Focal reducer.

[vince 66]

Can a focal reducer be used for visual use or are they just for AP . If they can be used for visual are there any restrictions can the be used with a SCT focuser etc.

[Pig]

Focal reducers can be used for both AP and visual,

I did try one but could not get it to focus. In all fairness to the reducer I did not attach it in the normal place on the back of the SCT, I tried it further up the optical path thus causing the focus issue.

Yes they can be used for SCT's quite successfully.

[iksose7]

Not sure but i dont see why not, it would just give you a wider FOV when looking through the eye piece?

[Alien 13]

My reducer has a T thread on it so i would need a T to eypiece holder adapter to try. Thats given me an idea i could use that on my M42 camera lenses too.

[michael.h.f.wilkinson]

My 0.63x SCT reducer works with the 1.25" visual back and diagonal, but it is pointless with the 2" visual back and diagonal. The focal reducer does not just reduce the focal length, it also reduces the size of the image circle from about 48mm to about 28mm, or suitable for 1.25" EPs with maximum field stop. If you are limited to 1.25" EPs, the focal reducer is very useful visually (I used it for many years visually with my C8). Once I got my first 2" EP (40mm Paragon with 45.6mm field stop), I stopped using the reducer (fewer optical components in the light path, less hassle.

0.33x reducers were only ever meant for small CCD chips, and I believe they do not have sufficient back focus for use with even a 1.25" star diagonal/

[Tinker1947]

My C11 works fine with the stuff in the images, not had a chance to compare with and without as the first time i attached the reducer it got stuck, i now use a 42mm rubber ring between the FR and the tube Adapter, a canon D1100 comes to focus with out the Diagonal  ok, the original C11 focuser has been replaced with a FeatherTouch its so much better now....

 

[michael.h.f.wilkinson]

If I calculated it correctly, the 30mm XW has a field stop of about 34mm. Maybe the vignetting is not that bad after all. I know I did get vignetting with the Paragon 40mm

[Tinker1947]

If I calculated it correctly, the 30mm XW has a field stop of about 34mm. Maybe the vignetting is not that bad after all. I know I did get vignetting with the Paragon 40mm

I checked Stellarium and have the Field Stop at 36.2, i can check in the box and see what's on the paper work later..

[vince 66]

Thanks for the replies. So a reducer is not a case of simply fitting one to your scope and away you go?. I may be better off just getting a bigger eye piece. Is this the case.

[michael.h.f.wilkinson]

Thanks for the replies. So a reducer is not a case of simply fitting one to your scope and away you go?. I may be better off just getting a bigger eye piece. Is this the case.

It depends. If you have a standard SCT 1.25" diagonal the reducer works very nicely with any EP you stick in. The only downside is that changing to the really low magnifications and back by inserting the reducer is a bit more hassle (due to the fine screw thread which can easily be cross-threaded if you are not careful), compared to swapping EPs. Like a barlow, it is a fairly low-cost way of extending the range of magnifications, and is better quality than cheap barlows. I never noted any degradation of the image. The SCT reducer also corrects for coma (but I never found coma to be a great problem visually).  Replacing the 1.25" diagonal supplied with the scope by a 2" type, and getting 2" EPs is more expensive, but ultimately more comfortable in use.