0.5X 1.25 Telescope Focal Reducer, 2-Element FMC Optics

I had to call a few places to get this info: Take the stock lens off the camera. Don't use it with this thing on. Focusing can be touchy. On my Astro Fi 130 with a Pegasus focuser I found that I was overshooting the focus point and seeing nothing because the camera takes a few seconds to get a lock in Sharpcap plus the focuser has 20,650 steps. The range of steps between fuzzing out/seeing anything/fuzzing out again was 150 steps. Until I went from 0 to 20,650 at 100 step intervals waiting 5 seconds for Sharpcap each time, I couldn't even tell if it would ever work. Finally I got a fair shot of Vega..... I don't know if it's any good for a 5 inch reflector but...eh.

This focal reducer screws into the nose of an astrophotography camera or 1.25" eyepiece. For visual use, it turns a 20mm eyepiece into a 40mm, both decreasing the magnification and increasing the field of view. In astrophotography, the focal reducers does that, but it also reduces the size of stars on the sensor by half, meaning you can image faster with a wider field of view. For example, an f/10 camera/scope is reduced to f/5 will image roughly six times faster (if my math is correct) because the focal reducer concentrates more photons on each well in the sensor. This focal reducer works well and gives a nice view. I highly recommend it!

I bought this focal reducer with the hope that I could use it with my 6SE telescope and two digital cameras. The threads fit the 1.25" threads on my eye pieces and cameras with appropriate adapters. Fit was not a problem at all. I had no problem getting my image into focus using this reducer with the SV305 camera. However, I could not get the right distance to bring anything into clear focus using my Canon 450D dslr. I have not been able to find the right combination of adapters to make it work - I've tried. The best I could do was use an eyepiece projection adapter, but the vignette was terrible despite a focused image. This 0.5x focal reducer did increase the field of view for the sv305 camera. The center of the image is fantastic. I was able to actually use the sv305 with this focal reducer to capture smaller deep sky targets - see the photos of M2, M30 the Jellyfish cluster, and M27 the dumbbell nebula. Unfortunately the outer area suffers from distortion. Stars are elongated and chromatic distortions are present. A field flattener is needed to help correct this. Its not a fault of this particular focal reducer. Pretty much any focal reducer will have the same effect on its own. If you are looking to increase the field of view this focal reducer will work providing about a 50% increase in the field of view assuming you can get the fight focal distance. Just don't expect it to do miracles. Its not the same as the much more expensive field reducers with field flatteners and shouldn't be compared to them. For daytime images this actually works even better as the edge distortions are much less noticeable.

The size looks right, but the threads don't hold. I almost lost the reducer down the focus tube. I have it held onto the SV205 with scotch tape. It works, but I'm not all that happy about it. I'm only using it for imaging the moon. I only just tested it tonight, and the wind makes it impossible to test the image quality, but nothing stands out as awful in the shots I took. ... I think I need even more reduction, to be honest, but that's not this part's fault.

Good quality optic for the price, works as described and fits perfectly.

I will post photos shortly. Mine works fine, visually. But we all know the wandering eye can be very forgiving when it comes to differences in focus between the center and the edge of view. So, what gives? According to Manish Panjwani and Brian Ventrudo at agenaastro, based on the book by Harrie Rutten and Martin Van Venrooij, the "ideal" or "designed" back focus "BF" of a reducer can be calculated as: BF = F_R *(1 -M) where F_R is the focal length of the reducer, and M is it's strength (x0.5, here). Most manufactures of these x0.5 1.25" reducers claim a focal length F_R = 85mm. This gives a back focus "BF" of 42.5mm. Add 1/2 the length of the optical tube of the reducer (to get to the center of it; e.g., 1/2 of 20mm = 10mm), and you arrive at 52.5mm - which is very close to the usually advertised BF of about 50mm. For example, my ZWO ASI585MC has a distance of 36.5mm between the sensor and the end of the 1.25" adapter. So, for that, I need about an 15mm spacer. Sure, for simple refractors, reducers can be used outside their designated range - but that will affect the reduction factor, FoV, and quality at the edge of view.

I was hoping that this would allow me to extend the field of view for some astronomy pictures but, as I got started, I was noticing some anomalies in the pictures so, didn't even bother to finish focusing. I have an f/6.3 which works well in a similar setup but, this just didn't appear to do anything similar to what I was expecting. I was expecting some vignetting but, not this much and, was somewhat expecting some aberrations but, not nearly as many. The product is a really good idea and, will continue trying to make it work but, at this moment, I cannot recommend for anyone using a similar setup to my own - 10" LX200 for Prime Focus photography. If I get it working, I'll share the trick and update the review.

Perfect with the sv 305 camera and the sv 105 mk. It is helpful that the maksutov is a telescope of high corrected optical. Also works great with high magnification lenses like 5mm on the same sv 105 mk. The images from the camera were compared on the page (astronomy.tools/calculator) and give similar proportions using the ZWO mini 290 as a reference. Same sensor size. For price you can not expect more. For me it is perfect.

It is easily fitted to the end of a camera to give a wider view.

Excelente reductor para roscar en el ocular.

Hatte mir mehr davon versprochen,nur bedingt brauchbar.

Este aditamento es útil para tener una visión más amplia, el vidrio me parece de calidad. Se.adapta a oculares, filtros e incluso lo he podido colocar al final del adaptador para la cámara fotográfica. Quizá es mi falta de pericia, pero su limpieza se me dificulta y es frecuente que ponga los dedos en el vidrio. No me pasa con otros aditamentos. Vale la pena.

Funciona, pero crea muchas "comas".