Trifid & Lagoon

[thegableguy (Chris)]

First time I've used a full-frame DSLR on my ED80, and I'm quite pleased with the result!

Orion ED80, 0.85 flattener
NEQ6 (unguided)
Nikon D600, 22 x 1m45s at ISO 1000

Compared to the cheap crop-sensor DSLR I usually use, the dynamic range is far superior - the centre of Lagoon isn't blown out, but there's tons of detail in the star field. I think I'm getting better at using the curves within DSS too.

Suggestions for improvement welcome. Anything I can do better?

Also - once again, every 7-8 minutes each sub is slightly blurry. 2-3 perfect shots then a slightly streaky one, consistently for an hour. It's happened before. Will this go away with guiding? Belt mod? PEC? Strip down & grease change? Any other suggestions?

[luka]

Very nice Chris. Very, very nice.

I remember reading somewhere that fractional ISO numbers should be avoided with DSLRs. In other words you should only be using ISO 400, 800, 1600, 3200 etc.

Also guiding will most likely sort out your blurry subs. The periodicity definitely implies periodic error of some sort. I would not do the strip and grease until you try guiding first.

edit:
You could try the trial version of StarTools or PixInsight for processing. Startools is much cheaper. The only limitation of the trial version is that you cannot save. However, you can use screenshots at the end of processing while trialing it. It is a big learning curve but there are quite a few tutorials on the net.

[_Jimmy (Loren James)]

I like this shot - I wouldn't know what to do to sort out you bad shots, I'm still to pick up an neq6 so will be just as interested to see what people's ideas are.

Originally Posted by luka

Very nice Chris. Very, very nice.

I remember reading somewhere that fractional ISO numbers should be avoided with DSLRs. In other words you should only be using ISO 400, 800, 1600, 3200 etc.

Yeah I heard this too, my understanding is that the 1/3 iso stops are being digitally pushed, which increases all (analogue and digital) noise. But the 2/3 stops are pulled from the next highest full-stop, which reduces the noise somewhat (analogue and but not necessarily digital by the same amount).

So what makes sense to me is if you shoot at 800 and need to increase the exposure by a third of a stop in PS or whatever, you are going to have a similar amplification of noise anyway as 1000 iso, it's either way. It would be more of an issue if you were shooting at 1000 then increasing by a third of a stop, because not only did you have the initial increase from pushing a third you are then pushing another third in PS: you would have less noise overall shooting at 1250 or 1600 and reducing it.

If I'm wrong, someone feel free to set me straight

Jimmy.

[thegableguy (Chris)]

Interesting! I didn't know that about 1/3 ISO stops. I just used the lowest ISO setting that would correctly expose the longest subs I thought I could pull off. Will keep it in mind for next time.

This particular camera has such wonderful low noise levels compared to the D3300 I usually use that noise just wasn't an issue at all. I might use it more often.

Thanks for the kind words too. Nice to have a shot I'm happy with for a change...!

[Atmos (Colin)]

It looks great Chris! Been nice seeing how your images have been improving over the last couple of months

I would suggest that there may be a bit of grit or something on some part of the RA worm drive gearing. If it happens only once every 7-8 minutes (I calculated a while ago that the PE of an EQ6 is ~7.5 minutes), this is how long it takes for the RA gear to do a full revolution. If there is something sufficiently large (still small btw) bit of grit in the gear guiding likely won't help. If it is relatively small then guiding may help minimise the problem.

Over the New Year I decided to strip my mount down and give it a clean as it was starting to get some random spikes more often than you. This suggested to me that it was in the worm mechanism and not the RA gear itself. Working well now

[thegableguy (Chris)]

Thanks Colin! It feels like I'm making some progress - great to hear that others think so too.

Yeah... As Luka said below, it would be best to try guiding first to see if the problem goes away before taking it all apart, but that means buying a guider and I don't really have $500 spare right now. Gotta wait a few months til I can slip more astro expenses past the boss.

How hard is it to strip it down? What tools will I need? I'm reasonably good with mechanical things, but I'm worried about doing expensive damage to small sensitive machine parts...