focal reducer question

[blinky]

Just a quick question, does a focal reducer widen the FOV the nearer or the further away it is from the CCD? And if it is nearer the CCD how close can you place it?

[iancandler]

I find placement wise using the T mount on the WO focal reducer to mount my DSLR via a T ring works out just about perfectly.

[Kaptain Klevtsov]

They're supposed to, in an ideal world, get "stronger" as you move them away from the camera chip. Plonk it on the chip, no effect, move it away and the FOV gets bigger. Most though, have a sweet spot, or at least a range, where they work well. This places limits on how far from the chip you can have the FR, but it adds to the fun that is imaging.

Kaptain Klevtsov

[blinky]

Thanks for clearing that up. I was a but confused when the short adapter said 0.7X and the longer adapter (this is on Ian Kings website) said 0.5. I assumed the image was 70% larger and 50%Larger but it means that with the 0.7 you see....no wait still confused Too early in the morning, will come back to this later!

[iancandler]

Which focal reducer where you looking at blinky? the reason I ask is because if its for the ZS66 not all work, it has an issue with not enough forward focus ("in" focus travel) with the standard sct focal reducers.

[blinky]

It's the Atik one Ian. I bought it with a short 1.25 nosepiece to make the effect 0.7 times. I can get it to focus with the short and the normal nosepieces but was wondering what one would give the widest FoV. I assume it is the 0.5 that makes it the widest but could not get my head round the numbers Surely a reduction of 0.7 is more of a reduction that 0.5?

No wait just opened up calc on my PC. If I assume my FoV is 10 (Degrees, minutes, bannana's, whatever) and I put in a 0.7 X Reducer that will make my FoV 7 (Or 70% of what I could previously see), If I put in the 0.5 it will make the FoV 5 (Or 50% i.e. Half of what I could see).

:withstupid: :withstupid: :withstupid: :withstupid: :withstupid:

[jgs001]

Craig, I'm not an expert on this, but a barlow, increases the magnification and decreases the FOV by a factor of 2 etc. Therefore I'd have thought that a focal reducer operates in the other direction, decreases the magnification and increases the FOV by a factor. I'm not certain of the relationship between the magnification and the FOV, but I'd expect that the magnification would be mulitplied by 0.7 rather than the FOV.

Very simplistically, and the factors are probably wrong for the adjustment on the FOV, but for a X2 barlow...

Mag = Mag X 2

FOV = FOV / 2

For a focal reducer of 0.7

Mag = Mag X 0.7

FOV = FOV / 0.7

[Ant]

They are effectivly oppisite of each other.

But the effect dpends directly to the distance between barlow/reducer and the EP/chip.

The greater the distance the more of an effect.

Ant