Basic exposure/processing Questions

[beren]

Last night i did some first steps with a Dig camera piggypack, anything longer then 3 min the image is a whitout , just wondering if anyone has any advice on procedures to go through before the exposure and processsing afterwards. I tried photoshop with the curves and RGB levels but i couldnt produce anything that was decent especially with one rthat was a 10 min 70mm 800iso shot of Orions belt/sword area . I set the noise reduction on the camera is there anything to adjust further like white balance for instance {D70 nikon}.

Heres the unaltered shot described above......

[[1ponders]]

My god, is that with iso800? Can't help you with the nikon but the canon at 3 minutes at 800 doesn't produce anything like that. I have no idea stuart. I think you might need to talk to Gary about this one

[beren]

Heres one thats 2 min unaltered....

[iceman]

oh my lord that's horrible!

The histogram looks way shifted to the red end.. also when I set the black point on the levels function, the image looks horribly compressed and chunky. Might need a less-compressed version to try it on.

Does the internal NR take a 3 minute dark frame after the 3 minute exposure? You might have to take your own 3 minute dark and subtract that from the washed out one above.

The second one isn't as bad, but still it's pretty washed out. Below is the 2nd one with the levels adjusted, but again the image is horribly compressed and chunky.

[beren]

Ice just checking the size and quality/format i had the camera set to it was .....image quality=Jpeg normal.....image size 3008x2000....optimize image setting=normal .As far as noise reduction goes i think the camera does it automaticlly.Any of these setting be the cause ?

[iceman]

I'm not talking about the camera settings, but when you reduced it to post on the forum, it has been compressed pretty hard down to 23k.

Did the camera sit there for 2 minutes after your 2 minute exposure? That's the only real way it can do noise reduction, but closing the shutter and taking an equivalent length dark frame, and subtracting that from the exposed shot.

It means your camera is tied up for 2 minutes after the first 2 minutes.

You should put the lens cap on and take a 2 minute shot next time, and post the 2 images, and we'll see if we can subtract them.

[beren]

Yep it does that ie:take exposure/then camera does its work.
Is this the procedure i should follow.......

1.) Take your actual exposure
2.) Put lens cap on
3.) Take "dark frame" exposure
4.) edit:
In photoshop, load the image, then copy in the dark frame image as a layer on top. Set blending mode on the dark frame layer to "difference" and opacity to 50%.

cheers

Ps;should any settings be adjusted though

[iceman]

I'm not sure about camera settings - what you have looks right. As long as NR is turned on, the rest looks fine.

[[1ponders]]

You don't have a light pollution problem where you are do you? I'd be a bit surprised if you had to change any camera settings. I just changed the iso, set it to manual to set the bulb control and snapped away. That's bizzare
This is a two minute exposure with my camera with very little colour adjustment just reset black point and sharpening adjustment. I basically accepted the camera defaults except I selected Raw for photo, bulb for exposure, didn't even take any dark frames.

[gbeal]

Beren,
My gut feeling is use it either of two ways.
I use the N/R feature, and shoot depending on the conditions, 2 - 5 minute exposures, and accept the equivilent amount of "downtime" while it does an automatic dark.
Alternatively you can shoot without the N/R and make this dark after the event, and manually subtract it.
If you do this, you can make a selection of library darks, and save time. You happy with this procedure?
If not just use the built in N/R, I find it works well.
My first shots were of Comets Neat and Linear, and using the old ugly Nikkor 300mm @f4.5, at about ISO800 - 1250. Exposure times were around the 2 to 3 minute mark, and were very good.
Go for it, and don't be put off by all the jealous Canon owners, Nikon rules.

[beren]

:) Thanks Garry ill try tonite with the manual dark subtraction and experiment , is it best when doing this to turn off the NR altogether or let it run and combine with a dark frame. Paul light conditons are somewhat poor ,typical urban conditons although i concentrated in a northerly direction where its better . For wide feild shots is there any advantage to take a series of sub 1 min shots and layer them in PS ,is it worth it.

Cheers

[[1ponders]]

Your shots weren't a complete loss, I did a bit of light pollution subtraction and the image turned out OK. I think it was the second one I downloaded.

I'll download the first and give it a try and see what comes out

[[1ponders]]

No go on the first one. Its a bit beyond my skills at the moment

[rumples riot]

Must Say Stuart I have never had a shot like those. I regularly take shots over 8 minutes and then NR for a further 8 Minutes. I set shots to fine or high (not tried raw yet) at ISO 800, 1250 and 1000. I must say though I have never done a wide field like yours.

Keep trying you will get the drift I am sure.

[beren]

Hey Paul your adjustments came out well , i think ill have to buy Photoshop for dummies or something . my exposure times are probrly to long for my location , ill try tonite with a longer lens and see if a smaller area can take longer shutter speeds . Ive found similar tutorials where people have had washed images and have finished with nice work with the aid of PS etc , most of the descriptions are over my head .

heres a link to a canon rebel tutorial/review.....pdf file

http://www.cloudynights.com/lab/astrophotography/rebel.pdf

[gbeal]

Beren,
I use the built in N/R.
If you are doing the manual do it yourself thing, then just shoot, and have the N/R off.
Gary

[[1ponders]]

Stuart

All I did was follow the instructions on this site http://pietertieghem.100free.com/astrophoto/tutorial1.html It's pretty straight forward step by step guide for removing LP. Have go with your shot. The settings I used were slightly different to his, particularly with the Gausian blur settings, I didn't need to go quite so high.

[beren]

Thanks Paul, im not having much luck with the steps ,just isnt computing for me {:}} might have to go through PS from basics.

[[1ponders]]

Which part are you having trouble with? Maybe I can offer some suggestions

[beren]

:P embarrasment i cant even get to first base .....do i load the washed image first ?unsure how to create layers ?:ashamed:

[[1ponders]]

np, open PS, open your file, then go into the menu *layer* select *new* - *layer*. When you select the *new layer* you don't have to name the new layer, just select *ok*. Then go up to the menu *window* and check that there is a tick beside *layers*, this will open the layers window.

[[1ponders]]

When the layers window opens you should see two layers. The background layer at the bottom, which is your original and the new layer above the background layer. This layer may look checkerboarded. One of the layers will have blue highlighting beside it. This is the active layer. Any changes made to the image will be made to any active layer.

[beren]

Thanks Paul i think ive got the hang of it now , although its still tough to make the washed out image look presentable .
Cheers mate.

[[1ponders]]

Drop me a line if I can help.