Focal Reducer for Edge HD

[jkm13]

Hi all......

I wonder if i buy ordinary focal reducer for my Edge HD 8", what problem happens to view or camera shooting?

there looks vignetting issue. but i can crop image. This could be a problem?

any advice would be welcome.

thanks in advance.

[ollypenrice]

The original item is a reducer and flattener  but the Edge already has a flat field, so using the original item will un-flatten it! This would be a bad idea.

If observing visually there is no point in using the reducer since, provided you have a 2 inch visual back and wiidefield eyepiece, you will reach the field limit of the optics without the reducer.

Remember the F ratio myth when thinking about imaging with this scope. The dedicated reducer will widen the field of view which is great if you want to do that. But, if you want to image a galaxy which will fit on the chip without the reducer, you will get no more galaxy photons with the reducer in place. You could shoot without it and resample the image downwards to get pretty much the same effect. (The F ratio/exposure time rule works when, as with camera lenses, you vary the aperture to vary the F ratio. It does not work for telescopes on small targets where you vary the focal length to vary the F ratio.)

Olly

[Dave In Vermont]

As the issue of focal-reducers has been raised, a 'caveat-emptor' has come to my attention recently. So I believe it should be passed along:

The Antares 0.5X 1.25" F-R is causing problems all over the globe. It seems the threads are poorly cut & don't fit eyepieces or diagonals. The threads don't engage/wear-down so the F-R just slides inside the barrel. Some have suggested wrapping it in Teflon® tape to get it to hold - but still...?!

I would suggest their distributers contact Antares and register a loud complaint. I'm told that optically these are quite nice. Seems a shame such nice optics are in a defective encasement.

Shop apprised,

Dave

Image by Mak the Night

[Waldemar]

I had an issue a couple of years ago with an Orion adjustable polarising filter and a set of colourfilters.
Measuring the threads it turned out they were 48 x 0,75 mm instead of 48x 1...

May very well be the same kind of issue with the Antares

[Dave In Vermont]

Not quite, Waldemar - allow me to explain:

Antares knew of a problem with these some time ago. They "made corrections" and my friend bought one from a new lot. It threaded on fine - for a few times. Then it was noticed they were 'shedding' a white-powder onto the eyepieces/diagonals this FR had been placed on. And then it lost it's threads again - sliding in & out again!

So it wasn't just a miss-cut of the thread-pitch. And their 'fix' was like a bad joke. On another note, no problems have been noted on the 2" version of these. Yet? I'm not going to be the Guinea-Pig.

All the best -

Dave

[jkm13]

19 hours ago, ollypenrice said:

The original item is a reducer and flattener  but the Edge already has a flat field, so using the original item will un-flatten it! This would be a bad idea.

If observing visually there is no point in using the reducer since, provided you have a 2 inch visual back and wiidefield eyepiece, you will reach the field limit of the optics without the reducer.

Remember the F ratio myth when thinking about imaging with this scope. The dedicated reducer will widen the field of view which is great if you want to do that. But, if you want to image a galaxy which will fit on the chip without the reducer, you will get no more galaxy photons with the reducer in place. You could shoot without it and resample the image downwards to get pretty much the same effect. (The F ratio/exposure time rule works when, as with camera lenses, you vary the aperture to vary the F ratio. It does not work for telescopes on small targets where you vary the focal length to vary the F ratio.)

Olly

@Supernova : Thanks for detailed explanation. it helped me. and did you means that there is way without reducer to shot outside of camera frame? for example, i want to shot andromeda on one frame. however, Edge HD 8" is too enlarge this object. so i thought reducer to reduce this. if just reduce in photoshop, what about outside of frame? sorry if i miss some point.

thanks