Flats

[Mac]

Another good thread concerning flats.

I am still just shooting them at mid histogram using the same iso as the lights with the ipad. Most of mine are about 1/80 second. Seems to do a pretty good job with dust motes, but every now and then I have to correct for uneven corner lighting (vignetting) in the Startools Wipe module.

Guess that I should try a lower shutter speed too.

Another interesting thread. Thanks Steve.

Thanks,
Jim

So much to learn and so little time to try it.

Now that I have a LP filter, I reckon that it should be left in while doing the flats and darks? Ah heck... I will just go try and see what happens.


Thank you Jim...

[Juno16]

You are right Steve. I have the tome being retired, but not too many nice nights. The weather here is like a roller coaster!

I could be wrong, but I don’t think that the filter would need to be in for the darks. Maybe the flats, because the filter is part of the imaging train.

Looking forward to responses.

Thanks,
Jim

[JayTee]

Hi Steve,

The point I was trying to make was that your first set of flats were good and usable right out of the chute.

The purpose of flats is to get rid of dust bunnies and vignetting. They only have to be decent not perfect. So I was trying to save you some work and worry.

Cheers,
JT

[Mac]

Hi Steve,

The point I was trying to make was that your first set of flats were good and usable right out of the chute.

The purpose of flats is to get rid of dust bunnies and vignetting. They only have to be decent not perfect. So I was trying to save you some work and worry.

Cheers,
JT

It was mentioned in the linked docs and by Baskevo to use a slow shutter speed, so that is what I did. The 2nd image isn't as grainy and does seem to show the dust motes slightly more, so I will use the longer shutter speed with the white sheet.

I am like Alfred E. Newman, " what, me worry "

Thanks JT

[Baskevo]

Hi Steve,

The point I was trying to make was that your first set of flats were good and usable right out of the chute.

The purpose of flats is to get rid of dust bunnies and vignetting. They only have to be decent not perfect. So I was trying to save you some work and worry.

Cheers,
JT

It was mentioned in the linked docs and by Baskevo to use a slow shutter speed, so that is what I did. The 2nd image isn't as grainy and does seem to show the dust motes slightly more, so I will use the longer shutter speed with the white sheet.

I am like Alfred E. Newman, " what, me worry "

Thanks JT

I found that website because my flats were not working for me at all, but try yours first to see if they work! If they don't, then I would try those other techniques. Flats aren't like lights, where some are better than others. They either work or they don't!

[Stuart]

I've posted multiple times about flat frames before. I caution against using the histogram as a guide for where your flats should be--in my experience that always leads to flats that are too dark. MUCH better is to measure the average ADU of the flat. The average ADU should be 45% of your max ADU. If your scale is 16 bit, your flat ADU should be about 25,000-35,000. If your scale is 14 bit, then your scale should be about 7000-8000. You can measure ADU with a number of different programs, but I use SGP and PixInsight.

[JayTee]

There is a free program called Astrophotography Lab. It will measure the ADU (and then some) of your images. http://lars-frogner.github.io/Astrophot ... index.html

Cheers,
JT

[Stuart]

Here is .5 secs at iso400 with the white pillowcase. I just had to turn down the brightness of the iPad to get to that exposure time.


Screen Shot 2020-01-04 at 6.31.08 PM.png


_JU97081.jpg

Hey Mactech, if you upload the RAW image one of us can measure the average ADU to see if you're in the ballpark.

[Mac]

Here is .5 secs at iso400 with the white pillowcase. I just had to turn down the brightness of the iPad to get to that exposure time.


Screen Shot 2020-01-04 at 6.31.08 PM.png


_JU97081.jpg

Hey Mactech, if you upload the RAW image one of us can measure the average ADU to see if you're in the ballpark.

Hey Stuart, thanks for the offer.

I've been reading how to do it in PixInsight but haven't measured one yet. I think I trashed all of the RAW files after creating the one above. I don't have the scope setup to take new ones at the moment.

[Stuart]

If you upload the master I could look at it. It'll give a similar reading.

[Mac]

If you upload the master I could look at it. It'll give a similar reading.

I need to create new ones and setup the scope. There may be a few hours tonight I can image and capture them.

Thanks