What is this star type thing?

its a UFO!..
no probably flare

Very small for lens flare (compared to total pic area), but I can't think of anything else it might be...

It looks like a reflection of a blue LED. Were you shooting through glass?

MyRomeo said:

Hey, I shot this a few weeks ago in the Lake district and wondered what it is. I took 3 or 4 shots, all 8 second exposure, ISO 400 and at 50mm, F1.8. Its the bright star below the zoomed in bordered bit.

All the shots I took had this same star appearing like in the attached shot. At first I thought I might have knocked the camera but for it to be the same in each shot it doesn't make sense.

I believe it was facing south but can not be certain, kinda get lost in the forest!

Processed in LR4.2, exported and the little zoomed in thing via photoshop 6


Any suggestions are welcome

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Your enlarged image looks like undercorrected coma, a common lens problem. Were you shooting wide open (maximum f/stop) with a wide angle lens?
Oops, I just reread your original post. Even though it's not a wide angle lens, coma will show up when you shoot a light source at the edge of the field with a lens that is not too well corrected for coma problems

MyRomeo said:

Coma? What's that!

The photo was not shot thru glass no, it was shot from my parents garden straight at the sky, no light sources direct or indirect, very dark.

The lens was a Nikon series e 50mm shot wide open at f1.8. I've recently serviced the lens so know its not got any grease or impurities in the glass but it is an old lens, some 30 years or so!

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The series E lenses were not well known for the best correction possible (read: cheap!). The problem of coma is one that all lens designers have to face and, if you have a problem with it in a lens, it can be minimized or eliminated by stopping the lens down from it's maximum apperature, usually a stop or two. Here is a definition list of the major problems that lenses have. Getting coma to a low level in a lens used wide open usually requires some major work on the part of the lens designer and sometimes requires the use of aspherical lens elements and the like.
Here's that list. It's pretty easy reading.
http://www.lensrentals.com/blog/2010/10/the-seven-deadly-aberrations

That's lens flare. Not coma, not aberration, not a UFO or a star.

Lens flare is greatly amplified with long exposures, exactly in the same manner as stars which you were trying to shoot! There's nothing wrong with the lens; it's just how exposure worked for that specific shot.

So whenever you're doing astrophotography, watch out for light pollution which may ruin the shot. Look for any light sources in front of the camera; my rule of thumb is, if you put yourself where the camera is and you can see the light, it's probably going to flare. If you're on full frame, a lens hood will do you mighty good but it won't cure the problem. If you're on a crop, try to find an appropriate lens hood for your 35mm-equivalent focal length (e.g. the Canon 17-40mm's hood's coverage is 17mm, so an EF-S 17-55mm hood, which has a 35mm-equivalent of 27.2mm must be used with the 17-40mm to get adequate focal length-appropriate coverage).

Also of note is that the in-camera flare correction DOES NOT WORK on this type of amplified flare.

As for why the flare is blue, the light was probably from a relatively hot street light (think 5500K) with the camera's AWB setting the shot's white balance to something ridiculously lower like 2500K. This results in a bluish tone throughout the photo, and it's what makes the sky appear blue despite it being completely dark.

Blame urbanization; there's street lights everywhere that ruin my shots all the time.

You might want to try your shot again with the lens stopped down to f2. It's not much of a change but it can fix some problems with under corrected lens aberrations.

Such is the problem with Astrophotography - your subject is always moving;-) I have a feeling that the bright star you were shooting may be the planet Jupiter. It's color would appear to be somewhat pale blue like your photo seems to show. That "E" lens you have is actually not that bad. I believe it was the lightest weight 50mm lens that Nikon ever produced. From around f2 or f2.8 it performs pretty well.
Good luck with your photos and enjoy it!

MyRomeo said:

Thanks for the replies, some interesting thoughts.

Prodo- there was no street lights in the area and the 'star' in question was visible over the tree tips with the naked eye. As for the area, it was shout east of Penrith aiming I believe south, no towns for miles in that direction, certainly no street lights.

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There's your problem. The moon is a light source as well, and since you shot south it's to the left of the frame and causes flare on the right side.
Any light source can cause flare, especially with a long exposure.

Also notice the small blob under the big one that you highlighted. That's of the same shape of the bigger one, which means it's from the same issue. This is another hint that it's lens flaring, as the elements will cast a similarly-shaped flare blobs of different sizes when it is flaring.

MyRomeo said:

thanks again for the input, I do appreciate the help.

A few questions

Would fitting a suitable lens hood reduce flares? If so what size would I need? I'm guessing since its shot using nikon D3100 and 50mm FX lens I need hood suitable for 75mm focal?

Any other tips for clearing this type of shot up either with the camera settings or post editing? I have LR4.2 and CS6 so can play around lots!

I'll try my next shoot at F2 or 2.8, see how that affects things. I've became quite a fan of the little E series 50mm, had some great shots from it, then again had some awful ones too but hey, thats the fun of learning a new skill!

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Yes, you'd need a 75mm hood. However, since the 50mm f/1.8E does not have a hood mount on its own (it itself takes a weird Chinese finger trap-style hood), you'll need a 52mm thread ~70mm focal length hood. However, these are somewhat hard to find since most screw-mount hoods only specify the filter thread diameter and not the effective focal length; the "telephoto" 52mm thread mount should work well, since most hoods are designed for the widest end of a lens and the most common wide angle for a tele lens is 70mm.

Just stamp (i.e. copy-paste) the flare out, using a starless portion of the sky as the source. Make sure to get all traces of the flare. Then go over it with a healing brush tool (also called retouch) to get rid of any trace of stamping.

For more complex shots, you'd be out of luck but thankfully the flare is in the middle of nothingness so this is easy to fix here. Here's an example.

As far as I know the 70-300 does not have a screw mount, so no.