Nexstar and Fastar

I'm thinking of getting the Fastar lens assembly for use with my NexStar 8 GPS which would allow me image at f/1.95 and stack unguided 30-second deep sky eposures with a CCD camera such as the Starlight Express MX5C. I assume the standard alt/az fork mount configuration is ok for such short exposures but would welcome comments as to the feasibility of this or whether a wedge is advisable. I would prefer not to have to buy a wedge as the cost of the CCD camera and fastar lens is high enough as it is!

Gordon

Gordon, FWIW... The Fastar assembly will doubtless give you short exposures - at F/1.95 its blazingly fast. And as such, the ALt-Az mount would be able to handle those short exposures. Of course, if you took images over an extended period, you'd just need to make sure you software of choice can de-rotate those images.

Another consideration depends on what deep sky objects you want to image. For those really faint objects, 30 second exposures, no matter how many you stack, are not going to amount to much.

How about forgetting the Fastar and just buying a wedge? You can then image for longer (tracking ability of the mount notwithstanding) or shorter. But I suspect its the f/1.95 that you want...

If you go Fastar, do you have to make sure the imager is as low a profiel as possible to avoid obstructing the lightpath to the primary? I think the Starlight Express cameras are cylindrical and presumably fit the bill....

I'd love to know how you get on

Cheers

Dave

Gordon, FWIW... The Fastar assembly will doubtless give you short exposures - at F/1.95 its blazingly fast. And as such, the ALt-Az mount would be able to handle those short exposures. Of course, if you took images over an extended period, you'd just need to make sure you software of choice can de-rotate those images.
Another consideration depends on what deep sky objects you want to image. For those really faint objects, 30 second exposures, no matter how many you stack, are not going to amount to much.

Thanks for the advice Dave. I think I would stick with short exposures and bright objects to start with.

How about forgetting the Fastar and just buying a wedge? You can then image for longer (tracking ability of the mount notwithstanding) or shorter. But I suspect its the f/1.95 that you want...

Yes! Fastar was one of the reasons I got the NexStar GPS instead of the newer CPC. It's possible to get f/1.8 with Starizona's Hyperstar alternative but it's a bit more expensive.

If you go Fastar, do you have to make sure the imager is as low a profiel as possible to avoid obstructing the lightpath to the primary? I think the Starlight Express cameras are cylindrical and presumably fit the bill....

Yes, it has to quite a low profile camera such as the ST237A or one of the Starlight Express models. May be a few months before I get all the bits.

Gordon

gordon

we're in the process of developing registax v4 which should incl a better rotate section for alt/az mounts. anyway 30 secs at f/1.8 is ok for field rotation

dave gradwell

I remember reading about fastar when it came out, it looked very enticing, I'm surprised that its take up has not been as big as I'd imagined, with such a low f ratio, its has a unique imaging potential.

we're in the process of developing registax v4 which should incl a better rotate section for alt/az mounts. anyway 30 secs at f/1.8 is ok for field rotation. dave gradwell

Thanks Dave. Looking forward to v.4.