Venus with Astromania UV filter

[Cosmic Geoff]

I received the Astromania budget 3-filter set today and this evening tried it out with my 127mm Mak.  Full setup:  127mm Celestron Mak,  Circle T prism diagonal, filter wheel, ADC, ASI462MC.  Video of 2000 frames.

I found that the exposure time with the UV filter was astoundingly long at around 460ms (2.4 frames/sec. 

Compare with visual band: 0.2ms, IR 0.4ms, and just for comparison, not imaged: OIII 7.8ms, methane 7.8ms.

I wonder if it is the UV filter or the sundry other components that causes the low sensitivity.   The ASI462MC camera is probably not ideal for this role but I expected better.

 

Edited June 15, 2023 by Cosmic Geoff

[Ibbo!]

My experience this time round

My SCT does not work think it is the corrector plate, I think the MaK glass will block.

Camera has to be able to be sensitive to the IR/UV definitely no blocking IR/UV which is fairly standard I believe, check the camera specs. My ZWO 178 is not sensitive to IR/UV as far as my results show.

Some barlows are more suited than others ,simple ones are recommended.

I managed to get a QHY5 462 mono (colour does sort of work) and I borrowed a 200 mm reflector and have got to go through all the capture data but in the first near in focus avi  run I had stucture in the cloud tops, but do yourself a favour and get a motor focus set up.

 

I got results a few years ago with the RC and a point grey chamleon cam, which must have been sensitive in the bands needed.

I am sure those that have done more with Venus will chip in later.

 

[Cosmic Geoff]

Some digging reveals that the ASI462MC  could have a relative response of 0.1 to 0.2 in the near UV,  the other (more expensive) UV pass filters have a relative response of 80% at around 320-380nm, and as for optical glass, it varies.  Some pass near UV while others act as an effective UV-cut filter.

Seeing the curves, one wonders why anybody would want to spend money on a UV-cut filter for any gear with glass elements...

[Kon]

I am not sure the Astromania filter is the issue here. I have been using it for all my Venus captures. Have a look at this link which summons my captures from March to June this year.(https://stargazerslounge.com/topic/410783-venus-from-march-to-june-2023/#comment-4388478). 

I had issues with the 462mc and their filter as it was giving me ghosting effects, not sure why. I then moved to 462mm and the ghosting went. With my 8" Dob, I can get 3ms at 300fps with a gain of ~80% with the 462mm. I found that capturing during daylight was the best for what I was doing but Stuart @Space Cowboy has some excellent images with the 462m at dusk (different filter but similar features to the Astromania).

Neil @neil phillipsis using the 178 and he is also pulling amazing UV captures (I think he has the same filter as Stuart).

Although I am not an expert on setups, looking at your imaging train there is a lot of glass there and I agree with @Ibbo! that it is likely the telescope than the filter/camera (no need for the ADC as your are effectively using the camera as mono with the filters). Yes 462mc is not great but I have got faint details on it before but I did have to up the exposure to 15ms.

QE seems to drop to around 30% for asi462mc and 80% for 462mm.

 

[Space Cowboy]

As Kon says the filter is not the issue it's the scope that's very unsuitable for UV imaging. Even a  5" Newtonian would struggle. You might have a chance of some detail with a 462 mono but I wouldn't bet on it. I've seen good UV detail using the 462 colour cam but only with a much larger scope.

[Cosmic Geoff]

Kon - your series of images looks great.

It seems that my Astromania filter is not the problem. I will try eliminating glass (eg prism diagonal & ADC) from the optical path of my Mak and 8" SCT  and see if that helps at all.

Edited June 16, 2023 by Cosmic Geoff

[Cosmic Geoff]

My experiments indicate that eliminating the prism diagonal and the ADC has some beneficial effect on the UV exposure rate.  I also found indications that the time of day (altitude) had a significant effect.

To support the latter, charts indicate some attenuation of UVA at zenith, and if one looks up "air mass coefficient" it can be seen that the path through the air increases with increasing zenith distance.  At least one Venus imager reported improved results with daytime imaging.

[Pete Presland]

Venus is a tough target, even when you have big aperture and a mono camera. The phase is showing quite nicely though.

I think my corrector plate blocks some of the signal, but obviously i have nearly twice your aperture. 

What time did you capture at?

[Cosmic Geoff]

14 hours ago, Pete Presland said:

I think my corrector plate blocks some of the signal, but obviously i have nearly twice your aperture. 

What time did you capture at?

Image above captured on 15th at 20:58 to 21:13 UT, exposure 425ms. (127mm Mak)

A test with the same kit the next afternoon, with Venus near the meridian, gave an exposure of ~35ms, and without the diagonal and ADC more like 9.4ms (times so much shorter that I thought something had gone wrong somewhere).

A test the same evening, with a 203mm SCT at around 21:30  UT and  thin cloud about, gave an exposure time of ~900 ms, without diagonal or ADC, so clearly not worth trying to take an image video.

I would like to try again with Venus near the meridian, but conditions have not been suitable, and I also need a means of aligning the SCT in daylight.

[Cosmic Geoff]

Another trial effort with my 127mm Mak, ASI462MC, and Astromania UV filter and other filters.

I got a UV image in mid-afternoon with an exposure of around 7ms and a satisfactory frame rate.  These are all from a 5000 frame video, cropped and centered in PIPP.  Visual exposure time ~0.06ms, IR exposure time ~0.15ms, so the UV exposure is 100 or 50 times longer.

While I got an UV image, it isn't very good.  The sky background was much brighter on the laptop screen than it appears here.

Interesting discussion here: https://www.cloudynights.com/topic/849249-are-newts-better-uvch4-planetary-imagers/

Among other things, a Classic Cassegrain should work well, and blue filters might show something if your scope has glass.

Bad news on this topic for SCT owners: https://www.researchgate.net/figure/Transmission-for-an-8-Celestron-SCT-Schmidt-corrector-plate-coated-with-Celestrons_fig3_241553344#:~:text=In-house transmissivity tests on a modern Celestron 8",H and J-bands was about 74% on average.  Steep dropoff below 400nm.

 

Edited June 22, 2023 by Cosmic Geoff
Added links

[ursamajorro]

With my Mak127 I never managed to capture Venus's clouds (or other). That's why I bought a C6 (keeping the weight target under 5 kg) and I'm satisfies by the results.

 

 See my posts starting from 4 June.  Usinng #47 filter I have 7 ms exposure and 225 gain. 460 ms seems huge for me.

[Cosmic Geoff]

Today I finally was able to make the trial on Venus I wanted to do a while ago, but was frustrated by clouds.  I took some images with Venus at its greatest height in the afternoon, with a SCT.

CPC800, filter wheel, Astromania UV filter, ZWO IR-cut, ZWO IR pass filter, ASI462MC

UV exposure 5.8ms, visible exposure 0.032ms, IR exposure 0.112 ms.   Note that the UV exposure is 180x the visible-band exposure.

While an exposure of 5.8 ms wouldn't be so bad for imaging Saturn at night, the result here was dismal.  The IR image turned out the best.  The SCT apparently does not perform better than my Mak in UV.

 

[Cosmic Geoff]

Today I tried another experiment I had been wanting to try but had been prevented by clouds.  At around 8pm I exposed the ASI462 camera to some blue evening sky, via the filter wheel but without a telescope, to measure the relative response through various filters., using Sharpcap Histogram. 

Taking the exposure time with the UV/IR cut filter as 1, the exposures with the UV filter was x72 and with the IR-pass filter x2.9.

So what can one conclude from this?  It seems that the long exposure with UV is caused by the low relative response of the camera and/or there not being much UV in the first place.   There is probably some UV cut in the Mak and SCT previously used but it is not clear how much.

[Kon]

2 hours ago, Cosmic Geoff said:

Today I tried another experiment I had been wanting to try but had been prevented by clouds.  At around 8pm I exposed the ASI462 camera to some blue evening sky, via the filter wheel but without a telescope, to measure the relative response through various filters., using Sharpcap Histogram. 

Taking the exposure time with the UV/IR cut filter as 1, the exposures with the UV filter was x72 and with the IR-pass filter x2.9.

So what can one conclude from this?  It seems that the long exposure with UV is caused by the low relative response of the camera and/or there not being much UV in the first place.   There is probably some UV cut in the Mak and SCT previously used but it is not clear how much.

When I initially tried my 462mc with the same filter, I had the ghosting and couldn't pull any details. It is a lot less sensitive to UV than my 462mm. I have not used it since I went mono. Someone was getting really nice images with the 462mc and a #47/ir block filter so it's not completely unresponsive. 8pm is getting quite low on horizon and it will lose more signal. Have you tried daylight, 6-7?

Edited July 12, 2023 by Kon

[Nik271]

11 hours ago, Cosmic Geoff said:

Today I tried another experiment I had been wanting to try but had been prevented by clouds.  At around 8pm I exposed the ASI462 camera to some blue evening sky, via the filter wheel but without a telescope, to measure the relative response through various filters., using Sharpcap Histogram. 

Taking the exposure time with the UV/IR cut filter as 1, the exposures with the UV filter was x72 and with the IR-pass filter x2.9.

So what can one conclude from this?  It seems that the long exposure with UV is caused by the low relative response of the camera and/or there not being much UV in the first place.   There is probably some UV cut in the Mak and SCT previously used but it is not clear how much.

I believe it is the thick corrector plate of the Mak which blocks a lot of the UV. Reflectors are better suited, as glass naturally blocks much of the near UV.

[Cosmic Geoff]

11 hours ago, Kon said:

Someone was getting really nice images with the 462mc and a #47/ir block filter so it's not completely unresponsive. 8pm is getting quite low on horizon and it will lose more signal. Have you tried daylight, 6-7?

Edited 11 hours ago by Kon

I made the observations (images) on 7 July above at around 4pm with Venus at its highest.   I could try yesterday's experiment again with the Sun near the meridian. 

I suspect that  OSC camera response divided by corrector plate attenuation results in a major loss of UV signal.

I am thinking of trying a Blue filter next time I get the chance.