Lightbox for Flats

[tooth_dr]

7 hours ago, carastro said:

Adam I believe you are using the Atik383, which has a mechanical shutter so your flats need to be longer to allow the shutter to get out of the way.  I used to own one of these and remember this being a right PITA.  Then of course binning 2 x 2 you really need shorter subs but you can't because of the shutter, so you need to use more paper.  With a light box of this design I can't see a better option, I used to do sky flats with thick layers of white fabric, but you can't squeeze them into a box.   Can you get thicker paper?

Carole 

 

Thanks Carole. I was just hoping for a more elegant solution, but paper seems to work so I’ll shall have to stick with it!

 

 

 

[Marmo720]

49 minutes ago, tooth_dr said:

Thanks Carole. I was just hoping for a more elegant solution, but paper seems to work so I’ll shall have to stick with it!

 

 

 

Would another piece of acrylic work? With potentially fewer papers if needed to further diffuse? Then you can stick both acrylic together (super glue the edges?) And have less to manage every time you need to take flats? 

 

[tooth_dr]

1 hour ago, Marmo720 said:

Would another piece of acrylic work? With potentially fewer papers if needed to further diffuse? Then you can stick both acrylic together (super glue the edges?) And have less to manage every time you need to take flats? 

 

I think it would help, a piece of card might do the trick too.

[carastro]

Yes I was wondering about another sheet of acrylic, but the trouble is you have to keep changing the length of flat subs according to whether binned or not and per filter, but if it means it works and still needing some paper, then less paper might be needed.

I have to say since I sold that camera and have a non shutter camera (Atik460EX) life has got very much easier even though I now have a smaller FOV plus it is far less noisy than the Atik383.

Carole 

[tooth_dr]

1 hour ago, carastro said:

Yes I was wondering about another sheet of acrylic, but the trouble is you have to keep changing the length of flat subs according to whether binned or not and per filter, but if it means it works and still needing some paper, then less paper might be needed.

I have to say since I sold that camera and have a non shutter camera (Atik460EX) life has got very much easier even though I now have a smaller FOV plus it is far less noisy than the Atik383.

Carole 

Last night it was 3.8s for 2x2 and 15.3s for 1x1 for luminance filter at same brightness on the panel.

 

[carastro]

What filter was 2 x 2?

Crikey that is a long flat for luminance, I can't remember how long my luminance subs were but don't think they were as long as that.  I don;t know why that camera has to have a shutter, I have used a bigger sensor than that QHY8 and there was no shutter on that camera.  

Carole

[tooth_dr]

6 minutes ago, carastro said:

What filter was 2 x 2?

Crikey that is a long flat for luminance, I can't remember how long my luminance subs were but don't think they were as long as that.  I don;t know why that camera has to have a shutter, I have used a bigger sensor than that QHY8 and there was no shutter on that camera.  

Carole

Both with the luminance filter.  I normally take dark flats too so I dont think it really matters too much on exposure time.  I take my flats at night when it's cloudy in the obsy with the roof close, to avoid light leakage in the rear of the scope.  I set it to run over night.  Thanks Carole.

 

 

Adam.

[Marmo720]

13 minutes ago, tooth_dr said:

Both with the luminance filter.  I normally take dark flats too so I dont think it really matters too much on exposure time.  I take my flats at night when it's cloudy in the obsy with the roof close, to avoid light leakage in the rear of the scope.  I set it to run over night.  Thanks Carole.

 

 

Adam.

I suppose that is an advantage to having an observatory in this country with all the clouds. I don't currently have one and the thought of going out on a cloudy cold night to set everything up and only image darks and flats is not appealing at all! I don't mind if I have a few hours of clear sky to collect lights and then do flats/darks once the clouds come in on the same evening.

[tooth_dr]

56 minutes ago, Marmo720 said:

I suppose that is an advantage to having an observatory in this country with all the clouds. I don't currently have one and the thought of going out on a cloudy cold night to set everything up and only image darks and flats is not appealing at all! I don't mind if I have a few hours of clear sky to collect lights and then do flats/darks once the clouds come in on the same evening.

Darks last a whole season so no issues there, do it once and it’s done 👍🏼. Flats - if you are setting up each night I’m not sure how much benefit it would be to setup just to taken them.  My scope and camera does not move between sessions so flats last me several sessions or longer. 

[Marmo720]

9 minutes ago, tooth_dr said:

Darks last a whole season so no issues there, do it once and it’s done 👍🏼. Flats - if you are setting up each night I’m not sure how much benefit it would be to setup just to taken them.  My scope and camera does not move between sessions so flats last me several sessions or longer. 

Good tip on darks  I didn't realise you could keep darks for a few months like you can with Bias frames? 

My flats are relatively quick so I take them at the end of the session. However, I have had so many issues with flats since the summer that I have had to setup several times with the aim of just testing flats and no imaging. Think I am almost there though with getting the issues resolved.

[carastro]

Mo, darks can only be re-used if they are the same temperature as the chip when capturing.  It might be worth keeping darks so long as you record the temperature and note the temperature when you are capturing.   DSLR's though are difficult for doing this as the temperature will vary through the night, but some people say they have been successful doing this.

When you have a cooled camera with set point cooling like Tooth Dr and I have life becomes a whole lot easier from the darks point of view.  Plus there is little thermal noise anyway. 

Carole

[Marmo720]

28 minutes ago, carastro said:

Mo, darks can only be re-used if they are the same temperature as the chip when capturing.  It might be worth keeping darks so long as you record the temperature and note the temperature when you are capturing.   DSLR's though are difficult for doing this as the temperature will vary through the night, but some people say they have been successful doing this.

When you have a cooled camera with set point cooling like Tooth Dr and I have life becomes a whole lot easier from the darks point of view.  Plus there is little thermal noise anyway. 

Carole

Ah - thanks for the clarification. I haven't kept an eye on temperature as I always do flats on the same sessions anyway. However, I have noticed for example winter temperatures are about 18C while summer is obviously higher so can't use same flats.

Since I do all my darks at the end (and normally after bias and flats), if the temperature has changed a few degress, it should be fine? Or should I be taking darks straight after lights to be as close as possible in temperature and then take flats/bias last?

Thanks,

Mo

[tooth_dr]

57 minutes ago, Marmo720 said:

Ah - thanks for the clarification. I haven't kept an eye on temperature as I always do flats on the same sessions anyway. However, I have noticed for example winter temperatures are about 18C while summer is obviously higher so can't use same flats.

Since I do all my darks at the end (and normally after bias and flats), if the temperature has changed a few degress, it should be fine? Or should I be taking darks straight after lights to be as close as possible in temperature and then take flats/bias last?

Thanks,

Mo

Although this isn't really applicable to this thread, I'll just add my view.  Carole is right about the temp - I assumed you had a set point cooled camera.  Doing your DSLR flats at any temperature close to your lights will be ok - they will be so short that there will be no thermal current building up anyway, and the same with the bias frames.  With darks it really does matter.  I wouldn't bother with darks with a DSLR, because no matter when you take them they wont be temp matched, and you wont get an accurate representation of the thermal noise.  Instead try dithering between frames.  If you do a search on this, it's be covered quite a bit.

[Marmo720]

4 hours ago, tooth_dr said:

Although this isn't really applicable to this thread, I'll just add my view.  Carole is right about the temp - I assumed you had a set point cooled camera.  Doing your DSLR flats at any temperature close to your lights will be ok - they will be so short that there will be no thermal current building up anyway, and the same with the bias frames.  With darks it really does matter.  I wouldn't bother with darks with a DSLR, because no matter when you take them they wont be temp matched, and you wont get an accurate representation of the thermal noise.  Instead try dithering between frames.  If you do a search on this, it's be covered quite a bit.

Thanks for the advise. I have been dithering for a couple of months but continued to do darks anyway as I didn't want lack of them to be reason for why I kept having issues with my stacked images. 

Now that flats issue is fixed, I will try experiment stacks with and without darks. If there is no difference, then I can save myself time or use the time for lights if clouds are clear. 

[carastro]

Yes I have heard that dithering saves having to take darks with DSLR.  

Carole 

[RolandKol]

23 hours ago, tooth_dr said:

Darks last a whole season so no issues there, do it once and it’s done 👍🏼. Flats - if you are setting up each night I’m not sure how much benefit it would be to setup just to taken them.  My scope and camera does not move between sessions so flats last me several sessions or longer. 

Have you tried darker paper? Grey or dark blue?
I never tried myself, - but it should help... I think...
 

[tooth_dr]

8 minutes ago, RolandKol said:

Have you tried darker paper? Grey or dark blue?
I never tried myself, - but it should help... I think...
 

I was worried about the effect of a colour on the light for the flats but maybe that isn't relevant?  Maybe grey acrylic would even do?

[carastro]

Good idea, if it's a mono camera shouldn't make any difference if it is in colour. 

Carole 

Edited January 10, 2020 by carastro

[don4l]

16 minutes ago, tooth_dr said:

I was worried about the effect of a colour on the light for the flats but maybe that isn't relevant?  Maybe grey acrylic would even do?

I never take binned flats.

My stacking software (CCDStack) happily uses unbinned flats with binned images.

Is it worth trying to use software binning?

 

[carastro]

I always take binned flats if I have done binned images, I have never tried stacking without binned flats.  I use Astroart for stacking.  Not sure if it would work, but could try it as an experiment I suppose, but in my case I have to take flats for the different filters anyway, so doesn't really make any difference if they are binned or not whilst i am taking them anyway. 

Carole 

[tooth_dr]

17 minutes ago, don4l said:

I never take binned flats.

My stacking software (CCDStack) happily uses unbinned flats with binned images.

Is it worth trying to use software binning?

 

Still doesn't resolve the issue as I still need several sheets of paper even to do unbinned flats.

[tooth_dr]

14 minutes ago, carastro said:

I always take binned flats if I have done binned images, I have never tried stacking without binned flats.  I use Astroart for stacking.  Not sure if it would work, but could try it as an experiment I suppose, but in my case I have to take flats for the different filters anyway, so doesn't really make any difference if they are binned or not whilst i am taking them anyway. 

I would take binned flats also, I think APP can do it, but it flags up some warning.

[RolandKol]

I cannot recall the article or forum thread, but I do remember someone like @vlaiv explaining, - color has no effect on Flats.
@vlaiv, if it was not you, - my apologies.

 

[Marmo720]

Just to update on this - it seems my issues with the imaging train and flats are fixed and I can finally do some astrophotography!!

I spent all of Friday night capturing the Rosette Nebula and I was able to get nice tracking for 3 mins and then 4 mins. My only attempt at 5 mins shows some star trails but didn't want to spend the cold night trying to fix that. The attached is auto save from DSS with 45 mins at 3 min subs and 40 mins at 4 min subs. I didn't need darks it seems either so only used lights, flats and bias. Flats I had to do manual instead of the auto setting on APT. 

Unfortunately, the rest of the nights imaging and also Saturday night are wasted as dew covered my lens and guidescope lens too so will be buying dew heaters at the Astrofest in 2 weeks.

Just wanted to say thanks to everyone who gave advise and helped with this. Excited to do some more imaging!! 

Thanks @RolandKol and @carastro for showing me what a processed image looks like too so I can practice on this data while the skies are cloudy.

Clear skies all.

Autosave_NGC2237.tif

[billhinge]

I had a big Aurora  several years ago but  it was really flimsy looking for what  it cost 

To replace it I just picked up  a nearly half  price 'bargain'  from  ebay  for a virtually new one (12" square one to cover my 11" SCT and refractor) - couldn't resist, still cheaper than a dedicated astro panel that size

Artograph's are expensive but supposedly top of the  market, should be  here at the weekend, even if no good for astro I'm sure it will come in handy

https://www.artograph.com/lightpadpro/

• Adjustable color temperature from 3000K-6200K, warm to cool white
• Variable brightness from 500 to 5500 lux with color temperature adjustment
• MAX brightness a blazing 11,000 lux at a fixed color temperature of 4600K
• Tempered glass cutting surface
• Edge designed for T-square use
• UV-free light safe for eyes and archival photos and documents
• Settings memory saves brightness and color temp
• Shines through 300 pound cold-pressed watercolor paper
• Square shape to fit any size or orientation
• Curved-edged frame for ergonomic ease
• Smooth base for lap comfort
• Capacitive touch controls
• Thin, sturdy design
• Long-life 50,000 hour LEDs

I like the idea of adjustable colour temp and  low bottom range brightness. (should also  work well for its intended purpose as a bonus)

I  presume 3000-4000k is optimal  for night sky?