Field flattening

[butlermike]

Hi,

this is just a thought as I don't even have a scope yet (still using a camera and lens) but is it possible to use Photoshop instead of a field flattener?

I may have the wrong idea but is a field flattener used to correct the equivalent of lens distortion in a scope?

This is obvious in some wide angle lens' where you get pin cushion and barrel distortion which can to a large extent be corrected in Photoshop.

Is there a case for setting up a custom lens distortion filter in Photoshop to correct for the scope?

Or do I have the wrong end of the stick?

Mike

[alan potts]

I have looked at the latest version of photoshop and you can change the rotation of the earth with that.

Seriously, I would have thought there would be too much going on at the edges of an unflatten FOV to put it right in PS. You would never get the same type of result, even field flatterner do not flatten everything, well not like a quality eyepiece and even they can introduce slightly unwanted effects at the very edges. With cameras the bigger the chip the more it will pick up and the greater the need to flatten. If you have a small chip you do not even need one.

I would have thought it would be more of an unsharp mask tool that would be required slow getting worse as you move outwards towards the edge.

I could be talking tommy rot though as I don't really know.

Alan

[butlermike]

Ok, thanks for that.

I might try it out one day just to see.

Like I say, I don't even have a scope yet it was just a thought as field flatteners are rather expensive. But that's the same with any quality glass that you put in the way of the light!

Chances are on a CMOS sensor I'll be cropping the edges out of most pictures anyway.

[alan potts]

Mike,

Expensive , not half. I have 5 scopes in all not that I use any for imaging but I want to. You need a different corrector for each scope.

I only have one F/R at the moment and that is for the Meade, ironically the one scope that I will most likely never use, I got it as you can reduce the focal lenght and use it with eyepieces to get a wider field of view. Now I have a full array of eyepieces that will do the same thing, so it's a dust collecter. People say that some eyepieces are expensive and they are but some of the reducers can top 400 pounds too.

I think I would agree with you and crop out the rubbish, I know though that some of the small CCD chips do not require them, I don't know at what point it starts to be seen, I would think also it would be different with each type of scope.

Alan

[dph1nm]

this is just a thought as I don't even have a scope yet (still using a camera and lens) but is it possible to use Photoshop instead of a field flattener?

I have done this in GIMP (with shots using the cheap Canon 50-250 zoom lens) and it works surprisingly well! It really can turn those streaky stars at the corners into round dots.

NigelM

[alan potts]

Nigel,

I would not have thought the effects from a as you call it cheap lens ( is any Canon lens cheap) would be the same as from a telescope of any type. I would have thought that the effect was much worse the wider you go. I also would think it was a completely different type of distortion.

This is interesting though,

BTW what is GIMP?

Alan.

[butlermike]

That's good to know Nigel, thanks. We'll have to wait and see if it will work on a scope...if I get to ever try it!

GIMP is a free, not so powerful (but apparently still good) version of photoshop. Google will tell you all about it!

[dph1nm]

I would not have thought the effects from a as you call it cheap lens ( is any Canon lens cheap) would be the same as from a telescope of any type. I would have thought that the effect was much worse the wider you go. I also would think it was a completely different type of distortion.

This is interesting though,

BTW what is GIMP?

I use the the term cheap in a relative fashion, of course! The GIMP lens distortion tool is very flexible and lets you alter the amount of correction (and its centroid) in x and y independently (I imagine Photoshop is the same, but I have never used it). So I just played around until I got something I liked! I haven't tried it on scope images, as I don't find distortion bothers me on my f6 Newt or f6.6 refractor. Some folks may be fussier I guess.

NigelM