Do I need a reducer? Skywatcher

[Mike d]

Hi all, 

I've been doing astrophotography for a couple of years so I'm still new. 

I have been useing my Canon 650D and  Skywatcher Explorer-150PDS (EQ3 PRO) and taken some real good shots of the moon and andromeda etc. 

I have now bought a ZWO asi 462, and started to use that. 

I see the moon is not full frame, 

Do I need to get a reducer? 

Cheers guys. 

 

[Cornelius Varley]

9 hours ago, Mike d said:

Hi all, 

I've been doing astrophotography for a couple of years so I'm still new. 

I have been useing my Canon 650D and  Skywatcher Explorer-150PDS (EQ3 PRO) and taken some real good shots of the moon and andromeda etc. 

I have now bought a ZWO asi 462, and started to use that. 

I see the moon is not full frame, 

Do I need to get a reducer? 

Cheers guys. 

 

A better (cheaper) alternative is to take a series of overlapping videos and then use a programme such as Microsoft Image Compositor (MiCE) to create a mosaic using the processed images. You can use EQMosaic to create a grid pattern to ensure all the captures overlap. EQMOD (sourceforge.net)

[michael8554]

Hi Mike

Perhaps you could explain your choice of the ZWO ASI 462 with a tiny 5.6mm x 3.2mm sensor, to replace the 650D with a 22mm x 15mm sensor, for "moon and andromeda" ?

You'd need a X0.50 Reducer (if such a thing exists for the 150PDS) to completely frame the moon.

Michael

[Mike d]

1 hour ago, michael8554 said:

Hi Mike

Perhaps you could explain your choice of the ZWO ASI 462 with a tiny 5.6mm x 3.2mm sensor, to replace the 650D with a 22mm x 15mm sensor, for "moon and andromeda" ?

You'd need a X0.50 Reducer (if such a thing exists for the 150PDS) to completely frame the moon.

Michael

Hi, 

So I've been doing a lot of moon shots with my Canon, stacking Pipp, Autostakkert and so on.  And i saw some advanced guys with some really detailed moon photos that I just could not get near. 

I asked how they got so much detail and they pointed me towards a ZWO or similar type camera. 

I then asked for advice from a telescope shop, which one would be suitable for my Skywatcher. They advised the ZWO ASI  462 MC. 

On using it I found I could get the great shots I was after, but not full frame. 

The previous comment above is a good idea about stitching the different processed photos together, so I will try that out next. 

Cheers. 

Moon shot, Canon 650d, skywatcher Explorer-150PDS

 

[michael8554]

Hi Mike,

"i saw some advanced guys with some really detailed moon photos that I just could not get near."

The ZWO ASI 462 is a good choice for detailed close-up moonshots.

But no good for whole moon images without mosaicing.

Michael

[Same old newbie alert]

Don't be afraid of doing mosaics, various ways to do it and in the long run they will be far more detailed than full disc images... They're fairly easy and fun to learn

[vlaiv]

1 hour ago, michael8554 said:

Hi Mike

Perhaps you could explain your choice of the ZWO ASI 462 with a tiny 5.6mm x 3.2mm sensor, to replace the 650D with a 22mm x 15mm sensor, for "moon and andromeda" ?

You'd need a X0.50 Reducer (if such a thing exists for the 150PDS) to completely frame the moon.

Michael

One of the reasons to use small sensor is coma

Diffraction limited field on F/5 scope is rather small - it is few millimeters in diameter.

Coma corrector reduces coma but introduces other aberrations that are usually not seen in long exposure imaging as seeing masks them (sometimes they are noticed like spherical aberration producing softer stars in long exposure imaging in simple two lens coma corrector designs). For this reason, planetary imaging that requires best sharpness out of optics is best done without CC and in central region of the field that is diffraction limited.

1 hour ago, Mike d said:

I then asked for advice from a telescope shop, which one would be suitable for my Skywatcher. They advised the ZWO ASI  462 MC. 

On using it I found I could get the great shots I was after, but not full frame. 

It's not only camera that is important for getting good sharp image - it is host of factors, I'll list few since you are already familiar with planetary stacking techniques (like using AS!3 for stacking and registax wavelets for sharpening).

- use very sort exposures, 5ms or less.

- use higher gain settings to limit read noise, but do be careful not to over expose (reduce exposure further if over exposing parts of the image)

- capture plenty of frames at high fps - like 20000-40000 per panel. Use 5-10% top quality ones in the stack

Don't use reducer for the same reason as CC above - it will introduce optical aberrations. Use just central part of the field.

Since you have F/5 scope that is 125/90 = 1.4mm radius or 2.8mm diameter.

You want diagonal of 2.8mm for your ROI. Your camera has 6.45mm of diagonal, so if you don't use barlow, you need to use less than half of sensor - 640x480px ROI to get best sharpness.

Alternative is to use barlow - and many imagers use barlow to achieve critical sampling rate (capture all the detail that their scope allows for).

Your camera has 2.9um pixel size and critical sampling F/ratio will be x4 that value (actual formula is pixel_size*2 / wavelength - but we use 500nm wavelength - that is 0.5um in microns because pixels are in micrometers and resulting formula is pixel_size*2/0.5 => pixel_size*4)

You need to be at F/11.6.

Your scope is F/5 so you need either x2 or x2.5 barlow (you can change magnification of a barlow by changing distance to sensor - so you can dial in x2.2 needed with either of those).

This will have additional benefit of allowing you to use full sensor instead of ROI because 2.8 x 2.2 = 6.14 (almost 6.45mm).

 

[Mike d]

Thanks for the great advice

[Mike d]

12 minutes ago, vlaiv said:

One of the reasons to use small sensor is coma

Diffraction limited field on F/5 scope is rather small - it is few millimeters in diameter.

Coma corrector reduces coma but introduces other aberrations that are usually not seen in long exposure imaging as seeing masks them (sometimes they are noticed like spherical aberration producing softer stars in long exposure imaging in simple two lens coma corrector designs). For this reason, planetary imaging that requires best sharpness out of optics is best done without CC and in central region of the field that is diffraction limited.

It's not only camera that is important for getting good sharp image - it is host of factors, I'll list few since you are already familiar with planetary stacking techniques (like using AS!3 for stacking and registax wavelets for sharpening).

- use very sort exposures, 5ms or less.

- use higher gain settings to limit read noise, but do be careful not to over expose (reduce exposure further if over exposing parts of the image)

- capture plenty of frames at high fps - like 20000-40000 per panel. Use 5-10% top quality ones in the stack

Don't use reducer for the same reason as CC above - it will introduce optical aberrations. Use just central part of the field.

Since you have F/5 scope that is 125/90 = 1.4mm radius or 2.8mm diameter.

You want diagonal of 2.8mm for your ROI. Your camera has 6.45mm of diagonal, so if you don't use barlow, you need to use less than half of sensor - 640x480px ROI to get best sharpness.

Alternative is to use barlow - and many imagers use barlow to achieve critical sampling rate (capture all the detail that their scope allows for).

Your camera has 2.9um pixel size and critical sampling F/ratio will be x4 that value (actual formula is pixel_size*2 / wavelength - but we use 500nm wavelength - that is 0.5um in microns because pixels are in micrometers and resulting formula is pixel_size*2/0.5 => pixel_size*4)

You need to be at F/11.6.

Your scope is F/5 so you need either x2 or x2.5 barlow (you can change magnification of a barlow by changing distance to sensor - so you can dial in x2.2 needed with either of those).

This will have additional benefit of allowing you to use full sensor instead of ROI because 2.8 x 2.2 = 6.14 (almost 6.45mm).

 

Thanks for the great advice