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I am using a 107 Refractor Triplet 700cm F6.5 with a Zwo asi1600 Pro Camera and filterwheel.

I take my flats in APT and set it from 0.000032 seconds to 2 seconds and it works well at around 20k ADU. Exposure times very short sometimes less than a second.

However since I added my 0.79 Focal reducer bringing the scope to F5.13 and around 553cm Focal Length to reach 20k ADU exposure times are around 1 Minute 45 seconds each varying slightly dependant on filter.

I understand there is more light going t0 my scope which is probably has something to do with the mess up I am having with the ADU.

I worked out that a 12 bit ADC camera has the range of 0-4096 ADU so maybe trying 2,000 ish would work better?

KIndest regards David

 

 

 

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While your camera has a 12 bit analog to digital converter, your files are 16 bit. This means that you either only use the lower range of those 16 bits, where white = 4095 (2^12 - 1), or the high range, where white = 65535 (2^16 - 1). In this case, 1 ADU = 16 DN. Better check this first. Then set the flat exposure time to somewhere in the middle of this. With the reducer, exposure time should be a little shorter, because each pixel receives more light than before, as it covers more area.

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On 22/02/2020 at 21:37, Prolifics said:

I take my flats in APT and set it from 0.000032 seconds to 2 seconds and it works well at around 20k ADU. Exposure times very short sometimes less than a second.

However since I added my 0.79 Focal reducer bringing the scope to F5.13 and around 553cm Focal Length to reach 20k ADU exposure times are around 1 Minute 45 seconds each varying slightly dependant on filter.

???

I'm seriously confused by what you've written here.

First - ASI1600 uses MSB format - you want your flat ADU to be around 40K (actual values are in range 0-65535 and are divisible with 16 and not in range 0-4095).

Now, back to above. You say that without focal reducer you need up to two seconds per filter to get to 20K, but using focal reducer you need 100+ seconds to get the same ADU level?

Reducer should lower your time and not increase it by factor of x50! If above is indeed true - please check your focal reducer - it might have something wrong with it that block the light.

Don't worry about short times with ASI1600 - I used flat exposures that were fractions of a second, and even milliseconds long (my flat panel is rather strong) and never had issues with flats.

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On 22/02/2020 at 21:37, Prolifics said:

 

I understand there is more light going t0 my scope which is probably has something to do with the mess up I am having with the ADU.

There is no more light getting onto your scope. You have not increased the aperture, you have reduced the focal length. This is not the same as moving the aperture setting on a camera lens where you do open up the diaphragm and admit more light when you reduce the F number.

However, something is clearly amiss here because each pixel receives a little more light, as Wim says, so exposure times should go down a little. They certainly shouldn't make the jump up in time which is surprising Vlaiv. You don't mention the light source you are using. Could it be this which was much, much dimmer when you tried the reducer flats?

Olly

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Thanks for the info I am going to set up my light panel and test it indoors. I am thinking its a bug with the latest version of APT. Use to be less than a second exposure now 1.5 minutes. Somethings wrong but it producing good images still.

 

I normally put a white t-shirt over the lens and a flat panel lit up by led on top. I have tried with and without the t-shirt but I will do some more tests.

 

Regards David

 

 

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I just tried indoors with 1 layer of white T-shirt and a led dimmly lit led panel on top of the T-shirt and it seems to have sorted itself.

It's managed 20,000 adu at 0.046 seconds exposure. Better than the 1m 36 seconds i got before :) Not sure what was going on maybe APT feaked out or partially crahed after a 8 hour session.

 

Regards David

 

 

 

 

 

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