Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

stargazine_ep9_banner.thumb.jpg.05c1bdd298547fd225896a3d99c9bc17.jpg

Recommended Posts

Posted (edited)

Hi guys, 

I recently bought an LED panel to film my astro videos with better lighting outside. Which then got me thinking... instead of using my laptop screen (notepad method) to take flats with, which is annoying, why not use the LED panel. Even though it's really quite small (around 7 inches long by about 5 or so inches wide) it fits over my scope. 

So I turned the brightness up to the highest it goes and rattled off some flats. Seem to have calibrated fine.

Things to make things easier are always welcome! So then I got thinking, I've always taken flats at the end of the night before packing away rather than waiting until the morning, and I've always left the scope pointing in whatever direction it was pointing in towards whichever target I was imaging.

I understand that everything in the optical train needs to be as is when taking flats, and the same ISO value, but is it ok to release the RA and dec clutches, point the scope straight up so that I can rest the LED panel on top of it without having to hold it? 

Edited by smr

Share this post


Link to post
Share on other sites

Thanks! Should've bought an LED panel a long time ago!

Share this post


Link to post
Share on other sites

Yes, point scope where you like.

But BTW flats don't need to be same ISO as subs. That's my view, some say otherwise though! 

 

Share this post


Link to post
Share on other sites
18 minutes ago, Tommohawk said:

BTW flats don't need to be same ISO as subs. That's my view, some say otherwise though! 

Most cameras work best at a particular ISO? Why wouldnt you just use the same ISO??

Share this post


Link to post
Share on other sites
1 minute ago, tooth_dr said:

Most cameras work best at a particular ISO? Why wouldnt you just use the same ISO??

Well you're likely to be imaging with highish ISO, maybe 800 / 1600. If you do flats at lower ISO they will be less noisy. It doesn't matter too much using higher ISO so long as you take plenty of flats. 

Some folk seem to feel that using the same ISO helps minimise any differences with flats compared to the lights, but if you're using a thumping great light panel there will be considerable differences already! 

Other viewpoints are available!

Share this post


Link to post
Share on other sites
8 minutes ago, Tommohawk said:

...but if you're using a thumping great light panel there will be considerable differences already! 

Other viewpoints are available!

Thanks for the reply.  I’m not understanding your point about the light panel, but as you say other viewpoints are available. 
 

@smr I did the same yesterday evening, seems to work well and as you say easier is a nice change in AP
500FE08B-B9DA-406C-8492-D8DA79F11FF0.thumb.jpeg.40d28296ade008479d543e9fcfcaedd4.jpeg

 

 

Share this post


Link to post
Share on other sites
28 minutes ago, tooth_dr said:

Thanks for the reply.  I’m not understanding your point about the light panel, but as you say other viewpoints are available. 

What I meant was that when doing flats you're trying to replicate/correct for vignetting and bunnies - its an optical thing rather than anything to do with dark currents etc.  With darks its important to have the same camera settings, but with flats this doens't matter. 

It's sometimes said that when doing flats you ought to replicate the ISO/gain, just to be safe and minimise the differences between the way that the lights are exposed and the way that the flats are exposed. 

However, because a light panel is so much brighter than the normal target brightness, there is already a huge difference in the optical exposure in terms of brightness/duration, so matching the ISO is perhaps not significant. I'm not knocking the idea of using a flat panel, I'm just suggesting that flats will be less noisy with a lower ISO/gain. 

  

Share this post


Link to post
Share on other sites

Rather than release the clutches I point mine to a star near the zenith, which is easy to do with goto.

I don't think there is a right or wrong way really.

Share this post


Link to post
Share on other sites

Given that a scope with a flat panel on it can't see the stars anyway, it really doesn't matter where it's pointing! Most people using a panel point at the zenith to avoid covering the floor with bits of broken panel... 😁

Olly

  • Haha 2

Share this post


Link to post
Share on other sites

A lower ISO flat will produce better SNR. Just remember if your using bias or a dark flat you will need a master bias or dark flat of the same ISO or gain to match the flat only. The lights need their own matching dark/bias frames.

  • Like 1

Share this post


Link to post
Share on other sites
Posted (edited)

Just a quick follow up question re using an LED panel. I have one,  but you can clearly see that the light distribution across the panel is not even. Is that a problem when taking flats with this method, or not really?

Edited by 5haan_A
Typo

Share this post


Link to post
Share on other sites

Uneven light distribution will be a problem. Calibration will add false gradients to your images.

You may be able to process them out or better still put something infront that will give better distribution, maybe some 30% or 40% translucent acrylic sheet.

Share this post


Link to post
Share on other sites
9 hours ago, MarkAR said:

maybe some 30% or 40% translucent acrylic sheet.

agreed - this seems to work well even where light source is very uneven. just make sure acrylic material is close fit to lens shroud so light doesnt sneak in. suggest brightish light /darkish room to minimise this. 

Share this post


Link to post
Share on other sites
10 hours ago, 5haan_A said:

Just a quick follow up question re using an LED panel. I have one,  but you can clearly see that the light distribution across the panel is not even. Is that a problem when taking flats with this method, or not really?

Those type of led panels are lit from one edge so give an uneven light field I filed mine in the bin .

Share this post


Link to post
Share on other sites
10 hours ago, 5haan_A said:

Just a quick follow up question re using an LED panel. I have one,  but you can clearly see that the light distribution across the panel is not even. Is that a problem when taking flats with this method, or not really?

You could rotate the panel during the run of flats. It wouldn't matter if it were moving during a single sub. Just keep turning it steadily during the run. That will blur out any unevenness. Even with a good panel I tend to turn it once or twice for good measure.

Olly

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.