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Nikor F2.8 Fstop and Exposure time quesiton

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#1 Gregk

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Posted 12 October 2012 - 02:36 PM

Hi

Trying a longer exposure time with my Canon 450D moded camera
I would like to go out 8 minutes but concerned about thermal noise The outside temps should be between 70-75 degrees May only get 6 darks but could add more later
however. Never considered a dark library.

Also I have an older 100mm Nikon F2.8 Lens I usually stop it down 2 stops to F5.6 Can I stop to F2.8 or F4 or Do I get bloated Stars I seem to remember this dilemma from a previous post.

target Cepheus Dark Site Queen Valley Az.

Thanks for any advice

Greg

#2 SKYGZR

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Posted 12 October 2012 - 03:09 PM

Try some at both f/4 & f/5.6 with various exposure times and ISO settings. I will be working on, (perhaps this weekend), data acquired this week using the aforementioned parameters.

#3 neutronman

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Posted 12 October 2012 - 04:31 PM

As Skygzr said -- Best advice is to simply test it yourself. You don't need long exposures, just 30 sec will suffice. You just wanna see the edges of the field to make sure the stars are tight and sharp. With several higher end lenses you can shoot wide open, but other less expensive options need to be stopped down a bit for good performance. The only way to really tell is to try it.

#4 fishonkevin

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Posted 12 October 2012 - 05:43 PM

You can go 8mins no problem, since your guiding. I do it all the time with my 450D, even this past summer when the temps here were in the 80's. Check my image of the Veil Nebula on Flickr.

#5 Gregk

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Posted 12 October 2012 - 06:38 PM

As Skygzr said -- Best advice is to simply test it yourself. You don't need long exposures, just 30 sec will suffice. You just wanna see the edges of the field to make sure the stars are tight and sharp. With several higher end lenses you can shoot wide open, but other less expensive options need to be stopped down a bit for good performance. The only way to really tell is to try it.


Thanks I can do a few test shots at 30 seconds Gets me warmed up

#6 Gregk

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Posted 12 October 2012 - 06:41 PM

You can go 8mins no problem, since your guiding. I do it all the time with my 450D, even this past summer when the temps here were in the 80's. Check my image of the Veil Nebula on Flickr.


Thanks How many dark's do U recommend I was so used to using my SS PRO and never had to worry about dark's much until it went bad

#7 hiro

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Posted 12 October 2012 - 08:38 PM

Hi Gregk,

I have tried exposure in relatively high ambient temperature around 79 degrees F in July 2009. I prepared 25 times 8 minute-light frames at F5.6 and ISO 6,400 and temperature matched 21 dark frames. Each single light frame looked far noisier than expected, but the stacked result was not so bad as in the link below.

http://www.flickr.co...roc/3754159425/

I feel that the most important factor was the exact matching of ambient temperature while taking dark frames. We can prepare many dark frames afterward in several nights in different ambient temperature in our backyard.

#8 fishonkevin

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Posted 13 October 2012 - 01:53 AM

As Hiro said matching the temp. is the important thing. I've been using BYE for image capture, so I use the built in dithering function that it has with PHD. My Veil image only had 4 darks. I did forget to shoot flats though :foreheadslap:.






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