Venus April 8th RGB

[Tommohawk]

Got set up in plenty of time ... but whilst trying to manually align Venus I nudged the laptop FTDI control cable and disconnected Stellarium and had to reconnect, then park then restart. Always has to be a bit of fun in every session!

Used unity gain with ASI290 and for 75% histo I got insanely short exposures all less then 1 millisecond, giving frame rates of around 380 fps. Bonkers, and probably not necessary, especially when I realised that after 3 runs of 3 x 60s RGB seequences I'd used 120Gb of drive!

So - lots of frames to play with ... but still no real detail in the image. I put everything through PIPP, kept best 15% which  then went into AS!3 and used 20% of that - so  best 3%. Registax wasn't really giving anything, so bit of sharpening and colour enhance in PS. and that's it. I think I need one of those fancy UV jobbies!

This was with the trusty SW200 (and 5x powermate) which in the past has given planetary images pretty much equal to the C9.25 and OMC200 which I've previously owned. 

Edited April 9, 2020 by Tommohawk

[CraigT82]

Great image scale there.. shows some real promise. Buy a UV filter you wont regret it! 

[Tommohawk]

Just now, CraigT82 said:

Great image scale there.. shows some real promise. Buy a UV filter you wont regret it! 

Yeah I looked at your Venus images and and was kind of envious!

[Tommohawk]

Craig, is most of the detail in the UV, or is there anything much in IR? As it happens the IR filter is relatively inexpensive but I'm out of slots in the filter wheel. 

Thanks!

[CraigT82]

It's pretty much all in UV. There is detail to be had in near IR (700nm to 900nm ish) which relates to base of the upper clouds, as opposed to the very cloud tops which are shown in UV, but this requires larger apertures: most detailed IR images I've seen have been done with C14s and the like.  I've tried a few times with a ZWO 850nm but havent seen anything yet. 

Edit: After some googling I've found a few images showing cloud detail using 742nm and a 10" newt, and a couple more done with a C9.25. I'm going to keep trying! 

Edited April 10, 2020 by CraigT82

[Tommohawk]

OK brilliant thanks for that - I think I'll lash out on a UV filter. Shame I didn't think that through sooner though with all this clear weather we're having!  

[Tommohawk]

BTW have you  any idea how fast the cloud patterns change? Rotation speed for Venus is slow, but maybe the clouds move faster?

[CraigT82]

Yes the cloud tops circumnavigate the globe every 4 days or so. 

As far as UV filters go I've been using the Baader U venus filter and am very happy with it, but I've seen good results with a wratten 47 (paired with an IR block as there is IR leak with this filter). 

[Tommohawk]

4 days - OK so still pretty slow. I can do my usual routine of 3x3 60s sets taking 27 mins and either separate them out or use the whole lot withou worrying about derotation then.

I've taken a punt and ordered the Optolong UV / Venus filter. (Its a £££ thing) It has a tiny IR leak at 875nm but only about 3% - if the transmission graph is accurate. I have an IR blocker so could always screw than in the train if its an issue. I saw an indy review here which suggests its OK.

Hopefully I can post test results back here soon.... dont hold your breath!

BTW one other thing - I found some difficulty keeping the whole image in focus. With the bright limb focused the lower part of the crescent seemed slightly "doubled". I can see this on other images, so its not just me. Maybe atmospheric? But at 35 - 40 degrees elevation would hope thats not too bad. Any thoughts?

[CraigT82]

That's great, looking forward to seeing the first UV results! 

I know what you mean about focusing and the double cusps you see. I think it is just atmospheric as opposed to something wrong with the focus. It doesn't seem to cause a problem for me as the soft limb/cusps can be tightened up in post process 

[Pete Presland]

The phase is showing very nicely there, it will be interesting to see your results with the new optplong filter.

[Tommohawk]

Hi Pete - thanks for the comment. 

Well I had a dabble with the UV filter last night - not very successfully!!! I'll post the image on a new thread as it has a slightly different topic header.

Edit - no new topic after all as the image was unpostably (real word?) bad.

Edited April 27, 2020 by Tommohawk