What am I seeing in C6S?

[chrisdg1968]

Hi all,

Managed to get out to have a look at Venus (showing a very nice cresent) and the Moon tonight.

Anyway, towards the end of the session noticed in my EP field of view some opaque darkening in a small area near the centre - not really noticeable unless moving the scope in RA against the background.

Now I am presuming this is simply an effect of the secondary obstruction, especially as this would be more evident with a very bright object such as the moon, but it was unusual as it clearly took the form of two parrallel (though not very straight) lines.

Put my mind at rest people! Could it be something other than the secondary obstruction?

Thanks!

Chris

[adamsp123]

What EP where you using?

[chrisdg1968]

I noticed the effect whilst using a 20mm SWA (70 degree) and a 32mm (52 degree).

Chris.

[beetlejuice]

I noticed the effect whilst using a 20mm SWA (70 degree) and a 32mm (52 degree).

Chris.

What you are seeing is 'kidney beaning'. In some long f.l. or wide angle eyepieces, it is sometimes necessary to move the eye closer to the eyepiece in order to see the edge of the field. When this occurs, parts of the field between the centre and the edge are cut off as a portion of the converging beam misses the eye's pupil. This appears to the observer as a kidney bean shaped dark region that meanders around the field as head moves.

[chrisdg1968]

Thanks Beetlejuice, Kidney Beaning sounds a distinct possibility although the 'parallel line' effect I am seeing is a little different to what I have read up on.

Anyways, I am certain it is not a fault with the scope so will just live with it!

Chris.

[The Warthog]

I'll differ here a little. Kidney-beaning appears as a dark area in the shape of (yea verily!) a kidney bean, and is usually not in the centre of the FOV. I believe what you are seeing is the secondary obstruction, which can become more obvious in longer, wider angle eps, as a dusky patch right in the centre of the FOV.

[dweller25]

Hello Chris,

Could dew have been forming on the corrector ???

[chrisdg1968]

Well, there is a small possibility there was some dew formation, quite a cold night as I recall though I did have the dew shield fitted.......think I just have to accept it was an observing effect caused by one thing or another and not a scope fault (unless anyone else has an alternative opinion!).

Chris.

[dweller25]

Chris,

I have a heated dew shield on my C9.25, but if I don't have enough heat going through it will still dew up causing all sorts of weird effects.

Might be worth checking next time.

[chrisdg1968]

Thanks, certainly something I will check out next time.

Chris.