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Nikkor 180 ED + ASI183MM Pro

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#1 Ibuprofen200mg

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Posted 23 July 2021 - 11:44 PM

I am in the process of switching over to narrowband imaging an plan to use the following:

 

Nikkor 180 ED

ASI183MM Pro

ZWO Nikon adapter & filter drawer (provides 56 mm back focus with filter)

7 nm Ha and Oiii filters - 1.25" using the ZWO 2" to 1.25" adapter inside the drawer

Skywatcher Star Adventurer

ASI120MM + mini guide scope

 

Does anyone see any potential pitfalls with this plan? My previous setup was using an AT60ED and Nikon D5300. While this was really fun, I seemed to hit a wall with OSC and my Bortle 8 skies. In my area even Bortle 5 skies are more than an hour away, so this is my plan to get better quality data from the comfort and convenience of my yard. I had initially been scared away for NB imaging due to the much longer exposures that most seemed to suggest would be required (5+ min) and my less than ideal mount, but after doing some research and maths I have convinced myself it should be OK...

 

Using Dr. Glovers ideal exposure time calc: Exp(s) = C (constant, using value of 10) * R^2/P, where R is the read noise (e-/pixel/s) and P is the light pollution rate (e-/pixel/second), I get a calculated ideal exposure using the Nikkor lens (@f/4) and the ASI183MM with a 7nm bandpass filter of right at 120s. This calculation is supposed to give a reasonable target exposure time where the read noise is swamped by the sky background. 

 

I was able to get 2 min guided easily with the AT60ED/D5300 combo at an image scale of 2.24"/pixel, so I am confident that I can get at least this or more if needed at the 2.75"/pixel image scale that this setup would give. While 2.75"/pixel isn't ideal it's not much worse than I had before which gave good detail.

 

So again, does anyone see any large potential issues here? I've seen a lot of mention of the shallow well depth on the 183MM, should I be concerned about this shooting in Bortle 8 at 2-3 minute subs? I would plan to shoot 2-4 hours per night on each filter and then combine in post. Also I assume the 1.25" filters will be OK for 183MM with it's sensor dimensions. 

 

Any input or tips for success is appreciated.

 

Thanks!

 

 



#2 idclimber

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Posted 23 July 2021 - 11:56 PM

I suspect you intend to shoot wide open but you may also want to try stopped down to say f/4 or even f/5 to get better stars along the edge. I have considered buying this lens for wide field and strapping it on my scope. 

 

You may also benefit from increasing the gain. I would guess 200, but others who have experimented with this exact camera may have better suggestion. 

 

I think you have an excellent plan. 


Edited by idclimber, 23 July 2021 - 11:57 PM.


#3 Ibuprofen200mg

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Posted 24 July 2021 - 12:18 AM

Idclimer, I was planning to shoot at f/4 which is one stop down on the 180 ED f/2.8. I have tested it at f/4 on my D5300 and can confirm it is very sharp. There is a little coma in the corners but it’s actually better than my AT60ED was in that regard even with the matched flattener.

 

PS: thanks for the input!


Edited by Ibuprofen200mg, 24 July 2021 - 12:20 AM.

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#4 Alec

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Posted 24 July 2021 - 06:56 AM

Idclimer, I was planning to shoot at f/4 which is one stop down on the 180 ED f/2.8. I have tested it at f/4 on my D5300 and can confirm it is very sharp. There is a little coma in the corners but it’s actually better than my AT60ED was in that regard even with the matched flattener.

 

PS: thanks for the input!

I have just bought (a month ago) a Nikon ED 180/2.8, and have tested starry skies on m4/3.
I can also confirm f/4 is sharper and has much less CA than at f/2.8.
Also, I have tested the same lens with a SpeedBooster on m4/3, and that is very successful, sharper and faster.
Though I don't know if you can organise the adapters to suit the back spacing for mounting on the ASI.


Edited by Alec, 24 July 2021 - 06:57 AM.


#5 dayglow

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Posted 24 July 2021 - 05:43 PM

With the ASI1600MM, I use the Nikon 180mm f/2.8 at f/3.5 by way of a step-down ring (I don't like diffraction spikes from the lens iris) and get good narrow band results with the provision that I focus meticulously for each filter.  I found a small Bhatinov mask with short ( 0.5 sec) exposures gave me better results than live view.

 

I did have to tinker with the working distance from lens bayonet to camera face just a little bit to get the outer parts of the image to have reasonably sharp stars.

 

The lens has considerable chromatic aberration so I found that LRGB or OSC imaging was not very good. 


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