[Theme] Night sky shots

[Akira]

Øivind, I'm glad that this fascinating series is kept going!

How do you think about the accuracy of the hot shoe as the mount for the red dot sight?  Was it easy to align the optical axes of the sight and the lens?

[Øivind Tøien]

Øivind, I'm glad that this fascinating series is kept going!

How do you think about the accuracy of the hot shoe as the mount for the red dot sight?  Was it easy to align the optical axes of the sight and the lens?

Thanks for your comment, Akira. The hot shoe that I sourced from a flash does not fit very precisely although it does have a screw to fix it better in place. There is some wiggle possible left/right - to that comes that my drilling of screw holes for the  hot shoe  in the plastic plate that the dovetail claw of the sight grabs was not too precise, it was a quick job before an imaging session. Vertically it is OK, and no adjustment seems necessary. So every time I start a session I center the cameras viewfinder on a star, and then I nudge the sight to the right (typically almost as far as it goes due to my imprecise drilling ) until the star is centered relative to the red dot. After that I am careful to not bump it too much... 

I have considered machining a new hot shoe + dovetail  adapter out of aluminum with better precision, but then I would loose the screw collar that fixes the hot shoe in place and prevents vertical play, and I am not sure if I would be able to make something that does not have the slightest wiggle; I need to do some experimenting there, and would also have to check for body to body variation of the hot shoe.  If it could made to fit precisely, then the red dot sight has the needed adjustment horizontally and vertically for one time fine tuning. So far I have not played with those. It would be very nice to not need to calibrate it for every use, but usually it is necessary to aim at a star for manual focus at the start anyway so the horizontal calibration does not add much to the procedure - it is just the worry of bumping it that bothers me.
 

[Akira]

Øivind, thanks for the details.

As I was reading your answer, it occurred to me that the vertical part of your L-bracket might serve you as a better base for the red dot sight, both in terms of stability and accuracy.  If your L-bracket has the markers of the optical axis, the alignment would be easier.  You can fix your red dot sight onto an Arca-Swiss clamp which should be fairly precisely manufactured.

[Øivind Tøien]

Øivind, thanks for the details.

As I was reading your answer, it occurred to me that the vertical part of your L-bracket might serve you as a better base for the red dot sight, both in terms of stability and accuracy.  If your L-bracket has the markers of the optical axis, the alignment would be easier.  You can fix your red dot sight onto an Arca-Swiss clamp which should be fairly precisely manufactured.

Thanks for the suggestion. I agree that it would be rock solid, however it would be a rather expensive solution though to a small problem, and could conflict the cable release, and the tracker when aiming vertically. Also keep in mind that parallax problems are non-existent with stars, so on-axis mounting is irrelevant. Unfortunately I do not have the vertical component of the bracket for my D5100 which I am likely to use when I do not need quite as high pixel density.

[Jakov Minić]

Øivind, this is fascinating again!
It is well worth the effort you put into creating such an image!
I cannot but say that I wish you could get closer so that we could see more detail in the whirlpool galaxy. I am sure you will manage 

[Akira]

Thanks for the suggestion. I agree that it would be rock solid, however it would be a rather expensive solution though to a small problem, and could conflict the cable release, and the tracker when aiming vertically. Also keep in mind that parallax problems are non-existent with stars, so on-axis mounting is irrelevant. Unfortunately I do not have the vertical component of the bracket for my D5100 which I am likely to use when I do not need quite as high pixel density.

Okay, that makes sense.  Hope you would find a better solution using the hot shoe.

[ColinM]

More images please

[Øivind Tøien]

More images please

As commanded 

This time I made an attempt during fairly bright moon light    on Bode's Nebulae and Cigar Galaxy (M 81 and M82) . It was really a test during my construction of a Bahtinov Mask (http://www.deepskywatch.com/Articles/make-bahtinov-mask.html) to aid focusing on stars, but came out better than my previous attempt on these DSOs as I got in more imaging time from a slightly less light polluted site. Focus came out fine too. Initial capture was 120 frames, but a number had to be discarded because of aurora bursts and beginning twilight towards the end.


61 image stack in DSS drizzle 2x, D7100 with 300mm PF @ f/4.5 ISO 1600, each frame 60 sec, 38 flats @ ISO 100, crop to < 1/3 of the frame.

 

[armando_m]

Impressive results !

What are the 38 flats ?

[Akira]

Another nice take, Øivind!

The diffused small spot in the top-left area appears to be another galaxy...

[Øivind Tøien]

Thanks for the kind comments both of you.

Amando, the flats are for compensating vignetting of the lens. As I used a portion of an overcast sky that might not have been completely  homogenous, I let DSS average out a number of them taken at different angles and locations. Some swear by doing the flats at the end of an imaging session by using a diffuser or light panel on the lens/scope. That would also compensate for dustbunnies etc.

Akira, yes the spot is a galaxy, NGC 3077. A wider view from the same captures also reveals a couple of other galaxies low in the frame, NGC 2959 and NGC 2976:

[Akira]

Øivind, thanks for the image of the wider view.  It is fascinating to realize how such plain diffused dots can stimulate lots of imaginations.

[Thomas G]

Thanks for showing these great pics. I'm watching with increasing interest,
Fascinated by what can be revealed with 'affordable' gear. Please continue your thread effort.

[Jakov Minić]

Øivind Tøien is Mr Spaceman!!!
I am truly enjoying the images!

[Øivind Tøien]

Thanks for further enthusiastic comments, Akira, Thomas and Jakov.
Per demand    here is my effort from last week to capture comet Comet C/2014 S2 (Panstarrs). It sort of closes the circle as my want for a tracker started with my attempt to capture comet Catalina earlier this year. The cool thing about comet C/2014 S2 is that it at the time passed between two very nice deep space objects, the Owl Nebula (M 97) and the M 108 Galaxy. The Owl Nebula is what is called a "planetary" nebula and is the remains after a red giant star lost most of it hydrogen fuel and there is only a white dwarf star remaining in the center while gases are being slung out at high speed. The Nebula is only 8000 years old, which of course is almost no time on the astronomical scale. https://en.wikipedia.org/wiki/Owl_Nebula.

Comet C/2014 S2 passed earth at only 2.10 lunar distances at the closest and thus moves very fast. I was lucky to be able to image the comet over four consecutive nights in spite of the bright moonlight with my 300mm PF on D7100 at f/4.5. Exposure time of each sub was 60 sec. totaling about 2 hours the first night while I went down to 30 sec. exposures the following nights because of the moonlight and only got 25 minutes to 1 hour total exposure due to aurora, drifting clouds and beginning dawn.  I am still trying to learn how to successfully stack so that both stars and comet get sharp; the following early processing is only aligned on the stars with the comet smeared.

Owl nebula left, M108 right and comet C/2014 S2 in the middle (in front of a star); there is a trace of the typical blue-green comet color in the smeared core.
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In #3-4 the comet mostly looks yellowish (also seen on images posted by others elsewhere), not sure if that is because most of the core has been evaporated by the sun.

I reserve the right to possibly re-post better version(s) once I have figured everything out, preferably with all 5 frames combined, but that might take a while as other tasks are waiting. Dark is anyway gone for the summer up here north now so there is plenty of time until I will be able to do more captures.