How long should my exposures be?

[Peter Reader]

Hi all,

Have been experimenting with different exposures with my EQ5 and 200P and can't decide what lengths to use for DSO imaging.

I get egg shaped stars after 20s but they don't have much longer trails at 45s or even 1 minute. What is best to go for?

I assume the longer the exposure the more dust and nebulosity you get.

What should I be able to get without guiding with my mount?

Thanks

Pete

[Kai]

If the stars are staying basically the same have you checked that the scopes collimation is 100% ?

[barkis]

Hi all,

Have been experimenting with different exposures with my EQ5 and 200P and can't decide what lengths to use for DSO imaging.

I get egg shaped stars after 20s but they don't have much longer trails at 45s or even 1 minute. What is best to go for?

I assume the longer the exposure the more dust and nebulosity you get.

What should I be able to get without guiding with my mount?

Thanks

Pete

Are you sure the trailing is in RA and not Declination due to poor polar alignment? Remember also, that trailing is longer for a given exposure length at lower latitudes, than for objects closer to the zenith and polar regions.

Edit: Also, what Kai has just said .

Ron.

[Peter Reader]

No idea how god my collimation is... the little black ring is pretty much right in the middle of the FOV when I look through the scope without an EP.

Trails are definitely in R.A. The only way I polar align is by using my polarscope. I get polaris circle right underneath the polar axis cross and then get polaris into the middle of it's circle.

I have only compared exposures form different targets (at different latitudes) so the test was unfair looking back.

However what exposures should I be able to get without egg stars? And is it better to take 1 minutes eposures of eggs and get the nebulosity or get less nebulosity but nice round stars? Is it just personal taste?

Thanks

[msinclairinork]

I am NO expert but have had a little experiance with unguided CG5/EQ5 clone and a 80mm refractor.

I could get round stars for 60seconds fairly comfortably using a polarscope alignment. That said I could on occasion go for more but periodic errors, wind, bad alignment etc etc would duff up more subs than if I had stuck to around the 60s mark.

Yes the more time you get the more photons you collect so more is better. You don't need to worry about over exposing and other issues until you get up into the 3,4,5min etc.

So egg shaped stars....or not..I would say, no thanks to them. Once you stack a heap of egg shaped subs your DSO is going to suffer alot from this it could even end up looking fairly blurry.

Why are you getting egg shaped stars at 20seconds would be my main question. Get this resolved and I would think you should be able to track well for atleast 60s.

A couple of things to try next time would be to offset your balance so that your gears are meshed better. Also I would just make sure everything is tightend up it just sounds to me like there is a little wiggle movement somwhere in it all? Like I said the motor gears (backlash) is the usual culpret and off-setting the balance helps alot.

That's about as far as my knowelage extends

Good luck and I am sure you will have it sorted soon.

Michael