How do i increase the field of view on my CPC 800

[Planet X]

Hi guys,i have a question regarding my CPC 800. Which would give me a wider field of view,a focal reducer and my standard Celestron 40 mm eyepiece or a two inch diagonal and 2 inch 40 mm eyepiece?  Also can i use, for instance, a Celestron f6 focal reducer and then attach my William Optics 2 inch diagonal and my Baader zoom MkIII?  If so will the focal reducer increase the field of view?  I am a bit confused about what i can and cant use together to increase my chances of a wider field.  

thanks in advance Carl

[Davey-T]

There's no way to increase the FOV as such' you can try to get the maximum available. On my 10"SCT I have a Peterson eyeopener and 2" diagonal but the FOV is still limited by the intrinsic design of the scope.

The focal reducer won't give more FOV just a smaller brighter view of what's already available.

Dave

[Planet X]

Forgot to mention,i am using a Baader steeltrack crayford focuser,i am not sure if this matters?

[John]

Hi Carl,

Whichever way you go the SCT is not a widefield scope. With a 2" 40mm wide field eyepiece in a 2" diagonal the widest field you can get is 1.4 degree true field and it might be a little less than than in reality. I think using the focal reducer with 2" eyepieces causes some vignetting (loss of light around the outer parts of the field of view).

It may sound crazy but it's often less expensive to buy another scope such as a used 200mm F/5 newtonian to get those wider fields of view.

[Planet X]

There's no way to increase the FOV as such' you can try to get the maximum available. On my 10"SCT I have a Peterson eyeopener and 2" diagonal but the FOV is still limited by the intrinsic design of the scope.

The focal reducer won't give more FOV just a smaller brighter view of what's already available.

Dave

Hi Dave,what is a Peterson Eye opener?  I thought that a f6 focal reducer would half the focal length of my scope and therefore increase the field of view?  Basically when i view the Moon for instance it pretty much fills the field of view with my 40mm eyepiece,i also struggle to get the Pleiades in the eyepiece.  I see that Antares make 1.25 and 2 inch focal reducers that can screw into the thread of a diagonal,yet they also make a f6 focal reducer that screws directly onto the thread of the SCT.  Which is more effective and which would work best with my Baader steeltrack focuser?

[Planet X]

Hi Carl,

Whichever way you go the SCT is not a widefield scope. With a 2" 40mm wide field eyepiece in a 2" diagonal the widest field you can get is 1.4 degree true field and it might be a little less than than in reality. I think using the focal reducer with 2" eyepieces causes some vignetting (loss of light around the outer parts of the field of view).

It may sound crazy but it's often less expensive to buy another scope such as a used 200mm F/5 newtonian to get those wider fields of view.

Hi john,yes im aware its not a great widefield scope,i just wanted to try and extract as much as i could out of it and wasnt sure how to go about it.  i hadnt really thought about buying another scope. if i did it would have to be something small which i could attach to my CPC and use the GOTO.  Not sure i want to get into that just yet though.  Cheers

[John]

The Pleiades needs a near 2 degree true field of view to fit it all in. Not sure there is any way to get that from an 8" SCT ?

[Davey-T]

Peterson eyeopener is a mod to screw direct to the SCT thread to gain the maximum FOV, not cheap and made for Meade scopes, don't know if it works on other makes, the amount of gain is not spectacular for the money. I piggy back a 100mm refractor for wide field, you could get a used ST80, cheaper than eyeopener and much bigger FOV.

Dave

[YKSE]

Carl,

The 2" eyepiece option gives a little wider true FOV (TFOV) than the f6.3 reducer. 2" eyepiece has 46mm field stop as max, assumning your scope has focal length 2032mm,  it gives

TFOV=57.3*46/2032=1.30 degrees

with the f6.3 reducer, the TFOV will be limited by field stop 1.25" eyepiece, with is usually 27mm, you get

TFOV=57.3*46/(2032*0.63)=1.21 degrees

[Grotemobile]

http://www.telescopehouse.com/acatalog/Revelation_30mm_Eyepiece_2__.html

I bought the 30mm 2" EP.I have the same

scope as you.Dont be put off by the

price.It is a good EP, for wide field

views. A lot better than the 40mm EP,

supplied with the scope.

Steve.

[Planet X]

http://www.telescopehouse.com/acatalog/Revelation_30mm_Eyepiece_2__.html

I bought the 30mm 2" EP.I have the same

scope as you.Dont be put off by the

price.It is a good EP, for wide field

views. A lot better than the 40mm EP,

supplied with the scope.

Steve.

Thanks Steve,i have just had a look at them on Telescope house and they are very cheap.its given me something to think about. When i view the moon with the standard  40mm that came with the scope it is almost exactly the same size as the field of view,does the two inch revelation make the image smaller?

Cheers Carl

[John]

The 1.25" 40mm that came with the scope will show a true field that is .84 of a degree and a magnification of 50x. The Moon's disk has an apparent diameter of around .5 of a degree so it will fit into the field of view of the 40mm eyepiece with a bit to spare. The 2" 30mm Revelation eyepiece linked to above will show a true field of 1 degree so there will be a little more sky framing the Moon and it will be magnified 68x.

So it moves a little way towards the direction you want to go in. You will need to get a 2" diagonal to use the 2" eyepiece, inf you have not already got one. 1.25" eyepieces can fit into a 2" diagonal via an adapter so you don't need to change diagonals when you switch between 2" and 1.25" eyepieces.

[Planet X]

The 1.25" 40mm that came with the scope will show a true field that is .84 of a degree and a magnification of 50x. The Moon's disk has an apparent diameter of around .5 of a degree so it will fit into the field of view of the 40mm eyepiece with a bit to spare. The 2" 30mm Revelation eyepiece linked to above will show a true field of 1 degree so there will be a little more sky framing the Moon and it will be magnified 68x.

So it moves a little way towards the direction you want to go in. You will need to get a 2" diagonal to use the 2" eyepiece, inf you have not already got one. 1.25" eyepieces can fit into a 2" diagonal via an adapter so you don't need to change diagonals when you switch between 2" and 1.25" eyepieces.

Thanks for the help John,really appreciated. I already have a William Optics 2 inch dialectric diagonal so i think i might go for the 30mm Revelation.  I see they make a 42mm at 65 degree field and a 50mm at 55 degree field.  Does the 30mm version give the widest apparent field of view out of the three eyepieces,say when observing the Moon again?

[John]

Assuming that the stated fields of view are accurate, the 42mm and 50mm Revelations will show the widest amount of sky, about 1.34 degrees. Personally I'd go for the 42mm as the field will appear more immersive.