ASI294 flats

[Anthonyexmouth]

Yes, this old problem again.

Just tried to take some new flats with the t-shirt method on a uniformly overcast sky with NINA and had to use 8 layers of thick cotton t-shirt to get in the 40% adu range which ended up as a 3.9ish sec sub. This seems like an excessive amount of t-shirt from what i remember doing the last time. If i removed a layer NINA said the image was too bright

I've ordered an EL panel, non controllable though. I'm hoping to get into some better work practise with my flats and take them more regularly but the 294 needs longish flats, any advice on how I can make this a more painless slap on and go kinda setup. I want something easily repeatable. 

APT flats wizard was no better. 

Heres a flat from NINA2022-05-14_10-35-47__-14.80_3.95s_0000.fits 

[The Lazy Astronomer]

What's wrong with 8 layers of tshirt? Are the flats properly correcting the lights? 

[Budgie1]

As above, do the flats work okay? Longer exposure flats do tend to work better then short ones with this camera.

I used to use sky flats, normally the morning after, but recently I've started using my Samsung Tab A6 with an app called LightBox and that seems to work well with the t-shirt. I create the flats at the end of the session and then I can put everything away. The app is dimable and has worked successfully with both UV/IR cut & NB filters.

Obviously, I'm using my Evostar 100ED DS Pro or 80ED DS Pro, so the tablet screen covers the end of the scope and you may not be able to use this if your scope opening is larger.

 

[Anthonyexmouth]

59 minutes ago, The Lazy Astronomer said:

What's wrong with 8 layers of tshirt? Are the flats properly correcting the lights? 

no idea if they are working yet, only took them this morning. 

I just dont remember ever having to use 8 layers before. 

I am hoping this EL panel I've got coming will help me make a more repeatable and easier process of taking flats. I kinda got lazy in the past having a permanent setup and went long periods between making new flats. 

[The Lazy Astronomer]

1 hour ago, Anthonyexmouth said:

no idea if they are working yet, only took them this morning. 

I just dont remember ever having to use 8 layers before. 

I am hoping this EL panel I've got coming will help me make a more repeatable and easier process of taking flats. I kinda got lazy in the past having a permanent setup and went long periods between making new flats. 

Ah yes, I see the filename now! At 10:35 this morning the sky would have been very bright (making the assumption you are in Exmouth) and the 294 is very sensitive (QE wise), so I'm not surprised. The panel will help with repeatability for sure, but with no brightness control you're likely to still need a fair amount of tshirt or paper to get the flats long enough I reckon. 

I use a cheap led tracing panel and even on the lowest brightness level (which is still pretty bright, mind) l need about 4 layers of a white pillowcase for the L filter - this is with the 294 mono. 

P.s. nothing wrong with being lazy!!😁

[Anthonyexmouth]

4 minutes ago, The Lazy Astronomer said:

Ah yes, I see the filename now! At 10:35 this morning the sky would have been very bright (making the assumption you are in Exmouth) and the 294 is very sensitive (QE wise), so I'm not surprised. The panel will help with repeatability for sure, but with no brightness control you're likely to still need a fair amount of tshirt or paper to get the flats long enough I reckon. 

I use a cheap led tracing panel and even on the lowest brightness level (which is still pretty bright, mind) l need about 4 layers of a white pillowcase for the L filter - this is with the 294 mono. 

P.s. nothing wrong with being lazy!!😁

it wasnt very bright this morning, thick cloud cover but very even, thought it would be ok. I tried a ligghtbox from amazon but it was side lit so didnt work very well so sent it back. I'll build a little mounting box for the EL panel and get some thin sheets of opaque acrylic and add layers until i reach the right level. 

Having the pier and everything always setup is lovely but breeds bad habits. 

[newbie alert]

8 layers of T shirts... Abit excessive..  they're  there only a diffuser.. take it you're doing this early morning or pre dark ?

[Anthonyexmouth]

3 hours ago, newbie alert said:

8 layers of T shirts... Abit excessive..  they're  there only a diffuser.. take it you're doing this early morning or pre dark ?

the 294 is a bit picky with flats, you need them to be quite long compared to other cameras so getting the light dim enough for the correct ADU can be hard. 

[newbie alert]

43 minutes ago, Anthonyexmouth said:

the 294 is a bit picky with flats, you need them to be quite long compared to other cameras so getting the light dim enough for the correct ADU can be hard. 

Yeah is it the osc version?

[Anthonyexmouth]

1 hour ago, newbie alert said:

Yeah is it the osc version?

yes

[newbie alert]

That sensor has weird colour gradient's

[terryf]

I have a 294MC Pro and use a cheap flat panel that I bought from Amazon (other good retailers are, I’m sure, available), and I modified it using the method detailed here - https://www.blackwaterskies.co.uk/2020/03/cheap-diy-remote-controlled-flat-panel/

The modification itself is easy, all you need is a soldering iron, pretty much, and the only issue I remember having was getting the program right on the Nano (it was the protocol was the issue, not the programming as such). Now I can plug my panel in and set the brightness or (in NINA) I can let it find the brightness level for a 3 second exposure - flats are so easy now. I also have two sheets of opalescent Perspex with a couple of sheets of white paper between then to drop the brightness a little, though that is not needed for NB flats.

Although the panel was cheap, I’ve tried it in various orientations on the scope and the flat does not change significantly, so the panel is producing reasonably uniform illumination.

[Hughsie]

For what it’s worth, I have been using the 294MC in recent nights after shelving it for nearly 2 years. With a second scope now available I resurrected the camera and struggled with flats. So, what have I found and let’s put some numbers on this.
 

First, I use SGPro and use the flats wizard to obtain a suitable exposure time. I also use a flat panel.
 

I aim for an adu of 28,500. As suggested, flat exposure is best over a longer period. I select a minimum exposure time of 4 seconds. Typically, I end up with these settings generating an exposure time of c 5 seconds and an histogram either side of the 50% mark. I also take dark flats with the same exposure time as the flats to calibrate the flats.
 

So far this has given me decent flats to remove dust motes and vignetting.