0.5 or f3.3 focal reducer flattener with refractor?

[mindburner]

hi I currently have a Meade 127ED F7.5 refractor and I am really happy with it. As clear nights have been few and far between, I use a Williams Optics 0.8 FF/reducer. It gives good overall results in imaging the brifgter DSO's etc.

I was toying with the idea of getting a much more aggressive focal reducer like 0.5 or even f3.3 to speed up the photon collecting.

I do not know so much about the specifics of optical theory, but I understand that vignetting may happen and possibly distortion or be unable to achieve focus.

I was hoping this may be minimal as I will using a small CCD chip in the Atik 428EX

has anyone had any experience attempting to use aggressive focal reducers with larger refractors?

as I suppose I am thinking , how far can I push it

I am tempted by a new scope such as the Quattro f4 but funds needed elsewhere

many thanks

[Scott]

I'm not sure the f3.3 is suited to refractors. the website doesn't seem to mention them. I would check with them before parting with £100+ of my money

[ollypenrice]

Not a chance for the 3.3, I think. Even in the scopes for which it was intended it will only cover a tiny webcam chip. Add to that the false colour of the 127 (not a bad scope and one I once owned) plus the fact that they are not matched, and I'm sure you'd just get a mess! I also think the 0.5 would be well out of its depth. Your chip, if I'm not mistaken, is a tad under 9mm on the long side? The little 0.5 reducer was, again, aimed at webcam chips.

Note that even Takahashi, at 106mm and not 127mm, only push down as far as F3.6 and that is in a dedicated Petzval costing an absolute fortune. The TeleVue NP127, also prodigiously expensive, is only F5.2 - which is very fast indeed for that kind of aperture in a refractor.

Slow F ratio is part of big refractor life, really. TEC don't do a reducer for the 140 I now use.

Olly

[mindburner]

hi Olly. Thanks for the advice. Yes I though I may have problems and the fact there was so little information on using these reduces with larger refractors was revealing. I suppose if I already had a reducer, it may be worth experimenting with but buying one in the hope of reducing imaging time would be foolish. The 0.8 works pretty well and gives flat stars on the 428EX and even on the DSLR sensor, so I will maybe stick with it