White Balance: Spectralon, Sintered Porous PTFE, Virgin White PTFE

[Andrea B.]

With our friend Klaus' kind permission, here is a link to a nice reflectivity comparison of Spectralon, sintered porous PTFE (spPTFE) and virgin white PTFE (vwPTFE). The link points to an article in Dr. Schmitt's ever interesting blog.

 

I don't have any specific experimental results about how much colour cast one might induce using the vwPTFE with its small reflectivity drift between approximately 68-75% in the 300-400nm band. But in my and others' experiences with a typical wideband UV-pass filter, vwPTFE will work just fine.

 

 

http://photographyof...ectralon-r.html

 

Thanks, Klaus!! :D

[Guest]

Wow - I'm surprised at how uneven vwPTFE is. Though I don't know why I should be, as until now I haven't measured or seen these measurements before. Maybe I just unconsciously wanted the Teflon to be an even reflector - because that's what I happen to have on-hand. Good info, good to know.

[Andrea B.]

Yes, the vwPTFE is somewhat uneven, but you/we are probably not recording much between 300-330nm anyway. We are only using the PTFE for white balance and not for judging the amount of UV reflectivity in a particular subject. So vwPTFE is OK for our practical WB purposes.

[JMC]

That's interesting - it's similar, but not the same as the run I did on PTFE sheet before (cleaned with soap and water vs light sanding);

The sheet I ran showed much less variability, especially in the 300-400nm range. As has been mentioned before these materials are prone to getting dirty very quickly (which is somewhat ironic for Teflon supposedly being non-stick). Minor contamination will lead to a lot of variability in the reflection spectra as the contamination wont be as even in its reflective properties across the full wavelength range.

[Andy Perrin]

Heh. The lesson I take from these is "don't sand your PTFE!"

[JMC]

Well, for me the lesson was 'don't sand it with 12 micron grit abrasive lapping film'. Also the sheet of PTFE I had was not sintered like the Spectralon samples, so that may behave differently, to the basic 'sheet' PTFE.

[Guest]

I have actually been using two PTFE targets for white-balancing, to test if one may be more useful than the other. One is vwPTFE, and the other is stainless steel impregnated PTFE [ssPTFE]. And it turns out that the ssPTFE yields appreciably better white-balance in PP (I do all my WB ops in PP). The image below (from a previous post http://www.ultraviol...__fromsearch__1) shows both the vwPTFE (center, white) and ssPTFE (outer, gray) targets I use. I wonder if there is a way I can charge the surface of the ssPTFE disc to help repel lint/dust (the bane of my UVIVF imaging!).

 

 

Left=VIS, Right=UVIVF

[Alaun]

That's interesting - it's similar, but not the same as the run I did on PTFE sheet before (cleaned with soap and water vs light sanding);

...

 

Klaus used the Spectralon as 100% reference

[Andrea B.]

I wonder if there is a way I can charge the surface of the ssPTFE disc to help repel lint/dust (the bane of my UVIVF imaging!).

 

I wish !!! Good old static electricity is a real close friend of Spectralon and PTFE. I keep canned air handy. A negative air hood (or whatever those things are called) would be a real pleasure, wouldn't it?

 

You could try one of the soft brushes used for sensor cleaning. Typically one charges up such a brush with canned air or by stroking it against a sheet of plastic. Sensor brushes are rather pricey because the sellers make a big deal out of there being no chemicals in the brush which might harm the sensor. How much of that is hype, I don't know. I think if you looked for a wide soft artist's brush, then it would charge up and work well to brush/attract lint off of white balance targets. (Hey, I just put 'soft artist's brush' on the shopping list!)

 

 

[side story: I was once desparate to separate fennel seeds from its assorted harvesting chaff which was static-electrically bound like glue to the seeds. A fan shaped sensor brush worked a treat !! Drug it over the surface of a thin layer of seeds and got all the chaff off in a few easy sweeps.]

[JCDowdy]

Remember the old Zerostat gun from the 1970's for neutralizing static charge on vinyl records?

 

I used to have one but, like my youth, it is long gone now.

 

Surprisingly they are still sold so if any of our members are vintage vinyl audiophiles perhaps one could be tested for repelling UVIVF dust.

[Andrea B.]

Well that is sure a nifty gadget - assuming it really works! I admit to being tempted.

 

The ad says it emits a "positive stream of ions". Does that mean positive ions, per se? Aren't positive ions "bad for you"? How I don't know exactly.

 

[i removed from this post an erroneous remark about my hair dryer, btw.]

[JCDowdy]

I will try to borrow one and see what it can do.

[ulf]

I used one of those Zerostat gadgets for my LPs, a long time ago, and it might still be here, but I have not yet all parts to do UVIVF-tests

 

I do not think the Zerostat will remove any dust. The purpose for it is to reduce the static charge you create on the disc surface when brushing away the dust.

As the vinyl is reasonably insulating it is easy to build a static charge by wiping the surface. That charge then attracted more dust.

 

In the industry there are solutions to reduce this kind of problem and remove dust by blowing with ionised filtered compressed air.

Simco is one of the companies in this area https://www.simco-ion.com/.

 

I have a Top-Gun from them that I used when converting my camera.

https://www.simco-io...product/top-gun

[Guest]

I don't know how well a ZeroStat gun would work for lint/dust under typical environmental conditions, but I used these quite some years ago working with lyophilized [powders] inside sterile isolators, under very low humidity conditions. They were marginally effective, if at all, and only very temporarily and at close range in a very small radius. Granted, the conditions I used them under were challenging to say the least. Maybe they would yield better results under the less stringent conditions we occupy in our normal daily lives. On the other hand, our 'typical' environments have a huge dust/lint load compare to the conditions I used the guns under, so maybe that would be too much for them to be effective. Who knows. Definitely worth a shot - anything (!) is worth a shot in the battle against lint/dust!

[Andrea B.]

I got a $3 2"-wide nylon art brushes today at Walmart. I'll charge it up with canned air and see how well that works to brush/attract dust off the Spectralon slab. And how long the stuff stays reasonably lint/dust free after clean-up.