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PostPosted: Fri Oct 29, 2010 2:57 am 
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So, I'm getting more interested in astrophotography each day! Although, I'm still a bit confused about what darks and flats are, how we take them, why we use them and how to apply them using DSS.

Also, I've noticed that when I shoot film, the film fogs up and I get a bit of a foggy effect. This doesn't apply with digital CMOS or CCD sensors, does it?

One more question please, to just do some shorter exposures with deep sky (Under 10 minutes let's say), would I need to shoot things like the Pleiads, M31 or the North-American nebula? I have the 200mm F4 35mm film prime, would that work if I tracked with the Celestron D8 and mount?

Thanks for your responses!

-Evan

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PostPosted: Fri Oct 29, 2010 6:17 am 
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Hi Evan,

Dark Frames are made by making photographs with the lens cap on your lens, and making an exposure that's exactly the same as the Light Frame you shot. This will result in a black photo, which you will load in DSS to remove noise. Important is that you take the Darks on the same place as you took the Lights, because the higher the temperature, the higher the noise wll become. So, if you finished the Lights, take after that DIRECT the Darks.

Flat frames are not that hard needed when you begin, Im a beginner too and Ive not used flats since Im started. Flats are used to remove the vignetting of the lens, and I think that a 200mm f/4 (sounds expensive) doesnt have that much vignetting. IF you have vignetting, you can load the stack in Ps (Photoshop) and remove it with the tab ''filter-lens corrections''.

If you scroll through the forum you will see some M31 shots made by me.
M31 is bright, and doesnt need very long exposures to see it (my exposure was 30s ISO1600). However, when you stack the photos (as I did) and take 100 Lights, you could get more and more details on the photo! This is a Light frame of M31: http://www.google.nl/imgres?imgurl=http://www.createduniverse.net/Libraries/EQMod_Testing_Images/M31_Andromeda_Galaxy_EQMod_Single_light_frame_ISO_800_10_minute_exposure.sflb.ashx&imgrefurl=http://www.createduniverse.net/eqmod.aspx%3FGalleryProv%3DLibraries%26GalleryItem%3D6bf0b35f-e2f4-4ea1-9264-36146d51757a&usg=__iBkZ80-2SV5fYRaL8HZNaOLEwdc=&h=2400&w=3600&sz=252&hl=nl&start=0&zoom=1&tbnid=is9go0BFozYIHM:&tbnh=176&tbnw=227&prev=/images%3Fq%3Dm31%2Blight%26hl%3Dnl%26biw%3D1024%26bih%3D653%26gbv%3D2%26tbs%3Disch:1&itbs=1&iact=hc&vpx=716&vpy=389&dur=611&hovh=176&hovw=264&tx=136&ty=173&ei=9WXKTL7AJobpObzq1ZIB&oei=9WXKTL7AJobpObzq1ZIB&esq=1&page=1&ndsp=12&ved=1t:429,r:11,s:0, and this could be the final result after stacking: http://www.google.nl/imgres?imgurl=http://images.astronet.ru/pubd/2005/12/22/0001210531/m31_gendler_Nmosaic1c50.jpg&imgrefurl=http://www.astronet.ru/db/xware/msg/1210528&usg=__VhrqECPINqIrDQSACFGd0zogifE=&h=528&w=721&sz=140&hl=nl&start=12&zoom=1&tbnid=-ho8kaXq4ZKD8M:&tbnh=153&tbnw=207&prev=/images%3Fq%3Dm31%2Blight%26hl%3Dnl%26biw%3D1024%26bih%3D653%26gbv%3D2%26tbs%3Disch:10,461&itbs=1&iact=hc&vpx=721&vpy=197&dur=1329&hovh=192&hovw=262&tx=138&ty=78&ei=OGbKTLbiGJDqOe6U3bYB&oei=9WXKTL7AJobpObzq1ZIB&esq=3&page=2&ndsp=12&ved=1t:429,r:3,s:12&biw=1024&bih=653

My advices: Make around 100 Lights of M31, 30s each at a high ISO (>800), try what your lens does wide open, take 30 Dark frames and few Bias' (same ISO as shot, fastest shutterspeed with lens cap) and stack them in DSS.

Cheers!

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Ruben

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PostPosted: Fri Oct 29, 2010 7:32 am 
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Dark frames are used to subtract noise, ampglow and dead pixels generated from the cameras sensor. Im not sure if the same applies to film. The key with darks is to make sure they are taken at the same temperature as the lights to ensure you are capturing the right level of noise, ampglow etc. Unlike flats they can be taken after the setup has been moved and must have an exposure length equal to that of the lights.

As Ruben said flats are harder to take and most people dont bother. If you want to take flats you need to ensure that the setup isnt moved and the focus isnt changed. Then you need to evenly illuminate the sensor with a diffuse light. You must also capture the flats ensuring that you only fill 2/3 of the sensors well capacity (I usually choose an exposure which tilts my histogram over to the right slightly.) Another key aspect is to ensure the aperture isnt altered. If you are using lenses as opposed to a scope then vignetting should be too much of an issue.

Have a read of this which will hopefully explain a few things:

http://deepskystacker.free.fr/english/index.html

Just be careful of Rubens statement about not needing very long exposures. Whilst this may be true of certain subjects, to capture any detail you are going to need to have an exposure of at least 120s minimum IMHO. The easiest way to think about it is in photon gathering terms. The longer the shutter is open the more photons you collect, therefore a stack of 5 x 120s exposures will have more detail than a stack of 20 x 30s despite the total exposure being the same i.e. 10mins. This is because in the 120s lights you will capture more detail!

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PostPosted: Fri Oct 29, 2010 7:43 am 
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Of course what Digz says is true, but I think that -to start with- 30s and then as many photos as you could take is easier.

But hey, have a try!

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PostPosted: Fri Oct 29, 2010 7:57 am 
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It will be easier, of course, but just dont expect any great detail to jump out despite taking lots and lots of lights. My post here on M31 only pulled out a limited amount of detail using 120s lights.

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PostPosted: Fri Oct 29, 2010 8:22 am 
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Of course you dont have to expect miracles, but your last M31, Digz, could use another edit, I think there's more detail in it than youve got out of it :wink:

Not sure though, but my M31 from 30s and 150 Lights has a bit more detail (havent posted that one though).
But 30s with M42 is more than enough, I made (in my opinion) a very nice stack of it, with lots of red.
But, it's all about trying to get the best out of your system!

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Ruben

Panasonic DMC-FZ18, Panasonic DMC-FZ28, Canon G5, Canon 350D, Canon 50D + BG-E2N
Tamron 17-50 2.8, Canon EF 70-200mm f/4L USM,
Canon 18-55 II plus lots of Minolta MD/M42 lenses and bodies


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PostPosted: Fri Oct 29, 2010 4:36 pm 
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Evan, what mount do you have with your Celestron?

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PostPosted: Fri Oct 29, 2010 10:07 pm 
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I have a kencor custom equatorial tracking mount, according to my father who purchased the scope and mount.

Anyways, so to get M31, I could take say, 100 lights of 30s, then 50 darks of 30s? How does that sound? I presume that I'd have to track, but the mount could do the tracking, and I wouldn't have to do manual tracking would I? Perhaps if it was a slightly longer lens and a longer exposure, but do I really need to manually track?

Also, what would I need to do if I wanted to do (My all time favorite) M51 and NGC 5195? I presume that a scope would work best there.

Thanks!

-Evan

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-Evan

Gear: 7 Nikon Nikkor AI-S and AF-S lenses, SB-700 flash, Nikon D7000, Nikon FM, variety of accessories

"There are no rules for good photographs, there are only good photographs."
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PostPosted: Sat Oct 30, 2010 7:53 am 
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Which lens are you going to use?
I made 150 Lights with the 200mm @ f/4 on my EQ3, tracked with motors.
Id give it a try.

Btw, you didnt have a dSLR didnt you?

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Ruben

Panasonic DMC-FZ18, Panasonic DMC-FZ28, Canon G5, Canon 350D, Canon 50D + BG-E2N
Tamron 17-50 2.8, Canon EF 70-200mm f/4L USM,
Canon 18-55 II plus lots of Minolta MD/M42 lenses and bodies


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PostPosted: Sat Oct 30, 2010 1:02 pm 
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Yes, I would try the 200mm probably. It's a nice prime, a bit slow for astrophotos, but it still is great with it's hard infinity stop.

And no, I don't have a DSLR. I'll either be getting a D90 or a D7000, I'm waiting for it to be released here in Canada before I compare them to see if the 7000 is worth the extra $500.

Also, what do you think of the Nikkor 70-300mm VR i AF-S tele zoom?

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-Evan

Gear: 7 Nikon Nikkor AI-S and AF-S lenses, SB-700 flash, Nikon D7000, Nikon FM, variety of accessories

"There are no rules for good photographs, there are only good photographs."
- Ansel Adams


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PostPosted: Sat Oct 30, 2010 1:22 pm 
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The telezoom is a bit slow, I think.
If I were you Id look to an old Nikkor lens (maybe 20 years old, who cares) because they are sharp and if you buy a pro lens (20 years ago it was pro, now it's prossible not pro anymore because it's a MF lens) you could have a very sharp and fast lens without spending too much.
Ive still some 20-30 year old lenses, MF, used on my 350D with an Minolta-Canon adapter. They are as sharp as they were 30 years ago, but very cheap, because nobody wants such lenses. I bought the Cosina 135mm f/2,8 for $15...........

My favourite shop of my astro stuff is this site, and they have a few lenses with fixed focal lenght, maybe something to consider? On eBay they could be really cheap..
http://www.teleskop-express.de/shop/ind ... ktive.html

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Ruben

Panasonic DMC-FZ18, Panasonic DMC-FZ28, Canon G5, Canon 350D, Canon 50D + BG-E2N
Tamron 17-50 2.8, Canon EF 70-200mm f/4L USM,
Canon 18-55 II plus lots of Minolta MD/M42 lenses and bodies


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PostPosted: Sat Oct 30, 2010 2:18 pm 
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Yes, old lenses are just as good. As I say, bodies come and go, but glass is forever!

do you have any recommendations on old telephoto lenses, that are relatively sharp and fast? Thanks!

For new lenses in general, I'd go for the 16-85. It looks like a nice, sharp zoom.

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-Evan

Gear: 7 Nikon Nikkor AI-S and AF-S lenses, SB-700 flash, Nikon D7000, Nikon FM, variety of accessories

"There are no rules for good photographs, there are only good photographs."
- Ansel Adams


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PostPosted: Sat Oct 30, 2010 3:40 pm 
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Im sorry, but look at eBay on Nikkor tele, look at lenses that have your budget and look at Google for reviews, the way I did buy the lenses was that way.

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Ruben

Panasonic DMC-FZ18, Panasonic DMC-FZ28, Canon G5, Canon 350D, Canon 50D + BG-E2N
Tamron 17-50 2.8, Canon EF 70-200mm f/4L USM,
Canon 18-55 II plus lots of Minolta MD/M42 lenses and bodies


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PostPosted: Sat Oct 30, 2010 6:28 pm 
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I can't seem to find that mount when I google it, does it come under another name? Can you post a pic?

If the mount has motor and can track then your halfway there. The accuracy of the tracking comes down to the build of the mount but also to how well you polar align. Basically good polar alignment will ensure good tracking (subject to periodic error) you should then be able to try 60-90sec lights. You can try and attach your camera, depending on the type of scope connections and saddle puck. Then you can use your camera lenses. If you want to use your scope will need to get a t-adapter and t-thread. That way you can try prime focus basically issuing the scope as a big lens.

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