Getting Venus-filter if ZWO ADC and ASI290MM pass enough UV

olav

Hi all,

Found an older thread on the topic. (http://zwoug.org/viewtopic.php?f=21&t=1973&p=3950)

New stuff, new guys, modified questions:

Anyone tried the ASI290MM with ZWO ADC (got both just now) and a Baader U filter?

http://www.baader-planetarium.com/en/filters/planetary/special-filters/baader-u-filter-(venus-and-uv---350nm).html

Btw I believe this is still only UV-pass filter around, for amateur astronomers.

Is the protective window of current cameras (the 290) still of a type that should be removed (temporarily) for doing UV?

I should also add that I'm using a C11HD, and preferably also my BPFFC barlow (Baader Fluorite Flatfield Converter).

Not just mirrors in these SCTs (both corrector glass in front and flattening elements in the baffle tube), and I can't even find anything on the supposedly beneficial fluorite elements, regarding UV-pass of the coatings.

I'm also looking for a sensitivity curve of the ASI290MM. There's apparently no dedicated manual to be downloaded, and the product page does not show how fast the curve drops below 400nm.

Any help on any of this would be much appreciated.

riklaunim

I did some UV imaging, also solar CaK from a CaK solar telescope. The cover glass of the camera AFAIK isn't a problem (you can start testing with/without if the image is dimmer than it should be). SCT glass elements also aren't a problem (but spherochromatism and spherical aberration is). The most noticeable light loss I had on a Meade 2x TeleXtender versus a fused silica Barlow (fused silica passes UV). You don't need Baader fluorite thingy, but if you already have one... Also with small pixels of ASI290 and f/10 SCT you may be ok with no Barlow (UV isn't very bright so max telescope resolution is hard to use).

As for 400nm on charts - it's common that those start at 400nm and only rarely someone makes them for shorter wavelenghts. Many AR coatings (like those on TeleXtender lenses) cut part or most of the UV below 400nm so vendors just skip what's unusable by them anyway.

olav

Thanks for letting me know what I'm up against, riklaunim.

Good idea, I'll try at f/10 for starters.

So I'll get the filter, not a big thing as I got the rest and Venus is more tempting for each evening to come :)

olav

Hi,

In case anyone has interest.

I asked Baader if the BPFFC Barlow or the C11HD will block too much UV.

The reply:

"since our U Filter is in the near UV it will work with both optics. From 350nm upwards there should be enough light, albeit the C11 will limit (not block) the transmission"

Guess I'll get one and try then.