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gnomus

Atik 460Ex or 383L?

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I no longer use Darks ( !! ). I use a combination of a Bad Pixel Map type calibration in tandem with a Sigma clip.....

...

Dave.

I am very grateful to everyone who has contributed to this thread.  It is proving to be extremely helpful.  

I have heard about a "Bad Pixel Map", but I have no idea how to construct one, or how to use it when processing the data.  Is this something that I do in PixInsight?  Would anyone be able to point me in the right direction to find out more about this - specifically a practical 'how-to' guide? 

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I use Maxim and it will automatically generate a bad pixel map of if you've got an hour to spare you can do it manually :)

Dave

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Harry's Astroshed tutorials covers PI's cosmetic correction procedure for removing hot & cold pixels.  I always use this procedure along with a super bias.  I have latterly used a dark library, but I'm not certain that the results are any better than simply using a super bias (another PI process that creates a 'super' bias from a master bias).

Barry

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Harry's Astroshed tutorials covers PI's cosmetic correction procedure for removing hot & cold pixels.  I always use this procedure along with a super bias.  I have latterly used a dark library, but I'm not certain that the results are any better than simply using a super bias (another PI process that creates a 'super' bias from a master bias).

Barry

I thought I'd watched all of Harry's videos!  I'll head back over there to see if I can find it.  I don't have Maxim DL - I have been using APT with my DSLR and PixInsight for processing.  If I understand correctly, the version of Maxim that I would need (for CCD and filter wheel control) is the 'Pro' version which seems to be a rather bracing £500! 

Edited by gnomus

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I am very grateful to everyone who has contributed to this thread.  It is proving to be extremely helpful.  

I have heard about a "Bad Pixel Map", but I have no idea how to construct one, or how to use it when processing the data.  Is this something that I do in PixInsight?  Would anyone be able to point me in the right direction to find out more about this - specifically a practical 'how-to' guide? 

Most stacking / calibrating software will support a BPM. They are normally created from a dark or stack of darks. As you seem to use PI then read here first - https://pixinsight.com/doc/tools/DefectMap/DefectMap.html  Sorry I can't help that much but I don't use PI.

I also suggest you read here even though you may never use the software - http://www.stark-labs.com/help/nebulositytutorials/files/Processing_HowTo.pdf You can't have too much information eh ? :)

DSS uses a similar technique but with a light. He calls it Cosmetic and it replaces a hot pixel with information surrounding that pixel. 

My own experience tells me that if I use a minimum of 9 subs, I can use SD mask in Maxim to get rid of most visible traces of hot pixels. PI will have a similar thing.

I have found that hot pixels in a 8300 chip are a total non issue.

Dave.

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You need to use a standard deviation based stacking rejection algorithm, like Pixinsight's. Many of the simpler stacking softwares don't do fancy stuff like sigma rejection.

I'm afraid Pixinsight doesn't make any sense to me at all, I have watched 3 demonstrations and didn't have a clue what was going on, so haven't bothered to attempt to lean it as I feel it's not for me especially I am quite happy with Photoshop.  

What I do use is Astroart for stacking, and sometimes I use DSS if AA is having a bad day and won't seem to stack for some reason (don't ask me why).  I use a sigma/kappa sigma stacking method.  

Anyway, I don't have that camera any more, so the problem has gone away. 

Carole 

Edited by carastro

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If I recall, the cosmetic correction procedure is within the Batch Pre Processing tutorial.

Regarding capture software, I use Sequence Generator Pro which at $99 is a real bargain: automated capture, auto meridian flips, plate solving, mosaic creation, auto focus v-curves, off-sets for NB filters and many more features.  It has a growing number of users, a responsive forum, and if you don't need full robotic software (ACP, CCDautopilot) is a very good all-round solution.  There are other good capture suites too, but why not give it a trial?

Barry

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I have both Maxim and Pixinsight. I process in Maxim but want to process in Pixinsight to combine all in one process and I'm also under "Harry's Spell" that Pixinsight's batch processing script gives better results... still learning.

Regards buying Maxim. would I buy it now with the abundance of software available.  Hard to say, I understand it's foibles, the guiding software is fantastic ( I had intermittent issues with PHD and with it being free - I certainly persisted).

If you guide using PHD persevere with Pixinsight's batch processing script and look at ccd commander for CCD control. Now regarding your CCD I have the Atik 460 and I love it. Next year I may part with my QHY 8Pro and invest in the 683 chip. But I won't be selling my 460.

Steve

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I use bad pixel maps/bias rather than darks in Astro Art and prefer the results. To make the BPM you just take a master dark and clip 2000 ADU of the bottom.

Olly

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I use bad pixel maps/bias rather than darks in Astro Art and prefer the results. To make the BPM you just take a master dark and clip 2000 ADU of the bottom.

Olly

Not sure I know what an 'ADU' is.

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Regarding bad pixels, I found the relevant 'Harry' video.  It is this one: http://www.harrysastroshed.com/pixinsight/pixinsight%20video%20files/pix%20videos/pixinsight%20cal%20mp4/pixinsight%20cal%20mp4.mp4

In this he talks about a "defect map" and the "Cosmetic Correction" process in PixInsight.  This begins at 6:30 into the video.  I assume that this is equivalent to "Bad Pixel Map".  ??

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Not sure I know what an 'ADU' is.

Very basically ADUs are the number of electrons collected by a pixel converted to a digital number, so for sixteen bits they go from 0, Black ,to 64K, (65.535) White in ADUs, some other electronic stuff goes on in reading the signal but we don't need to know how that works.

Have a read of this

Dave

http://www.qsimaging.com/blog/understanding-gain-on-a-ccd-camera/

Edited by Davey-T
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I'm still researching this matter.  I had all but settled on the 383L, when I read this thread - http://stargazerslounge.com/topic/185839-another-atik-314-or-460490-thread/?hl=%20atik%20%20383%20%20filters - and discovered this series of posts:

Have to love the FoV of the 383

but not the noise and dark frames  :grin:


Steve

...and not the relatively sluggish response, either.

I don't know if you were thinking of electric filterwheels but, if you were, I'd get a humble manual one instead and up the spend on the camera. The 460 is very attractive, fantastically responsive and smooth. I was processing data from a guest's 460 yesterday. The hot pixel count on his chip was - ah - zero. No columns either. Not like my snowstorm of an 11 meg! Darks or defect maps are no big deal but those Sony chips are easy to love. Check out Rob's comments on his Bubble image.

Olly

I've never used a CCD before, and  hadn't considered the issue of "sluggishness" (indeed, I'm not sure I know exactly what it means).  Would anyone be able to expand upon this?  (I assume that it relates to things like focussing and download times, but I don't really know.)  

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The 383 sensor appears to be the only one of it's size that is affordable, the pixel size may not lend itself to ideal arc secs pixel results and it may be noisy etc and all that is relevant when compared to  other sensors but the only thing physically comparable is a debayered DSLR.

I've been holding off buying a new CCD camera hoping something will turn up that doesn't require a second mortgage but wan't to get something to put on the WO Star 71 before the autumn. 

Sluggish is another thing I wouldn't worry about, I have an Atik 314L that downloads in the blink of an eye and an Atik 4000 that takes over 20secs to download so the bigger the sensor the longer the download on the same computer, maybe someone is working on a USB3 version like a lot of planetary cameras are now.

Dave

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I'm following this with interest as I might be in a similar position later in the year.

Gnomus, "Sluggish" will be download time because of the size of the file. My dslr is sluggish compared to the "breezy" 314's [emoji3]

But that's not a problem just the time it takes to move that amount of data over USB2. Something else I haven't seen mentioned is the mechanical shutter on the 383. Aside from being aware of the "wipe" & treating accordingly are there any other considerations I wonder?

Sent from my iPhone using Tapatalk

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The QSI 683 claims to download in 1sec depending on your computer.

Dave

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That one second is in high speed mode, which you only use for focusing and the like as image quality and noise are more prominent. Normal speed (called "high quality") takes the usual amount of time.

/per

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That one second is in high speed mode, which you only use for focusing and the like as image quality and noise are more prominent. Normal speed (called "high quality") takes the usual amount of time.

/per

I assume that downloading from the 383 shouldn't take any longer than downloading from the DSLR that I am using just now (Canon 600d). I'm very close to deciding that it should be the 383. I've got the 7x36mm EFW 2 coming, and the filters themselves arrived today.

How critical is it to get the space between focal reducer and sensor correct? I think I'm nearly there, but I might be 0.5mm out. Would that be a problem?

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My 683 takes about 12-14 secs to download. the 583 about 23 secs, in normal mode, I never bother with the fast setting, ( I might forget to reset it and screw up subs.)

If you want a flat field then the distance from the rear of the Field Flattener to the CCD chip is reasonably critical. QSI give a dimension of 113.13mm when using the WO TMB Field Flattener. But each bit of glass you insert into the optical train will reduce this distance by an amount dependant upon the Refractive Index of the glass inserted. If you have some adjustment available then trial and error will work either side of the published figure.

The figures that the manufacturers give for the CCD behind the window and its thickness are also not particularly accurate. There is always some deviation from the published figure. I think it is Atik, that on some cameras allow you to tilt the camera to correct for orthogonality to the light path.

Derek

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Remember to adjust backfocus for thickness of the filters. I had the imaging specialist at my equipment supplier help me get the precise backfocus for my rig. This part of the upgrade can be difficult if the correct spacers are not readily available.

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Remember to adjust backfocus for thickness of the filters. I had the imaging specialist at my equipment supplier help me get the precise backfocus for my rig. This part of the upgrade can be difficult if the correct spacers are not readily available.

Martin at FLO said that the spacing should be 55mm, but that I should add 1mm when using filters.

Out of interest, what would happen (what would I notice) if I didn't get this right?

Edited by gnomus

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I won't have the flattener spacing problem with the WO Star71, the problem I have is finding camera with a large sensor and small pixels other than a DSLR, the KAF8300 with 5.4nm pixels is the nearest compromise.

Dave

post-21198-0-25487300-1434997226.png

Edited by Davey-T

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Martin at FLO said that the spacing should be 55mm, but that I should add 1mm when using filters.

Out of interest, what would happen (what would I notice) if I didn't get this right?

When adding a filter into the light path between field flattened and the ccd you shorten the distance, not add distance! The inclusion of a filter reduces the effective optical path length. Very roughly, for a filter you shorten the distance by one third of the filter thickness. This is due to the refractive index of the filter. (One third is for a refractive index of n=1.5 only, but for other values of "n" it must be calculated).

So for an astrodon filter of 3mm thickness remove 1mm approximately. For a Baader filter of 2mm thickness remove 0.66mm and for Astronomik 1mm remove 0.33mm, approximately.

Derek

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When adding a filter into the light path between field flattened and the ccd you shorten the distance, not add distance! The inclusion of a filter reduces the effective optical path length. Very roughly, for a filter you shorten the distance by one third of the filter thickness. This is due to the refractive index of the filter. (One third is for a refractive index of n=1.5 only, but for other values of "n" it must be calculated).

So for an astrodon filter of 3mm thickness remove 1mm approximately. For a Baader filter of 2mm thickness remove 0.66mm and for Astronomik 1mm remove 0.33mm, approximately.

Derek

Thank you for this.  I got the advice in an e-mail, which I have re-read.  That advice was definitely to lengthen (from 55mm to 56mm).  I have the Baader LRGB filters.  I assume it would make sense to stick with Baader if/when I get a set of NB filters in light of this backfocus issue?

Given that I have received conflicting advice, is there somewhere where I can double check the information?  Here's what I have been told:

  • The normal spacing requirement is 55mm.
  • I need to add 1mm I need to reduce this by 0.66mm
  • The 383 has 17mm of back focus (the 460 has 13 mm of backfocus)
  • EFW 2 with M54 to M42 adapter = 23mm
  • M48 to T2 adapter = 10mm

Total length required = 54.33mm

For 383

17mm + 23mm + 10mm = 50mm; so I require a T2 extension tube 4.33mm long.

For 460 

13mm + 23mm + 10mm = 46mm; so I require a T2 extension tube 8.33mm long.

How do I go about finding extension tubes of such odd lengths?

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