or acquired from added measurements or tests.

(This is against the newly stated edit time rule, but I hope that posts can temporarily be unlocked for such additions, even after a long time.)

 

If new data is added after the first post, the information could be reviewed and verified before adding it back to the first post.

 

To get a good structure we should have a template to use for each new lens topic.

The template could have several empty sections for different properties like pictures of a lens, spectrometric measurements of different kinds, mechanical properties, sharpness tests, focal shift tests...

I would like the -3stop cutoff as a parameter (see below), but also the much more interesting -50% relative cutoff-point and also the absolute transmission at around 365-370nm. Ideally a correct transmission graph for the full spectrum might be nice.

 

The sections might be separated with a line like this:


I think it is very important to document the test object and measurement methods well, to make it more likely that the tests could be interpreted, compared and repeated.

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I have gone back to the original list where I am marking with bright yellow those lenses for which we have no data.

Those are the ones to test if possible.

 

I'm not done yet. The "Under Edit" is still present in the Title.

 

I very much like Ulf's idea of a lens template where information for each lens could be provided and linked to through the Lens Sticky. The primary problem, as always, is obtaining standardized measurements from standardized tests. We simply do not have a way to do this.

 


 

Side Note: The edit time rule has always been there. We've always been happy to help with that in those few cases where it has been needed. :grin:

 


 

Interestingly over all these long years in being online as a UV admin (or whatever it is called), I have very very rarely seen anyone - with the notable exception of Dr. Klaus and Dr. Birna - perform lens tests beyond measuring "reach". Sometimes I get comments about focus shift. I have occasionally posted encouragements about testing more than reach, but to no avail. It is quite time consuming though. So I am not particularly surprised by the lack of info about lenses. I myself rarely find the time to perform tests. About two years ago I tried to start testing for chromatic aberration with a "tin foil" test, but it did not get too far.

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Ulf,

Linking the lens to the forum topic or outside link for why it maybe good, is exactly what I did for the AF lens list I compiled. But maybe a lot of work for Andrea.

Best would be forum posts where the spectrum was obtained for the lens.

 

I mostly would summarize the best Af UV lens to be the Canon 40mm f2.8 pancake lens, that Jonathan discovered. It can be mounted via adapter to any modern camera. Sorry Pentax and old Nikon F mount people. But it does seem to work the best and Jonathan has posted its spectrum a couple of times.

 

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Ulf,

Linking the lens to the forum topic or outside link for why it maybe good, is exactly what I did for the AF lens list I compiled. But maybe a lot of work for Andrea.

 

I hope that we can do this without generating much extra job for Andrea.

The job to harvest added information from the added posts and incorporating it into the first post could be done by someone trusted to do that as long as the post is unlocked for editing if needed, after a request to the admins. Without knowing I do not think that is very time consuming task.


Maybe we should start to collect possible tests that might be separate sections in the template.

The text formate and disposition should be refined later.

Here are some suggestions for some possible parameters:

Please suggest more.


Definition of test object: Lens type with make, mount serial# and picture. Extra info like front thread...


Relative normalised transmission spectrum to define the deep cutoff wavelength as Klaus's list


Absolute transmission spectrum, measured with an integrating sphere. Might be done at a few wavelengths or if the equipment allows for wider ranges of wavelengths.


Relative speed of a lens compared against a better known lens, measured through a known filter like a Baader U.


Focal shift for defined wavelengths at a few working distances.


Chromatic aberration with a "tin foil" test.


Sharpness tests at defined wavelengths and apertures. (Task - find suitable test target for macro range)


...

 

It is also important to document test setups and their limitations. If possible an estimation of the accuracy of some tests will be welcomed.

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I'll always do what I can to help. This is a good outline, Ulf.

It is just something to start building with. I hope it can mature to something really usable where several types of input from different contributors can be gathered.

 

I hope we get suggestions about additional tests and parameters that might be added to the list of tests/information that can get sections in the template.

 

For "Definition of test object:" we might look at some of Klaus's lens pages to get some inspiration about what to add. http://www.macrolenses.de/objektive_sl.php?lang

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We do already list Brand, Model, Focal Length, Speed (Aperture), and Mount which are also headers in Klaus' list. I also have front filter size and range.
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Andrea, You should pull that Kyoei 35mm out and compare it with the UV-Nikkor, maybe hard to do given the different focal lengths? But using the same UV filter, would be interesting to compare false color, exposure time, etc.,

Might be interesting, I have never seen that done.

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I'll put that on the list.

 

I'm not sure how best to compare a 105mm with a 35mm for exposure times because the framing is different.

 

We can certainly compare the false colour.

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Would it be possible to make a standard test with commonly available equipment ?

Like with a UV Convoy S2 torch & a UV light meter ?

Placing the UV Convoy S2 torch, lens & UV light meter at specific distances from the front & rear elements & on the same centre axis, & placing a UV light proof fabric over the light path & recording the reading.....?

Just my thoughts.....?

Col

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I want to do this, but I am not sure how best to compare, given the difference in focal length.

 

The only crazy idea I have thought of so far, is to shoot a photos using the UV-Nikkor 105mm,

then using the Kuri 35mm, move the camera closer to the subject in order to adjust the Kuri 35mm frame to be the same size as was shot with the UV-Nikkor 105mm.

Any thoughts on that idea?

 

By the way, the Kyoei 35mm functions the same as the Kuri 35mm.

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With a standard test, like I have suggested above, each lens, brand, focal length & aperture, will have their own value, which should be repeatable universally ?

If there are differences in serial numbers / batches, that would be soon established.

Change the brand & focal length, etc & you have a new table of values.

Col

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Basic schematic of a Standard UV Lens Transmission Test.

A cheap UV light source like the Convoy S2 365nm torch needs to be agreed upon.

An agreed 365nm UV Meter needs to be agreed upon.

Details...

 

post-31-0-00262800-1574578022.jpg

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Well, I will be doing an actual photo/scene test comparison.

So I think the best way to do that with 35mm vs 105mm is to adjust the camera/lens distance to the same target to compensate for the difference in focal length / frame.

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Well, I will be doing an actual photo/scene test comparison.

So I think the best way to do that with 35mm vs 105mm is to adjust the camera/lens distance to the same target to compensate for the difference in focal length / frame.

 

I think you must keep the distances the same to make this technically meaningful.

This is just me reasoning theoretically about the optical setup and I hope my reasoning is correct.

 

I would suggest to do the test like this instead:

Take a sheet of clean matted pure PTFE. Mount it with the surface at a slightly slanted angle against lens and flashlight, to avoid direct reflections as from a mirror.

Illuminate the sheet with the Convoy and take pictures with the different lenses at the same F-stop setting.

Take series of exposures in RAW with different exposure times, in the smallest steps possible, for both lenses.

 

Compare the images from the two series.

Do the comparison from RAW-files NOT jpeg!

You can use Raw-Digger or FastRawViewer for this.

 

Find the exposure time offset where the exposure-level of the hot spot peak matches.

That match should be true for at least parts of the two series.

This offset is an indication of the transmission difference if the F-stop setting is correct and comparable.

 

The distance to the PTFE-sheet must be constant, both to the flashlight and the entrance pupil of the lens.

This must be done very carefully.

 

You could do the test with just one pair of images, but a series pair helps verify that there is no saturation effects in the test.

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Basic schematic of a Standard UV Lens Transmission Test.

A cheap UV light source like the Convoy S2 365nm torch needs to be agreed upon.

An agreed 365nm UV Meter needs to be agreed upon.

Details...

 

post-31-0-00262800-1574578022.jpg

 

I think you will see similar problems with this setup as you'll get with spectrometers and collimators.

UV-meters are designed to measure in a even homogen light field. The flash lights do have an uneven light pattern with a more or less pronounced hotspot.

Different lens designs have different beam pattern leaving the lens and the beam pattern will cover the light meters sensor area differently and will also reach it at different angles.

 

You will get some readings, but it is difficult to say how accurate and meaningful they are.

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I was hoping for something simpler.

I just want to take a picture, not as interested in exposure time as the false color.

I can also do a Sparticle test on each. However, I really don't expect much difference given that all the usual UV-only filters will probably limit each lens about the same.

There might be a slightly faster exposure time with the UV-Nikkor due to a slightly stronger 300nm-350nm range.

I think I will just take some shots first, and see how those compare. Even that should give me some feeling for any difference.

The 105mm should be good for some things, because getting real close to something with the 35mm can be hard sometimes.

I really don't know, because I hardly ever shoot with anything in UV except the Kuri 35mm. I keep telling myself to shoot with the Kyoei 80mm, but I never do.

I have used the El-Nikkor lenses for close up some, but usually the Kuri.

Maybe some day I will get a spectrometer even, but not holding my breath. Maybe when Andrea gets one. :smile:

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Basic schematic of a Standard UV Lens Transmission Test.

A cheap UV light source like the Convoy S2 365nm torch needs to be agreed upon.

An agreed 365nm UV Meter needs to be agreed upon.

Details...

 

post-31-0-00262800-1574578022.jpg

 

I have 2 convoys and they are significantly different in intensity and leak.

We would need a standard test that some how would divide out any issues of various light intensity or sensor intensity.

You could use a Camera, but some will be less sensitive to less than 350nm due to low pass filter sensor coverglass or intact dust shakers.

I will have to think of an intensity neutral common test. That is why I liked dividing out but the EL 80mm f5.6 lens to get relative T UV light stop values.

But then I ran into issues with older lenses not consistently opening the aperture to the same value. Need to rotate the aperture ring twice between 3 repeat shots. To get consistency.

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I'm not sure I would use a Convoy for any kind of lens test. That 365nm peak is going to skew results.

 

I'll try something similar to what Ulf suggests. But not with a Convoy. Rather in the bright sunlight with readings taken from my UVA/B meter between each set up. The point of metering the UV is not to get an absolute measurement, but to track how the UV might be changing during the photography session. UV amounts can drop fairly rapidly in the late afternoons. This can skew results. You want to try to get the phtographs made during a stable interval.

 

However.......we are due up for a big snow storm, so I'm not really sure when I'm going to get the clear cloudless sky again. Maybe next week sometime? We have lots of sunshine here, so it will not be too long a wait.

 

I'll list my shooting protocol along with the results.

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Surely with the Convoy or any UV light it is the percentage in & the percentage out...?

You measure the UV output without the lens & measure the UV output with the lens ?

Col

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