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Blooming spikes on DSLR

beamish

By beamish
in Imaging - Discussion

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brendant

brendant

Posted
Posted

Any pics to show the problem you are getting Karlo, have never experienced blooming spikes with a DSLR, sure it is not something in the imaging train that is causing the problem. It the problem there on your refractor ?.

Brendan

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beamish

beamish

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Well, it has appeared before, usually with bright objects and regardless of the camera being on the cape (reflector) or the 66.

I've investigated the optics etc and can't see anything same with the filters, looked at the filter in the camera -nothing ?

here's an eg central star and a few others if you look around.

I'm more than happy if any other suggestions come.

Karlo

post-13438-133877369354_thumb.jpg

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Psychobilly

Psychobilly

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I don't think they are blooming spikes as they would run tend to run "vertically" through a column of pixels and not at an angle across the chip.. I can get my Nikon D200 to "Bloom" when trying to do very long exposures that contain a bright target - like when i try and capture the moon and stars that are being occulted in the same image.

To me they are the result of the scope moving.. if you look closely they are "radial" being more curved on one edge of the frame than the other...

Peter....

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beamish

beamish

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Yup, so once it flips so the scope is on the west I have to move the weights down the c/w shaft, just a tad mind. I think that's according to what I've read in the past, correct, keep the rising eastern side a slight bit heavier- I'm more than happy to be put right.

The problem I originally highlighted isn't consistant, but has/does occur once in a while. I was going thru loadfs of old RAW files seeing whether I could go back and reprocess some with the knowledge learned over the last few months and was reminded about it . So thought I'd flag it up and see what peeps thought

Karlo

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Naz

Naz

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Mirror slap? Do you expose from the moment the shutter is opened?

Try holding a black card over the front of the scope as you open the shutter, then after a second remove it, see if that is the problem.

If that cures the problem, then you may have to beef up the arrangement so that the shutter doesn't cause movement.

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beamish

beamish

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Naz, it may be but TBH I just can't see mirror slap manifesting itself quite so dramatically on such a heavy mount et al.

I've been out tonight and was getting it again- I now suspect it's a balance issue for sure, I corrected it slightly and seems to have done the trick-we'll see

I've decided to go down the firmware hack route for the 300D to enable mirror lock and see if that improves things though just in case. :)

Karlo

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Naz

Naz

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It all depends on how solid / secure your set up is Peter, On one tripod I had, the D70 was ok on standard exposures, but anything over a 1/4 sec, bounce! A solid set up should be able to hold the camera steady. It all depends on the force that the mirror bangs into the up position with, can very from model to model, even with the same manufacturers.

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Psychobilly

Psychobilly

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40+ kg of scopes and mount on 45kg of pier on 600kg of concrete foundation with 5 foot deep angled steel piles tends to sort it :)

But yes on a lighter mobile setup it could be an issue .... like when I use the "66" on a photo tripod...

Karlo - I wouldnt fancy puitting "dampers" on the mirror or mirror box...

Peter....

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jgs001

jgs001

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Can it not be countered by putting little felt pads or the like on mirrored side ?

Karlo, you probably don't want to be doing that. The mirror cell in the camera is a bit delicate... I've not tried without using mirror lockup... I'm sure I'd probably get away with it, but it only adds 2 seconds to the exposure so not a big deal. I know if I put the Skymax on my camera tripod (rated for a 10Kg load) the mirror box in the 450d will cause a manifest shake even at reasonable ish shutter speeds 1/25 etc for the moon.

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