Dandelions & Speedwell

[dabateman]

You don't need an integrating sphere to just know the cut offs. You need sensitive and exact alignment.

If the slope into that cut off is really shallow, than you maynot know exactly where it ends. But for me it would be too shallow to care and camera sensitive is low, so wouldn't matter.

 

[Andrea B.]

Andrea, why would you need an integrating sphere to determine just the lens cutoff?

oh I don't know. I just like doing things neatly. Precisely, accurately, repeatably, completely. Too meticulous, I know, I know.

 

Yes, it is nice to know what you are looking at. And mostly we do. But we also have to know when it really matters and when it is just nice.

 

Also there was some big swinging going on up there when there should not have been.

 

And you know how I get about that falseColour-to-wavelength mapping thing.

[Andrea B.]

IxnaX -- The flowers are very nicely photographed.

[Andy Perrin]

Andrea, why would you need an integrating sphere to determine just the lens cutoff?

oh I don't know. I just like doing things neatly. Precisely, accurately, repeatably, completely. Too meticulous, I know, I know.

Andrea, you get all of those (precision, accuracy, repeatability) for the cutoff number without the sphere. You just need a simple spectrometer for cutoff. The sarcasm here is unjustified.

[Andrea B.]

Well, it was not intended to be sarcastic but I probably should have elaborated on that above.*

 

The point is that I want to see all information about a lens, not just cutoff. There is too much emphasis on cutoff.

 

A cutoff at, say, 310 nm is not so great if, say, the transmission at 360 nm is only 45%.

A cutoff at 310 nm is not so great if the left shoulder does not have a reasonably steep slope.

A cutoff at 310 nm is not so great if the lens has little to no chromatic corrections.

I know you get what I'm getting at.

 

There is so much more to a good UV-capable lens than just how far it reaches. One of the nicest dedicated UV lenses out there does not "reach" all the way to 300 nm. I'm referring to the Coastal 60/4.0, of course. But it has a lovely image quality and superb correction.

((I do have somewhat of a love/hate relationship with that lens due to the peculiarities of its hotspot at certain mags, but I cannot deny the beauty of the CO 60 images in UV, Vis or IR.))

 

Ulf has been trying to supply complete info about lens transmittance with his recent work.

And Bernard has helped also by looking at resolution, aberrations and other chart matters.

 

 

 

*I always think I am talking too much.

[dabateman]

No that makes some sense.

 

But its about testing order. I think first you need to know where your lenses cut off to see if they are worth taking the time for a more detailed analysis. Once they pass the first check then you can evaluate them for their other properties or imaging strengths.

[colinbm]

No that makes some sense.

 

But its about testing order. I think first you need to know where your lenses cut off to see if they are worth taking the time for a more detailed analysis. Once they pass the first check then you can evaluate them for their other properties or imaging strengths.

 

And that is where a simple sparticle test come into play.

 

Like a pregnancy test....you just have to know...

[ulf]

Andrea, why would you need an integrating sphere to determine just the lens cutoff? I think even Colin’s gadget can get the cutoff. Getting absolute transmission numbers needs the sphere probably but that’s not what the discussion was about. Ulf can check me on that. We do care a bit about the cutoff because it’s nice to know what we are looking at. I mean, I love pretty pictures but if that were the whole story I could just photoshop a visible light image to have any colors I wanted.

Colins gadget ha an integrating sphere as an input port.

 

The integrating sphere is important when measuring lenses only if you want the full information about absolute transmission.

Depending on how you want to define the cutoff level, by a well chosen intensity drop or not, that is more or less important.

 

If you just want to detect when there is almost no light passed by the lens a simple well aligned collimated system is OK, even if the maximal detected signal is very different for different lenses.

If you then make an educated guess of the transmission at say 400 nm or above and use that for a normalisation you are not that far off.

However the dispersion in refractive collimating optics distort the measurement result for different wavelengths, making the method less accurate.

That is the way I used to do with my deuterium light-source before I got a more powerful light-source and a proper integrating sphere.

[Andrea B.]

IxnaX, I hope we didn't become too intense here! Your work is good. Anytime you want to add an identified wildflower in UV or IR to the botanical section, it is OK to do so. I can help with the formatting and references.

[ulf]

IxnaX, I hope we didn't become too intense here! Your work is good.

 

 

That is also my opinion.

I like them very much.

I hope to see more images from you, especially as I like to explore the border region around 400 nm.

 

IMHO your images are a great proof that deep UV-reach is not that important, if you are not into special light sources and narrowband filters like David and Bernhard, here on the forum.