guiding through a newt

[little col]

does anybody know or has anybody done this:-
guide through a newtonian while imaging through a refractor

[iceman (Mike)]

There's no reason why this can't be done, and I'm sure is done by some people.

A webcam with the appropriate barlows will give you the right focal length for the guide star. You can either do it manually on the laptop or feed it into software if you have an autoguiding port etc.

[little col]

hmm sounds prommising mike , may have to give it a whirl to see if i can get some really long widefield exposures

[seeker372011 (Narayan)]

I have been guiding with a 130 cm, 900mm focal length newt and imaging with an ED80 600 mm focal length for the last two years or so
10 minute exposures routinely

[seeker372011 (Narayan)]

ps i use PHD guiding now -after using guidedog for a long while and i love it

[little col]

thats great , i have phd guiding setup for the webcam and ten minutes sounds pretty good

[Geoff45 (Geoff)]

Common wisdom is that guiding through a reflector is not a good idea because of mirror flop/shift. However, I suspect this is a hangover from the days of film when exposures went for an hour or more. The last thing that you would want would be for the image to shift slightly and spoil the exposure. These days, with shorter subs and stacking, it shouldn't be an issue--who cares if you have to discard one of the subs.
Geoff

[little col]

interesting point that i never considered , i will have to give it a try and find if it is viable or not , i believe that a 10 minute exposure will recieve more photons onto the chip from faint objects than 10 x 1 minute exposures

[iceman (Mike)]

If the newt is for guiding, then the exposures are short because you're using a webcam on a guide star.
I can't see how it would be an issue these days.

[little col]

dont know what to attempt now , does anybody think that guiding through a newt is a bit long winded , dont forget i only have about 1 night a month in the uk when its clear

[gbeal]

Just guide with whatever you have. YES, some problems could rear their heads, but if you don't guide or image at all, just cos some say not to, you will never do it.
Go for it I say.

[little col]

suppose you are right , best to give it a bash and see what the results are

[Terry B]

Originally Posted by little col

interesting point that i never considered , i will have to give it a try and find if it is viable or not , i believe that a 10 minute exposure will recieve more photons onto the chip from faint objects than 10 x 1 minute exposures

I think this is incorrect. 10 mins of photons is ten minutes of photons but the signal to noise level will be better on the single 10 min exposure.
I tend to use 3 min exposures because my camera will regularly have saturated stars at that time and they start to bloom. I also can't be bothered doing a big run of longer dark frames.
The longer exposures are better but you still have to trash some of them because of satellites, planes and cosmic ray hits. I would rather trash a 3 min exposure rather than a 10 min exposure.

[little col]

hmm ,good point that is terry , i think i will take your advice and stick with 3 minute exposure stacks