Lens influenced white balance?

[Kristine]

Hello,

I recently realized, by accident, that my Canon EF-M 22mm pancake lens appears to let as much UV through as the Soligor 35mm f/3.5 and El-Nikkor 80mm f/5.6. That was an interesting surprise, since the EF-M lens provides much sharper pictures. 

 

In order to compare them, I took these pictures after doing an in-camera custom white balance with the Soligor lens on a PTFE sheet. All shots were taken with a LaLaU filter with 1600 ISO, their respective exposures were determined by the camera light meter in manual mode and were taken within minutes of each other under similar illumination. Natural UV light is low here at this time of the year, so the exposure times were long. The subjects are a plush plant (no wind blurriness here!) and a grapefruit. 

 

This is with the Soligor 35mm f/3.5         0.25 second

 

This is with the El-Nikkor 80mm f/5.6       0.60 second

 

This is with the EF-M 22mm f/3.5            0.50 second

 

This is with the EF-M 22mm f/2.0            0.125 second

 

The EF-M 22mm appears to transmit UV well overall, but it causes a shift in the white balance of the picture and I wonder why. Could it be because it blocks shorter wavelengths that the Soligor and El-Nikkor allow through?

[Doug A]

@Kristinegreat question! Just ran into the same thing. RAF just delivered a 27-52 adapter ring to use the Pentax 40mm pancake with 52mm filter stack. Used my standard in camera custom UV white balance to compare the Igoriginal 35 F3.5 to the Pentax 40. Similar WB shift you observed. All the other lenses, EL-Nkkkor 80 & 135, Vivitar 105, and even the multicoated Olympus OM 80 macro share a similar WB with the 35. 

 

Thanks,

Doug A

[colinbm]

Nice photos Kristine
The Canon EF-M 22mm pancake is only getting you down to about 365nm, but that is OK.
The Canon EF-M 40mm pancake gets you closer to 340nm.
the Soligor & El-Nikkor are getting you closer to 330-320nm, that is why you are getting some yellow showing.
The WB on PTFE is very sensitive to these changes.
 

[nfoto]

The cold blue hue is indicative of a restricted penetration into (upper) UV-A. Not very surprising for a modern lens.

 

At least the two first shots seem to be overexposed as there are bright areas burning out.

[ulf]

5 hours ago, colinbm said:

Nice photos Kristine
The Canon EF-M 22mm pancake is only getting you down to about 365nm, but that is OK.
The Canon EF-M 40mm pancake gets you closer to 340nm.
the Soligor & El-Nikkor are getting you closer to 330-320nm, that is why you are getting some yellow showing.
The WB on PTFE is very sensitive to these changes.
 

The EF-M 40mm is not as close to 340nm as stated above. That sounds rather optimistic. When the transmission has dropped 3-4 stop, (10-20%), there are not much meaningful contribution to an image, with a wide-band UV-Pass filter like a LaLaU. Compare the transmission graphs below for the EF-M 40mm and the 35mm Soligor below. 

 

 

[dabateman]

That shift in white balance is one of thr signs that it doesn't transmit UV well.

You are mostly seeing the end of what we call UV. This typically,  but not always looks blue like that. So you are definitely seeing to 380nm.

The yellow or is a signature,  but not always for seeing to 360nm or 370nm.

If its a strong green, than you might be seeing deep UV, into the UVB area. But not always,  and some will argue these colors.  But that is the general color filter sensitive response. 

[Kristine]

Well, that explains it. Thank you everyone for your replies. Out of necessity I used this EF-m 22mm with a UV+blue filter for a portrait the other day. The result was nice in black and white, but I felt a lack of UV contribution to the details of the face. This lens probably allowed much more blue than UV to reach the sensor. 

[Cadmium]

Nice photos.

A flower such as a dandelion (still have some late bloomers here in the yard) or rudbeckia (those are out of season now) would be a good target.
Those would test a little lower UV range with their yellow in UV.

Yes, the lens determines the range of the photo, limits the range of any filter.

The El-Nikkor 80mm (old style with chrome base/mount) is one of the best lenses for UV wand width. So you should get some dandelion yellow from that.