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Fast telescopes v/s high resolution

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188 replies to this topic

#176 jhayes_tucson

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Posted 14 November 2018 - 01:58 PM

Agree ! By daring I mean that after having spent over 50K USD in mount, shipping, travels, scope....psychologically the tendency would be not to believe, even after sound reasoning that a 2K camera could do the job on the other side of the world.

 

Stevan

Ok....got it.  I run $40k worth of equipment at a remote site using that same camera for guiding and other than a few glitches (that I believe are temperature related) it's worked pretty reliably--taking thousands of images every clear night.

 

John


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#177 TareqPhoto

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Posted 14 November 2018 - 01:59 PM

Could be a bit off topic, but you can get good, very wide field, narrow band images by using a short and cheap telephoto lens with a small-pixel sensor like the IMX183MM or IMX178. However, depending on the telephoto lens performance it may not really quality as "fast."

 

Here is a recent thread with some results from a $110 telephoto lens mated to an ASI183MM Pro camera:

 

  https://www.cloudyni...s/#entry8802611

Oh my, why did you assume i only as about very cheap lenses? i have Canon lenses that are being of top of the line but old models, have one new but that also became old but still a high class lens, so no, i wasn't asking about $100-200 lenses at all to be honest.

 

Also, the lens i want to really try to use is in this lens but it is version 1 not 2, can you find any mount ring for this lens to be used with ZWO/QHY cameras maybe? and how to mount this lens on EQ mount?

 

https://www.bhphotov..._120mm_f_4.html

 

And what about this lens because i have this, it is F2 lens, say w will stop it down to about F2.8 or even f3.2, this isn't fast enough then?

 

https://www.amazon.c...s/dp/B000053HC5

 

I do have ASI290MM which has 2.micron, and later i will buy ASI174MM and next year i will add either ASI178mm or ASI183MM depends on what lens i will buy and what i already have, and my plan for getting 174mm and 178mm are for planetary and solar system imaging only and maybe use for guiding sometimes, but i wouldn't mind to use one of those into DSO if necessary.



#178 james7ca

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Posted 14 November 2018 - 02:21 PM

Oh my, why did you assume i only as about very cheap lenses? i have Canon lenses that are being of top of the line but old models...

I didn't say that you had very cheap lenses, what I was providing is that you can even use cheap lenses and still get good results when imaging in the narrow band (if you can find the right "cheap" lens).

 

However, I think this is straying somewhat from the main topic and camera lens selection and topics like the needed adapters is yet another fairly extensive point of discussion (best not to be done here, I think).


Edited by james7ca, 14 November 2018 - 02:23 PM.


#179 AtmosFearIC

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Posted 14 November 2018 - 03:11 PM

1) You have a typo: The FWHM of the stacked frame is 3.66% larger than the single frame.

2) This is a nice demo but I want to add that there are two things that help to ensure a clean stack with the least blurring. First, filter the input images by FWHM and eccentricity to insure that there aren't any significant outliers. Second, blink through the registered stack to make sure that nothing went wrong in the alignment process. Alignment errors actually happen pretty often and they are easy to catch using the blink function. Sometimes I have to go to great extremes to get the slightly misaligned frames under control. They are almost always only slightly wrong and the error can be driven by a lot of different effects but it requires a lot of attention to detail to catch and fix this stuff. Meridian flipped data that requires a rotation is especially suspect because you can get registrations errors that vary with distance from the center of the frame. In my view, getting everything properly aligned is a much bigger concern than the negligible errors introduced by interpolation.

John


1) OOPS! Fixed :)

2) I’ve never bothered checking the registered frames to see that everything has been correctly registered. It sounds like something that I should be doing in the future though especially considering how quick and easy it is to check.

I personally put the FWHM increase down to much better samples stars in the stack. In the stacked image it is sampling proper looking stars as opposed to a lot of lines and blocks and incomplete stars.

When I get some spare time I might go through and try a few different registration methods to see if there are any in PI that make it substantially worse. Regardless, Auto did a good job.

#180 TareqPhoto

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Posted 14 November 2018 - 03:16 PM

I didn't say that you had very cheap lenses, what I was providing is that you can even use cheap lenses and still get good results when imaging in the narrow band (if you can find the right "cheap" lens).

 

However, I think this is straying somewhat from the main topic and camera lens selection and topics like the needed adapters is yet another fairly extensive point of discussion (best not to be done here, I think).

Ok, i understand that, thank you very much!

 

The question is still applied "How fast is fast?" what is fast anyway?



#181 Stevan Klaas

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Posted 14 November 2018 - 06:56 PM

Ok....got it.  I run $40k worth of equipment at a remote site using that same camera for guiding and other than a few glitches (that I believe are temperature related) it's worked pretty reliably--taking thousands of images every clear night.

 

 

 

I am following you in astrobin every week, as a one of the masters to learn from...


Edited by Stevan Klaas, 14 November 2018 - 06:59 PM.


#182 TareqPhoto

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Posted 14 November 2018 - 07:12 PM

I am following you in astrobin every week, as a one of the masters to learn from...

And your Astrobin isn't bad at all either, i will follow you both and more to learn, anyone can be an inspiration to me.


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#183 Gene3

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Posted 14 November 2018 - 08:23 PM

Dhaval,

Let me know how it works, but I suspect that you are going to be a bit underwhelmed by the signal level.  Oversampling at F/11 leads to a very low signal along with a lot of photon noise.  The good news is that if you can bin it 2x2, it will work noticeably better.  

 

I've had both the 16803 and the 16200 on my scope and the 16803 works a LOT better.  I have identical frames with identical cooling and exposures from both cameras that I keep meaning to post to demonstrate the difference.  I'll have to get around to it one of these days.  It's a good demo of the effects of sampling differences with the only variable being the pixel size.

 

John

Hi John,

I would like to understand what is it about the 16803 that makes it better. If the same applies to my situation then maybe I should trade up to a 16803.

 

Thanks,

Gene



#184 mvas

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Posted Yesterday, 09:23 AM

Ok, i understand that, thank you very much!

 

The question is still applied "How fast is fast?" what is fast anyway?

"How fast is fast" is very subjective ...

I consider f-ratios greater than f/6 to be "slow", like f/8, f/10, f/15, etc

I consider f-ratios less than f/6 to be "fast", like f/4, f/3, f/2, etc



#185 jhayes_tucson

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Posted Yesterday, 12:24 PM

Hi John,

I would like to understand what is it about the 16803 that makes it better. If the same applies to my situation then maybe I should trade up to a 16803.

 

Thanks,

Gene

 

Gene,

I think that I've gone over all the gory details in this thread.  It's all about matching your camera to the scope you are using.  The KAI-16803 isn't perfect for every scope but if you have the right system (with a blur diameter greater than about 16 microns and a well corrected field,) it's a superb sensor.  Of course, you also have to be comfortable with the cost.  16803 based cameras are not inexpensive.

 

John


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#186 TareqPhoto

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Posted Yesterday, 05:50 PM

"How fast is fast" is very subjective ...

I consider f-ratios greater than f/6 to be "slow", like f/8, f/10, f/15, etc

I consider f-ratios less than f/6 to be "fast", like f/4, f/3, f/2, etc

I see, so F/6 is like the deciding f-ratio, thank you very much!



#187 Gene3

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Posted Today, 01:28 PM

Gene,

I think that I've gone over all the gory details in this thread.  It's all about matching your camera to the scope you are using.  The KAI-16803 isn't perfect for every scope but if you have the right system (with a blur diameter greater than about 16 microns and a well corrected field,) it's a superb sensor.  Of course, you also have to be comfortable with the cost.  16803 based cameras are not inexpensive.

 

John

Thanks John.

Actually now looking at a 50100 for use with FSQ130ED. I think the 50100 would be a better than 16200.



#188 jhayes_tucson

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Posted Today, 02:02 PM

Thanks John.

Actually now looking at a 50100 for use with FSQ130ED. I think the 50100 would be a better than 16200.

Agreed.  That's an impressive chip and well suited to any system with enough field.  If you can afford it, that seems like a great way to go!

 

John


Edited by jhayes_tucson, Today, 02:08 PM.


#189 TareqPhoto

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Posted Today, 02:26 PM

So, not only the mount or scope that are expensive, but also cameras, and thus someone will pay nearly $50k maybe more or slightly less to have the three of those items at ultimate or high end?

 

I think i have to minimize my targets and minimize my quality request or requirement so i will save myself from big spending budget for lifetime.

 

Thanks all, keep up those threads!




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