Crux 22 April

[supernova1965 (Warren)]

37 x 10 sec frames @ 1600 ISO 50mm f1.8
Stacked in DSS processed in Startools and Gimp

[supernova1965 (Warren)]

HELLO ANYONE OUT THERE Tips and advice please you won't hurt my feelings

[DJT (David)]

HI

OK..Its a really well framed shot but you are just a touch out of focus. If you can tighten up the focus this would be a really great shot and I like the trails across the frame.

However, your stars are also a bit bloated. You are pushing ISO 1600 but also on F1.8, an absolute light bucket so there are a hell of a lot of photons hitting the chip. This and the fact that its just a little bit out of focus means you are bloating away and as I think you have cropped this image its exagerrated.

Try stopping down the aperture a bit. You might find a bit of trial and error would help.

Am thinking you have used these settings because you are not tracking and the best you can get without recording star trails is around 8 seconds. Thats great but I reckon you can get away with reducing the aperture and get a good picture over the same exposure time

[CapturingTheNight (Greg)]

Are you running a tracking mount or fixed tripod Warren? I'm going to guess from the camera settings that you are on a fixed tripod and I'm also going to guess that you are not running a full frame camera. In that case you are really shooting at 80mm with your 50mm lens. The 600 rule for fixed tripods determines the maximum shutter speed length before stars begin to trail to much and it is 600 divided by the true focal length. So for you in this shot 600/80= 7.5 seconds maximum shutter speed. The 600 rule is fine for wide angle shots but because you are trying to capture finer deep sky detail here I would go for a 500 rule (6.25 seconds) or even a 400 rule (5 seconds) to stop the issue of elongated stars like you have here. I would also advise stopping down that lens one or two stops (F/2 or F/2.8) to tighten up the stars at the edges of frame. Now I know that this is going to limit the amount of detail you are going to get in each subframe but that can be dug out again later in post processing as long as you take lots and lots and lots of subs.
Of course if you are running on a tracking mount then things become easier.
Once you get your base data better then you can start worrying about image processing. On that score your colours look ok and you have not blown out the stars to much
Hope this helps a bit.
Cheers
Greg

[supernova1965 (Warren)]

Originally Posted by DJT

HI

OK..Its a really well framed shot but you are just a touch out of focus. If you can tighten up the focus this would be a really great shot and I like the trails across the frame.

However, your stars are also a bit bloated. You are pushing ISO 1600 but also on F1.8, an absolute light bucket so there are a hell of a lot of photons hitting the chip. This and the fact that its just a little bit out of focus means you are bloating away and as I think you have cropped this image its exagerrated.

Try stopping down the aperture a bit. You might find a bit of trial and error would help.

Am thinking you have used these settings because you are not tracking and the best you can get without recording star trails is around 8 seconds. Thats great but I reckon you can get away with reducing the aperture and get a good picture over the same exposure time

Great tips thanks this is the first time I have used this lens on the sky and I put the focus right to infinity so I need to back it back a little. I did crop it as I had stars that were streaky in the corners I know there is a term for this but can't remember it Yep I did some test shots at longer exposures and I had trailing but 10 sec seemed good. When you say to reduce the aperture do you mean a lot or maybe 2 to 3

Thanks for your feedback

[supernova1965 (Warren)]

Originally Posted by obsidianphotos

Are you running a tracking mount or fixed tripod Warren? I'm going to guess from the camera settings that you are on a fixed tripod and I'm also going to guess that you are not running a full frame camera. In that case you are really shooting at 80mm with your 50mm lens. The 600 rule for fixed tripods determines the maximum shutter speed length before stars begin to trail to much and it is 600 divided by the true focal length. So for you in this shot 600/80= 7.5 seconds maximum shutter speed. The 600 rule is fine for wide angle shots but because you are trying to capture finer deep sky detail here I would go for a 500 rule (6.25 seconds) or even a 400 rule (5 seconds) to stop the issue of elongated stars like you have here. I would also advise stopping down that lens one or two stops (F/2 or F/2.8) to tighten up the stars at the edges of frame. Now I know that this is going to limit the amount of detail you are going to get in each subframe but that can be dug out again later in post processing as long as you take lots and lots and lots of subs.
Of course if you are running on a tracking mount then things become easier.
Once you get your base data better then you can start worrying about image processing. On that score your colours look ok and you have not blown out the stars to much
Hope this helps a bit.
Cheers
Greg

You are right I used a fixed tripod I am not sure about the full frame or what this means it is a Nikon D200. You have given me a gold mine of info here I will take some time to fully understand and impliment it

[CapturingTheNight (Greg)]

My pleasure Warren. Full frame is in reference to the size of the sensor in the camera. A full frame digital camera has a sensor equivalent to the old 35mm film size. The Nikon D200 isn't a full frame camera and is what is known as a crop sensor. My figures were based on a Canon crop sensor which is the focal length multiplied by 1.6. Nikons crop sensors are slightly different and it is multiply by 1.5. So now that I know that your 50mm is actually 75mm. 600/75= 8 seconds absolute maximum.

[supernova1965 (Warren)]

Here is one of the LMC that I spent the day processing

Same details as the Crux one except there were 42 frames.