Flats???

[Larry 1969]

Good day all!
I've been struggling terribly trying to get my flats to correct my vignetting properly...
I use a Pegasus Flat Panel and APT's "Flats Aid" and have tried 20,000 to 32,000 ADU. Sometimes they seem to work while others turn out like this. Here's a screenshot from APP. This is the final stacked image with an auto-stretch applied. The problem is obvious but the solution eludes me... These flats were taken immediately following my session, before I put everything away...

Even if the secondary mirror was out of adjustment the flats would still correct the vignetting right?

At my wits' end...

Larry

[Greenman]

How are you making your flats? I use a flat panel on top of the upright scope - this makes sure the illumination is parallel to the lens. If you are using the tee-shirt method are you sure the sky you are using has no obstructions on it - looks like a side gradient.

[Larry 1969]

How are you making your flats? I use a flat panel on top of the upright scope - this makes sure the illumination is parallel to the lens. If you are using the tee-shirt method are you sure the sky you are using has no obstructions on it - looks like a side gradient.

I'm using a Pegasus Flat Panel on an upright scope like you mentioned. No Tee-shirt.

Larry

[STEVE333]

I would suggest using a Tee-shirt between the flat panel and the telescope. The Tee-shirt will prevent any reflections. I bought an embroidery hoop with a diameter just a little larger than my scope dew shield. The hoop holds the Tee-shirt taught to prevent any wrinkles. Works perfectly. I place it over the end of the telescope and then you could put the light panel on top of it. You can purchase these hoops either online or at any fabric store (if you can find one). They come in many sizes and are inexpensive.

Steve

[Greenman]

How are you making your flats? I use a flat panel on top of the upright scope - this makes sure the illumination is parallel to the lens. If you are using the tee-shirt method are you sure the sky you are using has no obstructions on it - looks like a side gradient.

I'm using a Pegasus Flat Panel on an upright scope like you mentioned. No Tee-shirt.

Larry

Steve has a point, I use 3 sheets of A4 paper as a diffuser on the flat panel.

[Larry 1969]

I would suggest using a Tee-shirt between the flat panel and the telescope. The Tee-shirt will prevent any reflections. I bought an embroidery hoop with a diameter just a little larger than my scope dew shield. The hoop holds the Tee-shirt taught to prevent any wrinkles. Works perfectly. I place it over the end of the telescope and then you could put the light panel on top of it. You can purchase these hoops either online or at any fabric store (if you can find one). They come in many sizes and are inexpensive.





Steve

Interesting...
I thought the purpose of my $430 flat panel wat to eliminate the need for further diffusion and to get a more consistent flat???

Larry

[SkyHiker]

If you have a white wall just point the scope at it with a headlamp. The wall will be out of focus so it smooths things out. I don't know if it fixes your problem but it sure is fool proof. You can also point at the blue sky the next morning. Testing that would take the extra apparatus out of the equation.

[STEVE333]

I would suggest using a Tee-shirt between the flat panel and the telescope. The Tee-shirt will prevent any reflections. I bought an embroidery hoop with a diameter just a little larger than my scope dew shield. The hoop holds the Tee-shirt taught to prevent any wrinkles. Works perfectly. I place it over the end of the telescope and then you could put the light panel on top of it. You can purchase these hoops either online or at any fabric store (if you can find one). They come in many sizes and are inexpensive.





Steve

Interesting...
I thought the purpose of my $430 flat panel wat to eliminate the need for further diffusion and to get a more consistent flat???

Larry

The flat panel will give uniform illumination, but, the front surface of the flat panel is reflective (like any glass surface) and might cause problems with any light reflecting back out of the telescope/camera combination. Don't know if it will help, but, it won't hurt.

Steve

[XCalRocketMan]

I use a LED flat panel on top of my OTA but I place anywhere from 3 to 6 sheets of paper to diffuse and dim the light a bit. Works great. And, I've determined how many sheets to use for NB and BB filters so I can keep the exposure about the same.