To Flatten or not to Flatten; That is the question!

[Crater101 (Warren)]

Folks;


As a relative newcomer to the imaging side of things, I've started to experiment with a more careful approach to astrophotography, and I'm wondering if I need a flattener for the setup to get the best results.


The Telescope:
Williams Optics Fluorostar 91
540mm focal length, f5.9



The Camera
ASI 183 MC Pro
Sony IMX CMOS sensor



Most of the information for the Flourostar recommends either the standard flattener or the 0.8x reducer/flattener to get the best imaging results for full frame cameras. The ASI 183MC Pro has a sensor size of 13.2 x 8.8mm (5496 x 3672 resolution). The standard flattener is almost three times the price of the 0.8 reducer, and while that's not really an issue, I want to make sure I get the correct setup.



Obviously the reducer will flatten the image while also shortening the effective focal length.


So my question is, do I need the flattener or the reducer to get the best imaging from the scope, or is the camera sensor size capable of giving me a decent image without it?


Thoughts and opinons very much invited.

[oska (John)]

I have no idea really (newb!) but I'd go the flattener, then later if you feel the need the reducer. To mine, there are very few targets that need less than 500mm. And for the ones that do, mosaic

The least expensive question you can answer yourself: take a shortish (30s?) exposure of a reasonable starfield and look at the star shapes in corners and centre. Stars will be elongated in the corners and tight in the centre if you need a flattener. Please post your results I'm keen to learn whatever I can

[Crater101 (Warren)]

Originally Posted by oska

The least expensive question you can answer yourself: take a shortish (30s?) exposure of a reasonable starfield and look at the star shapes in corners and centre. Stars will be elongated in the corners and tight in the centre if you need a flattener. Please post your results I'm keen to learn whatever I can

You make an excellent point, and it's not a bad way to find out an answer to the question. I should have thought of that myself.


And don't worry - the photographic side of this is new to me too.

[ChrisV (Chris)]

I can't answer which will produce the flatter image. Both probably similar??

Then there's two things
1. The reducer will make the scope faster - good.
2. The reducer will lead to a wider field of view but less resolution - personal preference.

But as said below. Take some shots first to see if you need the flattener with a sensor which is much smaller than full frame

[Camelopardalis (Dunk)]

Either would be worthwhile, but I’d go for the reducer…it makes the scope photographically faster and the 183 likes photons. The small pixel size will make up for any sacrifice in theoretical resolution.

[Crater101 (Warren)]

Again, some good advice.



My thanks for the thoughts folks. Much appreciated.

[agprasun (Prasun)]

I would suggest the reducer as you get an overall faster system

[Crater101 (Warren)]

Originally Posted by agprasun

I would suggest the reducer as you get an overall faster system

Thanks again. Certainly leaning in that direction.