Tracker, D610, 20mm f1.8G, exposure settings

Hi

I've recently bought an LX3 tracker and so far I'm pretty pleased. Test shots using a 70-300 have given sharp stars at long exposures with the odd duff frame

I'm heading to the desert in a couple of weeks for new moon. Very little light pollution bortle 2 but hot like 35C and may be low level dust in the atmosphere.

I'll be using the 20mm and I usually shoot 16 s f2. 2 ISO1600 to 3200 for static untracked frames. I use the histogram to get an idea of exposure and balance left center.

Using the tracker, I can increase exposure to 2 minutes no problem and I was thinking of f2. 8 to f4 for better coma and sharpness. I'll be shooting 16 lights 16 darks 16 bias and stacking, possibly with separate foreground untracked.

Be interested in hearing what exposures any of you use when tracking and is there much benefit in dropping to ISO 800 for dynamic range. Do you drop the exposure a touch when stacking?

I don't want to expose too long given the ambient temp. I'll have a tablet for LV focusing to reduce sensor heating from the lcd panel

Also colour temp. It can be quite orange with the dust there so 4000k to 4500k would pull it back a little?

Thanks

For me the main concern about exposure length, F ratio, aperture and ISO setting is star colour.

That's where you get hit first - losing star colour and you get all white stars which detracts from an image.

Depending on the camera some have a dual gain converter meaning the read noise drops at that point. For example the Sony A7riii has this at ISO640.

Its a good place to start.

The downside of too low an ISO is it makes framing harder and focusing harder so best to do that at a high ISO so you can see the image clearly then drop it as needed to match the exposure time.

By the way I have not noticed a gain from doing say a 3 minute exposure and 6 x 30 seconds stacked plus you are more likely to safeguard your star colours.

I tend not to expose longer than 30 seconds these days and stack instead. This also takes pressure off getting the polar alignment really accurate. A rough alignment simply using smartphone apps of an inclinometer and a compass gets me round stars at 24mm and 30 seconds. If you go longer focal lengths then you will need the higher accuracy polar alignment and perhaps balancing the load.

Best to do an untracked landscape shot as well and a tracked sky. The landscape may benefit from longer exposures and more open F ratios.

My principle is to keep it simple, easy to setup and reliable because a lot of these images are taken at places that are hard to access, you may be going back there and its done in the dark. So settle on a routine and then just enjoy the different locations you can image from without attention on the "how to do it".

Greg.

Just another comment. I am not sure you need bias frames. The dedicated astro cameras that use these same sensors don't use bias frames as they are not the same frame after frame and stacking does not make them work either.

Usual practice is to use flat darks meaning a dark shot at the same exposure length and temperature as the light.

I don't use dark or flats in my nightscapes. I am not sure many do. That is a deep sky imaging technique.

These latest cameras have such low read noise and dark current that there is little to be gained. Some have amp glow and a good dark will get rid of that but its usually hard to see.

I wouldn't bother with all of that, needless complication.

Greg.

I shoot 3 minute subs at f/2.8 ISO 1600 for my mosaics with the Art 40 and 105.

I shoot 5 minute subs at f/4.0 ISO 1600 for my mosaics and nightscapes with the Art 14mm

I have shot them all wide open and used much shorter subs with good results but i am getting a hell of a lot more critical of stellar profiles now and choose to stop down to improve the quality of the data.

The only way you are going to be happy is field testing. Everyone has their own goals and tastes so any advice only serves as a baseline for your own experiments.

It sounds like you have a good grasp of the fundamentals. Good luck in the field

True.

Stopping down seems to be a requirement for a lot of lenses for this type of imaging.

Greg.

Thanks for your responses Gentlemen, appreciated

ChrisBeere said:

I shoot 3 minute subs at f/2.8 ISO 1600 for my mosaics with the Art 40 and 105.

I shoot 5 minute subs at f/4.0 ISO 1600 for my mosaics and nightscapes with the Art 14mm

I have shot them all wide open and used much shorter subs with good results but i am getting a hell of a lot more critical of stellar profiles now and choose to stop down to improve the quality of the data.

The only way you are going to be happy is field testing. Everyone has their own goals and tastes so any advice only serves as a baseline for your own experiments.

It sounds like you have a good grasp of the fundamentals. Good luck in the field

Click to expand...

Cheers! I've done a bit of background reading and been out a couple of times but the tracker is new territory.

The Nikon 20mm is a great lens but I get coma up to f2. 2 and I tend to be critical with my images. The increased DOF using the tracker will help focusing I think using LV.

I'll do a test exposure or two to check image and histogram.

I'll do two runs I think at 2 minutes f2. 8 and 4 minutes f4. 0. The LX3 will go to 5 minutes max at that focal length and I don't want to work on the limit

Iso will depend on test shot histogram but to avoid blown stars I assume the histogram edge should be left middle third, or can I push it to the center? If stacking I assume I can keep the histogram lower?

I find Iso 1600 pretty good on the D610. Plenty of colour and noise isn't bad at all

Yes, I aim for a skyfog origin separation of 30-40 percent on my back of camera histogram.

I shoot at ISO 1600 on my Canon 6D MK II because that's the sweet spot for swamping read noise with the skyfog and maintaining good dynamic range. It is an older sensor and not ISO invariant.

This might help you:

ISO vs DR for the Nikon 610

https://www.photonstophotos.net/Charts/PDR.htm#Nikon D5,Nikon D610

You can switch off the D5 series using the list on the right, i copied the link from another post.

Bottom line 1600 looks good for the 610.

Astrophotographer 10 said:

Just another comment. I am not sure you need bias frames. The dedicated astro cameras that use these same sensors don't use bias frames as they are not the same frame after frame and stacking does not make them work either.

Usual practice is to use flat darks meaning a dark shot at the same exposure length and temperature as the light.

I don't use dark or flats in my nightscapes. I am not sure many do. That is a deep sky imaging technique.

These latest cameras have such low read noise and dark current that there is little to be gained. Some have amp glow and a good dark will get rid of that but its usually hard to see.

I wouldn't bother with all of that, needless complication.

Greg.

Click to expand...

Greg appreciate your threads and replies here, I like your ethos and I am learning a lot.