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Old 11-05-2018, 04:49 PM
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Focal Length

I used to put four holes in what you could call the cover on my little reflector and take pictures of the Moon in the belief I could better photos will the longer focal length.I am pretty sure I actually took photos this way and they were great but that nay be a dream..
I dont trust memories I I dont have the notes and photos what I did and how I thought or what I thought...no notes rares it as possibly imagination.

Now we all know the longer the fl the more you restrict light and need to lengthen exposure times...but is there any advantage to try for a long focal length.
Say I did the four hole thing on the eight inch ...still get a lot of light ...Maybe it gets more detail but you would think not....anyways any thoughts.

Alex
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Old 11-05-2018, 04:52 PM
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Originally Posted by xelasnave View Post
I used to put four holes in what you could call the cover on my little reflector and take pictures of the Moon in the belief I could better photos will the longer focal length.I am pretty sure I actually took photos this way and they were great but that nay be a dream..
I dont trust memories I I dont have the notes and photos what I did and how I thought or what I thought...no notes rares it as possibly imagination.

Now we all know the longer the fl the more you restrict light and need to lengthen exposure times...but is there any advantage to try for a long focal length.
Say I did the four hole thing on the eight inch ...still get a lot of light ...Maybe it gets more detail but you would think not....anyways any thoughts.

Alex
Alex, doing that doesnt change the focal length, only the apeture/F-ratio - as you dont change the mirror at all, the FL does not change.
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Old 11-05-2018, 04:58 PM
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As Logan says, it won’t change the focal length.
It also has the downside of effectively giving you MASSIVE spider veins and quite a large central obstruction. Both of these significantly dropping the C.J. tears of your images
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Old 11-05-2018, 05:53 PM
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Originally Posted by Lognic04 View Post
Alex, doing that doesnt change the focal length, only the apeture/F-ratio - as you dont change the mirror at all, the FL does not change.
Thanks Logan...Yes of course what was I thinking.
Alex
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Old 11-05-2018, 06:00 PM
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As Logan says, it won’t change the focal length.
It also has the downside of effectively giving you MASSIVE spider veins and quite a large central obstruction. Both of these significantly dropping the C.J. tears of your images
I dont know why I tried it...or maybe I was just trying to minimise light for Moon shots originally ...the things you think of...I am thinking about cats..I like cats..and dogs and horses...thanks.
Alex
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Old 11-05-2018, 06:02 PM
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And a pet pig and a ferret.
And more horses, they are so cool, so interesting..so responsive and interactive...and a donkey I am definitely getting a donkey ..rhe horses would be ok but I am not sure...but I will get one tomorrow ..where do you buy a donkey.
Alex
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Old 11-05-2018, 06:09 PM
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Look at those ears..they are so cute.
Alex
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Old 11-05-2018, 06:28 PM
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Erm...a bit unrelated?
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Old 11-05-2018, 06:41 PM
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The relationship is that I have lost the plot...something so obvious but I miss it is what I did...and all the while knowing that could not work ...there was a guy who got a write up years ago using a plate with holes in it maybe some thing in the article had me rushed headlong and eliminating something...and thinking of pet animals ...
Anyways althought its cold I am going out to get me some photons.
Alex
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Old 11-05-2018, 07:22 PM
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Hi Alex,

Was it an apodizing mask?

http://www.telescope-optics.net/apodizing_mask.htm

http://www.astronomyhints.com/apodize.html

Cheers,
Rick.
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