0.5x or f6.3 reducer?

[traveller]

Can someone explain to me the difference between a f6.3 reducer and a 0.5x reducer. There is a bit of dollar difference between them. From what I can understand a f6.3 will turn a f10 sct to a f6.3 and a 0.5 will make the same scope a f5. Is this too simplistic?
Also, I think most f6.3 also have field flatteners in their optics, which is ideal for wide field astro photo work, but 0.5x is a plain reducer. Have I got this right?
:thanx:

[tempestwizz]

Basically you are correct in your simplistic assumptions. The purpose of the focal reducers is to increase the available angle of view through a given optic system.
Nothing is ever perfect however, there are always compromises in performance.
These can include reduced flat image area (hence why some claim to include a flattening feature), increased coma around the edges and vignetting.
A number of manufacturers produce reducers, but mostly are matched for their own prime optics. WO, Tak and Televue are prime examples.
Many people have employed the reducers effectively to compensate for the relatively smaller imaging area of their CCD cameras (especially earlier versions) over the available DSLRs.
I have not tried it, but I suspect you would not be happy with the results if you used a 35mm format DLSR on a F:10 SCT fitted out with a .5x reducer.
There would only be a very small portion in the centre of the image that may be useful.
If you were using a CCD imager with much smaller imaging area, such as a DSI Pro, you may well be quite pleased with your results.

AS for the flattening feature, I'm not 100% certain, but I don't believe the reducing feature automatically flattens your image at the same time. Some reducers claim flattening features, some don't. You need to read the specs very carefully.

HTH,

BC

[traveller]

Thanks Brian, I have a DSLR, a Quickcam and a Philips SPC9000c and tried with some success with them both. I am waiting for my Celestron 8se to arrive, it only has a 1.25" visual back and the standard AZ mount which really limits me to some basic planetary work with webcam.
I do intend to get a 2" vb soon and then a EQ6 later for DSO work.
Based on what I can establish and what you are telling me, a reducer with flattener will only be of use with DSO and an auto guider.
Cheers, Bo