Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Jupiter & GRS, 23-May-19, C14, 7300mm

  • Please log in to reply
6 replies to this topic

#1 Rouzbeh

Rouzbeh

    Vostok 1

  • -----
  • topic starter
  • Posts: 185
  • Joined: 28 Jun 2006

Posted 27 May 2019 - 07:33 AM

Jupiter & GRS, 23-May-19, C14, 7300mm

Using the ASI290mm.

Seeing was all over the place.

 

Attached Thumbnails

  • 2019-05-23 -RGB INFO shrp.jpg

  • Sunspot, Jeffrey C., troyt and 14 others like this

#2 Kokatha man

Kokatha man

    Voyager 1

  • *****
  • Posts: 12454
  • Joined: 13 Sep 2009
  • Loc: "cooker-ta man" downunda...

Posted 27 May 2019 - 07:57 AM

Nicely processed despite the seeing conditions Rouz! waytogo.gif

 

Excuse me if I'm incorrect but it looks like you're using an iR for the r in this one also..?confused1.gif

 

I still think 7300mm is ott except in very good seeing brother, especially for these 2.9um cameras on the C14 - nearly f20.5 - but that's just my personal opinion! ;)



#3 Rouzbeh

Rouzbeh

    Vostok 1

  • -----
  • topic starter
  • Posts: 185
  • Joined: 28 Jun 2006

Posted 27 May 2019 - 08:33 AM

Nicely processed despite the seeing conditions Rouz! waytogo.gif

 

Excuse me if I'm incorrect but it looks like you're using an iR for the r in this one also..?confused1.gif

 

I still think 7300mm is ott except in very good seeing brother, especially for these 2.9um cameras on the C14 - nearly f20.5 - but that's just my personal opinion! wink.gif

Thanks Darryl :) No this one is pure RGB no IR used. Seeing was frustrating but I was up and powered through, not the sharpest image.

 

Its at around 1.85x, I could remove 1 final spacer and it goes down to 1.75x. The Astrophysics page recommends 1.8x for this barlow, perhap I could try 1.75x again.

 

The other option is my 1.45x Siebert but I feel that's too low? looks pretty small. 

 

I see a lot of people use 2x or 2.5x with the 290mm that's got me puzzled confused1.gif

 

Chris Go recommended I go for longer shutter and more histo (over 90%).

 

I'm currently using 3ms shutter speed at 440 gain. Would you recommend slowing it down?

 

Perhaps you could shed some light on this situation  laugh.gif



#4 Kokatha man

Kokatha man

    Voyager 1

  • *****
  • Posts: 12454
  • Joined: 13 Sep 2009
  • Loc: "cooker-ta man" downunda...

Posted 27 May 2019 - 08:39 PM

Apologies bro, the red channel overlaps had me think that was possible but I've had a go at re-aligning your channels & could do no better - Reg6 suggested 1 pixel displacements each way for r&b but made the image no better, which can be the case at times when using manual shifting of all 3 channels in something like AstraImage or R6's "auto align" - you wind up correcting for the central image regions only...seeing can do this in my experience.

 

I'm sorry but I don't have any recent ASI290MM capture data - mine had been playing up for some time & Sam generously replaced it for me: I only have some capture data from 10th April using the new ASI290MM using a short f/l (5000mm) when we were playing with new barlows & different imaging trains.

 

Your "1.85x" is where I got the "f20.5" I mentioned above from the f/l you stated - even extending that "rule of thumb" from 5x to 6x the camera's pixel sizing (2.9um) only means f17.4...hence my belief that you're wanting darn good seeing to justify f20.5. (over 7x the pixel sizing)

 

This is all my own thoughts but not only do I like to drizzle images in processing but I always find beyond a certain scale I found no benefits, only poorer performance outcomes more at the mercy of the seeing whatever night produced.

 

Can't answer for anyone else of course but <"I see a lot of people use 2x or 2.5x with the 290mm that's got me puzzled"> is way ott for a C14 with this camera to me - some folks (like us) have used the Televue 2x barlow but this is only the lens element unscrewed from the chrome barrel & upper black body...used like this you can go down to about 1.25x because only the "telecentric" barlows don't rely on the rest of the barlow as extension tubing to achieve their rated amplification.

 

This is my own opinion of course Rouz but 90%+ histograms are ridiculously high - full stop! Nothing wrong with 3ms exposures if you're achieving around 330fps & of course you then need to apply more gain for any given f/l (which does connect with what I've said here) but striving for histograms that high (90%) is doubly taxing on the gain required! wink.gif

 

No great revelations in what I've said I realise wink.gif but we aim for 55%-60% maximum histograms & once we start getting the type of weather that will allow us to revert to the ASI290MM we'll aim for the 290MM's equivalent of the 6100mm f/l scale we used for the last 2 or 3 capture nights on the 224MC with its 3.75um pixels.

 

Very rough calculations with a fuzzy head says the 5x rule for the ASI224MC equals f18.75 - but the 6100mm f/l we used on a pretty good night on the 22nd equated to f17.16...which is fine from our perspective & how we normally like to capture. (ie, slightly "under" wrt image scale & said "thumb rules") 

 

For the ASI290MM this equates to just under 5000mm f/l (I think! lol.gif ) which is what the April 10th scale was with our new ASI290MM replacement...smaller apparent diameter also then but I would normally aim for around 5800mm with this mono camera. (around f16.5, a bit above the 5x2.9um figure but fine imo)

 

I should add here that I normally "eyeball" the planet's apparent onscreen image size at the start of a session & have our imaging train behind the barlow usually adjustable slightly so that I can make some alterations to scale if I think they're warranted...if I think we can get a sharper image by decreasing the apparent scale somewhat I will & vice-versa - all before slewing to a star to collimate of course! wink.gif


  • Rouzbeh and leoyasu like this

#5 Rouzbeh

Rouzbeh

    Vostok 1

  • -----
  • topic starter
  • Posts: 185
  • Joined: 28 Jun 2006

Posted 28 May 2019 - 11:08 AM

Darryl, excellent feedbackwaytogo.gif Members like you are an asset to the whole community!

 

I usually don't have channel misalignment issues, I believe its from Winjupos as I had to pick subs many minutes apart, most stacked images were useless. It was frustrating because the Meteoblue forecast was 5&4 for seeing, turned out to be cr**.

 

I can reduce to 1.7x, f18.7, 6650mm. With the 2.9micron pixels that's still 6.4 times.

 

I agree 90 to 95% seems abnormally high, I'm usually at 70 to 75% with 3ms shutter it maxes out at 256fps @ 700x700 ROI. Perhaps I'll try to increase the shutter and reduce the gain from 440 to under 400. Drizzle results are always lacking contrast with me, so maybe with a smaller scale and higher SNR things might improve.

 

The next step down is the 1.44x which I may be forced to use and then try drizzle.

 

I have even contemplated going for a bigger aperture allowing lower f ratios. A 16-18 truss Newtonian with a smaller secondary and no corrector to increase brightness.

 

14 Cassegrain (16" like CFF is painfully expensive) at native f17 or f20 and ditch the barlow + corrector. Perhaps GSO will increase the new truss cassegrains to larger sizes, but the secondaries don't look promising so far at 33% and f12 still needs a barlow.



#6 Kokatha man

Kokatha man

    Voyager 1

  • *****
  • Posts: 12454
  • Joined: 13 Sep 2009
  • Loc: "cooker-ta man" downunda...

Posted 28 May 2019 - 08:41 PM

<"I'm usually at 70 to 75% with 3ms shutter it maxes out at 256fps @ 700x700 ROI. Perhaps I'll try to increase the shutter and reduce the gain from 440 to under 400.">

 

The general rule in FireCapture is to try & equalise the "Maximum" frame rate with the "Actual" frame rate as closely as possible Rouz...265fps equates to just under 4ms exposure, so in effect a 3ms exposure means you are robbing yourself of light...which of course means that you are using more gain than required for no benefit whatsoever. wink.gif



#7 Rouzbeh

Rouzbeh

    Vostok 1

  • -----
  • topic starter
  • Posts: 185
  • Joined: 28 Jun 2006

Posted 29 May 2019 - 01:09 PM

<"I'm usually at 70 to 75% with 3ms shutter it maxes out at 256fps @ 700x700 ROI. Perhaps I'll try to increase the shutter and reduce the gain from 440 to under 400.">

 

The general rule in FireCapture is to try & equalise the "Maximum" frame rate with the "Actual" frame rate as closely as possible Rouz...265fps equates to just under 4ms exposure, so in effect a 3ms exposure means you are robbing yourself of light...which of course means that you are using more gain than required for no benefit whatsoever. wink.gif

Yes, I do try to do that usually. I figured with the twitchy seeing, perhaps the shorter shutter time might help "freeze" more.

 

I'll be lowering the F ratio and with that increasing both brightness and ROI. Let see how that increases SNR.




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics