Atik 383L flats

[wxsatuser]

I'm trying to take flats with the 383L

I'm using an Artesky flat panel laying directly on a Canon 70-200mm L lense.
There is an Astrodon 1.25" Ha filter right up against the front glass of the Atik.

I ended up exposing for 7secs and the white point was 24200ish

Does anyone think this was to long, any help is appreciated

I expect some vignetting but does this flat look ok?

[daz]

Possibly not long enough. What does the histogram look like?

[Singlin]

Artesky flat panels come in 2 versions.

One of the versions which is a little more expensive has a bigger range of power on the variable luminosity switch.

Which version did you purchase?

[wxsatuser]

37 minutes ago, Singlin said:

Artesky flat panels come in 2 versions.

One of the versions which is a little more expensive has a bigger range of power on the variable luminosity switch.

Which version did you purchase?

This one from FLO

Think I'm on about mid range, it's quite variable and hard to tell.

https://www.firstlightoptics.com/flat-field-generators/artesky-premium-250mm-flat-field-generator.html

[wxsatuser]

46 minutes ago, daz said:

Possibly not long enough. What does the histogram look like?

In Artemis it was a small hump about one third from the left and the peak was about halfway up the vertical.

[Davey-T]

Looks a bit overexposed to me.

Dave

Atik 314 flat

 

[wxsatuser]

Whats the best way to display the flat?

I just stretched with STF in PI, is that ok or not a good idea?

It looks slightly different in Artemis.

[Singlin]

I think that they only sell the prem ones now, So you are ok.

Have you been trying to take them in daylight?

If so try again in the evening with your flat panel .

[ollypenrice]

Looks absolutely fine to me. You don't need to worry about the look of the histo since the white point is telling what you need to know. If that's around the 20,000 to 30,000 mark, as it is, you're bang on. Seven seconds is perfectly OK. On shutter cameras you can't do ultra short flat exposures because you'll record the wipe of the shutter over the chip. Probably a minimum of two or three seconds? I've never had one so I don't know from experience. I suppose that, in principle, very long flat subs would eventually need dedicated darks for flats because you'd get thermal noise coming in. In reality flats are short enough for a master bias to make a perfectly good dark for flats. It's important to subtract a 'master bias as dark for flats,' though.

The flat looks convincing because, as well as the white point being correct, you have good credible vignetting and no gradient. Don't worry about how bad the vignetting looks when stretched. If you open it in a programme which allows you to mouse over the pixels to read out their values you'll find out what the real difference in brightness is between centre and corner. It won't be all that much. In fact if you look at the black point value in Artemis and compare it with the white you'll have a very good idea of the range recorded by the flat.

Olly

[wxsatuser]

Thank you Olly.

I tried various lengths of exposure and thought I could detect the shutter up to 3seconds.
Will do a batch and see how it goes.

 

[Singlin]

I have the same product and use it on my Quattro 10" F 4 scope.

The other day I used it on my ED 80 for the first time and had the same problems as you in that I had to have too long exposures in order to capture enough light.

I was using it in broad daylight.

I then used it when it was dark and managed to get my exposure time right down to 4 sec with the histogram at about 45%

[wxsatuser]

It was daylight but in a dark obsy.

Yes, I think 4 to 5secs is doable, will give it a go, it's quite cloudy here so I can have a play in the evening.

[gnomus]

I have a 383 and I would say that your flat looks fine.  I assume that without applying the STF it looks like a flat grey.  When you STF you are (quite aggressively) stretching an image that (at 20-30000 ADU) does not actually need to be stretched.  Incidentally, the 383 has a mechanical shutter, so aiming for an exposure of 5+ seconds is correct in order to avoid the possibility of shutter shadow.

[swag72]

The flat looks fine to me..... How does it work in practice? Thats what I'd be looking at before I even bothered to look at the flat itself. 

 

[ollypenrice]

Yes, one of our full frame rigs has heavy vignetting because of our mistaken choice of mounted 2 inch filters, recording 19,000 ADU in the corners and 23500 in the centre. That's a lot, but it calibrates out perfectly well. I doubt you're anywhere near that.

Olly

[wxsatuser]

On 1/16/2017 at 11:59, gnomus said:

I have a 383 and I would say that your flat looks fine.  I assume that without applying the STF it looks like a flat grey.  When you STF you are (quite aggressively) stretching an image that (at 20-30000 ADU) does not actually need to be stretched.  Incidentally, the 383 has a mechanical shutter, so aiming for an exposure of 5+ seconds is correct in order to avoid the possibility of shutter shadow.

Thanks gnomus.
Yes it's a flat grey and will give 5secs a try, sounds good.

On 1/16/2017 at 12:10, swag72 said:

The flat looks fine to me..... How does it work in practice? Thats what I'd be looking at before I even bothered to look at the flat itself. 

 

Thanks Sara.
Will try it the 4 subs I got the other night, seems to be cloudy all the time, now I can image again.