Weird Flats?

[StevieO]

Hi all,

Still getting to grips with new ATIK 383 plus NB filters and wheel.

Have just been out setting up and taking clear sky flats while I'm at it. All (Ha, OIII, SII) exhibit a shadow in the top left  corner. Is this normal or have I got some sort of gremlin in my optical path?

Here they are, any comments welcomed.

Regards

StevieO

[kookoo_gr]

is the duration of the flat uder 4s? if yes then it is the shutter casting a shadow as it opnes/closes and you need to decrease the bightness of the flat-box and increase the capture time in order to get rid of this issue

[StevieO]

Of course, you're absolutely right, I'd forgotten about the mechanical shutter on the 383.

Yes, the exposure for all were less than a second in order to get the histogram right, so I need to wait until the sky darkens a bit more or revert to plan B which is to use my Ipad Infiniti-lite.

Many thanks.

StevieO

[carastro]

If you're using the sky, then just put more T shirts or pieces of typing paper across the aperture until you get the right ADU making sure the flat is at least 3 seconds long with a 383.  With an Ipad of EL panel ditto.  

Carole 

[StevieO]

If you're using the sky, then just put more T shirts or pieces of typing paper across the aperture until you get the right ADU making sure the flat is at least 3 seconds long with a 383.  With an Ipad of EL panel ditto.  

Carole 

Will try that. thanks.

All a bit moot now though, since despite forecasts of clear skies by Met Office, Meteo Blue and Clear Outside, there's nothing but cloud up there at the moment. Gonna give it a while yet but confidence is low for any meaningful imaging tonight.

StevieO

[ollypenrice]

Not connected with the shutter wipe, but if you are going to shoot flats before you shoot your lights you'll need to know you are in focus. It doesn't have to be 'critical focus' in my opinion but it needs to be close.  If your kit remains set up or you've noted focus position then fine. A strip of plastic cut to fit between the back of the OTA and the focuser body is handy.

Olly

[StevieO]

Not connected with the shutter wipe, but if you are going to shoot flats before you shoot your lights you'll need to know you are in focus. It doesn't have to be 'critical focus' in my opinion but it needs to be close.  If your kit remains set up or you've noted focus position then fine. A strip of plastic cut to fit between the back of the OTA and the focuser body is handy.

Olly

I'd had the scope off the mount from the previous session but the optical train was untouched so I knew the focus would be about right but not perfect. It was a bit of an experiment to see if I could use my setup time a bit more efficiently, but I probably won't do it again, firstly because the twilight sky gets darker as the flats come in, and secondly, since I didn't get any subs at all due to cloud cover (thanks, Met Office for your forecast of clear skies) it was all a waste of time anyway.

Back to  the good ol' Ipad plus t shirt for me, then.

BTW, Olly, (a bit off topic) congrats on your runner-up photograph of the year. With great respect to the winner, I thought yours was the most stunning image I've seen, period. I'd love to see a room-sized print.

Regards

StevieO

[ollypenrice]

I'd had the scope off the mount from the previous session but the optical train was untouched so I knew the focus would be about right but not perfect. It was a bit of an experiment to see if I could use my setup time a bit more efficiently, but I probably won't do it again, firstly because the twilight sky gets darker as the flats come in, and secondly, since I didn't get any subs at all due to cloud cover (thanks, Met Office for your forecast of clear skies) it was all a waste of time anyway.

Back to  the good ol' Ipad plus t shirt for me, then.

BTW, Olly, (a bit off topic) congrats on your runner-up photograph of the year. With great respect to the winner, I thought yours was the most stunning image I've seen, period. I'd love to see a room-sized print.

Regards

StevieO

That's very kind of you. Thanks.

Olly