Is it dirt/dust or something else?

[carastro]

Quote

I you have to strip down your kit do you need to take new flats every time. I would have thought that as your focus is going to be the same you could get away with using the old ones. I guess you have the chance of moving bunnies or new ones being added to the imaging train though.

Definitely as the chances of getting your camera inserted in exactly the same spot are pretty negligible, and the dust won't line up.  No point in wasting data by removing the camera and presuming the flats from another occasion will do and then finding they won't as it will be too late then.

I once had almost dismantled my kit from a night away location and then realised just before I removed the camera that I had forgotten to take my flats.  So I took the scope and camera home intact (carefully packed so the camera didn't move), and did them when I got home. 

Carole 

 

 

[ollypenrice]

2 hours ago, spillage said:

All I can add is that I have ditched darks for master bias and only bother using my L flats, I only have the baader filters so not sure how parfocal they are. 

I think the filters are highly parfocal but the optics usually are not - which is to say that, even in a apo, there will be a slight difference in focal length depending on the wavelength. Whether this is enough to merit a refocus also depends on your pixels scale. I find I don't need to refocus the TEC at 1.8"PP but that I do at 0.9"PP. The Taks, at a coarse 3.5"PP are effectively entirely parfocal. I found my Baby Q parfocal with my camera but when Sara bought the scope for use with smaller pixels she found it not to be so.

In any event this will never affect your flats in my view.

Olly

[Stub Mandrel]

6 hours ago, carastro said:

Totally agree with Olly, I never takes flats during an imaging session, I always take them either at the end with a light box or the following day as sky flats.  I only ever heard one person say that flats were temperature dependent and I have never cooled my flats.  

It probably depends on your setup.

With my cooled 450D I found uncooled darks and flats added noise, while cooled ones drastically reduce it.

[ollypenrice]

3 hours ago, Stub Mandrel said:

It probably depends on your setup.

With my cooled 450D I found uncooled darks and flats added noise, while cooled ones drastically reduce it.

You should be able to take sufficient flats to eliminate noise. Also, while professional flats do contain pixel by pixel information, amateur flats probably don't - or don't have to. You could try noise reducing your flats. I never have, not having a problem to solve, but it might be an interesting experiment. Just thinking aloud.

Olly

[Stub Mandrel]

1 hour ago, ollypenrice said:

You should be able to take sufficient flats to eliminate noise. Also, while professional flats do contain pixel by pixel information, amateur flats probably don't - or don't have to. You could try noise reducing your flats. I never have, not having a problem to solve, but it might be an interesting experiment. Just thinking aloud.

Olly

Until I got the time to take cooled flats, I tried a gaussian blur on the master flat, which improved things, but not as much as using cooled ones.

 

[celestron8g8]

Worrying about taking flats in between sessions is an easy fix if one cares to do it this way . You don't have to move your scope or adjust focus in either way . I learned a technique long ago how to take flats without touching the scope at all . Buy a sheet of Flat Black Art paper and tape it to the inside of a shoe box lid using double sided stick tape and place on the shoebox lid first then press the Flat Black Art paper onto the inside of the shoe box lid . This way the tape cannot reflect any light source . Hold the Lid with Flat Black Paper side up close in front of the scope or camera lens and expose for flats . Actually if you didn't want to hold it while doing flats you can make a card board mount to slip onto the front of your scope like a solar filter does , the kind that just slides on snug enough to hold while taking flats , and tape the Flat Black Art paper to the inside of that mount so that it covers all the inside of the card board . 

[ollypenrice]

40 minutes ago, celestron8g8 said:

Worrying about taking flats in between sessions is an easy fix if one cares to do it this way . You don't have to move your scope or adjust focus in either way . I learned a technique long ago how to take flats without touching the scope at all . Buy a sheet of Flat Black Art paper and tape it to the inside of a shoe box lid using double sided stick tape and place on the shoebox lid first then press the Flat Black Art paper onto the inside of the shoe box lid . This way the tape cannot reflect any light source . Hold the Lid with Flat Black Paper side up close in front of the scope or camera lens and expose for flats . Actually if you didn't want to hold it while doing flats you can make a card board mount to slip onto the front of your scope like a solar filter does , the kind that just slides on snug enough to hold while taking flats , and tape the Flat Black Art paper to the inside of that mount so that it covers all the inside of the card board . 

I'm not sure I follow this. Where does the light get into the scope? Round the edges of the box? And you find this gives an even illumination? Pictures would be good if you had any.

Olly

[celestron8g8]

2 hours ago, ollypenrice said:

I'm not sure I follow this. Where does the light get into the scope? Round the edges of the box? And you find this gives an even illumination? Pictures would be good if you had any.

Olly

Let me back up and correct a mistake , sorry . Using the Art Paper I spoke of is used with darks and bias frames . Flats I use the T-Shirt method . Been a while since I have imaged since I've basically retired from imaging any more . To better explain here is a video on YouTube that explains the method I used cause I used the DSS (Deep Sky Stacker) program and I used a Canon XSi D450 DSLR . Hope this helps some :  

 

[ollypenrice]

3 hours ago, celestron8g8 said:

Let me back up and correct a mistake , sorry . Using the Art Paper I spoke of is used with darks and bias frames . Flats I use the T-Shirt method . Been a while since I have imaged since I've basically retired from imaging any more . To better explain here is a video on YouTube that explains the method I used cause I used the DSS (Deep Sky Stacker) program and I used a Canon XSi D450 DSLR . Hope this helps some :  

 

OK, that's clearer. Personally I'm not convinced that darks can be done by excluding light from the scope. I've tried it using the metal lens cap on a Takahashi which is a tight fit, for an imaging rig with sealed electric filterwheels, but darks done this way always had a little light getting in. Don't ask me how it got in there but it did. Darks worked best for me when I used the metal screw-fitting chip cover supplied with the CCD camera. Any light ingress at all will wreck a dark. I often use 30 minute subs so that probably added to the problem with 30 minute darks.

Olly

[celestron8g8]

True with a CCD camera is totally different cause of light sensitivity is way over matched for a CCD dedicated camera . As you say the sensor cover is best . In the video it works best with a DSLR camera . They can’t compete with a CCD sensitivity sensor . 

[spillage]

I could not see this mentioned but if you are guiding and using software to control you camera and mount then you can just dither and ditch the darks. You can use your bias master as a dark and see if that makes your image better or worse.

[RolandKol]

On 20/03/2018 at 09:57, spillage said:

I could not see this mentioned but if you are guiding and using software to control you camera and mount then you can just dither and ditch the darks. You can use your bias master as a dark and see if that makes your image better or worse.

Thanks for letting me know, - I was not aware of dithering option... Will google it and maybe will manage to try it this night.

Yesterday, was the first proper night I could try out all I read in relation to the topic I started.

I cleaned all surfaces and started doing flats and all dust bunnies are gone!   thanks for all advises.

I also recollimated the scope and pushed the primary mirror to the limit and it looks like there's no need in Focuser's tube "circumcision". 

Below is my first results with 30 Flats, darks, bias and 120 subs [ISO800 - 60sec].
I am still very new to EQ mount and longer than 10sec exposures, so accept my apologies for the "Space Eggs" instead of Stars, still learning to guide properly.

P.S. picture was verrrrry noisy, I guess, we had a "feather clouds" as I was not able to get longer than 1min exposures with ISO800 and LP filter....

This is a cropped version, I was too shy to send the full one.

[spillage]

Have a look here. Astrophotography Tool is a free program thay you might find useful. I have used it for over a year now and it has done everything I need.

[carastro]

You've made another step forward Roland, you can definitely see the improvement from using flats.  

Carole