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stretching of stars at the edges of widefield shots


Sammyb

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Hello I've been having a go at using my D3100 attached to my EQ5 pro for some widefield shots of the nights using the standard 18-55mm lens kit.

I've noticed a frustrating effect whereby the stars at the edges of the field aren't nice and sharp but rather elongated.

Is this an artefact of the lens? is there a way this can be reduced?

Thanks,

Sam

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Without seeing an example I'd say yes, it's probably a lens artefact. My Canon 18-55mm does the same. Stopping it down a stop or two may help, otherwise cropping them out seems to be the only option.

James

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You must remember that your kit lens has two things going against it. The first is price;because it is a kit lens it is not an cheap option and they are usually not particularly well made - good enough for general photo's but, as you are finding, not very good if really tested. The second thing is the fact that it is a zoom and that brings many extra elements into the image train and each will have an detrimental effect on the lens quality. It is far better to use a 'prime' lens for the sort of work you are doing, a 50mm, 135mm, 200mm etc, as these use fewer elements and have better image control than a zoom could ever hope for.

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Ahh cheers.

I don't suppose a great deal can be done about that either?

I have a half an hour of M45 subs that looks all purple and flared on the brighter stars, I was kind of expecting a bit better results but like Richard said I think it's down to the cheap glass on the zoom lens more than anything.

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Here is one, I wasn't picking up any nebula in the subs and there is only a slight hint of it in the stacked pics.

It also looks out of focus but I spent a bit of time trying to get the focus right but I guess it could be internal reflections messing around with what I'm seeing.

It's a 30 second sub at iso800.

post-8383-0-57576500-1354006349_thumb.jp

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Yeah, the cheap kit lenses are great for the price, but you have to go up a few magnitudes in price to get distortion free edges usually. I wish I had a Carl Zeiss Distagon 15mm but alas, for a fraction of the price, the kit lens and it's distortion don't bother me that much :)

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