Re: Close up of M81 without CCDT67


Mike Shade
 

Please do not send big files to the group.  Some people live rural and DO NOT have fast speeds.  Provide a place where people can see them if interested.

 

Mike J. Shade: mshade@q.com

Mike J. Shade Photography:

mshadephotography.com

 

In War: Resolution

In Defeat: Defiance

In Victory: Magnanimity

In Peace: Goodwill

Sir Winston Churchill

Already, in the gathering dusk, a few of the stars are turning on their lights.

Vega, the brightest one, is now dropping towards the west.  Can it be half

a year since I watched her April rising in the east?  Low in the southwest

Antares blinks a sad farwell to fall...

Leslie Peltier, Starlight Nights

 

International Dark Sky Association: www.darksky.org

 

From: main@ap-gto.groups.io [mailto:main@ap-gto.groups.io] On Behalf Of Robert Chozick via Groups.Io
Sent: Friday, February 28, 2020 8:33 AM
To: main@ap-gto.groups.io
Subject: Re: [ap-gto] Close up of M81 without CCDT67

 

I took the test shots you suggested.  I used Pollux and shot 1,3,5,15.30 sec exposures inside and outside of focus.  The 1 and 3 sec seemed to look the best but tell me if you want the 5, 15 and/or 30 sec shots.  Nebulosity saves in 32 bit fits so let me know if you need it changed.  The secondary vane that is wider is where I have tape to hide the wires for my secondary dew heater.  Please let me know if you think I should take them off and if they may interfere with my images.  I did not have much focus left inside of focus so my outside version is further out of focus than my inside version.

 

Robert

 

 

 

 

 

 

 

On Feb 15, 2020, at 4:52 PM, uncarollo2 via Groups.Io <chris1011@...> wrote:

 

One thing would be interesting, before you mask it down. Aim the scope at a medium bright star, defocus the star image until it has a diameter of about 150 pixels and take a 16 bit Fits image but don't let any of it saturate. Do one for both inside and outside of focus. Crop it, 16 bit Fits and post the results (or send me the images). This will tell right away what the state of the correction is and if there are any edge zones.

 

Rolando

 

 

 

-----Original Message-----
From: Robert Chozick via Groups.Io <rchozick@...>
To: main <main@ap-gto.groups.io>
Sent: Sat, Feb 15, 2020 4:45 pm
Subject: Re: [ap-gto] Close up of M81 without CCDT67

Thanks. I have a pier set up in my backyard and can do testing. With the scope tilted up I can just lay the mask over it for the test. 

Robert 

 



On Feb 15, 2020, at 11:46 AM, uncarollo2 <chris1011@...> via Groups.Io <chris1011@...> wrote:



Well, sometimes I don't think things thru when i suggested tape over the edge of the mirror. That, of course is bad advise.

 

I may be wrong about what I am seeing in your bright stars, and it may indeed be the very high gain of your camera. Here's what I would do: just try a thin cardboard mask over the edge and compare the result with no mask. If you don't see any difference, then your edge correction is fine and you won't need to mask it down.

 

Rolando

 

 

 

-----Original Message-----
From: Robert Chozick via Groups.Io <rchozick@...>
To: main <main@ap-gto.groups.io>
Sent: Sat, Feb 15, 2020 11:11 am
Subject: Re: [ap-gto] Close up of M81 without CCDT67

Thanks for the optics lesson. 



On Feb 15, 2020, at 9:34 AM, uncarollo2 <chris1011@...> via Groups.Io <chris1011@...> wrote:



Actually it is not a good idea to put any tape on the reflective surface. On the Lomo RC scopes they used a metal disc which was on standoffs that were attached to the rear cell. I would make a paper disc and carefully lay it on the edge of the mirror and attach it to the side of the mirror with Scotch tape. Being careful to not rub the aluminum surface.

 

Roland

 

 

 

-----Original Message-----
From: Robert Chozick via Groups.Io <rchozick@...>
To: main <main@ap-gto.groups.io>
Sent: Fri, Feb 14, 2020 9:57 pm
Subject: Re: [ap-gto] Close up of M81 without CCDT67

If I were to attempt to mask the edge what kind of tape can you use that wouldn’t harm the coatings?

Robert 

 



On Feb 14, 2020, at 8:40 PM, Robert Chozick via Groups.Io <rchozick@...> wrote:

 Can you start making some smaller RC’s😀Thanks for the suggestion. One of the problems is how sensitive the CMOS cameras are. It is very easy to blow out stars. With my FSQ at f/5 I can’t shoot over 2 1/2 -3 minutes before bright stars are blown. 

 

I worked hard on my collimation and it seems to have paid off.  I bought a focuser collimation ring and used a laser to collimate.   

 

Robert 

 



On Feb 14, 2020, at 4:56 PM, uncarollo2 <chris1011@...> via Groups.Io <chris1011@...> wrote:



I like the resolution on that Running Man image. Very nice.

 

Try masking down the outer 1/8 inch of the mirror, see if that reduces the spray of light around the brightest stars. If that works, think about adding a disc in front of the mirror with a diameter perhaps 1/4 inch smaller than the mirror.

 

I have seen this on all Russian RCs (RC Optical scopes) where a disc of slightly smaller aperture really helped. Most of the RC mirrors from Lomo had turned edge and were only spec'd to 95% of the full aperture. The very outer part produced a heavy spray of light around bright stars.

 

Rolando

 

 

 

-----Original Message-----
From: Robert Chozick via Groups.Io <rchozick@...>
To: main <main@ap-gto.groups.io>
Sent: Fri, Feb 14, 2020 3:47 pm
Subject: Re: [ap-gto] Close up of M81 without CCDT67

So, would you say the new advantages of the small pixel CMOS cameras is that they bring high sensitivity to small pixels?

 

I also got a shot of the Running Man with the 1600mm setup:

 

https://pbase.com/rchozick/image/170381415

 

I got M101 at 1600 but the seeing was worse and guiding not as good. 

 

https://pbase.com/image/170399423

 

Robert

 

 

 

On Feb 14, 2020, at 3:10 PM, uncarollo2 via Groups.Io <chris1011@...> wrote:

 

You are running 0.6 arc sec per pixel, which to me is not oversampling for high resolution imaging. In fact, for galaxies i prefer 0.3 to 0.4 arc sec per pixel which really brings out fine detail. My 17"F8 astrograph and the QSI 683 has such pixel scale and really does a superb job on small faint galaxies, even here in Northern Illinois. You have to have good tracking, of course, and on the best nights I can get below 0.15 arc sec RMS with the 1600 encoder mount.

 

I see a lot of images that are way undersampled (3 to 4 arc sec per pixel) with poor guiding that produces thick stars and very little resolution. To me these images resemble Brownie camera snapshots versus images taken with an 8x10 view camera. (shows my age, doesn't it)  :^))

 

Rolando

 

 

 

-----Original Message-----
From: Robert Chozick via Groups.Io <rchozick@...>
To: main <main@ap-gto.groups.io>
Sent: Fri, Feb 14, 2020 2:14 pm
Subject: Re: [ap-gto] Close up of M81 without CCDT67

Thanks Roland.  My last dark sky outing was my first use of this scope and camera.   I am really confused on the whole image scale question.  I bought this camera because it has the largest pixels of any of the CMOS cameras. The image scale is .6 with this camera and 1600mm.   My scale is about 1.8 with my FSQ 106 - 530mm.  If the recommended guidance of a scale of 1-2 for image scale is used the 1600mm should be too small an image scale.  Most CMOS cameras have only 2.5-3.5 micron pixels vs 4.63 on my ASI294.  Is oversampling bad?  The .6 scale in my image sure looks ok.    What about .4 or .3?  I intentionally did not get larger than a 1600mm focal length because of this issue (and yes, guiding issues are not as bad vs 2000 and over).  Everyone asks why I got an 8 RC instead of a 10 or 12 inch RC.  The above reason is why.   Each new CMOS camera that comes out still has really small pixels.   How good would 2.5 micron pixels look on a 2500 mm scope?  

 

Robert

 

On Feb 14, 2020, at 1:18 PM, uncarollo2 via Groups.Io <chris1011@...> wrote:

 

That's really nice. Sharp and great color.

 

A question: do you think that 1600mm is a sweet spot for all kinds of deep sky imaging, especially for high resolution work? Especially since the newer Cmos cameras have such small pixels and would be able to take advantage of a high resolution optic for small faint galaxies.

 

Rolando

 

 

 

-----Original Message-----
From: Robert Chozick via Groups.Io <rchozick@...>
To: main <main@ap-gto.groups.io>
Sent: Fri, Feb 14, 2020 12:06 am
Subject: [ap-gto] Close up of M81 without CCDT67

I got another shot of M 81 on the same trip as the M81-82 image, this time at f/8 1620mm.

 

https://pbase.com/image/170419535

 

Robert Chozick

rchozick@...

 

 

 

 

Robert Chozick

rchozick@...

 

 

 

 

Robert Chozick

rchozick@...

 

 

 

 

Robert Chozick

 

 

 

Join main@ap-gto.groups.io to automatically receive all group messages.