Quote:
Originally Posted by multiweb
The flattener is also a reducer. If you image the central area of your corrected field without the reducer it won't look as good as a crop of the same fov with the corrector on. So the answer would be no. Keep the flattener on.
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Is that optically possible or is that another WO marketing hype claim?
I know the Astrophysics 155TCC is a reducer and I think its a fairly flat field although I have not tested it in CCD Inspector. Usually they are 2 different accessories.
I suspect marketing BS especially from WO who had no qualms claiming fluorite lenses when they were ED glass (which has a lot of fluorite in it).
Generally you use a reducer to get a wider FOV and also a faster F ratio meaning faster exposures due to more light coming from the wider FOV.
With full frame it takes a pretty high end reducer to give round stars to the corners. Usually a flattener is needed and it tends to be one or the other. If your use of it shows round stars to the corners and CCD Inspector shows a flatter field I'll stand corrected.
A wider FOV is handy for extended objects and a higher F ratio is handy for getting a bright exposure quickly. So the answer is it depends on the imaging target.
Have a look at Marcus Davies' images. He uses a flattener for regular targets, a reducer for wider extended objects and an extender to capture some galaxies/smaller objects. That's with a Tak TOA150.
Objects like the Large and Small Magellanic Clouds, Orion, Vela Supernova Remnant, Pleiades, Rosette, Eta Carina all are going to look nicer generally speaking with a wider FOV and faster F ratio to get extra depth.
Objects like NGC253 (Sculptor Galaxy), M83, Centaurus A, The Running Man Neb, perhaps the Horsehead require a bit more focal length so the reducer would not be used. In that case you would need a dedicated flattener as your scope may not give round stars to the corners on a full frame sensor - in fact it almost certainly will not. Virtually no scope does without a flattener/corrector of some type.
Often a flattener slightly extends the focal length by a small margin as with Astrophysics dedicated flatteners.
Greg.