Alternative UV-pass filters for imaging Venus' clouds?

[NenoVento]

Hi all,

As you know, baader, astrodon and idas UV-pass filters, which are the ones used for imaginh Venus' clouds, are quite expensive. However, by searching on the Inertnet for similar (at least by name)  kind of filters, I came across with a possible alternative:

https://es.aliexpress.com/item/32969203564.html

According to the provided transmitance graph, the filter seems to reduce visible light considerably, while leaving UV and some IR to pass:

Honestly, being so cheap, I'm really tempted to try one. Unfortunately, they don't have an M28.5 version that I can directly thread to my cameras or to my 1,25" filter wheel so, in order to find a way to use it, and assuming that being advertised as a 48mm filter it will be able to slide inside a 2" barrel, purchasing the adapters that my scope requires (which, if I am not mistaken, are a SCT female to 2" and a M49 female to M48 male so as to thread the filter into my 2" barlow) will increase the overall costs considerably, reaching to about 26 GBP for the whole set.

What do you think?.

Regards,

NV

 

 

Edited January 15, 2020 by NenoVento

[Thalestris24]

11 hours ago, NenoVento said:

Hi all,

As you know, baader, astrodon and idas UV-pass filters, which are the ones used for imaginh Venus' clouds, are quite expensive. However, by searching on the Inertnet for similar (at least by name)  kind of filters, I came across with a possible alternative:

https://es.aliexpress.com/item/32969203564.html

According to the provided transmitance graph, the filter seems to reduce visible light considerably, while leaving UV and some IR to pass:

Honestly, being so cheap, I'm really tempted to try one. Unfortunately, they don't have an M28.5 version that I can directly thread to my cameras or to my 1,25" filter wheel so, in order to find a way to use it, and assuming that being advertised as a 48mm filter it will be able to slide inside a 2" barrel, purchasing the adapters that my scope requires (which, if I am not mistaken, are a SCT female to 2" and a M49 female to M48 male so as to thread the filter into my 2" barlow) will increase the overall costs considerably, reaching to about 26 GBP for the whole set.

What do you think?.

Regards,

NV

 

 

I bought a 42mm diameter version of one of these but I don't recall doing anything astro with it. A problem is that mono or full spectrum sensors tend to be more sensitive to the near ir than to the violet/near uv. Plus 380nm can still be considered to be in the visible spectrum. Pure UV pass filters are hard to make so that's reflected in their price, plus not so many made because not many people bother with them. Since the zwb ones are cheap, maybe still worth a play if you fancy.

Louise

Edited January 16, 2020 by Thalestris24

[NenoVento]

Thanks @Thalestris24 (Louise) for your comments, yes, 380nm is very close to the visible spectrum (400-700 nm) and also the filter seems to have an IR window (that reach to about 30%) overlapping the 700 nm zone... I guess that it won't probably work with Venus, or at least not in the way that the baader and the rest do. However, since you have one of them, maybe you could give it a go 😉.

Although the ZWB filters are indeed cheap, in my case, since I have to get two adapters (at least for the M49 one, I haven't found an M42 one), their added costs makes this a rather pricey experiment for me to pursue right now, really...

Best regards,

NV

Edited January 16, 2020 by NenoVento
typos

[Thalestris24]

50 minutes ago, NenoVento said:

Thanks @Thalestris24 (Louise) for your comments, yes, 380nm is very close to the visible spectrum (400-700 nm) and also the filter seems to have an IR window (that reach to about 30%) overlapping the 700 nm zone... I guess that it won't probably work with Venus, or at least not in the way that the baader and the rest do. However, since you have one of them, maybe you could give it a go 😉.

Although the ZWB filters are indeed cheap, in my case, since I have to get two adapters (at least for the M49 one, I haven't found an M42 one), their added costs makes this a rather pricey experiment for me to pursue right now, really...

Best regards,

NV

Hi

To be honest I can tell it wouldn't be very useful from the transmission spectrum. The visible (violet) and near ir it lets through would drown out the uv. I'm afraid I don't do planetary and have no view of Venus anyway.

Cheers

Louise

[vlaiv]

What camera are you going to use it with?

Both color and mono planetary cameras that don't have UV/IR cut filters are quite sensitive in IR part of spectrum - and that light is going to swamp your sensor and reduce contrast.

If you are going to try ZWB1 filter for UV then I suggest combining it with wratten #38A dark blue filter. This is going to reduce transmission significantly but it will eliminate IR pollution completely.

As you can see from the graph - this filter eliminates everything above 620nm and above ZWB1 passes IR above 660nm. Problem is of course that UV part of spectrum is also reduced to less than 30% with this filter.

This was just a quick search - maybe there is another affordable filter that will do the same trick and not reduce UV that much.

Other than that, if you want cheapest pure UV filter - maybe look at photometric filters instead?

https://www.teleskop-express.de/shop/product_info.php/info/p7021_Baader-1-25--photometric-filter---U-Filter.html

It has about 60% peak transmission - but same spectral range of about 300-400nm.

[NenoVento]

Hi @Thalestris24 (Louise).

I agree with your assesment on this issue and won't pursue it any further. Thanks a million! 😀.

NV

[NenoVento]

Thanks for your comments @vlaiv . The #38A dark blue filter does look interesting and quite afordable, but if you add its cost together with the ZWB1 and the adapters, the high risk of failure for this experiment makes it too expensive, at least for me.

Best regards,

NV

PS: If I am not mistaken, the cost of these photometric filters are slightly cheaper than the IDAS UV-Pass filter.