Small Galaxies - Increasing magnification ED80 & Canon 1000D Or Mak127

[PhantomAstro]

Hi,

 

This maybe a stupid question, I am wanting to try and capture some smaller galaxies....

What do I need to do to increase magnification/focal length with my ED80 and canon 1000D at prime focus?  Is there a barlow that is required or an extension tube?

OR

Would I be better sticking with my Mak 127mm and either the Canon 1000D or the ASI120MC-S?

 

Thanks.

[vlaiv]

I'd say go with Mak and Canon.

First spend some time to understand what is max resolution that you'll be able to achieve with your setup - either Mak or ED80 and mount you have (guiding performance) and skies and then see how to best match that resolution with your camera.

Next thing - figure out just how "close in" you'll be getting and learn to accept that .

For example, I think that best resolution with 4" scope and good regular mount, that one can hope for, will be something like 1.6"/px.

Let's say you want to image M77 that is about 11 arc minutes in diameter. That is 660 arc seconds in diameter or about 410px across.

That is it - your whole galaxy will be something like 410px across if you properly sample it.

[ollypenrice]

4 hours ago, vlaiv said:

I'd say go with Mak and Canon.

First spend some time to understand what is max resolution that you'll be able to achieve with your setup - either Mak or ED80 and mount you have (guiding performance) and skies and then see how to best match that resolution with your camera.

Next thing - figure out just how "close in" you'll be getting and learn to accept that .

For example, I think that best resolution with 4" scope and good regular mount, that one can hope for, will be something like 1.6"/px.

Let's say you want to image M77 that is about 11 arc minutes in diameter. That is 660 arc seconds in diameter or about 410px across.

That is it - your whole galaxy will be something like 410px across if you properly sample it.

So would I, but Mak plus Canon plus much more exposure time.

Olly

[vlaiv]

18 minutes ago, ollypenrice said:

So would I, but Mak plus Canon plus much more exposure time.

Olly

Compared to what?

To ED80 at same sampling rate? What happened to aperture at sampling rate?

Even if we account for central obstruction and mirror losses, 127mm (which is 5" not 4" as I wrote above) is going to be much more clear aperture than 80mm.

[ollypenrice]

6 minutes ago, vlaiv said:

Compared to what?

To ED80 at same sampling rate? What happened to aperture at sampling rate?

Even if we account for central obstruction and mirror losses, 127mm (which is 5" not 4" as I wrote above) is going to be much more clear aperture than 80mm.

But the sampling rate's not the same?

Olly

[pete_l]

5 hours ago, PhantomAstro said:

This maybe a stupid question, I am wanting to try and capture some smaller galaxies....
What do I need to do to increase magnification/focal length with my ED80 and canon 1000D at prime focus?  Is there a barlow that is required or an extension tube?

OR

Would I be better sticking with my Mak 127mm and either the Canon 1000D or the ASI120MC-S?

You could add a Barlow, however they are often said to reduce image quality. You could also try eyepiece projection with a suitable adapter.

But since you already have the Mak, I'd say just give it a try. See whether the images please you and which targets are suitable.

[vlaiv]

56 minutes ago, ollypenrice said:

But the sampling rate's not the same?

Olly

But that would be up to the "operator" right?

Let's say we are after 1.6"/px or there about resolution. We have 1500mm of focal length and pixel size of about 5.71µm.

Natively this gives ~0.79"/px, but since we have OSC sensor, simple super pixel debayering will give double that so ~1.57"/px.

There you go, no need to do anything else. If on the other hand, one was aiming to match sampling rate of the ED80 - they would simply bin data further. One scope has 1500mm of FL and other has about 500mm FL (with x0.85 FF/FR that ends up 510mm or so?) - that is very nice 3:1 ratio so x3 bin will get almost perfect match between the two.

In any case, I would just leave things as they are and go for Mak with Canon 1000D and super pixel debayering to get 1.6"/px, provided of course that mount and guiding support it.

[ollypenrice]

10 hours ago, vlaiv said:

But that would be up to the "operator" right?

Let's say we are after 1.6"/px or there about resolution. We have 1500mm of focal length and pixel size of about 5.71µm.

Natively this gives ~0.79"/px, but since we have OSC sensor, simple super pixel debayering will give double that so ~1.57"/px.

There you go, no need to do anything else. If on the other hand, one was aiming to match sampling rate of the ED80 - they would simply bin data further. One scope has 1500mm of FL and other has about 500mm FL (with x0.85 FF/FR that ends up 510mm or so?) - that is very nice 3:1 ratio so x3 bin will get almost perfect match between the two.

In any case, I would just leave things as they are and go for Mak with Canon 1000D and super pixel debayering to get 1.6"/px, provided of course that mount and guiding support it.

Agreed.

Olly