Will Flats Fix This?

[Ross G]

Hello,

I am relatively new to astrophotgraphy and so far things have gone smoothly. I have not bothered with darks or flats, relying on ICNR and I have been happy with my photos.

However the slightly elongated stars at the edges of my photos have started to bother me so I recently purchased a WO Field Flattener II for my WO Megerez 110mm f5.95 refractor.
I tested it the other night, shooting 10 min exposures of the Horse Head region in Orion from my backyard in suburban Sydney. Although the stars in the corners were much better, I also noticed a darkening of the corners.
Upon using DSS to stack about 10 of these exposures, I was surprised to see the corners very dark...see the attached photo.

My question is, can I compensate for this by using flats or is the vigneting too severe? If so, are there any other solutions?

Thank you.

Ross

[[1ponders] (Paul)]

Hi Ross.

They most certainly will.

maybe even all of it.

[Ross G]

Good morning Paul,

Thank you for your advice.

I'll read up on Flats and give it a try.

Thanks.

Ross.

[madwayne (Wayne)]

Hi Ross

Best way to do it is to use a light box. You take your light frames and then immediately after, so camera orientation and focus are in exactly the same position, run off your flats. It takes no time at all to do and, as Paul has already indicated, it will remove your vignetting and any dust spots and other imperfections.

If you are after a light box there is a really nice guy in Adelaide, exfso on the forum see the ad in the classifieds, who will make them at a very reasonable price. I have no affiliation just a satisfied customer. Of course if you have the ability and the tools you should be able to make them yourself. I don't so I bought mine .

All the best.

Wayne

[madwayne (Wayne)]

PS

Your stars look nice and tight and given you are imaging from suburban Sydney your data looks pretty good to me.

Looks like you have your gear well setup - well done.

Wayne

[rat156]

Hi Ross,

Flats will fix the vignetting, no problemo.

You should look at you polar alignment though, looks like it's a little off to me as you seem to have some field rotation in the image presented. Were you guiding on a star just a bit higher and right of centre?

Cheers
Stuart

[leon]

Yep, mate do as the experts say, it will solve the problem.

Leon

[Ross G]

Good evening all,

Thank you for your replies. You have saved me a lot of time by setting me on the right path.

Paul and Leon, thank you for your expert advice.

Wayne, thank you for the tips on taking flats and the light box. I will certainly get one. Also, thank you for the positive comments. Encouragement like this does wonders to ones confidence.

Stuart, thank you for your expertise and your eagle eye! My polar alignment was off. I was so desperate to get some shots before the clouds rolled in that I quickly used a compass and an inclinometer to set up the mount and then started shooting...hoping the autoguiding would compensate for any errors in polar alignment.

Again, thank you all.


Ross.

[Astrobserver99 (Rob)]

I believe if you adjust the distance between the field flattener and camera ccd chip (move the field flattener closer), it may also fix the problem.

[Ross G]

Hi Rob,

Mine seems to have a very small range of in/out movement. Probably no more than 2mm. Would this small amount of travel make a significant difference?

Ross

[Astrobserver99 (Rob)]

2mm is not going to make a difference.Where is it currently mounted - on the front of the 2" adapter tube? You could use a shorter adapter if you have one. I am not familiar with the WO equipment - someone else might know more...