Industar 50-2 surprise transmission?

[Nate]

So I've never taken my Industar 50-2 out with my current filters because I didn't realize I had a 35.5mm adapter that I bought the same time as the EL Nikkor 80 adapters.

These lenses have no clicks for the iris, so I just closed it a bit.

 

This is the Sunflower patch at the  University of Idaho Arboretum.  77D   .5sec   iso200   Baader U/uvroptics NIR block

 

A little closer shows some great detail. 1/3sec  iso400   same filter stack

 

This is from one of the videos I took, digital zoomed in so quality isn't there. It was quite busy at the Sunflower market. same filter stack

 

After taking a few pics out there, I thought I'd test the spectrum with my window slit and diffraction grading. I'm kind of surprised it shows the same or possibly lower than both my EL Nikkor 80mm metal versions going by the lines.

77D , Industar 50-2 ,BaaderU/uvr optics NIR block

Can someone confirm that this line is correct?

 

Thanks

 

[colinbm]

These look very good.

 

[Nate]

Thanks @colinbm The first lens I bought for UV turns out way better than I thought.

[ulf]

2 hours ago, Nate said:

So I've never taken my Industar 50-2 out with my current filters because I didn't realize I had a 35.5mm adapter that I bought the same time as the EL Nikkor 80 adapters.

These lenses have no clicks for the iris, so I just closed it a bit.

 

This is the Sunflower patch at the  University of Idaho Arboretum.  77D   .5sec   iso200   Baader U/uvroptics NIR block

 

A little closer shows some great detail. 1/3sec  iso400   same filter stack

 

This is from one of the videos I took, digital zoomed in so quality isn't there. It was quite busy at the Sunflower market. same filter stack

 

After taking a few pics out there, I thought I'd test the spectrum with my window slit and diffraction grading. I'm kind of surprised it shows the same or possibly lower than both my EL Nikkor 80mm metal versions going by the lines.

77D , Industar 50-2 ,BaaderU/uvr optics NIR block

Can someone confirm that this line is correct?

 

Thanks

 

I have a few Industar 50-2 and can confirm that they have a good UV-reach in a similar range as the old EL-Nikkor 80mm.

I did not use them at all beside from checking the transmission with my spectrometer, as the mechanical build quality was quite low and I did not have any suitable step ring.

I suspect that the optical quality is not top rank either. That is why I never posted any lens topic for this lens

 

My best 50mm lens with a really good UV-reach is the Focotar-2. https://www.ultravioletphotography.com/content/index.php?/topic/4367-leitz-50mm-f45-focotar-2/

That lens is very sharp and with a better UV-Reach than my Kyoei-made Soligor.

[Nate]

Thanks for the info @ulf I think I might have got a good one, mechanically pretty good. Looks to be hard to find a Focotar -2, there's a FOCOTAR 50MM F4.5 ENLARGING LENS, but doesn't say -2.

[Kai]

Hi Nate,

The pictures with this lens look good! Can you say something about the aperture value?

The result of your sprectrum looks very good. The Industar 50-2 is apparently transmissive to below 340 nm.
Attached is a list of some spectral sun lines that interest us.
The upper part of the image shows a solar spectrum that I took with an old magnifying lens. The focal length is a bit longer (75mm), so the resolution is a bit higher. The Schott DUG11X filter I use here lets less longer-wave light through than the Baader-U. As a result, the color transition from yellow-green to blue-full is naturally shifted towards shorter wavelengths ("white balance").

[Nate]

Hey @Kai I can't really tell how much I closed the iris as I have a bunch of tape and sticky adhesive for grip when focusing. But I did close it a few millimeters.

 

I did compare what I got from yours in another post. Thanks for posting that.

 

[ulf]

52 minutes ago, Nate said:

Thanks for the info @ulf I think I might have got a good one, mechanically pretty good. Looks to be hard to find a Focotar -2, there's a FOCOTAR 50MM F4.5 ENLARGING LENS, but doesn't say -2.

There are several different versions of the Focotar 50mm. The latest Focotar-2 is the best, but quite rare.

Many of the later Focotar50 are quite good too and more common and with a more reasonable price.

Do avoid the oldest ones and the LFE Focotar 50mm as they do not have a good UV reach.

Sometimes the LFE is sold as a Focotar-2, but it is not correct. Look at the mechanical design and front lens diameter.

 

Look here: https://www.ultravioletphotography.com/content/index.php?/topic/2492-focotar-50mm-f145-from-first-year-to-last-transmission-difference/#comment-18378

Many things are often investigated so it might be a good idea to search the forum.

Have you found this yet?

https://www.ultravioletphotography.com/content/index.php?/forum/645-uv-lens-technical-data/

Here is info of many of my enlarger lenses, with ambitious transmission data and other information.

I see that I have hoarded six different Focotar lenses for testing.

 

The only problem might be that it is a bit tricky to arrange a front mount for the filter. 

With mirrorless cameras a rear mount might be OK.

 

When I investigated these lenses I just had my modified Canon DSLR.

[Nate]

Thanks again for more info @ulf I did just order a couple to play with, plus another one. I'm thinking I wouldn't reach infinity at 50mm with the 1500D and 77D bodies, so I ordered a M42 to EOS M adapter.

[Nate]

I tested all my cameras with the Industar 50-2 and BaaderU, I guess If I want to reach the lowest in uv it'll be the T7(1500) 

I had to make the focus a little off on the window slit to get things in focus on the lower end, and defocusing the other way made the higher 375 range better. Wondering why this is a thing, but glad I figured it out.

 

Here's what I get with the T7/BaaderU/Industar 50-2      Sunlight, Summer, 9:45am, window facing South

[ulf]

6 hours ago, Nate said:

Thanks again for more info @ulf I did just order a couple to play with, plus another one. I'm thinking I wouldn't reach infinity at 50mm with the 1500D and 77D bodies, so I ordered a M42 to EOS M adapter.

Here is Cadmium's excellent description for adapting a front filter on a Focotar-2 50mm. It is also valid for the older 50mm lens

https://www.ultravioletphotography.com/content/index.php?/topic/2216-focotar-2-50mm-front-filter-adaptor/

 

 

[Nate]

Thanks ulf

[Kai]

Since the UV portion of sunlight decreases quite strongly below 350 nm, I have - as described some time ago - made an emission light source that delivers a line spectrum up to 300 nm (and probably lower).
This shows that the de-filtered Canon 500D is sensitive to around 300 nm. As a "lens" I used a pin hole. Only the grating (DVD), a quartz plate as sensor protection and the air were between the sensor and the light source (sparks).

Focus change: One reason could be: The refractive index of the glasses depends on the wavelength. The focal length of a lens can shift extremely towards short wavelengths. I also observe this again and again in spectral images.

 

But that always raises the question for me what a "deep-reach" is good for from a photographic point of view. With the sun as the light source, the amount below 340/350 nm is quite small. I would like to see comparison pictures of a real UV lens against two or three lenses with different UV reach. What does the "UV-reach" bring apart from a little more light overall?
On the other hand, an advantage of a limited UV range is the reduction of chromatic errors and a focus over the entire wavelength range. If the UV yellow is not so strong - you can selectively increase that a bit.
To some, that may sound like blasphemy. I'll discuss it anyway...

[Nate]

Thanks for your tests @Kai. They give me a reference to compare to.

I wonder if the focus difference in my grating spectrum affects pictures at all. 

I get lost trying to go as deep as possible with my gear into UV sometimes, that I bypass the ease of just taking UV pics. My Canon 40mm is so easy to use with autofocus in UV and the pics turn out decent. The clouds in the sky are more noticeable with less reach in uv I'm discovering, but most things that absorb UV are still dark. I too would like to see a comparison of a UV dedicated lens and one that reaches to 330nm. I'm thinking not much because sensor limitations.

[Andy Perrin]

Quote

Nate:

 I too would like to see a comparison of a UV dedicated lens and one that reaches to 330nm. I'm thinking not much because sensor limitations.

Exactly. And this is why (assuming the lens can capture some false yellows) the standard advice around here is to not worry all that much about reach and concentrate on other lens quality issues like corner sharpness, distortion, chromatic aberrations, and focal shift with vis and IR. 

[ulf]

I concur.

 

In most typical cases there is no need to just focus on deep UV-reach, just as Kai and Andy say above.

That is true for situations when using a full spectrum modified camera with reasonable UV-reach and filters like the Baader U or stacks including UG11 or UG1 or similar and a suitable BG glass like BG39 2mm or S8612 2mm

 

Deeper UV-reach will become more important when trying to work in UV-B or even UV-C, but then you'll need rather special filters and light-sources, and preferably a monochrome converted camera.

 

I found that I needed more UV-reach than I got from my UV-Nikkor 80mm in one setup only. Before that I have seen no problem at all with most of my lenses with reasonable UV-reach worse that the EL-Nikkor 80

 

The need for more reach happened when checking my rather extreme ZWB1, 8mm and the U-340, 4+4mm stack and outdoor sunlight.

That filter in combination with the not extreme UV-reach of the sensor of my full spectrum modified Sony A7 III gave a very limited palette of false colours that was impossible to WB properly.

 

When I changed lens to my simple fused silica PCX lens, that WB problem went away, and I got a more normal false colour image but the image quality was not very high.

 

I'll start a topic showing that rather soon.

[Kai]

That sounds good, Ulf. I am excited.

[Nate]

That makes a lot of sense ulf, thanks. Also looking forward to your topic on that.

[Yves W]

I have just found a Focotar 2 N°3120683, in France 129€, I will see for the assembly of the filter.

Thanks Ulf for your advice

[ulf]

That is a very nice price. Normally they goes for at least two times that.

Are you sure it is not a LFE Focotar?  There should be printed FOCOTAR-2 on the barrel of the lens.

[Yves W]

Thank you Ulf, it is written Focotar 2 and very beautiful MINT

Links for the filter adapter no longer work

 

[Stefano Rosoni]

Hi Kai,

How is it possible so many colors into a narrow band as 300-400 nm ?   

In the upper message you wrote: 

Since the UV portion of sunlight decreases quite strongly below 350 nm, I have - as described a while ago - made an emission light source that gives a line spectrum down to 300 nm (and probably lower).
This shows that the unfiltered Canon 500D is sensitive to around 300nm. As a "lens" I used a pinhole. Only the grating (DVD), a quartz plate as sensor protection and air were between the sensor and the light source (sparks).

[Google translation]: Poiché la porzione UV della luce solare diminuisce abbastanza fortemente al di sotto di 350 nm, ho - come descritto qualche tempo fa - realizzato una sorgente di luce ad emissione che fornisce uno spettro di linee fino a 300 nm (e probabilmente inferiore).
Ciò dimostra che la Canon 500D defiltrata è sensibile a circa 300 nm. Come "lente" ho usato un foro stenopeico. Solo il reticolo (DVD), una lastra di quarzo come protezione del sensore e l'aria erano tra il sensore e la sorgente luminosa (scintille).

 

I should like to understand how is it possible to have so many colors into the narrow 300-400 nm spectral band, in which operates only the blu channel ... or not?

Thanks.

[ulf]

6 hours ago, Stefano Rosoni said:

 

I should like to understand how is it possible to have so many colors into the narrow 300-400 nm spectral band, in which operates only the blu channel ... or not?

Thanks.

The narrow 300-400 nm spectral band affect all three colour channels R, G and B on the camera sensor.

They respond differently for different wavelengths giving the multicolour images.

[Andy Perrin]

Yep, and this makes a nice lesson on why you should never try to extrapolate a spectrum outside the measurement range. In this case based on naïve extrapolation one might expect only the blue pixels to show a response in UV. But in reality all of them do.

[OlDoinyo]

17 hours ago, Andy Perrin said:

Yep, and this makes a nice lesson on why you should never try to extrapolate a spectrum outside the measurement range. In this case based on naïve extrapolation one might expect only the blue pixels to show a response in UV. But in reality all of them do.

With laminar sensors (e.g. Foveon or color film) one does in fact get response mostly in the blue channel. But reseau sensors are different because the sensels lie side-by-side in the focal plane and UV can strike any of them. The dye responses outside the visible range are not something the manufacturer cares about, and in general these dyes do not block all UV.