Flats

[dark star]

Hi, I attach s link to my first attempt at flats. They don't seem to work, at least they don't remove vignetting form my images. I took it with a Canon DSLR, 250mm f4.8 reflector pointing at a totally grey sky, because of clouds, at night. ISO 800, AV mode. I assume they are not working because I took them at night, which I haven't seen recommended anywhere! I am just curious as to why this is not a good idea? I tried stacking them in DSS, but no success. The blue colour is due to a CLS clip light pollution filter.

I tried using a computer screen, however my reflector is too big compared to my laptop!

I will try taking photos of a clear blue sky, but given our usual weather this could not be for long time!

https://dl.dropbox.com/u/82184859/flat.JPG

David

[Davey-T]

Doesn't seem to be any detail, try on gradually darkening twilight sky or in daylight experimenting with different layers of white cloth over lens. Check histogram to see if anything is registering.

Dave

Have a look at the post on flats just down the page a bit

[dark star]

Thanks, I will try a white t-shirt in daylight!

David

[Gina]

That's what I use Good luck

[Cath]

When you see the flats from a pro telescope (see video) you wonder how they produce such nice images. You'd need a 'big' t-shirt for this one! ..

[Ant]

I used white T shirt for years... it does work. If you take the flats in daylight (as I used to) make sure that the scope is point directly opposite the sun (if it's bright), as having a bright light source hitting the t shirt as an angle isn't good.

If you are using a newt, remember to cover the mirror end with something to stop light getting in.

ant

[Cath]

If you take the flats in daylight (as I used to) make sure that the scope is point directly opposite the sun (if it's bright), as having a bright light source hitting the t shirt as an angle isn't good.

Looking at David's flat it looks as if it's not evenly illuminated ..

[ollypenrice]

Even illumination I always found hard to get with T shirt flats. I gave up and now use an EL panel.

Make sure you expose till the peak of the histogram is about a third of the way over to maximum brightness. Something isn't working because an F4.8 Newt couldn't possibly show so little vignetting.

Was the back of the tube sealed? If not, you're splashing light around inside like nobody's business!

Olly