New Scope time, a few fears.

[FiveByEagle]

Hello all!

Been scope shopping for a about 2 months and I have narrowed it down to two choices. I will be using this scope with my ASI183MC Pro camera. And I very much intend this scope to be a "destination" piece for me. As I have many other life expenses and financially I have to cut this hobby off.

The two are the AT115EDT from Astro-Tech. With the .8x flattener we are at 644mm and without it, we are at 805mm. My worry here is that the pixel scale for my camera is too small, at 2.4microns. My guiding is OK at best, so I fear lots of frustration on guiding and non-round stars.

My FIRST pick.. is the WIlliam Optics GT81IV with its 2 flattener choices. It gives me 380 and 480 in one scope.. and I have no fears here. This will work, however I am not sure if 480mm is enough reach for me.

644mm sounds very interesting to get in close on these DSO's, but is it worth the frustration?

 

[vlaiv]

I'd probably go with first option as all round imaging scope.

Second choice is really wider field offering.

You have color camera and it effectively samples at twice calculated resolution. Use super pixel mode to turn your pixels into 4.8µm pixels.

In good seeing with focal reducer that will give you ~1.5"/px. If seeing is poor - either go with native and bin once more to get around 2.5"/px or go reduced and bin once more for 3"/px.

[FiveByEagle]

 

46 minutes ago, vlaiv said:

I'd probably go with first option as all round imaging scope.

Second choice is really wider field offering.

You have color camera and it effectively samples at twice calculated resolution. Use super pixel mode to turn your pixels into 4.8µm pixels.

In good seeing with focal reducer that will give you ~1.5"/px. If seeing is poor - either go with native and bin once more to get around 2.5"/px or go reduced and bin once more for 3"/px.

When you Super Pixel mode, do you mean Binning? I have never heard of super pixel mode.

[vlaiv]

43 minutes ago, FiveByEagle said:

When you Super Pixel mode, do you mean Binning? I have never heard of super pixel mode.

Super pixel mode is very similar to binning in some respect, but it does not involve addition of four pixels.

With binning (x2 version) - you take group of 2x2 pixels and add/average their values to get one resulting pixel. This is usually done on mono data.

With super pixel mode, you again take group of 2x2 pixels but instead of adding/averaging them, you create single color pixel that has 3 values - R value, G value and B value. R value of resulting pixel is simply value of R pixel from Bayer 2x2 matrix. So is B value - just a copy of corresponding B value. Since we have 2 green pixels - we can average those to get single resulting G value.

Super pixel mode therefore has similar effect on final image - resolution is halved. In addition to that color information is constructed from individual color pixels without "making anything up". With regular debayering missing pixel values are "made up" - or rather filled in from existing values by averaging them. In effect, you gain nothing by doing this except satisfied customers that get image with same resolution as sensor pixel count, but in fact - that is "empty" resolution. One could do similar with mono image - just enlarge it by factor of x2 and fill in missing pixels by averaging existing ones. But if we do that we simply get larger image without additional detail - not something that we want.
 

In any case, super pixel mode is supported in software - take a look at Deep Sky Stacker tech info:

http://deepskystacker.free.fr/english/technical.htm

There is description of Super pixel at the bottom of the page. There is also option in DSS to use that type of debayering:

[Adam J]

5 hours ago, FiveByEagle said:

Hello all!

Been scope shopping for a about 2 months and I have narrowed it down to two choices. I will be using this scope with my ASI183MC Pro camera. And I very much intend this scope to be a "destination" piece for me. As I have many other life expenses and financially I have to cut this hobby off.

The two are the AT115EDT from Astro-Tech. With the .8x flattener we are at 644mm and without it, we are at 805mm. My worry here is that the pixel scale for my camera is too small, at 2.4microns. My guiding is OK at best, so I fear lots of frustration on guiding and non-round stars.

My FIRST pick.. is the WIlliam Optics GT81IV with its 2 flattener choices. It gives me 380 and 480 in one scope.. and I have no fears here. This will work, however I am not sure if 480mm is enough reach for me.

644mm sounds very interesting to get in close on these DSO's, but is it worth the frustration?

 

I agree with what Vlaiv just said grab the 115 and use super pixel mode for now. The get a better camera later, the ASI183mc is a introductory to dedicated astronomy camera imaging, but I would not let it dictate your future purchases as most likely you will upgrade down the line. 

I would also say that I suspect the GT81 is not a scope you will settle on for long. Despite the AT115EDT not having top end ED glass like the GT81 its a solid triplet lens design and I believe that like the TS Optics copy incorporates a Lanthanum doped  rear element in addition to the core ED element (FLP51). It produces colour correction that would surprise most for its cost, apperture and glass.

I am a really big fan of this lens and don't recall ever having seen one produce poor quality stars (when used correctly) on astrobin. Pleanty of other scope riddled with pinching, poor colimation, turned edges, decentred elements and worse. I considered this one long and hard before chosing the more expensive Esprit 100 and in some ways I still wonder if i made the right choice as a little more apperture is always nice.

If you want to see what you can do with one of these I am a huge fan of Maicon Germiniani's work on Astrobin:

https://www.astrobin.com/users/GerminianiMaicon/

He uses it for most of his imaging although it is the TS Optics branded version of the scope. A large number of his images also use the ASI183mm pro. I think if you take a look you will agree that the small pixels are not holding him back.

https://www.astrobin.com/399934/B/?image_list_page=2&nc=&nce=

Astrobin Image of the Day:

https://www.astrobin.com/full/394045/D/

I would get the TS copy btw that way your sure it has the Lanthanum doped element.

Hope that helps,

Adam

 

Edited November 13, 2020 by Adam J

[newbie alert]

I'd match the camera to the scope and not the scope to the camera.. cmos technology is changing so fast that by the time you've saved for a particular model it's superseded by another one... or totally discontinued.. so basically you're going to change the camera before changing the scope