Horizon monochrome and C-14 Hyperstar

[Altouch]

I have been playing with a Horizon I monochrome camera on a CGE-1400 Fastar.  Nice f/2 imaging providing 1.5x1 degree field of view. I am using Atik Infinity to capture images. I have had it about a month and getting nice images. Anyone else doing this?  Any experiences learned that should be shared?  One question/observation I have is regarding a fairly smooth gradient in the flat field from top to bottom. The top is darker than the bottom (accentuated by the automatic stretch applied). Is this unusual?

[Crooro]

Can you post a photo to see !?

Surely in the recovery phase it is necessary to avoid
to shoot too low on the horizon, close to the Moon and in general from observation sites with
high light pollution. Alternatively, the use of narrow band filters (for example H-alpha)
it can help a lot. If the footage is not for scientific purposes and only after correcting
vignetting and electronic noise respectively with flat field and dark frame, you can use the
"remove gradient" function present in all image processing software. If the
nature is electronic, attention must be paid to calibration images, especially darks
frames that must be taken at the same temperature and with the same duration as the light image.
There are two ways to solve the problem: the first and best way is to shoot dark frames
correct, while the second is to remedy it by applying a bias frame (not necessary
when subtracting correct dark frames).

[Altouch]

The attached picture is NGC281.  This was done with LRGB and dark frames. I did not shoot flats or bias frames. I stacked the images for each individual color in Affinity Photo, and then combined them with appropriate colors also in Affinity Photo.  There is no gradient top to bottom.  However when I shoot flat fields at 0.001 second (my flat light panel is too bright to shoot slower until I design some neutral density filters for a 355mm aperture) I get a strong top to bottom gradient which is not present in the astrophoto. I am thinking it is a function of shooting flats at such a rapid exposure time - but will do trials this weekend. A sample flat field is attached in the next message. The flat does not match the vignetting I see in other images.  Processing with this flat does not produce a useful image. 

[Altouch]

Here is a sample flat mentioned in the previous post.

[Crooro]

The flats are so wrong - exposure of 0.001seconds does nothing. Then you have to see what you use to make the flats, maybe the light is not homogeneous. When I flat with various filters I use homogeneous plexi to put the light in front to decrease intensity or I move the panel farther away from the optical tube .

[vince]

Hello,

The Infinity software is not really designed for taking calibration files. You will need to use something Artemis Capture or Dusk, for very short exposures with the Horizon you will need to have the "even illumination" box ticked or you will see the gradient you are seeing, this is caused by the sensor readout method.

I hope this helps.

Vince

[Altouch]

Excellent!  I will stop using infinity and switch to Dusk or Artemis capture for calibration images (and maybe play with lights as well). Great news. I had though about readout method but was thinking it was associated with he exposure being so short. Change software and check the correct box.  Flats tonight!  Thank you.

[Altouch]

I was able to take flats that look about right. I have attached one. Dusk worked well.  If I run too long an exposure the top end saturates - but well before 65535. It had a limit at about 4095. This makes sense if the Horizon digitization is 12 bit and not scaled up to 65535. 

Thanks for the advice to use Dusk and not use Infinity for calibration frames.

[Altouch]

Image didn’t appear to make it. Did find the fix for saturation at 4095. Apparently for the Horizon one must check the pad box to pad it out to 16 bit.

[Altouch]

Can I make the flat frame actually show up in the forum?  Let’s try one more time.

[nicolas]

Can I make the flat frame actually show up in the forum?  Let’s try one more time.

Hi Altouch

I have the Atik Horizon 2 mono.. and I have the same problem (gradient) to do the flats...
You speak about to use DUSK... I will try. You have tried with DUSK and all is OK for your flats ?
Thanks a lot
Nicolas

[Altouch]

Hi Nicolas. Dusk worked well for flats (and darks). There is a box to check for even illumination - which is what flats are about. Remember to uncheck even illumination for light frames. I shoot flats, darks, dark flats. I also have bias frames but with darks and dark flats my mentors say don’t use bias frames. I have had a good experience using dusk.

I have used Dusk to somewhat automate imaging. I can’t use a filter wheel with my setup.  I have to manually change filters. It is fantastic for shooting darks. I can automate temperature, duration, and number to take. Set it up and walk away. I found dusk reliable. Always remember to set the pad appropriately. You can have it on (0-65535) or off (0-4095) but be consistent. Darks, flats, or lights without pad don’t mix well in the processing with the same that are padded.

Do you have a focus motor? Dusk moves my focus motor appropriately, finds the best focus point, but then I have to command it to go to that focus point. Maybe some setting I am missing.

Regards, Altouch.

[rabbleoily]

Here is a sample flat mentioned in the previous post. word hurdle

These flats are completely inaccurate; a 0.001 second exposure has no effect. When this occurs, it's time to examine the materials you're working with to create the flats; perhaps the lighting is inconsistent. When flattening with many filters, I either place a homogeneous plexi panel in front of the light source to diffuse it or I move the panel further away from the optical tube.

[okonignacio]

For calibrating images, I'll stop using infinity and switch to dusk or artemis capture. good news I had considered the readout method, but I was assuming it had to do with the exposure being so brief. Check the appropriate box and switch the software. Tonight, flats! I'm grateful.  geometry dash