William OpticsFlattener III .8x Reducer/Flattener

[spacebloke]

Hello,

I have been advised that this focal reducer can be used on a 80ed ds pro. Does anyone on here use one with theirs?

If so how do hey compare to the skywatcher ones?

Cheers

Stuart

[carastro]

I have used this flattener for 2 years. It is OK on the whole but does give misshappen stars in the far corners. Up until recently I never used to use the full frame so it didn't matter.

Have a look at the recent images I have done on my website, in particular the Witches Broom and M31 done on 2-7-2011. If you click on the thumbnail this will open up an indivudal page, then scroll down, there is a link to the full image which you can enlarge and examine the corners.

I have now bought myself a new flattener (but only done the Bubble on it so far), partly to sort out the corners but also for another reason which I won't go into now.

Carole

[shaunster]

I would avoid the FF3 from WO, its pretty poor at the best of times...

Skywatcher make a dedicated one for the ED80, that would be your best bet.

[Deneb]

Or buy yourself a televue trf2008, which btw is nearly double the cost of the sw one. But can be used on scopes between focal lengths of 400-600mm.

TeleVue Focal Reducer 400-600mm 0.8 x

Nadeem.

[spacebloke]

I think it's going to be more beneficial to get the dedicated sw one.

[steppenwolf]

It worked well enough on my ED80 but stars in the corners of the frame took on a 'spiky' appearance - much better than elongated stars without the correction but not as good as I would have hoped for.

[ScubaMike]

I don't understand what the flattener is supposed to do.

If you click on the thumbnail this will open up an indivudal page, then scroll down, there is a link to the full image which you can enlarge and examine the corners.

What am I looking for? I can't see anything wrong with this.

Maybe I've got much lower standards than you

[JamesF]

I have used this flattener for 2 years. It is OK on the whole but does give misshappen stars in the far corners. Up until recently I never used to use the full frame so it didn't matter.

Have a look at the recent images I have done on my website, in particular the Witches Broom and M31 done on 2-7-2011. If you click on the thumbnail this will open up an indivudal page, then scroll down, there is a link to the full image which you can enlarge and examine the corners.

Am I right in thinking here that the problem is the diagonal "stretching" of the stars (a bit like entering hyperspace , perhaps most evident in the top right of the M31 pic?

James

[JamesF]

I don't understand what the flattener is supposed to do.

I *think* the issue is that to get perfectly-shaped stars across the entire image, you'd need a curved chip. Imagine shining spotlight onto a big screen when it's right in front of you. When the light is in the middle, you get a nice circle of light. As you turn the spotlight towards the corners it becomes elongated. If the screen were curved like a sphere with you at the centre, that wouldn't happen -- you'd get perfect circles everywhere.

I guess there's also potentially a problem in that the corners of the chip are further from the point of focus than the centre of the image, so the entire surface can't be in focus at the same time.

I assume the flattener is intended to address this problem by "straightening" the light cone before it hits the chip, thus bringing more into focus and reducing the elongation of the stars at the extremes.

How's that?

James

[Steve 1962]

I'm with Carole on this - I have a WO 0.8 FRIII and in the corners of my DSLR chip it gives me radial distortion (coma?) and circumferencial arcs (no idea what this is called!) so my corner stars look like little crosses.

I tried to get the spacing spot on between the Flattener and the DSLR chip but 5mm was too much and 4mm was too little

I would not recommend one of these to anyone - If I had my time again I'd get the SW one or the TV TRF 2008 as recommended by Nadeem if funds allowed.

Steve