Star photography, weird star shapes?

[Stagecoach]

I had been undertaking some star shots to practice stacking and PP on them using my usual 28-75 Tamron at f/3.2, results were as expected.

Following this I gave the Nikon 50mm 1.4 a try at took a couple of frames with the intention of seeing the results I could achieve at f/2.

The result achieved on both has me baffled. This image has had only minor pp, no exposure change just added a bit of contrast and basic sharpening.

What is the likely cause for the very sharp triangulation of some stars, most noticeable right upper and lower?

Unfortunately before I had a chance to investigate and experiment more the clouds came over.

f/2, 4s, ISO 3200, 50mm


A crop lower right ..........


A crop upper left ..........


Mirror slap? Radial mirror slap? but not experienced using another lens.


Grahame

[bnnrcn]

I can see them not only on the RHS bot also on the LHS Grahame. May be fast moving stars ?

[Stagecoach]

I can see them not only on the RHS bot also on the LHS Grahame. May be fast moving stars ?

Yes, they are on both sides Binnur and appear to be at the circular extremities of the lens mostly

[bnnrcn]

Grahame, by looking at the cropped image , I can see that the ones in the middle have a similar but not very strong triangular shape. The ones on the RHS and LHS look strongly blown out, but I don't know why

[Stagecoach]

Grahame, by looking at the cropped image , I can see that the ones in the middle have a similar but not very strong triangular shape. The ones on the RHS and LHS look strongly blown out, but I don't know why

From my limited experience so far Binnur blown out stars have just shown a radial fuzzy area around them

[PRSearls]

I'm pretty new to this kind of photography but I think this may be lens coma. I think it is usually worse toward the edges of the frame. Some lenses are corrected for this better than others. Star photography is very demanding of lens performance since you are trying to capture tiny pinpoints of light.

PRS

[Stagecoach]

I'm pretty new to this kind of photography but I think this may be lens coma. I think it is usually worse toward the edges of the frame. Some lenses are corrected for this better than others. Star photography is very demanding of lens performance since you are trying to capture tiny pinpoints of light.

PRS

It looks as if you are are correct Paul.

A Google search on the phenomena has found a number of references to it, here's just one http://intothenightphoto.blogspot.co...rry-night.html

I can now do some experimentation and determine if the 50mm f/1.4 is a viable option or just continue with my 28/75 f/2.8 which has not been showing this to any noticeable degree.

[IzzieK]

Interesting lens study, Grahame. I was thinking that perhaps with that lens you can adjust the SS but reading Paul's response, I came upon this link below after googling "len's coma".

http://intothenightphoto.blogspot.co...on-part-2.html

I have the 50th anniversary of the Tamron 24-105 that is supposed to be soft at the edges but it is hardly noticeable in my Nikon FF.

[JBW]

I've read that comma can be solved by shooting at a higher F/ number. perhaps you could try F/3 or thereabouts?

[bnnrcn]

Very useful info, thanks for starting such a thread Grahame

[vaez]

nice done

[Mike Buckley]

It's disappointing to learn that all conspiracy theories have already been determined to be impossible before they have been offered.

[ajohnw]

I don't think it's possible to determine if it's coma from the shots. Coma is usually shown in diagrams as a point and then a series of circles getting larger and offset radially. There would be none in the centre and get progressively larger towards the edge. This page gives and idea of what all of the usual aberrations will do and what causes them after a fashion.

https://www.edmundoptics.com/resourc...l-aberrations/

There are some examples from a photographer here

https://www.lonelyspeck.com/a-practi...erration-test/

Bright stars are a terrible test for problems like these.

John
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[Stagecoach]

nice done

Thank you Vaez

[Stagecoach]

Very useful info, thanks for starting such a thread Grahame

I've read that comma can be solved by shooting at a higher F/ number. perhaps you could try F/3 or thereabouts?

It appears it can be helped in this situation by stopping down Brian, and in your case fortunately it's less noticeable because you are using a FF lens on a crop frame camera.

I don't think it's possible to determine if it's coma from the shots. Coma is usually shown in diagrams as a point and then a series of circles getting larger and offset radially. There would be none in the centre and get progressively larger towards the edge.

For the purpose of what I'm doing the type of aberration is not really important.

My aim will now be to determine which lens handles this best at the settings I can work with. My goal is to include stars and the milky way within my sea/landscapes, not just stars on their own.

When the clouds clear, which is not looking good for a while, I will run each lens through its wide apertures maintaining necessary shutter speed and exposure and record the results.

At present I'm also looking at 'exposure' as there seem to be two trains of thought, one is produce a bright image, the other is to produce a darker image that is as you see it. This will have a bearing on the 'brightness' of the stars that affects aberrations.

[Stagecoach]

It's disappointing to learn that all conspiracy theories have already been determined to be impossible before they have been offered.

My first thought was that the aliens are out there flying around guarding the edge of the universe