Filter Transmission Chart: UVROptics MidMostU

[dancingcat]

This filter is new with UVROptics.com and not on the website yet.  Chart is from Reed at UVROptics.

[Doug A]

@Sue great scoop! Do you know if it is dichroic and when it will be a available? 

Thanks for the breaking news,

Doug A

[dancingcat]

@Doug A Reed at UVROptics said a couple of weeks or so to me.  I had ordered his SEU ultraviolet bandpass filter (353BP61). but he said that he is not making it any more due to a problem with the availability of the glass involved.  I don't know what glass he is using in the new version, but he ought to explain when it gets up on his website.  As soon as it comes I'll shoot with it and post.

 

Let me know whatall folks would like me to use as test subjects.. as I'm a rookie with this.  I have plenty of dandelions around but not much else in the way of flowers blooming now.

 

[Andy Perrin]

Dandelions are good for testing IR leakage because the center should be very black if there is no leak. A muddy or lighter center would suggest some leakage. To be honest I'm sure Reed would have tested it carefully anyway, but since leakage depends on the light source spectrum very critically, you will need to establish what circumstances you can use the filter with no additional blocking and which ones require extra blocking. Testing with sunlight vs. flash for example.

 

A more systematic way to check for leaks is to take two photos, one with the UV filter/stack to be tested, and one with the same filter/stack plus a long pass filter (e.g. Hoya R72 for IR or a Tiffen 12 if you think there might be visible leakage) using the exact same exposure settings and lighting. Edit both photos identically. If the first photo is normally exposed, then the second photo SHOULD be all black, provided there is no leakage.

[Doug A]

@Suethanks for the added info. Dandelions are a good start. There are lots of their pictures, with every filter imaginable, on this site to compare to.

 

Looking forward to your post,

Doug A

[ulf]

Actually the blackness in UV of the center can vary for different Dandelions.

I am not sure if that is due to that different species of the family are different or if it depends on the location where they grew, but they are a good start anyhow.

[dancingcat]

Wondering how this filter glass is made to make the transmission drop like a stone at 380nm...

[Andy Perrin]

It’s probably mixed glass and dichroic? That’s how the Baader works. Steep drops usually mean dichroic coatings. 

[Andrea B.]

Ulf, that is probably for different Dandelion species? Let's get Birna's observations.

In the US we don't have many species. The two non-alpine Taraxacum versions are quite alike, both UV-dark bulls-eyes.

Europe, however, surely does have many more kinds of Dandelions!

[nfoto]

The term "dandelion" tends to be applied in a very broad sense, thus a lot of species not being true dandelions are swept together under the same designation.

 

For the yellow-flowered members of the Asteraceae (Daisy Family, or Compositae) to which Dandelions (Taraxacum spp.) belong, the UV appearance tends to be either more or less pale yellow with darker disc flowers, whitish-light blue with a darker centre, or more or less black all over. What goes under the name "Desert Dandelion" in the US belongs to the latter group. A few have more like a greenish cast to the UV appearance. Iridescence due to conical cells on the ligules tends to add to the complexity of UV signature.

 

The European Dandelions comprise many (some would say, *far too many*) apomictic microspecies and their UV signatures are quite variable although most have the classic bulls'eye rendition to some extent. So we would indeed expect a Taraxacum sp. to have a darker centre.

[Andrea B.]

To clarify, the US Desert Dandelion is not a Taraxacum species.

[nfoto]

My point, exactly.

[Andy Perrin]

The only ones I’ve ever seen (here in the northeast US) are yellow with dark center in UV. I don’t know if those are Desert Dandelions or what. 

[dancingcat]

Aside from the common dandelion Taraxacum all over local lawns, Texas also has Pyrrhopappus pauciflorus, Texas dandelion or false dandelion.. also an Asteraceae but taller and stouter than Taraxacum.  I'll shoot it in the UV when it blooms in a month or so.  Maybe the seeds do UVIVF like it's smaller cousin.

 

See https://www.wildflower.org/plants/result.php?id_plant=pypa4

 

 

 

[Andrea B.]

Andy, the NE dandelions are Taraxacum.

There are lots of shaggy yellow flowers in the NE which look dandelion-like, but the leaves are diagnostic.

 

Sue, that Texas dandelion would be a nice addition to our botanical section. Looking forward to seeing it here.

[Andy Perrin]

Wow, I would not have imagined anyone would apply the name "dandelion" to that flower, Sue.

 

Andrea, the ones I was thinking of look like this. I am not sure if they are dandelions, or just poor fakers. Caveat that I don't recall how much I increased saturation on these. This was with 330WB80 filter on the Noflexar 35/3.5 at F16 for 1" ISO100. Nice light leak in the corner! 

 

[nfoto]

These look likie the real thing.

[Andrea B.]

In the US the term "Dandelion" means that low growing weed in the lawn with the shaggy yellow flower. "-)

 

It's the leaves which tell the tale, Andy. Those do look like Dandelions, but there are a *lot* of shaggy yellow flowers in the US with UV-dark centers. hawkbeards, hawkbits, cat's ears, sowthistles and more.

[Stefano]

Andy's dandelions look just like mine (when they appear in spring).

[nfoto]

Only basal leaves in a rosette, and hollow unbranched scapes with milk sap and ending in a single flower head.. If the plant is in fruit, the familiar "mop" with small achenes equipped with a feathery parachute. Then we have a Dandelion.