Astro engineering 0.6x focal reducer

[Johnboy]

Hi folks,

I am interested in buying one of these to use with my CPC 1100:

http://www.firstlightoptics.com/proddetail.php?prod=AE_focal_reducer

It will reduce the focal length of my scope from 2800 to 1680. The thing I am concerned with is that it states in FLO's description 'the use of extension tubes and/or carefully positioned filters can provide a useful focal reduction ranging from around 0.5x to 0.65x.'

By this I presume it means that if the FR was moved away from the end of the eyepiece via a filter or tube, then the reduction can be varied. If I am correct, and with this in mind, would the greater distance from the eyepiece to the FR via a binoviewer make a difference and if so what would this be?

I am asking this as I use both single eyepieces and a binoviewer and wanted to check before I buy.

Thanks folks.

John

[Merlin66]

These were originaly designed for used with webcams. They are not suitable for "serious" imaging with a CPC1100 unless obviously you're using a webcam.

[Johnboy]

These were originaly designed for used with webcams. They are not suitable for "serious" imaging with a CPC1100 unless obviously you're using a webcam.

Hi,

Sorry, I should have said it would be for visual only. I'm trying to get a wider FOV for some objects and these seem to fit the bill.

Thanks.

John

[Merlin66]

I wouldn't use it.

An SCT x0.63 would be a better bet.

[Johnboy]

I wouldn't use it.

An SCT x0.63 would be a better bet.

I tried a x0.63 but couldn't achieve focus with it in place. It was fine until I upgraded the diagonal from a 1.25" to a dual 1.25"/2". It seems the reducer didn't like the new diag.

Thanks for your suggestion though Merlin.

[Merlin66]

Hmmm

The backfocus requirement for the SCT x0.63 reducer is 110mm

I would have thought you'd have had that amount of space available?

[Johnboy]

I've never quite understood why the scope wouldn't focus with the x0.63 in place. It was fine with the stock diagonal but not with the Revelation 2" I fitted so I assumed that was the problem. To be honest I regret selling it as most people say they are a very useful addition. I wish I still had it so I could give it another go. I can't help doubting myself now....

[brianb]

Sorry but using a focal reducer to get a wider field of view is a chimera ... the field is ultimately limited by the size of the secondary mirror & the baffle tube.

With a CPC1100, the best field of view is obtained by:

1. Removing the visual back and the large sct adapter

2. Obtaining a 2" push-in visual back which fits the large SCT (3.25") thread directly

3. Using a quality 2" push-fitting diagonal - if needed, actually you get more FoV by omitting the diagonal if you can cope with the eyepiece position

4. Using a wide angle eyepiece of focal length around 40mm. A 60 to 70 deg AFOV is as much as is needed, any more than that will suffer from vignetting. An eyepiece longer than 40mm is likely to cause issues with shadowing due to the central obstruction, but you may be able to "get away with" 50mm if you have dark skies and young eyes ... in which case a standard (50 deg AFOV) Plossl will fully exploit the maximum field available.

Focal reducers inevitably reduce contrast and cannot increase the angular size of the illuminated field of view, in fact the usually reduce it to some extent. They're very valuable for imaging with cameras with smaller chips but not for visual work.