M42 second try, vignetting problem

[wouter]

Hello all,

Now I have my focal reducer I really wanted to try it out on M42 to get a wider view.

Last night was really good seeing so I took 15 subs at ISO 800, 90sec exposure.

I'm having a really bad problem with vignetting.

I still have no clue how I can make a flat image....

So I tried creating an artificial flat in my photoshop trial version.

But as you can see that didn't really solve the problem.

What do you think of my photo?

Any comments, advice or suggestions?

Thanks

Wouter

[Cuffbertt]

I know absolutely nothing about AP, but I think it looks fantastic Nice!

[Ant]

Best way to take a flat, is to leave everything attached (Camera / scope), leave the focus position where is was during the imaging run. The next day get a white t shirt (make sure it's clean and is plain white) and cover the end of the scope (tightly) with the T shirt.

Try to make sure that the end of the telescope is evenly lit (i.e. if the sun is out aim the scope directly away from the sun), then take some images. The exact exposure time will depend on a number of things. My flats are either around a second each, or if using filters can go up to 12 seconds each.

I usually get the ADU level to around a 1/3 of saturation. Which with my camera is around 20,000 ADU. I'm guessing if this is the first time you're going to have to go by trial and error. I would start of with taking 21 flats at 1 second, then take 21 flats at 2 seconds.

You can then add each batch into the staking process (one batch at a time) and see what happens, if you leave the scope/camera assembled if it needs a different exposure you can take further flats till you get one that works.

Sorry can't be more specific, but I'm away from home, and have no access to any of my software.

Cheers

Ant

[StarRaver]

If you have a laptop open note pad to full screen and place it in front of the scope but don't touch the focus, I usualy take the scope off the mount and place it on the table so the laptop screen is only a few centimetres away from the end of the scope, switch the cam to av mode leaving the ISO at what you took your lights at and click away, I have found that I needed to angle the screen slightly to get decent flats. Hope this helps

Dale

[stem1989]

I love it, nice image... I don't know enough about AP yet to give advice on flats though , good luck & good work

[Daniel-K]

that looks like you clipped the black data more than anything have you got a single subs image

[Cath]

It is black clipped around the edge but not much. You can see the none flatness though in the background area, not seen one like yours before

You could maybe try taking some sky flats whilst it's still dark of a dark part of the sky (no nebula, galaxy etc) then remove the stars and use what's left to create your flat?

[wouter]

Thanks a lot everyone!

Thank you for your sharing good ideas to make a flat image Ant.

Unfortunately I had already taken off the camera and changed the focus.

I tried to take 21 flats at 1sec and 21 flats at 2secs with the white T shirt method at a focus I thought to be close to the focus I shot the light frames at. It didn't fully solve the problem, but it looks a little better already now

If anyone would be interested in the subs and see what you can make out of it, that would be really nice.

I've just uploaded all the subs to my drop box.

Wouter

[Cath]

If anyone would be interested in the subs and see what you can make out of it, that would be really nice.

I've just uploaded all the subs to my drop box.

Where's that Wouter?

[wouter]

Cath, do you have drop box?

I'm new to it, I don't know how I can make a public sharing link to post here on the website, but if you would tell me your e mail address, I could invite you to share the folder

[wouter]

edit: I've just figured it out:

this is the link:

https://www.dropbox.com/sh/c3i5zic9ss2clbv/Dw1onc4vv4

I'm still uploading the files now, will be completed in a bit less then half an hour later

[Cath]

This is a single image of yours (removed all colour balance to get a raw image). The vignetting is quite high but in your single sub images it's got a smooth curve to it, unlike the stacked image your originally posted. Theirs also a lot more detail around the bright part of orion in your subs that your stacked.

Had a quick look at the flats you've taken but they don't show the vignetting you have in your sub images, they are very under exposed.

[Gonzo]

Cath, how do you get that graphic please?

[adamsp123]

I use the Tshirt method and when using a DSLR I simply turn the camera from manual mode to Av and fire away, the camera will sort out the exposure times for you - simple.