ap with f8 reflector?

[ollypenrice]

In my view the only sane way to decide on exposure time is to experiment. Unless you have a very dark site you will soon be up against the skyglow in broadband. Just try short runs of exposures of different lengths and don't be frightened to try long ones. You won't know unless you try. 

Olly

[alacant]

It turned out not to be the one pictured which gave me added bargaining power;) Anyway I took it to bits, showered it (sic) replaced the bits that were missing, un-seized the secondary adjustment screws and apart from a few dents, it looks good. A few questions about...

Collimation. With the supplied clamps, it doesn't hold. It needed proper rings and thick alloy plate top and bottom to stabilise it. More confusingly, there seems to be no offset; collimating as per my pn208, all the reflections are concentric. Anyone collimated a 150-1200 from scratch? TIA.

[DaveS]

At f/8 the reflections will be pretty much concentric, it's only when you get down to f/6 or below that you have to allow an offset due to the geometry of cutting a cone at 45 deg. At the f/4 that you were working at the offset will be very noticeable.

[alacant]

10 minutes ago, DaveS said:

you have to allow an offset

Hi. The thing is, I don't make any allowances. The offset just appears; it has to be like that to get the secondary agreeing with the primary via the cross hairs on the sight tube. With the 150, it's dead centre. Thanks for the confirmation.

[alacant]

First light test snaps and, yayyyy... It works. There's some coma visible around the edges on the raw frames; stacking seems to remove most of it. But OMG, coming from f3.9 to f8, you really notice the difference; a 4s flat frame at f3.9 needs 20s, f8. 5 times the exposure!

But hey, it really does get you closer, even with a rusty old EQ6. Over 9 frames, I lost only one to DEC which occasionally has a mind of its own, especially after being hit by the dither.

Next will be the wobbly focuser which is currently held by only 2 screws, getting the dec balance right and the backlash on the mount. Any advice most gratefully accepted. TIA, for looking and putting up with the noise. m39: 8 x 120s, 700d

[alacant]

The contrast is deafening (not passing through any glass maybe?). I think there's even a hint of detail in the ring...

 

 

[alacant]

And a globular to see if the mount really could do it...