Another Shot At Andromeda tonight

[Maxrayne]

Having another crack at Andromeda tonight, my last chance before the weekend, and I've got opportunity to be in a dark skies pretty much (going by local light pollution data maps.)

I've noticed that my last couple of attempts I've totally blown the core. Trying to find the optimal ISO to shoot it at as I've been doing 10000 and 12800 in heavy light pollution.

Working with a Nikon d5300 at 200mm and f / 4.8, which I know is far from ideal but for now that's the kit I have to work with. Doing 2 second exposures with darks and offsets.  

Any quick advice would be much appreciated ?

[Starlight 1]

Not been out for a long time as I give up astro. I thing I start with ISO 800 /doing 300sec , see how that look.

[Maxrayne]

Will an ISO of 800 be enough to pick out the dust trails? I'm hoping to get a total of at least 20 minutes of light data (600 light frames)

[Stargazer33]

You could try a number of exposures at a lower ISO to capture the core. You then process in a layer based program like Photoshop or the freeware gimp. If you have the core as the bottom layer and the outer arms as the top layer. You then mask out (with a feather edge) the top burnt out core, revealing the correctly exposed core from the layer below. You then merge down and save as a new single layer image

HTH

[Maxrayne]

Never used layers before so this is going to be an experience. Thank you, I like the idea tbh ???

[bobro]

It might seem strange, but the ISO makes no difference to the image captured by the sensor - what really makes a difference is the exposure time. For unguided imaging with a 200mm fl lens, try 15 second exposures to start with. The idea is to maximise the exposure length without star trailing, therefore capturing as much detail as possible on the sensor. The ISO determines the amplification used when reading the image from the sensor and is less important, with a value of 800ISO being a good starting point. 

When an image is processed it can be 'amplified' in a similar way to the ISO setting on the camera.

Andromeda is not an easy target due to a bright core and faint detail further from the centre.

[Maxrayne]

15 seconds at 200mm? Will that not give a huge amount of trailing?

[Starlight 1]

He did not say if unguided or not , so bobro is right you may be down to only 15 sec . so try  1 at  15 /1 at 20 so on till you see trailing ,  its the only way to find out how good you set the mount up.

[Maxrayne]

My bad, thought I'd included in the setup, shooting solely DSLR on a bog standard tripod. My fault, thought I'd put that in there ?

[Starlight 1]

The Sky is not the same in any 2 night so never go by your setting its just a guide .

[Maxrayne]

I'm certainly discovering that one! ?

[bobro]

For comparison, here is an image of 10 sec taken with my a 50mm fl lens. Trailing is just starting. So 2 sec doesn't seem too far off for 200mm fl static lens.

[MarsG76]

Try doing a few different exposures, get a set of subs with the core properly exposed than a set of exposures to capture the faint detail.. perhaps also do a set in between the two than stack, resulting in a HDR image with all parts properly exposed.

 

[happy-kat]

Have a look at this video by Forrest Tanaka. Shooting Andromeda from a static tripod.

corrected link here

Edit: wrong video off to get the right one - done.

[Maxrayne]

Thanks all, managed to get out there last night with my two eldest boys. The looks on their faces seeing the band arching overhead was worth a million images. They live in the city so have never seen that number of stars before. 

Just processing the images now. Tried a 500 shot stack of Andromeda, some Milky Way and what I hope was the Dumbbell Nebula (Star Walk 2 was pointing me just to the right of Altair which was where I pointed the lens.)

So need to get myself a scope and GoTo them at least I can start tracking/guiding and grab something halfway more decent....

[happy-kat]

You don't always need a telescope in that many object objects fit nice with a camera lens.

Sounds like you had a really good night.

[Starlight 1]

Sound like a good night out, all ways hard to give any setting its all down to seeing and mount .

[ollypenrice]

I always feel that the need for short subs to manage bright cores is exaggerated and I very, very rarely take any. If you look at the linear capture (that is a sub exposure without any stretch at all) you'll see what the brightest part of the core is really like. If it is OK in linear form then it can, with the right stretching, be OK in the stretched form. You may need to use layer masking to combine different stretches of the same data but often you won't need to do this.

I'm not aware of any image, professional or amateur, which has found detail right to the core of Andromeda. Most experienced imagers seem to get to about the same point before it becomes a smooth featureless glow.

Olly

[carastro]

Trying to get an image with no tracking is going to be very difficult.  What kit are you using?

Quote

Doing 2 second exposures

I can't imagine such short exposures as you are taking would be enough to blow out the core.

Carole 

[Maxrayne]

Managed to get that from the centre of Nottingham a couple of weeks ago. Can't remember the exact EXIF other than it was a ridiculously high ISO (12800) at 200mm with 1.6 second exposures.

Brought the iso down last night to 8000 and increased shutter to 2 seconds. Roughly 500 shots. Hoping for better results with it being a darker sky and no light pollution

[carastro]

That's very good for such short exposures.  I have found the answer to not blowing out the core in M31 is to anchor down the core in curves and stretch the rest of the nebula bit by bit rather than in one big stretch, each time anchoring down the core.

It looks like your image would benefit from flats as well. 

Carole 

[MarsG76]

7 hours ago, Maxrayne said:

Managed to get that from the centre of Nottingham a couple of weeks ago. Can't remember the exact EXIF other than it was a ridiculously high ISO (12800) at 200mm with 1.6 second exposures.

Brought the iso down last night to 8000 and increased shutter to 2 seconds. Roughly 500 shots. Hoping for better results with it being a darker sky and no light pollution

Good start... needs more data... but a very good start.

[Maxrayne]

5 hours ago, carastro said:

That's very good for such short exposures.  I have found the answer to not blowing out the core in M31 is to anchor down the core in curves and stretch the rest of the nebula bit by bit rather than in one big stretch, each time anchoring down the core.

It looks like your image would benefit from flats as well. 

Carole 

Um....?

[Maxrayne]

2 hours ago, MarsG76 said:

Good start... needs more data... but a very good start.

Definitely more data needed, and ty ?

[Maxrayne]

On 16/08/2017 at 18:57, MarsG76 said: