Focal reducers, Backspacing and Optical Distance

[richardmjordan]

Jo, With the Infinity and the usual "train" of a focal reducer, an adapter of 2" to 1.25" adapter, LP filter or some other filter and camera, how critical is it to calculate the optical distance? Rod Mollise in his S&T review of Oct 2016 doesn't mention optical distance or backspacing  considerations in the review. Just notes the very nice, noise free images.  I have a C11 with a Meade f/3.3 focal reducer and an AP .72 Quad TCC2 focal reducer for my F/7 TEC refractor.
Rick

[richardmjordan]

Jo in case the measurements are critical, are there any specifications available for the Color Infinity regarding the distance from the camera sensor to the shoulder of the 1.25" nose piece? Thanks. Rick

[Steve]

Hi,

The back focus is 13mm.  The sensor in the Infinity is not particularly big so spacing is less critical.  If you move the focal reducer further away from the sensor you will get more focal reduction and vice versa.
best
Steve

[richardmjordan]

Thank You Steve. Rick

[2star]

I have two FR Celestron 6.3 and a on loan to me Meade 3.3 (yet to use)
I have been using the 6.3 FR with a 50 mm T adaptor, this gives me 63mm (back focus of infinity being 13m). I have been getting decent images. the 6.3 works best with the infinity I am informed at approx 105mm focal train, I have ordered some cheap & cheerful spacers from China to gain the approx 105mm, waiting to use and compare, the Meade 3.3 i have been informed was intended for ccd's with a smaller chip than the infinity, but although there may be some vignetting it still does a job with the infinity
again so I have been informed ha ha . Waiting for the clouds to clear !!!!

[2star]

The Meade 3.3 FR is different, it requires a lot less than 105mm focal train when used with the infinity.

[2star]

I have the Meade FR operating quite well at total focal train of 65mm,(this includes the  infinity back focus)

[manu33]

Hi :

http://www.astrosurf.com/pitalugue/red33.htm

focal reducer 6.3 : 85mm

Manu

[JimH123]

For what it's worth, I have been using this focal reducer from High Point Scientific and getting great results:

http://www.highpointscientific.com/telescope-accessories/focal-reducers/0-5x-focal-reducer-1-25

Here are their talking points on this product:

High Point 1.25" - 0.5X Focal Reducer

    The 0.5X Focal Reducer cuts your telescope's focal length in half

    Delivers a wide field and reduces exposure times for astrophotography

    The 0.5X Focal Reducer from High Point has a 2 element optical design with fully multi coated optics

    The lens cell is anodized black to reduce stray light reflections

    The 1.25" 0.5x focal reducer is a great accessory that allows for great flexibility when customizing your set up

The 1.25" 0.5x Focal Reducer from High Point essentially cuts the focal ratio of your your telescope in half which results in a wider field of view. This Focal Reducer is a great addition to any astrophotography set up as it can cut your exposure time down considerably! Our focal reducer has a 2 element optical design with fully multi-coated optics. Built to last, all optical elements sit in a strong black anodized cell. This focal reducer is compatible with most 1.25" accessories.

[Messier27]

Very, very new to the Atik but...we used an 89.5mm extender on a Celestron Edge HD with an Optec Lepus f/.62 focal reducer and things were fine.  On the same scope we used an Antares .5 focal reducer...screw into the camera 1.25" adapter and in a 2" diagonal...it was okay.  This past weekend we used a Celestron f/6.3 focal reducer in front of a 1.25" dielectric diagonal and it worked very nicely...actually very nicely attached to the standard Celestron 8" sct.  The reason for diagonals has been clearance issues in an alt/az sct.  When using the Optec setup...we had the max Alt range set at 70°.

Do not know what this means...being a rookie...but this is what has worked for us.  We have also used the Infinity directly into an 80mm f/7.5 refractor with no reduction and the image size was similar to the Lepus and Antares reduction on the 8".

FWIW...John

[bwa]

I'm using a GSO 0.5x reducer with the Infinity and have found 35mm (filterwheel plus 10mm spacer) yields almost exactly 0.5x reduction.

bwa

[2star]

I have the Meade FR operating quite well at total focal train of 45mm, for f5 (this includes the  infinity back focus)

[2star]

The Meade 3.3 FR is different, it requires a lot less than 105mm focal train when used with the infinity.

Now using the Meade 3.3 at f5

[2star]

Celestron EVO 9.25, Focal length of Meade 3.3 is 85mm, so around 45mm required to get F5 ( taking into account back focus of infinity) only about 32mm spacer required,
Information courtesy of CN EAA imaging.
eric