the longest realistic lengh of subs at prime focus

[garethmob]

im just wondering, as i dont really want to waste a clear sky night to find out but what is the realistic leangth i can get with a megrez 72... prime focus with my canon 300d

heres its specs

Aperture 72 mm

Focal Ratio F/6

Focal Length 432 mm

Tube Length 300 mm (11.8") Fully Retracted

it will be on my kson mount so there is that unknone factor there...

and it will have to be unguided as the mount dosent support guiding

thanks for any help

gaz

[ollypenrice]

Without guiding you will be limited by periodic error, which might be anything. It will be very easy to see any ill effects, though. You just have to pitch in with a sub at about 3 mins and see how it looks. If it's trailed try 2. Etc.

If/when you start guiding the limiting factor will be the lack of cooling on the camera which will probably be 5 to 8 minutes depending on ambient temp.

Olly

[Stephen]

Without guiding you will be limited by periodic error, which might be anything. It will be very easy to see any ill effects, though. You just have to pitch in with a sub at about 3 mins and see how it looks. If it's trailed try 2. Etc.

If/when you start guiding the limiting factor will be the lack of cooling on the camera which will probably be 5 to 8 minutes depending on ambient temp.

Olly

Do those DIY cool boxes for SLRs help much?

[ollypenrice]

Do those DIY cool boxes for SLRs help much?

I believe so, yes. Until switching to CCD, Frans Kroon, who comes here regularly, used first just gel packs for physio and latterly a cool box. His friend Robert went further still with a Peltier mod of some kind.

Have a look on Frans's equipment page at www.franskroon.nl

Olly

[garethmob]

thanks olly as usually your advice is spoton i just need to wait till i get it now! excited isnt the word!!!!!!! gotta feeling my eyepeices are gona let it down as well as the diagnonal