M81 & M82 - Dithering Question

[Aramcheck]

A couple of nights ago I had a bash at M81 & M82 with the SW 200dps & Canon 600d on an AZ-EQ6 GT Pro GEQ/AZ mount. I'm using a SW 50mm finderscope as guidescope fitted with a ZWO 120MM. Took 90 x 180 second subs, but had to ditch 10 where the dithering timed out in APT after 180s & the next exposure started before the mount had finished in Declination.

In APT I had the dithering distance set to 4 & to dither after each image. According to a formula I found on another forum this equates to a max distance of roughly 50 pixels. Would setting the APT distance to 2 (25 pixels) be too severe? What about setting the program to dither after every other exposure, in order to increase the amount of subs in a given time-frame.

Any help much appreciated!

Ivor

[michael8554]

Dither for DSLRs is usually about 12 pixels, which is what answers in that link suggest ?

Michael

[KP82]

25 pixels dithering in your imaging scale should be enough for DSLRs afaik. My settings in BYEOS and PHD2 result in about 20 pixels dithering with my guiding to imaging ratio.

I've read that Spiral dithering yields better results than Random for DSLRs, but personally I haven't noticed any difference.

With my local light pollution level most of my subs are between 90 and 180 secs. And I usually dither every other frame in order to maximise the number of subs within a given time-frame. I only dither every frame if I'm using my triband filter on some nebulae targets and my subs are 4 - 5 mins long. My setup usually recovers from dithering within 25 to 30 secs (this includes the standard 10 sec calm down time in BYEOS). So if yours timed out after 180 sec, you may want to double check the balances and backlash in your mount.

Edited April 19, 2021 by KP82

[rickwayne]

Wow, I'm using a 183MM and I think I have it set to 2 pixels or something, which was the default in StellarMate.

Really nice detail in M82. Last time I tried it I could barely make out that there was supposed to be hydrogen there!

[Aramcheck]

Thanks for all the replies - I've tried a couple of different settings & I'll be using a setting of either 2 or 3 in future and probably dithering every other sub, just to maximise our rather limited spells of clear skies.

Cheers
Ivor