wornish

I recently got the HD925 and the ASI290MC.  So far when imaging Jupiter  I find I get more detail when NOT using my 2x Barlow, and staying at the native F11.  But I have learnt from Vlaiv in an earlier post that in non-perfect seeing conditions its best to go for slightly longer exposures of around 6ms to get the best details.  I don't think there is one mathematic ally correct answer as there are so many variables.  Practice and experimentation certainly pays off.

Had another go last night.

This is using 317 gain and 6ms exposure best 5% of 20000 frames.

Think its a bit better but  still not what I hoped for

2 hours ago, Tommohawk said:

Sounds the same as mine - it's the ZWO one marked IR cut, and I can't find the spec for this to check if it cuts UV too- it does seem to work well though.

I did find this though on the ZWO forum. It's dated 2013 so I think ours must be that version - and the graph posted shows that this version cuts UV too.

Hope that helps.

Excellent news.  Yes mine is the one called ZWO IR Cut.   

Update:  The box says IR Cut but just looked at the actual filter and printed on the side it says UV/IR Cut so that's good news.

1 hour ago, vlaiv said:

 

It looks like ASI290 does not have UV/IR cut filter, but simple AR coated window. You should be using proper UV/IR cut filter. Not sure if the one you are using is only IR cut filter but if it is - get proper UV/IR cut filter to filter both UV and IR part of spectrum - both can lower contrast and blur out features.

Thanks for the extra  info.

The filter I have is the ZWO 1.25 IR Cut not the  UV/IR Cut.  I am going have a go with it removed to see if it is contributing to the blurring. 

Depending on the outcome then will get the UV/IR cut as you suggest.

1 hour ago, runoffshed said:

Hi Dave, I am far from being a particularly experienced imager but I wonder how good the focus was to start with?  I was out the other night imaging Mars and had a hell of a job getting decent focus as the seeing was poor and I don't have a remote/electronic focuser so the image was leaping all over the place.  I must have spent about 10 minutes before each run going back and forth trying to nail it.  I probably never did and am going to try a 'Y' mask the next clear night.  Do you use any mask/software to help with focus?

Anyway, just a thought and good luck.

 

John

On my refractor I have an electronic focuser which works great.  But on the HD925 I am using my eyes and manual focussing.  I got the scope specifically to have a go at planetary and lunar imaging and was aware of the focus challenges.  This why I also got the Baader Steeltrack focuser to try and make manual focussing a bit easier.  I use the built in focuser on the back of the scope to get the best focus I can and as you say the image does jump around all over the place when adjusting it that way. But then I use the fine adjustment on the Steeltrack to try and get even sharper focus and using that method the image stays put.  As the scope is new I haven't tried to do any collimation and when I look at a star it seems to be OK.  But I think you might be right getting it spot on is a challenge and not helping.  The focus assistant tool in Firecapture and the one on Sharpcap don't impress me but I haven't really had a serious go using them.

I see the images posted on here and get so frustrated that I can't seem to get anywhere near the level of clear detail they show..  I know some are taken in other countries and that the jetstream is a nightmare in the UK.  But there are people who live in nearby counties to me that seem to be able to just nail the imaging.  It's all part of the challenge and fun and it would be boring if everything just worked:)   I might take the advice posted earlier and get the Atmospheric Disturbance Corrector.  Would like to hear from anyone that's using one if they really do make a difference, ideally with pictures to show an image taken with and without one.

34 minutes ago, vlaiv said:

Exposure length should be as long as possible without loosing ability to do lucky imaging. Maximum exposure time depends on something called coherence length / coherence time for particular location and particular sky conditions.

It depends on seeing cell size vs aperture size used and speed at which these cells move. This is why jet stream is not good - it moves cells at very fast rate thus shortening coherence time extremely.

If one goes with shorter exposure time they are just lowering their SNR without any good reason. Exposure length needs to be long enough to "freeze" the seeing without effects of motion blur which happen when successive cells move over aperture in single exposure. In any case - in most conditions and on most locations 5-6ms is coherence time for 8" aperture. 10ms exposure is reserved for those nights of excellent seeing.

With 1.4ms exposure - you are in effect not gaining anything with respect to lucky imaging, and on the other hand you are increasing your effective read noise at least two fold (1.4ms * 4 = 5.6ms - stacking 4 exposures of 1.4ms is equivalent of capturing single 5.6ms exposure but with x2 read noise)

Only if camera can operate with 700+ fps - which it can't (at least not on 640x480 ROI). USB speed will be limiting factor here.

Zwo website states:

640×480: 184/381.2

as max achievable fps for 640x480 in USB 3.0 version. I would say that real FPS was about 200-250 if 8bit mode was used (due to computer and storage speed). Which means that effective time for each sub was 4ms (again - this shows that you are wasting imaging time if going with short subs). This would put video at two minute duration which is ok, and I would suggest going up to 4 minutes with AS!3 as it can compensate some of rotation with alignment points.

Thanks for explanation.  

I will do at lest a two minute run first and push the exposure time up to 6ms and perhaps drop the gain a touch.  I have tried to keep the histogram at about the 70% mark up till now but I think I will push it towards 90% to see what happens.  If conditions allow I will have a go at a 3 minute run as well.  

One thought could the IR cut filter be affecting the quality of the image? I have seen others say the camera benefits by using one hence I fitted the ZWO one right next to the sensor.

Think I will splash out on the ADC as well.

Managed to have another go these were taken at Gain 317 exposure 4.16ms. ( pushing it to 6  maxes out the histogram and everything seemed to be just white so didn't give it a go)

22000 frames.

Best 5 %,  25%. and 80%

Thanks for your help.  I will re process in AS3 again. 

Think I might've another go tonight as its forecast to be good seeing again and that happens once a blue moon here.

Thanks for the suggestions.

I only used about 8 align points.

I have attached the raw stack as tif file

2020-09-13-1932_1-DT-IR-Jup_ZWO ASI290MC_Gain=401(off)_Exposure=1.4ms_lapl6_ap30.tif

I did increase the image size in PS. The original was 640 x 480

I have attached it here.

I wasn't using a Barlow.  

The details of the file created by FireCapture are:

2020-09-13-1932_1-DT-IR-Jup_ZWO ASI290MC_Gain=401(off)_Exposure=1.4ms.ser

The output info from AS3 was:

ASI290MC_Gain=401(off)_Exposure=1.4ms.ser
  Stack quality 0.00000000 
  Median quality 51.22 ( quantiles 47.68, 51.22, 55.87 )
  Frame count 33703.

The image was a stack of the best 10%.

I did have the ZWO 1.25 IR Cut filter in front of the sensor but that would make things better not worse I hope.

Seeing last night was the best for months, an 8 on the scale from 0 - 10 as published by met check

http://www.metcheck.com/HOBBIES/astronomy_forecast.asp?zipcode=Congleton&locationID=57638&lat=53.2&lon=-2.2

Had another go last night and think I am making progress but I can't seem to get any of the detail others on here do.

This is taken using Firecapture with my ASI290MC on my HD925 best 10% of over 20000 frames stacked in AS3 and Wavelet sharpened in Registax6.

What am I doing wrong

Like you I set up my AZ-EQ6 each time close to my house and do have mains power available.   I use a Skywatcher Powertank 17Ah for short runs to power the mount, dew heaters, cooled camera, focuser and a Raspberry Pi.  With everything full on it for it will last for for about 2 hours. If I want to do a longer run then I use a mains power supply. I got one that provides 12V at 30 amps and is waterproof. I put this in its own plastic box as a double protection against dew as you can never be too careful when mains is around outside.

Me too.  Looks like Sunday might be the next chance🙏

Thanks for this it seems to be exactly what I am looking for!

I have been struggling in poor seeing conditions and starting to worry why I can't get the detail I hoped for on planets.

It's the first time I have heard it called the Nominal Back Focus.  I will read with interest.

11 hours ago, JamesF said:

Yes, I think we could end up in a maze of twisty-turny postings, never quite sure which telescope the comments apply to.  I believe I may be able to offer some enlightenment, @wornish , so if you want to start a new thread I'll be happy to ramble a  bit in that

James

Didn't mean to mess up this topic sorry. Seperate thread started.  

But is it the best possible focus?

What is the back focus figure meant for ? and does it change with the focal length setting?

Starting this as a separate thread as requested.

I am struggling to understand what the published back focus figure for my scope actually means.  According to  Celestron the back focus distance on the Edge HD925 is 146.05mm.

In the base config (pic 1) the distance to the sensor is 80mm and I can achieve focus using the Celestron's main focussing knob.

If I use the Baader fully retracted the sensor distance is 115mm. (Pic 2) Again I can achieve focus by using the main focussing knob on the scope.

So what is the 146.05mm all about? What am I missing?

If I then add a Barlow in to the mix the same thing happens.

Certainly need more info.  

Operating system ? Windows -   XP, 7, 8, 10 ?

PH2 ? do you mean PHD2 ?

What computer are you using ?

I only do astrophotography, no visual, and have recently bought a C9.25 and a a Baader Steel-Track focuser to help with planetary shots.

The focuser is certainly well made and a quality piece of engineering, but it seems to create more issues than it solves. 

The whole back focus definition seems to be a mine field and is driving me crazy at the moment - what does it actually mean?

The main focus knob on the C9.25 moves the backfous well before and after the so called published distance. I really don't understand what's going on!

I guess that to to achieve the published focal length the back focus is as what is published but that does not mean you can't get focus at different distances. - or does it?

I would really like someone to explain ??

Glad you got there in the end.  Have to say stories like this put me off changing to an iOptron mount. 

Excellent images.

What gear did you use?

As said, you need to change the mode in PS to use 16 bit rgb.  Its probably set at 8 bit and that's why you get the banding effect.

One word of caution some filters and plugins for PS only work in 8 bit mode so will be greyed out/ won't work in 16 bit.

I just tried to update mine and it says no updates available - strange.

Great images.

I have the ASI290MC on order from FLO. can't wait to give it a go.

Plus 1 for APP.

It just makes creating Mosaics so easy.