altair 26c bit underwhelmed! or is it me?

[Rob20236]

hi all. just purchased an altair 26c after seeing many impressive images form either the 26c or 2600 mc with same sensor. but after a few imaging sessions im left a bit underwhelmed. upgraded from a altair 183c protec  paired to a william optics gt71  with a .8 recucer\flattener also with the altair 7nm dual band filter all on a neq6 pro.

after my first session with 300 second exposures and being not very impressed with the 26c i done a sharpcap sensor analysis with results attached. full well capacity showing just under 3k from stated value but no problem. ran another session this time using the optimal exposure calculator in n.i.n.a so this time ran 180second exposures. still not overly impressed.

ive  stacked but not  processed  2 of the 5 sessions sessions so far and  with comparible intergration time to the 183c on the same target again left feeling a bit under whelmed  . i may well be jumping the gun but after 5 sessions  looking at single lights compared to the 183c, the 26c seems more "noisey".

once again it may be just me or something im doing or not.

but any way please find attached 2 images from my 26c, 1 at 180sec and 1 at 300 sec with 1 image from my 183c at 300sec, also my sharpcap analysis.

thank you in advance for any advice\help

2022-06-16_01-18-11__-10.00_300.00s_0003.fits 2022-06-22_00-43-25__-10.10_180.00s_0001.fits 2022-05-29_02-49-09__-9.80_300.00s_0004.fits aa 26c.txt

Edited June 22, 2022 by Rob20236
corrections

[mackiedlm]

I moved from DSLR to ASI2600mc just over a year ago and I am honest when I say that I am still blown away by the quality of the images the 2600mc produces. So my immediate advice would be to not write it off at this stage. I think that you will eventually be impressed with the camera.

What gain and offset are the 26 c images above taken at.

 

I have looked at all your the images in Pixinsight and compared them to a very recent single frame taken with my 2600mc, SW 80ED, L-enhance gain 100. - so similar coditions but slightly longer FL (I've attached that frame here so you can look at it). Now I'm not someone who can do the fancy anaytical stuff in pixinsight so i'm just eyeballing them and I note the following. 

1. your 26 c does "look" noisier than your 183c - but you need to remember that there is a difference in pixel size and that could be part of what we are seeing.

2. your 26 c image looks similar to my 2600 mc image

3. your and my images were taken under less than perfect conditions - mines was only 2 weeks from longest day at 53N so hardly even dark

I've also attached my final version from that imaging session which ended up as only 2 hours total integration. While its not an award winner, i think that considering its only 2 hours in astro twighlight, its an indication of what the IMX571 sensor can produce under difficult conditions.

So I guess I'd be saying dont panic at this stage. Get some time on target, process it out and I will be very surprised if at the end you ar still not happy with it.

Good luck

 

PLANSHORT_L_IMGID_2329_OBJNAME_M16_GAIN_G100_EXP_180s_EXIF__-10C.fit

Edited June 23, 2022 by mackiedlm

[Rob20236]

thank you for your reply. the more i look into it i do think i am jumping the gun. as you say the pixel size is different an the resolution is higher so im looking at smaller compressed image on my monitor. and yes i think one session was taken on the longest day. which is why im using the 7nm dual band filter even in my bortle 4 area. also my viewing is pretty east limited and lately the clear nights have been during full or nearly full moon.

also im right now stacking about 7 hours of data so ill see how that turns out.

more patience required.

thank you again

[Rob20236]

mackiedlm, comparing the single frame to yours the overall look and "noise" looks the same but im noticing a lot more green and red random spots in my image. im using the same gain as you at 100 but my offset is at 60 rather than 50. same at -10 c. have no idea what they may be but hopefuly wil be removed in processing with calibration frames.

would be good to compare with any other imx 571 users if any kind people out there would mind sharing single frames.

i apologise if i sound like im whinging. and maybe in a way i am. but this kit costs us all a lot and when you finally get your dream camera id just like to make sure all is good or maybe i just need more help learning. which places like this help a hell of a lot.

so thank you all

Edited June 23, 2022 by Rob20236

[tomato]

As requested, here are a couple of single 3 minute RGB subs, cameras at -20 C, taken last year with an Esprit 150 in Astro darkness, Bortle 5/6 location.

The first is a QHY268c, the second is a RisingCam IMX571c, which I think is essentially the same as the Altair version.

I agree with the previous posts, in that I don’t think you will be disappointed with the camera once you have some experience of using it under better sky conditions.

I’m currently imaging under light skies with these cameras and ‘fast’ optics, I’m frankly amazed at what level of detail can be captured with minimal integration times under these conditions.

QHY268c, Gain 30, Offset 30

RisingCam IMX571c, Gain 100, Offset 10

 

[Rob20236]

thank you . literally just finished stacking my data and while the red and green dots have indeed been removed  does anyone think there should be any concern to them in the showing in the single subs?

oh an heres a preview of my stacked image

[Richard_]

8 minutes ago, Rob20236 said:

thank you . literally just finished stacking my data and while the red and green dots have indeed been removed  does anyone think there should be any concern to them in the showing in the single subs?

oh an heres a preview of my stacked image

Depending on how many you have, it's not a problem at all. If you dither during imaging and stack using a rejection algorithm like sigma clipping, you can eliminate these entirely. 

[david_taurus83]

4 hours ago, Rob20236 said:

 im using the same gain as you at 100 but my offset is at 60 rather than 50. same at -10 c. 

I'm pretty sure that 100 gain on the Altair camera will not be the same as that of a ZWO or QHY version so you can't use that as a comparison. Can you post up a screenshot of your sensor analysis results?

[Richard_]

Below is a tabulated version of the sensor analysis taken from OP's text file. 

Highlighted in orange is the Gain you chose (100). However, the Gain you should be using is highlighted in blue (200).

The tell tale sign is the sudden drop in Read Noise and the increase in Dynamic Range. If you use a Gain of 200 with your camera, your images will have about one third of the read noise compared to images taken with Gain 100.

[david_taurus83]

19 minutes ago, Richard_ said:

Below is a tabulated version of the sensor analysis taken from OP's text file. 

Highlighted in orange is the Gain you chose (100). However, the Gain you should be using is highlighted in blue (200).

The tell tale sign is the sudden drop in Read Noise and the increase in Dynamic Range. If you use a Gain of 200 with your camera, your images will have about one third of the read noise compared to images taken with Gain 100.

Ah, I didn't see the txt file. Yes, that's what I was getting at. These cameras have a low gain and high gain threshold where the read noise drops. Also, Sharpcap gain might not be the same as NINA gain etc

https://forums.sharpcap.co.uk/viewtopic.php?t=4633

 

[Rob20236]

8 hours ago, Richard_ said:

Below is a tabulated version of the sensor analysis taken from OP's text file. 

Highlighted in orange is the Gain you chose (100). However, the Gain you should be using is highlighted in blue (200).

The tell tale sign is the sudden drop in Read Noise and the increase in Dynamic Range. If you use a Gain of 200 with your camera, your images will have about one third of the read noise compared to images taken with Gain 100.

thank you so much ill give that a try next clear night. allways learning and allways somone here willing to teach.

and while im her if i may ask for more help. as my final image come out so red looking and i have been struggling a bit in post processing, is that down to my filter im using? do i need to adjust white balance or black levels? even though i cant seem to find the option to do that in nina?

thank you in advance

Edited June 24, 2022 by Rob20236

[Budgie1]

1 hour ago, Rob20236 said:

and while im her if i may ask for more help. as my final image come out so red looking and i have been struggling a bit in post processing, is that down to my filter im using? do i need to adjust white balance or black levels? even though i cant seem to find the option to do that in nina?

thank you in advance

The red will be due to the dual-band filter you're using.

Normally you wouldn't use a dual-band filter for galaxies or planetary nebula, these are more broadband objects and only need a UV/IR cut or LP filter. Although adding images taken with a dual-band filter to those taken without may enhance any Ha data in the target, but I have tried it and I'd imaging you'd have to be careful not to over do the red in processing.

Where you would use the dual-band filter is when imaging emission nebula with strong Ha & Oiii signals, the Veil Nebula is a prime example.  

[Richard_]

3 hours ago, Rob20236 said:

thank you so much ill give that a try next clear night. allways learning and allways somone here willing to teach.

and while im her if i may ask for more help. as my final image come out so red looking and i have been struggling a bit in post processing, is that down to my filter im using? do i need to adjust white balance or black levels? even though i cant seem to find the option to do that in nina?

thank you in advance

As @Budgie1 mentioned, dual bandpass filters are perfect for Hydrogen Alpha and Oxygen rich targets (such as emission nebula). Galaxies emit light virtually across the whole spectrum of light and are reffered as 'broadband' targets. You could just use a UV-IR filter here to cut out IR and UV wavelengths which is important, as IR signal can sometimes cause your stars to bloat in size (I notice this with my refractor and ASI533MC-Pro camera). 

It makes sense that your image of M31 has a red hue to it, as this represents a strong signal from H-alpha in the red channel whilst there is very little Oxygen being picked up in the blue/green channel. Some clever people take images of galaxies in colour (RGB), then image with a H-alpha filter (or take the Red channel from a dual bandpass filter) and add this to colour image. This would be called HaRGB which makes the red H-alpha "pop" in the colour image. Here's an example of NGC 1300 with HaRGB (note: this image was created with Hubble data, not amateur back garden astro equipment!). Notice how well that red pops! 

https://www.astrobin.com/f8tzww/?q=Hargb

Edited June 24, 2022 by Richard_

[Rob20236]

thank you all again.

sorry to ask again for help, but right now im redoing my darks library and ive noticed these like checkerboard patterns with light parts to the image. before changing gain to 200 it would probably only do it on the first image but now im doing 180second and 300 second frames and its showing up in probably every  other image. or mabey 3 or 4 in a row. seems random. ive just lost half my darks to it.

anyone have any ideas please.?

thank you again in advance

2022-06-24_21-03-53__-9.50_180.00s_0012.fits

Edited June 24, 2022 by Rob20236

[Budgie1]

How are you taking your darks? Is the camera still on the scope with the lens cap on or have you removed the camera from the scope and put the cap over the sensor?

The second way is better because it reduces the likelihood of light-leaks, although I'm not sure that's what you've got on that single dark.

[Rob20236]

camera still on scope with cap on. all ive changed is the gain, from 100 to 200. it was happening before on gain 100 but only usually on the first frame. wether it be lights or darks. now it just seems to be happening at random and more often.

thank you 

Edited June 25, 2022 by Rob20236

[mackiedlm]

On 24/06/2022 at 22:09, Rob20236 said:

thank you all again.

sorry to ask again for help, but right now im redoing my darks library and ive noticed these like checkerboard patterns with light parts to the image. before changing gain to 200 it would probably only do it on the first image but now im doing 180second and 300 second frames and its showing up in probably every  other image. or mabey 3 or 4 in a row. seems random. ive just lost half my darks to it.

anyone have any ideas please.?

thank you again in advance

2022-06-24_21-03-53__-9.50_180.00s_0012.fits 49.49 MB · 7 downloads

Can you share one of the darks that dont show this pattern. And also one of your good darks at gain 100.

Also, what capture software are you using?

 

 

[Rob20236]

i use nina with altair selected ,not ascom driver. i used sharpcap to do sensor analysis which is in original post.

heres  a "good" dark at 100 gain 60 offset

thank you for any help

2022-06-21_21-45-26__-11.00_180.00s_0000.fits

[mackiedlm]

I wanted to see that just to confirm that there was nothing going wrong with frames that initially seemed good. And it looks fine.

So this is, as you said, an intermittent problem where some frames are showing this checkerboard. Its not light leak as one frame is good and the next can be bad. That suggests to me some sort of communication issue. I'd suggest the following,

• Confirm you have all the most recent drivers and update as necessary. thats both the drivers directly from Altair and then any updates/drivers in Nina. (With ASI and APT I need to ensure both driver sets are in place otherwise things go strange very quickly)
• Download and try captures with the Altair capture software (download from Altair website) This will remove Nina from the mix just to help diagnose.
• If that still shows the issue then go though a systematic check of all cables (dodgy USB's can have strange effects), remove any usb hubs, check that the power supply (I believe Altair provide one with the camera) is correct and functioning. I dont know Nina or Altair but in APT there is a way to adjust the speed of the USB connection, try adjusting that, try a USB2 connection if you are currently using USB3 as USB3 can sometimes be unstable with AP cameras.

If none of that works then I think you need to get in touch with Altair support.

Good luck and do get back to us here when you work it out.

[Rob20236]

Thank you again mackiedlm and everyone else.

i will give all cables a check. i did update the altair drivers after first seeing this issue, with no change. nina is latest version (non nightlies), all i can think of is it did show up more after Richard_  recommended using 200 gain looking at my sharpcap analysis. (thank you), but  i did get a quick 2.5 hour session on andromeda last night and a look throught the subs they all look good . so fingers crossed. also with no filter this time (thank you Budgie1)

also i did fire off a ticket to altair and they ran a comparison against another 26c and said mine looked ok ,so that put my mind at rest a bit (thank you altair) ,they  havent got back  to me yet about the other  intermittent issue ,but again fingers crossed it could just be a communication issue somewhere and thats to me to figure out. and learn how to use and love this camera more.

i will say im getting some good data on andromeda now. learning more each time with help from people here, so heres a peak at my latest attempt. it may not be to everones taste but as im also learning processing and experimenting at the same time. heres my latest experiment. well i like it

thank you again all 

[ONIKKINEN]

23 hours ago, Rob20236 said:

i use nina with altair selected ,not ascom driver. i used sharpcap to do sensor analysis which is in original post.

heres  a "good" dark at 100 gain 60 offset

thank you for any help

2022-06-21_21-45-26__-11.00_180.00s_0000.fits 49.49 MB · 4 downloads

There are pixels with a value of 0 in this dark, which is an issue for calibration as you cant divide or multiply by 0. How big of an issue? Probably not that big, but offset should be increased anyway. There are practically no downsides to having an offset of 500-1000 ADUs with this model of camera as the full well depth is plenty large enough.

Its just a hunch, but it might have something to do with weird patterns, as the sensor probably has some consistency to its readout pattern as to where the cold pixels are situated, and in your case they are clipped to 0.

Below is a screenshot of the histogram, the left edge is abruptly cut off when in reality it should continue as the right edge does.

Edited June 28, 2022 by ONIKKINEN
Added histogram

[Rob20236]

23 hours ago, ONIKKINEN said:

There are pixels with a value of 0 in this dark, which is an issue for calibration as you cant divide or multiply by 0. How big of an issue? Probably not that big, but offset should be increased anyway. There are practically no downsides to having an offset of 500-1000 ADUs with this model of camera as the full well depth is plenty large enough.

Its just a hunch, but it might have something to do with weird patterns, as the sensor probably has some consistency to its readout pattern as to where the cold pixels are situated, and in your case they are clipped to 0.

Below is a screenshot of the histogram, the left edge is abruptly cut off when in reality it should continue as the right edge does.

thank you. so should i keep adjusting offset and checking histogram until the left edge is no longer cut off? start with 100 and go from there?

thank you again

[ONIKKINEN]

9 minutes ago, Rob20236 said:

thank you. so should i keep adjusting offset and checking histogram until the left edge is no longer cut off? start with 100 and go from there?

thank you again

You have enough offset when you dont get any 0 value pixels in the frame. I just used siril and checked the statistics of the frame and it reported the minimum value as 0. Increase the offset until the minimum pixel value is anything but 0, but remember to check this on the gain values that you are going to use the camera in.

In my Rising cam (ToupTek made, as is the Altair) at a gain value of 100 (corresponds to your 200) i need an offset of at least 500 or there will be 0 - value pixels, but since the default in mine was 768 i just left it at there. Your mileage may vary but the 60 offset definitely looks too low.

[Rob20236]

hows this one looking? i adjusted in increments of 50 until the left edge wasnt cut off at offset 300 (in nina).

as this was only a 5 second sub. will i need to adjust down as the xxposure length increases?

this is all becoming very interesting. love the learning as much as i love the imaging and processing. but the technical side and the knowlege of people here is amazing.

think i should change the title header to "overwhelmed"

thank you

2022-06-29_22-19-58__23.50_5.00s_0000.fits

Edited June 29, 2022 by Rob20236

[ONIKKINEN]

3 minutes ago, Rob20236 said:

hows this one looking? i adjusted in increments of 50 until the left edge wasnt cut off at off set 300 (in nina).

as this was only a 5 second sub. will i need to adjust down as the xxposure length increases?

thank you

2022-06-29_22-19-58__23.50_5.00s_0000.fits 49.49 MB · 0 downloads

Still at 0. Try 700?

Also, better to take a bias frame or the shortest exposure possible. Try 0.00001 or something as the exposure time.