Flats

[RayD]

2 minutes ago, ollypenrice said:

Firstly it's incredibly fast. This encourages you to try alternative stacking routines, darks, no darks, bias as dark, bad pixel map, sigma, average, etc etc etc to find out what works best for you. It supports bad pixel maps, it has sophisticated and adjustable hot pixel filtration. It has a great 'repair line' function which will zap aircraft trails which haven't be dealt with by Sigma (though the Sigma routine is excellent and has improved since AA4.) It has a good suite of post processing filters like DDP, Deconvolution, Unsharp Mask, Gradient Removal, etc. (Many of these I don't use because I have them elsewhere but I already have Pixinsight and PsCS3 etc.)

It calibrates and combines a stack of 25 full frame CCD lights using bias, defect map, Sigma Clip, Hot pixel filtration and collumn defect repair on my old Win7 machine in maybe forty seconds. And above all the results are clean.

Many people (I think Carole might be one of them) who see it in use here just buy it on the spot. I'm not on commission, nor do I get any freebies. How bad is that??

lly

That's really useful thanks.  Yes Carole demonstrated how quick it was by firstly trying to stack some subs using DSS on a slowish laptop, which took quite some time, and then doing the same in AA5 and it was done in a matter of seconds.  Quite an impressive difference.

You should copy all you AA praises and send to them in a very long email, I'm sure you'd get free lifetime upgrades 

[ollypenrice]

2 minutes ago, RayD said:

That's really useful thanks.  Yes Carole demonstrated how quick it was by firstly trying to stack some subs using DSS on a slowish laptop, which took quite some time, and then doing the same in AA5 and it was done in a matter of seconds.  Quite an impressive difference.

You should copy all you AA praises and send to them in a very long email, I'm sure you'd get free lifetime upgrades 

But then I wouldn't be able to claim impartiality and I'm very particular about that!

Olly

[Luna-tic]

I feel like I was standing ankle deep in the local creek and then there was a sudden flash flood and I'm being carried downstream while trying to keep from drowning. Suddenly the "water" got way over my head.

[ollypenrice]

7 hours ago, Luna-tic said:

I feel like I was standing ankle deep in the local creek and then there was a sudden flash flood and I'm being carried downstream while trying to keep from drowning. Suddenly the "water" got way over my head.

Get used to it, it never changes! I have a backlog of things to learn about PI and APP and CMOS data which gets deeper and faster flowing by the week...

Olly

[geoflewis]

8 hours ago, Luna-tic said:

I feel like I was standing ankle deep in the local creek and then there was a sudden flash flood and I'm being carried downstream while trying to keep from drowning. Suddenly the "water" got way over my head.

This hobby is definitely like peeling an onion......!! Regarding your original question on flats, my advice is to shoot some (say 15-20), create a master flat and initially just resuse it to see how it works with your data. It will correct any vignetting in your optical train and if your optics and sensor are clean that may be all that you need. As I mentioned previously if you don't have a light source to shoot them at night then just shoot them during the day, though unfortunately the Moon won't be around during the day for a couple of weeks to aid focus as it doesn't rise until it is already starting to get dark now. Of course if you able to leave your camera coupled to your scope, then you could focus on a star at night then with the camera still focused shoot some flats during the day, but you will need to do this using an evenly lit, cloudless region of the sky. Good luck.

[wxsatuser]

2 hours ago, ollypenrice said:

Get used to it, it never changes! I have a backlog of things to learn about PI and APP and CMOS data which gets deeper and faster flowing by the week...

Olly

No chance for us mere mortals then.

I do now take flats with a ccd but never did with a dslr, they were a mystery to me.
Now they are second nature, my first set lasted 4months until I took the Atik of the lens to remove a stubborn desiccant screw.
Got a new set now, should last until the setup comes apart again in the future.
 

[Luna-tic]

It will be a while before I buy a dedicated camera for AP, the DSLR is doing okay for my purposes. I keep it (sensor) meticulously clean, never have a lens off without immediately covering the front, same as with the EP's, corrector and rear cell opening on the telescope. I think a set of flats would last a bit.

The "high water" I was speaking of is all the flood of jargon in the last few posts: binning, Sigma clip, defect map, column defect, bias, etc. I'm also not really up on the CCD AP camera models, so I have no idea what to picture in my mind when one gets mentioned.

[ollypenrice]

Flats won't help with dust on the sensor. Under the dust there is no signal. It's into Photoshop for the clone stamp!

Olly

[Anne S]

On 01/11/2017 at 15:25, ollypenrice said:

Flats: it depends on whether or not you disturb your gear between images. My setups are observatory based and don't get changed or taken apart. Flats may work perfectly for 6 months, or I may get a new dust bunny at any time. I don't shoot them for the sake of it, I shoot them when the ones I have stop working!

Ollie, what do you do about focus changes, ie because of temperature changes? I thought that would need fresh flats? I’ve got a permanent setup and I’d love to use the same flats for several batches of images!

Anne

[carastro]

Quote

Can you do without them entirely? What does it do to the processed composite if you don't make flats?  If you know your optical train is clean, does it make them unnecessary?

Short answer - NO.  I find I cannot process my images without flats, it's just too much hard work.  

Here's an example of the Horsehead I did many years ago and for demonstration purposes I deliberately stacked it without flats:

This is the actual stacked flat, check the vignetting and dust specs.

This is the final image with the flats applied.

Quote

Many people (I think Carole might be one of them) who see it in use here just buy it on the spot.

Bang on Olly.  I have never used it for re-sizing images though, and have never worked out how to stack colour images, but since I rarely do DSLR imaging, have not persevered.

Carole 

[RayD]

13 minutes ago, carastro said:

Short answer - NO.  I find I cannot process my images without flats, it's just too much hard work.  

Here's an example of the Horsehead I did many years ago and for demonstration purposes I deliberately stacked it without flats:

What a great example.  Thanks for that Carole.

[ollypenrice]

4 hours ago, Anne S said:

Ollie, what do you do about focus changes, ie because of temperature changes? I thought that would need fresh flats? I’ve got a permanent setup and I’d love to use the same flats for several batches of images!

Anne

I find focus changes can be ignored in so far as their effect on flats goes and I think you'll find this is the consensus in the community. If you were doing scientific imaging or photometry then perhaps you'd need theoretically perfect flats but, for our purposes, a small adjustment for temeperature will not perceptibly alter the viability of your flats. I also find that our scopes, which have rotators ahead of everything in the imaging train bar the objectives, can have the whole rear end rotated without invalidating the flats. Anything creating bunnies rotates as one with the chip, there is no droop in the focusers to displace the vignetting and the objective cannot create bunnies. (Think of secondary mirrors...)

So for our setups flats tend to be long lived.

Olly