focal reducer & SCT questions

[Trevor-Austin]

I have an LX90 8" F10

If I get the Antares F6.3 reducer I am pretty sure this will ensure better imaging results but will it make improvements to visual observations of deep space objects as if it was truly an F6.3 1260mm FL scope or is it just "fooling" the DSLR into thinking that?

Thanks

Trevor

[Dave Smith]

I have a 0.63 focal reducer for my SCT and for visual observations it is like having another telescope.

So for me it works fine for imaging and observing. I know nothing about your particular scope or FR but I imagine it should be fine.

Dave

[barkis]

I think at f6.3, it would work fine visually. It is the 3.3 reducer that is suitable only for Imaging.

Ron.

[cgarry]

I have a Celestron f6.3 Focal Reducer for my F10 SCT and it is amazing for visual observations. The magnification is reduced and you get more sky in your EP.

Cheers,

Chris

[Trevor-Austin]

Thanks for the replys

Can you also see fainter objects/nebulae? Or is it just an increased FOV?

[Johnboy]

I had one for my CPC1100 but couldn't focus with it in. The only mod I did was change my diagonal to a 2" one but that seemed to be enough to cause the problem.

[cgarry]

Can you also see fainter objects/nebulae? Or is it just an increased FOV?

Yes, because the same amount of light is spread over less area those objects appear brighter. I have yet to try the reducer out with dark skies to see just how well this works.

[Trevor-Austin]

That's what is confusing me though, isnt it the same amount of light over a wider area? i.e. bigger FOV?

[cgarry]

With the reducer in place the object appears smaller. So the same amount of light in the smaller area makes the object look brighter. The same effect is seen with planets, the more they are magnified the dimmer they get because the same light is being spread over a larger area.

This is not true for stars though, because they are always a point of light no matter how much magnification is used.

[Mr Spock]

Visually, some of the above is not logical, therefore...

If you put an extra wad of elements in the light path you will lose some light.

At f10 a 40mm eyepiece is fine, but at f6.3 the exit pupil will be too large and light will be lost.

The focal reducer limits the field of view slightly so you get less field of view at f6.3 not more. Though you can get larger focal reducers.

So, my C9.25 is capable of 1.3° at f10 before vignetting sets in. My 42mm 70° eyepiece at x56 gives exactly that.

At f6.3 the magnification would be lower (x35) but the field size would be slightly less (42mm on the reducer as opposed to 48mm on the scope) and light would be lost due to an oversized exit pupil (6.7mm), plus the central obstruction would become visible. Not a win really.

Photographically, the reducer gives shorter exposure times but smaller objects.

[Trevor-Austin]

Ok, that makes sense.

So visually I would not get a better view of, say, the ring nebula, using the reducer as opposed to using a 2" widefield eyepiece like the panaview?

[cgarry]

I cannot use 2" EPs with my scope, hence I never considered them. The 2" widefield eyepiece is probably your best way forward. The Celestron reducer instructions states that an EP with a focal length of greater than 35mm should not be used for some of the reasons Mr Spock lists.

In my case (No reducer):

TeleVue 32mm Plossl: Mag x46.88 AFOV 50 degrees TFOV: 1.07 degrees

TeleVue 40mm Plossl: Mag x37.50 AFOV 40 degrees. TFOV: 1.07 degrees

With reducer:

TeleVue 32mm Plossl: Mag x29.53 AFOV 50 degrees TFOV: 1.69 degrees

So the reducer has increased my TFOV from 1.07 degrees to 1.69 degrees.

[Mr Spock]

So visually I would not get a better view of, say, the ring nebula, using the reducer as opposed to using a 2" widefield eyepiece like the panaview?

That's right. For the ring nebula I would use my 22mm (x107) and 13mm (x181) because of it's small size anyway. Plus higher powers give a darker background.

I'd drop down to the 42mm (x56) for clusters.

Going the 2" route gives you a better option. At f10 you can use a simpler eyepiece with fewer elements and get good results and better light transmission. A PanaView will be fine.

At f6.3 you are getting close to having to use more expensive eyepieces such as a Nagler / Panoptic / LVW. Those plus focal reducer will give less light transmission.

[sixela]

Ok, that makes sense.

So visually I would not get a better view of, say, the ring nebula, using the reducer as opposed to using a 2" widefield eyepiece like the panaview?

The ring nebula is extremely small, so it's not a very relevant example.

Visually, what the reducer is doing for you is make it possible to see large true fields of view with smaller focal length eyepieces, which makes it possible to achieve them without using 2" eyepieces.

If you have 2" eyepieces, the only advantage is that a very wide field of view is also slightly flatter, so if you have trouble accommodating for focus differences, you'll notice the coma at the edge of the field less.

Visually a reducer doesn't allow you to see more by concentrating light over a smaller area, because visually you're adjusting that by picking the right eyepiece anyway; with a reducer in place you may pick a different eyepiece, but at the same magnification the surface brightness of objects will essentially be the same.

[Trevor-Austin]

Thanks, that's helped me make my mind up. No reducer for visuals, just more 2" eyepieces, really love the panaviews.