M45 - in UV!

[Thalestris24]

Hi

Last night wasn't really an imaging night (very murky and lots of cloud) but I decided to have a quick play with a B+W 403 UV filter. I wasn't sure whether I'd be able to pick much up but (after removing the cls-cc lp filter.... ) to my surprise I was able to get images ok on my 550d mono dslr. This is the result of stacking the best 9 of quite a few 60s exposures, in dss. I just did some stretching in dss - nothing fancy! Quite pleased with the result and it's great to not have any lp gradients!! Unfortunately, some horizontal artefacts have crept in instead. I don't know what caused the lines - doesn't seem likely to be the filter itself. They were visible on individual subs with a lot of stretching. When I get a minute I'll try some daytime pics and see if they are at all visible then.

Anyway, here you go - 9 x 60s at iso800 (resized and very stretched):

Of course, I can almost hide the lines by adjusting the black point:

 

 

Had conditions been better I would have done longer exposures - and more of them!

I'll may try some IR also

Louise

[Demonperformer]

Novel approach to a popular target.

Am I right that the halos are a result of optical equipment not being designed to focus the UV perfectly, or is something else going on?

[Thalestris24]

7 minutes ago, Demonperformer said:

Novel approach to a popular target.

Am I right that the halos are a result of optical equipment not being designed to focus the UV perfectly, or is something else going on?

Hi

There aren't any halos... The brighter stars are somewhat bloated - they probably are giving off loads of UV! I'm not sure why they are fuzzy - may be to do with the conditions, may be a property of the UV/optics. It's the first time I've tried this and I'll have another go when (if?) conditions ever get better! Maybe someone else here has done some UV imaging? (to compare notes with  )

ps I should probably have mentioned I used a f4 200mm Takumar lens  

Louise

[Uranium235]

Begone foul cursed lines!!!

For info:

1) Noels "remove horizontal banding" action

2) Ps Calculations (pixel math) to remove uneven background

 

[Thalestris24]

2 minutes ago, Uranium235 said:

Begone foul cursed lines!!!

 

Clever boy!  Mind you, I think I can see blotchy lines instead but it might just be my eyes!

Louise

[Uranium235]

Yea, the background is still a little noisy - not much can be done about that without a fair amount of exposure to bring the noise down. Perhaps doing a bias subtraction would help.

[alacant]

Hi. Not sure why it's uv if we can see it. Does the filter and/or camera convert the uv to visible? I just tried a uv filter by accident and it made the stars smaller. Confused!

[Thalestris24]

3 hours ago, Uranium235 said:

Yea, the background is still a little noisy - not much can be done about that without a fair amount of exposure to bring the noise down. Perhaps doing a bias subtraction would help.

Yeah, I stacked with bias and flats though didn't have any 60s darks but I don't think they'd have made a difference. I'm pretty sure I've not seen the problem before with the 550d.

Louise

[Uranium235]

Hmmm not sure where the noise (horizontal lines) is from then... just an idea - but ensure the USB cable from the camera is routed well away from any power cables.

[Thalestris24]

3 hours ago, alacant said:

Hi. Not sure why it's uv if we can see it. Does the filter and/or camera convert the uv to visible? I just tried a uv filter by accident and it made the stars smaller. Confused!

Hi 

It's only the camera that can see in UV - preferably a full-spectrum modded one without a UV blocking filter. Of course, UV blocking filters are frequently used in daytime photos. The B+W 403 also passes in the near-IR so I guess my images are a mix  

Louise

[Thalestris24]

3 minutes ago, Uranium235 said:

Hmmm not sure where the noise (horizontal lines) is from then... just an idea - but ensure the USB cable from the camera is routed well away from any power cables.

It's a possibility! I did do things in a bit of a rush and I'm out of practice!

[Thalestris24]

3 hours ago, alacant said:

Hi. Not sure why it's uv if we can see it. Does the filter and/or camera convert the uv to visible? I just tried a uv filter by accident and it made the stars smaller. Confused!

Just to clarify - most so-called UV filters are UV blocking. The B+W 403 passes UV and blocks visible, plus passes some near IR. So the filter itself looks black.

Louise

[alacant]

9 hours ago, Thalestris24 said:

The B+W 403 passes UV and blocks visible

Ah, so the camera must convert it to visible (?).

[riklaunim]

33 minutes ago, alacant said:

Ah, so the camera must convert it to visible (?).

Silicon imaging sensors are sensitive to UV and IR. They don't convert it to "visible", they just see it.

[Thalestris24]

Hi

You could say the camera can make the invisible visible

Louise

[Waldemar]

On 27-9-2016 at 19:45, alacant said:

Hi. Not sure why it's uv if we can see it. Does the filter and/or camera convert the uv to visible? I just tried a uv filter by accident and it made the stars smaller. Confused!

You were using an UV/IR cut filter... that passes the visible light and blocks UV and IR

Louise used an UV pass filter. Totally different filter. That one blocks the visible light and passes UV... exactly the opposite.

CCD as well as CMOS sensors are sensitive to UV and IR, in fact 'see' a wider spectrum than our eyes. That is why normal (DSLR) camera's use a blocking filter, so they give a 'natural' looking image, which is removed or replaced for AP conversion, because the H-alpha frequency lies in the NIR (near infra red)range, and is blocked by the standard filter.

Waldemar