What could cause this

[leon]

Hi All,

Last night was reasonably clear and cold and i was lucky enough to image 5 different objects with some success.

I used the Canon 300mm F/2.8 Lens, attached to the 5D, and fired away, however after downloading the images I thought what have i here, never really seen this before, so maybe some kind person could assist, and suggest what I, or the camera and lens combo did wrong.

This only happed on the first object photographed, which was the star Acrux and the surrounding star field.

This also appeared on the other objects imaged, but not quite as bad as this first one.

This is what i did..

300mm lens and 5D mounted on G11 and tracked for 1 minute exposure at 400 ISO, drop in Hutech 52 mm filter used in the rear of the lens.

10 exposures aligned and combined in Image Plus, this is a full size image and no cropping has been done.

So what has happened here.

Thanks Leon

[avandonk]

If your lens was clear of any condensation Leon, this is usually caused by weak fog or thin cloud or both.

Bert

[Gama]

I agree with Bert that its more likely condensation, as the centre is more fogged up than on the outer rim. Especially the star down along the bottom a little to the left.

Theo

[RB (Andrew)]

Yep I think it's condensation on the lens, if not it's Bert said fog or thin cloud.

Try a dew strap around that beautiful lens Leon but just watch the temp on it.

I had it happen to me once too with similar results.

[ballaratdragons (Ken)]

I had it all night long too Leon! It was both condensation on the lens (which I kept 'hair-drying' off) and a thin layer of fog. It got worse as the night progressed, but it only seemed to effect really bright objects, until I got completely fogged out.

[gbeal]

Really, unless you are lucky enough to never have dew, you need to have a dew removal system of some sort. I have a dew strap on every lens, including the finder, so with the new TSA I have never had dew. Most likely only 50% of the time it was necessary, but the the trouble with dew is you don't know when it is there until it is, if you get my drift.

[leon]

Thank you guys, now that i think about it more, you are all probably correct, although i do have a dew strap for the lens, i think what has happened is this.

The observatory is pretty warm and stays at about 8-9 degrees, and i did have the dew controller on prior to opening it up, but the outside air was only 2 degrees, this is why it probably fogged up badley on the first image run until it reached temp out side.

Thanks again.

Leon

[avandonk]

Only someone from Ballarat would say 8 to 9 deg was warm!

Bert

[leon]

Ah Bert, we love Ballarat weather,

Leon

[ballaratdragons (Ken)]

Originally Posted by avandonk

Only someone from Ballarat would say 8 to 9 deg was warm!

Bert

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