1600 workout (first NB)

[Demonperformer]

It is wonderfully clear here at the moment, with not a breath of wind, and I am having a marvelous time giving the 1600MM a good workout. I'm not sure the setup I am using is ideal - there seems to be some distortion towards a couple of the corners. The PA seems fine (the star in the centre of the field is staying put very precisely in the cross-hairs).

Anyway, I am using the 200mm lens (f 2.8), with an OIII filter (my first time), taking 30s subs with a gain of 500 and a temperature of -30.

I was quite surprised at how much is visible through the filter with quite short exposures - I was using 1-2s exposures to focus and align my subject and it was quite bright on the screen.

Currently about 60 frames in, with at least another 140, maybe another 240, planned. I will post the result after processing, if I think it is good enough (so don't hold your breath!)

Thanks.

[Tiny Small]

It will be interesting to see the results of this. 500 is quite a high gain, though the relatively large pixels on the 1600 might go some way to offset the noise caused by the gain. Good luck

[Demonperformer]

I am basing my figures on what Gina has been doing.

Rather than do another 200 @ 30s, I might try upping the exposure time and doing 100 @ 60s. Of course, that will mean I will need to take two sets of darks!

[Demonperformer]

Have decided to go for 60s - it will only take me 15m to get 10 darks at each time. And this evening is only really a "testing session", so might as well do this.

Previous "playing" has shown me that trying to get down to -30 during the day is not feasible, so I will want to take the darks tonight. I already have a master-bias for this camera and will take the flats tomorrow, when temperature does not matter (I will keep the camera and lens attached until them).

[StuartJPP]

It is wonderfully clear out there because I'm not out there...

[Demonperformer]

You have my gratitude for staying in, Stuart.

I've just been visited by one of our local foxes.

[Demonperformer]

Just taking the 30s darks now and then packing up. It's still a great night, but just rather tired.

[Demonperformer]

Flats and Dark-flats all now taken. The ambient chip temperature was 13C, so I used the cooler to drop it to 10C so that (i) it would not take too long to get there, and (ii) any changes in ambient temp while doing them would not affect them. Not sure this was necessary, but did it anyway.

2 lots of 10* flats, 0.2s (ADU: 24517), rotating the ELT 90 degrees between the two sets to average out any errors in the ELT.

20* dark-flats. I know some people say that these don't matter, but it only took ~3m, so wasn't exactly a strain to get them.

All now being transferred from laptop to usb drive, so they can be processed on my desktop.

I think I have this right:
Main tab - master bias (taken previously) + flats (20) + dark-flats (20)
tab 1 - 30s lights (100) + 30s darks (10)
tab 2 - 60s lights (100) + 60s darks (10)

If this is wrong, someone will no doubt let me know.

Thanks.

[Demonperformer]

I would have to describe this result as EXTREMELY disappointing.

All of the images were taken on the same camera/lens setup, I am using one master bias (which is, admittedly, a TIFF rather than a FITS) amd all of the other files are individual FITS files.

I will now go and try to get my thumb surgically removed from my mouth.

 

[Demonperformer]

OK, pity-party over (they don't usually last long).

I have found out what is wrong and there is not a great deal I can do about it to rescue last night's results. It turns out that, while imaging in Sharpcap, I had left the setting on MONO8 instead of changing it to MONO16. So, 8-bit lights and darks - just what you need with a NB filter! The flats, dark-flats and bias are all 16-bit.

Having dismantled the optical train after taking the flats & DFs this morning, they are not recoverable, but I have run off a set of 8-bit bias frames, so I should at least be able to see what (if anything) I was capturing. I have also "saved" the Sharpcap settings as 16-bit for this camera from now on. Apart from that, I think it is going to have to be a case of "chalk it up to experience" ... maybe it will be clear again tonight.

Thanks.

[Tiny Small]

Oops. Now that's a pity. If it makes you feel any better, it was clear here for a few hours last night but I was stuck in, attempting to resurrect an old XP desktop to run my gear from  Thankfully it's all sorted (issues with dell proprietary software insisting you use a floppy drive to install third party hardware drivers at install). I'm sick of Windows 10 updating halfway through a sequence. 

Two questions though:

1. Why did you only set the cooler to 10C? I drop mine down to -20C as soon as I plug it in, and it's there before I've finished focusing.

2. Why did you rotate the ELT for flats? I was under the impression that everything had to stay exactly where it was for flats. I have to admit, I don't usually bother as most of the defects that they address are an easy fix in Photoshop.

[Demonperformer]

1. Temperature for flats is immaterial. When I was outside taking the lights (and darks) it was set to -30. All I was trying to achieve with the flats (next morning) was taking it below the ambient temp a couple of degrees, so that, if temperature changed slightly while I was taking them, they would not be affected.

2. The optical train does have to stay exactly the same. The ELT is the light source, that (in theory) provides a perfectly-evenly-illuminated light. However, I am naturally suspicious of anything that says it does something perfectly. I suspect that there are minor differences in the light source, so by rotating the source through 90 degrees, I am moving any irregularities and these should be minimised when all the flats are combined into a master-flat. I suppose, to get it as perfect as possible, I should rotate it 1/20 of a circle after each exposure - but I think that might be taking things to extremes!

I should point out that both of these answers are based on my (currently very limited) understanding of how flats work (I have only recently started doing them) - so they are subject to amendment. I have seen posts from experience AP-ers on SGL that flats are more important than darks (but that may just be personal preference rather than cast-iron fact - dunno).

Thanks.