Taken flat

[Anthony1979]

I have never taken flat frames and i havent got a clue how to take them.... Would it be a good idea to practice taking them before i go out again

[bottletopburly]

What camera are you using dslr or ccd ? And what will be your light source this will help others answering your query .

[Anthony1979]

Im using nikon d3500 with sw 150p and i will probably use a white t shirt with an a4 tracing light pad 

[Anthony1979]

Im more worried that if i do them wrong on the night im imaging then i would have wasted a lot of time get the main images... Because ive been told that flats are a must

[scitmon]

They are not difficult to do once you have your light source setup.  Use the cameras AV Mode (I assume Nikon's have that mode?) with the same ISO you used for your light images.  20-30 shots should suffice and its important to not change focus or orientation of your camera from what they were set to for lights.

 

If you were not able to take flats for whatever reason, the issues you make come across are changes in light levels on edges of the images and possible dark areas where there was dust particles on the camera image sensor and/or lenses.

[carastro]

I am not familiar with Nikons, but my first Canon DSLR I used to set the camera to Av and 100iso and the camera would taken the right length flat using the daytime sky and a sheet of paper across the aperture to diffuse.   However when I bought my 2nd DSLR this did not work, so I had to devise a different method.  

The idea is to take an image of just the light train so any vignetting and dist in the train will show up and thus calibrate out of your images.  If the flats are over or under exposed they won't work.  I have come across 2 people using the Flats plan in APT which also did not work so the best way in that case is to take a manual flat, depending on the light source, this could be around 1/80 sec. 

The basic plan is to get the histogram at 1/3 to under halfway across from the left.  Yes it is best to practice in the day time until you get the hang of it, no fun trying to experiment at night in the freezing cold.  In fact flats can be taken the following day if you like (I do that regularly) but if you need to disassemble your kit, leave the camera still attached to the scope without moving it and same focus, or the dust bunnies won't line up.

Carole 

[Anthony1979]

It really is confusing but the only way is to try.... I put an image of M45 on the other day if i took some bias frames and stacked them with the image would it improve the picture a bit

[ollypenrice]

On 22/01/2020 at 13:00, Anthony1979 said:

It really is confusing but the only way is to try.... I put an image of M45 on the other day if i took some bias frames and stacked them with the image would it improve the picture a bit

You don't stack the bias frames with the images. You put them in the stacking software's appropriate box and the software will know what to do with them.

With a Newt I would shoot my real flats in the dark. You don't want stray light getting into the bottom of the tube. Practice by day, though, certainly.

Olly

Edited January 23, 2020 by ollypenrice

[Anthony1979]

Thanks everyone..... Still confusing though 

[spillage]

Flats are relatively easy. When taking a flat you are taking an image of all the dust and rubbish in the imaging optical train and this dust and rubbish will be present on you lights. Stacking software will stack your lights and flat files and use the flat image to remove the dust from your light image.

As you can imaging dust will move around so it is best if possible to leave your camera attached to your scope,, your covers on when not in use and make sure nothing is rotated and this will allow you to use the same flats over and over again (until you see issue with a finished image).

Most capture software or camera displays will show a histogram and you are aiming for the flats to be about 1/3 in from the left hand side. This is achieved by using a light source (clear sky, light panel or even a white laptop screen). If its too bright then you can add material or sheets of white paper over the end of the scope to the required amount. Then take about 30-50 frames.

Maybe have a look here. Sorry if I have already repeated other peoples advice. Or made no sense!🙄

[Anthony1979]

Ive just took this with light panel with paper over the panel and took it with lens on camera where do i need to be for my flats